Full text of "Strasburger's Text-book of botany"

See other formats

rores u

FOKTRY

c Of AGRICULTURE

STBASBUEGEE'S
. TEXT-BOOK OF BOTANY

MACMILLAN AND CO., LIMITED

LONDON • BOMBAY • CALCUTTA • MADRAS
MELBOURNE

THE MACMILLAN COMPANY

NEW YORK • BOSTON • CHICAGO
DALLAS • SAN FRANCISCO

THE MACMILLAN CO. OF CANADA, LTD.

TORONTO

STBASBUBGEB'S

TEXT-BOOK OF BOTANY

BE-WEITTEN BY
DR. HANS FITTING DK. LUDWIG JOST

PROFESSOR IN THE UNIVERSITY PROFESSOR IN THE UNIVERSITY

OF BONN OF HEIDELBERG

DR. HEINEICH SCHENCK DR. GEOEGE KAESTEN

PROFESSOR IN THE TECHNICAL PROFESSOR IN THE UNIVERSITY

ACADEMY OF DARMSTADT OF HALLE/SAALE

FIFTH ENGLISH EDITION
REVISED WITH THE FOURTEENTH GERMAN EDITION BY

W. H. LANG, M.B., D.Sc, F.E.S.

BARKER PROFESSOR OF CRYPTOGAMIC BOTANY IN THE UNIVERSITY
OF MANCHESTER

WITH 833 ILLUSTRATIONS, IN PART COLOURED

MACMILLAN AND CO., LIMITED

ST. MAETIN'S STEEET, LONDON

1921

First English Edition, 1898
Second English Edition, 1903
Third English Edition, 1908
Fourth English Edition, 1912
Fifth English Edition, 1921

AGRIC. DEPT.

PKEFATOKY NOTE

THE original * authors of this text-book as it appeared in 1894
were Professors Eduard Strasburger, Fritz Noll, Heinrich Schenck,
and A. F. W. Schimper. The death of Professor Strasburger
since the last English edition was published renders it inaccurate
to give his name as an author of the work. His position as the
original founder of the text-book requires to be recorded and is
therefore indicated by the name Strasburger's Text-Book, which
has been in current use in this country. In the present edition
the division on Morphology is by Professor Fitting, that on
Physiology by Professor Jost, that on Thallophyta, Bryophyta,
and Pteridophyta by Professor Schenck, and that on Spermato-
phyta by Professor Karsten. Their names are therefore given as
the authors on the title-page.

The first edition of the English translation was the work of
Dr. H. C. Porter, Assistant Instructor of Botany, University of
Pennsylvania. The proofs of this edition were revised by Pro-
fessor Seward, M.A., F.E.S. The second English edition was
based upon Dr. Porter's translation, which was revised with the
fifth German edition. The third English edition was revised
with the eighth German edition, and the fourth English edition
with the tenth German edition. The present edition has been
similarly revised throughout with the fourteenth German edition.
Such extensive changes, including the" substitution of completely
new sections on Morphology, Physiology, and Spermatophyta,
have, however, been made in the work since it was first translated
that it seems advisable to give in outline the history of the

4812.

vi BOTANY

English translation instead of retaining Dr. Porter's name on the
title-page.

The official plants mentioned under the Natural Orders are
those of the British Pharmacopoeia instead of those official in
Germany, Switzerland, and Austria, which are given in the
original.

WILLIAM H. LANG.
MANCHESTER, 1921.

CONTENTS

PAGE

INTRODUCTION 1

PART I. GENERAL BOTANY

DIVISION I. MOKPHOLOGY
SECTION I. CYTOLOGY

I. Form and Size of Cells ....... 10

II. The Living Cell Contents. The Protoplast . . . .11

A. The constituent parts of the cell . . . . .11

B. Main vital phenomena of protoplasts . . . .13

C. Chemical properties of the protoplast . . . .14

D. Structure of the parts of the protoplast . . . .15

E. Origin of the elements of the protoplast . . . .21

III. The Larger Non-living Inclusions of the Protoplasts . . .27

IV. The Cell Wall ........ 34

SECTION II. HISTOLOGY

I. The Formation of Tissues ....... 40

II. Kinds of Cells, Tissues, and Tissue-systems . . . .45

A. The formative tissues . . . . . .46

B. The permanent tissues . . . . . .47

SECTION III. ORGANOGRAPHY

I. Vegetative Organs ........ 73

A. TheThallus ........ 73

B. The Cormus ........ 83

1. Construction of the Typical Cormus . . . .84

(a) The shoot ....... 84

(a) The growing point . . . . .84

(jS) The axis of the shoot . . . • . .87

(7) The leaves . . . . . .106

(5) The branching of the shoot . . . .119

vii

vin BOTANY

(6) The root . . . . . . .131

(c) Secondary growth in thickness of the cornius . . 140
2. Adaptations of the Cormus to its Mode of Life and to the Environment 165

A. Autotrophic cormophytes . . . . . .165

(a) Adaptations to the humidity of the environment . .165

(b) Adaptations for obtaining light . . . .181

nutrition . . . . . . .185

B. Heterotrophic cormophytes . % . .188
II. Organs of Reproduction ... .192

SECTION IV. THE THEORY OF DESCENT AND THE ORIGIN
OF NEW SPECIES

A. The theory of descent .... .206

B. Formation of species and the origin of adaptations .... 210

DIVISION II. PHYSIOLOGY

Essential phenomena of life . . . . . . .215

SECTION I. METABOLISM

I. The Chemical Composition of the Plant ... . 220
II. The Nutrient Substances ; their Absorption and their Movement within

the Plant ....... .222

III. The Assimilation of the Food Materials . . .247

IV. Translocation and Transformation of Assimilates . . . 263

V. Respiration and Fermentation ... . 269

SECTION II. DEVELOPMENT

I. Introductory Remarks ... . . 278

1. The measurement of growth ... . 278

2. The phases of growth .... .282

II. The Factors of Development ... . 288

A. External factors ... .288

B. Internal factors .... .296
IH. The Course of Development and its Dependence on External and

Internal Factors . . 301

A. Resting condition and the commencement of growth . . 303

B. Growth and cell division ...... 306

C. Further periodic changes in vegetative form . . 307

D. Duration of life .... . 309

E. Reproduction ..... . 310

F. Heredity, variability, origin of species . . . 316

CONTENTS ix

SECTION III. MOVEMENT

PAGE

I. Movements of Locomotion . . . . . . . . 327

II. Movements of Curvature ....... 332

A. Hygroscopic movements ...... 333

B. Movements of curvature in the living plant .... 335

1. Autonomic movements of curvature .... 335

2. Paratonic movements ...... 337

(a) Tropisms . . . . . . .338

(b) Nastic movements . . . . . 356

PART II. SPECIAL BOTANY

DIVISION I. THALLOPHYTA. BRYOPHYTA. PTERIDOPHYAT

THALLOPHYTA ......... 367

Bacteria ....... . 370

Cyanophyceae ........ 376

Flagellata .... .... 378

Myxomycetes . . . . . . . .381

Dinoflagellatae ........ 386

Diatomeae ......... 387

Conjugatae . . . . . . . . .392

Heterocontae ........ 396

Chlorophyceae ........ 398

Phaeophyceae . . . . 409

Characeae ....... . 418

Rhodophyceae . . . . . . . .421

Phycomycetes . . ... . 428

Eumycetes ......... 436

Lichenes ... ..... 469

BRYOPHYTA .... . . 475

Hepaticae ...... . 483

Musci ......... 489

PTERIDOPHYTA . . . . . . . . . 496

Filicinae ......... 503

Equisetinae . . . . . . . . .517

Sphenophyllinae ........ 522

Lycopodinae ........ 523

Pteridospermeae ........ 534

DIVISION II SPERMATOPHYTA

The Transition from the Pteridophyta to the Spermatophyta . . . 539

Scheme of Alternation of Generations . 543

BOTANY

PAGE

Morphology and Ecology of the Flower • 544

1. Morphology ... • 544

Gymnosperms
Angiosperms

2. Ecology .

Development of the Sexual Generation . . . 561

A. Gymnosperms .... • 561

(a) Cycadeae and Ginkgo .

(6) Coniferae. . .566

B. Angiosperms ..... • 570

The seed .... .579

The fruit . . -582
Distribution of seeds

Germination .... • 587
Arrangement of the Classes, Orders, and Families
I. GYMNOSPERMAE .

Cycadinae . -589

Ginkgoinae ..... • 591

Coniferae .... .592

Gnetinae ... .602

FOSSIL GYMNOSPERMS ... • 604

II. ANGIOSPERMAE .....

DlCOTYLAE

CHORIPETALAE ... . • 609

MONOCHLAMYDEAE . • • 609

Juglandiflorae ... .609

Querciflorae . • 609

Saliciflorae ..... . 614

Urticinae ... • 616

Loranthiflorae . • 620
Polygoninae ....... 621

Piperinae .... .621

Hamamelidinae .... • 623

Tricoccae .... • 623

Centrospermae .... • 627

DlALYPETALAE

Polycarpicae ..... • 629

Rhoeadinae .... • 639

Cistiflorae .... .646

Columniferae . .647

Gruinales .... .651

Sapindinae . . • 655

Frangulinae ..... • 657

CONTENTS xi

PAGE

Rosiflorae ......

. 658

Leguminosae ......

. 664

^ —Myrtiflorae ......

. 673

Umbelliflorae ......

. 677

SYMPETALAE . . ...

. 684

PENTACYCLICAE ......

. 684

Ericinae ......

. 684

Diospyrinae ......

. 686

Primulinae ......

. 687

TETKACYCLICAE ......

. 687

(a) Ovary superior —

Contortae ......

. 687

Tubfflorae ......

. 690

Personatae ......

. 696

(b) Ovary inferior —

Rubiinae ......

. 704

Synandrae ......

. 707

MONOCOTYLAE ......

. 718

(a) Flowers actinomorphic —

Helobiae ......

. 719

Liliiflorae ......

. 721

Enantioblastae .....

. 730

(b) Flowers more or less reduced —

Glumiflorae ......

. 730

Spadiciflorae ......

. 737

Scitamineae ......

. 742

Gynandrae . . . ...

. 745

FOSSIL ANGIOSPERMS .....

. 749

INDEX OF LITERATURE .......

. 751

SYSTEMATIC INDEX OF THE OFFICIAL AND POISONOUS PLANTS

. 773

INDEX .........

777

INTRODUCTION

ORGANISMS are customarily distinguished as animals and plants and
a corresponding division of Biology, which treats of living beings
generally, is made into the sciences of Zoology and Botany.

The green, attached, flowering, and fruiting organisms are dis-
tinguished as plants in contrast to animals, which are usually capable
of free movements and seek, capture, and devour their food. Easy as
it appears on a superficial acquaintance to draw the boundary between
the vegetable and animal kingdoms, it is really very difficult. In the
case of those very simply constructed organisms with little external or
internal differentiation, which are usually regarded as lowest in the
scale, all distinguishing characteristics may fail us. The following
important properties are in fact common to both animals and plants :

1. Plants and animals both consist of one or many microscopically
small cells, which increase in number by a process of division. They
have thus a FUNDAMENTALLY SIMILAR INTERNAL STRUCTURE.

2. Plants and animals are living beings and AGREE IN THEIR MOST
IMPORTANT VITAL PROCESSES. The processes of nutrition and of
reproduction, of growth and of development, are, broadly considered,
essentially similar in animals and plants. A plant also respires with
the production of heat, and exhibits powers of movement and
irritability of various kinds.

3. This profound agreement in the manifestations of life in plants
and animals becomes less surprising when it is realised that THE

LIFE OF BOTH IS ASSOCIATED WITH A VERY SIMILAR UNDERLYING
SUBSTANCE, THE PROTOPLASM OF THE CELLS.

These and many other facts indicate that plants are really related
among themselves and to the animals. This assumption of a GENETIC
RELATIONSHIP finds its expression in the THEORY OF DESCENT which
may be regarded as the fundamental biological theory. The idea of
a 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. It was especially through the work of
CHARLES DARWIN (*), who accumulated evidence for a reconsideration

BOTANY

of the whole problem of organic evolution, that the. belief in the
immutability of species was finally destroyed. From the study of the
fossil remains and impressions of animals and plants it has been
established that in earlier geological periods 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 corresponding
genera into one family and of families into higher groups in a
"natural" system serves to give expression to a real relationship
existing between them. The evolutionary developments, i.e. the
transformations which an organism has undergone in its past generations,
were termed its PHYLOGENY by ERNST HAECKEL(2). The develop-
ment or series of changes passed through by the individual in attaining
the adult condition he distinguished as the ONTOGENY. It is assumed
on the theory of descent that the more highly organised plants and
animals had their phylogenetic origin in forms which perhaps
resembled the simplest still existing. The phylogenetic development
proceeded from these, on the one hand in the direction of the higher
animals, and on the other in the direction of well-defined plants. On
this assumption, which is supported by the properties which animals
and plants have in common and by the impossibility of drawing a sharp
line between animal and plant in the lowest groups, all living beings
form one NATURAL KINGDOM.

The following may be mentioned as distinctly marked character-
istics of plants. The external development of the important surface of
the body, which serves to absorb the food in plants, contrasts with the
internal body surface to which the mouth gives entrance in the
animal. The investing walls of vegetable cells are already represented
in certain series of lower organisms which afford the probable starting-
point for the phylogenetic development of plants. Lastly, the green
chromatophores of plant-cells are characteristic. 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 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,

INTRODUCTION

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 resemblances, 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 give any strict definition of a
" plant " which will sharply separate plants from animals, a distinction
between organisms and non-living bodies is more easy. We know no
living being in which protoplasm is wanting, while active protoplasm
is not to be demonstrated in any lifeless body. Since in the sphere
of organic chemistry sugars have been synthesised by EMIL FISCHER
and the way towards the synthesis of proteids opened up, there is
increased justification for the assumption that the protoplasm forming
the starting-point of organic development had an inorganic origin.
In ancient times such a " spontaneous generation " was regarded as a
possibility even for highly organised animals and plants. It was a
widely-spread opinion, shared in by ARISTOTLE himself, that such
living beings could originate from mud and sand. It is now known
from repeated experiments that even the most minute and simplest
organisms with which we are acquainted do not arise in this way but
only proceed from their like. Living substance may, however, have
arisen from non-living at some stage in the development of the
earth or of another planet when the special conditions required for its
formation occurred. In order that the organic world should have
proceeded from this first living substance, the latter must from the
beginning have been able to maintain itself, to grow, and to trans-
form matter taken up from without into its own substance. It must
also have been capable of reproduction, i.e. of multiplying by
separation into a number of parts, and further of acquiring new and
inheritable properties. In short, this original living substance must
have already possessed all the characteristics of life.

Botany may be divided into a number of parts. MORPHOLOGY is
concerned with the recognition and understanding of the external
form and internal structure of plants and of their ontogenetic
development. PHYSIOLOGY investigates the vital phenomena of plants.
Both morphology and physiology take into consideration the relation
of plants to the environment and the external conditions, and endeavour
to ascertain whether and how far the structure and the special
physiology of each plant can be regarded as adaptations to the
peculiarities of its environment. These parts of morphology and
physiology are often separated from the rest under the name ECOLOGY.
SYSTEMATIC BOTANY deals with the description of the kinds of plants
and with the classification of the vegetable kingdom. The GEOGRAPHY
OF PLANTS has as its objects to determine the distribution of plants

BOTANY

on the surface of the earth and to elucidate the causes of this.
Extinct plants and the succession of plants in time form the subject
matter of PALAEOPHYTOLOGY, which is thus the historical study of the
changes which have taken place in the vegetation of the earth. All
these are subdivisions of PURE or THEORETICAL botany.

Botany does not, however, pursue theoretical aims only ; it is also
concerned with rendering the knowledge so obtained useful to
mankind. For instance, accurate information is obtained regarding
plants of economic value and how to better employ these, and
adulterations of substances of vegetable origin are detected. There
have thus to be added to the divisions of pure botany the numerous
branches of APPLIED BOTANY, e.g. the study of medicinal plants and
drugs, of vegetable food-substances, of technically valuable plants and
their products, agricultural botany, and that part of plant pathology
which is concerned with the prevention and treatment of diseases of
plants.

In this work, which is primarily concerned with pure botany, a
division is made into a general and a. special part. The object of
GENERAL BOTANY is, by well-devised experiments and by comparison,
to ascertain the most distinctive properties of plants in general or of
the main groups. General botany is further divided into the two
sections treating of morphology and physiology.

The object of SPECIAL BOTANY is to describe the structural
features, the methods of reproduction, and the modes of life of the
various groups of plants. It attempts also to express the more or less
close relationships which exist between plants by arranging them in
as " natural " a system as possible. In this special part a few main
facts as to some branches of applied botany, especially regarding
pharmaceutical plants, are inserted. The results of palaeophytological
study are placed in relation to the description of the particular groups
of existing plants. Lastly, the geography of plants is touched on,
though no connected account of it is attempted.

PART I
GENEKAL BOTANY

DIVISION I
MORPHOLOGY

GENERAL BOTANY

DIVISION I
MOEPHOLOGY

MORPHOLOGY is the study of the external form and the internal
structure of plants and the ontogenetic development of the plant body
as a whole and of its members. In seeking to establish the signifi-
cance and the phylogenetic origin of the parts of plants and the causes
of the formative processes, it aims at a scientific understanding of the
forms of plants.

1. The outer and inner construction of a living being can only be
understood when it is clearly realised that the animal or plant is a
living ORGANISM, i.e. a structure the main parts of which are not
meaningless appendages or members, but necessary ORGANS by the
harmonious co-operation of which the life of the whole is carried on.
Almost all the external parts of plants, and of animals also, are such
organs performing definite functions. They can, however, only play
their parts in the service of the whole organism when they are
appropriately constructed, or, in other words, when their structure
corresponds with or is adapted to their functions. Since the
various parts of the higher plants have diverse functions, it is easy to
see why the plant is composed of members very unlike in form and
structure.

In order to fully understand the construction of an organism it is
further necessary to know the conditions under which it lives and to
be acquainted with its environment. Every plant, or animal, has
structural peculiarities which enable it to live only under certain
conditions of life which are not provided everywhere on the earth's
surface. The conditions of life, for example, are very different in
water from those in a desert, and water plants and desert plants are
very differently constructed. They can only succeed under their
usual conditions or such as are similar, and the desert plants would
not grow in water or the water plants under desert conditions. The

BOTANY PART i

life of an organism is thus only possible when its construction is in
agreement with its environment, and it is ADAPTED TO THE CONDITIONS
OF LIFE.

More penetrating morphological investigation soon shows that,
while almost every member of the plant body has its functions,
every peculiarity in construction cannot be regarded as adapted
to these functions or to the environment. This can only be said
of some of the characters of any part of the plant ; for example, the
abundance of the green pigment and the expanded form of foliage
leaves stand in relation to the main functions of the leaf. Such
characters are spoken of as useful to the organism. Many other
characters are indifferent, such as, for example, the nature of the
margin of leaves, described as entire, serrate, crenate, etc. Others
may even be unfavourable so long as they are compatible with life,
e.g. the absence of the green pigment from large portions of the leaf
in many cultivated forms of Sycamore. Many adaptations appear to
be less perfect than they could be. A character may be useful in one
species while it is indifferent or even harmful in another. Such facts
show clearly what care is requisite in judging of the significance of
organic forms and structures; it is no easy matter to prove such
assumptions by investigation (3).

2. There is a second direction in which morphology endeavours
to attain a scientific understanding of the forms of plants. All
existing plants are regarded as genetically related, the most highly
organised with their diverse organs having gradually arisen phylo-
genetically from simple, unsegmented, unicellular forms. The
organism and its parts have thus undergone manifold transformations in
which, for example, particular organs by change of their structure
took over new functions or became adapted to new conditions of life.
It is thus a very important object of morphology to derive phylogenetic-
ally one form from another. Since the genetic development cannot
be directly traced but has to be inferred, morphology is dependent on
indirect methods in this problem. The most important indications
are obtained by the study of the ontogeny of organisms and by the
comparison of existing plants with one another and with those that
lived in preceding ages. Within certain limits the ontogeny often
repeats the phylogeny and thus contributes to the discovery of the
latter. Comparative study connects divergent forms by means of
intermediates. Since, however, the ontogeny never repeats the
phylogeny completely or without alterations, and the connecting forms
are often wanting, the results of morphology in this direction are
correspondingly imperfect.

When the conviction has been reached after full investigation
that diversely formed members of the plant body had a common
phylogenetic origin, the hypothetical form from which we derive
them is termed the PRIMITIVE FORM, and the changes undergone by it

DIV. I

MORPHOLOGY 9

in the course of descent its METAMORPHOSES. One of the most
important results of morphology is the demonstration THAT THE

VARIOUSLY FORMED PARTS OF EVEN THE MOST HIGHLY DIFFERENTIATED
PLANTS ARE TO BE TRACED BACK TO A FEW PRIMITIVE FORMS. Those

organs which have developed phylogenetically from a common primitive
form are spoken of as HOMOLOGOUS, however different they may appear.
The same morphological value is ascribed to them. For example,
foliage leaves and the leaves of the flower (sepals, petals, stamens, and
carpels) are homologous, and this extends to the leaf-tendrils (Fig. 209)
and the leaf-thorns (Fig. 197). Organs of completely different
structure and functions can thus be homologous. On the other hand,
organs with similar construction and functions (e.g. tubers (Figs. 203,
205, 206), thorps (Figs. 197-199), tendrils (Figs. 208-210)) have
often been genetically derived from different primitive forms. Such
organs are spoken of as ANALOGOUS (for examples cf. p. 165 ff).

Little differentiated structures with ill-defined functions, which we
have reason to believe will in the future become transformed into
more complete organs with well-marked functions, are termed RUDI-
MENTARY organs. Incomplete structures which have retrograded
from more perfect ones are REDUCED organs.

3. Lastly, it is an aim of morphology to ascertain the causes or
conditions which underlie the processes of external and internal
differentiation of the plant and its parts, and of their inherited
(phylogenetic) transformations. In this way it may be possible to
ascertain clearly how in the course of descent adaptive, characters
have arisen. The study which concerns itself with such questions is
EXPERIMENTAL MORPHOLOGY. Most of the problems of this are more
conveniently dealt with as a section of physiology in relation to the
other vital processes of the plant (developmental physiology or
mechanics of development).

Morphology may be divided into external morphology and internal
morphology or anatomy. Such a division would not, however, be
suitable here, when it is desirable to regard the parts of the plant
as organs with definite functions. For this it is necessary to show
the intimate connection that frequently exists between the function
of an organ and both its form and internal structure. From the
outset we must be concerned with the plant as a living organism and
not as a dead structure. The first question to be faced is with what
life is most intimately connected, and this proves to be with a part
only of the whole substance of the plant, namely, with the protoplasm.
The protoplasm is, as a rule, enclosed in the cells which can be regarded
as the elementary parts of the organism. The part of morphology
which is concerned with the structure of cells is termed CYTOLOGY
and will be dealt with first. The tissues formed by associated cells
will then form the subject of a second part of morphology to which
the name HISTOLOGY is given. Lastly, ORGANOGRAPHY deals with

10 BOTANY PART i

the external members of the plant as its organs, taking into considera-
tion both their external form and internal structure.

SECTION I

CYTOLOGY

THE CELLS AS THE BASIS OF LIFE

I. FORM AND SIZE OF CELLS

As already mentioned, both plants and animals are constructed of
elementary parts known as cells. In the case of plants these are
microscopically small chambers, the walls of which are formed of a
firm membrane. In this respect they differ from animal cells. In
the simplest cases the cells are spherical, but more commonly they
have the form of small cubes, polyhedra, or prisms, which are
associated in large numbers in the multicellular organs of plants.
Elongated cells forming fibres or tubes are also of frequent occurrence.
These chambers, each of which consists of the
cell wall or cell membrane enclosing the cavity
or lumen of the cell, are as a rule so small as to
be visible only when highly magnified. Their
mean diameter is frequently between the hun-
dredth and tenth of a millimetre. Owing to
this it was long before the existence of cells
was recognised. Occasionally cells attain a much
greater size. Some sclerenchyma fibres adapted
to special functions are 20 cm., while laticiferous
°[ tubes may be some metres in length.

bottle-cork, which he de- The most important part of the cell is the
scribed as "Schematism protoplast or cell body occupying the cavity en-

or t6xt/ur6 of cork. Cf. i in , i 11 n • i • • i i . .

Fig> 58> closed by the cell wall, since this is the living

portion of the cell. On this account it is now

natural to think rather of the living protoplast than of its enclosing
chamber as the cell ; a cell wall is completely wanting in the case of
many "naked cells." In dead cells, it is true, the protoplasts have
almost or completely disappeared, and such cells are only empty cell
cavities. With the death of their protoplasts these cells need not
lose their use to the plant. They are indeed essential in the construc-
tion of the more highly organised plants in which dead cells form the
water-conducting tracts and contribute to mechanical rigidity.

It was due to the investigation of the cell walls that cells were recognised first
in plants. An English micrographer, ROBERT HOOKE, was the first to notice

DIV. I MORPHOLOGY 11

vegetable cells. He gave them this name in his Micrographia in the year 1667,
because of their resemblance to the cells of a honeycomb, and published an illus-
tration of a piece of bottle-cork having the appearance shown in the adjoining
figure (Fig. 1). The Italian, MARCELLO MALPIGHI, and the Englishman, NEHE-
MIAH GREW, whose works appeared almost simultaneously in 1671, a few years
after HOOKE'S Microyraphia, were the true founders of vegetable histology. The
living contents of the cell, the protoplast, was not recognised in its full significance
until the middle of last century. Only then was attention turned more earnestly
to the study of cytology, which, based on the works of SCHLEIDEN, HUGO v. MOHL,
XAGELI, FERDINAND COHN, and MAX SCHULTZE, was especially advanced by
STRASBUEGER.

II. THE LIVING CELL CONTENTS. THE PROTOPLAST (4)

A. The Constituent Parts of the Cell

If a thin longitudinal section of the growing point of the stem of
one of the higher plants is examined under the high power of the
microscope it is seen to consist of nearly rectangular cells (Fig. 2),
which are full of protoplasm and separated from one another by
delicate walls. If sections in various directions through the apex
are compared, the conclusion is reached that
the cells have the shape of small cubes or
prisms.

In each of the cells a spherical or oval
body, which fills a large part of the cell
cavity, is distinguishable. This body (k)
is the NUCLEUS of the cell. The finely
granular substance (pi) filling in the space
between the nucleus (k) and the cell wall

(ro) is the cell plasm, or CYTOPLASM. In the FIQ 2 ^ cell from the
cytoplasm there are to be found around the root-tip of the Oat. fc. Nucleus;

nucleus a number of Colourless and highly to, nuclear membrane ;n,nucle-

refractive bodies : these are the PLASTIDS or 5«£**Ki "££

CHROMATOPHORES (ch). THE NUCLEUS, what diagrammatic, x about
CYTOPLASM, AND CHROMATOPHORES ARE 1500' After LEWITZKT.)
THE LIVING CONSTITUENTS OF THE CELL.

They form together the protoplasm of the living cell body or PROTO-
PLAST. The nucleus and the chromatophores, which are always
embedded in the cytoplasm, may be regarded as organs of the
protoplast since they perform special functions. It is true that the
particular functions of the nucleus are unknown, but it is certain that
the interaction of nucleus and cytoplasm is necessary to maintain the
life of the cell. In the lowest plants (Cyanophyceae and Bacteria)
such a division of labour in the protoplasm is not certainly proved, the
existence of the nucleus being still a matter of dispute (5). Chromato-
phores are wanting in the Bacteria and Fungi as in all animal cells.

BOTANY

PART

In many animal cells an additional constituent of the protoplast has been
demonstrated as a small body which is called a CENTRIOLE, in the immediate
neighbourhood of the nucleus. Similar bodies are
found in the vegetable kingdom in the cells of some
Cryptogams, but are not of general occurrence even
in them (Fig. 21 A).

It is only the embryonic cells of the plant,
as they are met with in the apices of stem and
root, which are thus completely filled with
protoplasm. This does not hold for the fully
developed cells of the plant which arise from
these by growth in size and alterations of
shape. During this transformation to cells
of the permanent tissues the embryonic cells
of plants, unlike those of animals, become
poorer in protoplasm, since this does not in-
crease in proportion to the growth of the cell.
In every longitudinal section of the growing
point of the stem it can be seen that at some
distance from the tip the enlarged cells have
already begun to show cavities or VACUOLES
(v in A, Fig. 3) in their cytoplasm. These
are filled with a watery fluid, the CELL SAP.
~cy The cells continue to increase in size, and
usually soon attain a condition in which the
whole central portion is filled by a single
large sap cavity (v in JB, Fig. 3). The cytoplasm
then forms only a thin layer lining the cell
wall, while the nucleus occupies a parietal posi-
tion in the peripheral cytoplasmic layer (Fig.
3 B, k). At other times, however, the sap
cavity of a fully -developed cell may be
traversed by bands and threads of cytoplasm ;
and in that case the nucleus is suspended
r" ~| in the centre of the cell (Figs. 5, 10). But

whatever position the nucleus may occupy, it
J£T3LJ± ±nth1 » Always embedded in cytoplasm ; and there
growing point of a phanero- is always a continuous peripheral layer ot
gamic shoot, k, Nucleus ; cy, cytoplasm lining the cell wall. This cyto-

cytoplasm ; v, vacuoles, re- ^ • -111 • vu

presented in B by the sap plasmic peripheral layer is in contact with
cavity. (Somewhat diagram- the cell wall at all points, and, so long as
50<X After the cel1 remains living, it continues in that
condition. In old cells, however, it frequently
becomes so thin as to escape direct observation (Fig. 10), and is
not perceptible until some reagent which attracts water and causes it
to recede from the wall has been employed.

DIV. I

MORPHOLOGY

B. Main Vital Phenomena of Protoplasts

In order to facilitate an insight into the real character of proto-
plasm, attention will first be directed to the SLIME FUNGI (Myxo-
mycetes), a group of organisms which stand on the border between the
animal and vegetable kingdoms. The Myxomycetes are characterised
at one stage of their development by the formation of a PLASMODIUM,
a large, naked mass of protoplasm (Fig. 4). The cytoplasm consists of
a clear ground substance, through which granules are distributed.
This substance is of the consistence of a tenacious fluid; its superficial
region is denser and free from granules, while these are numerous in
the less dense central portion. The granules enable the internal
streaming movements of the cytoplasm to be recognised. The
currents are constantly changing
their direction, moving either
towards or away from the margin.
The formation and withdrawal of
processes of the margin stand in
relation to the direction of the
currents. When naked masses of
protoplasm such as these plas-
modia encounter foreign bodies,
they can enclose them in vacuoles,
and, when of use as food, digest
them.

Even though bounded by a
cell wall the cytoplasm frequently
exhibits movements comparable to
those of the naked amoebae and
plasmodia of Myxomycetes. These

movements are usually found in somewhat old cells. The stimulus
caused by wounding the tissues in making the preparation frequently
increases the activity of the movement (6) ; apparently it quickens
the transport of nutrient material toward the wound. Such move-
ments show that here also the protoplasm is of the nature of a
tenacious fluid. When freed from the cell wall it assumes the form of
a spherical drop. The cytoplasm, enclosed by a cell wall, may either
exhibit isolated streaming movements, the direction of which may
undergo reversals, or a single stream, the direction of which is
constant. These two forms of movement are distinguished as CIR-
CULATION and ROTATION respectively. In rotation, which is found
in cells with the cytoplasm reduced to a layer lining the wall, the
single continuous current follows the cell wall. In circulation, on
the other hand, the movement is found both in the layer lining the
cell wall and in the strands traversing the vacuole. In no case does

BURGER.)

BOTANY

PART I

the boundary layer of the protoplasm take part in the movement.
Circulation is common in cells of land-plants, while rotation is more
usual in water-plants.

When the protoplasm is in rotation, the cell nucleus and chromatophores are
usually carried along by the current, but the chromatophores may remain in the
boundary layer, and thus not undergo movement. This
is the case with the Stoneworts (Characeae), whose long
internodal cells, especially in the genus Nitella, afford
good examples of well-marked rotation. A particularly
favourable object for the study of protoplasm in circu-
lation is afforded by the staminal hairs of Tradescantia
virginica. In each cell (Fig. 5) currents of protoplasm
flow in different directions in the peripheral cytoplasmic
layer, as well as in the cytoplasmic threads, which traverse
the sap cavity. These cytoplasmic threads gradually change
their form and structure, and may thus alter the position of
the cell nucleus.

Movements in limited regions of protoplasts are seen
in many of the lower Algae, especially in their swarm-spores.
Near the anterior end of the swarm-spore the protoplasm
may contain one or several minute pulsating vacuoles which
appear and disappear rhythmically at short intervals. They
empty suddenly, then reappear and slowly increase to their
full size (Fig. 333, 1 v). The protoplast of the swarm-spore
also possesses one or a number of threadlike contractile pro-
cesses (cilia, flagella) which vibrate rapidly and serve as the
motile organs of the cell.

Only within a narrow range of temperature
is the protoplast actively alive, though life is
preserved through a slightly more extended range.
It dies and coagulates, as a rule, at temperatures
slightly above 50° C. Alcohol, acids of suitable
concentration, solution of mercuric chloride, etc.,
rapidly coagulate the protoplasm, and such substances are largely
employed as fixing reagents in microscopical technique (7).

FIG. 5. — Cell from a
staminal hair of Tra-
descnntia viTginica,
showing the nucleus
suspended by proto-
plasmic strands. ( x
240. After STRAS-

BURGEB.)

C. Chemical Properties of the Protoplast (8)

Active protoplasm generally gives an alkaline, under certain con-
ditions a neutral reaction, but never an acid one. It is not a simple
substance chemically, but consists of a mixture of a large number of
chemical compounds. Some of these undergo continual changes, upon
which undoubtedly many important manifestations of the life of the
protoplast depend. The most important components of the mixture
are the proteids. The protoplasm thus shows the reactions of proteids,
and when incinerated gives off fumes of ammonia. A whole series of
proteids occur in the living protoplasm. In the nuclei proteids contain-

DIV. i MORPHOLOGY 15

ing phosphorus (nucleo-proteids) predominate ; these are not dissolved
by pepsin, and only with difficulty by trypsin. Products of the dis-
sociation of proteids, especially amides, are also contained in the
protoplasm. Other components are enzymes, carbohydrates, and
lipoids, such as fats and lecithin, in the condition of a fine emulsion ;
phytosterin (aromatic alcohols with the formula C2l?.H45OH), and
sometimes alkaloids and glucosides. The ash left after incineration
shows that mineral substances are not wholly wanting in the
protoplasm.

By the action of a dilute solution of potash, of chloral hydrate, or of eau de
javelle, all parts of the protoplast are dissolved. Iodine stains it a brownish-yellow
colour ; acid nitrate of mercury (Millon's reagent), rose-red: Such reagents kill
the protoplasm, afte/ which their characteristic reactions are manifested. These
reactions are given by proteid substances, but are not altogether confined to them.

D. Structure of the Parts of the Protoplast

Great assistance in the investigation of the structure of the proto-
plast is afforded by the processes of fixing and staining. Certain
fixing agents harden and fix the protoplasm almost unaltered, but
it is necessary to be on guard against the appearance of a structure
in the process of coagulation (9).

The importance of staining depends upon the fact that the various constituents
of the protoplast absorb dyes with different intensity and hold them more or less
firmly when the preparation is washed. As a general rule only dead protoplasm
is readily stained. For staining fixed vegetable protoplasts, solutions of carmine,
haematoxylin, safranin, acid fuchsin, gentian violet, orange, methylene blue, etc.,
are employed.

1. The Cytoplasm. — This when highly magnified is seen to con-
sist of a clear, hyaline, more or less tenacious fluid (HYALOPLASM) in
which more or less numerous minute drops or granules (MICROSOMES)
are embedded. The latter evidently are various products of the
metabolism, and characterise the granular protoplasm or POLIOPLASM.
The hyaloplasm itself is, however, not a simple solution. AVhen
investigated with the help of the ultra-microscope, an instrument
which reveals granules and droplets too minute to be seen with the
highest powers of the ordinary microscope, it is found to contain
countless numbers of ultra-microscopic particles (10). This is a general
characteristic of those solutions which the physical chemist recognises
as COLLOIDAL SOLUTIONS or SOLS. The demonstration that protoplasm
is a colloidal solution, and, in fact, an emulsion, is of fundamental
importance. By its help many vital manifestations become susceptible
of a physico-chemical explanation.

An extremely thin boundary layer free from granules is found at
the periphery of the protoplast, and a similar layer bounds every
vacuole present in the cytoplasm. The peripheral boundary layer and

BOTANY

PART I

the vacuole walls can be formed anew, but are nevertheless very
important parts of the protoplast, since they determine the taking up
of substances. They are semipermeable membranes, i.e. they allow
water to pass, but are impermeable or only slightly permeable to
many other substances.

Living protoplasm has frequently a foam -like structure. In
dividing protoplasts fine filaments may appear which cease to be
evident in the resting condition of the cell. It is not known whether
the cytoplasm has a still finer internal structure which is not visible.
When fixed and stained, a reticulate or honeycomb - like structure
with embedded granules is formed as in other coagulated colloidal
solutions.

In addition to the structures alluded to above, there have recently been
demonstrated in the cytoplasm of both embryonic and permanent cells certain
filamentous, spindle-shaped or dumb-bell-shaped structures.
These are best seen after special fixation and staining, and
agree so closely with the CHONDRIOSOMES (mitochondria) of
embryonic animal cells that they have been given the same
name (u). Probably they include bodies of various nature
such as minute vacuoles, filamentous structures in the cyto-
plasm, young chromatophores, etc. They have been observed
in some Mosses in the embryonic cells beside the chromato-
phores, and also in the Fungi.

2. The Nucleus (12) has as a rule a spherical,
oval, or lenticular form, but in long cells may be
correspondingly elongated. In embryonic cells its
diameter may amount to two-thirds of the total
diameter of the protoplast. In full-grown cells of
the permanent tissue, on the other hand, the
nucleus is much less conspicuous, since it has not
increased in size. Large nuclei are found in most
Conifers, in some Monocotyledons, and in the
Ranunculaceae and Loranthaceae among the Di-
cotyledons. Secretory cells are as a rule provided
.-- Wuith especially large nuclei. On the other hand,
gus, Hyphoioma fasti- the nuclei of the majority of Fungi (Fig. 6) and of
cuiare, containing five many Siphoneae are very small.

While the cells of the Cormophytes are almost
always uninucleate, in the Thallophytes, on the
contrary, multinucleate cells are by no means infrequent. In many
Fungi (Fig. 6), and in the Siphoneae among the Algae> they are
the rule. The whole plant is then composed either of but one single
multinucleate cell, which may be extensively branched and exhibit
a complicated external form (Fig. 346), or it may consist of a large
number of multinucleate cells, forming together one organism. Thus,
on suitable treatment, several nuclei may be detected in the peripheral

nuclei, (x 500. After
KNIEP.)

DIV. I

MORPHOLOGY

- n

cytoplasm of each of the cells of the common filamentous fresh -water
Alga Cladaphora glomerata (Fig. 7).

The living nucleus has a finely dotted appearance. It usually
contains one or several larger, round, highly refractive granules or
droplets, the use of which is unknown but which are called NUCLEOLI
(Fig. 2 n). The nucleus, the consistence of
which appears to be that of a tenacious fluid,
is surrounded by a NUCLEAR MEMBRANE
(Fig. 2 kw) by which the surrounding cyto-
plasm is separated from the NUCLEAR CAVITY.

Some insight into the finer structure of
the nucleus is obtained from properly fixed
and stained preparations. In these a deeply
staining reticulum of CHROMATIN, which
appears to consist mainly of proteids con-
taining phosphorus, is evident. The nucleoli
are situated in the meshes of the network
within the nuclear cavity which is filled with
the NUCLEAR SAP. The nucleoli stain deeply
but differently from the chromatin.

In many nuclei the reticulum appears to be formed
of a substance called LIXIN that stains feebly, and
the chromatin to be embedded in this as minute
granules. In some Algae and Fungi the nucleoli
contain a proportion of the chromatin. They are
thus not strictly equivalent to the nucleoli of the
higher plants, as is further shown by their behaviour
in the process of nuclear division (13).

It is still unknown what part the nucleus
takes in the vital phenomena of the proto-
plast. It is, however, clear that it is neces-
sary for the maintenance of life in nucleated
cells. It also appears to be of great import-

ance as the main bearer of the hereditary FIG. 7.— A ceil of

characters glomerate, fixed with 1 per cent

3. The Chromatophores(»).-In the ™"£"
embryonic cells of the embryo and of growing After STRASBURGER.)
points, where the chromatophores (Fig. 2 ch)

are principally located around the nucleus, they first appear as small,
colourless, highly refractive bodies of circular, spindle-shaped or fila-
mentous form. In older cells they attain a further development, as
CHLOROPLASTS, LEUCOPLASTS, or CHROMOPLASTS. Since these bodies
have the same origin they are all termed CHROMATOPHORES.

(a) Chloroplasts. — In parts of plants which are exposed to the light
the chromatophores usually develop into chlorophyll bodies or chloro-
plasts. These are generally green granules of a somewhat flattened

BOTANY

PART I

ellipsoidal shape (Fig. 8), and are scattered, in numbers, in the
parietal cytoplasm of the cells. All the chloroplasts in the Cormo-
phytes, and for the most part also in the green Thallophytes, have
this form. In the lower Algae, however, the chlorophyll bodies may
assume a band-like (Fig. 328 C\ stellate, or tabular shape. They are
often reticulately perforated, e.g. Cladophora (Fig. 9). In these cases
the chloroplast often includes one or more PYRENOIDS (Fig. 9 py) •
these are spherical protoplasmic bodies containing an albuminous
crystalloid, and are surrounded by small grains of starch. No further
structure can be distinguished
in the living chlorophyll grains,
which have a uniformly green
colour. The green pigment,

FIG. 8.— Two cells from a
leaf of Funaria hygro-
metrica. cl, Chloroplasts;
n, nucleus. (x 300.
After SCHENCK.)

FIG. 9.— Reticulate chloroplast of Cladophora
arcta. py, Pyrenoids ; k, nuclei. (After
SCHMITZ.)

chlorophyll, is essential for the decomposition of carbon dioxide in the
chloroplasts.

The most recent investigations (15), especially those of WILLSTATTER and his
pupils, have shown that four pigments are present in the chloroplasts. There are
two closely related green pigments (chlorophyll a and &) in the proportions of 3 to
1, and two yellow pigments. The chlorophylls are esters of phytol, an alcohol of
the formula C20H39OH, and a tri-carbon acid. They are thus compounds with
large molecules containing carbon, oxygen, and hydrogen into the construction of
which nitrogen and magnesium enter, but not, as was previously assumed, either
phosphorus or iron. The blue-green CHLOROPHYLL a has the formula C55H7205N4Mg,
while that of the yellow-green CHLOROPHYLL b is C55H7006N4Mg. The yellow
pigments are the orange-red crystalline CAROTIN, hydrocarbons of the composition
C40H56, one of which also occurs in the root of the carrot arid the yellow crystalline

DIV. i MORPHOLOGY 19

XANTHOPHYLL (oxide of carotin, C^H^O^}. Only the chlorophylls are concerned
in the assimilation of carbon dioxide.

All four pigments can be extracted from the fresh or dried chloroplasts by
various solvents, e.g. by acetone or 80-90 % alcohol. . A deep-coloured solution
containing all the pigments can be most readily obtained by pouring boiling alcohol
on fresh leaves. Owing to the contained chlorophyll such a solution is deep green
by transmitted light, but blood-red, owing to FLUORESCENCE, by reflected light.
Its spectrum (Fig. 248) is characterised by four absorption bands in the less refractive
portion and three in the more refractive half. The individual pigments can be
separated by shaking the solution with various solvents. Thus benzol extracts
the chlorophyll and accumulates as a green solution above the alcoholic solution
which is now yellow. The amount of chlorophyll present in green parts of plants
is relatively small, amounting, according to WILLSTATTER, to O'5-l'O % of the dry
substance.

The variegated forms of some cultivated plants have larger or smaller areas of
the leaf of a white or golden colour. The cells here contain colourless or yellow
chromatophores instead of the green chloroplasts.

Many Algae are not green but exhibit other colours. In the blue - green,
verdigris-green, blue, or less commonly violet-coloured Cyauophyceae, and in the red,
violet, or reddish-brown chloroplasts of the Rhodophyceae, there are, in addition to
the four pigments of the green chloroplasts, a blue pigment called PHYCOCYAN, and
a red pigment, PHYCOERYTHRIN. These may occur singly or together, and both
are readily dissolved from the dead cells by water containing a little alkali or
neutral salt and yield a beautifully fluorescent solution. The phycocyan may often
be found as a blue border surrounding one of the Cyanophyceae dried upon paper.
Both pigments appear to be of proteid nature. Little is known as to their
significance (16). In the Brown Algae the colour of the brown or yellow chloroplasts
is due to their containing, in addition to chlorophyll a and a little chlorophyll b,
carotin and xanthophyll, the reddish-brown FUCOXANTHIN (C^H^Og), which is
allied to the last-named pigment (17).

The colourings (18) which the leaves of trees assume in autumn before they fall
are connected with a breaking down of the chloroplasts and then* pigments. There
remain in the protoplasts, in addition to a watery and often reddish-coloured fluid,
only some oil-drops, crystals, and yellow highly refractive spheres. The case is
different in those Coniferae whose leaves turn brown in winter and again become
green in the spring ; the changes undergone by the pigments in the chloroplasts
are here reversible. The assumption of a brown colour by dying foliage-leaves is a
post mortem phenomenon in which brown pigments soluble in water are produced.

In some phanerogamic parasites the chloroplasts are replaced by
colourless, brownish, or reddish chromatophores, which may, however,
in some of these plants still contain a trace of chlorophyll. In the
Fungi chromatophores are completely wanting, as has already been
mentioned.

(b) Leucoplasts. — In the interior of plants, where light cannot
penetrate, leucoplasts are developed from the rudiments of the
chromatophores instead of chloroplasts. They are usually of minute
size (Figs. 5, 10 /), mostly spherical in shape, but often somewhat
elongated in consequence of enclosed albuminous crystals (Fig. 28 AT).
If the leucoplasts become exposed .to the light, they may change into

BOTANY

PART I

chloroplasts. This frequently occurs, for example, in the superficial
portions of potato tubers. The leucoplasts have, in many cells at
least, the special function of transforming sugar into grains of starch,

which appear within them.

(e) Chromoplasts. — These give the
yellow and red colour to many parts of
plants, especially to flowers and fruits.
They arise from the colourless chromato-
phores of embryonic cells or from previously
formed chloroplasts. They may resemble
the chloroplasts in shape but are often
smaller, while their colour is yellow or
orange-red. This depends either on xantho-
phyll or carotin. The pigments are not
uniformly dissolved in the chromoplast
but form minute droplets (grana) in the
FIG. lo.-ceii from the epidermis of piasmatic substance (the stroma) (19). The

Rhoeo discolor, n, Nucleus with . • 11 .1 L* J'l

its nucieoiusoo, and surrounded pigments, especially the carotin, readily
by the leucoplasts (i). Proto- crystallise out and the chromoplasts then
B^^to^ety^rotopk^ become needle-shaped, triangular, or rhombic

which is not represented, lining in form (FigS. 11, 12).

the wall, (x 240.)

The origin and significance of the red EYE-SPOTS

which are found in the cells of many Algae, especially in their motile cells, are
insufficient!}' known. The eye-spot occurs in the neighbourhood of the chloroplast
and is often connected with this (Fig. 333, 1 a). Some investigators hold that it

FIG. 11. — Cell from the upper surface of the
calyx of Tropaeolum majus, showing
chromoplasts. (x 540. After STRAS-
BURGER.)

FIG. 12.— Chromoplasts of the Carrot, some
with included starch grains, (x 540.
After STRASBUROER.)

should be reckoned with the chloroplast and that it serves for the perception of
light somewhat as the eye does. The red pigment, which has been termed HAEMATO-
CHROME, is simply carotin.

DIV. i MORPHOLOGY 21

E. Origin of the Elements of the Protoplast (4)

All the living elements of the protoplast, the cytoplasm, the nucleus,
and the chromatophores, are never newly formed but always arise from
the corresponding elements of previous generations. They increase
in mass by a process of growth, BUT THEY INCREASE IN NUMBER, LIKE

THE PROTOPLAST AS A WHOLE, ONLY BY DIVISION OF THEIR KIND. In this

way the properties of the living constituents of a germ cell are trans-
mitted to all the cells of an organism and ultimately to its reproductive
cells, the uninterrupted continuity of the life being maintained. The
division of the protoplast is usually initiated by the division of the
nucleus. In the case of uninucleate cells this intimate association of
nuclear- and cell-division is necessary in order to ensure that each
daughter cell has a nucleus. In the multinucleate cells (e.g. of Algae
and Fungi) this is not essential, since each daughter protoplast
would obtain the requisite nuclei, and as a matter of fact cell division
in such cases is often independent of nuclear division.

It sometimes happens that the protoplast of a cell, without
dividing, abandons its old cell wall. This process, which is called
REJUVENATION of the cell, has nothing to do with cell division.

The rounding off of the protoplast in a cell of the green alga Oedogonium, and
its emergence from an opening in the old cell wall as a naked swarm-spore, is an
example of rejuvenation. Another is afforded by the protoplasts of the spores of
mosses or ferns and of the pollen-grains of seed-plants surrounding themselves with
a new cell wall within the old membrane, which then perishes.

1. Typical Division of the Protoplast, (a) Nuclear Division.—
Except in a few cases, nuclei reproduce themselves by MITOTIC or
INDIRECT DIVISION. This process, often referred to as KARYOKINESIS,
is somewhat complicated.

Indirect Nuclear Division (20). — In its principal features the pro-
cess is similar in the more highly organised plants and in animals.
Its stages are represented in a somewhat diagrammatic manner in the
following figure (Fig. 13) as they occur in a vegetative cell such as
those which compose the growing point.

The fine network of the resting nucleus (Fig. 13, 1 n) becomes
drawn together at definite points and separated into a number of
bodies (Ffg. 13, 2 ch), the outline of which is at first irregular.
Their form soon becomes filamentous, and the filaments become
denser and at the same time shorter and thicker (3, 4), and stain more
deeply. The filaments are called CHROMOSOMES. Each chromosome
undergoes a longitudinal split which continues to become more
marked (5). The chromosomes, which become shorter, thicker, and
smooth (6), are moved into the plane of division where they constitute
the nuclear or equatorial plate (7 kp\ a stellate figure (aster) which

BOTANY

PART

usually lies in the future plane of division of the cell. It is seen in
surface view in Fig. 14.

While the nuclear network is separating into the individual
chromosomes, cytoplasmic filaments become applied to the nuclear
membrane, surrounding it with a fibrous layer. This layer becomes
raised up from the nuclear membrane at two opposite points
(6 Jc) and forms the polar caps. The filaments converge at the poles,

FIG. 13.— Successive stages of nuclear and cell division in a meristematic cell of a higher plant.
Somewhat diagrammatic. Based on the root of Najas marina, fixed with the chrom-osmium-
acetic mixture and stained with iron haematoxylin. n, Nucleus ; nl, nucleolus ; w, nuclear
membrane ; ch, chromosomes ; k, polar caps ; s, spindle ; kp, nuclear plate ; t, daughter nucleus ;
v, connecting fibres ; z, cell-plate ; m, new partition wall. The chromatophores are not visible
with'this fixation and staining. ( x about 1000. After CLEMENS MOLLER.)

where they constitute two pointed bundles. At this stage the nucleoli
(nl) are dissolved and the nuclear membrane disappears. The fibres
proceeding from the polar caps can thus become prolonged into the
nuclear cavity (7). Here they either become attached to the chromo-
somes, or filaments from the two poles may come into contact and
extend continuously from the one pole to the other. In this way the
nuclear spindle (7 5) is formed. The two halves of each chromosome
separated by the longitudinal split now separate in opposite directions

DIV. I MORPHOLOGY 23

as the daughter chromosomes in order to form the daughter nuclei
(10-12 /). During this stage (diaster) the chromosomes are as a rule
U-shaped with the bends towards the poles of the spindle. Having
reached the poles they crowd together, while the surrounding
cytoplasm forms the nuclear membrane delimiting the new nuclei.
Within the latter the chromosomes again assume a reticulate
structure (11) and unite with one another to form a network (12),
within which their individual limits are not distinguishable. We are
compelled, however, to assume that the individuality of the chromo-
somes is not lost. The young nuclei enlarge and one or more nucleoli
again appear within them (12).

The end attained by this mechanism of division is that the
substance of the ^nucleus, and especially of the chromosomes, is dis-
tributed as equally as possible to the two
daughter nuclei at each division. From this
it may be concluded that the chromatin is
especially important for the life of the cell and
of the whole organism, and that the chromo-
somes play the main part in the transmission
of hereditary qualities.

The number of chromosomes occurring in
any nucleus is a definite one, and when a
deviation from the usual number is met with, FlG- u.— Young ceils from a
it is due to some of the chromosomes having 1™""^
remained united end to end (21). The chromo- showing a nuclear plate in
somes of a nucleus may be of different sizes the Polar view- The chr0'

/T,. , . v , i i-rt» • • mosomes are grouped in

(Fig. 14) ;^ when such differences in size exist ^^ (x 160C. AfterSxRAs-

they persist in successive divisions. The BURGER.)

smallest number of chromosomes which has

yet been found in the nuclei of vegetative cells of the more highly

organised plants has been six ; as a rule the number is much larger.

In the lowest divisions of the vegetable kingdom, in some Algae
and Fungi, the process of indirect nuclear division is simplified, the
masses of chromatin being less carefully divided between the daughter
nuclei (13).

The changes occurring in a mother nucleus preparatory to division are termed
the PROPHASES of the karyokinesis. These changes extend to the formation of the
nuclear plate, and include also the process of the longitudinal division of the chromo-
somes. The stage of the nuclear plate is the METAPHASE. The separation of the
daughter chromosomes is accomplished in the ANAPHASE, and the formation of
the daughter nuclei in the TELOPHASE of the division. The real purpose of the
whole process is attained in the quantitative and qualitative division of the
chromosomes, resulting from their longitudinal splitting. The anaphases and
telophases of the karyokinesis are but a reverse repetition of the prophases. The
reversal of the stages in the process of nuclear division commences with the
separation of the daughter chromosomes. The stage of the nuclear plate at

24 BOTANY PART i

which the progressive is replaced by the regressive movement tends to last a
considerable time.

It is uncertain in what way the chromosomes are so precisely moved in the
process of karyokinesis as described above. STRASBUHGER assumed that the fibres
of the spindle which appear to end at the chromosomes (traction fibres) by their
shortening drew the daughter chromosomes from the nuclear plate to the poles,
while the fibres extending from the one pole to the other were supporting fibres
to the spindle. This assumption does not, however, explain the movement of the
chromosomes toward the nuclear plate.

In certain reproductive cells of plants and animals resulting from fertilisation
the nuclear division proceeds in a special manner and differs from the typical
process just described. It is termed the reduction division, or meiosis (cf. p. 203).

Direct Nuclear Division (22). — In addition to the mitotic or
indirect nuclear division there is also a DIRECT or AMITOTIC division,
sometimes called FRAGMENTATION. Direct division of the nucleus
occurs in nuclei which were themselves derived by indirect division.
It is essentially a process of constriction which need not, however,
result in new nuclei of equal size. Instructive examples of direct
nuclear division are afforded by the long internodal cells of the
Stoneworts (Characeae).

In the case of the Stoneworts, after a remarkable increase in the size of the
nucleus, several successive rapid divisions take place, so that a continuous row of
beadlike nuclei often results. While in uninucleate cells indirect nuclear division
is followed by cell division, this is not the case after direct nuclear division.

(b) Multiplication of the Chromatophores. — This is accomplished
by a direct division, as a result of which, by a process of constriction,
a chromatophore becomes divided into nearly equal
halves. The stages of this division may best be observed
in the chloroplasts (Fig. 15).

^ Division °f the Cytoplasm. — In the uninucleate
cells of the higher plants cell division and nuclear division
are' generally> closely associated. The fibres of the
spindle extending from pole to pole persist as CON-
FIG. 15. — chioro- NECTING FIBRES between the developing daughter nuclei
phyii grains from (Fig. 13, 9 v\ and their number is increased by the inter-
£^"££JE position of others (Fig. 13, 10, 11). In consequence of
rica, resting, and this a barrel-shaped figure, the PHRAGMOPLAST is formed,
in process of divi- At the same time the connecting fibres become thickened
c\°udedTtarch (^g- 13, 11) at the equatorial plane, and the short
grains are rod-shaped thickenings form what is known as the CELL
present in the PLATE> ln the case of cells rich in protoplasm or small
After STRAS- in diameter the connecting fibres become more and more
BURGER.) extended, and touch the cell wall at all points of the

equatorial plane. The elements of the cell plate unite
and form a cytoplasmic limiting layer, which then splits into two. In
the plane of separation the new partition wall is formed of cell-wall

DIV. I

MORPHOLOGY

substance, and thus SIMULTANEOUSLY divides the mother cell into
two daughter cells (Fig. 13, 12 m).

If, however, the mother cell has a large sap cavity, the connecting utricle
cannot at once become so extended, and the partition wall is then formed
SUCCESSIVELY (Fig. 16). In that case, the
partition wall first commences to form at the
point where the utricle is in contact with
the side walls of the mother cell (Fig. 16 A}.
The protoplasm then detaches itself from
the part of the new wall in contact with
the wall of the mother cell, and moves
gradually across until the septum is com-
pleted (Fig. 16 B an<2 O) ; the new wall
is thus built up by successive additions
from the protoplasm.

FIG. 16.— Three stages in the division of a
living cell of Epipactis palustris. (x 365.
After TREUB.)

the Thallophytes, even in
the case of uninucleate cells, the

partition wall is not formed within connecting fibres, but arises
either simultaneously from a previously formed cytoplasmic plate, or
successively, by gradual projection inwards from the wall of the
mother cell. In this form of cell division the new wall commences
as a ring-like projection from the inside of the wall of the mother
cell, and gradually pushing farther into the cell finally extends com-
pletely across it (Figs. 17, 18). In a division of this sort, in

«f ch ck

FIG. 17.— Cell of Spirogyra in division, n,
One of the daughter nuclei ; w, develop-
ing partition wall : eft, chloroplast
pushed inward by the newly forming
wall, (x 230. After STRASBURGER.)

FIG. 18.— Portion of a dividing cell of Clado-
phora fracta. w, Newly forming partition
wall ; eft, dividing chromatophore ; k,
nuclei. ( x 600. After STRASBURGER.)

uninucleate cells, nuclear division precedes cell division, and the new
wall is formed midway between the daughter nuclei (Fig. 17).

In multinucleate cells a cell division does not follow on each
nuclear division. Among Algae and Fungi there are large and
externally segmented forms which consist internally of a single

BOTANY

PART I

protoplasmic mass with many nuclei ; this is not divided into
chambers by cell walls.

2. Deviations from typical Cell Division. — The main deviations
from typical cell division which are found here and there in the
vegetable kingdom are MULTiCELLULAR FORMATION, CELL-BUDDING, and

FREE CELL FORMATION.

(a) Free Nuclear Division and Multicellular Formation. — The nuclear division
in the multinucleate cells of the Thallophy tes may serve as an example of free nuclear
division, that is, of nuclear division unaccompanied by cell division. In plants
with typical uninucleate cells, examples of free nuclear division also occur. This

method of development is especially
instructive in the embryo-sac of
Phanerogams, a cell, often of re-
markable size and rapid growth,
in which the future embryo is
developed. The nucleus of the
rapidly growing embryo-sac
divides, the two daughter nuclei
again divide, their successorsrepeat
the process, and so on, until at
last thousands of nuclei are often
formed. No cell division accom-
panies these repeated nuclear divi-
sions, but the nuclei lie scattered
throughout the peripheral cyto-
plasmic lining of the embryo-sac.
When the embryo-sac ceases to en-
large, the nuclei surround them-
selves with connecting strands,
which then radiate from them in
all directions (Fig. 19). Cell plates
make their appearance in these
connecting strands, and from them
FIG. 19.— Portion of the peripheral protoplasm of the ce^ wans arise. In this manner
embryo-sac of Reseda odorata. showing the commence- ,, • r i f 4-v,Q

ment of multicellular formation. This progresses the **&** protoplasm of the
from above downwards. From a fixed and stained embryo - sac divides simultane-
preparation. (x 240. After STRASBTJRGER.) ously into as many cells as there

are nuclei. All intermediate stages

between simultaneous multicellular formation and successive cell division can
be found in embryo-sacs. Where the embryo-sac is small and of slow growth,
successive cell division takes place, so that multicelluiar formation may be
regarded as but a shortened process of successive cell division, induced by an
extremely rapid increase in the size of the cell.

(b) Cell-budding.— This is simply a special variety of ordinary cell division, in
which the cell is not divided in the middle, but, instead, pushes out a protuberance
which, by constriction, becomes separated from the mother cell. This mode of cell
multiplication is characteristic of the Yeast plant (Fig. 20) ; the spores, known as
conidia and basidiospores, which are produced by numerous Fungi, have a similar
origin (Fig. 398).

DIV. I

MORPHOLOGY

from those formed by the usual mode of cell division, in that the free nuclear division

is followed by the formation of cells, which have no contact with each other, and in

the formation of which

the whole of the cyto- _*<

plasm of the mother cell

is not used up. This

process can be seen in

the development of the

swarm cells of some

Algae, in the developing

embryo of the Gymno-

sperms, in Ephedra, for

example, and also in the

formation of the spores

of the Ascomycetes. *A

single nucleus is present

FIG. 20. — Saccharomyces
cerevisiae. 1, Cells
without buds ; 2 and
3, budding cells. ( x
540. After STRAS-

BURGER.)

;

FIG. 21. — Successive stages of the delimitation of a spore in the
ascus of Erysipht, communis. s, Nuclear network ; n, nucleolus.
(x 1500. After HARPER.)

to begin with in each ascus of the Ascomycetes. By successive divisions eight
nuclei lying free in the cytoplasm are derived from this. A definite portion
of cytoplasm around each of these nuclei becomes limited by a peripheral layer,
which then forms a cell wall. Thus eight separate spores arise (cf. Fig. 381).
As the researches of Harper (23) have shown, the formation of the peripheral* layer
proceeds from a centrosome-like mass of kinoplasm (Fig. 21 A) which formed a pole
of the spindle in the preceding nuclear division. The nucleus is drawn out towards
this mass of kinoplasm. From the latter kinoplasmic radiations proceed (kp]
which surround the spore as it becomes delimited, and finally fuse to form its
peripheral layer (Fig. 21 B, C, Z>).

III. THE LARGER NON-LIVING INCLUSIONS OF THE
PROTOPLASTS (24)

In addition to the minute microsomes which are always present
in the cytoplasm, larger non-living inclusions make their appearance
in the cytoplasm and chromatophores of all cells as they pass from
the meristematic to the mature condition. The cell sap, which in
larger or smaller vacuoles is hardly ever absent from a cell of the
mature tissues of a plant, has already been mentioned. Besides these
droplets of a watery solution, fats and oils and also solid bodies
in the amorphous or crystalline condition frequently occur in the
cell sap or the cytoplasm itself. Many of these included substances

28 BOTANY

are of great value in the life of the plant as RESERVE MATERIALS.
They are accumulated in considerable quantity for future use in the
cells of storage organs (bulbs, tubers, seeds). Others are end products
of metabolism which may, however, be of great ecological importance.

A. Inclusions of the Cytoplasm

1. Fluid Inclusions of the Cytoplasm, (a) The Cell Sap. — This
name is given to the watery fluid in the larger vacuoles or the single
sap cavity of vegetable cells (Fig. 3). It is more or less rich in
various dissolved substances, which are sometimes reserve materials
and at others end products of metabolism ; solid inclusions, especially
in the form of crystals, also occur in it. The substances in the cell
sap may be the same or different from those in the protoplasm. The
dissolved substances may differ in the various vacuoles of the
same cell.

All cell sap contains in the first place INORGANIC SALTS, especially
nitrates, sulphates, and phosphates. Its reaction is usually acid owing
to the presence of ORGANIC ACIDS (e.g. malic acid, which is constantly
present in the leaves of succulent plants, tartaric acid, oxalic acid, etc.),
or salts of these.

The SOLUBLE CARBOHYDRATES are especially important constituents
of the cell sap, often as reserve materials. Various SUGARS (cane-sugar,
maltose or malt-sugar, glucose or grape-sugar) are the most important.
Cane-sugar is frequently stored as a reserve material, as in the sugar-
beet, carrot, the stem of the sugar-cane, and other plants from which
sugar is obtained. A similar place is taken by the carbohydrate
INULIN in the Compositae and by GLYCOGEN in the Fungi. Carbo-
hydrates are transported throughout the plant in the form of sugar.

If preparations containing glucose be placed in a solution of copper sulphate, and,
after being thoroughly washed, are transferred to a solution of caustic potash and
heated to boiling, they will give a brick-red precipitate of cuprous oxide. If cane-
sugar or saccharose be present, this treatment gives only a blue colour to the cell
sap. Treated with alcohol, inulin is precipitated in the form of small granules,
which may be redissolved in hot water. When portions of plants containing much
inulin, such as the root tubers of Dahlia variabilis, are placed in alcohol or dilute
glycerine, the inulin crystallises out and forms sphaerites, spheroidal bodies com-
posed of radiating crystal needles ; these sphere - crystals often show distinct
stratification and are easily broken up into wedge-shaped portions.

GLYCOGEN, which is of frequent occurrence in animal tissues, occurs in the
Fungi, Myxomycetes, and the Cyanophyceae in the form of droplets. In the
Fungi it takes the place of other carbohydrates such as starch and sugar.
Cytoplasm containing glycogen is coloured reddish -brown with a solution of
iodine. This colour almost wholly disappears if the preparation be warmed, but
reappears on cooling.

MUCILAGE is often found in the cells of bulbs, as in Allium cepa and Urginea
(Sdlla) maritima ; in the tubers of Orchids ; also in aerial organs (Fig. 22), especially

DIV. i MORPHOLOGY 29

in the leaves of succulents, and also outside the protoplasts in the cell wall
(cf. p. 38).

AMIDES, especially Asparagin and also ALBUMINOUS SUBSTANCES,
occur in the cell sap as reserve materials or as intermediate products
of the metabolism (cf. p. 1 4 for reactions).

Highly refractive vacuoles filled with a concentrated solution of
TANNIN (25) are of frequent occurrence in the cytoplasm of cortical
cells, and may often grow to a considerable size. ALKALOIDS,
GLUCOSIDES, and BITTER PRINCIPLES allied to these are also not
infrequent in the cell sap. All these are usually end products of
metabolism.

The dark-blue or green, colour reaction obtained on treatment with a solution
of ferric chloride or ferric sulphate, and the reddish-brown precipitate formed
with an aqueous solution of potassium bichromate, are usually accepted as tests
for the recognition of tannin, although equally applicable for a whole group of
similar substances. The tannins are not further utilised in the plant. They
often impregnate cell walls, which then persist and resist decay.

The cell sap is often coloured, principally by the so-called ANTHO-
CYANINS, a group of non-nitrogenous glucosides. They are blue in
an alkaline, and red in an acid- reacting cell sap, and, under certain
conditions, also dark-red, violet, dark-blue, and even blackish-blue.
Alkalies frequently change the colour to green. Anthocyanin can be
obtained from the cell sap of a number of deeply coloured parts of
plants in a crystalline or amorphous form. Less commonly yellow
substances, ANTHOCLORE and ANTHOXANTHINE, are found dissolved in
the cell sap as in the yellow floral leaves of the Primrose and the
yellow .Foxglove. A brown pigment called ANTHOPHAEINE occurs in
the cells of the blackish -brown spots of some flowers.

The researches of WILLSTATTER and his pupils (a) have advanced our knowledge
of the chemical constitution of the anthocyanins. They are glucosides in which
cyanidins (aromatic pigment components, hydroxyl compounds of phenylbenzo-
pyrilium, and apparently related to the flavones), are combined with sugar, e.g.
in the Cornflower cyanidin (C15H1006) and in the flower of the Larkspur delphinidin
(C15H1007). In red flowers the cyanes are united with acids and in blue flowers
with alkalies-, while the pigments in violet flowers are neutral. The anthoxanthins
also are glucosides with aromatic pigment components which belong to the flavones.

Blood-coloured leaves, such as those of the Copper Beech, owe
their characteristic appearance to the united presence of green
chlorophyll and anthocyanin. The autumnal colouring of leaves
also depends on the formation of anthocyanin. The different colours
of flowers and fruits which often serve to attract animals are due to
the varying colour of the cell sap, to the different distribution of the
cells containing the coloured cell sap, and also to the different com-
binations of dissolved colouring matter with the yellow, orange, or
red chromoplasts and the green chloroplasts.

30 BOTANY PART i

(b) Vaeuoles containing Fats (Fatty Oils). — These substances are
of common occurrence as reserve materials ; about nine-tenths of all
Phanerogams store them in their seeds. In seeds especially rich in
oil this forms highly refractive droplets distributed through the
cytoplasm (e.g. castor-oil in seeds of Ricinus) and may form 70 °/Q
of the dry weight. Fats are glycerine esters of fatty acids, especially
of palmitic acid (C16H3202), stearic acid (C18H86O2), and oleic acid
(C18H3402). Since fats provide a greater amount of energy than
other storage substances, the space available is best utilised for them.

(c) Vacuoles with Ethereal Oils and Resins (27).— These also occur as highly
refractive droplets. They are found in the cells of many petals. Special cells,
often with corky walls and filled with resin or ethereal oils, are found in the
rhizomes of certain plants, as for instance in those of Acorus Calamus and of
Ginger (Zingiber officinale) ; also in the bark, as, for example, of Cinnamon trees
(Cimiamomum) ; in the leaves, as in the Sweet Bay (Laurus nobilis).; in the
pericarp and seed of the Pepper (Piper nigrum} ; in the pericarp of Anise (Illicium
anisatum}. Ethereal oils and resins have antiseptic properties. In flowers their
scent assists in attracting insects. Under some conditions the oil assumes the
crystalline form, e.g. in rose petals.

2. Solid Inclusions of the Cytoplasm, (a) Crystals of Calcium
Oxalate. — Few plants are devoid of such crystals. They are formed
in the cytoplasm as end products of metabolism, within vacuoles
which afterwards enlarge and sometimes almost fill the whole cell. In
such cases the other components of the cell become greatly reduced ;
the cell walls at the same time often become corky, and the whole
cell becomes merely a repository for the crystal. The crystals may
be developed singly in a cell, in which case they are of considerable
size (Fig. 130 k, 175 Bk, 184 k), or many minute crystals may fill the
cell as a crystalline sand. In other cases they form crystal aggregates
(Fig. 130 k, 186 k), clusters of crystals radiating in all directions from
a common centre, or many needle-shaped crystals lie parallel forming
a bundle of raphides (Fig. 22). The various types of crystals pre-
dominate in different plants.

The LARGE SOLITARY CRYSTALS belong to the tetragonal or to the monosym-
metric system, the concentration of the mother-liquor from which they crystallise
out determining which system is followed. The stellate CRYSTAL AGGREGATES
radiating from an organic nucleus are particularly common. In Monocotyledons
and in many Dicotyledons RAPHIDES are of widespread occurrence (Fig. 22), the
bundle of crystals being always enclosed in a large vacuole filled with mucilage.

SILICEOUS BODIES, which are only soluble in hydrofluoric acid, are found in
the cytoplasm of many cells, especially of Palms and Orchids, and often com-
pletely fill the whole cell.

(b) Aleurone Grains. Proteid Crystals. — Albuminous substances
may be stored in a dissolved form in the cell sap of succulent parts of
plants. Thus they can be precipitated by treatment with alcohol in
the cells of the potato tuber. In dry structures, such as many seeds,

DIV. I

MORPHOLOGY

proteid substances occur as solid granules called ALEURONE GRAINS,
which are especially large in oily seeds (Fig. 23). They are formed
from vacuoles, the contents of which are rich in albumen, and harden
into round grains or, sometimes, into irregularly shaped bodies. The
albuminous substances of which they consist are mainly globulins (2S).
A portion of the albumen often crystallises, so that frequently one
and occasionally several
crystals are formed within the ^
aleurone grain. In aleurone
grains containing albumen

FIG. 23.— A, Cell from the endosperm of Ricinus
communis, in water ; B, isolated aleurone grains
in olive oil ; k, albumen crystals ; g, globoid.
(x 540.

FIG. 22. — Cell from the cortex of Dra-
caena rubra, filled with mucilagin-
ous matter and containing a bundle
of raphides, r. (x 1GO. After

BCHKNCK.)

FIG. 24.— Part of a section of a grain of wheat, Triticum,
vulgare. p, Pericarp ; t, seed coat, internal to which
is the endosperm ; oZ, aleurone grains ; am, starch
grains ; n, cell nucleus, (x 240. After STRASBURGER.)

crystals there may often be found globular bodies termed GLOBOIDS
(Fig. 23 g\ which consist of globulins combined with the calcium and
magnesium salt (phytin) of an organic phosphoric acid (phytic acid).
Crystals of calcium oxalate are also found enclosed in aleurone grains.
Free globoids are found in the cytoplasm of some seeds. In the
cereals the aleurone grains, which lie only in the outer cell layer of
the seeds (Fig. 24 al\ are small, and free from all inclusions; they
contain neither crystals nor globoids. As the outer cells of wheat

32 BOTANY PART i

grains contain only aleurone, and the inner almost exclusively starch,
it follows that flour is the richer or poorer in albumen, the more
or less completely this outer layer has been removed before the wheat
is ground. The aleurone layer remains attached to the inner layer
of the seed-coat, in the bran.

Reactions for aleurone are the same as those already mentioned for the
albuminous substance of protoplasm. Treatment of a cross-section of a grain of
wheat (Fig. 24) with a solution of iodine would give the aleurone layer a yellow-
brown colour.

ALBUMEN CRYSTALS. — Crystals of albumen are of relatively frequent occurrence
in vegetable tissues and are often found in aleurone grains (Fig. 23) ; especially
large crystals are found in the endosperm of the Brazil nut (Bertholletia excelsa).
Albumen crystals may also occur directly in the cytoplasm ; as, for instance, in
the cells poor in starch, in the peripheral layers of potatoes, and in chromato-
phores (Fig. 28). Albumen crystals are sometimes found even in the cell nucleus.
This is particularly the case in the Toothwort (Lathraea), and in many Scrophu-
lariaceae and Oleaceae. Albumen crystals usually belong either to the regular
or to the hexagonal crystal system. They differ from other crystals in that, like
dead albuminous substances, they may be stained, and also in that they are
capable of swelling by imbibition.

B. Inclusions of the Chromatophores

Crystals of albumen and of pigments have already been mentioned
as occurring in chromatophores (Fig. 28), but the most important
inclusion is STARCH (29). The chloroplasts in plants exposed to the
light almost always contain starch grains (Fig. 15). These grains of
starch found in the chloroplasts are formed in large numbers, but as
they are continually dissolving, always remain small. Large starch
grains are found only in the reservoirs of reserve material, where
starch is formed from the deposited products of previous assimilation.
Such starch is termed RESERVE STARCH, in contrast to the ASSIMILA-
TION STARCH formed in the chloroplasts. It also only arises in
chromatophores, in this case the LEUCOPLASTS or starch-builders which
form it from sugar.

All starch used for economic purposes is reserve starch. The
amount of starch contained in reservoirs of reserve material is often
considerable ; in the case of potatoes 20 per cent of their whole
weight is reserve starch, and in wheat the proportion of starch is as
high as 70 per cent. The starch flour of economic use is derived by
washing out the starch from such reservoirs of reserve starch. In
the preparation of ordinary flour, on the contrary, the tissues contain-
ing the starch are retained in the process of milling.

The reserve starch consists of flat or roundish (oval or circular)
grains, differing in size in different plants. A comparison of the
accompanying figures (Figs. 25-27), all equally magnified, will give

D1V. I

MORPHOLOGY

an idea of the varying size of the starch grains of different plants.
The size of starch grains varies, in fact, from 0'002 mm. to O'lTO

FIG. 26.— Starch grains from the
cotyledons of Phaseolus rul-
garis. (x 540. After STRAS-
BURGER.)

FIG. 25.— Starch grains from a potato. A, simple;
B, half- compound ; C and D, compound starch
grains ; c, organic centre of the starch grains.
( x 540. After STRASBURGER.)

FIG. 27.— Starch grains of the oat,
Arena sativa. A, Compound
grain ; B, isolated component
grains of a compound grain.
(x 540. After STRASBURGER.)

mm. Starch grains O'lTO mm. large may be seen even with the

naked eye, as minute bright bodies. The starch grains stored as

reserve material in potatoes are comparatively large, attaining an

average size of 0'09 mm. As shown in the above figure (Fig, 25 A),

they are plainly stratified. The stratification is due to the varying

densities of the successive layers ;

thicker denser layers which appear

clear by transmitted light alternate

with thinner less dense layers which

appear dark. They are excentric in

structure, since the organic centre,

about which the different layers are

laid down, does not correspond with

the centre of the grain but is nearer

to one margin. The starch grains of

the leguminous plants and cereals, on

the other hand, are concentric, and

the nucleus Of their formation is in FlG. 2S.-Leucoplasts from an aerial tuber

the centre of the grain. The starch

grains of the kidney bean, Phaseolus

ruh/aris (Fig. 26), have the shape of

flattened spheres or ellipsoids ; they

show a distinct stratification, and are crossed by fissures radiating

from the centre. The disc-shaped starch grains of wheat are of

of Phajiis g randifol i us. A , C, D, viewed
from the side ; B, viewed from above ;
st, starch grain ; kr, proteid crystal,
(x 540. After STRASBURGER.)

34 BOTANY PART i

two very different sizes, and only indistinctly stratified. In addition
to the simple starch grains so far described, half-compound and com-
pound starch grains are often found. Grains of the former kind are
made up of two or more individual grains, surrounded by a zone of
peripheral layers enveloping them in common. The compound grains
consist merely of an aggregate of individual grains unprovided with
any common enveloping layers. Both half -compound (Fig. 25 B) and
compound starch grains (Fig. 25 C, D) occur in potatoes, together with
simple grains. In oats (Fig. 27) and rice all the starch grains are
compound. The compound starch grains of rice consist of from 4 to
100 single grains; those of the oat of about 300, and those of
Spinada glabra sometimes of over 30,000. Starch grains have thus
distinctive forms in different plants.

The structure of starch grains becomes intelligible in the light of
their mode of formation. If the starch grain is uniformly surrounded
by the leucoplast during its formation, it grows uniformly on all sides
and is symmetrical about its centre. If the formation of a starch
grain begins near the periphery of a leucoplast, the grain will grow
more rapidly on the side on which the main mass of the leucoplast
is present, and the starch grain thus becomes excentric (Fig. 28).
Should, however, several starch grains commence to form at the
same time in one leucoplast, they become crowded together and form
a compound starch grain, which, if additional starchy layers are laid
down, gives rise to a half-compound grain.

Starch grains are composed of a, carbohydrate with the formula
(C6H1005)n. When it is to be employed further in the metabolism of
the plant, starch is again transformed into sugar by the action of an
enzyme called DIASTASE.

Starch grains may be regarded as crystalline structures, sphaero- crystals, or
sphaerites, which are built up of radially arranged, needle-shaped crystals of a- and
/3-amylose. With polarised light they show, like inorganic sphaerites, a dark cross,
an appearance depending on the doubly-refractive nature of the elements of the
starch grain. The stratification may be the expression of differences in form and
abundance of the crystalline needles in the successive layers.

Starch grains are as a rule coloured, first blue and then almost black, by a
watery solution of iodine ; the grains of glutinous rice, however, stain wine-red,
possibly consisting of amylodextrine. They are easily swollen at ordinary
temperatures in solutions of potash or soda and by chloral hydrate. They also
swell and form a paste in water at 70°-80° C. They dissolve, i.e. are transformed
into sugar without previous swelling, in concentrated sulphuric acid. Heated
without the addition of water, or roasted, the starch is transformed into an
imperfectly known substance that is soluble in water.

IV. THE CELL WALL (30)

Each protoplast in plants is as a rule enclosed by a firm invest-
ment called the cell wall. This is formed on the outside of the

DIV. I

MORPHOLOGY

protoplast and is not itself regarded as living. Many plants
commence their development as naked protoplasts, e.g. swarm-spores
or egg- cells. These cells, before developing further and dividing,
secrete a thin cell wall clothing the surface. In cell division, as has
already been described, a partition wall is usually formed between the
new cells so that each protoplast remains enclosed by a cell wall.

The form of cells is usually dependent on the cell wall, for the
naked protoplast behaves like a fluid drop. The relatively small and
uniformly shaped meristematic cells attain their ultimate size and
special shapes by the growth in surface of their walls. This growth
is sometimes the same all round, and at other times is limited to

-B

tne tip or an

a girdle -like zone, or some other

circumscribed region. It comes

FIG. 29.— A , Spherical stalked cell
of Saprolegnia with circular
pits in the wall. B, One pit
of this in optical section more
highly magnified.

FIG. 30.— Sclerotic cell from the shell of a walnut
showing stratification of the wall and branched
pits. The canals of some of these pass ob-
liquely out of the plane of section. (ROTHERT,
adapted from RELNKE.)

about as a result of the stretching and sometimes the rupture of the
wall and the secretion and deposit of new cell-wall substance by the
protoplast (GROWTH BY APPOSITION), or else by the insertion of new
material between the particles of the existing wall (GROWTH BY
INTUSSUSCEPTION).

The cell wall serves to protect and also to give rigidity to the
protoplast. This is attained both by the tension of the membrane
(TURGOR, cf. p. 225) and by the growth in thickness of the cell wall.
The thin and structureless walls become as a rule thickened either
uniformly or so that parts remain relatively thin, while others grow
in thickness. In many cells the whole extent of the wall is thickened
with the exception of small circular, elliptical, or spindle-shaped
areas which form the PITS. These appear in the thickened wall as

BOTANY

depressions (Fig. 29) or tubular canals (Fig. 30), closed at one end, as
a rule the outer, by the unthickened portion of the cell wall which
forms the pit membrane (Fig. 29 J5). Sometimes with the increase
in the thickness of the wall the canals of several pits unite forming
BRANCHED PITS. Such branched pits have usually very narrow canals
and occur for the most part in extremely thick and hard cell walls as,
- [B|I IP _ j_q . ^or ^stance, those of sclerotic

'"f ' f ,jBl-.» ••JJIIII «IJ^ , ^k ^ gcjere-cjeg £pj^ gQ^

^z-^^^^^^^ In other colls the greater part

FIG. 31.-Portion of a tubular rhizoid of Marchantia with °f the wal1 is Only slightly

local peg-like thickenings of the wall. thickened, while narrowly

circumscribed portions

thicken greatly and assume the form of projections, warts, simple or
branched pegs (Fig. 31), spines (Fig. 32), ridges, bands or a network
(Figs. 67, 68). Such thickenings may form either on the outside
(centrifugal) or on the inner surface of the wall (centripetal). Small
projections often occur on hairs, while the thickenings of spores
and pollen grains (Fig. 32) and in many water-conducting cells of
the higher plants (Figs. 67, 68) are characteristic.

A very peculiar form of thickening with calcium carbonate deposited in it and
localised to one small region of the wall is seen in the CYSTOLITH which forms a
stalked body, hanging in the cell like a bunch of grapes (Ficus elastica, Fig. 33).

The growth in thickness, which commences during the growth in
surface of the wall, continues after this is complete. It is usually
effected by apposition, i.e. the
deposition of material by the
protoplasm on the already exist-
ing wall in the form of new
layers or lamellae. In this way
a concentric stratification of the
cell wall arises (Fig. 30). In
the thickened wall thicker, denser
lamellae alternate with thinner
and less dense layers, which are
often not only richer in water but

chemically different from the FlG- 32-— -4, Pollen-grain of CucurUtaPepo in surface
, rpi -i , view, and partly in optical section, rendered

denser layers, Ine latter are transparent by treating with oil of lemons.
more highly refractive and appear ( x 240.) B, Part of transverse section of pollen
brighter. In many, apparently srain of CucurUta verrwosa. (x 540. After

11 vi i STRASBURGER.)

homogeneous, cell walls such

stratification can be recognised after swelling has been brought about

by treatment with strong acids or alkalies.

Not uncommonly growth in thickness also depends on the
introduction of new material into the existing wall (intussusception).

Centrifugal thickening of the wall is frequently brought about by intussusception.
This can take place at some distance from the protoplasm and be associated with

DIV. I

MORPHOLOGY

chemical and structural differentiation of the cell wall, which thus behaves almost
as if it were a living structure. The centrifugal thickening of the walls of cells
which have arisen by free cell formation (e.g. ascospores) is effected by the
periplasm from which the cells have been cut out (cf. p. 27). Similarly the
thickenings of many pollen grains and spores are deposited from without by
the protoplasm of the tapetal cells which line the cavities in which they are
developed. The protoplasts of the tapetum fuse to a periplasmodium surrounding
the young spores or pollen grains (31).

In some cases fine striae, running obliquely to the longitudinal axis of the cell,
are apparent when the thickening layers are viewed from the surface (Fig. 34).
This striation depends either on a distinction in the individual thickeuing layers
of regions of different density, the denser frequently projecting into the cell cavity,
or (in many Algae such as Cladophora)

on a wave-like folding of ,the lamellae.
If the wall is distinctly stratified the
striae in successive thickening layers are
usually inclined in opposite directions
(Fig. 34).

FIG. 33.— Cell of Fieus elastica contain-
ing a cystolith. c. (x '240. After
SCHEXCK.)

FIG. 34.— Part of a sclerenchymatous fibre
from Vinca major. The striations of
the outer layers are more apparent than
those of the inner layers. The thick-
ness of the wall, as seen in optical
section, is also shown, (x 500. After
STRASEURGEB.)

Chemical Nature of the Cell Wall (32). — Although capable of the
above processes of growth the cell wall is from the outset not a living
portion of the protoplast but a product secreted by the latter. In
course of time it can undergo changes of a chemical nature. In
living cells it is al \vays permeated by water and swollen, but shrinks
correspondingly when the water is more or less completely removed.
The lamellae of the wall consist of CARBOHYDRATES, in the main of
CELLULOSES, but also of HEMICELLULOSES or PENTOSANES, and as a rule
of several of these substances. The cell walls thus never consist of
pure cellulose. The celluloses occur in the walls of all plants with
the exception of most fungi ; they are polysaccharides, the composition
of which is expressed by the formula (C6H1005)n. They stain blue
with chlor-zinc-iodide solution but not with iodine alone. This

38 BOTANY

reaction holds for many hemicelluloses which are also polysaccharides.
The cell wall nearly always contains other substances in considerable
amount, some of which are stained other colours than blue by chlor-
zinc-iodide. The PECTIC SUBSTANCES are especially important ; these
take a yellow colour with this reagent. It depends on this that many
" cellulose walls " do not give a pure blue with chlor-zinc-iodide but
stain violet, brownish violet, or brown. CHITIN is present in the walls
of most Fungi and Bacteria. This substance, formerly regarded as
peculiar to the animal body, replaces cellulose in the case of
the Fungi (33).

The celluloses are insoluble in dilute acids and alkalies ; even concentrated
potash solution does not dissolve them. They are, on the other hand, soluble in
ammonia-oxide of copper, by concentrated sulphuric acid after conversion into
dextrose, and by a special enzyme (cytase) formed by plants. After treatment
with sulphuric or phosphoric acid a watery solution of iodine will colour them blue,
and a similar reaction is obtained by the simultaneous action of a concentrated
solution of certain salts, such as zinc-chloride or aluminium-chloride, and of iodine.
Accordingly chlor-zinc-iodide, on account of the blue or violet colour imparted by
it, is one of the most convenient tests for cellulose. The name of hemicelluloses is
given to a series of substances which are nearly related to the celluloses, but are
transformed by even dilute acids into soluble sugars other than dextrose. They
are often insoluble in ammonia-oxide of copper. As the celluloses are poly-
saccharides with large molecules produced from hexoses (CtjH1206), the pento-
sanes (C5H804)n are corresponding condensation products of peutoses (C5H1005)
such as arabinose and xylose. The pectins are characterised by the ease with
which they dissolve in alkalies after previous treatment with dilute acids. In
contrast to cellulose, they- stain deeply with safranin and niethylene blue. The
pectins are complex compounds in which monohexoses, pentosane, and in addition
methyl alcohol behaving as an ester and calcium and magnesium behaving as salts,
are united to tetragalacturic acid (G^sfizsi a condensation product of galacturic
acid C6H1007) (*»).

Chitin is a polysaccharide containing nitrogen ; it contains acetyl-acetic-acid in
an acid-amide-like combination.

The cell wall frequently undergoes chemical changes of various
kinds during the life of the cell ; sometimes layers already deposited
change, in other cases the newly deposited layers are different from
those first formed. These transformations stand in the closest relation
to the requirements of the plant to which the cells contribute. As
regards "cellulose walls," these in young cells are less elastic but
relatively more extensible than in older cells ; this is advantageous in
relation to the active growth in length of young parts. Such walls
offer little resistance to the diffusion of water and dissolved substances.

Cellulose walls not infrequently become MUCILAGINOUS, their sub-
stance being transformed into a gelatinous or mucilaginous mass which
swells greatly in water. Frequently cell walls undergo LIGNIFICA-
TlON, SUBERISATION, or CUTINISATION. Lignification diminishes the
extensibility of the cells considerably, and increases their rigidity

DIV. r MORPHOLOGY 39

without lessening the permeability of the wall to water and dissolved
substances. Corky and cutinised walls, on the other hand, are
relatively impermeable to water and gases, and greatly diminish
evaporation. The cell walls are frequently coloured dark by deriva-
tives of tannins, and thus, as in seed-eoats and in the old wood, are
protected against decay. In old cell walls inorganic substances often
accumulate in considerable amount. Silicic acid is frequent, calcium
carbonate less common, while organic salts such as calcium oxalate also
occur.

LIGNIFICATION depends on the introduction into the carbohydrate layers of the
cell wall of various substances which are mainly benzole derivatives. The inner-
most layers of the wall of lignified cells consist, however, in many cases of cellulose.
Characteristic reactions for lignin are a yellow colour with acid aniline sulphate,
and a red colour with phloroglucin and hydrochloric acid. With chlor-zinc-
iodide lignified walls stain yellow, not blue. KLASON C32) regards these reactions
as dependent on a condensation product of couiferyl- and oxyconiferyl- alcohol
which he calls lignin.

SUBERISATION is as a rule limited to the middle thickening layers of a cell wall.
The corky lamellae consist of SUBERIN only and thus contain no carbohydrate.
CUTINISATION is closely related to suberisation but not identical. It consists in a
secondary deposit of CUTIN on a cellulose wall, or its introduction into the
substance of the wall. No sharp distinction can be drawn between cutin and
suberin. Both are coloured brownish yellow by chlor-zinc-iodide and take a nearly
identical yellow colour with potash ; they stain red with sudan-glycerine and are
both insoluble in concentrated sulphuric acid or ammonia-oxide of copper. Cutin,
however, resists the action of potash better. Both cutin and suberin behave
differently to reagents according to their special mode of origin. According to
VAN WISSELIXGH (^ suberin is a fatty substance which is composed of glycerine
esters and other compound esters of phellonic, suberic, and others of the higher fatty
acids ; the phellouic acid, which is a constant constituent of suberin, is wanting
in cutin.

CALCIUM CARBONATE occurs in the walls of certain plants, e.g. of most Characeae,
in such amount that they become rigid and brittle. SILICIC ACID is present in the
peripheral cell walls of grasses, horse-tails, and many other plants (e.g. of the
unicellular diatoms), and makes them more rigid. CALCIUM OXALATE when present
is usually in the form of crystals.

The pigments belonging to the flavone group which occur in the technically
valuable woods are also localised in the cell walls.

Solid cell walls may undergo a transformation into GUM, as in the gummosis
of wood. In species of Pmnus and Citrus the thickening layers of the cell wall
become swollen one after another in this process, and ultimately the cell contents
are involved in the change (36).

BOTANY

PAET I

SECTION II
HISTOLOGY (3T)

THE CELLS AS ELEMENTARY UNITS OF THE BODY

I. THE FORMATION OF TISSUES

A. The Idea and Significance of Cellular Tissues

Every close association of protoplasts enclosed in cell walls is
termed a tissue.

Only the lowest organisms are composed of a single uninucleate or
multinucleate protoplast and are thus unicellular throughout their life.
Usually the body of a plant is multicellular, consisting of many
protoplasts separated by cell walls and thus forming a tissue. The
attainment of large size and more complex external organisation
is as a rule associated with such a structure. There are, it is true,
certain Algae (Siphoneae) which are externally highly organised,
while they consist internally of a single multinucleate protoplast.
These may be contrasted as non-cellular organisms with the ordinary
cellular plant, to the construction of which they form an exception.
The formation of a cellular tissue is of the greatest importance in the
development of more highly organised plants in enabling a division of
labour to be effected in the protoplasm of the body. The division of
the protoplasm into numerous protoplasts provides elementary parts
which can take over different duties. The cell walls separating the

protoplasts isolate the latter more or less,
while at the same time increasing the
cohesion and the internal rigidity of the
whole body formed of the numerous soft
protoplasts.

A very imperfect tissue formation is found
in those organisms the cells of which separate
from one another at each division, but remain
connected by the mucilage derived from the
FIG. 35.— Gloeocapsa polydermatica. swollen cell walls. Such unions of more or less
A, ^Commencement ^of division; independent cells that have had a common origin
may be termed cell families or cell colonies. The
Schizophyceae, to which group Gloeocapsa (Fig. 35)
belongs, and the orders of the Volvocales and
Protococcales among the Green Algae afford numerous examples, and the descrip-
tions in the special part should be consulted.

In the cell filaments and cell surfaces of those lower Algae in which the cells
are all equivalent but are united together, the characters of a definite tissue begin
to make their appearance. With the increasing number of cells composing the
organism we get a contrast between base and apex and the appearance of a growing
point, and also progressive division of labour among the cells.

B, (to the left) shortly after divi-
sion ; C, a resting stage. ( x 540.
After STRASBURGER.)

DIV.

MORPHOLOGY

B. Origin of Tissues

A continuous aggregation of cells in intimate union is called a tissue.
The origin of vegetable tissues is, in general, attributable to cell division.
In Hydrodidyon among the Algae a tissue is formed by the apposition
of free cells. In the Fungi and
Siphoneae a tissue arises through the
interweaving of tubular cells or cell
filaments (Fig. 37). In such cases,
where the filaments are so closely
interwoven as to form a compact

FIG. 36. — Transverse section of the sclero-
tium of Claviceps purpurea. (x 300.
After SCHEXCK.)

FIG. 37. — Longitudinal section of the stalk of
the fructification of Boletus edulis. (x 300.
After SCHENCK.)

mass of cells, the tissue thus formed has the same appearance as the
tissues of higher plants (Fig. 36). The mutual interdependence of
the cells of a tissue is manifested both by the conjunction of their pits
and by the general similarity of their wall thickenings.

C. The Cell Walls in the Tissues

When sections of vegetable tissues are examined under a low
magnification the attention is attracted mainly or only by the cell walls.
These appear to form a network of threads something like a woven
tissue, and the name takes its origin from this inaccurate comparison.

The cell walls exhibit peculiarities resulting from the connection of
the cells and characteristic of particular tissues.

1. Stratification. — All the septa arising in the course of cell
divisions in tissues are at first very thin and simple lamellae, common
to the two cells the protoplasts of which they separate. The cell wall
never remains in this condition. Even in meristematic cells it becomes
thickened as the membrane grows in surface extent. Thickening only
ceases long after the cell has reached its ultimate size. It varies
according to the functions taken over by the cell as part of a
permanent tissue, especially thick walls being found in cells which
contribute to the mechanical rigidity of the plant (Fig. 38). As a

BOTANY

PAKT I

rule the thickening of a partition wall is effected by the two adjoining
protoplasts depositing new lamellae on both sides of the original thin
septum (Figs. 38, 40, 62). The thickening may thus be equal or
unequal on the two sides and each protoplast comes to have its own
surrounding layers. The common middle region of the wall is called
the middle lamella (Fig. 38 m). It is as a rule very thin, only widen-
ing out somewhat at the angles where several walls meet (Fig. 71 Cm*),
and consists mainly of pectic substances containing calcium ; it is
relatively easily dissolved. In lignified and suberised tissues the
middle lamella is also lignified.

In soft tissues even boiling in water may swell the middle lamella and so
separate the cells (e.g. many kinds of potatoes). In ripe fruits this separation

FIG. 38. — Strongly thickened cell from the pith
of Clematis vitalba. m, Middle lamella ; i, inter-
cellular space ; t, pit ; w, pitted cell wall in
surface view, (x 300. After SCHENCK.)

FIG. 39. — Cells from the endosperm
of Ornithogaluin umbellatum. m,
Pits in surface view ; p, closing
membrane ; n, nucleus, (x 240.
After STRASBURGER.)

occurs naturally. Treatment with Schulze's macerating fluid (potassium chlorate
and nitric acid) or with concentrated solution of ammonia will separate other cells
by destroying the middle lamella. The macerating fluid will thus isolate the
elements of wood. There are also certain Bacteria which ferment pectic substances
and thus bring about the separation of the cells ; in this way the mechanical cells
of Flax are isolated in the process of retting.

The thickening layers are distinguishable from the middle lamella
both by their optical and chemical properties. Since they usually
lie equally on both sides of the middle lamella the whole wall acquires
a more or less symmetrical construction (Figs. 38-40, 41, 62) which
extends to the pitting. Three distinct layers can frequently be
distinguished in strongly thickened cell walls, such as those of the
wood, a primary, a secondary, and a tertiary thickening layer; these

DIV. I

MORPHOLOGY

differ in their optical appearance and their chemical composition.
The secondary thickening layer is usually the most strongly developed,
and forms the chief part of the cell wall. The tertiary or innermost
layer is usually more highly refractive (Fig. 71 Ci) ; it consists as a
rule of cellulose.

Cell walls which do not adjoin other cells (Figs. 40, 44) and
especially the external walls of the plant are, on the other hand,
asymmetrically constructed. In such cases thickening layers can only
be deposited on the side of the original
cell wall which faces the cavity of the
cell.

2. Pitting. — The cell walls which
separate the protoplasts will evidently
render difficult the passage of materials
from cell to cell in proportion to the
thickness of the wall. The life of the
organism could not continue without
such transport of material. It is there-
fore necessary that this should not be
too greatly hindered by the thickening
of the walls that ensures rigidity. The
difficulty is met by the formation of pits
in the walls between the protoplasts,
while pits are as a rule wanting in the
free external walls.

The pits, which in greatly thickened FlG- ^o.-ceiis from the cortex of iris
walls form canals with circular (Figs.
38 w, 39 m) or elliptical cross section,
meet accurately, and would form one
continuous canal were it not that the unthickened primary wall
persists as a pit membrane (Figs. 38 t, 39 p, 40 t). The openings of
narrow elliptical pits into adjoining cells usually appear to cross one
another obliquely.

The structure of pits may be very easily seen in the greatly thickened and
abundantly pitted cell Avails of the seeds of various Palms, Liliaceae, and other
Monocotyledons (Ornithogalum, Fig. 39). The thickening here consists of a herni-
cellulose which forms a reserve material in the seed, and at germination is dissolved
by an enzyme. The walls have a gleaming, white appearance, and are so hard that
such seeds, e.g. of the Palm, Phytelephas macrocarpa, are technically known and
employed as vegetable ivory.

3. Connections of the Protoplasts in Tissues. — The harmonious
co-operation of all the living parts of the body, which is such a striking
feature of the life of an organism as a whole, would hardly be possible
if the protoplasts forming the tissues were completely divided from
one another by the cell walls. It can in fact be shown that the
protoplasts of the plant are united together by extremely find

florentina. t, Pits in the stratified cell
wall ; i, intercellular spaces. ( x about
400.)

BOTANY

cytoplasmic filaments, which proceed from the boundary layer of the
cytoplasm and are known as plasmodesms (3S). Such filaments are
mostly confined to the pit membrane (Fig. 41 s), but may also
penetrate the whole thickness of the cell wall (Fig. 42 pi). The
existence of these connecting filaments of living substance between
the protoplasts confers an organic unity on the whole body of the
plant, serving for the conduction both of substances and of stimuli.

4. Cell Fusions. — Rapid transport of substances within the body
of the multicellular plant is necessary, for instance from one organ
to another, as from the leaves
to the roots. The process of
diffusion through the cell walls
or the movement of substances
in the very fine plasmodesms

FIG. 41. — A cell from the cortex of the
Mistletoe (Viscum album) ; the protoplast
has been properly fixed and stained and
the wall (m) swollen. The pit membranes
(s) are traversed by connecting threads ;
ch, chloroplasts ; n, nucleus, (x 1000.
After STRASBURGER.)

FIG. 42. — A, A swollen portion of cell wall
from the endosperm of the Vegetable Ivory
Palm (Phytelephas macrocarpa). At s, s,
simple pits filled with cytoplasm ; in the
intervening pit membrane are fine connect-
ing threads (plasmodesms) ; pi, other threads
traversing the whole thickness of the wall,
(x 375.) B, The contents of two opposed
pits and the connecting threads of the pit
membrane, (x 1500.) C, the opening of
a pit and the connecting threads of the
pit membrane viewed from ' the surface.
The smaller circle indicates the canal of the
pit, while the larger circle is the pit mem-
brane; the dark points on the latter are
the plasmodesms. ( x 1500. After STRAS-
BURGER.)

does not suffice to meet this need, even when assisted by the presence
of the pits, which have been seen to correspond in the walls separating
adjoining cells. The cavities of many cells, especially those which
serve for transport, therefore become continuous by relatively wide
openings, so that they form tubular structures or CELL FUSIONS.
Such openings arise singly or in numbers by a solution of the cell-wall
substance, especially in the end walls of adjoining cells.

5. Formation of Intercellular Spaces and the Ventilation of the
Tissues. — Usually as the meristematic cells are transformed into
permanent tissue and the cell walls thicken, the middle lamella splits

PIV. I

MORPHOLOGY 45

locally, especially at the angles of the cells. At these points the walls
of neighbouring cells separate and INTERCELLULAR SPACES filled with
air arise throughout the plant (Figs. 38, 40 i). In accordance with
their mode of origin the smaller intercellular spaces are triangular or
quadrangular in transverse sections. They form a connected system
of narrow, branched canals (INTERCELLULAR SYSTEM) which traverse
the tissues in all directions. From their mode of origin by the
splitting of cell walls such intercellular spaces are termed SCHIZOGENOUS.
Unequal growth of the tissues may lead to the complete isolation of
cells or the formation of larger chambers or passages of more or less
regular form. Intercellular spaces can also arise by the dissolution
or breaking down of cells and are then termed LYSIGENOUS. Some-
times spaces, that are in their origin schizogenous, are further enlarged
lysigenously. Whole regions of the tissue may be stretched and
broken down by unequal growth. Hollow stems arise in this fashion.
In tissues which have arisen by a weaving together of filaments
(Fig. 37) the intercellular spaces are present from the outset.

Intercellular spaces usually contain air and are of great importance
for the living cells forming the tissues. A single cell in water or air
can obtain at any time the gases, especially oxygen, which are essential
to its life from the surrounding medium. The life of the numerous
protoplasts in the tissues of a plant requires a supply of oxygen.
This introduction and circulation of gases in the tissues is carried out
by the system of intercellular spaces.

II. KINDS OF CELLS, TISSUES, AND TISSUE-SYSTEMS

Only in the lower multicellular plants does the tissue consist of
equivalent, spherical, polyhedral, and cylindrical cells (cf. e.g. Fig. 84),
which are similarly able to perform all the vital functions. This
tissue may be termed parenchyma. As the division of labour
between the protoplasts increases, with increase in size and progressive
external organisation, cells or groups of cells acquire diversity in
form, structure, and function. There results in the higher plants a
segregation of the originally uniform cells into variously constructed
kinds of cells, connected, it is true, by intermediate forms. Com-
parative study of the various organs of a plant, or of the higher
plants, shows that the number of these KINDS OF CELL is limited, and

that DEFINITE FORMS OF CELLS RECUR IN THEM ALL.

Similar cells are usually associated in groups which constitute a
KIND OF TISSUE. These are distinguished by the form, contents, and
the walls of their constituent cellular elements, and each kind of
tissue has its special function or functions. More highly organised
plants are composed of a number of kinds of tissue, but, as in the
case of kinds of cells, this number is small, since they recur in the
most diverse plants. It is not uncommon for single cells (idioblasts)

46 BOTANY PART i

or cell groups of a different structure and content to be found in an
otherwise uniform type of tissue.

In the higher plants particular kinds of tissue may occur in
considerable amount and extend in unbroken connection for a distance
or through the whole plant body. These may often include several
associated kinds of tissue and constitute MORPHOLOGICAL TISSUE
SYSTEMS. Such compound associations of tissues may be characterised
structurally and have different main functions. The functions of the
different kinds of tissue within them tend to complement one
another.

In a PHYSIOLOGICAL TISSUE SYSTEM are' grouped together all cells that agree iir
their main functions, irrespectively of their morphological connection, or of their
ontogenetic origin. Such physiological systems are thus something quite different
from morphological tissue systems.

The tissue systems of the more highly organised plants can be
divided into two main groups: (1) the meristematic or formative
tissues ; (2) the mature or permanent tissues.

A. The Formative Tissues

These are also termed MERISTEMS and consist either of relatively
small cubical or isodiametric cells, or of prismatic, flattened, or elongated
cells with thin walls, abundant protoplasm, large nuclei, and few and
small vacuoles (cf. Fig. 2). The numerous cell divisions that occur in
their cells is characteristic. These formative tissues, from which the
permanent tissues are developed, are distinguished according to the
place and mode of their origin into PRIMARY and SECONDARY

MERISTEMS.

1. Primary Meristems. — These arise by the division of the
germ cell and at first compose the whole embryo. Later they become
localised at the growing points of the branches and roots (Figs. 102,
157), where the increase in number of meristematic cells and the
formation of the rudiments of many lateral organs takes place
(apical growth).

One or a number of the cells at the extreme tip of the growing
point always remain meristematic, and multiply by growth and
continued cell division following on this. The meristematic cells thus
produced, after undergoing further divisions, become gradually trans-
formed into cells of the permanent tissue. When there is a single
cell at the tip distinguished by its form and size from the other
meristematic cells it is called an APICAL CELL (Figs. 100, 101, 156);
when there are a number of cells in one or more layers they are
spoken of as INITIAL CELLS (Figs. 102, 157). The latter may resemble
apical cells, but are often more like the other meristematic cells.

A short distance behind the growing point the similar cells of the
primary meristem begin to grow differently and give rise to strands

DIV. I

MORPHOLOGY 47

and layers of variously shaped formative cells, which at first retain
the general characters of meristematic cells (Figs. 100, 102, 157).
Intercellular spaces, absent in the meristem itself, now arise. At a
somewhat greater distance from the growing point the characters of
the various permanent tissues make their appearance and become
more marked basipetally until the mature structure is attained. In
this process of tissue-differentiation groups, strands, or layers of cells
may retain the meristematic characters and serve as places of origin
later for a renewed formation of meristematic and mature tissues.
Their power of division may persist throughout the life of the plant.

In many Monocotyledons the basal region of the internodes remains
for a long time meristematic, and serves, in addition to the growing
point, as a place of production of permanent tissue. In this way the
intercalary growth of these and other plants is brought about.

2. Secondary Meristems are derived either from the above-
mentioned inactive remains of the primary meristem or are newly
formed from cells of the permanent tissue, which alter their function
and by new cell divisions are transformed into meristematic cells.
Their elements resemble those of the primary meristems, but as a rule
have the form of elongated or flattened prisms. Such secondary
meristems, which get the name CAMBIUM, give origin to cork and to
the secondary growth in thickness of woody plants. They form a
thin layer of prismatic meristematic cells (Figs. 169, 185) parallel to
the surface of the organ at the outside of the cylinder of wood. In
the cambium a middle layer of initial cells undergoes continued
tangential divisions which cut off daughter cells to both the inside
and outside in the radial direction. These cells after some further
divisions are transformed into cells of the permanent tissues.

The new cell walls arising in the cell divisions of a meristem are flat and as a
rule, though not without exception, placed at right angles to the pre-existing
older walls. Walls more or less parallel to the surface of the organ are termed
PERICLINAL, and those at right angles to this ANTICLINAL.

B. The Permanent Tissues

The cells of the permanent tissues differ from the meristematic
cells in being as a rule larger, with relatively little protoplasm and
large vacuoles, and sometimes completely dead. Cell divisions are
not usually taking place in them, and the cell walls are variously
thickened and often chemically altered. The permanent tissue is
composed of a variety of kinds of cells and tissues with diverse
functions. It is usually provided with intercellular spaces.

In developing from the meristem the cells of the permanent tissue
enlarge, separate at places from one another, undergo thickening and
chemical alterations of their walls, modify or lose their cell contents,
and sometimes fuse by dissolution of the partition walls. In enlarging

48 BOTANY TART i

or elongating the cells may behave independently (Fig. 174), so that
the ends of some which elongate greatly push past, or in between, other
cells (SLIDING GROWTH) (39).

The permanent tissues may be classified in various ways. Thus
according to their origin primary and secondary permanent tissues
may be distinguished arising from the corresponding meristems.

A morphologically useful division of the permanent tissues is
obtained when all the differences of the component cells are taken
into consideration together.

It was formerly usual to take the dimensions of the cells into special considera-
tion, and on this ground PARENCHYMA and PROSENCHYMA were distinguished. By
parenchyma was understood a tissue the cells of which were isodiametric or, if
elongated in one direction, were separated by transverse walls. Prosenchyma was a
tissue the elongated cells of which were spindle-shaped and pointed at both ends,
which fitted between those of the associated cells, These two groups do not, however,
suffice to give a survey of the variety of kinds of tissues, and the underlying
conceptions are out of date, especially in the case of parenchyma.

On examining the tissues of the higher plants comparatively there
is found in the first place a tissue which, like that composing the
lowest multicellular plants, consists of cells with living contents
and thin cellulose walls, and is capable of performing a diversity of
functions ; this will be termed PARENCHYMA. Other tissues may
be sharply distinguished from this parenchyma by peculiarities of
structure and special functions. The most striking tissues in the light
of their main functions are the BOUNDARY TISSUE, the MECHANICAL
TISSUE, and the CONDUCTING TISSUE. The PARENCHYMATOUS SYSTEM,

the EPIDERMAL SYSTEM, the MECHANICAL SYSTEM, and the CONDUCTING

SYSTEM correspond on the whole to these tissues. In addition the
SECRETORY TISSUE and GLANDULAR TISSUE may be recognised.

The permanent tissues are frequently divided into epidermis, vascular bundles,
and ground tissue.

1. Parenchyma. Parenehymatous System. — The parenchyma
cell is characteristic of this type of tissue, the relative primitiveness of
which has been referred to above (cf. p. 45). It may be isodiametric
or elongated and of various shapes, and possesses the following further
characters (cf. Figs. 3 B, 9, 40, 41). The cell wall, which as a
rule consists of cellulose, is only moderately thickened and provided
with simple round or elliptical pits ; it thus facilitates the diffusion of
substances from cell to cell. Living protoplasm is usually present,
and the large vacuole may contain a considerable amount of nutritive
material. The chromatophores, which have the form of chloroplasts
or leucoplasts, often contain starch. Parenchyma is usually traversed
by a ventilating system of intercellular spaces. Parenchyma may
form part of other primary or secondary tissues and serves a
variety of functions. The most important vital processes of the

MORPHOLOGY 49

full-grown plant take place in it, such as the preparation, conduction,
and storage of nutritive materials, water storage, and the process
of respiration. The presence of abundant cell sap contributes to the
maintenance of the general rigidity of the plant body. The structural
differences between parenchyma cells are relatively slight when the
multiplicity of functions they perform are considered. When the
cells have numerous chloroplasts they are spoken of as ASSIMILATORY
PARENCHYMA (Fig. 8) in reference to their main function of forming
organic substance from carbon - dioxide. The parenchyma of the
subaerial parts of plants is often of this nature so far in as light can
penetrate, while the deeper tissues are colourless. The term STORAGE
TISSUE (Figs. 23 A, 24) is applied when these cells are rich in
organic contents such as -sugar, starch, fatty oils or proteids, or have
hemicelluloses accumulated in the thickened walls (Fig. 39) ; these
substances are stored against future use in the metabolism. WATER-
STORAGE PARENCHYMA as a rule consists of large thin-walled cells with
little protoplasm but abundant cell sap that is somewhat mucilaginous ;
these cells diminish in size on losing water. Conduction of organic
food-materials, especially of carbohydrates, takes place in parenchy-
matous cells, which are elongated in the main direction of transport
to facilitate this function. Such CONDUCTING PARENCHYMA often
forms a sheath, without intercellular spaces, around other masses of
tissue. Parenchyma which has large intercellular spaces, serving for
ventilation or the storage of gases, is termed AERENCHYMA.

2. Boundary Tissues. — In the case of the multicellular tissues
composing the bodies of land plants the whole body or particular
tissues may require protection against excessive loss of water,
mechanical injury, excessive heat (40), and frequently against the loss
of diffusible substances. This function
is carried out by cells which have cer-
tain peculiarities of structure and are
often arranged in sheathing layers.
In this way another group of tissues
can be distinguished, the main elements
of which are the epidermal cells and
the suberised or cork cells. The epi-
dermis together with some other types
of cell form the epidermal system.

(a) Epidermal System. 1. EPI-

rpi • , . , . , FIG. 43. — Surface view of the epidermis

DERMIS. — 1 hlS IS derived trom the from the upper side of a leaf of Mercuri-

superficial layer of the primary meri- aitsperennis. (x 300. After H.SCHEN-CK.)
stem (the dermatogen, cf. p. 86) and

is thus one of the primary permanent tissues. It encloses the
plant body as a protective investment while permitting exchange
of materials with the environment. The epidermis is typically a
single layer (Fig. 45 B) of tabular or more elongated living cells,

BOTANY

PART I

without intercellular spaces between them. The lateral walls are
often undulated or toothed, which increases the firmness of the union
of the cells. In transverse section the cells are of uniform depth and
are rectangular or lens-shaped. The protoplasts of the epidermal cells
are commonly reduced to thin layers lining the walls and enclosing
large vacuoles filled with colourless or coloured cell sap. The
epidermis of the parts exposed to light in most Ferns and in many
shade-loving Phanerogams is provided with chlorophyll and takes
part in assimilation. With progressive division of labour, however,
chlorophyll is absent from the epidermis, which then serves merely to
protect the more internal tissues especially against desiccation.

The outer walls of the epidermal cells of all subaerial parts of
the plant, which last for a considerable time, are thickened. In this

FIG. 44.— Transverse section of a node of the sugar-cane, SaccJiarum officinarum, showing
wax incrustation in the form of small rods, (x 540. After STRASBUROER.)

respect they contrast with the epidermal cells of the more fugitive
petals and of submerged and subterranean parts. This holds especially
for roots in which the epidermis has very different functions, such as
the absorption of water and salts. The thickening of the outer walls
results from the apposition of cellulose layers, the outer of which
usually, but not always, become more or less strongly cutinised
(Fig. 190).

The outer walls of the epidermis, whether thickened or not, except
in the case of those forming the surface of subterranean organs and
especially roots, are covered by a thin continuous cutinised film called
the CUTICLE. This is formed on the primary walls of the epidermal
cells. The cuticle is often somewhat folded and in surface view appears
striated. The cuticle and the cutinised layers of the wall are only with
difficulty permeable to water and gases, and prevent the injurious loss of
water by evaporation. The thickening also increases the mechanical

DIV. I

MORPHOLOGY

rigidity of the epidermal cells. On the other hand, the absence of
cuticle from the root facilitates the absorption of water and salts from
the soil. Deposits of wax are also present in the cutinised layers of the
epidermis, and consequently water will now off the epidermis without
wetting it. The wax is sometimes spread over the surface of the
cuticle as a wax covering. This is the case in most fruits, where,
as is so noticeable on plums, it forms the so-called bloom.. The
wax coverings may consist of grains, small rods (Fig. 44), or crusts,
soluble in ether or hot alcohol.

The epidermis may not only protect the more internal tissues from loss of water
by hindering evaporation, but also by serving as a place of storage of water. The
unthickened lateral walls of these cells become folded as the water is withdrawn

FIG. 45. — Epidermis from the under side of a leaf of Tradescantia virginica. A, In surface view.
5, in transverse section ; I, colourless rudiments of chroma tophores surrounding the nucleus,
(x 240. After STRASBURGER.)

from the cavity and stretch when the cell becomes again filled. Such an epidermis
is frequently also composed of several layers of cells.

The mechanical strength of the outer walls of epidermal cells is increased in
some plants by the deposition of calcium carbonate or of silicic acid. In the case
of Equisetum the silicification is so great that the tissues are used in polishing tin-
ware. The pericarp of the Grass, Coix lachryma, is almost as hard as the opal.

The epidermis of fruits, and particularly of seeds, exhibits a considerable variety
of modifications in its mode of thickening and in the relations the thickening
layers bear to one another. The purpose of these modifications in the epidermis
becomes at once evident when it is taken into consideration that, in addition to
protecting and enclosing the internal parts, the epidermis has often to provide for
the dissemination and permanent lodgment of the fruits and seeds.

Among the ordinary cells of the epidermis there occur as a rule
stomata and hairs which are especially characteristic of this tissue.

2. STOMATAL APPARATUS (41). — The presence of stomata in the
epidermis is characteristic of most parts of the more highly organised
plants that are exposed to the air. Each STOMA is an intercellular
passage or pore bounded by a pair of curved, elliptical or half-moon-
shaped cells called GUARD CELLS. The pore and guard cells together

BOTANY

PART

FIG. 46.— Epidermis with stomata from the lower surface
of the leaf of Helleborus niger. (x 120. After STRAS-
BURGER.)

constitute the STOMATAL APPARATUS (Figs. 45 A, 46). The largest
stomata are found in grasses; thus in the wheat they measure 0'079
mm. in length by 0'039 mm. in breadth, while the pore itself is
0-038 mm. by O'OOT mm.

The PORE interrupts the continuity of the epidermis. It is an
air-filled intercellular space opening below the epidermis into a large

intercellular space (Fig.
45 B), which is spoken of
as the respiratory cavity
although it has nothing to
do with respiration. This
cavity is in communication
with the intercellular spaces
of the parenchyma. The
stomata are of great im-
portance to the plant, for
they place the system of
intercellular spaces, which
serves to ventilate the
tissues, in communication
with the external atmo-
sphere. This connection is
necessary on account of the difficulty with which gases pass across the
epidermis in order to renew the air in the intercellular spaces, and
especially to replace the carbon-dioxide as this is used up. On the
other hand, oxygen, which forms a considerable proportion of the air,
can usually penetrate into the plant in sufficient quantity through
the cuticle and the epidermal cells.

The GUARD CELLS always contain chlorophyll and are character-
ised both by their shape and the mariner in which their walls are
thickened. This is best shown in transverse sections (Figs. 45 B,
47 B). There are usually an upper and a lower thickened band
on the side of the guard cell which faces the pore, the portion
of the wall between and the rest of the wall of the guard cell being
relatively thin (Fig. 45 B). This structure stands in relation to the
changes in form of the guard cells by means of which the size of the
pore is varied. The pore is closed by a diminution of the curvature of
the guard cells when there is danger of too great escape of moisture ;
while it is widely opened by increase in the volume of the guard cells
and consequently of their curvature at other times. The stomata
regulate the gaseous exchange and the transpiration.

As the transverse section in Fig. 45 B shows, the thickening ridges project both
above and below the pore. There is thus an anterior chamber and a posterior
chamber in relation to the narrow region of the actual passage. The thickened
outer walls of the epidermal cells immediately adjoining the guard cells often
have a thinner portion which acts as a kind of hinge and enables the changes

DIV. I

MORPHOLOGY

in shape of the guard cells to be effected without hindrance from the surrounding
cells (cf. Fig. 47 B). The guard cells, as is seen in Fig. 45 A, are often surrounded
by special cells called subsidiary cells ; these may be less thickened or shallower
than the other epidermal cells.

Differences are found in the construction of the guard cells and in the
mechanism of opening and closure of the stoma which depends upon this. Two main
types of stoma may be distin-
guished but they are connected by
intermediate forms. In the first
the change in form of the guard
cells takes place mainly in the
tangential direction, parallel to
the epidermal surface ; in the
second in the radial direction at
right angles to the surface^ TYPE
I. — According to the form of the
guard cells the pore is opened in
various ways, (a) The type of
the Amaryllidaceae (Fig. 47) is
found in the majority of Mono-
cotyledons and Dicotyledons.
The dorsal Avail of each guard cell
(Fig. 47 B) is unthickened, while
the ventral Avail (towards the
pore) is thickened and usually
shoAvs the upper and lower
thickening bands. When the
cell becomes turgid the thin
dorsal Avail is more stretched than
the thickened Avail, and the cell,
which in the flaccid condition
Avas almost straight, becomes
curved in the tangential plane
to a semilunar shape, (b) The FIG. 49.

type of the Gramineae (Fig. 48) FIGS. 47-49.— Types of Stomatal Apparatus. The thick
is met Avith in the Gramineae and lines indicate the form of the guard cells in the open
Cyperaceae The guard cells are condition, the thin lines when the stoma is closed,
dumb-bell-shaped; the widened ^"ZgZZZSZ™™* + *"*"*"•
ends being thin-Availed, while the PIG> 48t_Type Of the Gramineae with the two subsidiary
narrower middle region has both cells. A, Surface view. B, Transverse section,
the outer and inner \valls strongly FIG. 49.— J/ntum-type in transverse section. (After
thickened (Fig. 48 B}. When HABERLANDT.) Further description in the text,

the turgor increases the stiff

middle portion of the guard cells are separated from one another by the expansion
of the oval thin-walled ends of the cells. TYPE II.— If/mm -type (Fig. 49) is
found in some Mosses and Ferns. In this the ventral walls of the guard cells
are thin Avhile the dorsal Avails are thickened. When the turgor of the guard cell
increases, the outer and inner walls are separated from one another, thus lessening
the projection iuAvards of the ventral Avail and opening the pore. The position
of the dorsal Avail remains unchanged.

The stomata are formed by the division of a young epidermal cell into two cells
of unequal size, one of which, the smaller and more abundantly supplied Avith

BOTANY

PART I

protoplasm, becomes the stoma mother cell ; while the larger, containing less
protoplasm, usually forms an ordinary epidermal cell. The stoma mother cell
becomes elliptical in outline and divides again, by a vertical wall, into the two
guard cells, between which, by a splitting of the wall, the intercellular passage
(pore) is formed. Before the formation of the definite stoma mother cell, succes-
sive divisions of the young epidermal cell often occur ; in such cases the finally
developed stoma is generally surrounded by subsidiary cells.

3. HAIRS. — The epidermis of almost all plants bears hairs
(trichomes). They are sometimes . unicellular structures and form

papillate (Fig. 50), tubular (Fig.
51), or pointed (Figs. 52, 55, 56
to the left) protrusions of the
epidermal cells. In other cases
they are multicellular and form
cell rows (Fig. 5), stalked or
unstalked cell surfaces (scale-

FIG. 50. -Surface of the upper epidermis of a petal hairs, Fig. 54) which may re-
of Viola tricolor, showing ridge-like infoldings semble Small leaVCS as in the

' papillae' ramenta of Feras> or cel1 masses-

The multicellular trichomes are
also developed from .young epidermal cells, and, indeed, usually
proceed from a single initial cell of the hair by its growth and
subdivision. Unicellular and multicellular hairs may further be
unbranched or branched (Fig. 53, stellate hairs). Their walls may be

FIG. 51.— Epidermis of the root in longitudinal section showing root-hairs (B)
and their origin (,4). (After ROTHERT, semi-diagrammatic.)

thin and delicate or strongly thickened and frequently calcined or
impregnated with silica, and sharply pointed at the tip (bristles, Fig.
55, right). The protoplasts may remain alive and resemble those of
the epidermal cells, or may die. In the latter case the cavity often
becomes filled with air and the hair appears white, or it may be
laterally compressed as in the case of the long hairs of the cotton-seed
(Fig, 52) from which the cotton of commerce is obtained. The basal
portion of the hair in the epidermis may be distinguished from the

DIV. I

MORPHOLOGY

freely projecting body of the hair. The epidermal cells around the
base are often arranged in a ring or radiate on all sides, and may
be called the subsidiary cells of the hair. The STINGING HAIRS
(Fig. 55), such as those of Nettles (Urtica) and of the Loasaceae, are
special forms of bristles.

They arise from single epidermal cells which swell in the course of their
development, and becoming surrounded by adjoining epidermal cells present the

appearance of being set in sockets ;
while, at the same time, by the multi-
plication of the cells in the tissue at
their base, the whole hair becomes
elevated on a column-like protuber-
ance. The hair tapers towards the
apex and terminates, somewhat
obliquely, in a small head, just
below which the wall of the hair
remains unthickened. As the wall
of the hair is silicified at the end and
calcified for the rest of its length,
the whole hair is extremely stiff.
The heads break off at the slightest

FIG. 52. — Seed -hairs of the cotton, Gossypium her-
baceum. A, Part of seed-coat with hairs (x 3).
Blt Insertion and lower part, -Bo» middle part, and
B3, upper part, of a hair. ( x 300. After STRAS-

BCRGER.)

FIG. 53.— Stellate hair in surface view from the
lower epidermis of the leaf of Matthiola
annua. (x 90. After STRASBURGER.)

touch, and the hairs piercing the skin pour out their poisonous contents, which,
especially in the case of some tropical nettles, may cause severe inflammation.
According to G. HABERLANDT this is due to the presence of a toxin of albu-
minous nature.

Hairs have thus various forms and perform very different functions.
They frequently contribute to the protection afforded by the epidermis,
forming a covering to full-grown parts of the plant and very
frequently to the young parts in the bud or expanding from this.
Such coverings, which may be composed of dead woolly hairs, serve

BOTANY

PART I

to diminish the transpiration and are a protection against direct
sunlight. The root-hairs (Figs. 51 J5, 158 r) are tubular prolongations
of living cells of the epidermis of the root and serve for absorption
of water. Very diverse substances are excreted by glandular hairs
(Figs. 75, 76, 77).

Certain hairs with abundant protoplasm and peculiar structure serve to receive
mechanical stimuli according to G. HABERLANDT (42). They occur on stamens,
petals, and the joints of leaves, and are known as tactile papillae, hairs, or bristles.

4. EMERGENCES, unlike hairs, are not formed solely by epidermal
cells, but a number of cells, lying more or less deeply in the sub-
epidermal tissues, also take part in their formation. They are some-
times glandular, and in other cases
serve as organs of attachment.

Thus, for example, only a few rows
of sub -epidermal cells enter into the
formation of the emergences (Fig. 56) on

FIG. 54.— Scale-hair from the lower side of the leaf of Shepherdia canadensis. A, Surface view.
B, Longitudinal section, (x 240. After STBASBURGER.)

the margins of the stipules of the Pansy (Viola tricolor], which are glandular.
Deeper-lying tissue takes part in the construction of the anchor-shaped attaching
organs, over 1 mm. long, which clothe the fruit of the Houndstongue (Cynoglossum)
and lead to its dispersal by means of animals. The prickles of the Rose or
Bramble are still larger emergences that are of assistance in climbing.

(b) Boundary Tissue formed of Corky Cells.— In many cases,
and especially when the epidermis does not remain alive and
functional during the life of the organ which it covers, the tissues
of the body become limited and protected even more efficiently by
suberised cells. Such cells also in the form of layers or sheaths serve
to bound and delimit certain living masses of tissue from others within
the plant body. Their origin may be primary or secondary. The
suberisation is brought about by suberised lamellae being deposited
on the pre-existing wall, while other layers of the wall frequently
become lignified. Three kinds of suberised boundary tissues can be
recognised: (1) The cutis tissue; (2) the endodermis; (3) the cork, r

DIV.

MORPHOLOGY

(1) The Cutis Tissue is a primary permanent tissue and arises by
the early suberisation of cells of the epidermis or of thinner or
thicker layers of parenchyma from which intercellular spaces are
frequently absent. A tissue of the latter kind not uncommonly
sheathes the outside of older parts of the plant (e.g. roots, Fig. 159 ex)
or delimits strands of tissue within the plant from the surrounding

tissue. The cells of this cutis tissue
usually retain their living contents.

In place of suberisation the introduction
of cutin or other substances that are imper-
fectly known chemically may render the mem-
branes less permeable to water.

(2) Endodermis. — This tissue is
formed of the endodermal cells (43).
It very frequently encloses and bounds,

FIG. 55. —Stinging hair of Urtica
dioica, with a portion of the epi-
dermis, and, to the right, a small
bristle, (x 60. After STRASBURGER.)

FIG. 56.— Glandular colleter from a stipule of
Viola tricolor, showing also to the left a uni-
cellular hair, (x 240. After STRASBURGER.)

as a sheath, a single layer of cells in thickness, living tissues within
the plant, but it may also form a limiting layer on the outside. Its
origin is sometimes primary and sometimes secondary. The elongated
prismatic living cells of the endodermis have no intercellular spaces
between them. When young the walls are not suberised, but a narrow
strip of the membrane, in the form of a band running completely
round the cell, has undergone a peculiar change by the introduction
of an imperfectly known (1 cork -like) substance (Caspary's band,

BOTANY

PART

Fig. 57 A). This band gives the appearance of a dark dot or a dark
lens-shaped body, Fig. 57 £, Fig. 161 S) in transverse sections, while
it appears as an undulated band in radial longitudinal
section. In older endodermal cells, as in the cells of
the cutis, a secondary layer of corky substance is
deposited all over the wall, and thick tertiary layers
of carbohydrate material that often become strongly
lignified may follow on this.

In the cutis tissue, when
this is a single layer, and
in the endodermis isolated
cells, characterised by their
and by their walls

rrn

not being corky, frequently
occur. These are known as
transfusion cells.

(3) Cork. — While the

FIG. 57.— A, Diagrammatic representation of a single endo-
dermal cell in the solid showing Caspary's band on the
radial walls. B, Endodermis in transverse section ; Gas- • ->
pary's band appears as the dark lenticular regions of the 6P1Cl

radial walls. tissue are alway s primary

permanent tissues the

cork is always a secondary tissue, and is developed from a secondary
meristem known as the CORK CAMBIUM. The cork forms either a
thin peripheral layer a number of cells thick which is smooth and
of a grey colour, or thicker fissured coverings of cork composed of
radial rows of cells (Figs. 58, 59). It forms where the epidermis
has been thrown off, or where living parenchyma has been exposed by
wounds. The cork cells usually contain air and are brown, owing to
the dead cell contents. They have a flattened prismatic form and are
extended tangentially, fitting together without intercellular spaces.
The secondary layers of the wall are suberised, while the middle
lamella is often lignified. Tertiary thickening layers are either
wanting or consist of cellulose forming the so-called cellulose layer
which may sometimes become lignified. Even a thin layer of cork
a few cells deep (Fig. 59) greatly diminishes the transpiration from
the surface of any part of the plant, and, as will readily be under-
stood, much more than the epidermis does. Thicker zones of cork
also prevent the entry of parasites. Since cork is a poor conductor
of heat it also protects the plant against over-heating.

Many old stems, tubers, bud scales, and fruits are covered with a layer of cork ;
thus the skin of a potato is of this nature. Bottle-cork is obtained from the
Cork Oak.

The mature cells of cork are very rarely pitted, and either remain relatively
thin (Fig. 58) or are more or less strongly thickened (Figs. 59, 185 p). Strongly
thickened cork cells form what is known as STONE CORK. The cells of cork may be
completely filled with dead contents (Fig. 59) which have usually a brown colour.

Frequently layers of suberised and unsuberised cells alternate in a corky tissue.
The latter cells, which do not differ greatly from the cork cells in structure and

DIV.

MORPHOLOGY

contents and may be thin- or thick-walled, arise in the same way and are called
PHELLOID TISSUE. The BARK, which is met with on still older stems as the
limiting tissue, consists of tissues of still more varied structure (cf. p. 163).

LENTICELS. — The formation of a covering of cork without inter-
cellular spaces in place of the epidermis would prevent gaseous

Fio. 58.— Transverse section of
bottle-cork, (x 120.)

Fio. 59.— Transverse section of the cork layer
of a Lime twig. The cell walls are left
white, while the dead contents are dotted,
(x 120.)

exchange between the interior of the stem and the atmosphere were
the stomata not replaced in some way. This is effected in some
plants (e.g. species of Clematis, Pitis, Lonicera) by porous cork, in

Pd pi

FIG. 60. — Transverse section of a lenticel of Sambucus nigra. e, Epidermis ; ph, phellogen ;
I, complementary cells ; pi, phellogen of the lenticel ; pd, phellodenn. (x 90. After STBASBUROER. )

which small circumscribed oval or circular areas consist of somewhat
smaller suberised cells with intercellular spaces between them. Usually,
however, lenticels are present, rough porous warts elongated or
spindle-shaped in outline which are readily seen by the naked eye
on the cork of most trees. They consist of dead unsuberised tissue
rich in intercellular spaces (COMPLEMENTARY TISSUE) interrupting

60 BOTANY PART i

the layer of cork (Fig. 60). The intercellular spaces open on the one
hand to the atmosphere, and on the other are in communication with
the ventilating system of the underlying living tissues.

The lenticels frequently form beneath stomata and at an early stage in the
development of the cork. The cork cambium which appears beneath the stoma has
radially-running intercellular spaces between its cells (Fig. 60 pi), and forms to the
outside complementary cells separated by intercellular spaces (Fig. 60 Z). The
lenticel soon breaks through the epidermis. Alternating with the complementary
tissue the cork cambium in the lenticels forms layers of more closely-connected
suberised and lignified cells (intermediate bands or closing layers). These are
developed to close the lenticel during the winter and are again ruptured in the
spring.

3. The Mechanical Tissue System (44). — Without a certain amount
of rigidity the definite form which is essential to the performance of
their functions in most plants would be inconceivable. In isolated
cells and in growing tissues this rigidity is attained by turgor (cf. p. 225)
and tissue tensions (cf. p. 286). Since, however, turgor and tissue
tensions are destroyed by any great loss of water, leading to the
wilting of the plant, they do not alone confer the necessary rigidity
upon plants. We therefore find special tissues, known as the
STEREOME, which have a purely mechanical function. These tissues
are the SCLERENCHYMA and COLLENCHYMA.

How great are the demands made upon the stability of plants will be at once
apparent from a consideration of a Rye haulm ; although it is composed of hundreds
of thousands of small chambers or cells, and has a height of 1500 mm., it is at its
base scarcely 3 mm. in diameter. The thin stems of reeds reach a height of
3000 mm. with a base of only 15 mm. diameter. The height of the reed exceeds
by two hundred times, and that of the Rye haulm by five hundred times, the
diameter of the base. In addition, moreover, to the great disproportion between
the height and diameter of plants, they often support a heavy weight at the
summit ; the Rye straw must sustain the burden of its ear of grain, the slender
Palm the heavy and wind-swayed leaves (which in species of Eaphia have a length
of 15 m. and a corresponding breadth), while at times the weight of the bunches
of fruit has also to be considered.

In plants, however, the rigid immobility of a building is not required, and they
possess instead a wonderful degree of ELASTICITY. The Rye straw bends before
the wind, but only to return to its original position when the force of the wind
has been expended. The mechanical equipment of plant bodies is peculiar to
themselves, but perfectly adapted to their needs. The firm but at the same time
elastic material which plants produce is put to the most varied uses by mankind ;
the wood forms an easily worked yet sufficiently durable building material, and
the bast fibres are used in the manufacture of thread and cordage and textile
fabrics (e.g. linen).

(a) Selerenehyma. — This is the typical mechanical tissue of fully-
grown parts of the plant and is formed of SCLERENCHYMA CELLS
(stone cells) or SCLERENCHYMA FIBRES ("bast fibres"). Both when
mature are as a rule dead cells with strongly thickened walls consisting

DIV. I

MORPHOLOGY 61

of lamellae of carbohydrate material, which is often lignified. The

sclerenchymatous cells or stone cells (Fig. 30) are more or less

isodiametric and polyhedral and have round, branched, or unbranched

pits. The sclerenchymatous fibres (Fig. 61), on the other hand, are

narrow, elongated, spindle-shaped cells with pointed ends, polygonal

in transverse section (Fig. 62). They have obliquely-placed, narrow,

elliptical pits. In their development sliding growth

frequently occurs and they only mature in fully- -

grown parts of the plant. These elements may

occur singly, but usually, especially in the case of

the fibres, they are closely associated in strands,

bands, rings, or sheaths, variously arranged so as to

ensure the requisite., rigidity of the organ against

bending, tension, or pressure while employing the

least mechanical tissue.

The firm thick walls of sclerenchyraatous cells and fibres
are not infrequently further hardened by deposits of mineral
substances. The resistance which these forms of tissue offer
when the attempt is made to cut, tear, or break them affords
sufficient evidence of their hardness, tenacity, and rigidity.

Sclerenchymatous fibres have always a length which for a
plant cell is considerable, on the average 1-2 mm. In some
plants they are much longer, e.g. 20-40 mm. in Flax, to 77
mm. in the Stinging Nettle, and in Boehmeria even 220
mm. Such long fibres are of economic importance in the
manufacture of textile fabrics. The long pointed ends render
the connection of the fibres more intimate than is the case for
the cells of other tissues.

SCHWENDENER has been able to determine their mechanical
value by means of exact physical experiments and investi-
gations. According to such estimates, the sustaining strength
of sclerenchymatous fibres is, within the limits of their
elasticity, in general equal to the best wrought iron or
hammered steel, while at the same time their extensibility FJG gl.— A scleren-
is ten or fifteen times as great as that of iron. It is true chymatous fibre, (x
that soon after exceeding its limit of elasticity the stereome about 100. After
of the plant becomes ruptured, while the limit of rigidity STRASBURGER.)
for iron is not reached until the load is increased threefold.

It is, however, of value for the needs of the plant that its limit of elasticity extends
almost to the limit of its rigidity.

(b) Collenehyma. — The sclerenchyma corresponds to the bony
skeleton of the animal body. Its elements are no longer in a condition
which allows of growth, and it cannot be employed in parts of the
plant which are still actively elongating. Where such parts of the
plant require special strengthening in addition to that given by the
tensions of cells and tissues, this is obtained by means of collenchyma.

The collenchymatous cells may be isodiametric but are usually
elongated ; they have transverse end walls (Fig. 64) or are pointed.

BOTANY

PART I

They resemble the cells of the parenchyma in being living cells, but

differ in the unequal thickening of their cellulose walls. This is

localised at the angles (angle collenchyma, Fig. 63) or on the

tangential walls (surface collenchyma). Non-living inclusions, other

than the large vaeuole, are wanting in them. Intercellular spaces are

absent or are very small. In spite of its high water - content

collenchyma possesses a considerable rigidity

against tearing owing to the thickening of the

walls of its component elements. It at the same

time allows and takes part in the growth of the

organ, and may be regarded as the cartilaginous

tissue of the plant. The distribution of the

collenchyma is in relation to its mechanical

functions. The extensive unthickened regions of

the cell walls, which are further provided with

round or elliptical pits, enable materials to be

rapidly transported within this tissue.

4. The Conducting Tissues. — As the body of

FIG. 62.— Transverse section
of the sclerenchyma in
the leaf of Phormium
tenax. (x 240.)

Fio. 63. — Transverse section of the
collenchyma of Cucurlita Pepo.
(X 240.)

FIG. 64. — A collenchyma-
tous cell seen from the
side, (x 240.)

a plant becomes larger and composed of more numerous cells, and
especially as more parts of it project from the soil or water into
the air, the need of rapid conduction of substances from one organ
to another (e.g. from leaves to roots and conversely) increases. The
movement of diffusion through the cross walls even of elongated
parenchymatous cells does not suffice, though facilitated by the
presence of pits in the wall and the complete suppression of inter-
cellular spaces. Special conducting tissues have therefore arisen, the
characteristically constructed elements of which are usually elongated
in the main direction of conduction, frequently present enlarged
surfaces for diffusion, and are further as a rule united to form con-

DIV. I

MORPHOLOGY

tinuous conducting channels. Such tissues are always associated in a
connected system traversing the whole plant.

(a) Sieve-Tubes. — The elements composing the SIEVE-TUBES (45)
are arranged in longitudinal rows and connected by open pores which
appear to serve for the transport of proteids and carbohydrates. The
transverse or oblique ends, and sometimes the lateral walls, have sieve-
like perforated regions the pores of which are filled with thick
protoplasmic strands. These are called the SIEVE-PLATES (Fig. 65
A, B). In many plants (e.g. the Cucumber, Fig. 65 A) the entire
transverse wall forms one area perforated by relatively coarse pores.

FIG. 65. — Parts of sieve-tubes of Cucurbita Pepo, hardened in alcohol. A, Surface view of a sieve-
plate. B, C, Longitudinal sections, showing segments of sieve-tubes. D, Contents of two sieve-
tube segments, after treatment with sulphuric acid, s, Companion cells ; u, mucilaginous
contents ; pr, peripheral cytoplasm ; c, callus plate ; c*, small, lateral sieve-plate with callus,
(x 540. After STRASBURGER.)

On the longitudinal walls the sieve-plates have the form of narrowly
circumscribed circular areas with much finer pores (Fig. 65 (7, c*) where
two sieve -tubes adjoin laterally. In other cases several finely-
perforated areas (sieve-plates or SIEVE-PITS) are found on the oblique
end wall of a sieve-tube (Fig. 66). The elements of a sieve-tube
(Fig. 65), each of which corresponds to a cell, contain a thin living
protoplasmic layer lining the wall, with a single nucleus, leuco-
plasts, and often starch grains. This encloses a watery, alkaline,
more or less concentrated, and coagulable cell sap which is rich in
albuminous substances and frequently in carbohydrates and inorganic
salts (phosphates). The walls of sieve -tubes are almost always
unlignified ; they .consist of cellulose and are elastically stretched by

BOTANY

PART I

their contents. As a rule they remain functional during one vegetative
period only. Before passing into the inactive condition their sieve-
plates become covered by highly refractive plates of CALLUS (Fig. 65 C\
which diminishes or prevents the exchange of materials between the
members of the sieve-tube. If the sieve-tube resumes its function
in the succeeding vegetative period this callus is again dissolved.

The callus plates consist of CALLOSE, a substance the chemical composition of
which is still unknown ; this is characterised by its insolubility in ammonia-
oxide of copper and its solubility in cold 1 % solution of potash. It is coloured

reddish-brown by chlor-zinc-iodide,
a shining blue with aniline blue, and
T, shining red with corallin (rosolic

acid).

(b) Vessels. — Special, and
ultimately dead, cells, which
are tube-like with a circular or
polygonal cross-section and are
elongated and arranged in longi-
tudinal rows in the main direc-
tion of conduction, serve for the
conduction and storage of water
in the plant. The lignified walls
of these vessels have striking
and characteristic thickening.
So long as they are functional

the V6SSels C0ntain Watei>> and
often also a limited amount of
air4 They are distinguished as

TRArTTFTr>™ nnfj TT>ArTTWAV
\ KAL.HJCA b,.

The tracheides are single cells
with pointed ends, and are as a rule of narrow diameter. Their walls
bear peculiar pits (Fig. 70 B). These elements frequently serve as
mechanical tissue, as in the stems of Coniferae. The tracheae, on the
other hand, are wider or narrower tubes formed from a number of
cells by the disappearance of their end walls. When the latter are
transversely placed they are completely dissolved, leaving only a
narrow annular rim which becomes further thickened (Figs. 67 (7, s,
69 /. q, q '). Obliquely placed, end walls, on the other hand, are usually
not pierced by a single large opening but by a number of elliptical
openings placed one above the other (scalariform perforation, Figs.
69 //., 173 tg). Some of the end walls are not perforated but merely
pitted, and the vessels are thus of limited length.

Some tracheae, in particular those of woody climbers or lianes, may be some
metres in length. In the Oak also tracheae two metres in length are frequent.
As a rule, however, they do not exceed 1 m. and are usually only about 10 cm. in

FIG. M.-A, Junction of two elements of a sieve-
tube of Vltis vinifera, the oblique wall being shown
in section, (x 600. After DE BABY.) B, A similar
wall in surface view showing the sieve-pits. (Dia-
grammatised by ROTHERT after DE BARY.)

DIV. I

MORPHOLOGY

length. The widest as well as the longest vessels are met with in climbing plants ;
in them they may be 07 mm. wide, while those of the Oak are about 0'25 mm. and
of the Lime 0'06 mm.

The terminology of the water-conducting elements is somewhat confused in
the literature. As a rule the distinction is drawn between tracheides and tracheae
or vessels. DE BARY, however, called all these elements tracheae and distinguished
between tracheides and vessels. The suggestion of ROTHERT which is adopted
here appears most convenient, viz. to distinguish within the collective conception
vessels, the tracheides and tracheae.

The thickening of the walls of vessels may have the form of
narrow bars, T-shaped in cross-section (Fig. 68) on the relatively thin

FIG. 67.— A, Part of an annular tracheide. B,

;Part of a spiral tracheide. C, Longitudinal FIG. 68. — Portion of a longitudinal section

section through part of a reticulate trachea through three spiral vessels and a row of

showing the remains of a partition wall, s. pareachyma cells of the Gourd (Cucurbita

(x 240. After H. SCHEXCK.) Pepo). (x 560. After W. ROTHERT.)

wall. These bars may form isolated rings, connected spirals, or
a network, and accordingly ANNULAR, SPIRAL, and RETICULATE
tracheides and tracheae are distinguished (Figs. 67, 68). In other
cases the thickening involves the greater part of the cell wall but
leaves numerous pits (PITTED VESSELS, Figs. 69, 70). The pits may
be circular, polygonal, or more or less transversely extended and
elliptical or slit-like. When transversely-extended pits stand above
one another in regular rows on the lateral walls the vessel is termed
SCALARIFORM (Fig. 69 //., 70 A). The pits of pitted vessels are
always BORDERED PiTs(46), the canal of which widens from the cell
lumen to the pit membrane (Fig. 71). They may be present on one
or both sides of a cell wall. The outline of the pit in surface view is
commonly circular and encloses a smaller circle (Fig. 71 A). The
smaller circle is the opening into the cell cavity, while the wider
outline is that of the pit cavity at its widest part adjoining the pit
membrane. The thickening of the cell wall thus overhangs the
pit membrane and forms the wall of the pit, between the outer and

BOTANY

PART I

inner circles. The pit membrane is frequently thickened in the
centre forming the TORUS (Fig. 71 (7), and this, when the membrane
is deflected to one or other side, may close the entrance like a valve

(Fig. 71 B, t). The wide mem-
brane of the bordered pits allows
readily of movements of water
from the one cell cavity to the
while the overhanging

FIG. 69. — A, Diagrams of tracheae in longi-
tudinal section. I., Wide trachea with
small elliptical bordered pits, and with
simple perforation of the end wall (q, q).
The further portion of the wall is cut away
in the upper portion of the figure. II.,
Narrow trachea with scalariform pitting
of the wall and perforation of the trans-
verse wall, q. B, The transverse walls
of the two tracheae in surface view.
(After ROTHERT.)

FIG. 70.— A, Lower third of a
scalariform tracheide from the
rhizome of the Bracken Fern
(Pteris aquilinn) ; t, the trans-
versely-extended pits on the
lateral walls ; q, the scalari-
form pitted end wall, (x 95.
After DE BARY.) B, A
tracheide with circular bor-
dered pits, (x 100. After
STRASBURGER.)

wall of the pit ensures that the rigidity of the wall is not unduly
diminished.

As Fig. 71 shows, the pits are bordered on both sides of a wall
separating two water-conducting elements. When, however, a vessel
abuts on a living cell, the pit is only bordered on the side of

DIV. I

MORPHOLOGY

the membrane toward the water-conducting element and the pit
membrane has no torus. On the other side of the wall a simple pit
is developed.

There are transition forms between the various types of vessels,
and the thickening bands, in annular and spiral vessels, correspond
to the walls of the bordered pits.

These thickening bars are in fact, as was mentioned above, always narrowed
at their attachment to the wall (Fig. 68). As a result of this they are readily
detached from the unthickened membrane in the preparation of sections, the spiral
thickening often lying within the cavity. The thin portions of the wall between
the thickenings correspond to the pit membranes, and, when occurring between
two water-conducting elements,

may be somewhat thickened A. "

like a torus.

Annular or spiral vessels
are formed in growing parts
of plants as they can undergo
extension or stretching.

The thickening of the
walls of water-conducting
elements increases the
mechanical rigidity of the
latter and prevents their
being crushed bv the ad- r

. . P .. . J FIG. 71.— Tracheides from the wood of the Pine, Pinus

JOimng living Cells. I he sylvestris. A, Bordered pit in surface view. B, Trans-
Hving Contents Of the verse section of bordered pit from a tangential section

vpwh diminish a<* trip of the wood ' *' torus' C' Transverse section of a
.Qim tracheide ; m, middle lamella, with gusset, m* ; i, inner

wall thickens and llltl- peripheral layer, (x 540. After STRASBURGER.)

mately completely disap-
pear. This does not happen in the tracheae until after the transverse
walls have been broken through.

System of Tissue of the Vascular Bundles. — The sieve -tubes
are usually associated with conducting parenchyma to form strands
or bundles of phloem which traverse the plant. The same holds
for the tracheides and tracheae, although isolated or grouped
tracheides may occur as a water-storage tissue in the parenchyma.
Such strands of phloem or of vascular tissue may be regarded as
INCOMPLETE VASCULAR BUNDLES. They are common in the secondary
permanent tissue as vascular strands in the wood and phloem strands
in the bast (cf . pp. 1 54, 1 5 9). In the primary tissues, however, the phloem
and vascular strands are united to form COMPLETE VASCULAR BUNDLES
which run as a rule parallel to the long axis of an organ, and are
united by cross connections into a network. The name VASCULAR
BUNDLE SYSTEM is given to this striking feature in the construction
of a plant. In these bundles the elements which serve for the con-
duction of water are associated with those which conduct organic

BOTANY

PART I

material, so that these different substances follow nearly the same
course though usually in opposite directions. This tissue system may
in its origin be primary or secondary.

Such complete vascular bundles contrast with the less dense
surrounding tissue by the narrowness of their elements, and the absence
of intercellular spaces ; they are often visible to the naked eye as in
the translucent stems of Impatiens parviflora. Strands of tissue of two
sorts are to be distinguished in each bundle,
the vascular portion or XYLEM, and the sieve-
tube portion or PHLOEM. The xylem and
phloem may be variously arranged in the bundles,
the transverse sections of which differ accord-
ingly (cf. p. 99).

Other names are used in the literature for the complete
conducting bundle and its parts. Thus the conducting
bundles are also termed vascular bundles, fibro- vascular
bundles, or mestome ; the xylem is spoken of as the
woody portion, vascular portion, or hadrome ; and the.
phloem as bast or leptome.

5. Secretory Cells and Secretory Tissue.
(1) SOLITARY CELLS. — Secretory cells isolated or
arranged in rows are of frequent occurrence in
• the most diverse tissues. They may be isodia-
metric or tubular, and contrast with the other
cells by reason mainly of their contents. Within
their diminished or dead protoplasts secretions
of the most varied kinds are contained. These
are end products of the metabolism and may have
an ecological significance as protective substances.
Mucilage, gums, ethereal oils, resin, gum-resin,
FIO. 72.— Portion of a latici- tannin, alkaloids, and crystals of oxalic acid
ferous cell of Ceropegia. /Fi 22) are among the most frequent secretions.

(x 150. After STRAS- \.. & ' , ,, .

BURGER.) The walls of these cells are often subensed.

The non-septate LATICIFEROUS CELLS which

contain the secretion called LATEX belong here. They are richly-
branched tubes without cross walls, with a smooth elastic cellulose
wall that is usually unthickened (Fig. 72). They have a layer of living
protoplasm with numerous nuclei lining the wall and sometimes
contain starch grains (47), which in many Euphorbiaceae are dumb-
bell-shaped. Their cell sap is a milky, usually white, watery fluid
which rapidly coagulates on exposure to the air.

Enzymes (inFicus Carica and Carica Papaya peptonising enzymes in addition),
tannins, poisonous alkaloids, and especially calcium -malate, occur dissolved in
the latex. As droplets in an emulsion gum -resins (mixtures of gum and

DIV. I

MORPHOLOGY

resin), caoutchouc, gutta-percha, fats and wax occur, and as a solid constituent
proteid granules.

The laticiferous tubes in Euphorbiaceae, Moraceae, Apocynaceae,
and Asclepiadaceae proceed from cells
which are already recognisable in the
embryonic plant, and with the 'growth of
the latter continue to grow, branch, and
penetrate all the organs so that they may
become many metres in length.

(2) CELL-FUSIONS. — A number of
secretory cells may unite to form a more
spacious reservoir for the secretion, by the
dissolution of the waflls between them.
This is most strikingly seen in the LATICI-
FEROUS VESSELS. They resemble the latici-
ferous cells in appearance and in their
contents, but differ in their origin by the
fusion of a number of cells forming a net-
work (Fig. 73). Eemains of the trans-
verse walls may be recognised in this.

The laticiferous vessels, like the lati-
ciferous cells, are limited to certain families
of plants, for instance the Papaveraceae
(Papaver, Ghelidonium, with reddish-orange FIG. 73.— Tangential section through
latex), the Campanulaceae, and in the
Compositae the Cichorieae (C ichor ium,
Taraxacum, Lacfuca, Scorzonera, Hieracium,
Tragopogon).

There is little ground for the widespread idea that the laticiferous cells and
vessels also assist in the transport of materials.

The MUCILAGE TUBES which occur in many Monocotyledons are in many

respects similar to the
laticiferous vessels. Their
mucilaginous sap consists
of albumen, starch, glu-
cose, tannins, and inor-
ganic substances.

the periphery of the stem of Scor-
zonera hispanica, showing reticu-
lately- united latex vessels, (x
240. After STRASBCRGER.)

(3) LYSIGENOUS
I NTERCELLULAR
SPACES. — Secretory
reservoirs frequently

FIG. 74.— Lysigenous oil-reservoirs from the leaf of Dictamnus arise as Spherical ir
fraxindla. A, Young. B, Mature after dissolution of the coll n , , ' -,

walls. (ROTHERT altered from RASTER.) regular, Or tubular

cavities by dissolution
of entire secretory cells, i.e. lysigenously (Fig. 74).

These lysigenous secretory reservoirs arise from groups of cells in

BOTANY

PART I

which the secretion has been formed and the walls gradually dissolved.
The secretory cavities filled with ethereal oils in the orange and
lemon have this origin.

6. Glandular Cells and Glandular Tissue. — Glandular cells,
which excrete substances from their protoplasts to the outside or into
the intercellular spaces, occur singly or in groups in the epidermis, in

FIG. 75. — Glandular hair from the
petiole of Primula sinensis. (x 142.
After DE BARY.)

FIG. 76. — Glandular scale from the female inflores-
cence of the Hop, Humulus lupulus, in vertical
section. A, before, B, after the cuticle has become
distended by the secretion. In B the secretion
has been removed by alcohol, (x 142. After
DE BARY.)

the parenchyma, and in other tissues. The glandular cells resemble
parenchymatous cells, but have as a rule abundant protoplasm and
large nuclei as in meristematic cells. The excreted substances are
usually end products of metabolism and frequently have an ecological
significance. Closely connected glan-
dular cells forming a layer constitute
a GLANDULAR EPITHELIUM.

Glandular epithelia or isolated
glandular cells are of frequent occur-

FIG. 77.— Sessile digestive gland from the upper side
of the leaf of Pinguicula vulgaris. A, In longi-
tudinal section. B, Seen from above. (ROTHERT
altered from FENNER.)

FIG. 78.— Schizogenous oil-reservoir in a
cross - section of the leaf of Hypericum
perforatum. S, the glandular epithelium.
(After HABERLANDT.)

rence in the epidermis and are often covered by a porous cuticle. In
this situation glandular hairs, the knob-shaped end cell of which is
secretory (capitate hairs, Fig. 75), -also occur. Other glandular hairs
may be scale-shaped (Fig. 76), and glandular emergences (Fig. 56)
are also found. The secretion is very often composed of resinous

DIV. I MORPHOLOGY 71

substances, and accumulates between the outer wall of the secretory
cells and the cuticle which is raised up and finally burst. The same
holds for the formation of other adhesive substances and mucilage.

According to the excreted products, which may have varied ecological uses,
the epidermal glands may be distinguished into mucilage, oil, resin, digestive
(Fig. 77) glands, also salt glands, water glands (hydathodes), and nectaries (48).
The last-named secrete a sugary fluid which attracts insects and occur as
glandular surfaces or hairs within the flower or in other situations (cf. Fig. 136 »).
These are termed respectively floral and extra-floral nectaries.

The glandular cells or epithelia enclosed within parenchymatous or
other tissues always abut on circular or irregular intercellular spaces or
tubular, branched, or unbranched canals which sometimes run through
the whole plant as a* connected system of tubes. These intercellular
spaces, which arise by the splitting apart of cells, form the schizogenous
secretory reservoirs (Fig. 78). Their contents consist of ethereal oils,
resin, gum, or mucilage, and corresponding distinctions are made in
naming these canals.

Schizolysigenous reservoirs also occur.

SECTION III

ORGANOGRAPHY (49)

THE EXTERNAL MEMBERS AS ORGANS OF THE PLANT

THE organisms included in the vegetable kingdom are variously shaped
and segmented. Some are unicellular throughout life, while others
are multicellular. Both may have very simple and regular geometrical
forms and have no external segmentation, or on the other hand may
possess a body with a very irregular outline owing to its being
divided into protrusions of the most various kinds.

I. Significance of the External Segmentation to the Organism.
—The construction and segmentation of any particular organism stand

as a rule in close relation to its needs and mode of life. The external
as well as the internal segmentation is usually the expression of a
DIVISION OF LABOUR between the parts or the cells of the multicellular
body. The external members are, in fact, usually ORGANS with definite
vital functions. The physiological progression from simpler to more
segmented organic forms consists in great part in the increase of this
division of labour.

II. Main Groups of Organs. — The activity of every organism has
two sides. It must nourish itself in order to maintain itself as an
individual, and it must reproduce in order that the race should not
perish with its death. The body of the plant subserves these two
fundamental vital impulses. Only in primitive plants does the whole

72 BOTANY PART i

mass serve both equally ; usually certain parts are concerned with the
nutritive processes and others with reproduction. There is thus
usually a clear division of labour between the vegetative organs and
the reproductive organs, which are fundamentally different in form
and structure as well as in function. These two groups of organs will
require separate consideration.

III. Relations of Symmetry. — The form of the whole segmented
or unsegmented organism and of its parts is determined by their
relations of symmetry. Like nearly all properties of organic forms
this is closely connected with the mode of life of the organism,
especially with the direction of growth of the plant and the position
of its members in space. As a rule, therefore, the symmetry of the
internal construction of a plant corresponds to that of its external
form.

Apart from a few very simple forms, the plant body and its
individual parts nearly always exhibit POLARITY and a distinction of
base and apex. Such a distinction is shown both in free motile
forms, in which the direction of progression is usually determined by
the polar construction of the body, and in attached forms, where the
organism is attached to the substratum by its basal pole.

Every section through a part of a plant parallel to the longitudinal
axis is a longitudinal section. When it passes through the axis it is
termed a radial longitudinal section, and when it is at right angles to a
radius but not in the plane of the axis itself a tangential longitudinal
section. Sections at right angles to the long axis are transverse
sections. An organism or a part of a plant which is almost similarly
constructed around its longitudinal axis is termed RADIAL or ACTINO-
MORPHIO (Fig. 525 A). Such a structure can be divided by a number
of radial longitudinal sections into approximately equal halves, which
are mirror images of one another ; it has thus a number of PLANES
OF SYMMETRY. When there are only two planes of symmetry
standing at right angles to each other the structure is called
BILATERAL (Fig. 107). Lastly, when there is only a single plane of
symmetry (the MEDIAN PLANE) the structure is DORSIVENTRAL or
ZYGOMORPHIC ; the two lateral halves correspond, while the anterior
and dorsal sides are unlike (Fig. 525 B). Plants or parts of plants
which grow vertically upwards or downwards (ORTHOTROPOUS) are
usually radial or bilaterally symmetrical. When, on the other hand,
they grow oblique or at right angles to the vertical (PLAGIOTROPOUS)
they are frequently dorsiventral. There are also ASYMMETRICAL
organic structures, which cannot be divided by any plane into corre-
sponding halves. Some dorsiventral structures, e.g. leaves, become
asymmetrical by the one half being differently formed to the other.
This is,- for example, the case with the leaves of Begonia, and in a less
degree with those of the Elm. The whole radially symmetrical
plant body is here composed of dorsiventral and asymmetrical parts.

DIV. i MORPHOLOGY 73

I. Vegetative Organs

The highest segmentation attained by the vegetative organs of
plants is that into ROOT, STEM, and LEAVES. Stem and leaves are
classed together as the SHOOT. A plant body composed of shoot and
root is termed a CORMUS, and plants so constructed CORMOPHYTES.
The fern-like plants, or Pteridophyta> and the more highly-segmented
seed plants derived from them are cormophytes.

The cormophytes arose phylogenetically from more simply
organised plants in which the plant body had not attained such a
profound segmentation ; in which roots were wanting, while leaf-like
branches though not true leaves were present. Such structures, as
well as quite simple and unsegmented plant bodies, are included
under the term THALLUS, and such plants may be contrasted with
the cormophytes as thalloid. The Algae, Fungi, Lichens, and all
Bryophyta have thalli.

The thalloid plants must not be confused with the Thallophyta. All thalloid
plants possess a thallus, but they are not all Thallophyta. Under this name
systematic botany includes only the Algae, Fungi, and Lichens.

A. THE THALLUS (50)

(a) Algae, Fungi, Lichens. 1. Simplest Forms. — The only forms
that are quite unsegmented externally are a number of microscopically
small unicellular or multicellular plants. The simplest form that can
be assumed by an organism is that of the sphere.

For example, such spherical cells are shown by some Algae that form a green
coating on damp walls (Fig. 35), and by many Bacteria (Fig. 80 b). The latter
include by far the smallest known organisms.

2. Increase of Surface. — Of all geometric figures the sphere has
the smallest surface for the same volume, and this surface bears a
smaller ratio to the volume the greater the latter is. Deviations
from the spherical form are thus connected with a relative increase of
the surface. In particular, as the volume of the body increases the
surface area is in this way increased relatively to the volume.
Cylindrical, rod-shaped, filamentous, ribbon-shaped, and discoid forms
thus occur, and ultimately bodies segmented by reason of their external
projections. The free surface of the body is of great importance to
the plant for the absorption of the gaseous and liquid substances
necessary for its nutrition and derived from the environment.

Even when spherical the cells of Bacteria on account of their minute size have
an extraordinarily large free surface as compared with cells of higher organisms.

The unicellular individuals of the beer Yeast (cf. Fig. 20) are ellipsoidal in
shape, while the cells of many Algae, such as species of Diatoms (Fig. 79), are
discoid or cylindrical. This group of Algae exhibits spindle, canoe, helmet, and

BOTANY

PART I

fan shapes, and also filamentous ribbon- and chain-like forms. Rod-shaped and
spirally-wound forms are met with in the Bacteria (Fig. 80 a, c, d}.

Such living beings may be attached by mucilage to a substratum or may float
free in water. The free-floating organisms of continental water surfaces as well as
of the ocean are termed PLANKTON in contrast to the firmly -attached aquatic
organisms which constitute the BENTHOS. The plankton flora, which is rich in
peculiar species, contains such forms as have been mentioned above. These may
have the power of active movement (swimming forms) due as a rule to projections
of the protoplast as slender contractile flagella or cilia which are special organs of

locomotion. This power of movement enables
many organisms of the plankton, responding
to stimuli, to seek for favourable nutritive
conditions or to avoid unfavourable spots.
Other forms of the plankton are suspended
without true power of movement in the water

FIG. 79.— Pinnularia viridis. A, Surface
view. B, Lateral view, (x 540.
After STRASBURGER.)

FIG. 80.— Bacteria from deposits on teeth, a,
Leptothrix buccalis; a*, the same after treat-
ment with iodine ; b, Micrococcus ; c, Spiro-
chaete dentium after treatment with iodine ;
d, Spirillum sputigenum. (x 800. After
STRASBURGER.)

(floating forms). Many of them, and other plankton organisms, show special
arrangements for flotation in the increase of body surface by long bristles, bars,
and plates. The friction of the body against the water is thus considerably
increased and sinking made more difficult (51).

3. Establishment of Polarity. — The next stage in progressive
complexity of form is the establishment of the distinction between
base and apex. In freely motile forms the cilia are frequently
attached at one pole. In fixed forms one pole forms an ORGAN OF
ATTACHMENT, as, for instance, a circular disc of attachment or
palmately-branched lobes. The further growth may at the same time
be restricted to a small region of the body or GROWING POINT. This

DIV. 1

MORPHOLOGY

in intercalary growth is a zone between the base and apex, while in
apical growth it is situated at the summit of the plant body. A
young plant of the green seaweed Ulva lactuca affords an example
of the latter condition (Fig. 81).

4. Flattening. — Many Algae and Lichens have a disc-shaped or
ribbon-shaped thallus (Fig. 83) by which the free surface is further
increased. The assumption of this form may therefore be regarded as
an adaptation to the nutritive relations of the organism. The latter
constructs its organic substance from the carbon dioxide which it can
decompose, but this process of assimilation only takes place in plants
that contain chlorophyll and in the light. Thus as

many chlorophyll grains as possible require to be
exposed to the *light, and this is attained even
in massive bodies by flattened form.

5. Dorsiventrality. — The majority of the forms
so far referred to are radial or bilaterally sym-
metrical. In those in which the thallus spreads
out on a substratum (e.g. in many Lichens), the
construction of the plant body further becomes
dorsiventral. Dorsiventral symmetry is character-
istic of forms in which the upper side is the more
strongly illuminated and is especially concerned in
assimilation.

6. Branching. — Filamentous, ribbon -shaped,
and discoid forms, the surface of which is extended
as branches, are still more highly organised. This
occurs in most thalli of Algae, Fungi, and Bryo-
phyta. The free surface is still further increased
by the branching, and the available space is better
utilised. Thus bushy, shrub-like, and dendroid
thalli arise ; these in the Algae have often delicate
branches moving with the surrounding water to
which they offer little resistance.

In branching the apex of the young plant may

divide into two new and equivalent parts (DICHOTOMOUS BRANCHING),
as happens repeatedly in the fan-shaped thallus of the Brown Seaweed,
Didyota dichotoma (Fig. 83 ; cf. the diagram in Fig. 82 a). In other
branched forms there is a new formation of growing points which
give rise to lateral branches (LATERAL BRANCHING), and in the higher
forms this becomes more and more limited to the apical region of
the thallus ; the youngest and shortest lateral branches are the nearest
to the apex. Such an ACROPETAL origin of new lateral members is
already evident in the filamentous Green Alga, Cladopliora (Fig. 84 ;
cf. also Fig. 89). In the simplest case of lateral branching a single
main axis (MONOPODIUM) continues its apical growth throughout the
branch system. It behaves as the parent axis to a large number of

FIG. 81.— Ulva lactuca,
young stage, show-
ing apex and base.
( x 220. After STRAS-

BURGF.R.)

BOTANY

PART I

lateral axes, arising successively on all sides. These grow less actively
than the main axes but can in turn branch similarly. This type
of branching is called racemose (cf. the diagram, Fig. 82 b).

All lateral axes which arise on the axis of the young plant are

.-U-»«-U".

a b

FIG. 82.— a, Diagram of dichotomous and, b, of lateral racemose branching. K, Axis of the young
plant ; H, main axis ; 1, 2, 3, U, lateral axes of corresponding orders.

spoken of as branches of the first order ; those which, in turn, arise on
branches of the first order as of the second order, and so on (cf. Fig.
82). The axis on which a daughter axis arises is termed relatively to

it a parent axis. Parent
axes may thus themselves
be daughter axes of the first,
second, third, etc., orders.

Cymose branching, which will
be described in connection with
the corraus, also occurs in Thal-
lophytes.

In contrast to the TRUE
BRANCHING described above,
what is known as FALSE
BRANCHING is found in
some low filamentous Algae
and Bacteria. It comes
about by the filament break-
ing into two portions, still, however, held together by the mucilaginous
sheath ; each new end arising by the rupture can grow on as a filament
(Fig. 86). When an unbranched thallus is subsequently split into a
number of lobes, as in the case of the flat thallus of Laminaria (Fig.
351), the term branching is not used.

The thallus in the Fungi, which do not assimilate carbon dioxide

FIG.

,—Didyota dichotoma. (f nat. size.
After SCHENCK.)

DIV.

MORPHOLOGY

but absorb organic substances, has a correspondingly peculiar aspect.
It is termed a MYCELIUM, and consists of thin, highly -branched,
cylindrical, colourless filaments (Fig. 87 and Fig. 6) called HYPHAE.
These penetrate the substratum, such as the humus soil of a wood, in
all directions and thus expose a large surface for the absorption of the

necessary food materials. Parasitic
fungi, if not inhabiting the cells, usually
send suctorial projections of the hyphae
(haustoria) into the living cells of the
host plant from the hyphae in the
intercellular spaces (Fig. 85).

7. Division of Labour between
the Branches of the Thallus. — The
most highly-segmented types of thallus
are met with in some Siphoneae and
in the Brown and Red Seaweeds
(PhaeophyceaeandRhodophyceae). The
external segmentation of some of these
resembles in a remarkable manner the
shoot in cormophytes. Some of these
Algae attain a great size, the thallus

FIG. 84.— Portion of Cladophora
glvnurata. (x 48. After SCHENCK.)

haust

FIG. 85.— Haustoria (haust) of Peroiiospora parasitica
in parenchyma tons cells of Capsdla. hy, The inter-
cellular hyphae. ( x 240.)

of the Brown Alga, Macrocystis, being 45 m. long. A good example
of high differentiation is afforded by the Red Seaweed, Delesseria
sanguined (Fig. 88), which has leaf-like lateral branches seated on the
cylindrical, branched, relatively main axes. In many such forms,
besides the formation of attaching organs or haptera and of branches,
a further degree of differentiation is attained. Some cylindrical
branches continue the growth and branching of the thallus as LONG
SHOOTS. Other branches borne on these are SHORT SHOOTS with

BOTANY

PART I

limited growth, and serve as leaf -like ORGANS OF ASSIMILATION.

These short shoots may
again exhibit a division of
labour among themselves.
Such forms are of the
greatest interest morpho-
logically, as they show how
the leaves of cormophytes
could have arisen from short
shoots.

Leaf- like short shoots have
evidently arisen independently in
a number of series of thalloid
plants. These organs, serving
for assimilation, have all as-
sumed similar leaf-like forms.
Thus the leaf -like branches of
the Siphoneae and Brown Algae
are not homologous with those of
the Red Algae but only analogous.

8. Internal Structure
of the Thallus. — Thalli,

whether segmented or unseg-
mented, may consist of a

FIG. 86.— False branching in Cyanophyceae. A, Plecto- single protoplast (e.g. SipllO-

nemaWollei; only the upper end of the broken filament neae Cdulerua Fio\ 346) Or

grows out as a branch. B, PI. miraUle; both ends r 11 1 ' T ° i i

proceed to grow. (OLTMANNS after KIRCHNEB and Ot many Cells- lu fcne latter

BORNET.) case the cells are arranged

in filaments (Fig. 84), sur-
faces, or are united to form a cell mass. The simplest multicellular
thalli are composed of uniform
cells all capable of division.
As soon as a growing point is
defined a distinction between

MERISTEMATIC and PERMANENT

cells is apparent. The extreme

tip of the apical growing point

is nearly always occupied by a

single cell termed the APICAL

CELL. This often differs little

from the other cells, as in the

case of Cladophora glomerata

(Fig. 84). The dome-shaped

apical cell is prominent on

the multicellular long shoots of the Brown Alga, Cladostephus verti-

cillatus (Fig. 89).

FIG. 87.— Portion of the mycelium of Penicillium.
( x about 35.)

DIV. I

MORPHOLOGY

Such an apical cell divides by transverse walls parallel to one another, which
cut off disc-shaped segments from its lower end. These divide further in a regular
way, first by longitudinal and then by transverse walls into a number of cells,
which are at first meristematic. The lateral branches, mostly developed as
shoots of limited growth, develop from lateral cells in acropetal succession, and
give the characteristic form to the plant (Fig. 89). Flat ribbon-shaped thalli
may have a similar but correspondingly flattened apical cell, as seen in the Brown
Seaweed, Dictyota dichotoma (5a) (Fig. 90). Flat segments are cut off from this by
walls convex backwards, and are then divided by longitudinal walls. Sometimes
the apical cell is divided by a longitudinal wall into two cells of equal size lying

FIG. 88. — Delesseria sanguinea. (i nat. size.
After SCHENCK.)

FIG. 89.— Cladostephus verticillatus. (x 30.
After PRINGSHEIM.)

side by side (Fig. 90 B, a, a), each of which forms one of the branches of the
dichotomy.

The permanent cells even of highly -differentiated thalli almost
always have the characters of parenchyma. There may be a distinction
of peripheral assimilatory parenchyma with abundant chlorophyll,
storage parenchyma, colourless and with abundant reserve materials,
and conducting parenchyma composed of elongated cells.

Since the multicellular Algae living in water do not require protection against
drying up, and when exposed to the air at ebb-tide are protected by a covering of
mucilage, a typical epidermal layer is wanting. The Algae show, however, an
outer lamella of the cell walls of their superficial cells, which stains brown with

BOTANY

PART I

chlor-ziuc-iodide. Rigidity of the thallus, especially in forms that grow exposed
to the surf, is provided for by thickening of the walls of the outer layers of cells
and sometimes by incrustation with calcium carbonate. In the Bladder Wrack
(Fucus vesiculosus) special mechanical cells, characterised by their thickened walls
and their great extensibility and elasticity, are present. The Laminarieae, which
are also Brown Algae, attain the highest grade of internal differentiation. In the
thick stem-like axis of these plants a cortex, a central body, and a loose medulla
can be distinguished. The cortex frequently contains mucilage canals, and the
medulla has rows of cells resembling sieve-tubes and serving for the transport of

materials ; such cells also occur
in some Rhodophyceae. The axis
grows in thickness by the con-
tinued division of a cortical layer,
which forms concentric zones of
^^ secondary tissue, recalling the

•"• annual rings of the higher plants.

The thalli of LICHENS arise
by the interweaving of fungal
hyphae and can assume a paren-
chymatous structure. The peri-
pheral layers in many species
form a protective rind owing to
the close association of the hyphae
and the thickening of their walls.

(b) Bryophyta(53).— The
fact that the Mosses and
Liverworts (Bryophyta) as-
similate carbon dioxide finds
expression in their external
form and internal structure.
There are Liverworts such as
Eiccia fluitans (Fig. 9 1 ) in

FIG. 90. — The growing point of Dictyota dichotoma, show- i • r ,-t j-V i

ing the dichotomous branching. A, Initial cell. whlch the dichotomously-

(x circa 500. After E. DE WILDEMAN.) branched ribbon-shaped body

resembles the thallus of

Dictyota (Fig. 83). In Blasia pusilla, another Liverwort (Fig. 92), the
ribbon-shaped thallus has a midrib and bears lateral lobes as if the
separation of leafy structures was commencing. The most completely
segmented Liverworts, such as Plagiochila asplenioides (Fig. 93), and
all the Mosses have cylindrical branched stems bearing such leaves as
organs of assimilation. The lateral branches stand beneath the leaves
on the main axis. These dorsiventral, bilateral, or radially-symmetrical
bodies, which are often in the Mosses associated in tussocks, are only
analogous to the shoots of the higher plants and are best regarded
as highly-differentiated thalli. Though these plants, in contrast to
the Algae, are mostly sub-aerial organisms they do not possess true
roots, but are attached to the soil by RHIZOIDS. These are unicellular
hairs, separated from the basal cell bearing them by a cross wall, or

DIV.

MORPHOLOGY

branched filaments of cells, and serve to absorb water. Many of
these plants can absorb water by their whole surface.

Fio. 91. — Riccia fluitans.
(Nat. size. After SCHENCK.)

FIG. 92.— Blasia pustila. r, rhizoid.
(x 2. After SCHKXCK.)

When the thallus lies on the substratum it is usually dorsiventral
as in Lichens, and frequently has abundant chlorophyll only on the
upper side exposed to the light (Fig. 95). In such cases the rhizoids
are confined to the lower surface.

In the Bryophyta, which are all rnulticellular,
the summit of the apical growing point is fre-
quently occupied by a single apical cell.

In ribbon -shaped Liverworts, such as Metzgeria and
Aneura, as in some similarly-shaped Algae, the apical
cell is wedge-shaped (Fig. 94), and cuts off segments in
two or sometimes four rows. The segments in the former
case are cut off by oblique walls inclined alternately to the
right and left ; the four-sided apical cell in addition cuts
off segments above and below. By further division the
segments give rise to the body of the plant. The apparently
dichotomous branching of Liverworts with growing points
of this type can be traced back to the early delimitation
of a new apical cell in the acroscopic half of a young seg-
ment (Fig. 94 at b}. In the erect radially -constructed
thalli of the Mosses the apical cell has the form of a
three-sided pointed pyramid, and cuts off three rows of
segments. The young leaves of the Mosses grow at first by
a two-sided apical cell, but later have intercalary growth.

FIG. 93.— Plagiochila asple-

The permanent tissues reach a higher level of nimdes with leaves over-
differentiation than in the Algae. This is con-
nected with the difficulties which the life on land
of the Bryophyta introduces. There is only
rarely a definite epidermis, though the superficial cells are covered by
a kind of cuticle. On the thallus of the Marchantiaceae, however,
an external layer of cells is clearly marked off from the underlying

lapping like the laths of
a Venetian blind. (Nat.
size. After SCHENCK.)

.BOTANY

PART I

tissue. It is perforated by air-pores (Fig. 95), which resemble in
origin the stomata of higher plants. Hairs, in the form of mucilage-
secreting papillae or flat leaf -like scales,
are of common occurrence.

A typical stomatal apparatus with two guard
cells enclosing a stoma is found, as GOEBEL (54) has
shown in the thallus of the Liverwort, Anthoeeros ;
it must be borne in mind that these stomata are
mucilage slits and do not contain air.

A peculiar capillary apparatus serving for the
absorption of water occurs in the Bog Mosses
(Sphagnaceae). The cortex of the stem consists
of three or four layers of empty cells, the walls of
which have annular and spiral thickening, and
are perforated by round holes ; these readily absorb
water. Similar cells lie singly in the leaves, which
are only one layer of cells thick, in the meshes of
a network of elongated living cells containing
chlorophyll.

Some Liverworts have a strand of elongated cells serving for
conduction. This is situated in the midrib of the ribbon-shaped
forms. Conducting strands clearly limited from the surrounding
tissue are, however, first met with in the Mosses.

A relatively simply-constructed conducting strand is shown in transverse section
in the stem of Mnium undulatum in Fig. 96 I. The most perfect strands of this

FIG. 94. — Diagrammatic representa-
tion of the apex ofMetzgeriafurcata
in process of branching, viewed
from the dorsal side, a, Apical
cell of pajent shoot ; b, apical cell
of daughter shoot. ( x circa 370.
After KNY.)

FIG. 95. — Surface view and transverse section of the thallus of Man-hantia polymorpha. In A, an
air-pore, as seen from above; in B, as seen in cross-section ass, assimilating cells, (x 240.
After STRASBURGER.)

kind are found in the steins of the Polytrichaceae. They contain elongated, thin-
walled, water-conducting elements, thick-walled mechanical tissue, and elongated
cells that contain proteids and starch. Strands of similar construction are also
found in the thick midrib of the leaves and are connected with that of the stem.

DIV. I

MORPHOLOGY

In some Mosses there are in addition elongated and pointed mechanical cells which
closely resemble sclerenchyma fibres.

(e) Gametophyte of the Cormophytes (53). In the developmental
history of the cormophytes a stage with a thalloid vegetative body
occurs. Two generations alternate regularly with one another, the
spore-bearing plant or sporophyte and the sexual plant or gametophyte.
The vegetative body of the former is a connus, while that of the latter
is usually a very simply segmented and constructed thallus (pro-
thallium). In Pteri-
dophyta the gametophyte
is usually a flat green
// structure attached to the

soil by rhizoids and living

FIG. 06. — Transverse section of the stem of Mnium undu-
latum. I, Conducting-bundle ; c, cortex; e, peripheral
cell layer of cortex ; /, part of leaf ; r, rhizoids. ( x 90.
After STRASBURGER.)

FIG. 97. — Asjndium filix mas. Pro-
thallium from the lower side.
rh, rhizoids. (x about 8. After
SCHEXCK.)

independently (Fig. 97). It is at most a few centimetres in length
and resembles a small Liverwort thallus. It may also consist of
branched filaments.

B. THE CORMUS

The vegetative organs of the sporophyte in the Ferns and fern-like
plants (Pteridophyta) and in the Spermatophyta, to which the name
cormus will be applied, are, as has already been mentioned, more
highly segmented than the thalli. The cormus is divided into shoot
and root, the shoot into the axis and the leaves. Stems, leaves, and
roots are thus the fundamental organs of the cormus, which evidently
is adapted to life on land by its outer and inner construction.

84 BOTANY PART i

As in many thalli the surface of the cormus is considerably in-
creased by branching. The shoot forms lateral branches, the roots
give rise to lateral roots, and by this branching, which in many plants
begins even in the embryo, a shoot-system and root-system arise.

The term cormus is usually employed as equivalent to shoot to denote a leafy
stem apart from the roots, and a shoot or cormus is then recognised in the leafy
Bryophyta. This view, however, dates from a period when the life-history of the
Bryophyta was not accurately known. It is now established that the "shoot" of
the Moss is not homologous with the shoot of the higher plants. It is therefore
advisable not to employ the terms shoot or cormus in speaking either of the
Bryophyta or of similarly organised Algae. There is nothing to prevent using the
conception of the cormus as a wider one than that of the shoot, and to understand
by it the vegetative organs of the cormophytes differentiated into shoots and roots.
Further, there are transition forms between roots and shoots (e.g. the rhizophores
of Selaginella) and between leaves and shoots (e.g. Utricularia).

1. Construction of the Typical Cormus

The fundamental organs of those cormi which can be regarded as
typical will be considered in the first place. Their peculiarities only
appear typically in such plants as our native trees, or even more
clearly in many herbs. The fundamental organs may undergo many
modifications and, in extreme cases, their distinction may be difficult.

(a) The Shoot

The shoot in land plants may be wholly or in part exposed to the
air (AERIAL SHOOT) or be partly buried in the soil (SUBTERRANEAN
SHOOT, Fig. 138); the latter is the case in many perennial herbaceous
plants (cf. Figs. 123, 138). It consists of the STEM or AXIS of the
shoot and the LEAVES. The latter on. the aerial shoots, which are
usually green, are developed as foliage leaves, while on the white or
colourless subterranean shoots (root-stocks or RHIZOMES) they are
mere scales. The stem bears the leaves and provides for the extension
of the shoot-systems ; this involves the elongation of the stem and
the formation of new leaves and lateral branches, the connection
between the leaves and roots, and the conduction of material between
these organs. The stem in most subterranean shoots further serves
as a place of storage of reserve materials. The foliage leaves, like the
leaf-like branches of thalloid plants, are the organs of assimilation and
transpiration in the cormophytes. The external form and internal
structure of the foliage leaves and stem stand in relation to these
functions.

(a) The Growing1 Point. — The shoot grows by means of an apical
growing point situated at the extreme tip of the stem. Since the
growing point is extremely small and scarcely visible to the naked
eye, it is best seen when longitudinal sections of the apex of the shoot

DIV. I

MORPHOLOGY

are examined with a magnifying glass (Fig. 98). It then appears flat
(Fig. 99) or convex (Fig. 98 t?), and sometimes distinctly conical
(Figs. 100, 102). The rudiments of the leaves (/) and of lateral
branches (g) arise laterally beneath the tip and appear as closely-
crowded exogenous projections or bulges of the surface. The leaves
arise in acropetal order and become larger on passing farther from
the apex, as is clearly shown in transverse sections of the growing
point (Fig. 99).

The growing point and the young leaves, which only arise from
the embryonic part of the apex, both consist of meristematic tissue.
In the majority of the Ferns and in the Horsetails a single apical cell

FIG. 98. — Apex of a shoot of a phanerogamic plant.
v, Vegetative cone ; /, leaf-rudiment ; g, rudi-
ment of an axillary bud. (x 40. After
STRASBCRGER.)

FIG. 99.— Apical view of the
vegetative cone of a shoot
of Euonymus japonica.
(x 12. After STRAS-

BTTRGER.)

is found at the summit of the growing point (Fig. 100 t). It has the
form of a three-sided pyramid (tetrahedron) with a convex base.

The apical cell (Fig. 100 t, 101 A) of the main shoot of the Common Horsetail
(Equisetum arvense) will serve as an example. Viewed from above (Fig. 101 A] it
appears as an equilateral triangle in which new walls are successively formed
parallel to the original walls. Each segment (£', S") becomes further divided by
partition walls. In the Pteridophyta which have apical cells the leaf rudiments
(/> /', /") usually commence their development with an apical cell which cuts off
the rows of segments (/). The activity of this usually ceases, and the development
of the leaf is continued by marginal growth due to a number of equivalent two-
sided cells. This is the case, for example, in Equisetum. The lateral buds (g} also
start from a single cell that becomes the apical cell.

In the Lycopodiaceae, among the Pteridophyta, and in Phanero-
gams, there is no such single apical cell at the growing point. In

BOTANY

PART

place of this a number of equivalent meristematic cells, which often
form regular concentric layers (Fig. 102), are met with.

The outermost layer of cells which covers the growing point and also the
developing leaves is termed the DERMATOGEN (d) because it gives rise to the
epidermis ; it usually divides by anticlinal walls only. The cells in which the
central cylinder of the stem ends at the apex form the PLEROME (pi), while the layers
between this and the dermatogen constitute the PERIBLEM (pr). The limit between
the periblem and plerome is often indistinct. The leaves and lateral branches arise
as multicellular projections (Fig. 102), which come about by local increase in
number of periblem cells, while the dermatogen undergoes anticlinal divisions only

FIG. 100.— Median longitudinal section of the vegetative cone of Equisetum arvense.
Explanation in the text, (x 240. After STRASBUROER.)

and keeps pace with the enlargement. In the case of the origin of leaves only the
dermatogen and periblem are concerned ; in that of the lateral branches the
plerome also (55).

Since, the rule that the new cell walls intersect at right angles holds for
growing points, the system of cell walls as seen in longitudinal sections often
forms a strikingly symmetrical figure, the periclinal as well as the anticlinal
walls forming systems of confocal parabolas (Fig. 266). The elements of the one
system cut those of the other nearly at right angles (SACHS). In transverse sections
of such growing points the periclinal walls form concentric circles.

BUD. — The formation of new members at the growing point is
followed by their increase in size and differentiation. This applies in
the first place to the young leaves, the growth of which exceeds that
of the stem apex and is most marked on their lower surfaces. As a

DIV. I

MORPHOLOGY

result of this the older leaves close over the growing point (Fig. 98)
and the younger leaf rudiments. The growing point thus becomes a
bud in which the delicate younger structures are protected against
desiccation by the older and larger, though still immature, leaves. A
bud is thus the young incompletely-developed end of a shoot.

VERNATION AND AESTIVATION.* — A section through a winter bud shows a
wonderful adaptation of the young leaves to the narrow space in which they are
confined. They may be so disposed that the separate leaves are spread out flat,
but more frequently they are folded, rolled (Fig. 103 I), or crumpled. The manner

FIG. 101.— A, Apical view of the vegetative
cone of Equisetum arrense. B, Optical
section of the same, just below the apical
cell ; I, lateral walls of the segments.
Further explanation in text, (x 240.
After STRASBURGER.)

FIG. 102. —Median longitudinal section of the
vegetative cone of Hippuris imlgaris. d, Der-
matogen ; pr, periblem ; pi, plerome ; /, leaf-
rudiment. ( x 240. After STRASBCRGER.)

in which each separate leaf is disposed in the bud is termed VERNATION. On the
other hand, the arrangement of the leaves in the bud with respect to one another
is designated AESTIVATION. In this respect the leaves are distinguished as FREE
when they do not touch, or VALVATE when merely touching, or IMBRICATED, in
which case some of the leaves are overlapped by others (Fig. 103 £). If, as
frequently occurs in flower -buds, the margins of the floral leaves successively
overlap each other in one direction, the aestivation is said to be CONTORTED.

(/3) The Axis of the Shoot. A. External Construction. — The

active elongation of the stem begins at some distance from the grow-
ing point ; with this the leaves in the bud begin to separate. It is
characteristic of shoots, especially aerial shoots, that this elongation is
not limited to a short region below the bud but extends many centi-

* [The use of these terms in the following paragraph differs from that customary in
England. By VERNATION is understood the arrangement of the leaves in a vegetative
bud as a whole. The folding of each individual leaf in the bud is termed PTTXIS. The
term AESTIVATION is applied to the arrangement of the parts in a flower-bud.— TRANS.]

BOTANY

PART I

metres (to more than 50 cm.) from this. It is not of course so active
in the successively distant zones. The elongation may, on the other

hand, be so slight that the mature
leaves of the shoot adjoin one
another without leaving any free
surface of stem between them.
As a rule, however, its amount and
distribution is such that the inser-
tions of the leaves become separated
by bare regions of stem (Fig. 1 1 5).
These are known as INTERNODES,
while the transverse zones of the
stem where the leaves are inserted
are the NODES. The growth in
length is much less in the nodes

internodes. In the
often limited to a

FIG. 103.— Transverse section of a bud of Populus than in the

nigra. fc, Bud -scales showing imbricated latter it is
aestivation [vernation] ; I, foliage leaves ,.

with involute J vernation [ptyxi*] ; ., each leaf naiTOW ZOne, for example at the

has two stipules, (x 15. After STRASBURGER.) base of the internode in the

Grasses. There are then a number

of zones of intercalary growth in the stem separated by fully -grown
regions. The nodes may be swollen (cf. Labiatae).

In the aerial shoots the internodes are usually thin, while they are frequently
very thick in subterranean shoots.

The length of successive internodes of an axis exhibits a certain regularity.
Usually it increases on ascending a main axis and then diminishes.

Leaf Arrangement (5G). — The distribution or arrangement of the
leaves is very characteristic of shoots, and exhibits great variety.
One or a number of leaves may be borne at each node. When there
are several leaves they form a WHORL and are termed the members of
the whorl, while the leaf arrangement is spoken of as VERTICILLATE.
When there is only one leaf at each node the arrangement is
ALTERNATE. A very remarkable and peculiar regularity is exhibited
by the arrangement of leaves on all sides of erect shoots ; it is often
at once evident when the growing point is looked at from above
(Figs. 99, 104). The youngest leaf-rudiments adjoin the older ones
in such a way as to best utilise the available space. The relations of
position are best shown when they are plotted diagrammatically on a
ground-plan. The position of the leaves is represented in the diagram,
which is of a plane at right angles to the axis of the stem, as if the
latter were conical and viewed from the tip; it is thus possible to
indicate a higher position on the stem by a more internal position in
the plan. Such ground-plans of leaf arrangements are called DIAGRAMS
(Fig. 105). The centre corresponds to the apex of the stem; the
leaves nearest to this are the youngest or uppermost, and those

DIV. I

MORPHOLOGY

farther out are successively older and lower. It is convenient to
indicate each node by a circle ; when there are several leaves at the
same node they are represented on the same circle. Such diagrams
agree with the figures of transverse sections of a bud in the neighbour-
hood of the apex of the stem (Figs. 99, 104).

It thus appears that EVEN AT THEIR APPEARANCE THE LEAVES ON

AN ERECT RADIAL SHOOT ARE DISPOSED AS REGULARLY AS POSSIBLE
AROUND THE STEM. THIS ENSURES THAT THE EXPANDED LEAVES DO
NOT SHADE ONE ANOTHER BUT MAKE THE FULLEST POSSIBLE USE OF

THE LIGHT. The distribution is so regular that the angle between
two successive leaves (e.g. in Fig. 105, leaves 1 and 2, 2 and 3,
etc.) is constant ; this is termed the ANGLE OF DIVERGENCE, or, when

FIG. 104. — Transverse section of a leaf- bud
of Tsuga canadensis, just below the
apex of the shoot, showing a ^ diverg-
ence, (x circa 20. After HOFMEISTER.)

FIG. 105. — Diagram showing \ position of
leaves. The leaves numbered according
to their genetic sequence. (After STRAS-

BURGER.)

expressed as a fraction of the circumference, the DIVERGENCE.
different in different kinds of plants.

It is

In the case of verticillately-arranged leaves the angle of divergence of a whorl
(Fig. 106) is the circumference divided by the number of leaves, which is usually
the same in each whorl. The members of successive whorls do not stand
immediately above one another but alternate, so that the members of one whorl
come above the intervals between those of the whorl below (Fig. 99, 106). The
result of this arrangement, combined with the equality of the angle of divergence
in each whorl, is that the leaves of such a shoot are arranged in twice as many
vertical rows as there are members in each whorl (Fig. 106). These longitudinal
or vertical ranks are termed ORTHOSTICHIES. A frequent case of verticillate
arrangement is that of whorls of two members (Figs. 99, 106). In this arrange-
ment, which is termed DECUSSATE, the angle of divergence is 180° ; the divergence
is thus ^, and there are four orthostichies. If there are three members in a
whorl the angle of divergence is 120°, the divergence ^, and there are six
orthostichies.

BOTANY

PART I

When the arrangement of the leaves is alternate the divergence may be \ (Fig.
107), i (Fig. 144), | (Fig. 105), T5T (Fig. 104), etc. Here also, owing to the
uniformity of the angle of divergence, the leaves will stand in orthostichies on the
stem. With a divergence of \ leaf 4 will stand vertically over leaf 1 (5 over 2,

6 over 3, 7 over 1, etc.) ; with a f divergence (Fig. 105) leaf 6 comes over leaf 1,

7 over 2, 8 over 3, etc. If one imagines the insertions of successive leaves connected
by the shortest line passing round the circumference of the stem, this line will be
a spiral. The alternate arrangement of leaves is therefore also spoken of as
SPIRAL ARRANGEMENT. The segment of this genetic spiral passing from leaf to
leaf till one vertically over the starting point is reached is called a CYCLE of the
spiral (e.g. in Fig. 105 from 1-6 or 3-8). In the case of i divergence the cycle
consists of three leaves and passes once round the stem. In | divergence (Fig.
105) the cycle consists of five leaves and passes twice round the stem. In the

fraction expressing a divergence the
numerator shows how often the cycle
passes round the stem, and the denomi-
nator how many leaves the cycle in-
cludes. The latter also indicates how
many orthostichies there are and which
leaf will next be found in the same
orthostichy. For example, in a T5-j

FIG. 106.— Diagram of the decussate arrange-
ment of leaves. The dotted lines are the
orthostichies. (Modified after STRAS-

BURQER.)

FIG. 107.— Diagram of two-ranked arrange-
ment of leaves. The dotted lines are
the orthostichies. (Modified after
STRASBURGER.)

divergence the stem will be passed round five times before the next superposed leaf
is met with, there are 13 orthostichies, leaf 16 stands over leaf 3 (3 + 13), and over
leaf 8, leaf 21 (8 + 13). Since the denominator always indicates the number of ortho-
stichies, the ^ divergence is also spoken of as two-ranked, the ^ divergence as three-
ranked, etc. When the leaves on a stem are crowded and in contact another series
of ascending spirals becomes more prominent ; these are the PARASTICHIES. They
come about by the contact of those leaves the lateral distance between which on the
axis is the least. The parastichies appear very clearly on pine-cones from which
Fig. 108 is prepared as a somewhat diagrammatic view from the base. In this view
the parastichies appear as spiral lines. Several systems of parastichies running in
the same direction are clearly apparent. One of these (indicated by the unbroken
lines I-VIII) goes in the direction of the hands of a clock ; two cross this system,
one being a flat and the other a steep spiral, and these are marked by the two types
of dotted lines. Two systems of equivalent parastichies that cross, can be used to
determine the divergence (cf. Fig. 108). Denoting any particular leaf by 1, the
number of the next leaf in the parastichy is obtained by adding to 1 the number
of the oblique ranks of that system which pass round the stem. There are 8

DIV.

MORPHOLOGY

parastichies indicated by unbroken lines, so that the next leaf in this parastichy
is 1 + 8 = 9 and the next to this 9 + 8 = 17, etc. Taking the opposite system of
spirals there are 5 marked by broken lines (13 marked by dotted lines), and thus
the leaves in the system with broken lines are 1 + 5 = 6, 6 + 5 = 11, and so on. In
the dotted parastichies, on the other hand, they are 1 + 13 = 14, 14 + 13 = 27, etc.
This regularity depends on the fact that in every system of parastichies there must
be as many leaves between the successive leaves of one parastichy as the remainder
of the parastichies of that system. (This, in the system indicated by unbroken
lines in Fig. 108. is 7, and seven leaves intervene between 1 and the next leaf of
the parastich}-. This leaf must follow on 1 + 7 and therefore be number 9.) If
all the leaves are numbered in this way the successive numbers 1, 2, 3, 4, etc., give
the genetic spiral and the
divergence. The pine-cone in
Fig. 108 has the leaf arrange-
ment -/i, and in accmxlance
with this the leaves 1, 22,
43 come above one another —
i.e. in the same orthostichy.
When the divergences are
determined in diverse plants
with alternately - arranged
leaves it is found that certain
divergences are particularly
common. The series ^, £, -|,
I, T\, -nr, H, etc., can thus be
arrived at. These fractions
have an evident connection
with one another ; the numer-
ator and denominator of each
are the sums of the numer-
ators and denominators re-
spectively of the two preceding

fractions. The divergences Fl0' 108.-Semi-diagrammatic view of a pine-cone seen from

c , , . . below. Divergence of scales /T ; I-VIII, system of para-

this series all he between £ sticMes running in the direction of the hands of a watch .

and | of the circumference of 1-5, system of parastichies running in the opposite direc-
the stem. They deviate the tion. For further description see the text,
less from one another as the

start of the series is departed from and approach more and more an angle of
1-37° 30' 28". This scries is termed the main series of leaf arrangements. There
are also other similar series, but the main series is characterised by the fact that
by its divergences the most uniform spacing of the leaves on an axis is attained
with the smallest number of leaves. The discoverers of this series -were CARL
SCHIMPER and ALEXANDER BEAUX.

Erect radial shoots with elongated intemodes or with broad leaves have usually
few orthostichies, while those with short internodes and narrow leaves have many.
In the latter case the divergences belong to the higher members of the series.

Changes in the original position of the leaves may be caused by torsions of the
axis. Thus the leaves at the growing point in species of Pandanus are laid down
in three vertical series, but subsequently come to be arranged by the torsion of the
stem in three spiral lines. In this way the leaves can better utilise the light.

The arrangement of the leaves on inclined dorsiventral stems is relatively
simple. A divergence of % or a similar arrangement is the most common ; by this

•—-4

92 BOTANY PART i

the leaf surfaces can be placed horizontally and obtain favourable illumination.
This is frequently attained by twisting of the internodes, which thus transforms
a decussate into a two-rowed arrangement on inclined shoots. Similar changes
occur in the case of alternately- arranged .leaves in relation to the best utilisation
of the light by the leaf surfaces. The position of the foliage leaves is nearly
always an adaptation to the needs of the plant as regards light. In some
horizontal subterranean shoots (e.g. of Ferns) the leaves stand in one row on the
upper side.

Practically nothing is known of the causes of the regularity in the arrangement
of leaves. The assumption of SCHWENDENER that purely mechanical causes
acting at the places of origin of the leaves determined the arrangement of the

latter has proved to be unfounded (57).
The leaves need not arise at the apex in
the order of their genetic spiral, nor
simultaneously as members of a whorl.
Sometimes one side of a growing point
may even predominate in the production
of leaf-rudiments.

B. Primary Internal Struc-
ture of the Stem (58). — The stem
exhibits a much more advanced
differentiation of tissues than the
long shoots of even the most
highly segmented thalli. On the
outside a typical EPIDERMIS forms
its boundary layer. Beneath this
in the internodes (the nodes have

PIG. 109.— Transverse section of an internode of a more Complicated structure to

the stem of Zea Mais, pr, Primary cortex ; pc, foe Considered later) COmCS a ZOUC
pericycle ; cv, vascular bundles ; ere. funda- ,. . ,. r i -> -i i

mental tissue of the central cylinder, (x 2. of tissue free from Vascular bundles

After SCHENCK.) and called the CORTEX. This sur-

rounds the CENTRAL CYLINDER

(Fig. 109), as the remaining tissue of the stem including the vascular
bundles is called.

It is practically desirable to maintain the conception of a central cylinder even
though in some Monocotyledons the cortex cannot be clearly distinguished from
the central cylinder and the vascular bundles occur close below the epidermis.

Cortex. — The cortex is mainly composed of parenchyma. In
green aerial shoots the peripheral layers contain chlorophyll, while
those farther in are colourless and serve for storage rather than
assimilation. In colourless subterranean stems, which often attain a
greater thickness, it is composed of colourless parenchyma which, like
the parenchyma of other regions of the rhizome, contains reserve
materials. Mechanical tissue is also developed in the cortex. The
stem in aerial shoots sustains the weight of the leaves and is exposed
to bending by the wind ; it must be sufficiently rigid against bending
in all directions. This is attained by the aid of mechanical tissue as

DIV. I

MORPHOLOGY

layers or strands of collenchyma or sclerenchyma ; this is placed as
near to the periphery as possible, sometimes lying just below the
epidermis of projecting ridges (Fig. Ill, 1, 2).

RIGIDITY AGAINST BENDING while the least possible mechanical material is
employed is best attained by placing this in a peripheral position. "When a
straight rod (Fig. 110) is bent the convex side elongates and the concave side
is shortened. The outer edges, a, a and a', a', are thus exposed to the greatest
variations in length, while nearer the centre (i, i ; i'y i'} the deflection and consequent
variations in length are less. If instead of the uniform rod the mechanically
effective material were disposed as economically as possible, it should be brought
close to the periphery. In this position it will oppose the greatest resistance to
bending, and if bending takes place will be less easily torn or crushed than less
resistant material. E^ery one knows how great is the resistance to bending of an
iron tube, even with thin walls. The builder attains a high level of resistance to

i i

FIG. 110.— 1. Longitudinal section of an elastic cylinder, before bending (dotted outline) and after
bending (heavy outline). After bending the convex side (a') is stretched and the concave side
(a) compressed. /, Connecting tissue.

2. When the connecting tissue (/) is not sufficiently firm, the bands of stereome (a, a') curve
independently and remain unaltered in length. (After NOLL.)

bending by placing at the periphery of structures bars of mechanically effective
material parallel to one another and to the longitudinal axis of the structure.
These are called girders. It is essential that these GIRDERS should be connected
and kept at their proper distances from one another by a sufficiently rigid but
elastic connecting tissue (Fig. Ill, 1). Each rod or girder then forms with the one
lying immediately opposite an I-girder, the material which occupies the line
between the two rods being the connecting material (Fig. 110). Were this
connection wanting each rod would be readily bent. In hollow structures,
however, it is sufficient that the girders should be joined laterally. In large
buildings the peripherally-placed bars have themselves the construction of I-
girders, each being constructed of two connected bars.

As SCHWENDENER (u) first showed, the mechanical tissues which render a
stem rigid against bending are arranged so as to make the best use of the material.
In many plants the mechanical tissue forms a peripheral hollow cylinder which
may either come next the epidermis or be more deeply situated (Fig. 112 pc) ; in
others there is a system of similarly-placed strands of mechanical tissue lying
side by side (system of simple girders, Fig. Ill, 1) ; the latter arrangement may be
combined with the complete hollow cylinder (Fig. Ill, 2). In other cases each of

94 BOTANY PART I

the peripheral strands has itself the form of an I-girder (Fig. Ill, 3) ; only the outer
bars of this consist of mechanical tissue, the connection being usually made by a
vascular bundle (system of compound I-girders). These arrangements are on the
whole better shown in the stems of Monocotyledons than in the primary structure
of the stems of Dicotyledons and Gymnosperms. In the latter the rigidity can be
increased by the secondary thickening. In stems which are green and carry on
assimilation the mechanical tissue is somewhat removed from the epidermis, being
separated from the surface by the green tissue for the functions of which light is
necessary ; in other cases the mechanical and assimilatory tissues share between
them the peripheral position (Fig. Ill, 2).

The innermost layer of cells of the cortex in the mature subaerial
stems of land plants is not usually specially characterised. There is

FIG. 111. — Rigidity against bending. 1. Transverse section of a young twig of Sambucus ; c, collen-
chyma. 2. Part of the transverse section of a haulm of grass (Molinia coerulea); Sc, ribs of
sclerenchyma ; Sc R, sclerenchymatous ring connecting them laterally ; A, green assimilatory
tissue ; MH, pith-cavity. 3. Diagram of double girder on a larger scale, g, g, Girders ;
/, connecting tissue represented by the vascular bundle. (1 and 2 after NOLL.)

then no sharp limit between cortex and central cylinder. This layer
may, however, be developed as a starch sheath, as a typical
endodermis (especially in the subterranean shbots of land plants and
in the stems of aquatic plants), or as a cutis. If developed as a
STARCH SHEATH (s/, Fig. 112 A, B) its cells contain large, easily-
movable starch grains.

The starch sheath is often present in the young shoots only and disappears or
remains limited to certain spots in the older condition. In place of a common
starch sheath or endodermis such sheaths may be found around the separate
bundles (Fig. 119 pp), or there may be single rows of cells containing easily-
movable starch.

Central Cylinder. — This is composed of various tissues. The
parenchyma, in accordance with its deep-seated position, is almost
or quite colourless, and serves mainly for conduction or storage.
Sclerenchyma frequently is present. The most important parts of
the central cylinder are, however, the VASCULAR BUNDLES which serve
for the carriage of water with the necessary salts from the roots to

DIV. I

MORPHOLOGY

the leaves, and on the other hand conduct organic substances from the
leaves to the root system. The bundles are embedded in the other
tissues of the central cylinder and contrast with these owing to the
narrowness of their elements and the absence of intercellular spaces.
When the central cjlinder and cortex are sharply delimited by a
sheath the vascular bundles do not as a rule abut on this, but are
separated by a zone one or more layers thick (Fig. 112 A, B, pc)
which is called the PERICYCLE.

The vascular bundles have a definite course and consequently a
special arrangement as seen in a transverse section of the stem. In
transverse sections of the internodes they appear arranged in a circle

. 112.— A, Part of transverse section of a young stem of -Aristolochia Sipho. e, Epidermis ; pr,
primary cortex ; st, starch sheath ; c, central cylinder ; pc, pericycle, in this case with a ring of
sclerenchyma fibres ; ci/, phloem, and cv", xylem portions of the vascular bundle ; cb, cambium
ring; m, medulla ; mis, primary medullary ray. (x 48.) B, Small portion of the periphery
of a similar section of a still younger, stem, e, Epidermis ; pr, primary cortex ; st, starch
sheath with easily-movable starch grains ; pc, outer layers of the pericycle. ( x 350. After
STKASBURGER.)

in the Horsetails (Equisetum) and most Gymnosperms and Dicotyledons
(Fig. 111/1). In most Ferns and in Monocotyledons (Fig. 109), on
the other hand, they are irregularly scattered. If the bundles form
a single circle (Fig. 112 A) the tissue within this, composed of
parenchymatous cells which are alive or may die at an early period, is
distinguished as the PITH (m). The tissue between the bundles forms
the MEDULLARY RAYS (ms). This distinction is wanting when the
bundles are scattered (Fig. 109).

There are also Dicotyledons in which the vascular bundles form two (Cucurbita.
Phijtolacca, Piper] or more circles (Amarantus, Papaver, Thalidrum). The more
internal circles are usually less regular.

The medullary rays may consist of parenchyma, but in a number of herbs their

96 BOTANY PART i

inner portion, between the xylera of adjacent bundles, is formed of sclerenchyma.
This contrasts with the outer parenchymatous portions situated in the region of

the phloem.

Subterranean shoots and submerged plants which have to withstand pulling
forces have their mechanical tissue more or less centrally placed ; it may be in
the pith.

Course of the Vascular Bundles. — In accordance with their
functions the vascular bundles form continuous strands which in macer-
ated preparations may be followed from the root-tips to the extremity
of the leaves. This can be done by letting herbaceous plants lie in
water until all the tissues except the more resistant vascular bundles
have decayed and disappeared.

The bundle of the root is traced to the base of the shoot, where it
is continuous with the more complicated system of vascular bundles
(cf. p. 137). The bundles in the stem may be traceable to the apex
without passing into the leaves. Such bundles are termed CAULINE,
and contrast with purely FOLIAR bundles which immediately on
entering from a leaf unite with cauline bundles.

Thus in the Pteridophyta there may be a network of cauline bundles or a
single central bundle (Lycopodium, etc.) with which the foliar bundles unite on
entering from a leaf-base.

As a rule, however, the bundles of the shoot bend outwards into
leaves and are COMMON bundles, the upper portion of which belongs
to a leaf and the lower portion to the stem. One or several such
bundles pass into a leaf and form collectively what is known as the
leaf-trace. The vascular system of the stem in the seed plants consists
as a rule entirely of these leaf-traces or common bundles.

The stems of some Dicotyledons (Begonia, Aralict) possess cauline bundles in
the pith enclosed by the circle of common bundles. At the nodes these cauline
bundles, which may be arranged in a ring concentric with the common bundles,
are connected with the latter.

The leaf-trace bundles may remain separate from one another in
the stem, but usually each descending bundle of the trace ends by
joining another bundle that has entered from a lower leaf. A
splitting or forking of the bundle may precede this junction. Such a
reticulate arrangement of the bundles ensures a uniform distribution
of the water supply, since each bundle of the stem as a consequence of
its subdivision provides water to a larger region of the shoot. The
general course of the bundles differs in different species according to
the length of the free course of the single bundles of the trace, the
course they follow, and the subdivision they undergo. The arrange-
ment of the leaves naturally determines the places of entry of the
leaf-traces into the stem. Their course in the stem is, however, quite
independent of the leaf arrangement, and can be very different for one
and the same type of this.

DIV. I

MORPHOLOGY

In the Horsetails, the Coniferae, and the Dicotyledons, all the leaf -trace
strands penetrate equally deeply into the stem to pass down this as parts of the
characteristic ring of bundles evident in transverse sections. The course of the
bundles in the internode can thus be indicated on the surface of a cylinder or
represented as if this surface were flattened in one plane. Complications occur
at the nodes by the leaf -trace strands being joined by transversely-placed
cauline strands ; cross connec-
tions of later development often
occur in the internodes also.

A relatively simple example
of the arrangement of vascular
bundles is afforded }jy the young
shoots of Juniperus nana (Fig.
113), the leaves on which are in
whorls of three. Krom each
leaf a leaf-trace consisting of
a single vascular bundle enters
the stem. This divides into

FIG. 113.— Diagram of the course
of the vascular bundles in a
young branch of Jit n iperus nana
shown on the unrolled surface
of the cylinder. At k, k the
vascular bundles passing to the
axillary shoots are seen. (After
GEVLER.)

FIG. 114. — Diagrammatic representation of the course of the
vascular bundles in a young twig of Taxus baccata. The
tube of bundles is slit up at 1, and spread out in one
plane.

two about the middle of the internode below, and the portions diverge right and
left to unite with the adjacent leaf -traces. The arrangement of the bundles in
a young twig of Taxus baccata as shown in Fig. 114 is less simple, though in this
case also the leaf-trace consists of only one bundle. Each leaf-trace can be
followed down through twelve internodes before it joins on to another bundle.
It first runs straight clown for four intemodes and then bends aside to give
place to an entering trace, with •which it later unites. In Taxus the leaf
insertions, and consequently the places of entry of leaf-traces, have a divergence
of -fg. An example of leaf-traces composed of three bundles is afforded by
young branches of Clematis viticella, the arrangement of the leaves on which is
decussate. The median strands of the leaf-traces (a and d, g and k, n and q,
t and x in Fig. 115) run down through one internode, dividing at the next
done into two arms which fuse with the adjacent lateral strands of the leaves?

BOTANY

PART I

inserted at this node. The two lateral strands of each leaf-trace (Fig. 115 b, c ;
e,f'} h, i; l,m; o,p; r, s] are also free through the internode, but at the node below
they curve inwards and become attached to the same lateral strands as the arms

of the median bundle of the trace.

The course of the bundles in the
Monocotyledons follows a wholly
different type (Fig. 116). The indi-
vidual bundles of the leaf-trace pene-
trate to different depths in the stem
and thus appear scattered on the cross-
section. This results from the prolonged
growth in thickness of the growing
point after the procambial strand of

ale

FIG. 115. — Clematis viticella. End of a branch
which has been made transparent by the re-
moval of the superficial tissues and treatment
with caustic potash. The emerging strands
have been slightly displaced by gentle pressure.
The two uppermost pairs of young leaves (bl 1,
bl 2) are still without leaf- traces, v, Apical cone.
(After NAGELI.)

FIG. 116. —Diagrammatic representation
of the course of the bundles in the Palm
type. Two-ranked leaves encircling the
seem are shown cut in their median
planes. The leaves (Aa, Bb, Cc) are
cut across close to the base ; the capital
letters indicate the median portion of
each. The stem is seen above in trans-
verse section. (After ROTHERT, adapted
from ROSTAFINSKI.)

the first and median bundle of the leaf is laid down. As a result of this
the successively-formed procambial strands of the later bundles are placed less
deeply. This arrangement is especially well marked in the Palms (palm type), in
which each leaf-trace consists of the numerous bundles which pass into the stem
from the leaf -base which completely encircles the stem. The median bundle
penetrates to the centre of the stem, the lateral bundles, as the median line of the

DIV. I

MORPHOLOGY

leaf is departed from, less and less deeply. In the longitudinal section of a stem
in Fig. 116 only the median bundle for each leaf (A, B, 0) and one lateral bundle
(a, b, c) are represented. In their further downward course the bundles gradually
approach the periphery of the stem, where they fuse with others. The number of
internodes whicli each bundle traverses varies, being greatest for the median
bundle.

Structure of the Vascular Bundles (59). — The bundles in the
stem are strands of tissue of circular or elliptical outline in cross-
section and always consist of xylem and phloem, i.e. are complete
bundles (cf. p. 67). The sieve-tubes are the most important com-
ponent of the phloem portion
and the water -conducting
vessels of the xylem portion
of the bundle. The bundles
are variously constructed in
different cormophytes, all
the types being represented xp-
in the stem (radial, concen-
tric, and collateral bundles).
These types are distin-
guished from one another
by the arrangement of the
strands of xylem and
phloem.

In RADIAL vascular
bundles (Fig. 117; cf . also
Figs. 161, 163) there are
a number of strands of xylem

, . , * FIG. 117. — Radial vascular bundle from the stem of

and phloem Which, as seen Lycopodium Hippuris. p.Pbloem; pp, primary phloem;
in a crOSS-Section of the *, xylem ; xp, protoxylem. (x 30.)

circular bundle, stand side

by side, alternating with one another. Seen from the side the vascular
strands run parallel to one another and to the longitudinal axis of the
part of the plant. The strands of xylem may meet in the centre of
the bundle and so constitute a star-shaped mass as seen in transverse
section. The ends of the rays are made up of the narrowest tracheides
(protoxylem), while the vessels towards the centre are always wider
(Fig. 117). The strands of phloem are situated in the depressions
between the rays, the narrow protophloem elements being at the
periphery. Radial bundles, though characteristic of roots, occur
relatively seldom in stems and are always solitary, as for example in
the stems of Lycopodium.

In CONCENTRIC bundles a central strand of xylem or phloem is
surrounded on all sides by a cylinder of phloem or xylem. The
bundle may be distinguished as concentric with internal xylem when
the xylem is centrally placed, and as concentric with outer xylem

100

BOTANY

PART I

when this tissue is peripheral. The bundles in most Pteridophytes
(Fig. 119) are of the former type, those in the rhizomes or stems of
some Monocotyledons (Fig. 118) of the latter.

In the Pteridophytes the narrow elements of the protoxylem (sp) lie in groups
in the strand of xylem, peripherally, centrally, or among the later-formed vessels.
The xylem is surrounded by a sheath of parenchyma (Ip). Outside this comes a
zone composed of sieve-tubes (o) and parenchyma (s), the narrow protophloem
elements being situated at the outer edge of this.

In COLLATERAL vascular bundles (Fig. 120 A), which consist of a
strand of xylem and as a rule a single strand of phloem, the xylem
lies beside or rather behind the phloem. The median plane of the

bundle is always placed radially
in the stem, the xylem being
directed inwards and the phloem
outwards. The protoxylem in
collateral bundles is usually
placed at the inner edge of the
strand of xylem, the proto-
phloem at the outer edge of
the phloem, as the bundle is
seen in transverse section. Such
collateral bundles are character-
istic of the shoots of the Sper-
maphyta and the Horsetails.
BICOLLATERAL bundles, in
which the xylem is accompanied
by a strand of phloem on the

FIG. 118.— Concentric vascular bundle with external inside as Well as On the OUtside,
xylem from the rhizome of Convallaria vwjalis. a|so occurs as for example in
ph. Phloem ; x, t, xylem ; s, protoxylem. (After , , ~ , . _

ROTHERT.) the stems of Cucurbitaceae. In

Monocotyledons the collateral

bundles, like the radial and concentric vascular bundles, are closed,
i.e. the whole bundle consists of permanent tissue, the xylem abutting
directly on the phloem (Fig. 120 A). In Gymnosperms and
Dicotyledons, on the other hand, the bundles are usually open, i.e.
the xylem and phloem remain separated by a layer of meristematic
tissue called the CAMBIUM (Fig. 121).

In all vascular bundles the strands of xylem are mainly composed
of narrower or wider lignified elements that serve for the conduction
of water. These may be tracheides and tracheae, or only tracheides.
They occur singly or in groups without intercellular spaces among
narrow, living, elongated and often unlignified cells of the conducting
parenchyma (xylem parenchyma), or are surrounded by a sheath of
this tissue (Fig. 119 Ip). Sclerenchymatous fibres are sometimes
present in addition. In the Pteridophyta only tracheides are present,
while in the bundles of Phanerogams both tracheae and tracheides

DIV. I

MORPHOLOGY

usually occur. In all bundles the narrowest vessels are annular or
spiral ; the others are usually reticulated or pitted, but in the Pteri-
dophyta the elements, apart from the protoxylem, are scalariform
(Fig. 70 A).

In the strands of phloem of the vascular bundles (Figs. 119, 120)
the sieve-tubes (v) which serve for the conduction of proteids are
always accompanied by other living cells. These are either the

FIG. 119. — Transverse section of a concentric bundle from the petiole of Pteris aquilina. sc,
scalariform vessels ; sp, protoxylem (spiral tracheides) ; sc*, part of a transverse wall showing
scalaiiform perforations ; Jp, xylem parenchyma ; v, sieve-tubes ; pr, protophloem ; pp, starch
layer ; e, endodermis ; s, phloem parenchyma, (x 240. After STRASBURGER.)

COMPANION CELLS (Fig. 120 s), which are usually shorter than the
elements of the sieve- tubes with which they connect by sieve-pits,
companion cells together with other elongated parenchymatous cells
(phloem parenchyma), or PHLOEM PARENCHYMA only (Fig. 119 s).
When the latter tissue is present the sieve-tubes are embedded in it
singly or in groups without intercellular spaces.

Companion cells only occur in relation to the sieve-tubes of Angiosperms.
They are sister cells to the members of the sieve-tube, cut off by a longitudinal

102

BOTANY

PART I

division, and later undergoing as a rule transverse divisions. They are narrower
than the sieve-tubes themselves, and are further distinguished from them by their
abundant protoplasmic contents. In some cases laticiferous- or mucilage-tubes
occur in the phloem.

The bundle as a whole is often more or less completely surrounded
by a BUNDLE SHEATH. This may have the form of parenchyma
without intercellular spaces, the cells often containing large starch grains

Fio. 120 A.— Transverse section of avascular bundle from the internodeof astemofZeaMais. a, Ring
of an annular tracheide ; sp, spiral tracheide ; m and m', vessels with bordered pits ; v, sieve-
tubes ; s, companion cells ; cpr, compressed protophloem ; I, intercellular passage ; rg, sheath ;
/, cell of fundamental tissue, (x 180. After STRASBURGER.)

(STARCH SHEATH) ; in other cases it is sclerenchymatous, or it consists
of endodermal cells or of cutis tissue. It is not regarded as forming
part of the vascular bundle itself. The sheaths frequently serve to
limit the conduction of material to the vascular bundle. Sclerenchy-
matous sheaths are most common at the outer side of the phloem,
forming semilunar masses (Fig. 120 A, 121 vg\ and are especially
developed in relation to the outermost bundles when these have a
scattered arrangement.

DIV. I

MORPHOLOGY

103

When a sclerenchymatous sheath surrounds a collateral bundle it is frequently
interrupted at the sides, opposite the junction of the xylem and phloem, by
parenchymatous or less thickened and lignified elements. These long strips
facilitate the exchange of water and nutritive substances between the bundle and
the surrounding tissues.

In order to understand the construction of the vascular bundles
and the differences between the various types their ontogenetic
development must be taken into consideration. The primary vascular
bundles are developed from strands of elongated meristematic cells.

ft1

FIG. 120 B.— Longitudinal section of a vascular bundle from the stem of Zea Mais, a and a', Rings
of an annular tracheide ; v, sieve-tubes ; s, companion cells ; cp, protophloem ; I, intercellular
passage ; vg, sheath ; sp, spiral tracheides. ( x ISO. After STRASBUROER.)

In these the differentiation of the tissues proceeds gradually over a
period of time. So long as the portion of the plant is still growing
actively in length the main portion of the strand of meristem remains
undifferentiated. Only at limited regions of the strand, usually at
the outer and inner margins, are a few elements transformed into
permanent tissue. These elements, which are suited to undergo
stretching, are on the one hand annular and spiral tracheides, and on
the other sieve-tubes with or without companion cells. They form
the protoxylem and protophloem respectively. Only when growth
in length is finished do the bundles become fully differentiated, the
differentiation proceeding from the protoxylem and protophloem. In

104

BOTANY

PART I

the xylem there is a succession of annular, spiral, reticulate, and finally
pitted vessels (Fig. 120 B). The first-formed elements of xylem and
phloem have ceased to be functional in the fully-developed vascular
bundle. The protoxylem elements are then frequently compressed
or torn by the stretching (Fig. 120 /, at a, a), and in some cases their
place is taken by a lysigenous intercellular space (Fig. 120 I). The

FIG. 121. — Transverse section of an open collateral vascular bundle from a stolon of Ranunculus
repens. s, Spiral tracheides ; m, vessel with bordered pits ; c, cambium ; v, sieve-tubes ; vg,
sheath. ( x 180. After STKASBURGER.)

walls of the protophloem elements (cp) are swollen and their sieve-
plates closed by callus.

In radial bundles the differentiation proceeds, in accordance with
the position of the first formed elements in the strands of xylem and
phloem, from the periphery towards the centre. In collateral bundles,
on the other hand, the elements are developed in succession from the
protophloem on the outside and the protoxylem on the inside towards

DIV. i MORPHOLOGY 105

the middle of the bundle. If the meristem is completely used up in
this process a closed collateral bundle results ; if some remains between
the xylem and phloem the bundle is an open one. In concentric
bundles the development does not follow a single type, and in
accordance with this the position of the protoxylem and protophloem
is various.

Bundles in which the protoxylem is situated at the inner margin of the xylem
(in collateral bundles) or in the centre, as is often the case in concentric bundles,
are termed endarch. When the protoxylem elements are at the outer margin of
the xylem. as in radial bundles, it is spoken of as exarch. When the protoxylem is
in one or more groups removed both from the inner and outer margin of the xylem
it is mesarch, e.g. in the petiolar bundles of the Cycadeae or in concentric bundles ;
the protoxylem in this*case is embedded among the wider vessels.

It is not at present known what relation holds between the arrangement of
xylem and phloem and the requirements of conduction in the plant, and whether
any one of the three types of bundle, e.g. the collateral, is superior in this
respect («• »).

The phylogeny of the types of bundle is also not clear. All the evidence points
to the assumption that a stem with a single central vascular bundle is relatively
primitive. Such a bundle is found in the stems of a number of living and extinct
Pteridophyta and in all roots. The simplest and phylogenetically oldest type of
vascular bundle appears to be the concentric bundle with a solid central strand of
xylem ; at least this appears to be present in the young plants of nearly all existing
Ferns. The radial bundle also may be a very ancient type, as is suggested by its
constancy in the roots of all living and extinct cormophytes so far as our knowledge
extends and in the stems of some cormophytes. No other type of bundle is found
in both stems and roots. The variety as regards the construction and arrangement
of the bundles, which is met with in the shoots of Pteridophyta as contrasted with
the Spermatophyta, leads to speculations upon the mode of origin of these various
types of construction from stems with a single concentric bundle. There are stems
in which the vascular tissue of the single central bundle has the form of a hollow
cylinder enclosing a central strand of parenchyma or pith (Gleicheniaceae,
Schizaeaceae). In others the hollow cylinder of xylem is lined with an internal
zone of phloem (e.g. Marsilia). Lastly, there are cases in which the hollow
vascular cylinder is perforated by rhombic leaf-gaps at the departure of the leaf-
trace bundles (e.g. Aspidium filix 'mas}. In this last case a cross-section of the
stem shows a number of typically constructed concentric bundles, with solid central
strands of xylem, arranged in a circle. There are also forms in which a cylinder
of xylem immediately surrounding the pith is divided by radial plates of parenchyma
into a number of longitudinally-running strands of xylem placed side by side, the
whole being surrounded by a continuous zone of phloem (e.g. Osmunda). Lastly,
there are cases in which the phloem is correspondingly divided so that the radial
plates of parenchyma separate, as medullary rays, the collateral strands composed
of xylem and phloem (e.g. rhizome of OpMoglossum}. These examples show how
either a reticulate tube of concentric bundles or a hollow tube composed of
collateral bundles can be derived from a centrally-placed concentric bundle. If we
assume that the phylogenetic development has proceeded on these lines, it is
clear that neither one collateral bundle of the Spermatophyta nor one of the
circle of concentric bundles found in many Ferns is homologous with the central
bundle of " primitively constructed " Pteridophyta. The totality of collateral or

106

BOTANY

concentric bundles in such stems would be homologous with the single central
concentric or radial bundle. According to this assumption, which is the essential
of the STKLAR THEORY (60), the single central bundle is termed the stele, and the
circle of collateral or concentric bundles with the enclosed pith would also be
regarded as a stele since it is derived from the primitive stele. A single bundle
may therefore represent the whole stele or a part of the stele. There is usually
only one stele or central cylinder in the stem of the Spermatophyta (monostely).
Cases are, however, met with when the stele is divided (polystely) as in the stems
of Auricula or Gunnera.

(y) The Leaves. 1. Development of the Leaves. — The leaves

Fio. 122.— Acer platanoides. A, External view of a bud, with two young leaves between which the
apical cone of the stem is visible ; sp, the leaf-blade, in which live segments are indicated,
the uppermost one being developed first ; st, the zone, by the growth of which the leaf-stalk
will arise later. B, An older leaf seen from the side ; the young vascular bundles, which will
later determine the venation, are indicated. (7, Fully-grown leaf, with the course of the
vascular bundles indicated diagrammatically. D, A transverse section of the basal portion of
a bud showing three vascular bundles in each leaf. E, A similar section at a higher level ;
the number of vascular bundles has increased by branching. (After DEINEGA, from GOEBEL'S
Organography. A, B, and E slightly magnified.)

have been seen to arise exogenously at the growing point of the stem
as lateral papillae or bulges (Fig. 98, 102/), which to begin with are
unsegmented. These are the LEAF PRIMORDIA (Fig; 125 A, b).
Usually a young leaf occupies only a part of the circumference of the
apex, but it may encircle the latter as an annular ridge. Several

DIV. I

MORPHOLOGY

107

leaves forming a whorl may arise in the same way and only later
appear as distinct structures on the ring-shaped outgrowth. When
whorled leaves arise independently they may either appear simul-
taneously or, as is more
commonly the case, in suc-
cession (58> 59).

In rare cases a leaf may be
terminal on the growing point.

While the shoot bymeans
of its growing point has an
unlimited growth, the growth
of the leaf primordia, which
only continues at their tips
for a short time, is limited.
The tip, which often develops
more rapidly than the rest of

FIG. 123. — Lily of the Valley (ConvaUaria mnjalis). nd,
Scale leaves ; Ib, foliage leaves ; hh, bracts ; b, flower ;
u-s, rhizome; aw, adventitious roots. (Somewhat
reduced. After STRASPURGER.)

G. 1 -24. — Bird Cherry (Prunus
arium). Bud-scales (1-3) and the
transition forms (4-6) to the foliage
leaf (7) ; sp, leaf-blade ; «, leaf-stalk;
nb, stipules. (Reduced slightly.
After SCHENCK.)

the leaf, is first transformed into permanent tissue. This assists in
the protection of the youngest parts of the bud, a function which has
already been seen to be undertaken by the leaves. The further growth
of the leaf is as a rule effected by intercalary growth. Most frequently
the change into permanent tissue proceeds from the tip towards the
base. The growth is thus greatest and most prolonged in the leaf-
base, where it continues until the leaf is fully developed.

108

BOTANY

PART I

The more rapid development of the leaf-tip is most striking in some tropical
plants, especially in climbers. In this case, according to M. RACIBORSKI, these
"fore-runner tips" perform the functions of the leaves before the remainder of the
leaf has attained the mature condition.

Well-marked and long-continued apical growth is found in the leaves of some
Ferns.

Welwitschia mirabilis behaves in a peculiar way unlike all other cormophytes.
Above the cotyledons only a single pair of foliage leaves is formed. The basal
zones of these grow in each annual period while the ends of the leaves are gradually
withering.

2. Different Forms of Leaves. — The leaves of the shoot have very
diverse functions and are correspondingly various in their form on the

same stem, although in their
origin they are alike.

The main axis of the
seedling bears first the COTY-
LEDONS or seed-leaves which
are situated on the hypocotyl
(Fig. 158) of the embryo
while it is yet in the seed.
In the Monocotyledons there
is only one such leaf, while

FIG. 125.— Development of the leaf in the Elm, Ulmus the Dicotyledons and SOme

campestris. A, Showing the vegetative cone, v, with ^ ,

the rudiments of a young leaf, 6, still unsegmented, C*ymilOSpermS have two

and of the next older leaf, exhibiting segmentation cotyledons and SOHie GymilO-

into the laminar rudiment, o and leaf-base g B sperms haye more than two>

Showing the older leaf, vie wed obliquely from behind. * .

(x 58. After STRASBURGER.) Following On the Cotyledons

in the case of subterranean

stems, and often also in those above ground, come a number of SCALE
LEAVES (Fig. 123 nd), then in the case of aerial shoots the FOLIAGE
LEAVES (lb)y and still higher simply formed BRACTEAL LEAVES (Aft).
The foliage leaves may be first considered since the other forms have
arisen by transformation of these.

A. The Foliage Leaves exhibit a great variety of form and
segmentation, and these characters are largely employed in descriptive
botany. They may be simple as in the needles of Coniferae ; in this
case the primordial leaf has only to increase in size and lengthen. As
a rule, however, the foliage leaf is segmented into the flattened, thin,
bright-green LEAF-BLADE (lamina, Fig. 124 sp), which is often
inaccurately spoken of as the leaf ; the stem-like LEAF-STALK (petiole,
Fig. 124 s) ; and frequently also into the STIPULES (nb) attached to
the LEAF-BASE close to the stem or into a LEAF-SHEATH (vagina, Fig.
133 v) more or less completely surrounding the stem above the node.
When the leaf -stalk is wanting the leaf is termed sessile; when
present it is petiolate. The segmentation is recognisable at an early
stage in the primordial leaves, which are differentiated shortly after

DIV. I

MORPHOLOGY

109

their origin into the leaf-base (Fig. 125 A and B, g) and the upper
leaf (Fig. 125 A, B, o). From the leaf-base the stipules (g) arise or it
forms a°leaf-sheath or a thickened pulvinus. Frequently it undergoes
no special further development and is not distinguishable in the
mature leaf. The leaf -blade (Fig. 116 A, sp) is developed from the
upper leaf, and so also when this is present is the leaf-stalk (A, st).
The latter develops relatively late by intercalary growth and is thus
intercalated between the already present leaf-blade and leaf-base ; it
is never inserted directly on the stem.

(a) The Leaf-blade. External Form (Fig. 127). — The leaf -blade,

FIG. 126. — Leaf of Crataegus with reticulate
venation, (f nat. size. After NOLL.)

Fin. 127. — Diagram of a foliage leaf.
.4, Surface view. B, Transverse
section ; s, plane of symmetry.
(After STRASBURGER.)

which is as a rule definitely dorsiventral and of a deeper green colour
on the upper side, may be entire or divided (Fig. 122 C), or composed
of a number of leaflets. Such compound leaves arise by a process
of branching from the margins of the primordia (Fig. 122 A), or
occasionally, as in the Palms, by splitting of the young lamina as it
unfolds. The leaves of Monocotyledons are usually simple, while
compound leaves are common among Dicotyledons.

A leaf-blade is termed PELTATE when the leaf-stalk appears to be inserted
centrally (Fig. 242). The margin of simple leaves (Figs. 123 Ib, 124 sp} may be
ENTIRE or slightly divided, and in the latter case is described as SERRATE, DENTATE,
etc. If more deeply divided the leaf is described as LOBED when the divisions do

110 BOTANY PART i

not extend half-way to the middle of the leaf-blade, when they reach half-way as
CLEFT (Fig. 135 sb), and when still deeper as PARTITE (Fig. 137 I). The lamina
is PALMATE (Fig. 137) or PINNATE (Fig. 136, 1-5), according to whether the
divisions are directed towards the base of the leaf-blade or towards the midrib.
Only when the separate divisions are so independent that they appear as distinct
leaflets borne, on a common petiole or on the original midrib is the leaf spoken of
as COMPOUND (Fig. 136, 1-5) ; in all other cases it is termed SIMPLE.

The leaflets of a compound leaf may be so segmented during their development
as to resemble the main leaf, and in this way a leaf may be doubly or triply com-
pound or more highly segmented. Simply pinnate or bi-pinnate leaves (Fig. 136)
bearing leaflets on the two sides of the rachis of the first or second order are of
frequent occurrence. The leaflets of a compound leaf may be entire or more or less
deeply incised. They may be inserted directly on the rachis or be stalked, and in
some cases, e.g. Phaseolus (Fig. 132 fg], Robinia, Mimosa, be provided with
swollen pulvini at their bases.

In laminae, which become more or less branched during their development, the
lateral divisions usually arise in basipetal order, i.e. proceeding from the tip
towards the base, but the opposite (acropetal) succession or a combination of the
two are also met with. The divisions of palmate and pinnate leaves of the Palms
arise by a relatively late process of splitting within the originally entire, enlarging
lamina. The direction of the dividing lines is determined by the folding of the
young leaf-blade (61).

Sessile leaves usually clasp the stem by a broad base. Where, as in the case
of the Poppy (Papaver somniferum), the leaf-base surrounds the stem, the leaves
are described as AMPLEXICAUL ; if, as in species of Bupleurum, it completely
surrounds the stem, the term PERFOLIATE is used. If the bases of two opposite
leaves are united, as in the Honeysuckle (Lonicera caprifolium), they are
said to be CONNATE. Where the blade of the leaf continues downwards along
the stem, as in the winged stems of the common Mullein ( Verbascum thapsiforme),
the leaves are distinguished as DECURRENT.

The leaf-blade is traversed by green nerves or veins which form
a branched net- work. The thicker ribs project more or less from the
surface on the lower side of the leaf, the upper surface often showing
corresponding grooves. The finer veins become visible when the leaf-
blade is viewed by transmitted light. Frequently the nerve in the
middle line of the lamina is more strongly developed and is then termed
the midrib ; in other cases several equally developed main nerves are
present (Fig. 122). Lateral nerves spring from the one or more main
nerves (Fig. 126).

The course of the nerves determines what is known as the VENATION of the
leaf. The leaves of most Coniferae are UNI-NERVED. In leaves with more
numerous veins, the DICHOTOMOUS VENATION must be distinguished as a special
type which is characteristic of many Ferns and is also found in Ginkgo biloba ;
there is no midrib present in this case. Most other leaves can be distinguished
according to their venation as PARALLEL VEINED or NETTED VEINED. In parallel
venation the veins or nerves run either approximately parallel with each other or
in curves, converging at the base and apex of the leaf (Fig. 133 s) ; in netted
veined leaves (Fig. 126) the veins branch off from one another, and gradually
decrease in size until they form a fine anastomosing network. In leaves with

DIV. I

MORPHOLOGY

111

parallel venation the parallel main nerves are usually united by weaker cross
veins. Netted or reticulately-veined leaves in which the side veins run from
the median main nerve or MIDRIB are further distinguished as PINNATELY VEINED
(Fig. 126), or as PALMATELY VEINED (Fig. 122, 135 sb), when several equally strong
ribs separate at the base of the leaf-blade, and give rise in turn to a network of
weaker veins. Parallel venation is characteristic, in general, of the Mono-
cotyledons ; reticulate venation, of Dicotyledons and of some Ferns.

Internal Structure. — In structure foliage leaves exhibit consider-
able variety but are usually markedly dorsiventral (bifacial), the tissues
towards the upper side being different from those below (Figs. 127,
130).

Many leaves, however, are similarly constructed above and below (equifacial,
centric, Figs. 187, 193). This is the case especially in forms which grow in
relatively dry situations, exposed to strong sunlight, but also occurs in submerged
aquatic plants.

(a) NERVES. — Within the nerves or veins one or more vascular
bundles run. The abundant branching of these bundles to form a
fine network is very characteristic of
the leaf-blade and is shown clearly in
leaf skeletons obtained by macerating
leaves.

The structure of the vascular bundles
in the lamina corresponds on the whole
to that seen in the stem. In Phanero-
gams the bundles are usually collateral,
and since they are continuations of the
leaf-trace bundles from the stem the
xylem is directed towards the upper,
and the phloem towards the lower
surface of the leaf.

The xylem parenchyma of the bundles in
the leaf usually forms flat plates, which in
cross-section appear as radial rows of cells in
the vascular tissues.

As the bundles continue to ramify in the
leaf-blade they become smaller and simpler in
structure. The vessels first disappear, and only FlG 128. _ Termination of a vascular
spirally and reticulately thickened tracheides bundle in a leaf of Impatiens parvi-
remain to provide for the water conduction. flora, (x 240. After SCHENCK.)
The phloem elements undergo a similar reduc-
tion. In Angiosperms, in which the sieve-tubes are accompanied by companion
cells, the sieve-tubes become narrower, whilst the companion cells retain their
original dimensions. Finally, in the cells forming the continuation of the sieve-
tubes, the longitudinal division into sieve-tubes and companion cells does not take
place, and TRANSITION CELLS are formed. With these the phloem terminates,
although the vascular portion of the bundles still continues to be represented
by short spiral tracheides. The ultimate branches of the bundles terminate blindly
(Fig. 128).

112

BOTANY

The bundles are surrounded by parenchymatous sheaths, which
are composed of a number of layers of cells in the thicker nerves but
of a single layer only in the finer branches. The cells of these sheaths
are as a rule elongated and have no intercellular spaces. Strands of
sclerenchymatous fibres are frequently present on one or both faces of
the bundle (Fig. 129, 1), especially on the phloem side. Here, in the
case of the larger bundles, the strand of sclerenchyma is curved ; in
cross-section it occupies the projection of the rib to the under side, and
serves to give rigidity against bending to the lamina. In some leaves
strands of sclerenchyma also occur between the bundles (Fig 129, 1)
and also at the leaf-margin. Such sclerenchymatous or collenchymatous
strengthenings of the margin are protective against shearing forces
that would tend to tear the lamina (Fig. 129, 2). Large leaf-blades

FIG. 129. — Leaf of Phormium tenax. 1. Transverse section ; Sc, plates and strands of sclerenchyma ;
A, green assimilatory parenchyma ; H, hypoderma serving for water-storage ; W, colourless
mesophyll (internal water-storage tissue). 2. Edge of the same leaf; E, thick brown epidermis ;
R, marginal strand of sclerenchyma fibres. (After NOLL.)

which lack such marginal protection are torn by the wind (e.g. the
Banana).

(b) EPIDERMIS AND MESOPHYLL. — The foliage leaf is bounded on
all sides by a typical epidermis. In this, especially on the under side,
there are numerous stomata, while on the upper side they are often
absent (e.g. in almost all deciduous trees).

On the under side there are on the average 100-300 stomata to the square
millimetre, but in some cases more than 700 may occur. Isolateral leaves as a
rule have stomata on both sides and floating leaves only on the upper surface.

The tissue of the leaf-blade between the upper and lower epidermis
in the intervals between the ribs consists mainly of parenchyma and
goes by the name of MESOPHYLL. The finer veins are embedded in
it. Beneath the upper epidermis (Fig. 130 ep) come, as a rule, one
to three layers of cylindrical parenchymatous cells elongated at right
angles to the surface. These are called PALISADE CELLS (Fig. 130 pi),
contain abundant chlorophyll, and have intercellular spaces between
them. They constitute an assimilatory parenchyma. The cells often
converge below in groups (Fig. 130) towards enlarged collecting
cells (s).

In the leaves of many trees, e.g. the Copper Beech, differences in the thickness
of the palisade layer are met with, its depth being much less in the " shade-leaves "

DIV. I

MORPHOLOGY

113

than in the " sun-leaves." According to NORDHAUSEN'S investigations (e2), however,
no direct influence of the illumination exists. There are also plants (e.g. Lactuca
scariola] which only form palisade cells in strongly illuminated leaves.

In some plants layers of cells placed parallel to the surface instead of at right
angles to it are found in the usual situation of the palisade tissue. In the leaves
of the Pine and some other plants the same position is occupied by large, more or
less isodiametric cells the internal surface of which is considerably increased by
foldings of the cell walls.

Below the palisade parenchyma comes what is known as the
SPONGY PARENCHYMA (sp), which extends to the lower epidermis (ep").
The spongy parenchyma consists of irregularly -shaped cells with
wide intercellular spaces and less chlorophyll than in the^ palisade

FIG. 130. — Transverse section of a leaf of Fagus sylvatica. ep, Epidermis of upper surface ; ep",
epidermis of under surface ; ep'", elongated epidermal cell above a vascular bundle ; pi, palisade
parenchyma ; s, collecting cells ; , sp, spongy parenchyma ; A% idioblasts with crystals, in f
with crystal aggregate ; st , stoma. ( x 360. After STRASBURGER.)

tissue. The wide intercellular spaces stand in immediate relation to
the stomata of the lower epidermis and serve for the transport of gases
to the palisade cells.

HABERLANDT has estimated the number of chloroplasts per square millimetre
of a leaf of Ricinus to be 403,200 in the palisade parenchyma and 92,000 in the
spongy parenchyma. Thus in this case 82 per cent of the chloroplasts would belong
to the upper and only 18 per cent to the lower side.

Colourless WATER -STORAGE TISSUE is frequently present in the mesophyll
(Fig. 129 W}. It may be surrounded by the assimilatory tissue or be situated
externally to this below the epidermis. In the latter case the water-storage tissue
usually consists of the more internal cells of a many-layered epidermis.

EPITHEMA and WATER -STOMATA C53). — The mesophyll of the Jeaf- blade in
certain families of Monocotyledons and Dicotyledons forms peculiar structures
between the swollen ends of vascular bundles and the epidermis. They are com-
posed of small living cells with colourless cell sap. the intercellular spaces being
filled with water. These masses of tissue go by the name of EPITHEMA and bring
about the excretion of drops of liquid water. In this process their function is

114 BOTANY PART i

mainly passive, since they represent places where the resistance to nitration is
least. The tracheides terminate in this epithema, and in the overlying epidermis
there is a peculiarly -constructed stomatal apparatus in the form of WATER-
PORES (Fig. 131), which are of larger size than ordinary stomata. The guard
cells usually lose their living contents and the pore then remains permanently
and widely open. The thickened ridges so characteristic of the guard cells of
ordinary stomata are usually lacking. The excreted liquid frequently contains
calcium carbonate, which may remain as a white incrustation over the water-
pores, as, for example, on the leaf margin in many species of Saxifraga.

At the tip of young leaves and of their marginal teeth such water-pores and
epithemata frequently occur, but are dried up on the mature leaf. Water-pores
also are found at the leaf-tips of submerged plants from which ordinary stomata

are absent. They tend to perish
early, breaking down with the ad-
joining tissue to leave open pits by
which water and dissolved substances
may be expressed.

Functions of the Leaf-
blade. — The leaf -blades, as
already mentioned, are the
most important organs of nutri-
tion, i.e. assimilation, and also
of transpiration in cormo-
phytes. Their form and struc-
ture, their arrangement, and
the position they assume with
regard to the direction of the
light, correspond to this. Since

FIG. 131. — Water-pore from the margin of a leaf of ,, , ' ., . r -,

Tropaeolum majus, with surrounding epidermal the decomposition of Carbon

ceils, (x 240. After STRASBUROER.) dioxide is dependent both on

light and on the presence of

chlorophyll, the green colour of the lamina, the large surface exposed
by it, its relative thinness and dorsiventral construction are readily
understood. The large surface enables a greater number of cells con-
taining chlorophyll to be exposed to the light without shading one
another ; it also enables the carbon dioxide to be obtained from the
small proportion in the atmosphere, and at the same time facilitates
the loss of water vapour in transpiration. Since the passage of light
through a few layers of cells filled with chlorophyll renders it
ineffective for decomposing carbon dioxide in the deeper layers, the
assimilatory tissue is placed towards the upper surface of the leaf-
blade. The carbon dioxide is mainly taken into the leaf through the
stomata of the lower surface. It can thus diffuse rapidly through the
wide intercellular spaces of the spongy parenchyma, which is essentially
a ventilating tissue, to the active assimilatory tissue of the upper side.
This will take place more rapidly the thinner the leaf is.

The extensively-branched network of vascular bundles ensures the

DIV. i MORPHOLOGY 115

rapid passage of the products of assimilation from the assimilatory
cells of every part of the leaf to the stem. At the same time it
facilitates the most direct supply of water to all parts of the transpir-
ing leaf-blade ; the leaf-blade serves for giving off water, while the
stem serves for conduction of water. Lastly, the venation increases
the rigidity of the lamina.

It has been seen that the leaves are so arranged on the stem that
the leaf-blades, which on erect shoots have a more or less horizontal
position, are exposed to the light with the least shading by one
another. Many leaves can place their blades at right angles to the
incident light by their power of movement. In the case especially of
dorsiventral, plagiotropous branches the leaf-blades seen from above
are found to fit together
more or less closely
in a LEAF MOSAIC, the
upper surfaces of all
being exposed to the
light.

(b) The Leaf-stalk
usually resembles a
stem, and in its internal

Construction agrees FIG. 1S2.— Imparipinnate leaf of Phaseolus with pulvini. kg, Main
with the midrib of the Pul™™ a* ^se of petiole ; fg, pulvinus of one of the pinnae.
. (i nat. size.)

leaf-blade or sometimes

with the stem. Typical assimilatory tissue is wanting, and the vascular
bundles in the case of Angiosperms are usually arranged in an arc
open above. The leaf-stalk serves to carry the leaf-blade away from
the stem and to place it suitably with respect to the light.

These movements of adjustment of the leaf to the light are sometimes carried
out by special localised swellings at the base or the summit of the leaf-stalk, or
in both situations. These LEAF-CUSHIONS or PULVINI work like hinges and occur
in many Leguminosae (Fig. 132).

Stalked leaves, which are more frequent among Dicotyledons than in Monocoty-
ledons, either have the lamina sharply marked off from the petiole or the one
passes gradually into the other, the petiole appearing more or less winged. When
leaves are arranged in a rosette the stalks of the lower leaves are often so long
that the laminae borne on them are not shaded by the upper leaves. This is
shown very beautifully in the floating rosettes of the Water Nut (Trapa natans).

(e) The Leaf-base (64).— When the leaf-base of a foliage leaf is
specially formed, it usually serves to protect the bud and the younger
leaves, enclosing the bud after the leaf-blade has unfolded.

Stipules are frequently developed from the leaf-base ; they stand
one on either side of the leaf to which they belong, forming a pair.
They may be inconspicuous (Fig. 124 nb) or larger, and yellow or
green in colour. When they serve only to protect the bud they are

116

BOTANY

PAET I

usually yellowish or brown, more simple in their structure than the
leaf-blade, and are soon shed.

The two stipules in such cases are frequently more or less completely united to
form a single structure standing in the axil of the leaf. They may also surround
the stem and form a closed tube which encloses the younger leaves of the bud.
This is the case in the India Rubber plant (Ficus elastica) which is frequently

grown in dwelling-houses ; in this the sheaths
are broken off at their bases and carried up on
the next younger leaf as it unfolds. In the
Polygonaceae they are broken through and

7i / remain as dry sheaths (ochrea, Fig. 617) sur-

rounding the stem.

When the stipules take part in the
assimilation of carbon dioxide they are
green and resemble the leaf-blade in
structure (Fig. 209).

In some species of Galium in which the
stipules completely resemble the leaf- blades,
there is an appearance of whorls of four,
six, or eight leaves ; in reality the arrange-
ment of the two leaves is decussate, each leaf
having one or more pairs of stipules according
to the species. Only the two leaves have buds
in their axils.

The leaf-base may form a sheath ;
this is more commonly the case in
Monocotyledons than in Dicotyledons.
In the Grasses (Fig. 133 v) the sheath
is split along one side, but in the
Cyperaceae it is closed. The sheath of

FIG. 133.— Part of stem and leaf of a grass, the grass leaf, which encloses andsilp-
h, Haulm ; v, leaf-sheath ; fc, swelling p0rts the lower delicate portion of the
of the leaf-sheath above the node; s. , .n • , j ,.

partofieaf-biade; z, iiguie. (Nat. size. stl11 growing uitemode, continues at the
After SCHENCK.) base of the sessile lamina into a mem-

branous outgrowth called the Hgula (/) ;

at its base immediately above the node the sheath is swollen
(Fig. 133 A).

Anisophylly and Heterophylly. — Some plants bear diversely-
formed foliage leaves either in different zones of the stem (HETERO-
PHYLLY, Fig. 135) or in the same zone, but on the two sides of the
shoot which thus becomes dorsiventral (ANISOPHYLLY, Fig. 134).
Asymmetry of the leaves is often associated with anisophylly. Many
water-plants exhibit heterophylly, having ribbon -shaped or liighly-
divided submerged water-leaves adapted to life in water and less
divided stalked aerial leaves (Fig. 135). The leaves which the Ivy

DIV. I

MORPHOLOGY

117

forms on the flowering shoots are essentially different in form from
those which the plant has previously borne. This difference is even
more marked in Eucalyptus globulus, which first bears oval sessile leaves
and then sickle-shaped leaves. Not uncommonly the lowest leaves
of the seedling (juvenile or primary leaves) are more simply formed
than the later leaves. The .

opposite case is illustrated r^ 1 _Jx"Vv.

by Acacia (Fig. 136). 3| <* "^ \

B. The Seed-leaves or ^^

Cotyledons may be stalked

\ / \

FIG. 134.— Selaginella Martensii. Ani-
sophylly of the dorsiventral shoot.
On the upper side of the stem are
two rows of smaller asymmetrical
green leaves and on either flank a
row of larger asymmetrical leaves
(slightly magnified).

FIG. 135. — Ranunculus aquatilis. ub, Submerged leaves ;
sb, floating leaves ; b, flower ; /, fruit. (Reduced.
After SCHEXCK.)

or sessile, and are always more simple in form than the foliage leaves.
They often, however, exhibit the same plan of segmentation.

The cotyledons may remain below the soil enclosed in the seed -coat
(HYPOGEAL). In this case they are usually fleshy structures serving to store
reserve food material and are composed largely of storage parenchyma. EPIGEAL
cotyledons, which burst the seed-coat and appear above ground, tend to become
green and then for a period assimilate carbon dioxide like the foliage leaves. In
Monocotyledons, which have a single cotyledon, only the sheath of this as a rule
emerges from the seed. It may remain below ground and colourless, or grow up
and turn green.

C. The Scale Leaves and Braeteal Leaves, while indistinguishable
from the foliage leaves in the early stages of development, are less

118

BOTANY

PART I

differentiated than these when mature, being usually scale-like and
sessile. They are developed by enlargement of the primordia,
mainly from the leaf -base, while the lamina remains more or less
undeveloped (Fig. 124 1-6, Fig. 137). Scale leaves, either colourless
or green, often occur on the aerial shoots before the foliage

leaves (Fig. 1 2 3 nd). They
are also the only foliar
organs on rhizomes, appear-
ing as hardly visible and
usually short-lived scales,
while in accordance with
the development in dark-
ness foliage leaves are
wanting (Fig. 123 ws, Fig.
138). The bracteal leaves,
on the other hand, re-
semble in construction
the scale leaves on aerial
shoots, but are often vari-
ously coloured and tend to
succeed the foliage leaves
as the subtending leaves
and bracts of the flowers
or inflorescences. The in-
ternal structure of both
scale leaves and bracts is

FIG. 136.-Seedling of Acacia pycnantha. The cotyledons simpler than that of the

have been thrown off. The foliage leaves 1-k are pinnate, ,. ,. r , mi , ,,

the following leaves bipinnate. The petioles of leaves foliage leaves. 1 hey hardly

5 and 6 are vertically expanded ; and in the following take part in the nutritive

leaves, 7, 8, 9, modified as phyllodes, bearing nectaries, nmpp™p<, V,,^ arft ncmallv
n. (About i nat. size. After SCHENCK.) 'CCSSCS, C USUally

protective structures for

the young leaves or the buds. They are, however, connected with
the foliage leaves by intermediate forms (Figs. 124, 137).

That scale leaves and bracts are to be regarded as arrested forms of foliage
leaves is shown not only by the developmental history but by the possibility
of deriving foliage leaves from their rudiments or primordia. Thus GOEBEL
succeeded in causing leaf primordia that would have formed scale leaves to become
foliage leaves by removing the apex and stripping the leaves from the shoots.
Subterranean stems, when forced to develop in the light, form foliage leaves from
the primordia which in the earth would have become scale leaves. In their
internal structure, however, the scale leaves and bracts are not merely arrested
foliage leaves but frequently exhibit special differentiations connected with their
particular functions (65).

3. Duration of Life of Leaves. — In many plants the leaves have
a shorter life than the stems on which they are borne. The leaves in
such plants are shed from the stems (LEAF-FALL) or, in the case of

DIV. I

MORPHOLOGY

110

The leaves and stems
LEAF-SCARS mark the

FIG. IBl.—Helleborusfoetidus. Foliage leaf (I)
and intermediate forms between this and
the bract (A). (Reduced. After SCHENCK.)

subterranean shoots, decay while still attached,
of the aerial shoots of herbs die off together,
places where the fallen leaves were
attached to the stem. Plants in which
the foliage leaves remain active for
several seasons are called EVERGREEN
in contrast to DECIDUOUS forms.

The fall of the leaves in phanerogamic
woody plants is effected by means of a
parenchymatous ABSCISS LAYER which is
formed at the base of the leaf-stalk shortly
before the leaf is shed. In this region all
the mechanical tissu%s of the petiole are
greatly reduced, only the vessels being
lignified. The separation of the leaf results
from the rounding off of the cells of the
absciss layer, the middle lamellae becoming
mucilaginous, while the vessels and sieve-
tubes are broken through. The protection
of the leaf -scar is effected by the cells
exposed by the wound becoming transformed
into a lignified cutis tissue and, later, by

the formation of a layer of cork produced from a cork cambium and continuous
with that covering the stem.

D. The Branching of the Shoot (56> 66). — The more foliage
leaves that can be exposed to the sunlight on a shoot the greater
will be the amount of organic substance formed by assimilation. In

this respect, as will be evi-

c d dent, a branched system of

shoots is greatly superior
to a single erect shoot.
The former can expose leaf-
surfaces to the full sunlight
over a much greater area.

As in thalloid plants
the branching of the shoot
can happen in two ways.
Rarely the shoot forks,

FIG. 138. -Rhizome of rolygonatum vudtiflorum. a, Bud of dividing into two daughter
next year's aerial shoot ; ft, scar of this year's, and c, d, e, G

scars of three preceding years' aerial shoots ; w, roots. ax6S (DICHOTOMY). Usually

(1 nat. size. After SCHENCK.) the branching is LATERAL,

the daughter axes being
thus formed on the main axis which continues its growth.

A. Diehotomous Branching. — This is confined to the shoots of
some Lycopodiaceae.

In such Club-Mosses, when a shoot is about to divide into two equal branches,

120

BOTANY

PART I

the circular outline of the growing point, in which no apical cell is recognisable,
becomes elliptical. In the position of the foci of this ellipse the two new growing
points project (Fig. 139). The successive dichotomies may take place in planes at

right angles to one another, in which case
the branch-system does not lie in one plane
as in the diagram in Fig. 82 a.
xiiMife mm Not uncommonly in plants of this kind

FIG. 139. — Longitudinal section of a bifurcat-
ing shoot (p) of Lycopodium alpinum,
showing equal development of the rudi-
mentary shoots, p', p" ; b, leaf- rudiments ;
c, cortex ; /, vascular strands. ( x 60.
After HEOELMAIER.)

FIG. 140.— Sympo-
dium arising
from successive
dichotomies.

FIG. 141.— Bifurcating shoot
(p) of Lycopodium inun-
datum, showing unequal
development of the rudi-
mentary shoots, p', p" ;
6, leaf-rudiments. ( x 40.
After HEGELMAIER.)

(e.g. in Selaginella] the branch-system deviates from the type described in that
only one of the branches of each fork grows on further and again dichotomises
(Fig. 140). If all the branches that in this way continue the branching are placed
nearly in the same direction to which the other branches stand obliquely, the
branch-system which results may readily be confused with racemose branching
(Fig. 82 &). The main axis is, however, only apparently single, each portion
being a daughter axis of the portion that precedes it. Such an apparent axis
is distinguished as a sympodium from a true main axis (monopodium), and the
branching is sympodial and based on dichotomy.

All transitions from dichotomous to lateral branching are seen in the
Lycopodiaceae. Some species form from the outset two growing points of unequal
size, the smaller being soon displaced laterally in respect to the larger one (Fig. 141).

B. Lateral Branching, (a) Place of Origin of the Lateral
Buds. — On shoots composed of axis and leaves the lateral branches
as a rule occur on the axis or at the extreme base of the leaf. They
are usually developed at the growing point of the parent shoot in
acropetal succession as exogenous outgrowths of the surface in the
same way as the leaf primordia arise (Fig. 98 g). The positions in
which the lateral shoots are developed are usually strictly determined.
In Pteridophyta they frequently arise beside the leaf primordia, but
in Phanerogams, as a 'rule, where the upper side of the papilla forming
the young leaf passes into the tissue of the growing point, i.e. in the
LEAF AXIL. In some cases the branch is more on the leaf-base, in
others it is distinctly on the main stem.

The primordium of a lateral branch may arise from the tissue of the axis close
above the leaf primordium and either after the origin of the latter (Fig. 142 /)

DIV. I

MORPHOLOGY

121

or before the leaf has developed. In the latter case the leaf-rudiment arises from
the tissue to the lower side of the branch primordium (Fig. 142 I1JT). On the

// 111

FIG. 142. — Diagrams of the developmental relations between the leaf primordium and the axillary
shoot. (After GOEBEL.)

other hand, the branch may be formed from the young leaf primordium (Fig.
142 II}. Lastly, in dorsiventral shoots extra-axillary shoots may arise laterally
from the leaf primordia.

In the longitudinal section of a growing point in Fig. 98 the
youngest rudiment of a lateral shoot (g) is already visible, projecting
in the axil of the uppermost leaf. In the axils of the following leaves
the branch primordia, since they arose in acropetal succession, are
larger and have begun to form their leaves. The shoots developed
from such AXILLARY BUDS are termed AXILLARY SHOOTS; the bud
which terminates the growing end of the main
shoot is termed, in contrast to the axillary
buds, a TERMINAL BUD. The leaf, in the axil
of which a bud stands, is its SUBTENDING LEAF
(Fig. 144 db). The plane passing through the
midrib of this leaf and the parent axis is the
MEDIAN PLANE of the leaf. Usually the axillary
bud is situated in the median plane of its sub-
tending leaf, but it may be displaced laterally.
It is the rule in Angiosperms that each foliage
leaf has a single axillary bud ; in some Gymno-
sperms, on the other hand, there is not an
axillary bud to every leaf.

As a rule, only one shoot develops in the axil of
a leaf, yet there are instances where it is followed by FIG. 143.— Samolus valerandi,
additional or ACCESSORY SHOOTS, which either stand over each axillary shoot (a) bear-
one another (serial buds), as in Lonicera, Gleditschia, ins its subtending leaf (0,
Gymnocladus, or side by side (collateral buds), as in many
Liliaceae, e.g. species of Allium and Muscari. A
displacement from the position originally occupied by the members of a shoot
frequently results from intercalary growth. A bud may thus, for example,
become pushed out of the axil of its subtending leaf, and thus apparently have
its origin higher on the stem ; or a subtending leaf in the course of its growth may
carry its axillary bud along with it, so that the shoot which afterwards develops

122

BOTANY

PART I

seems to spring directly from its subtending leaf ; or, finally, the subtending leaf
may become attached to its axillary shoot, and, growing out with it, may thus
appear to spring from it (Fig. 143).

It is the rule in Phanerogams that normal shoots arise from the embryonic
tissue of the growing point of the parent shoot. When they are apparent at a
greater distance from the apex it can usually be shown that embryonic substance
has been reserved at the proper points for their formation.

Shoots developing in predetermined positions on young parts
of the plant are designated NORMAL, in contrast to ADVENTITIOUS
SHOOTS, which are produced irregularly from the old or young portions
of a plant, such as stems, roots, or leaves, and usually arise from
permanent tissue which returns to the meristematic condition.
Adventitious shoots, which arise from the older parts of stems or
roots, are almost always ENDOGENOUS. They must penetrate the

FIG. 144.—^, ground plan or diagram, and B, lateral view of a lateral bud of a Monocotyledon
with a divergence of £ ; m, parent axis ; db, subtending leaf borne on this ; t, the daughter
axis ; vb, bracteole on this ; h, posterior, and v, anterior sides of the daughter shoot.

outer portions of their parent shoot before becoming visible. Adven-
titious shoots formed on leaves, however, arise, .like normal shoots,
exogenously.

Such adventitious shoots frequently spring from old stems, also from the roots
of herbaceous plants (Brassica oleracea, Anemone sylvestris, Convolvulus arvensis,
Rumex Acetosella], or of bushes (Rubus, Rosa, Corijlus), or of trees (Populus,
Ulmus, Robinia). They may even develop from leaves, as in Cardamine pratensis,
Nasturtium officinale, and a number of Ferns. An injury to a plant will frequently
induce the formation of adventitious shoots, and they frequently arise from the
cut surface of stumps of trees. Gardeners often make use of pieces of stems,
rhizomes, or even leaves as cuttings from which to produce new plants (6V). When
the buds in this case do not arise from existing growing points but are new-formed
from permanent tissue, the process is spoken of as REGENERATION (of. the section
on Physiology).

(b) The Position of the Leaves of Lateral Buds. — When the
relations of position in a lateral branch of any order are to be

DIV. I MORPHOLOGY 123

examined the branch is placed with its subtending leaf towards the
observer (ANTERIOR), and the parent axis POSTERIOR (Fig. 144 A),
and so that the median plane of the subtending leaf coincides with
that of the observer. Structures on the lateral branch, which are
directed towards its subtending leaf, are termed anterior, those
towards the parent shoot posterior, while right and left refer to
structures lying to either side of the median plane of the subtending
leaf in the TRANSVERSE PLANE.

Independently of the phyllotaxis, the lowest leaves of a lateral
bud which come next above the subtending leaf tend to occupy a
definite position in relation to the latter and to the parent axis.
They connect the phyllotaxy of the lateral branch with that of the main
shoot. In Monocotyledons there is one such BRACTEOLE (Fig. 144 vb),
while in Dicotyledons there are two bracteoles ; they are usually scale
or bracteal leaves. The bracteole in Monocotyledons is median and
stands on the posterior side of the branch towards the main axis. It
frequently has two lateral veins appearing as keels, while a middle
vein is wanting (Fig. 144 A)\ it may thus be regarded as arising
from the union of two lateral bracteoles C38). In Dicotyledons the two
bracteoles (a and /5) stand as a rule right and left in the transverse
plane, the later leaves following in a different arrangement.

Apart from this the lateral buds may show the same leaf arrange-
ment as the parent axis or may differ from this.

When the phyllotaxy is spiral the genetic spiral of the branch may either run
in the same direction as that of the main axis (homodromous) or in the opposite
direction (antidromous).

(c) Construction of the Branch System. — The general aspect or
habit of every shoot-system depends, in addition to the direction of
growth of its main axis, on the following features : the number of
orders of lateral axes that develop; the position on the main axis
of the buds which grow out as lateral branches ; the intensity of the
growth and the orientation of the lateral axes of various orders in
relation to one another and to the parent axis. The variety in the
general habit of the shoot-systems frequently also stands in relation
to the mode of life of the plants.

1. DIRECTION OF GROWTH OF THE MAIN Axis OF THE SHOOT-
SYSTEM. — This, in the first place, determines the general type of the
shoot-system.

If the main axis stands at right angles to the soil, the shoot is termed
ORTHOTEOPOUS and the plant erect. In this case the more or less plagiotropous
and dorsi ventral lateral branches tend to be distributed radially when the plant is
growing freely. If the main axis is growing obliquely or horizontally, and is thus
PLAGIOTROPOUS, the arrangement of the branches is usually dorsiventral ; when
such a main axis with its lateral branches remains on the surface of the soil or
grows horizontally beneath this, the plant is CREEPING. The lateral branches tend

124 BOTANY PART i

to come from the flanks and the roots from the lower surface of the main stem.
In such a plant, when lateral branches grow up at right angles to the soil, they
behave as regards their further branching like erect plants.

2. THE ORDER OF SEQUENCE OF SHOOTS. — If the vegetative cone of the primary
axis of a plant, after reaching maturity, is capable of reproduction, a plant with
but one axis will result, and the plant is designated UNIAXIAL or HAPLOCAULES-
CENT. Usually, however, it is not until a plant has acquired axes of a second
or third order, when it is said to be DIPLOCAULESCENT or TRIPLOCAULESCENT, or
of the ?tth order, that the capacity for reproduction' is attained. A good illustra-
tion of a plant with a single axis is afforded by the Poppy, in which the first
shoot produced from the embryo terminates in a flower. As an example of
a triplocaulescent plant may be cited the common Plantain (Plantago major],
whose primary axis produces only foliage and scale leaves ; while the secondary
axes give rise solely to bracteal leaves, from the axils of which finally spring
the axes of the third order, which terminate in the flowers. In the case of
trees, only shoots of the nth order can produce flowers. Thus a division of
labour commonly occurs in a branched plant, which finds its expression in
differences of form between the successive shoots. These differ in appearance
according to the special function performed by them, whether nutrition, storage,
or reproduction. In addition to the essential members in the succession of shoots
developed in a determined order, there are non-essential members which repeat
forms of shoot already present. These may appear simultaneously with the
essential shoots, and serve to increase the size of the plant, as in many annuals ; in
many perennial plants they arise as yearly innovations on the stock.

3. THE DISTRIBUTION OF UNFOLDING BUDS. — Only in relatively
few cases, as, for example, in herbs, do all the lateral buds of a main
axis proceed to grow on as shoots. As a rule many more lateral buds
are formed than ever unfold. The remainder become DORMANT BUDS
or perish. It would be a needless or even injurious expenditure of
material on the part of the plant were all the buds to expand, since
the branches would overshadow one another and some would perish.

Almost all trees possess, especially in the lower region of each annual growth,
such dormant buds, which remain for a longer or shorter period capable of further
development and can unfold under special conditions. The dormant buds of the
Oak, Beech, etc., may be a hundred years old. The shoots that arise on old stems
often come from these buds and are thus not adventitious.

The unfolding of lateral buds may proceed acrope tally or basi-
petally, or exhibit no definite order. On highly -branched shoot-
systems the more peripheral buds are favoured since they have the
best opportunity of favourable exposure of the leaves to the light.

Nearly all our native trees form only resting buds through the summer while
the main shoots are elongating. Later, usually at the commencement of a new
period of growth, some of the uppermost buds formed in the preceding season
grow into lateral branches. These branches may form a whorl or an apparent
whorl (Araucaria, Pinus) ; more commonly the highest buds form long shoots
while those below them become short shoots (Pear, Apple). In other shoots,
especially those that grow erect, every second, third, or fourth, etc., bud unfolds

DIV. i MORPHOLOGY 125

so that the resulting shoots are regularly arranged at similar distances from one
another both longitudinally and laterally.

The habit of the branch-system depends on the distribution of the expanding
buds, whether this is alternate or in whorls. When the buds are opposite a kind
of dichotomous branching results as in the Horse Chestnut or the Elder.

4. DIRECTION AND INTENSITY OF GROWTH OF THE LATERAL
BRANCHES in relation to one another. The lateral angle between
adjacent lateral branches on an orthotropous branch may be very
constant in any kind of plant (e.g. in Araucaria or Pinus). On the
other hand, the intensity of growth of the lateral axes on the same main
axis may show much variety. Frequently, with the appearance of a
division of labour, only some of the branches are of unlimited growth,
the others forming short shoots. The latter have usually a shorter
life, tend not to branch, and do not take part in the persistent branch-
system of the tree. In the Larch, for example, the short shoots form
short rosettes of needles on the older shoots of unlimited growth.

5. DIRECTION AND INTENSITY OF GROWTH OF THE LATERAL
BRANCHES IN RELATION TO THE MAIN Axis. DIFFERENT TYPES OF
LATERAL BRANCHING. — The angle at which the lateral branch is
inclined to its main axis also tends to be very constant in any species
(e.g. Pine).

The lateral branches may grow at the same rate as the parent
axis, or less rapidly, or much more rapidly. In the last case they
take precedence of the main axis, the growth of which may cease
entirely, while one or more lateral branches take over the continuance
of the branching. Diversity in the resulting branch -systems must
evidently result from such differences in the growth of the daughter
and parent axes. This has led to the distinction of various types
of lateral branching, a knowledge of which is indispensable to the
understanding of the morphological construction of the higher plants.
The differences are especially well seen when the branches are close,
as in the region where the reproductive organs or flowers are borne
as lateral branches. The INFLORESCENCES may therefore serve as
favourable examples of the different types of branching.

The bracts and bracteoles in the inflorescence are usually developed as scale
leaves and do not resemble the foliage leaves. They do not serve for assimilation
but only for the protection of the young lateral branches in their axils. If the
branching of a lateral branch is continued, this proceeds as a rule from the axils of
the bracteoles. It is further characteristic of many inflorescences that the axillary
buds of all the bracts are developed further. Owing to this the inflorescences,
in contrast to the vegetative shoot-systems, form crowded branch-systems, very
numerous flowers being formed in a small space.

(ft) The term racemose branching is applied when the main axis
grows MORE ACTIVELY than the lateral axes of the first order, and
these in turn more actively than the branches of the second order
arising on them ; also when the main axis grows as actively as its

126

BOTANY

daughter axes. In the former case a true main axis or MONOPODIUM
can be followed throughout the entire branch-system (cf. Fig. 82 b).
Such typical MONOPODIAL BRANCHING is exhibited, for example, by
the Pine and other Conifers with a pyramidal outline; the radial
orthotropous main shoot grows vertically up-
wards under the influence of gravity (cf. p.
339), while the dorsiventral lateral branches
of the first order diverge on all sides horizon-
tally from the main axis. If the lateral branches

FIG. 145. — Spike of Plantago
lanceolata. (After Du-

CHARTRE.)

FIG. 146. — Catkin of Corylus
americana. (After Du-

CHARTRE.)

FIG. 147. — Raceme of Linaria
striata. d, Bracts. (After

A. F. W. SCHIMPER.)

of the first order grow erect, as in the Cypress and in many shrubs,
there may be no difference in length between them and the main
axis ; the branch-system has in such cases an oval or spherical form.

The racemose inflorescences may be divided in the following way :
I. The main axis grows more strongly than the lateral axes.

(a) Lateral axes nnbranched.

1. RACEME : stalked flowers borne on an elongated main axis (Fig. 147,

Fig. 150 A).

2. SPIKE : flowers sessile on an elongated main axis (Fig. 145, Fig. 150 B}.

A spike in which the axis is thickened and succulent is termed a
SPADIX ; a spike which, after flowering or after the fruits have ripened,
falls off as a whole is a CATKIN (Fig. 146).

(b) Lateral axes branched.

3. PANICLE : a main axis bearing racemes laterally (Fig. 150 E, Fig. 149).

DIV. I

MORPHOLOGY

127

II. The main axis grows as strongly as the lateral axes.

4. UMBEL : a whorl of lateral axes bearing flowers on a main axis which

grows to the same length and ends in a flower (Fig. 150 C, Fig. 148).

5. COMPOUND UMBEL : an umbel which has small umbels in place of the

single flowers (Fig. 150 F).

6. CAPITULUM or HEAD : flowers sessile on a shortened main axis (Fig.

150 Z>).

(b) The term eymose branching is applied when the main axis
grows LESS STRONGLY than the lateral axes, which continue the
branching and in their turn are overtopped
by the branches they bear. The resulting
appearance differs according to whether
several, equally strong, lateral axes of the
same order, or only* one lateral
axis, continue the branch-system.
In the latter case an apparent
main axis or SYMPODIUM is
formed.

In many cases of eymose branching
the parent axis not merely grows more
slowly than the daughter axes but its
tip dies or is cast off. This happens
in many of our trees such as the Willow
or the Lime.

FIG. 148.— Umbel of the Cherry.
(After DUCHARTRE.)

FIG. 149. — Panicle of Yucca filamentusa.
(After A. F. W. SCHIMPER. Reduced.)

I. If more than two lateral branches of the same order continue the branching
the term PLEIOCHASIUM is used. Such lateral branches are usually approximated
to the upper end of the parent axis and radiate on all sides obliquely upwards, in
some cases being arranged in a whorl. The inflorescence of Euphorbia affords an
example.

II. If two lateral branches of the same order continue the branching and stand
opposite to one another, forming an acute or right angle, the term DICHASIUM is
used. This is shown diagrammatically in ;Fig. 151, with which the dichasial
inflorescence in Fig. 153 may be compared. A branch system of this kind, another
example of which is afforded by the Mistletoe, which grows parasitically on trees,
simulates a dichotomy. The successive pairs of lateral branches do not lie in one

128

BOTANY

I'ART I

plane as in the diagram but stand at right angles to one another so that they
diverge on all sides. Only a ground plan (Fig. 155 E] can therefore represent
the true arrangement of the members of the branch- system.

III. When the branching is continued by a single lateral branch the term

FIG. 150.— Diagrams of racemose inflorescences. A, Raceme. L, Spike. C, Umbel.
D, Capitulum. E, Panicle. F, Compound umbel. (After KARSTEN.)

MONOCHASIUM is used. Frequently this branch continues the direction of the
parent shoot, the tip of which is displaced to one side (Fig. 152). In this way
a branch-system with a sympodial axis composed of lateral members of successive
orders is formed, as was seen to be the case sometimes in dichotomous branching
(p. 119 ff.). Such a branch-system may closely resemble monopodial branching,

DIV. I

MORPHOLOGY

129

especially when, as is frequently the case, the sympodium stands vertically and
the arrested ends of the branches appear as if home laterally upon it. They
are distinguishable from truly lateral
branches, however, by the regular absence
of a subtending leaf, while a leaf which
stands opposite to each apparent branch s /*

is really the subtending leaf of the
daughter shoot that continued the sym- \

podium (cf. Fig. 152). The further V J[

branching may also be sympodial. The
branching of many trees, such as the Lime
and Beech, is of this nature, but the

Fin. lol.— Diagram of the sympodial construction is not recognisable
Dichasium. H, Axis of jn the stems and branches. It remains
the seedling ; l, S, 3, *evident however, in many subterranean Fl°- ^.-Diagram
daughter axes of the cor- At- ^ -^ , „,,-.-,

responding first, second,. shoots such as the rhizome of Polygo-
and third orders. natum multiflorum (Fig. 138). The

terminal bud of each year's growth be-
comes the aerial shoot, while an axillary bud continues the growth of the rhizome
in the soil.

According to the relation of the lateral shoots of different orders to each other

of the Monocha-
slum. Cf. Fig.
151.

FIG 153. — Cymose inflorescence (dichasinm) of Cerasti u m
collinum. t-t"", Successive axes. (After DUCHARTRE.)

FIG. Ib4.—Heliotropium Curassavicum,
Cincinnus. (After EXGLER-PRANTL.)

there arise monochasial branch- systems of diverse and very characteristic construc-
tion. The branching frequently proceeds from the axil of a bracteole.

130

BOTANY

PART I

A. The median plane of all the lateral shoots may coincide with the median
plane of the lateral shoot of the first order.

(a) The successive lateral branches are on the anterior side of the parent axis,
i.e. between the latter and the subtending leaf (cf. p. 121). In lateral view they
thus fall on the same side, DREPANIUM (Fig. 155 C, D).

(/3) The successive axes stand on the posterior side of the parent axis (cf. p. 123)
and in lateral view appear alternately right and left, RHIPIDIUM (Fig. 155 A, B}.

rir
A ,

FIG. 155. — A, Rhipidium from the side ; B, rhipidium in ground plan ; C, dre-
panium from the side ; D, ground plan of drepanium ; E, ground plan of
dichasium (the red line indicates the mode of derivation of the cincinnus
and the blue line of the bostryx) ; F, ground plan of bostryx ; G, ground
plan of cincinnus. 1-9, successive, relatively main axes. In order to| make
the relations clearer the successive axes in A-D and F, G are indicated in
different colours. The subtending leaf borne by each axis has the same
colour as the axis from which it springs. (A-G, after EICHLER, the rest
modified from KARSTEN.)

B. The median plane of each lateral shoot (of the 1st, 2nd, 3rd order, etc.)
is always transverse, i.e. right or left of the median plane of the subtending
leaf on the parent shoot. Such branch-systems can only be represented in ground
plan.

(a) The successive lateral shoots are placed always to the same side, either to
the right or the left, BOSTRYX (Fig. 155 F).

(]8) The successive lateral shoots stand alternately to the right or left, CINCINNUS
(Fig. 155 G, Fig. 154).

DIV. I

MORPHOLOGY 131

The bostryx and cincinnus are readily understood by deriving them from the
ground plan of the dichasium (Fig. 155 E).

Various types of branching are frequently combined in one branch-system.
Thus cymosely-branched lateral shoots may be borne on the racemose main shoot.
The combinations are especially varied in the case of inflorescences.

(b) The Root

The ROOTS of plants, which are usually situated in the soil (subter-
ranean roots) and less commonly exposed to the atmosphere (aerial
roots), NEVER BEAR LEAVES. In this respect, as well as by the absence
of the green colour, their appearance differs from that of shoots ; even
of colourless subterranean shoots. Their chief functions are to attach
the plant to the soil and to absorb from this water and salts that
are conducted to the shoot-system. The functions of roots are thus
very different from those of most shoots, which mainly serve for the
assimilation of carbon dioxide.

1. Growing Point. — The root grows in length at the tip, exhibiting
APICAL GROWTH by means of its conical GROWING POINT. The latter
requires to have the thin-walled meristematic cells specially protected
since, as the root grows, it is forced forwards like a needle between the
angular particles of the soil. This protection is afforded by a special
organ composed of permanent tissue which is called the ROOT-CAP or
CALYPTRA ; it covers the tip of the root as a thimble does that of the
finger, the true growing point having an intercalary position within
the tissue of the root-tip. The outer cell walls of the root-cap become
mucilaginous, and this makes the forward passage of the root easier.
The root-cap is usually only recognisable in median longitudinal sections
through the root-tip (Figs. 156, 157), but in some cases (Pandanus)
the cap is to be clearly seen on the intact root.

The very noticeable caps on the water roots of Duckweed (Lemna) and of some
Hydrocharitaceae are not really root- caps, as they are not derived from the
root, but from a sheath which envelops the rudimentary root at the time of its
origin. They are accordingly termed ROOT-POCKETS. As a general rule, however,
roots without root -caps are of rare occurrence, and in the case of the Duckweed the
root-pocket performs all the functions of a root-cap. The short-lived root of the
Dodder (p. 190) affords another example of a root devoid of a root-cap.

The growing point of the root, as has been already mentioned, is
composed of meristematic cells from which the permanent cells of the
root-cap are derived on the side towards the tip and the permanent
tissue of the root on the basal side.

In most Pteridophytes the root, like the shoot, has a three-sided
apical cell (t, Fig. 156) with the form of a three-sided pyramid.

In addition to the segments cut off parallel to the three inner walls which
contribute to the root itself, segments are formed parallel to the outer wall (£).
These undergo further divisions and form the root-cap.

K 1

132

BOTANY

PART I

The growing points of the roots of Phanerogams, on the other hand,
have no apical cells. They consist of equivalent meristematic cells
that are frequently arranged in regular layers.

The apex of a root of one of the Gramineae (Fig. 157) may be described as an
example. The stratified meristem, from which the permanent tissue of the root
arises, is separated into an outer layer of cells, the DERMATOGEN (d) ; a central
region formed of several layers which gives rise to the central cylinder of the root
and is called the PLEROME (pi) ; and into a number of layers between the derma-

Fio. 156. — Median longitudinal section of the apex of a root of Pteris cretica.
t, Apical cell ; A-, initial cell of root-cap ; k", root-cap, (x 240. After STRASBUROER.)

togen and plerome which form the PERIBLEM. The dermatogen (d) and periblem
(pr) unite at the apex in a single cell-layer, outside of which lies the CALYPTROGEN
(k) or layer of cells from which the root-cap takes its origin.

In many other roots, however (in the majority of Dicotyledons), the formation
of the root-cap results from the periclinal division of the dermatogen itself, which,
in that case, remains distinct from the periblem. In Gymnosperms, and in many
Leguminosae, the dermatogen, periblem, and calyptrogen are not marked out as
distinct regions. In roots, the plerome cylinder (pi) almost always terminates in
special initial cells.

2. External Features of the Root. — Behind the growing point

DIV. I

MORPHOLOGY

133

the meristematic cells enlarge greatly as they are transformed into
permanent tissue, a marked elongation of the root accompanying these
processes. By this growth in length, which begins close behind the

157. — Median longitudinal section of the apex of a root of the Barley, Hordeum vulgare.
k, Calyptrogen; d, dermatogen; c, its thickened wall; pr, periblem; pi, plerome; en, endodennis;
i, intercellular air-space in process of formation ; a, cell row destined to form a vessel ;
r, exfoliated cells of the root-cap. ( x 180. After STRASBURGER.)

apex and in subterranean roots is limited to a zone only 5-10 mm.
long, the root becomes a cylindrical colourless structure.

In the shortness of the zone of elongation subterranean roots contrast with aerial
shoots. In aerial roots this zone may be many centimetres in length. Its short-
ness in subterranean roots is evidently connected with the conditions of their life.

At some distance from the root-tip, about the region where growth

134

BOTANY

PART I

in length ceases, the ROOT-HAIRS (69) (Fig. 158 r, Fig. 51), which are
important appendages of subterranean roots, appear. They are
localised tubular protrusions of the living epidermal cells with thin
walls covered with mucilage. When seedlings, e.g., of Wheat are grown
in a moist chamber they can be seen with the naked eye, forming a
delicate down on the surface of the root. They occur in enormous
numbers (e.g. about 42T) per sq. mm, in Zea
Mays). Their length varies, according to the
kind of plant, between 0'15 and 8 mm. They
enlarge the surface of the root greatly (in
Pisum, for example, twelvefold) and penetrate
between the particles of the soil and become
attached to them. Thus in the soil they do
not retain the cylindrical form seen in moist
air but are bent to and fro, and flattened,
club-shaped, or lobed at the top (Fig. 239).
They serve to absorb water and dissolved salts.
They only live for some days, the older root-
hairs dying off as new ones form nearer the
tip : thus only a limited zone of the young
root some centimetres or millimetres in length
is clothed with them. The older smooth portion
of the root serves for conduction, but has
ceased to absorb the water. The surface often
shows transverse wrinkling brought about by
subsequent contraction of this region of the
root. This shortens the root so that, like a
tense support, it anchors the shoot more firmly
in the soil (cf. Fig. 207, 6).

Root- hairs are wanting in some plants, especially
those which can readily obtain water, as is the case
with many aquatic and marsh plants. The roots of
Fio. 158.— Seedling of Carpinns some aquatic plants, such as Nuphar luteum, form
Betulus. r, Zone of root- root-liairs when they penetrate the soil ; the roots of
hairs near root-tip; h, hypo- h , t . h Carex paludosa, when there is

cotyl; hw, mam root'; sw, f

lateral roots; I, V, leaf; e, lack ot water,
epicoty 1 ; c, cotyledons. (Nat.

size. After NOLL.) 3. Primary Structure of the Root—

When the transformation of the meristematic

cells into permanent tissue has taken place the same kinds of tissue
are recognisable in roots as in shoots, their arrangement being as a rule
radially symmetrical.

The surface of the younger portions of the root is bounded by the
thin- walled EPIDERMIS which, with the root-hairs borne upon it, serves
for absorption. The ABSENCE OF STOMATA and of a CUTICLE is
characteristic of this layer. The epidermis of the root dies off with

DIV. I

MORPHOLOGY

135

FIG. 15y.— Transverse section of an adventitious root of
Allium Cepa. ep, Remains of the epidermis ; ex, exo-
dermis ; o, primary cortex ; e, endodermis ; cc, central
cylinder, (x 45. After M. KOERNICKE.)

the root-hairs. The outermost layer of the cortex then forms a cutis-
tissue called the EXODERMIS (70) on the surface, the cell walls
becoming more or less suber-
ised (Fig. 159 ex).

Some of the cells of the exoder-
mis often remain unsuberised and
serve as transfusion cells. They
are regularly placed among the
corky cells and smaller than the
latter.

The remaining tissues of

the root can be distinguished

into cortex and central

cylinder.

The primary cortex of

the root is composed of

colourless tissue, which is

usually parenchymatous. In

the outer layers the cells

are in close contact with one

another, but intercellular spaces are present more internally. These

intercellular spaces often widen into air-cavities or passages. In

many roots a hypoderma giving
mechanical support to the epi-
dermis or exodermis is present.
The innermost layer of the
cortex is usually developed as
an ENDODEKMIS (71) (Figs. 159,
160 e, 161 S, 163 *), which
sharply marks the limit between
cortex and central cylinder.
The endodermis consists of
somewhat elongated, rectan-
gular, prismatic cells which in
transverse sections show the
dark Caspary dots on their
radial walls. The nature of
these strips of the wall (cf. p.

Fi<;. MO.— Transverse section of central portion of 58) shuts off to SOme extent
the root of Acorus Calamus, m, Medulla ; *, xyleni; tne central Cylinder from the
r, phloem ; p, pericycle ; e, endodermis ; c, cortex. . J . . ,

(XPO. After STRASBURGER.) primary cortex ; the tangential

walls of the young endodermal
cells, however, allow of passage of water between the two regions.

In the older parts of the roots the cells of the endodermis become corky, and in
many Monocotyledons are greatly thickened, but generally on one side only.

136 BOTANY PART i

Should thickening occur at an early stage, special eudodermal cells, directly
external to the xylem strands, remain unthickened and serve as TRANSFUSION
CELLS (Fig. 163 d).

The outermost layer of cells of the central cylinder lying
immediately within the endodermis (Figs. 160^, 161 pc, 163 p) forms
the PERICYCLE ; this is usually a single layer and in rare cases is
wanting. The strands of xylem and phloem run longitudinally in the
central cylinder and in all roots form a radial vascular bundle (59)
(cf. p. 99). They are separated from one another by one or more

Fm. 161.— Transverse section of the radial bundle of the root of Ranunculus acer. R, Cortical
parenchyma; S, endodermis; pc, pericycle; ph, phloem; px, protoxylem; G, pitted vessels.
(x 200. ROTHERT modified from DIPPEL.)

layers of cells that usually have the characters of conducting
parenchyma. The orientation of the strands of xylem in the root
contrasts with that found in the stem. In the stem the narrow
elements of protoxylem were situated internally, but in the root the
internal vessels are the widest, and the narrow elements of the proto-
xylem are found close to the periphery of the vascular bundle.
Annular, spiral, reticulate, and pitted vessels thus follow in order from
without inwards. The protophloem is situated at the outer margin of
the phloem strands, which are more or less circular in cross -section.
Roots are described as diarch, triarch, polyarch, etc , according to the
number of the vascular strands. Thus the root in Fig. 160 is octarch

DIV. I

MORPHOLOGY

137

and that in Fig. 163 pentarch. The vascular strands may either meet
in the centre (Figs. 161, 163) or there is in this position a central
strand composed of parenchyma
or sclerenchyma or a mixture
of these tissues (Fig. 160).
Most roots have to be con-
structed to resist pulling strains,
and the mechanical tissue is
accordingly mainly placed com-
pactly in the central pith (Fig.
162).

For an organ that ^ias to resist
tension it is immaterial at what part
of the cross-section the mechanical
tissues are placed. Their association

in the centre to form a single strand is of advantage, since, if many thinner strands
were situated peripherally, a one-sided pull might rupture some of these more
readily.

The continuity of the xyleni and phloem strands of the radial bundle of

FIG. 162.— Mechanical tissue of roots. 1, Centrally
placed to resist longitudinal pulling strains ; 2, a
prop root with a peripheral layer of mechanical
tissue (P) to resist lateral pressure, in addition
to the central strand. (After XOLL.)

FIG. 163. — Transverse section of the radial bundle of the root of Allium ascalonicum. s,
Endoder mis with the inner walls thickened ; d, transfusion cells ; p, pericycle; g, large central
—1. (ROTHERT after HABERLANDT.)

the root with the corresponding tissues of the differently -constructed bundles
of the stem is effected at the junction of the root and stem of the seedling.
It need only be briefly described for the most common case of plants in
which the bundles of the stem are collateral. The essential fact of the transition

138

BOTANY

PART 1

is that each of the strands of xylem of the root rotates through 180° round its
longitudinal axis, bringing the protoxylem to the inner side of the strand which is
the characteristic position in the stem. -A number of collateral vascular bundles
are reconstituted from the tissues of the radial bundle of the root by the radially-
arranged xylem and phloem taking up the collateral position. This happens in
different ways, of which two main types may be distinguished : 1. The strands
of xylem when rotating follow a straight course from the root to the stem ; the
strands of phloem of the root, on the other hand, divide radially, the two halves
separate tangentially, and, uniting with the portions derived from adjoining
strands of phloem, come to lie outside the
xylem strands. 2. The phloem strands of
the root follow a straight course into the
stem, but the strands of xylem which rotate
through 180° split radially ; the halves
separate tangentially (as the phloem strands

FIG. 164.— Transverse section of the root
of Vicia Faba showing the origin of a
lateral root (r). e, Endodermis ; p, peri-
cycle ; d, cortex ; g, xylem strand ; v,
phloem strand of the radial bundle,
(x 40. Somewhat diagrammatic.)

FIG. 165.— Portion of a longitudinal section
of a root of Amarantus showing the origin
of a lateral root, e, Endodermis, already
absorbed opposite the young root; d, cor-
tex ; p, pericycle ; sp, spiral tracheide ; r,
young lateral root, (x about 200. After

PH. VAN TlEGHEM.)

did in Type 1) and, uniting with the portions derived from the adjoining strands
of xylem, place themselves internal to the strands of phloem to constitute the
collateral bundles.

4. Branching of the Root. — By this process, in which a root
always gives rise to roots, the root-system can penetrate the soil in
all directions and obtain from the whole space thus occupied water
and dissolved salts.

DiCHOTOMOUS branching by an equal division of the growing
point only occurs in some Pteridopliyta (Lycopodinae).

With this exception the branching of the root is LATERAL (Fig.
158), the lateral roots, in contrast to the lateral shoots, originating at
some distance from the growing point where the meristematic cells
have been transformed into permanent tissue. They arise ENDO-
GENOUSLY (Figs. 164, 165) within the tissues of the parent root and
in acropetal succession. The growing point of the new root is formed
from the innermost layer of the cortex in Pteridophytes and from
the pericycle in the Phanerogams ; a group of parenchymatous cells
commences to divide, the cells returning to the meristematic condition.

DIV. I MORPHOLOGY 139

The lateral roots break through the whole thickness of the cortex as
they emerge in the order of their development from the main root.
The ruptured cortex is frequently recognisable as a sort of collar
round the base of the lateral root. Other lateral roots may form
subsequently between those already developed and on older parts of
the root.

The lateral roots always stand in VERTICAL SERIES on the parent
root (72). This arrangement is determined by their always arising
either opposite one of the longitudinally-running strands of xylem
(Fig. 164), or opposite the plate of conducting parenchyma which
separates a strand of xylem from one of phloem. The number
of vertical series of roots is thus either the same as the number of
strands of xylem, »or twice this. In the former case the lateral
distance between any two adjacent roots is equal, while when the
roots arise right and left of a strand of xylem these two vertical
rows are approximated.

The structure of the lateral roots corresponds with that of the
main root, and the xylem and phloem are continuous from the
one to the other.

5. Roots borne on Shoots. — Roots not only arise from other
roots but may be developed from the shoot, both from stems and
leaves. They are usually endogenous. In Ferns they arise from
meristematic tissue in the region of the growing point of the shoot.

The place of origin of such adventitious roots is not fixed beforehand but may
be more or less definite. This is especially the case in marsh and water plants
where the roots arise from the lower nodes of the stem between, and alternating
with, the leaves ; they replace the primary root-system which has been lost when
the older part of the plant died off (73). They are especially numerous on the
under side of rhizomes (Fig. 138) and creeping shoots. A young shoot, or a
cutting planted in moist soil, quickly forms adventitious roots, and roots may
also arise in a similar manner from the bases of leaves, especially from Begonia
leaves when planted in soil (74).

Dormant root-rudiments occur in the same manner as dormant buds of shoots.
Willow-twigs afford a special case of the presence of such dormant rudiments of
adventitious roots, the further development of which is easily induced by dark-
ness and moisture.

6. Appearance of the Root- System. — The lateral roots of
successively higher orders are as a rule thinner and grow less strongly
than their respective parent roots. The whole root -system is thus
typically RACEMOSE. The alternate branches are usually short arid
have a limited period of existence ; they may be termed ABSORBENT

ROOTLETS.

The root-system, like the shoot-system, further owes its general
appearance to the fact that the main and lateral branches take up
distinct positions in space relatively to one another ; this depends on
differences in their geotropism (cf. p. 339).

140 BOTANY PART i

Many Dicotyledons (e.g. Lupin, Oak) and Gymnosperms (Pine)
possess a radial MAIN-ROOT or TAP-ROOT (Fig. 158) which, from the
seedling onwards, forms the downward continuation of the main stem
and grows vertically down into the soil (orthotropous). On this
radial lateral roots of the 1st order arise, which penetrate the soil
horizontally or obliquely (plagiotropous). The lateral roots of the
2nd order arise in turn on those of the 1st order. They tend to
grow on all sides from the latter so that the branches of the root-
system penetrate the soil as uniformly as possible in all directions,
and, as branching continues, do not leave a cubic centimetre unused.

A tap-root is usually wanting in Monocotyledons since it becomes
arrested in the seedling stage. In its place numerous roots arise
from the base of the stem and penetrate the soil vertically, obliquely,
or horizontally. They branch monopodially, bearing lateral roots of
successively higher orders which penetrate the soil in all directions.
In the Wheat, for example, there is no tap-root, but the root-system
continues to extend in a horizontal plane.

The length of all the roots of a plant taken together is surprising.
Thus for a plant of Wheat it may amount to some hundreds of metres.

Some of the roots of trees in tropical forests are developed in a
peculiar fashion. The extraordinarily high and thick stems of many
such trees are supported at the base by strong vertically - placed
BUTTRESS-ROOTS. In other cases support is given by aerial roots
growing down from the branches to the earth and attaining the
thickness of woody trunks (PROP-ROOTS, e.g., in species of Ficus).

(e) Secondary Growth in Thickness of the Cormus

It has been seen that the additions to the root and shoot
made by the increase in number of the meristematic cells in the
growing points increase in length as they mature. A certain increase
in thickness of the parts is associated with this growth in length •
this depends on the enlargement of the cells on passing from
the meristematic condition and not on increase in their number
(PRIMARY GROWTH IN THICKNESS, cf. Figs. 98, 100, 102, 115). This,
as a matter of fact, is slight, but is often followed in stems and roots
by processes of growth that will now be considered.

The larger the shoot- system becomes the more readily will it
escape overshadowing by other plants and form more organic
material. Thus in many plants the growth of the small seedling
with a few leaves leads, with the accompanying branching, to a cormus
of the size of a large tree bearing a very large number of leaves.
The increase in the aerial shoot-system and in the number of leaves
makes progressively great demands on the water supply from the
roots, which can only be met by the increase of surface and the
branching of the root-system ; in many cases additional roots are

BIV. I

MORPHOLOGY 141

developed from the stem. All increase of the root-system, however,
depends on a supply of organic food materials manufactured in the
leaves. Thus the further development of the crown of foliage and of
the root-system are intimately related to one another. The increase
in size of the shoot- and root-systems further presupposes that a
sufficient number of conducting tracts in the stems and roots can be
developed, both for water and for organic materials, and that the stem
should be strong enough to support the increasing weight even when
exposed to wind. There is thus an intimate connection between the
size of the cormus and the formation of conducting tracts in its axes
and the rigidity of the shoot.

The rigidity requires to be greater the larger the plant becomes
and the longer it lives. Plants or shoot-systems which only live for a
limited period and die off after bearing reproductive organs have
usually herbaceous structure (HERBS). Large cormi which live for
many years and bear fruit repeatedly have as a rule the rigidity
of their stems and roots increased by the formation of wood. Such
woody plants are called SHRUBS if they do not exceed a moderate
height, and retain their lateral shoots so that their branches are
formed near the ground. They are called TREES (75), on the other
hand, if they attain a greater height, have a main stem or trunk
(which must have the type of rigidity possessed by a pillar), and
usually lose their lower branches at an early period.

In catalogues and descriptions of plants the duration of the period of growth
is usually expressed by special symbols : thus 0 indicates an annual ; 0 a biennial,
and ^ a perennial herb ; \i is employed to designate shrubs, and for trees the
sign ^ is in use. A special type of tree is found in the columnar and usually
unbranched stems of Palms and Tree-ferns ; in them secondary thickening, and
a true woo ly mass resulting from this, are wanting.

The requirements, both as regards the number of conducting
tracts and the necessary rigidity, are met in a variety of ways in
cormophytic plants. In the first place, there are plants in which the
main axis of the seedling and any lateral branches that arise attain
a sufficient thickness and develop sufficient mechanical and conduct-
ing tissues before growth in length ; when this takes place later the
thickness is adequate for the future increase in size of the plant.
The primary root in such cases remains thin and usually dies off
early, while as many roots as are necessary arise from the basal
portion of the shoot. Secondly, there are plants in which long
slender stems and roots with only a few conducting and mechanical
elements are first developed. A limit would soon be set to the supply
of water to the leaves and of nutritive material to the root-system,
and thus to the increase in size of the plant, by the small number of
conducting elements in the primary stem and root. Provision is,
however, made for an increase in the conducting and mechanical

142 BOTANY PART i

tissues corresponding to the needs of the growing plant. This is
effected by a continued process of cell division forming secondary
tissues and leading to a SECONDARY GROWTH IN THICKNESS of the
stem and roots. Secondary tissues are those that are added to or
replace the primary tissues as a result of the activity of a secondary
meristem or CAMBIUM (cf. p. 47). Such secondary growth occurs
in herbaceous as well as in woody plants.

To the FIRST TYPE (76) belong the mostly herbaceous Pteri-
dophytes and Monocotyledons, including nearly all the forms that
have definite stems (Tree-ferns, Palms, Pandanaceae, certain Lilii-
florae). Thus in these stem-forming Monocotyledons the embryonic
stem remains very short on germination. The primary meristem of
the flattened growing point increases in breadth, leading to the axis
of the seedling from which the stem will continue having a consider-
able thickness from an early stage.

In such forms as the Palms and Pandanaceae the stem may continue to
increase slightly in thickness after the permanent tissues have developed by a
process of expansion of the cells. The cells of the sclerenchymatous strands
which accompany the phloem of the vascular bundles may thus increase in
diameter leading to an enlargement of the strand as a whole. In places this
growth in thickness may be accompanied by divisions in parenchymatous cells
(e.g. in some Palms).

The majority of herbaceous and woody Gymnosperms and Dicoty-
ledons and some arborescent Liliiflorae belong to the SECOND TYPE C77).
The primary thickening or maturing of the stem and root dependent
on the enlargement of cells is in them followed by increase in number
of the cells in a special meristematic zone, the cambial ring.

The secondary thickening in annual, scrambling, and twining plants often only
begins in older internodes which have long attained their full primary size. In
the twigs of trees, on the other hand, the secondary growth may start early, even
before the primary tissues are fully developed.

Secondary growth in thickness was present in certain Pteridophytes known
to us as fossil remains, but only became of general occurrence in the Gymnosperms
and Dicotyledons.

Secondary Growth in Thickness of Monocotyledons.— In some
arborescent Liliiflorae (Dracaena, Cordyline, Yucca, Aloe) the axis
exhibits growth in thickness due to a secondary meristem. This
arises in the cortex where it abuts on the central cylinder in which
the vascular bundles are scattered in the manner characteristic of
Monocotyledons. In transverse sections divisions can be seen to
begin in an annular zone of mature cortical cells. In Dracaena this
happens at a considerable distance from the growing point, but in
other cases it may start close to it. A cylindrical meristematic zone
a number of cells deep is thus formed ; the cells are prismatic and fit
together without intercellular spaces. As a result of the formation of

DIV. I

MORPHOLOGY

143

tangential walls, cells continue to be cut off towards the inside, and
later some are formed to the outside. The latter become secondary
cortical tissue ; the cells to
the inside develop into con-
centric vascular bundles, in
which the xylem surrounds
the phloem, and parenehy-
matous tissue with thickened
and lignified walls (Fig. 166). ?h~

The meristematic cells have a
rectangular shape in transverse
and radial section^, while in tan-
gential section they are polygonal ;
they are thus tangentially-placed
flattened prisms (cf. Fig. 169 A, IT],
So long as the meristem is only
forming new tissues on the one
side, the initial cells can be re-
placed at the expense of the inner
permanent cells of the cortex.
When, however, the meristem is
active on both sides the initial layer
persists.

True secondary thickening of
the root in Monocotyledons is only
known in the case of the genus
Dracaena. The cambial ring arises
in the cortex of the root just out-
side the endodermis.

Secondary Thickening of
Gymnosperms and Dicotyle-
dons. 1. Formation, Struc-
ture, and Activity of the

Cambium in Stems. In the FlG. ice.— Transverse section of the stem of Cordyline

(Dracaena) rubra. f, Primary vascular bundles ;
/", secondary vascular bundles ; /"', leaf - trace
bundle within the primary cortex ; m, parenchy-
matous fundamental tissue ; s, bundle-sheath ; t.
tracheides ; c, cambium ring ; cr, cortex, the outer
portion being primary, the inner secondary cortex ;
ph, cork cambium ; I, cork ; r, bundles of raphides.
( x 30. After STRASBURGER.)

open vascular bundles of the
Gymnosperms and Dicotyle-
dons the formation of second-
ary tissues may take place as
soon as the primary tissues
have matured, or may even

begin before this. Only the

former case need be considered here. The primary meristem remain-
ing between the xylem and phloem of the bundle becomes the
cambium and commences again to divide actively. The vascular
bundles are usually arranged in a circle. When the cambial activity
has commenced in the bundles, cambium also forms across the
medullary rays, by parenchymatous cells dividing tangentially. This

144

BOTANY

PAIIT I

FIG. 167.— Transverse section of a stem of Ansto
lochia Sipho 5 mm. in thickness, m, Medulla

INTERFASCICULAR CAMBIUM connects the FASCICULAR CAMBIUM within

the bundles, forming a complete hollow cylinder of meristematic tissue.

The cells grow in the radial
direction and undergo division
by tangential and by transverse
walls ; from time to time cells
appear to be divided by radial
walls.

Figs. 167 and 168 represent the
formation of the cambium as shown
particularly clearly and simply in a
transverse section of the stem of
Aristolochia Sipho. A single bundle
with the adjacent interfascicular cam-
bium from the stem in Fig. 167 is
more highly magnified in Fig. 168.
The cambium is actively dividing,
and two partially-developed secondary

fv, vascular bundle ; vl, xylem ; cb, phloem ; fc, vessels are seen at m". The outline of
fascicular cambium; ifc, interfascicular cam- the parenchymatous cells of the medul-
bium; p, phloem parenchyma; pc, pericycle ; j wMch ye Qri in to the

sk, ring of sclerenchyma ; e, starch-sheath; c, . - . , , . ... ,

primary cortex; d, collenchyma in primary interfascicular cambium., can still be
cortex, (x 9. After STRASBURGER.) recognised.

The cambium cells fit together without intercellular spaces and
form radial rows. They have the shape of elongated prisms more
or less flattened tangentially and with both ends pointed ; thus
the form of the cell appears very different in tangential, radial, or
transverse section (Fig. 169). The tangential walls, which form the
polygonal or rhombic main faces of the prismatic cell, are thin ; the
radial walls, on the other hand, are fairly thick and frequently pitted.
A middle layer of cells in the cambial zone forms the INITIAL LAYER.
Its cells remain permanently in the meristematic condition. They grow
in the radial direction, dividing by tangential walls, and so give off
daughter cells (tissue mother cells) to both sides, but more abundantly
on the inner side. These daughter cells in their turn may undergo
tangential divisions, . and, often after growing greatly in length and
breadth (Fig. 174) and changing their shape, become gradually trans-
formed into permanent cells of the secondary tissues.

The cambium in giving off cells inwards must itself, as the stem grows in
thickness, be carried gradually outwards. The circumference of the cambial ring
must therefore be increased. This can only be effected by growth and increase in
number of the cells in a tangential direction. In transverse sections it appears as
if this came about by radial division of some of the cells. KLINKEN (78) has,
however, shown in Taxus that such divisions do not occur ; the number of cells in
the tangential direction is increased by an initial cell of the cambium dividing
transversely, and the ends of the two resulting cells becoming placed side by side
tangentially by sliding growth.

DIV. I

MORPHOLOGY

145

All the permanent tissue formed on the inner side of the cambium
is termed wood ; this is usually hard and composed of more or less
lignified cells. The tissue formed to the outside by the cambium
usually consists of unlignified cells and is termed the bast.

FIG. 168.— Transverse section of a stem of Aristolochia Sipho in the tirst year of its growth, showing
a vascular bundle with cambium in active division, p, Xylem parenchyma ; vlp, proto-
xylem ; m' and m", vessels with bordered pits ; ic, interfascicular cambium in continuation
with the fascicular cambium ; v, sieve-tubes ; cbp, protophloem ; pc, pericycle ; sk, inner part
of ring of sclerenchymatous fibres. ( x 130. After STRASBURGER.)

In contrast to the primary cortex all the tissues to the outside of the cambium
may be regarded as forming secondary cortex.

The secondary tissue formed internally by the fascicular cambium
resembles the xylem, and that to the outside the phloem of the
primary vascular bundle. By the activity of the interfascicular
cambium the primary medullary rays are continued through the wood
and the bast. Their breadth is, however, usually diminished, since

146

BOTANY

PART I

the interfascicular cambium in great part gives rise to tissues similar
to those formed by the fascicular cambium. Thus, in place of the
original broad medullary rays, the cambium forms at definite points
narrower radial rows of medullary ray tissue. These medullary rays,
which are spindle-shaped when cut across (Fig. 170), traverse the
wood and the bast, connecting the pith with the cortex as PRIMARY
MEDULLARY RAYS. As the thickness of the secondary wood and bast
increases, SECONDARY MEDULLARY RAYS are developed from the
fascicular cambium. In one direction the secondary medullary rays

CZI

FIG. 169.— Diagrammatic
figure of the shape of
cambial cells. A, I and
II, the two forms
which occur, seen from
the tangential face ; B,
in radial section ; C,
in transverse section.
(After ROTHERT.)

FIG. 170. — A diagrammatic tangential
section to illustrate the subdivi-
sion of a primary medullary ray
into many smaller rays on the
commencement of secondary thick-
ening. I, I; Adjoining primary vas-
cular bundles ; pm, primary medul-
lary ray transformed by the
activity of the interfascicular cam-
bium into many small spindle-
shaped medullary rays and reticu-
lately - connected secondary vas-
cular bundles.

end blindly in the wood and in the other in the bast ; the later they
develop the less deeply do they penetrate the tissues on either side of
the cambium (Fig. 179).

The cambial cells which give rise to medullary rays are shorter and
their end walls are more horizontal, for when a medullary ray is to be
initiated the ordinary cambium cell becomes divided transversely or
obliquely.

The origin of the cambium and the nature of its activity can be distinguished
into three main types according to the primary construction of the stem :
1. The stem has a circle of collateral vascular bundles separated from one
another by broad medullary rays ; the breadth of %the medullary rays is main-
tained during secondary growth, the interfascicular cambium producing only
medullary ray tissue. This is the»case for many herbaceous plants, but among

DIV. I

MORPHOLOGY

147

woody plants is only found in the lianes. In those herbs '^in which the inner
portion of the medullary rays between the primary strands of xylem consists of
sclerenchyma (cf. p. 95), the interfascicular cambium forms similar tissue on its
inner side. 2. The stem as in the first type has a circle of collateral leaf- trace bundles
separated by broad medullary rays. Before the primary growth in thickness is
completed there arise from the still meristematic tissue of each medullary ray,
that now assumes the characters of a cambium, one or a number of small, cauline,
intermediate bundles which anastomose
tangentially ; the intervening meshes are
occupied by narrow primary medullary
rays that are spindle-shaped when cut
across (Fig. 170). The original medullary
rays become filled up in this way in many
herbaceous and woody plants. 3. In the
transformation of the primary meristem
to permanent tissue there arises, instead
of a circle of collateral bundles, a vascular
tube, which appears like a concentric
bundle with a central pith and internally-
situated xylem. There is a layer of meri-
stematic tissue between the xylem and
phloem that later becomes the cambium.
The vascular tube may be traversed by
very narrow spindle-shaped primary
medullary rays, or these maybe completely
wanting. This type is found in many
trees.

The primary xylem of the bundles in
stems which have undergone secondary
thickening projects into the pith.

2. Formation and Activity of
the Cambium in the Root. — As

has been seen (Figs. 160, 161), the
strands of xylem and phloem alter-
nate in the central cylinder of the
root ; they are separated by inter-
vening parenchymatous tissue.
When secondary thickening begins
in such a root cambial layers arise

internal to the strands of phloem, and between these and the strands
of xylem, by divisions taking place in some of the parenchymatous
cells ; the cambium forms wood towards the centre and bast towards
the outside. These arcs of cambium meet in the pericycle just outside
the xylem strands and the cambial ring is completed from -the peri-
cycle. The wavy outline of this is shown in Fig. 171-4; by the
activity of the cambium in producing new tissues the depressions
in the ring are soon evened out (Fig. 171 B). Primary medullary
rays are absent from the wood and bast, but secondary medullary rays

FIG. 171. — Diagrammatic representation of the
growth in thickness of a dicotyledonous
root, pr, Primary cortex ; c, cambium
ring ; g', primary vascular strand ; s',
primary phloem strand; p, pericycle; e,
endodermis; g", secondary wood ; s", second-
ary bast; fr, periderm. (AfterSxRASBURGER.)

148

BOTANY

PART I

originate as in the stem. In some plants wide parenchymatous rays
are formed by the cambium opposite the strands of primary xylem
(Fig. 171 B). A cross-section of a root in which the secondary growth
has continued for some years can scarcely be distinguished from a
cross-section of a stem ; by careful examination, however, the character-
istic strands of primary xylem can be recognised in the centre of the
root.

Repeated Formation of Cambium in Stems and Roots. —Deviations from the
usual type of secondary growth as found in most Gymnosperms and Dicotyledons

are met with in some cases.
These anomalous types are
characterised by differences in
the distribution and in the
activity of the cambium.

In some Cycadeae and cer-
tain species of Gnetum among
the Gymnosperms and in the
Chenopodiaceae, Amaranta-
ceae, Nyctaginaceae, Phyto-
laccaceae, and some other
families of Dicotyledons, the
first ring of cambium, which
arose in the usual way, ceases
to function after a time. A
new zone of cambium forms
usually in the pericycle, ie.
external to the bast, or else in
tissue derived from the earlier
cambium. The new cambium
forms bast externally and wood
internally, these tissues being

traversed by medullary rays. Its activity in turn comes to an end and its place
is taken by a new cambium formed outside this zone of bast. The process can be
repeated and leads to the production of concentric zones each composed of wood
and bast. This is seen, for example, in the transverse section of the stem of Mueuna
altissima, a liane belonging to the Papilionaceae which is represented in Fig. 172.
Such concentric zones of wood and bast are met with in some succulent roots
which persist for two or more vegetative periods. This is the case in the Beet
(Seta vulgaris), where the zones can be readily recognised with the naked eye on
cross-sections. They arise as described above, but, as in the case of the typical
secondary growth of other succulent roots, parenchymatous tissue which serves for
storage of reserve materials forms a large proportion of the newly-developed tissues.

3. The Wood. A. Kinds of Tissue and their Functions. — The con-
struction of the wood is complex, and in Dicotyledons it is usually com-
posed of three distinct types of tissue the walls of which are more or
less lignified. These are: (1) longitudinally-running strands of dead
VESSELS (Fig. 173 g, ty) ; (2) longitudinally-running strands of scleren-
chymatous fibres, WOOD-FIBRES (h), that are usually dead ; (3) STORAGE

FIG. 172. — Transverse section of the stem of Mueuna altis-
sima. 1, 2, 3, Successively -formed zones of wood;
1*. 2*, 3*, successively-formed zones of bast ; 3, 3* are
commencing to form within the pericycle. (f nat. size.
After SCHENCK.)

DIV. I

MORPHOLOGY

149

PARENCHYMA (hp), which forms longitudinally-running strands, and
in the medullary rays is also directed radially ; this constitutes the

WOOD PARENCHYMA and PARENCHYMA OF THE MEDULLARY RAYS.

Corresponding to this the wood serves (1) for water- conduction, (2)
to render the stems and roots rigid against pressure and bending, and
(3) for the storage of organic materials. The properties which make

ef hp

FIG. 173. — Tracheae, tracheides, wood-fibres, and wood parenchyma of a Dicotyledon with
transition-forms between the various elements. Diagrammatic, Explanation in text. (Modified
after STRASBURGER.)

wood such a valuable building material depend upon its natural
function as a mechanical tissue.

The various kinds of cells of which the wood is composed can be most readily
studied by treating wood with SCHULTZE'S macerating mixture (cf. p. 42).

The vessels are pitted or less commonly reticulately thickened.
The tracheae may be wide and composed of short segments, or narrow
and formed of more or less elongated cells (Fig. 173 g, tg}\ the
tracheides are narrow and elongated and serve both for conduction
and as mechanical tissue. The wood-fibres (h) are usually very long

150

BOTANY

PART I

and narrow, pointed at both ends, and with thick walls provided with
narrow oblique pits. The cells of the storage parenchyma (hp) are
rectangular and prismatic or are spindle-shaped ; they are usually
elongated in the direction of the long axis and have either thin or
thick walls with small, circular, simple pits. They contain abundant

reserve materials (starch, oil, or sugar).

Intercellular spaces only occur in the paren-

chymatous strands.

In many Leguminosae, in the Willow, Poplar,
and species of Ficus, the water-conducting elements
of the wood consists of tracheae only.

The tracheides and wood-fibres are frequently
more than 1 mm. in length and are considerably
longer than the cambial cells from which they arose.
This increased length, like the increased width of
the larger tracheae, is attained by sliding growth
(p. 48 ; -Fig. 174). In the formation of wood paren-
chyma the cambial cells undergo repeated transverse
divisions. The resulting parenchyma thus consists
of rows of cells, the origin of which from a cambial
cell is indicated by the row ending above and below
in a pointed cell (Fig. 173 hp}.

The walls between cells of the wood parenchyma
or medullary rays and the vessels have bordered
pits on the side towards the vessel only, while the
larger pits in the living cell have no borders ; such
pits, in contrast to those bordered on both sides,
are characterised by the absence of a torus from
the pit membrane. The walls separating vessels
and wood - fibres and those between the latter and
parenchyma cells are, on the other hand, usually
without pits.

In woods composed of vessels, wood-fibres, and
parenchyma there are frequently transition forms
between the typically - constructed elements, and
there is a corresponding lack of sharp distinction
as regards function. Narrow tracheae (Fig. 173 tg}
lead on to the tracheides (Fig. 173 gt, t). Narrow,
sharply-pointed tracheides (fibre tracheides, ft), the
function of which is mainly mechanical, form the
transition to the wood-fibres (h). Slightly thickened

wood-fibres which retain their living contents (ef) and are either without or with
transverse walls (gli) form the transition to the cells of the wood parenchyma (7^).

In the wood of Gymnosperms there are only tracheides with
typical bordered pits, together with some wood parenchyma and a
considerable amount of parenchyma of the medullary rays. The
division of labour is here less advanced, the same elements being
concerned with the mechanical and water - conducting functions.

y-^(

wood-fibres. /, In tangential
longitudinal section ; II, in
transverse section along the
dotted line in J. A, I, II, cells
in the young condition ; B, I, II,
after sliding growth has taken
place. (After ROTHERT.)

DIV. I

MORPHOLOGY

151

y belonging to the Magnoliaceae, is a Dicotyledon with wood
composed of tracheides and parenchyma only.

B. Arrangement of the Tissues in the Wood. — In the
Gymnosperms (Figs. 175-177) the wood of the stems and roots has
thus a relatively simple structure. The tracheides are arranged
in regular radial rows (Fig. 175 A), in correspondence with their
mode of origin. Since they increase in size mainly in the radial
direction, and hardly at all in the tangential and longitudinal

FIG. 175.— A, Transverse section of the wood of a Pine at the junction of two'annual rings. /, Spring
wood ; s, autumn wood ; t, bordered pit ; a, interposition of a new row of tracheides ; h, resin
canals ; m, medullary rays; g, limit of autumn wood, (x 240.) B, Part of a transverse
section of the stem of a Pine, s, Late wood ; c, cambium ; v, sieve-tubes ; p, bast parenchyma ;
fc, cell of bast parenchyma containing crystal ; cv, sieve-tubes, compressed and functionless ;
m, medullary ray. (x 240. After SCHEXCK.)

directions, they retain the same form as the cambial cells (Fig. 169).
They have large, circular, bordered pits frequently only upon their
radial walls : the pits are thus seen in surface view in radial sections
(Figs. 70 £,71 A).

In the wood of most Gyrnnosperms there is relatively little parenchyma. In
the Pines, Firs, and Larches parenchyma is found only around schizogenous resin-
canals which run longitudinally in the wood (Figs. 175 A, h ; 179 A), and are
connected by others which run radially in some of the broader medullary rays.
For this reason'considerable amounts of resin flow out from the wounded stem of a
Pine or Fir. In the other Conifers the wood parenchyma is limited to simple rows
of cells, the cavities of which may later become filled with resin.

152

BOTANY

PART I

The medullary rays in the wood of Gymnosperms are numerous,
and for the most part only one layer of cells broad (Figs. 175 m,
177 sm, tm; 179 ms). Every tracheide abuts in the course of its
length upon one or more of these medullary rays. The cells of the
medullary ray are elongated in the radial direction ; they contain
abundant starch and are associated with intercellular spaces (Fig.
177 i). They serve to transfer the products of assimilation, formed
in the leaves and conducted downwards in the bast, in a radial
direction into the wood of the stem or root, where storage takes

FIG. 176.— Radial section of a Pine stem, at the junction of the wood and bast, s, Autumn
tracheides ; t, bordered pits ; c, cambium ; v, sieve-tubes ; vt, sieve-pits ; ttm, tracheidal
medullary ray cells ; sm, medullary ray cells in the wood, containing starch ; sm', the same, in
the bast; em, medullary ray cells, with albuminous content, (x 240. After SCHENCK.)

place ; they also conduct water from the wood outwards. The
medullary rays are suited to perform these functions, since, as has
been seen, they extend into both the wood and the bast (Figs. 175 B,
176, 179). The intercellular spaces communicate with the intercellular
system of the cortex and allow of the necessary gaseous exchanges
between the living cells in the wood and the external atmosphere.

In certain Gyranosperms, especially the Pines, single rows of cells of the
medullary ray in the wood (usually the marginal rows) are tracheidal and without
living contents ; they are connected with one another and with the tracheides by
means of bordered pits (Fig. 176 tm). They are protected against compression by
the living turgescent cells of the medullary ray by means of special thickening of

DIV. I

MORPHOLOGY

153

their walls. These tracheidal cells facilitate the conduction of water in the radial
direction between the tracheides, which are only pitted on their radial walls. In
most other Conifers, in which such tracheidal elements in the medullary rays are
wanting, there are tangentially-placed bordered pits in the tracheides of the wood,
and these allow of the movement of water in
a radial direction. The parenchymatous cells
of the medullary rays of the wood are connected
with the tracheides by means of large pits
bordered on one side (Fig. 177 et).

Owing to climatic variations, the
cambial tissue of Gymnosperms, as of
most Dicotyledons, exhibits a periodical
activity which *is expressed by the for-
mation of ANNUAL RINGS (79) of growth
(Figs. 178, 179). In spring, when new
shoots are being formed, wider tracheal
elements are developed than in the follow-
ing seasons (Fig. 175^4). For this reason
a difference is perceptible between the
EARLY WOOD (spring wood), which is
composed of large elements especially
active in the conveyance of water (Fig.
175/), and the LATE WOOD (autumn
wood), consisting of narrow elements
which impart to a stem its necessary -;- > '^~<

rigidity (Figs. 175 A, s, 179). Through- ' vc -\

out the greater part of the temperate L/

zone, the formation of wood ceases in

the latter part Of AugUSt Until the follow- Fl°- m«- Tangential section of the
, , - autumn wood of a Pine, t, Bordered

ing spring, when the larger elements of

pit ; tm, tracheidal medullary ray cells;
sm, medullary ray cells containing
starch ; et, pit bordered only on one
side; i, intercellular space in the
medullary ray. (x , 240. After
SCHENCK.)

the spring wood are again developed.
Owing to the contrast in the structure of
the spring and the autumn wood, the
limits (Figs. 175 g, 179 i) between suc-
cessive annual rings of growth become
so sharply denned as to be visible even to the naked eye, and thus
serve as a means of computing the age of a plant. The limits
between the annual rings are less evident in the root, all the wood
resembling spring wood. The cambium of the root may remain active
throughout the winter and only pass into a resting condition at the
commencement of the new vegetative period.

In a stem or root that has undergone secondary thickening fewer annual rings
will be seen on the cross-section the nearer this is made to the growing point.
The older annual rings and the older layers of bast disappear in order of their age
as the tip is approached.

Under certain conditions the number of annual rings may exceed the number of
years of growth. When the leaves are destroyed by frost, caterpillars, or other

154

BOTANY

PART I

injurious influences, the buds destined for the succeeding spring may unfold, and
the formation of the new foliage brings about a second formation of spring wood.
On the other hand, woody plants that usually have definite annual rings may
exceptionally show a smaller number of rings than that corresponding to their
age, owing to the limits between some of the rings not being clearly marked. In
this way the number of rings on one
radius of the stem may be less than
when they are counted on another
radius.

The wood of the stems and
roots of Dicotyledons can be
readily distinguished from that
of a Gymnosperm even when
only slightly magnified (Figs.

FIG. 178. — Transverse section of a stem of
Tilia ulmifolia, in the fourth year of its
growth. pr,iPrimary cortex ; c, cambium
ring ; cr, bast ; pm, primary medullary
ray ; pm', expanded extremity of a primary
medullary ray ; sm, secondary medullary
ray ; g, limit of third year's wood. ( x 6.
After SCHENCK.)

FIG. 179. — Portion of a four-year-old stem of the
Pine, Pinus sylvestris, cut in winter, q, Transverse
view ; I, radial view ; t, tangential view ; /, spring
wood ; s, autumn wood ; m, medulla ; p, proto-
xylem ; 1, 2, 3, k, the four successive annual rings
of the wood ; i, junction of the wood of successive
years ; ms', ms"', ms, medullary rays in trans-
verse, radial, and tangential view; ms", radial
view of medullary rays in the bast ; c, cambium
ring ; b, bast ; h, resin canals ; br, bark, external
to the first periderm layer, and formed from
the primary cortex. ( x 6. After SCHENCK.)

180, 181, 182). Not only are wood-fibres and usually wide tracheae
present, in addition to tracheides and parenchyma, but the unequal
growth of the various component elements leads to a departure from
their original radial arrangement. In the spring wood there are
numbers of very wide vessels (Figs. 180, 181 m), while narrow
wood-fibres (/) and fibre tracheides (t) predominate in the autumn
wood.

In some Dicotyledons the annual rings are not distinct because the various
elements of the wood are nearly uniformly distributed in the season's growth.
This is the case in the Willow, and in the Wild Vine it may be impossible to count
the rings. In the woody plants of tropical regions, when there is no seasonal

DIV. I

MORPHOLOGY

155

interruption of growth, annual rings may also be wanting, but in many cases zones
resembling the annual rings occur.

The water-conducting elements of the most recently formed annual rings are
the only ones that are in direct connection with the leaves of the corresponding
period of vegetation. Since there is a sudden demand for a considerable amount
of water for transpiration when the leaves unfold in the spring, the provision of
conducting channels in the spring wood is readily comprehensible. In many
woody plants the foliage is not further increased during the summer, and the
cambium can therefore form mechanical tissue in the autumn wood.

FIG. 180.— Portion of a transverse section of the wood of Tilia -ulmifolia. m, Large pitted
vessel ; t, tracheides ; ?, wood-fibre ; p, wood parenchyma ; r, medullary ray. (x 540. After
STRASBURGEK.)

In spite of the variety in the structure of the wood of Dicotyledons
there are some constant features in the arrangement of the different
tissues. The vascular strands composed of tracheae and tracheides,
while they ramify in the radial and tangential directions, form
continuous longitudinal tracts from the roots to the finest tips of the
branches. Were this not so the needs of the shoot-system as regards
its water supply would not be met. Wood parenchyma (Figs. 180,
181 p), which is well developed in most dicotyledonous woods, also
forms longitudinal strands or layers which, however, end blindly
above and below. These form along with the medullary rays a
connected system of living cells. The vessels always stand in
connection with these living cells, being sometimes surrounded

156

BOTANY

PAKT I

by them and in other cases in contact with them on one side
(Fig. ISQp).

The wood parenchyma surrounds the vessel in Acacia, etc. ; it forms tangential
bands in which the vessels are embedded or with which they are in contact in

Walnut, Chestnut, Oak, etc. ; in some cases
it is limited to the outer side of the annual
ring.

The MEDULLARY RAYS (FigS. 178

pm, sm; 180, 181 r) resemble those of
the Gymnosperms in being radially-
placed bands of tissue, of greater or
less vertical height, and one or a
number of cells in breadth ; they may
be branched or unbranched (Fig. 182
tm, sm). They are continuous across
the cambium into the bast (Fig. 178).
The vascular strands are in contact
with them at places. The parenchyma
of the medullary rays thus connects
the parenchyma of the bast with that
of the wood, and unites all the living
tissue of the stem and root into a single
system. Assimilated material moving
downwards in the bast can thus pass
radially into the wood and be carried
in this for some distance upwards or
downwards, to be stored as starch in
the living parenchymatous cells. The
intercellular spaces, which accompany
the medullary rays and the strands

of TUia uimifoiia. m, Pitted vessel ; of wood parenchyma, allow of the
t, spiral tracheides ; P) wood paren- gaseous exchanges necessary for the

chynia ; I, wood-fibres ; r, medullary ? ' . •• /. . , n

rays, (x 160. After SCHENCK.) living elements of the WOOd.

The intervals between the strands

of vessels and of parenchyma and the medullary rays are occupied
by strands of wood-fibres (sclerenchyma).

The height and breadth of the medullary rays are most readily seen when they
are cut across in tangential longitudinal sections of the stem ; the rays then appear
spindle-shaped (Fig. 181 r). In most woods their size varies only within narrow
limits, but in others, such as the Oak and the Beech, the range is greater. In the
Oak there are medullary rays which are 1 mm. wide and 1 dm. high, while
numerous small rays occur between these. In the Poplar, Willow, and Box all
the rays are so small as to be with difficulty distinguished even with the aid of
a lens. In some lianes (e.g. Aristolochia] the primary rays are particularly wide
and high, and may extend for the length of a whole internode.

DIV. I

MORPHOLOGY

157

In Dicotyledons also, as is very well shown in the Willow, the marginal cells
of the medullary rays usually stand in relation to the adjacent water-conducting
elements by means of pits bordered on one side ; these living cells are higher
than those of the middle rows (Fig. 182 tm}. The latter are more extended
radially and have no special connection with the water-conducting elements.
They serve for the conduction and storage of'assimilated materials (Fig. 182 sra).

The parenchymatous cells of the medullary rays and of the wood which
adjoin the vessels take water from the latter and hand it on to the other living
cells. In spring, on the other hand, they pass a large part of the stored assimilated
material (especially glucose and small amounts of albuminous substances) into the
vessels, so that these substances can be quickly transported to the places where

FIG. 182.— A radial section of the wood of
Tilia ulmi folia, showing a small medul-
lary ray. g, Vessel ; I, wood fibres ; tm,
medullary ray cells in communication
with the water-channels by means of
pits ; sm, conducting cells of the
medullary ray. (x 240. After
SCHEXCK.)

FIG. 183. — Transverse section of a vessel from
the heart-wood of Robinia Pseudacacia, closed
by thy loses ; at a, a is shown the connection
between the thyloses and the cells from which
they have been formed. (x 300. After

SCHENCK.)

they are required. Owing to this, sugar and proteids can be demonstrated in the
vessels during the winter and early spring. These substances are also present in
the sap that exudes when holes are bored in the stems of Birch, Maple, and other
trees in the spring.

Grain of the Wood. — The technical value of certain woods is affected not
only by the colour but by the graining. This depends in the first place on the
arrangement of the annual rings and medullary rays, but also in many cases
(e.g. Hazel) upon a wavy course of the elements of the wood ; this may be brought
about by the crowded arrangement of lateral or adventitious buds or lateral roots,
or by the stimulus of wounding.

C. Subsequent Alterations of the Wood. — In the majority
of trees the living elements in the more centrally - placed older
portions of the woody mass die and the water channels become
stopped up, leading to the formation of what is known as the

158 BOTANY TART i

HEART-WOOD. Only the outer layer of the wood composed of the
more recently -formed annual rings thus contains living cells and
constitutes the SPLINT-WOOD. Eeserve materials can only be stored
in the splint-wood, and water-conduction is also limited to this, and
indeed to its outermost portion, since, as has been seen, it is only the
peripheral vessels that are in connection with the leaves and the
youngest lateral roots. The heart-wood serves only for strength.
Less commonly the whole of the wood persists as splint-wood (species
of Maple, Birch). The heart-wood is usually darker in colour than
the splint-wood and is also denser, harder, and stronger \ it is protected
against decay by impregnation with various substances. In other
cases the heart- wood is not distinct in colour from the splint-wood
and readily decays ; this leads to the hollow stems so often found in
old Willows.

The whitish yellow splint-wood contrasts most strongly with the heart-wood
when the latter is dark in colour ; thus in the Oak it is brown and in the Ebony
(Diospyros) black. The heart-wood appears to be more durable the darker it is.
Before their death the living cells of the wood, which lose their reserve materials,
usually form various organic substances, especially tannins, which impregnate the
walls of the surrounding elements, while resinous and gum-like products accumu-
late in the cavities. The tannins preserve the dead wood from decay, and their
oxidation products give its dark colour. The vessels are sometimes occluded by
accumulations of gum, and at other times by cells which fill up the lumen more
or less completely, and are spoken of as THYLOSES (80) (Fig. 183) ; they originate
by the adjoining living cells growing into the vessels through the pits, the
membrane of which they press inwards. Thyloses also form in wounded vessels
and occlude the lumen. Inorganic substances are not uncommonly deposited in
the heart-wood ; thus calcium carbonate occurs in the vessels of Ulmus campestris
and Fagus sylvatica, while amorphous silicic acid is deposited in the vessels of
Teak (Tectona grandis). Colouring matters are obtained from the heart- wood
of some trees, e.g. Haematoxylin from Haematoxylon campechianum L. (Campeachy-
wood, Logwood).

4. The Bast. A. Kinds of Tissue and their Functions.—

Three types of tissue can also be distinguished in the bast (Figs. 175
B, 184): (1) Longitudinally-running strands of SIEVE-TUBES (v) with,
in the Dicotyledons, COMPANION CELLS (c) ; (2) in many plants longi-
tudinal strands of SCLERENCHYMATOUS FIBRES (BAST FIBRES) that are
as a rule dead (Fig. 184 /) ; and (3) PARENCHYMA with intercellular
spaces arranged both longitudinally (p) and in the medullary rays
(Figs. 175 B, m; 184 r). In addition SECRETORY CELLS of various
kinds may be present containing crystals (k) or latex. The bast, like
the phloem of the vascular bundles, serves mainly to conduct the
products of assimilation. It also is of use for the storage of organic
substances and frequently as a mechanical tissue. In many plants
the sieve-tubes have oblique end-walls (Fig. 184 v*) ; they are thin-
walled and unlignified, contain proteids, and usually remain functional
only for a short period. The bast fibres are long and narrow and

DIV. I

MORPHOLOGY

159

have strongly -thickened walls that may be lignified or not. The
parenchymatous cells are elongated in the direction of the strand ;
they are living cells with abundant reserve materials and thin
unlignified walls.

At a certain distance from the cambium the sieve-plates become overlaid by
callus. During the vegetative period following their development the sieve-
tubes become empty and compressed together (Fig. 175 B, cv). Less often, as in
the Vine, the sieve-tubes remain functional for more than one year ; the callus is
removed when their activity is resumed. The rows of bast parenchyma cells
containing albuminous substances which are found in some Conifers undergo
disorganisation at the same time as the adjacent sieve-tubes ; the bast parenchyma

FIG. 184. — Portion of a transverse section of the bast of Tilia ulmifolia. v, Sieve-tubes ; v*,
sieve-plate ; c, companion cells ; t, cells of bast parenchyma containing crystals ; p, bast
parenchyma ; I, bast fibres ; r, medullary ray. (x 540. After STRASBURGER.)

cells which contain starch, on the other hand, continue living for years, and even
increase in size, while the sieve-tubes become compressed.

B. Arrangement of the Tissues in the Bast. — This re-
sembles the arrangement in the wood. The strands of sieve-tubes
form branched tracts in which the sieve- tubes have a continuous
course from the roots to the foliage. The sieve-tubes, and the
longitudinally-running bast parenchyma, are related at intervals to the
medullary rays (Fig. 179 ms"\ which have been seen to be the
continuation of the medullary rays of the wood. Thus the products
of assimilation from the foliage can either pass in the bast towards

160

BOTANY

PART I

the roots or through the medullary rays to be stored in the living
cells of the wood.

The different tissues of the bast are often arranged in very regular
tangential bands only interrupted by the medullary rays (Fig. 184).
The periodicity of the cambium is not, however, evident in the bast, and
there are no annual rings. The cambium continues to produce bast
after the formation of the autumn wood has ceased.

In the Lime, for example (Fig. 184), there is an alternation of zones of sieve-
tubes (v) with companion cells (c), starch-containing bast parenchyma (p), cells
containing crystals (k), bast fibres (I), and flattened cells of bast parenchyma (p),
followed again by sieve -tubes. The differences in the appearance of the bast of

cot

FIG. 185. — Transverse section of the outer part of a one-year-old twig of Pyrus cominunis made in
autumn. It shows the commencement of the formation of the periderm. p, Cork; pg,
phellogen ; pd, phelloderm ; col, collenchyma. The cork cells have their outer walls thickened
and have brown dead contents, (x 500. After SCHENCK.)

different woody plants are due to the greater or less diameter of the sieve-tubes,
the presence or absence of bast fibres, and to the mode of arrangement of the
various elements.

In the Pine and various other Abietineae, rows of cells with abundant
albuminous contents occur at the edges of the medullary rays (Fig. 176 em}. They
are in close contact with the sieve-tubes and connected with them by sieve-pits,
and become empty and compressed at the same time as the sieve-tubes. In
Dicotyledons the medullary rays in the bast are more simply constructed than in
the wood. The pitting of the cells of the medullary rays of Dicotyledons, which
connects them not only with the bast parenchyma but also with the companion
cells of the sieve-tubes, stands in relation to the taking up of assimilated material
as it is passing downwards.

Effect of the Secondary Thickening on the Tissues external to
the Cambial Ring. 1. Dilatation. — Since the cambium continues

DIV. I

MORPHOLOGY

161

to form wood to the inside, and bast to the outside, the stem or root

exhibits a secondary increase in thickness. Those permanent tissues

which are situated externally

to the cambial ring (the epi-

dermis, cortex, primary phloem,

and the bast) are naturally

affected by this. They are

tangentially stretched, com-

pressed, displaced, or torn ; they

may also grow in the tangential

direction (DILATATION). This

latter process^ is naturally

limited to the living cells of

the cortex, the phloem, and the

bast, including those of the

medullary rays ; in some woody

plants even the epidermal cells

take part in the dilatation (81).

All these cells may grow con-

siderably in the tangential direc-

tion and then become divided

by radial walls. In the bast

such growth is frequently very

marked in the case of the

medullary rays ; in the Lime

this leads to the formation of a

secondary meristem which gives

off rows of parenchymatous

cells to either side in the tan-

gential direction, so that the

medullary rays of the bast widen

year by year towards the OUtside FIG. 186. - Transverse section of the peripheral

(Fig. 178 pm). The sieve- tubes
and their companion cells, which
only remain functional for a short
time and then die, are com-
pressed along with the secretory
cells. The sclerenchymatous
cells of the cortex and bast,
which are usually non-living
elements, also take no part in
the dilatation.

tissues of the stem of Quercus sessiliflora. 1, 2, 3,
Successively formed layers of cork ; pr, primary
cortex, modified by subsequent growth ; in-
ternally to pc, pericycle; sc, sclerenchymatous
fibres from the ruptured ring of sclerenchy-
matous fibres of the pericycle ; s, subsequently
formed sclereides ; s1, sclereides, of secondary
growth ; er, bast fibres with accompanying crystal
cells ; fc, cells with aggregate crystals. All the
tissue external to the innermost layer of cork
is dead and discoloured and has become trans-
formed into bark, (x 225. After SCHENCK.)

When a hollow

cylinder of sclerenchyma is present in the cortex (Fig. 186 sc), it
becomes torn in the tangential direction ; the parenchymatous cells
grow into the spaces, and in many plants become transformed into
thick- walled stone cells (Fig. 186 s). Parenchyma cells, or groups

162 BOTANY

of them in the cortex and bast, may also be developed as scleren-
chymatous cells during the process of dilatation.

The epidermis may continue to expand for years in some species of Rose,
Acacia, Holly and Maple, and in the Mistletoe. The outer walls of the cells are
usually strongly thickened, and when ruptured on the surface become reinforced by
new layers of thickening deposited within.

2. Periderm. — As a rule, however, the epidermis does not take
part in the dilatation but is passively stretched and ultimately
ruptured. A new limiting tissue is thus required to protect the
underlying tissues from drying up. This arises as the CORK by the
activity of a special secondary meristem, situated at the periphery
of the organ (Fig. 18,5).

This CORK-CAMBIUM or PHELLOGEN is usually formed in the first
season, soon after, or even before, the commencement of secondary
growth. It may arise from the epidermis by tangential division of
its cells. More usually, however, it is formed from the layer of
cortex just below the epidermis, less commonly from a deeper layer
of the cortex or from the pericycle. The last case is the rule for
roots (Fig. 171 B, k). The meristem and all the products of its
activity are known collectively as the PERIDERM. The cells cut off
to the outer side become CORK-CELLS ; those developed to the inner
side become unsuberised cells with abundant chlorophyll, which round
off and are added to the cortex. With the formation of the periderm
the surface of the stem appears brown.

The cells formed on the inner side by the phellogen are termed collectively the

I'HELLODEKM.

The cork-cambium is as a rule a typical initial cambium (cf. p. 46), at least
when it forms both cork and phelloderm. An initial layer may, however, be wanting,
e.g. in many Monocotyledons ; in this case the permanent cells from which the
cork cambium proceeds divide into a number of cells which become cork-cells, and
the process is repeated in adjacent cells of the permanent tissue.

Periderm formation takes place at a later period in those plants in which the
epidermis continues to expand for years ; it is wanting only in the species of
Mistletoe.

True cork is wanting in Cryptogams, even in the Pteridophy tes. When protec-
tion is required its place may be taken by the impregnation of the cell walls with
a very resistant brown substance or by the addition of suberised lamellae to the
walls, that is the transformation of certain layers of cells into a cutis tissue (82).

As the result of the activity of the cork -cambium thick fissured
incrustations of cork may arise as in the Cork Oak from which bottle
cork is obtained. The stratification which this exhibits marks the
annual increments. In other cases a corky layer with a smooth outer
surface only a few layers of cells thick is formed (Figs. 59, 185).
This may allow of the secondary growth in thickness of the stem
continuing for a long time before it ultimately becomes torn and
is shed.

DIV.

* MORPHOLOGY 163

Bottle cork (Fig. 58) is formed of thick layers of soft wide cork-cells, interrupted
by thin layers of flat cork-cells marking the limits of the year's growth ; this can
be recognised in an ordinary cork. The pores filled with a loose powder which
penetrate the whole thickness of the cork in a radial direction are the lenticels
(cf. p. 59). The first layer of cork of the Cork Oak is artificially stripped off down
to the cork-cambium after fifteen years. A new cambium then forms a few cells
deeper which provides the cork of economic value ; this is removed every 6 to 8
years. Since such dead coatings of cork cannot keep pace with the dilatation of
the stem they gradually become fissured.

3. Formation of Bark. — All tissues external to the cork-cambium
are cut off from supplies of water and food materials and consequently
die. The dead tissue, including the layer of periderm, is termed BARK.
According to the depth at which the periderm is formed this may
include only the epidermis or a larger or smaller proportion of the
cortex. The first layer of cork-cambium in stems and roots usually
soon ceases to be active ; this does not happen in the Beech. A
new layer of cork forms deeper in the stem, and its activity in turn
comes to an end ; another layer forms still more deeply as shown in
Fig. 186. Ultimately the layers of cork are forming in secondary
tissues, in the living parenchyma of the zone of bast ; thus in old
stems all the living tissue external to the cambium is of secondary
origin and the bark includes dead secondary tissues. These are
emptied of their food material and contain only by-products of the
metabolism. The bark cannot follow the further increase in thickness
of the stem or root, but is cast off in scales or torn by longitudinal
fissures. It forms an even more complete protection than the cork
against both loss of water and overheating.

Since in the formation of bark the more external and oldest parts
of the bast are thus shed, the zone of bast remains relatively thin.
Mechanical tissues can only be permanent constituents of the stem
when formed internal to the cambial ring, i.e. in the wood.

If the layers of the secondary periderm constitute only limited areas of the cir-
cumference of the stem the bark will be thrown off in scales, as in the SCALY BARK of
the Pine, Oak. and Plane tree ; if, on the contrary, the periderm layers form com-
plete concentric rings, hollow cylinders of the cortical tissues are transformed into
the so-called KINGED BARK, such as is found in the Grape-vine, Cherry, Clematis,
and Honeysuckle.

When the bark peels off from the stem in layers this is not a purely mechanical
result ; it depends on an ABSCISS LAYER consisting of thin-walled cork-cells or
phelloid cells (cf. p. 59) which are formed between the other layers of cork with
thickened walls. These absciss layers are ruptured by the hygroscopic tensions set
up in the bark. Bark which is not easily detached becomes cracked by the con-
tinued growth in thickness of the stem, and has then the furrowed appearance so
characteristic of the majority of old tree-trunks.

The usual brown or red colour of bark, as in similarly coloured heart-wood,
is occasioned by the presence of tannins, to the preservative qualities of which
is due the great resistance of bark to the action of destructive agencies. The

164 BOTANY PART i

peculiar white colour of Birch-bark is caused by the presence of granules of
betulin (birch-resin) in the cells.

Healing of Wounds (83). — In the simplest cases among land plants the wounded
cells die and become brown and dry, while the walls of the underlying uninjured
cells become impregnated with protective substances and sometimes also form
suberised lamellae. In the case of larger wounds in the Phanerogams a cork-
cambium forming WOUND-CORK develops below these altered cells. Thus the leaf-
scars left by the fall of the leaves (p. 119) are in the first place protected by the
lignification and suberisation of the exposed cells, and later by the development of
a layer of cork that becomes continuous with that covering the stem. The open
ends of the vessels in the leaf-scar become occluded with wound-gum or thyloses
or both ; the ends of the sieve-tubes become compressed and lignified.

When young tissue is exposed by a wound, a formation of CALLUS usually takes
place. All the living cells which abut on the wound grow out and divide, becoming
closely approximated. The surface of the new growth may at once become corky
and thus afford the necessary protection. In most cases a cork -cambium forms
in the peripheral layers of the callus and gives rise to cork. In stems of Gymno-
sperms and Dicotyledons, wounds which extend into the wood become surrounded
and finally overcapped by an outgrowth of tissue arising from the exposed cambium.
While the callus tissue is still in process of gradually growing over the wounded
surface, an outer protective covering of cork is developed ; at the same time a new
cambium is formed within the callus by the differentiation of an inner layer of
cells, continuous with the cambium of the stem. When the margins of the over-
growing callus tissue ultimately meet and close together over the wound, the edges
of its cambium unite and form a complete cambial layer, continuing the cambium
of the stem over the surface of the wound. The wood formed by this new cambium
never coalesces with the old wood which is brown and dead. Accordingly, marks
cut deep enough to penetrate the wood are merely covered over by the new wood,
and may afterwards be found within the stem. In like manner, the ends of severed
branches may in time become so completely overgrown as to be concealed from
view. The growing points of adventitious shoots often arise in such masses of
callus. As the wood produced over wounds differs in structure from normal wood,
it has been distinguished as CALLUS WOOD. It consists at first of almost iso-
diametrical cells, which are, however, eventually followed by more elongated cell
forms. In the Cherry instead of normal wood-elements nests of thin- walled paren-
chymatous cells which undergo gummosis (p. 39) are produced on wounding
the cambium.

Restitution. — Secondary tissues often take part in the process of
restitution, i.e. the replacement of parts that have been lost.

In the more highly organised plants the direct replacement of lost parts is
extremely rare. It occurs most readily in embryonic organs, such as growing
points, when portions have been lost, and is most often found in seedlings. Thus in
seedling plants of Cyclamen even a severed leaf-blade has been found to be replaced.
As a rule, however, when regeneration processes are requisite in higher plants, and
the necessary preformed organs are not present in a resting or latent condition, the
older tissues return to the embryonic condition and give rise to new growing points
of shoots. Since this provision for the indirect replacement of lost parts exists in
plants, the fact that direct regeneration is far more frequent among animals than
plants is-readily comprehensible.

DIV. I .MORPHOLOGY 165

2. Adaptations of the Cormus to its Mode of Life
and to the Environment C84)

The form and structure of the corrnus are closely connected with
its mode of life, which in turn depends on the environment. Practi-
cally all plants thus appear adapted to the environments in which
they are usually found. The uniform physiognomy exhibited by the
plants of any locality, as well as the differences in the physiognomy
of the vegetation in localities which differ in climate, depend upon
this. The vegetative organs are therefore not typically constructed
in all cormophytes, but are frequently altered or metamorphosed in
a variety of ways. Very careful developmental or anatomical investiga-
tion may be required to show that the variously-constructed organs
of many cormophytes are derived by the metamorphosis of the three
primary organs, root, stem, and leaf, and to ascertain with which of
these any particular structure is really homologous. The external
form and the functional activity of mature organs may be very mis-
leading. One organ may assume the form and functions of another,
e.g. a stem resembling a leaf ; different primary organs may take on
the same forms in relation to performing the same functions and thus
be analogous but not homologous. As a rule, however, when all the
characters of an altered organ are taken into consideration, some will
leave no doubt as to its morphological origin.

The form of a plant and of its parts is determined in the first
place by its mode of nutrition. Thus there are striking and important
morphological differences between cormophytes which require only
inorganic food materials (AUTOTROPHIC PLANTS) and those which
require organic food (HETEROTROPHIC PLANTS).

A. Autotrophie Cormophytes

The green plants are structurally adapted to autotrophic life. The
typical features of the construction of autotrophic cormophytes have
been described above. The green cormophytes may exhibit consider-
able variety among themselves, for their structure is adapted to the
different features of the environments in which they occur.

Among the numerous factors in the differing external conditions
WATER and LIGHT have by far the greatest influence on the form of
green plants. This is evident, for the plant can only carry on its
life when sufficient water is available, and only when there is sufficient
light can it construct organic substance from inorganic food materials
and thus be autotrophic.

(a) Adaptations to the Humidity of the Environment

1. Water Plants. Hydrophytes (S5). — Special peculiarities in
structure are found in plants which live in water. These can

166 BOTANY PART i

absorb both water and nutrient salts and also the necessary gases
(carbon dioxide and oxygen) from the water by the whole surface
of their stems and leaves. In considering the conditions of life in
water it is essential to know the amounts of various gases which can be
dissolved and to contrast this with their presence in the atmosphere.
One litre of air contains about 210 c.cm. oxygen and 0'3 c.cm. of carbon
dioxide. In one litre of water at 20° C., on the other hand, there
can be dissolved only about 6 c.cm. oxygen, but 0'3 c.cm. carbon
dioxide. There is thus available for the submerged plant as much
carbon dioxide, or even somewhat more. There is, however, little
oxygen, especially in the case of still water, since the diffusion of
this gas in water is very slow.

Roots may be absent (Utricularia, Ceratophyllum, Wolffia) or
only serve to attach the plant to the soil. The shoot, on the other
hand, has become similar to a root, in that the thin walls of its

epidermal cells have a
very thin cuticle that
offers little hindrance
to the entrance of water.
The large surface ex-
posed by the fine sub-
division of the lamina
of the submerged leaves
(fiatrachium, Fig. 138,

PIG. 187.— Transverse section of the leaf of Zannichellia palustris. Utricularia, MyriOpliyl-

(x 146. After SCHENCK.) ium^ Ceratophyllum)

stands in relation to

the slowness of the diffusion of gases in water ; floating and
aerial leaves of water plants, on the other hand, are typically
formed (heterophylly, cf. p. 11 6). As regards their anatomy
the submerged leaves are characterised by the absence of stomata,
and usually of hairs from the epidermis, the cells of which
contain chlorophyll; the mesophyll has large intercellular spaces,
and consists of uniform parenchyma, .not showing the distinction
of palisade and spongy tissue. The leaves in transverse section
thus appear bilaterally symmetrical (Fig. 187). The feeble develop-
ment of water -conducting elements in the stems and leaves, and
the absence of secondary thickening, are related to the absence of
transpiration, and of active transport of water. The support afforded
by the surrounding water renders mechanical tissues unnecessary ;
the pulling forces exerted in quickly -flowing water are met by the
central position of the vascular bundle.

The great development of the intercellular spaces is a striking
feature of almost all aquatic and marsh plants. They are wide, and
form a regular system of air-filled chambers and passages, which are
separated by parenchymatous partitions, usually only one cell thick :

DIV.

, MORPHOLOGY

167

this is the case, for example, in the stems of Papyrus, Potamogeton,, etc.,
in the petioles of the Nymphaeaceae, and in the roots of Jussieua.
Such tissue is termed AEREXCHYMA. Since its wide air-passages
serve for the storage of air, and allow of ready diffusion of gases
within the body of the plant, the rapid transport of oxygen from
the assimilating green organs to the colourless organs greatly
facilitates respiration.

In some swamp plants, the subterranean organs of which are in swampy soil with
little oxygen, special organs are concerned with obtaining this gas ; respiratory

roots (PNEUMATOPHORES,

Fig. 188) grow erect from
the muddy soil, obtaining
oxygen from the air by len-
ticel - like PNEUMATHODES,
and conducting it by the
aerenchyma to the subter-
ranean parts. Such plants
are found among the Palms
and in the Mangroves of
tropical coasts, some of
which are also anchored to
the mud by a system of
aerial stilt-roots springing
from the shoots (Fig.
189) (84).

2. Land Plants. —

These usually obtain
water and nutrient salts
from the soil, and
oxygen and carbon
dioxide from the atmo-
sphere ; their aerial

shoots give off water in the form of vapour in the process of
transpiration.

A few plants of very moist habitats, especially the Hymenophyllaceae of
tropical forests, which can absorb water by the general surface, form an exception.
Some of them develop no roots but have a system of water-absorbing hairs on
their stems or leaves which considerably increase the absorbent surface.

The construction of land plants differs according to their occur-
rence in constantly moist localities, dry localities or climates, or
intermittently moist climates.

(a) Adaptations to constantly moist Habitats. Hygrophytes (S6).

—Terrestrial plants which inhabit situations in which the atmosphere

is permanently moist, such as many tropical shade plants, are spoken

of as HYGROPHILOUS or HYGROPHYTES. Like water plants they have

no need of arrangements to diminish transpiration but, on the

FIG. 188.— Respiratory roots of Sonneratia alba. (Reduced
from a figure in Vegetationsbtidern by JOH. SCHMIDT.)

168

BOTANY

PART I

contrary, require to facilitate the giving off of water from the aerial
shoots. Only in this way can a sufficiently active movement of

. ' water from the roots in the soil

to the organs above ground be
ensured to supply the requisite
quantity of nutrient salts. Many
hygrophytes, especially those that
inhabit the moistest situations,
resemble water plants in form and
structure.

Hygrophytes show a variety of ar-
rangements to favour transpiration such
as expanded thin leaf-blades, thin cuticle,
and the situation of the stomata on
exposed projections raised above the
general surface. There are also peculi-
arities in their leaves which, as STAHL
showed, tend to get rid of the water after
heavy rainfall as quickly as possible.
Thus a drawn-out tip to the leaf-blade
(DRIP-TIP) or waxy coatings rendering
the surface of the leaf unwettable
facilitates the shedding of water from
the leaf; while a velvety surface, due
to the presence of papillae, spreads drops

of water by capillary action into an extremely thin film which readily evaporates.
According to STAHL also the presence of pigments which absorb the rays of
light and heat falling on variegated leaves raise the temperature of the leaf and
maintain transpiration even in a saturated atmosphere. In guttation or the giving
off of drops of liquid water from water-excreting organs or HYDATHODES, some of
these plants have the means of giving off sufficient water when transpiration is com-
pletely stopped. These organs are glandular surfaces or hairs which secrete water,
or are special clefts in the epidermis through which water derived from the vascular
bundles is forced (cf. Fig. 131).

(b) Adaptations to physiologically dry Habitats or to dry
Climates. Xerophytes (84>87). Plants, the shoots of which are
exposed to dry air while they have difficulty in obtaining an adequate
or sufficiently rapid supply of water to make good the loss in trans-
piration, require arrangements to diminish the latter process. The
ordinary limitation of transpiration by closure of the stomata is not
sufficient in the case of plants of exceptionally dry habitats or
climates. Only a few cormophytes can withstand drying up, as do
many Lichens and Bryophyta (cf. p. 222), and most of them die when
wilting is carried far.

Plants with such arrangements to diminish the loss of water are
termed XEROPHILOUS or XEROPHYTES. They are recognisable by
their general habit. The morphological peculiarities which are

FIG. 189.— Stilt-roots in Rhizoplwra mucronata
in the Malay Archipelago. (After KARSTEN.)

DIV. I

3IORPHOLOGY

169

involved in arrangements to diminish transpiration are referred to
collectively as the xerophytic structure (XEROMORPHY). Desert
plants, the plants of dry rocks and many epiphytes, are naturally
extreme xerophytes (cf. p. 183).

It is, however, a striking fact that xerophytic structure is also met
with in plants of quite different modes of life, where it is not at first
sight comprehensible, e.g. in plants of high mountains or of high
latitudes, in many swamp plants, in plants of the sea-coast (HALO-
PHYTES) (Fig. 195), even when, as in the case of the Mangrove
vegetation of tropical coasts, they grow directly in the water, and
lastly in many trees of the tropical rain-forest. Though much is still
obscure regardipg this, it is safe to assume that the majority of these
plants are, at least
periodically, in danger
of losing more water
by transpiration than
they can make good by
absorption from the
soil. When they occur
in relatively moist soils
these appear to be more
or less physiologically
dry for the plants, i.e.,
to be such as to render
the absorption of water
difficult.

Both morphological FlQ igo.—Transverse section of the epidermis of Aloe nigricans.
and anatomical arrange- i, Inner, uncutinised thickening layer, (x 240. After

ments are concerned STRASBURGER.)
in diminishing trans-
piration. Some of these adaptations may at the same time be pro-
tective against strong insolation or overheating.

The following are anatomical features which serve to diminish
transpiration : thick epidermal cell walls and cuticle ; formation of
waxy and resinous coatings, and, in the case of stems and roots,
layers of cork ; reduction in the number of stomata ; narrowing of the
stomata and their occlusion by resin ; sinking of the stomata below
the general level of the epidermis, either singly (Fig. 190) or in
numbers in special flask-shaped depressions of the under side of the
leaf (e.g. Oleander), or the over-arching of the stomata by adjoining
cells so that they come to be situated in cavities protected from the
wind. Hairs, whether woolly, stellate, or scaly, which early become
filled with air and give the plants a whitish or grey appearance
(Edelweiss, Australian Proteaceae, Olive), may serve as a protection
against the sun's rays. On the other hand, evergreen leaves may be
small, leathery, and relatively poor in sap (e.g. sclerophyllous evergreen

170 BOTANY

PART I

plants of the Mediterranean region, such as the Laurel and Myrtle).
The small size of the intercellular spaces in the mesophyll is
characteristic of the leaves of well-marked sclerophylls (Fig. 193);
there is often no spongy tissue, but frequently several layers of
palisade cells beneath both upper and lower epidermis so that the
structure of the leaf becomes bilaterally symmetrical. Some xero-
phytes are independent of such protections against transpiration, since
their highly concentrated cell sap enables them to absorb water from
very dry soil (p. 228).

These anatomical arrangements are usually associated with
morphological peculiarities of the external form.

Many xerophytes with small leaves have the branches crowded
together to form a dense cushion (e.g. many Alpine plants, Fig. 191) :
not only is transpira-
tion checked by this,
but a protection
against too strong in-
solation is obtained.

A very effective
protection against
transpiration and
light is obtained by
the leaf surface being
placed vertically

FIG. IQl.—Baoulia mammillaria from New Zealand, showing the (Australian Acacias
cushion-like shape of the individual plant. (From SCHIMPER'S and MyrtaCCae) ; this
Plant-Geography.) ig of{en agsociated

with a reduction of

the lamina and a flattening of the petiole (PHYLLODES, Figs. 136, 192).
A similar position of the leaves is met with in some of our native
plants such as Lactuca scariola, the Compass Plant in which all the
leaves stand vertically and in the direction of north and south. Such
leaves avoid more or less completely the rays of the sun when this is
at its highest, and excessive heating and transpiration are thus
prevented.

Very commonly the leaf surface is reduced. This takes place in
the grasses of exposed situations by the mi-oiling of the upper surface
(Fig. 194). In the Ericaceae, Genisteae, Cupressaceae, and some
New Zealand species of Veronica (cf. also Fig. 195), it is effected by
reduction of the lamina, which is completely lost in Cactaceae, in tree-
like species of Euphorbia, and in some Asclepiadaceae. With the
reduction in the leaf-surface the assimilation of carbon is also
diminished, and a compensatory development of chlorophyll-containing
parenchyma takes place in the stems of such plants. The twigs of
the Broom (Sarothamnus scoparius), which bear only occasional leaves
that are soon shed, are elongated and green (sclerocaulous plants).

DIV. I

MORPHOLOGY

171

A striking modification is exhibited by shoots which only
develop reduced leaves, while the stems become flat and leaf-like and
assume the functions of leaves. Such leaf-like shoots are called
CLADODES or PHYLLOCLADES, and GOEBEL proposes to distinguish
those flattened shoots which have limited growth and specially leaf-
like appearance as phylloclades, and to term other flattened axes

cladodes. An instructive example of
such formations is furnished by Ruscus
aculeatus (Fig. 196), a small shrub of
the Mediterranean region whose stems
bear in the axils of their scale-like
leaves (/) broad sharp-pointed cladodes
(cl) which have altogether the appear-
ance of leaves. The flowers arise from
the upper surface of these cladodes,
in the axils of scale leaves. These
phylloclades afford a good example of
the analogy between organs. Their
appearance and functions are those

Fio. 192.— Acacia marginata, with vertically-
placed phyllodes. (From SCHIMPER'S Plant-
Geography.)

Fio. 193. — Transverse section of the leaf
of Capparis spinosa, var. aegyptiaca.
(x 40. SCHIMPER after VOLKENS.)

of leaves, but the morphological features mentioned above show that
they are shoots. A leaf-like flattening of the massive stems which
thus form cladodes is met with in the well-known Opuntias (Fig.
197), the bases of the branches remaining narrow.

The great development of sclerenchyma in the shoots of many
xerophytes is associated with the development of THORNS. Thus
spiny shoots, though not lacking in other regions, are characteristic
of many xerophytes of deserts and steppes. The thorns are lignified

172

BOTANY

PART I

and rigid pointed structures that may either be unbranched or
branched. They originate by the modification of leaves or parts of
leaves (LEAF-THORNS), of shoots (SHOOT-THORNS), or less commonly of
roots (ROOT-THORNS). In the Barberry (Berberis vulgaris) the leaves
borne on the main shoots are transformed into thorns which are
usually tri-radiate, while the lateral branches bearing the foliage
leaves stand in the axils of these thorns. In the Cactaceae also
(Fig. 197) the thorns arise from leaf-primordia. In Bobinia (Fig. 198),
and in the succulent species of Euphorbia, the two stipules of each leaf

FIG. 194. — Transverse sections of the leaf of Stipa capillata. The leaf above in the closed state,
the half leaf below expanded. U, lower surface, without stomata ; 0, upper surface, with
stomata (S) ; C, chlorophyllous mesophyll. (x 30. After KEENER VON MABILAUN.)

form thorns. Shoot-thorns are found in Prunus spinosa, Crataegus
oxycantha, and Gleditschia (Fig. 199). In Colktia cruciata all the shoots
are flattened and spiny, so that, in addition to serving as protective
structures, they perform the duties of the leaves which are soon lost.
The plant is an American shrub belonging to the Ehamnaceae and
grows in dry sunny situations. Root-thorns occur on the stems of
some Palms (e.g. Acanthorrhiza).

Xerophytes may have swollen or succulent leaves or stems. The
green, columnar, prismatic, cylindrical, or globular Euphorbiaceae and
Cactaceae are examples. Many xerophytes not merely utilise water
economically, but, when it is obtainable, store water in special tissues
against periods of need. When typically developed such water-storage

DIV. I

MORPHOLOGY

173

tissue consists of large colourless cells containing a large vacuole. Every

epidermal cell may be regarded

as storing water. In some cases,

however, the epidermal cells attain

a huge size and constitute a large

proportion of the leaf, or they

may be divided parallel to the

FIG. 196. — Twig of Ruscus aculeatus. /,
Leaf; d, cladode ; W, flower. (Nat.
size. After SCHENCK.)

Fin. 195. — Salicomia herlacea, a character-
istic halophyte. (From SCHIMPER'S
Pla nt- Geography. )

FIG. 107. — Opuntla manacantha, Haw., showing
flower and fruit. (J nat. size. After
SCHUMANN.)

upper surface and give rise to a many-layered water tissue (various

174

BOTANY

PART I

Piperaceae, Begoniaceae, species of Ficus, Tradescantia). The water-
storage tissue often has a more central position, and when largely

developed gives the char-
acter of succulent plants.

In rare cases the roots

are transformed for water-
storage (e.g. Oxalis tetra-

phylla). Leaf- succulents

are more common (e.g.

Sedum, Sempervivum,

Agave, Aloe, Mesembryan-

themum), while examples

of stem -succulents are

afforded by theCactaceae,

species of Euphorbia,

Stapelia, and other As-

clepiadaceae (Figs. 197,

200) and Kleinia among

the Compositae. The

columnar or spherical
Cactaceae are especially characteristic of arid regions in the new
world, while Euphorbias of similar habit take their place in the
eastern hemisphere. Similarity in the mode of life has thus

FIG. 198. — Part of stem and com-
pound leaf of Eobinia Pseud-
acacia, n, Stipules modified
into thorns ; g, pulvinus.
(£ nat. size. After SCHENCK.)

FIG. 199.— Stem-thornof
Gleditschia triacanthos.
(£ nat. size. After
SCHENCK.)

FIG. 200.— Plants with succulent steins, a, Stapelia grandijk>ra; ft, Cereus Pringlei ;
c, Euphorbia erosa. (| nat. size.)

brought about a corresponding form in widely distinct plants (cf. Fig.
200, a-c). This phenomenon of CONVERGENCE OF CHARACTERS is not
infrequent. In extreme cases the form of the stem or the leaf of
succulent plants may approach that of a sphere ; this, for a given

DIV. i MORPHOLOGY 175

volume, exposes the minimum surface and is thus advantageous in
diminishing transpiration. NOLL has estimated that the loss of water
from a spherical Cactus is 600 times less than from an equally heavy
plant of Aristolochia sipho.

Special interest attaches to some xerophytes in which the stems
as well as the leaves are reduced. Thus in the epiphytic orchid
Taeniophyllum (Fig. 201) the flattened green roots represent the
vegetative organs and carry on the functions of the leaves.

(e) Adaptations to periodically moist Climates. Tropophytes (84).
In some moist and warm regions of the tropics the climate remains
almost equally favourable to the growth of plants throughout the
year. Wherever, however, there is a marked periodicity in the
climate, with an alternation between a period favourable to the growth
of plants and a more or less injurious season, a corresponding

FIG. 201.— Taeniophyllum Zollingeri. A xerophytic orchid without leaf or stem but with green
flattened roots. (Xat. size. From SCHIMPER'S Plant-Geography, after WIESNER.)

PERIODICITY is found in the vital processes of the plants. The resting
period may be brought about either by dry ness or by the cold of a
winter season. Many of the plants living under such a climate show
differences in structure as compared with those of uniformly moist
tropical regions. Only those forms will succeed that can endure the
unfavourable period in one way or another. The main danger when
a cold winter alternates with a summer period lies in death from
lack of water during the physiologically dry cold period. This
danger does not threaten extreme xerophytes since they are suited
to dry habitats in the favourable period, but does affect plants the
structure of which is not xerophytic. Since the leaves as the organs
of transpiration are especially concerned, the shedding of the leaves
before the unfavourable period in the case of deciduous trees or the
dying down of the leafy shoots in many herbaceous plants is readily
understood. Further, the embryonic tissue, from which the lost parts
will be replaced at the commencement of the favourable season, may
require to be specially protected from the risk of desiccation.

176

BOTANY

PART I

The majority of our native cormophytic plants show such pro-
tective arrangements against an unfavourable season. In the favour-
able period they resemble hygrophytes in not requiring any special
protection against excessive transpiration, but they behave as extreme
xerophytes during the unfavourable period. Such plants are spoken
of as tropophytes.

The plants of periodically moist climates may be perennial woody
plants (trees and shrubs), perennial herbaceous plants, and annual
herbs. Each of these groups exhibits special means of protecting

the transpiring surface and the embryonic
tissues against drying.

1. The woody plants (with the ex-
ception of a few evergreens with xero-
phytic leaves, such as Ilex, and the Corii-
ferae) shed their leaves. The evergreen
and the deciduous forms alike contrast
with many tropical plants in protecting
the growing points within WINTER BUDS
(Fig. 202).

kits

Such buds are protected by the BUD-SCALES
which are in close contact. These may be derived
from entire primordial leaves that remain unseg-
mented but more commonly are formed from
the enlarged and modified leaf-base. The upper
portion of the leaf may scarcely develop or may
be recognisable at the tip of the bud-scale in a
more or less reduced condition. Thus in an
opening bud of the Horse Chestnut (Aesculus
FIG. 202,-Winter buds of the Beech Mppocastanum) in the spring the small leaf-
(Fagus silvatica). kns, Bud-scales, blade can be clearly seen in the case of the inner
(Nat. size. After SCHENCK.) bud-scales, while it is scarcely visible on the outer

scales. In other cases (e.g. in the Oak) the

bud-scales arise from stipules and thus also belong to the leaf-base. The base of
a subtending leaf may remain and cover the axillary bud after the rest of the leaf
is shed.

Bud-scales are thick, leathery, and hard, and usually brown in colour. They
are rendered even more effective in protecting the buds from desiccation by corky
or hairy coverings, by excretions of resin, gum, or mucilage, and by the enclosure
of air between the scales. Resin, etc., are usually secreted by peculiar, stalked,
glandular hairs or COLLETERS (cf. Fig. 56) ; in the case of the winter buds of many
trees (e.g. the Horse Chestnut) a mixture of gum and resin is thus secreted and,
becoming free on the bursting of the cuticle, flows between the scales, sticking
them together. When the buds open in the spring the bud-scales as a rule are
shed. The internodes between them being very short, the scales leave closely
crowded scars on the shoots by the help of which the growth of successive years
can be recognised.

2. The perennial herbs sacrifice not only the leaves but whole
leafy shoots with their buds, so far as these project in the air and are

DIV. I

MORPHOLOGY

177

exposed to the danger of drying. The buds that persist through the
winter may be just above the surface of the soil but protected by
fallen leaves or by snow, or they are subterranean and more effectively
protected both against desiccation and frost by the surrounding earth.

When the persisting buds are above ground they may be borne on creeping
surface shoots (e.g. Saxifraga, Stellaria holostea, Thymus, etc.), or are subterranean
shoots or rhizomes, as in the perennial rosette plants (Bellis, Taraxacum, Primula},
and in biennials which pass the winter with a rosette of leaves (e.g. Verbascum,
Digitalis, etc.). Here
also, as in the case of _ ,*_

geophytes, subterra- ff^^jj^

nean storage organs ^ i-..

may occur. *

In the GEO-
PHYTES (^ or
herbs with subter-
ranean buds which
persist through the
winter, the parts
which bear the buds
have a construction
corresponding to
their life in the soil.
They may be meta-
morphosed shoots
(RHIZOMES,TUBERS,
BULBS), or meta-
morphosed roots FIG. 203.— Part of a growing Potato plant, Solanum tuberosum. The
(ROOT-TUBERS).The whole plant has been developed from the dark -coloured tuber

buds that form new
shoots in the spring
require a supply of food materials, especially when they are placed
some distance below the surface. These food materials were constructed
in the preceding favourable season before the aerial shoots died down.
The subterranean organs, formed largely of storage parenchyma, are
naturally thick or swollen, to allow of the accumulation of reserve
materials. Such storage organs may be modified stems, leaves, or
roots. They become gradually depleted at the commencement of
the period favourable for vegetation, and then (except in the case of
many rhizomes) perish and are replaced.

(a) Root -stocks or RHIZOMES and STEM -TUBERS are colourless
subterranean shoots, the former being thick or relatively thin with
shorter or longer internodes (Figs. 123, 138), while the latter (e.g.
the Potato-tuber, Fig. 203) are greatly thickened. The leaves, as is
the rule in subterranean shoots, are developed as scales. The reserve
materials are stored in the stem, which is on this account usually

n the centre. (From nature, copied from one of BAILLON'S
illustrations, £ nat. size. After SCHENCK.)

178

BOTANY

swollen. By the presence of scale leaves, with their axillary buds,
the absence of a root-cap and the internal structure, a rhizome or
tuber can be distinguished from a root. While all transitions between
rhizomes and shoot-tubers exist, roots are usually absent from the
latter, while the rhizomes, which may grow horizontally, obliquely, or
vertically, and be branched or unbranched, as a rule bear roots.

In Fig. 138 is shown the root-stock of Solomon's Seal (Polygonatum multi-
florum), which has been already referred to as an example of a sympodium. At

c, d, and e are seen the scars of the aerial shoots
of the three preceding years ; at b may be seen
the base of the stem growing at the time the
rhizome was taken from the ground, while at
a is shown the bud of the next year's aerial
growth.

FIG. 204. — Longitudinal section
of Tulip bulb, Tulipa Gesneriana.
zk, Modified stem ; zs, scale leaves;
v, terminal bud ; Ic, rudiment of a
young bulb ; w, roots. (Nat.
size. After SCHENCK.)

FIG. 205.— Root- tubers of Dahlia variaUlis.' s, The
lower portions of the cut stems. (\ nat. size.
After SCHENCK,)

The tubers of the Potato, of Colchicum autumnale, and Crocus sativus, are
examples of stem-tubers. The tubers of the Potato (Fig. 203) or of the Jerusalem
Artichoke (Helianthus tuterosus) are subterranean shoots with swollen axes and
reduced leaves. They are formed from the ends of branched underground shoots
or runners (STOLONS), and thus develop at a little distance from the parent plant.
The so-called eyes on the outside of a potato, from which the next year's growth
arises, are in reality axillary buds, but the scales which represent their subtending
leaves can only be distinguished on very young tubers. The parent plant dies
after the formation of the tubers, and the reserve food stored in the tubers
nourishes the shoots which afterwards develop from the eyes.

In the Meadow Saffron new tubers arise from axillary buds near the base of the
modified shoot, but in the Crocus from buds near the apex. In consequence of this,

DIV. I

MORPHOLOGY

179

in the one case the new tubers appear to grow out of the side, and in the other
to spring from the top of the old tubers.

The Radish is also a tuberous stem, although only a portion of a single
internode, the hypocotyl of the seedling, is involved in the swelling.

(b) BULBS also belong to the class of subterranean metamorphosed
shoots. They represent a shortened shoot with a flattened discoid
stem (Fig. 204 zk), the fleshy thickened scale leaves (zs) of which are
filled with reserve food material. The aerial shoot of a bulb develops
from its axis, while new bulbs are formed from buds (k) in the axils
of the scale leaves.

(c) Other herbaceous perennials of periodically moist climates
(e.g. the Dahlia and many Orchids) form ROOT-TUBERS (Figs. 205, 206).
They resemble the stem-
tubers, though their true

nature can be recognised
by the presence of a root-
cap, the absence of leaves,
and the internal structure.
Tuberous main roots are
found in the Carrot and
the Beet, both of which are
biennial plants.

The morphology of the
tubers of the Orchidaceae is
peculiar. They are, to a great
extent, made up of a fleshy
swollen root terminating above FIG. 206.— Root-tuber of Orchis somewhat diagrammatically
in a shoot-bud. At their lower represented, t', The old root-tuber ; t", the young root-

•j. AT, j. -u -4.1 tuber ; &, floral shoot ; s, scale leaf with axillary bud, k,

extremity the tubers are either from ^ ^ new ^ ^ aris(m . ^ «££* ^

simple or palmately segmented. titious ^^ . ttj the scar on the old tuber ^^g its
In the adjoining figure (Fig. attachment to its parent shoot, (f nat. size.)
206) both an old (f) and a young

tuber (t"} are represented still united together. The older tuber has produced its
flowering shoot (b), and has begun to shrivel ; a bud, formed at the base of the
shoot, in the axil of a scale leaf (s), has already developed an adventitious root
which has given rise to the younger tuber. Roots of ordinary form arise from
the base of the stem above the tuber.

Many bulbs, tubers, and rhizomes occur at a SPECIFIC DEPTH,
which may, however, vary with the nature of the soil. Thus the
rhizome of Paris is placed at a depth of 2-5 cm., that of Arum at
6-12 cm., of Colchicum at 10-16 cm., and of Asparagus officinalis at
20-40 cm. The seeds of these plants germinate close to the surface
of the soil so that the subterranean shoots of the young plants must
penetrate more and more deeply into the earth. This may be effected
by the movements of growth of the stem (cf. p. 345) or by contractile
roots. Thus in Lilium (Fig. 207) all the roots are highly contractile ;
this is best seen in Fig. 207, 3, where the two lowest roots have con-

180

BOTANY

PART I

tracted strongly and so altered the position of the bulb that the higher
roots appear curved near their attachment. When the bulb has
reached the proper depth it is only drawn down each year to compen-
sate for the onward growth of the growing point. In other cases all
the roots are not contractile (Arum), or only one or a few contractile
roots are developed (Crocus, Gladiolus, Oxalis elegans). While the above

FIG. 207. — 1-k, Germination of Lilium martagon (reduced). The horizontal line marks the surface
of the soil ; the vertical line is graduated in centimetres. 1, Seedling attached to seed ;
2, plant at end of the second year ; 3, young plant still descending in the soil ; A, full-grown
plant at its normal depth. 5, Colchicum autumnale (somewhat reduced). The original
position of the tuber, which has been altered by the contraction of the roots, is shown by
the dotted outline. 6, Contracted root of Lilium. (x 6. After RIMBACH.)

examples are of lateral roots a similar result may be brought about by
the main root. Thus in some rosette plants the main root continues
to contract as secondary growth proceeds, so that the growing point of
the shoot is drawn down each year as much as it is raised by its own
growth, and the rosette of leaves remains pressed against the surface
of the soil (e.g. Gentiana lutea).

3. Annual herbs do not retain their vegetative organs during
the unfavourable season, which they pass safely in the form of dry
seeds.

DIV. I

MORPHOLOGY

181

The more uniformly favourable for vegetation the climate is
throughout the year (as in the moist tropical regions) the more do
evergreen woody plants preponderate, though evergreen perennial
herbs often with subterranean shoots are also present. On the other
hand, as the periodicity in the climate becomes more extreme, as in
the steppes with a long dry period or in climates with severe winters,
the percentage of tropophytes with marked protective arrangements
increases, while annual plants and geophytes preponderate among the
herbs.

(b) Adaptations for obtaining Light (84)

In the luxuriant vegetation produced under favourable climatic
conditions plants of large or gigantic size are met with. As mentioned

FIG. 208. — Portion of stem and leaf of the common Pea,
Pisum satimm. s, Stem ; ;i, stipules ; b, leaflets of the
compound leaf ; r, leaflets modified as tendrils ; a, floral
shoot. (£nat. size. After SCHENCK.)

FIG. 209.— Lathyrus Aphaca.
s, Stem ; «, stipules ;
b, leaf tendril. (£ nat.
size. After SCHENCK.)

above, the primeval tropical forest is composed of such large trees,
beneath the shade of which larger and smaller evergreen shrubs and
evergreen herbaceous plants live. The direct sunlight is in large
part intercepted by the foliage of the upper strata of this vegetation.

The cuticle of the leaves of tropical trees is often smooth and reflects a portion
of the light, giving rise to the characteristic glitter on the foliage in these regions.
This is possibly a protective arrangement against too great insolation. Other
adaptations to the same end were considered on p. 169.

The smaller SHADE PLANTS of the primeval forests and also of our
native woods have usually large leaves, and are adapted to the assimila-
tion of carbon dioxide in light of low intensity.

In the struggle for light two groups of cormophytes of character-
istic construction have emerged, in addition to trees and shrubs.

182

BOTANY

PART I

These are the CLIMBING PLANTS or LIANES and the EPIPHYTES. They
are specially characteristic of the tropics, though also represented in our
native flora.

1. Lianes OP Climbing1 Plants (s9). — These are able without great
expenditure of material in the construction of columnar stems to raise
their foliage above the shade of the forest and obtain stronger light.
Their slender stems climb by the help of the shoots, trunks, and
branches of other plants. It is the rope-like stems of lianes that
render many parts of the tropical jungle
almost impenetrable.

Climbing is effected in a number of
different ways. Some plants SCRAMBLE by
means of hooked lateral shoots, by hairs and
prickles, by a combination of these or by
means of thorns (e.g. Galium aparine, Roses,
Solanum dulcamara) ; others climb by means
of roots (ROOT-CLIMBERS, e.g. Ivy, many
Araceae), or by twining stems (TWINING
PLANTS, e.g. Hop, Scarlet Runner Bean) ; in
others tendrils are developed as special organs
of attachment (TENDRIL CLIMBERS). Tendrils
are slender, cylindrical, branched or unbranched
organs ; they are irritable to contact (cf. p.
353), and thus able to encircle supports to
which they attach the plant. They may be
METAMORPHOSED SHOOTS (stem-tendrils) as in
the Vine, the Wild Vine (Fig. 210), and the
Passion-flower. In other cases they are
TRANSFORMED LEAVES as in the Gourd, the
Cucumber, and Lathyrus aphaca (Fig. 209) ;
in the last example the functions of the leaf-
R, R, stem -tendrils, blade, which has become the tendril, have
(I nat. size. After NOLL.) been assumed by the expanded stipules. In
the Pea (Fig. 208) and many other cases the
uppermost leaflets of the pinnate leaf form a branched tendril.

In some forms of the Wild Vine (Parthenocissus quinquefolia) and in
other species of this genus such as P. tricuspidata (Fig. 210) the branched
tendrils bear attaching discs at their tips and can thus fasten the plant
to flat surfaces.

5 The great width of the vessels and sieve-tubes is characteristic of almost all
lianes. In tropical climbers anomalous secondary growth is frequently met with,
resulting in a subdivided woody mass that renders the long rope-like stems capable
of withstanding bending and twisting. A very peculiar structure is exhibited by
many lianes of the Bignoniaceae, the wood of which is cleft by radially-projecting
masses of bast (Fig. 212). The primary stem of the Bignoniaceae shows the
ordinary circular arrangement of the vascular bundles. Wood and bast are at first

no. 2io.-pa^enOC™

DIV. I

MORPHOLOGY

183

produced from the cambium ring in the usual manner, and an inner, normal wood
cylinder of AXIAL wood is formed. Such normally-formed axial wood cylinders
are common to many otherwise abnormally developed lianes. The cambium ring
of the Bignoniaceae, after performing for a time its normal functions, begins, at
certain points, to give off internally only a very small quantity of wood, and
externally a correspondingly large amount of bast. As a result of this, deep
wedges of irregularly - widening bast project into the outer so-called PERIAXIAL
WOOD (Fig. 212). The originally complete cambium becomes thereby broken into
longitudinal bands, which are broader in front of the projecting wood than at the
apices of the bast wedges. As the periaxial wood is always developed from the

FIG. 211.— Transverse section of
the stem of Serjania Laruot-
teuna. sk, Part of the rup-
tured sclerenchymatous ring
of the pericycle ; I and I*, bast
zones ; Ig, wood ; in, medulla,
(x 2. After STRASBURGER.)

FIG. 212. — Transverse section of the stem of one of the
Bignoniaceae. (Nat. size. After SCHENCK.)

inside and the wedges of bast from the outside of their respective cambium bands,
they extend past each other without forming any lateral connection. Several
woody cylinders are found in a number of tropical lianes belonging to Serjania
and Paullinia, which are genera of the Sapindaceae. This anomalous condition
arises from the unusual position of the primary vascular bundles, which are not
arranged in a circle but form a deeply -lobed ring ; so that, by the development
of interfascicular cambium, the cambium of each lobe is united into a separate
cambium ring. Each of these rings, independently of the others, then gives
rise to wood and bast (Fig. 211).

2. Epiphytes (90). — In another group of cormophytes the leaves
obtain stronger light by the plants being able to establish themselves
on the stems and branches of high trees instead of being rooted in the
ground. Such plants are termed epiphytes. Since the trees only
afford them support they may be replaced by inorganic substrata such
as rocks. The supply of the requisite water and nutrient salts will
evidently be a difficulty. Consequently special adaptations are found
to meet this ; in many epiphytes shoot-tubers serve for water storage

184

BOTANY

PART I

-st

(e.g. in the Orchidaceae), being replenished in moist periods, or there
may be adaptations to catch water more directly.

In our latitudes epiphytes are represented only by some Algae, Lichens, and
Bryophyta growing on the bark of trees. In the tropics, however, owing to the
humidity of the atmosphere and the frequent and heavy downpours of rain, many
cormophytes live as epiphytes. These plants, which belong especially to the
Pteridophyta and the families Orchidaceae, Bromeliaceae, and Araceae, have no

connection with the
water-supply in the soil.
Their difficulty in
obtaining water explains
why the tropical epi-
phytes are nearly all
well-marked xerophytes
(Fig. 201). They are
fastened by ATTACHING
ROOTS which are rela-
tively short, unbranched,
and negatively helio-
tropic, and grow round
and clasp the branch on
which the plant grows.
In addition to these
attaching roots, much
longer ABSORBENT ROOTS
are found in many
Araceae, hanging down
freely in the air without
branching until they
reach the soil. Most
epiphytes, however, are
dependent on the rain-
fall for their water-
supply, and frequently
have special arrange-
ments for collecting and

FIG. 213.— A, Dischidia liajflesiana with foliage leaves (Z)and pitcher
leaves (fc). B, Pitcher cut longitudinally ; o, opening ; st, stalk ;
w, root. (A about J, B about \ nat. size. After TREUB.)

retaining this. The
many-layered epidermis
of the aerial roots of
many Orchids, and of
various Aroids, under-
goes a peculiar modifica-
tion and forms the so-called VELAMEN, a parchment -like sheath surrounding
the roots, and often attaining a considerable thickness. The cells of this
enveloping sheath are generally provided with spiral or reticulate thickenings,
and lose their living contents. They then become filled with either water or
air, depending upon the amount of moisture contained in the surrounding
atmosphere. These root -envelopes absorb water like blotting-paper; when the
velamen is filled with water the underlying tissues impart a greenish tint to the
root ; but if it contains only air the root appears white. In other epiphytic
Orchidaceae and Araceae there are upwardly-directed roots forming a branched

DIV. I

MORPHOLOGY

185

network in which falling leaves, etc., are caught and transformed into hunms that
retains moisture. Among the Ferns also there are epiphytes which collect humus
by means of their leaves. In Asplenium nidus the leaves form a rosette enclosing
a funnel-shaped cavity above the summit of the stem, and humus accumulates in
this. In species of Polypodium and Platycerium special pocket-leaves and mantle-
leaves serve for the accumulation of humus and water. The transformation of
the leaves of the Asclepiadaceous plant Dischidia rafflesiana (Fig. 213) goes still
further. Some of the leaves form deep pitchers with narrow mouths in which
the water of transpiration becomes condensed ; roots which branch freely grow into
the pitchers, and obtain not only water but valuable nitrogenous substances. The
pitchers are, in fact, usually tenanted by colonies of ants, and their excreta and
remains form a source of food to the plant.

The American Bromeliaceae afford an extreme type of epiphytic plants in which
the roots may be •completely wanting (e.g. Tillandsia usneoides) or serve for
attachment only. The absorption of water is entirely by means of peculiar, expanded,
peltate hairs borne on the leaves. In many of these plants water collects in the
cavities formed by the closely associated leaf-bases, and the plants are spoken of as

CISTERN EPIPHYTES.

The so-called
referred to here

INSECTIVOROUS Or CARNIVOROUS PLANTS must be

T). These are plants provided with arrangements
for the capture and retention of small animals,
especially insects, and for the subsequent solu-
tion, digestion, and absorption of the captured
animals by means of enzymes. All these

FIG. 214. — Leaves of Drosera rotundifolia. That on the left with its partly incurved tentacles is
viewed from above, that on the right with expanded tentacles from the side, (x 4. After
DARWIN.)

insectivorous plants are provided with chlorophyll, and can thus live
autotrophically.

A great variety of contrivances for the capture of insects are made
use of by carnivorous plants. The leaves of Drosera are covered with

186

BOTANY

PART I

stalk-like outgrowths (" tentacles "), the glandular extremities of which
discharge a viscid acid secretion (Figs. 214, 215). A small insect
which comes in contact with any of the tentacles is caught in the
sticky secretion, and in its ineffectual struggle to free itself only
conies in contact with other glands and is even more securely held.
Excited by the contact stimulus, all the other
tentacles curve over and close upon the captured
insect, while the leaf-blade itself becomes concave
and surrounds the small prisoner more closely.
In Pinguicula it is the leaf margins which fold

FIG. 215. — Digestive
gland from Drosera
rotundifolia. ( x 60.
After STRASBURGER.)

FIG. 216. — Utricularia vulgaris. A, Part of leaf with several
bladders (x 2). B, Single pinnule of leaf with bladder (x 6).
C, Longitudinal section of a bladder ( x 28) ; v, valve ; a, wall
of bladder. (A, B, after SCHENCK; C, after GOEBEL.)

over any small insects that may be held by the minute epidermal glands.
In species of Utricularia (Fig. 216), which grow frequently in stagnant
water, small green bladders (metamorphosed leaf-segments) are found
on the dissected leaves. In each bladder there is a small quadrangular
opening closed by an elastic valve, which only opens inwards. Small
crustaceans can readily pass through this opening, but their egress is
prevented by the trap-like action of the valve, so that in one bladder as
many as ten or twelve crustaceans will often be found imprisoned at the
same time. The absorption of the disorganised animal remains seems to
be performed by forked hairs which spring from the walls of the bladder.
More remarkable still, and even better adapted for its purpose, is

PIV.

MORPHOLOGY

187

the mechanism exhibited by some exotic insectivorous plants. In

the case of Venus's fly-trap

(Dionaea), growing in the

peat-bogs of North Carolina,

the capture of insects is

effected by the sudden closing

together of the two halves

of the leaf, which are fringed

with long bristles. Fig. 217

shows a leaf of Dionaea in the

expanded condition, ready for

the capture of an jnsect. The

European water-plant Aldro-

* v „ • i £__.„-,] FIG. 217.— A leaf of Dionaea muscipula, showing the

has Similarly -formed sensitive bristles on its upper surface, which, in the
parts shaded, is also thickly beset with digestive
glands. ( x 4. After DARWIN.)

leaves.

FIG. 219.— Pitchered leaf of a
Nepenthes. A portion of the
lateral wall of the pitcher
has been removed in order to
show the digestive fluid (F),
excreted by the leaf -glands.
FIG. 218.— Nepenthes robusta. (£nat. size. After SCHEN.K.) (£ nat. size. After NOLL.)

In the case of other well-known insectivorous plants (Nepenthes,

188 BOTANY PART i

Gephalotus, Sarracenia, Darlingtonia), the traps for the capture of
animal food are formed by the leaves which grow in the shape of
pitchers (Figs. 218, 219). The leaves of Nepenthes, for example, in
the course of adaptation to the performance of their special function,
have acquired the form of a pitcher with a lid which is closed in
young leaves, but eventually opens. The pitcher, as GOEBEL has
shown, arises as a modification of th'e leaf -blade. At the same time
the leaf-base becomes expanded into a leaf-like body, while the petiole
between the two parts sometimes fulfils the office of a tendril. These
trap-like receptacles are partially filled with a watery fluid excreted
from glands on their inner surfaces. Enticed by secretions of honey
to the rim of the pitcher (in the case of Nepenthes), and then slipping
on the extraordinarily smooth surface below the margin, or guided by
the downwardly-directed hairs, insects and other small animals fall
into the fluid.

B. Heterotrophie Cormophytes (92)

The green cbrmophytes utilise the light and by means of their
chlorophyll construct organic substance from carbon dioxide and
water ; they also require to transpire in order to accumulate the
nutrient salts from the soil in sufficient amount. Besides these forms
others, which obtain some or all of their organic substance directly
from the environment, are met with among cormophytes just as they
occur among the thalloid plants. They do not depend upon light
or transpiration, and frequently live at the expense of other living
organisms as PARASITES. The peculiar form of these plants and the
contrast they present to the green cormophytes are related to their
special mode of nutrition. From the changes in their external appear-
ance it is evident how far-reaching is the influence exercised by the
chlorophyll. With the diminution or complete disappearance of
chlorophyll, and consequent adoption of a dependent mode of life,
the development of large leaf -surf aces, so especially fitted for the
work of assimilation and transpiration, is discontinued. The leaves
shrink to insignificant scales, or are completely wanting. The stems
also are greatly reduced and, like the leaves, have a yellow instead
of a green colour. Since there is no active transpiration the roots
in many forms are reduced. Consequently the xylem portion of the
vascular bundle remains weak, and secondary wood is feebly developed.
In contrast to these processes of reduction resulting from a cessation
of assimilation, there is the newly-developed power in the case of
parasites to penetrate other living organisms and to deprive them of
their assimilated products.

.Many exotic parasitic plants, especially the Eafflesiaceae, have
become so completely transformed by their parasitic mode of life that
they develop no apparent vegetative body at all, and do not show the

DIV. i MORPHOLOGY 189

characteristic segmentation of cormophytic plants, but grow altogether
within their host plant, whence they send out at intervals their extra-
ordinary flowers. In the case of Pilostyles, a parasite which lives on
some shrubby Leguminosae, the whole vegetative body is broken up
into filaments of cells which penetrate the host plant like the mycelium

FIG. 220. —Branch of a leguminous plant from the surface of which the flowers of a parasitic
plant (Pilostyles Ulei, Solms) are protruding. (From GOEBEL'S Organography.)

of a fungus. The flowers alone become visible and protrude from the
stems and leaf-stalks of the host plant (Fig. 220). The largest known
flower, which attains a diameter of 1 metre, is that of the Sumatran
parasitic plant Rafflesia Arnoldi ; it is seated immediately on the roots
of its host plant, which is a species of Cissus.

Cuscuta europea, (Fig. 221), a plant belonging to the family of the Convolvu-
laceae, may be cited as an example of a parasitic Phanerogam. Although, owing to
the possession of chlorophyll, it seems to some extent to resemble normally'assimi-

190

BOTANY

PART I

lating plants, the amount of chlorophyll present is in reality so small that it is
evident that Cuscuta (Dodder) affords an example of a very complete parasite.

The embryonic Ouscula plantlet, coiled up in the seeds, pushes up from the
ground in the spring, but even then it makes no use of its cotyledons as a means
of nourishment ; they always remain in an undeveloped condition (Fig. 221 at the
right). Nor does any underground root-system develop from the young rootlet,

PIG. 221.— Cuscuta europaea. On the right, germinating seedlings. .In the middle, a plant of
Cuscuta parasitic on a Willow- twig ; b, reduced leaves ; Bl, flower-clusters. On the left, cross-
section of the host plant W, showing haustoria H of the parasite Cus, penetrating the cortical
parenchyma and in intimate contact with the xylem v and the phloem c of the vascular
bundles ; s, displaced cap of sheathing sclerenchyma. (After NOLL.)

which soon dies off. The seedling becomes at once drawn out into a long
thin filament, the free end of which moves in wide circles, and so inevitably
discovers any plant, available as a host, that may be growing within its reach.
In case its search for a host plant is unsuccessful, the seedling is still able to creep
a short distance farther at the expense of the nourishing matter drawn from the
other extremity of the filament, which then dies off (t) as the growing extremity
lengthens. If the free end, in the course of its circling movements, comes

DIV. I

MORPHOLOGY

191

ultimately into contact with, a suitable host plant, such as, for example, the

stem of a Nettle or a young Willow shoot (Fig. 221 in the centre), it twines

closely about it like a climbing plant. Papillose protuberances of the epidermis

are developed on the side of the parasitic stem in contact with the host plant,

and pierce the tissue of the host. If the conditions are favourable, these PRE-

HAUSTORIA are soon followed by special organs of absorption, the HAUSTORIA (H).

These arise from the internal tissues of the parasite, and possess, in a marked

degree, the capability of penetrating to a considerable depth into the body

of the host plant. They invade the tissues of the host, apparently without

difficulty, and fasten themselves closely upon its vascular bundles, while single

hypha-like filaments produced from the main part of the haustoria penetrate the soft

parenchyma and absorb nourishment from the cells.

A direct connection is formed between the xylem and

phloem portions of tbe bundles of the host plant and

the conducting system of the parasite, for in the

thin- walled tissue of the haustoria there now develop

both wood and sieve-tube elements, which connect

the corresponding elements of the host with those of

the parasitic stem (Fig. 221 at the left). Like an

actual lateral organ of the host plant, the parasite

draws its transpiration water from the xylem, and

its plastic nutrient matter from the phloem of its

host.

The seeds of Orobanche (Broom rape), another
parasite, only germinate when in contact with the
roots of the host plant ; only its haustoria penetrate
the roots, and its light yellow, reddish-brown, or
amethyst - coloured flower -shoot appears above the
surface of the ground. Orobanche (Fig. 764), like Cus-
cuta, contains a small amount of chlorophyll. Both
are dreaded pests ; they inflict serious damage upon
cultivated plants, and are difficult to exterminate.

A similar appearance to Orobanche is presented by
some plants which grow in the humus soil of woods,
and are, therefore, not at first sight regarded as para-
sites: certain Orchids (Neottia, Coralliorrhiza, Epipogori] and Monotropa. The
absence of chlorophyll, the reduction of the leaves to scales, and (in Coralliorrhiza]
the absence of roots also (cf. Fig. 222), are indications that these plants obtain
organic material from without. They cannot themselves directly utilise the humus,
but fungi, which obtain food from this, are harboured in their subterranean parts
as a MYCORRHIZA. A proportion of the fungal hyphae is later digested »by the
plant. These cormophytes are thus in a sense parasitic on the fungi of the humus.

In contrast to these parasites, which have come to be almost entirely dependent
on other plants for their nourishment, there are others which, to judge by
external appearance, seem to have a high degree of independence, since they
possess large green leaves and are capable of assimilation. They are, however,
parasitic, since they can only develop normally, when their roots are connected
by means of haustoria with the roots of other plants ; they are spoken of as
PARTIAL PARASITES. Thesium belonging to the Santalaceae, and the following
genera of the Rhinanthaceae, PJtinanthus, Euphrasia, Pedicularis, Bartsia, Alelam-
pyrum and Tozzia, may be mentioned as examples ; in Tozzia the parasitism is
especially well marked in the earliest developmental stages.

FIG. 222.— Rhizome of Corallor-
rhiza innata. a, Floral shoot ;
6, rudiments of new rhizome
branches. (Nat. size. After
SCHACHT.)

192 BOTANY PART i

The Mistletoe (Fiscum album), belonging to the Loranthaceae as do many
similarly parasitic exotic forms, possesses good-sized leaves, but reduced roots;
it is so well provided with chlorophyll as to be able to manufacture all the carbo-
hydrates it requires.

II. Organs of Reproduction (93)

A. Significance of Reproduction to the Organism. — A natural
or an accidental death is the end of every organism. For the mainten-
ance of living beings reproduction is thus as essential as nutrition.
The main feature of reproduction lies in portions of an individual
continuing after its death, with the power of developing into new
individuals. On account of the possibility of accidental death, repro-
duction takes place before this occurs naturally, and usually involves
the formation of special germs, which separate from the parent plant
and, repeating the development of this, grow into new individuals.

In most plants a division of labour is apparent between the vegeta-
tive and reproductive organs. This becomes more striking in the
more highly organised forms, in which an increasing number of parts
co-operate in reproduction.

B. General Properties of the Germs. — The construction of the
germs, as in the case of the vegetative organs, is closely connected
with the purposes they have to serve.

The small size of most reproductive bodies, in comparison to
the vegetative organs, is characteristic. The parent plant can thus*
produce numerous germs without excessive expenditure of material,
while at the same time the distribution of the germs is facilitated.

The object of reproduction is not merely the production of a new
individual in place of the parent, but an increase in the number of
individuals. Since the majority of the germs may not meet with
favourable conditions for their germination and growth, and a large
number will perish before they can in turn reproduce, the pro-
duction of only a single germ would result in the speedy extinction
of the species. An apparently prodigal production of germs is thus
the rule. A cap-fungus or a fern may form millions of spores ; a
poplar tree, according to BESSEY, may ripen twenty-eight million
seeds annually.

Provision is further necessary for the separation of the germs
from the parent and their dispersal widely from it. In the immediate
neighbourhood there may not be the conditions for germination, or
there may be no room for the development of the progeny.

Lastly, it is necessary for the germs to be provided with reserve
food materials from the parent organism, in order that their develop-
ment, until they are able to nourish themselves, should be ensured.

Frequently the reproductive bodies serve to carry the organism
over cold or dry periods that are unfavourable to active life. They

DIV. I

MORPHOLOGY 193

pass into a resting condition (p. 305), in which they are more
resistant to injurious influences (desiccation, frost, heat). Such germs
are usually thick- walled, and only germinate on the return of
favourable conditions.

C. Types of Reproductive Bodies. — The germs which can develop
into plant bodies composed of many cells may themselves be
unicellular (spores) or multicellular (gemmae and seeds). Both kinds
may be produced irregularly on the plant, or be restricted to definite
regions, which are specially constructed for reproduction, and exhibit
great variety. These differences are of primary importance for the
division of plants into classes, orders, families, etc. Two types of
reproduction are ^ readily distinguished in plants of nearly all the
classes of the vegetable kingdom.

In the first type, cells or multicellular bodies are formed which can
develop into a new independent individual on their separation
from the parent, either at once or after a period of rest. This
kind of reproduction is termed VEGETATIVE, ASEXUAL, or MONO-
GENETIC.

In SEXUAL REPRODUCTION, the second of the two modes of
reproduction, two kinds of reproductive cells, each of which carries
the characters of the organism producing it, are formed, but
neither is directly capable of further development, and both perish
in a very short time, unless opportunity is given for their fusion with
each other. Not until the one cell has fused with the other cell does
the product acquire the capacity of development and growth. This
mode of reproduction is termed SEXUAL or DIGENETIC reproduction.

Most plants have both methods of reproduction. Sexual repro-
duction is wanting only in the lowest groups (the Bacteria, Cyano-
phyceae, and some Algae and Fungi). Some plants have several
methods of asexual reproduction.

In certain exceptional cases a sexual cell may proceed to develop
further without fertilisation. This is termed PARTHENOGENESIS (94).
This has been found in the vegetable kingdom in Cham crinita, one of the
Algae, and in the development of the embryo from the unfertilised ovum
in a number of families of higher plants (Compositae, Ranunculaceae,
Rosiflorae, Thymeleaceae, Urticaceae), and in the Marsiliaceae.

The process of fertilisation of sexual cells may, in particular cases, be replaced
by the fusion of the nuclei of adjoining vegetative cells (95). This is the case in the
prothallium of certain cultivated forms of Ferns (e.g. of Dryopteris (Lastraea) and
Athyrium). The product of this fusion effects the reproduction, the sexual organs
of the prothallium being reduced.

D. Alternation of Generations (°6). — In plants there is frequently
an alternation of two generations differing in their modes of repro-
duction ; these may be morphologically distinct and independent
individuals. The life-history of such a plant is thus composed of

194 BOTANY PART i

two kinds of individuals, which regularly alternate with one another,
are frequently very different in form and structure, and bear different
reproductive organs. The reproduction of the one generation (sporo-
phyte) is asexual ; that of the other (gametophyte) is sexual. The
Fern may be taken as a typical example. The leafy fern plant is
the sporophyte, and produces only asexual spores. The spore on
being shed does not grow into a new fern plant, but into a small
thalloid structure .known as the pro thallium (Fig. 97), which is
the gametophyte, and reproduces sexually. The fertilised egg-cell
develops into a leafy fern plant. The reproductive cells of the one
generation give rise to the other generation, and there is thus a
regular alternation of the sporophyte and gametophyte. The two
generations may, however, as in the case of the Brown Alga, Dictyota,
resemble one another.

Frequently the two generations are not represented by inde-
pendent individuals, but the one remains permanently connected to

the other like a parasite on its host plant.
Careful investigation may then be required
to establish the existence of an alternation
of generations. This is the case for the
Bryophyta and the Seed-plants.

Both generations may be able to reproduce
their like by vegetative reproduction. Multicellular
gemmae formed on the prothalli of some ferns grow
into new prothalli ; on the fern plant bulbils,
which grow into new leafy plants, may be
produced.

1. Multiplication by Multicellular
Vegetative Bodies (Budding)

This occurs in many Bryophyta, e.g. in
Marchantia, where the gemmae are formed
in special receptacles on the thallus (Figs.
444, 445). It is also widely spread in
the form of budding in Pteridophyta and

FIG. 223.— Shoot of Dentaria bulbi- Phanerogams.

/era, bearing bulbils, br. (Nat.

size. After SCHENCK.) Specially-formed lateral shoots serving to repro-

duce the plant are seen in the runners or stolons

produced above or below ground by many plants. The RUNNERS of the Strawberry
are slender cylindrical branches from the axils of the leaves of the rosette ; they
root from the terminal bud, which becomes independent by the subsequent decay
of the runner. Many BULBS and TUBERS serve for reproduction in the higher plants,
as do also BULBILS (Fig. 223) and the winter buds which become detached as the
HIBERNACULA of a number of aquatic plants (e.g. Hydrocharis, Stratiotes}.

Buds may also arise in places where no growing points are normally present ;
they are then adventitious. Such buds are most commonly found on leaves,

DIV. i MORPHOLOGY 195

sometimes on the leaf-blade, e.g. in the notches of the leaf margin in Bryophyllum,
and on the leaves of Cardamine pratensis. The leaves of Begonia, Drosera, etc.,
only produce buds after they have been separated from the plant.

Many herbaceous perennials, without forming special organs of vegetative repro-
duction, increase in number of individuals by the decay of the older portions
of their branched rhizomes isolating the branches. Among Sea-weeds also the
mechanical action of the surf may separate portions of the thallus which can grow
into new tlialli. Caulerpa is propagated in this fashion.

2. The Formation of Reproductive Cells

(a) Asexual Reproductive Cells (Spores). — Many unicellular
Thallophyta (Flagellata, Bacteria, Cyanophyceae, Diatomeae) are
multiplied vegetatively by dividing into two, the daughter cells
separating from one another. In others, such as the Protococcaceae,
the protoplast within its wall divides into several or many daughter
protoplasts ; these separate from one another and emerge from the
parent cell through a pore or split in the cell wall. The unicellular
organism in these cases has at the period of reproduction become
converted into a receptacle containing the germ cells, or a SPORAN-
GIUM ; the germ cells which give rise to daughter organisms may be
termed ENDOSPORES or SPORANGIAL SPORES.

Among the multicellular Thallophytes simply-organised forms are
met with that might be regarded as cell colonies, in which the body
sometimes dissociates into the individual cells ; these then serve for
vegetative multiplication. In other forms the protoplasts of all the
cells, usually after preliminary division into daughter protoplasts,
emerge at the period of reproduction from the cells which have thus
become sporangia.

The more highly organised multicellular Thallophyta exhibit a
division of labour, only some portions or cells, which often have a
definite structure and position on the thallus, producing asexual
reproductive cells. Such spore-producing parts are often united in
numbers to form fructifications of more complex structure.

Thus in many Fungi the hyphae concerned in reproduction become associated
within the soil into more or less massive and variously-shaped FRUCTIFICATIONS
which later emerge to the surface.

The mode of origin of the spores is similar in the higher and
lower forms. In many Fungi germ cells are isolated by budding and
constriction from certain hyphae as EXOSPORES or CONIDIOSPORES
(Fig. 224). In other Fungi and in the majority of the Algae the
asexual cells originate as ENDOSPORES or SPORANGIAL SPORES from
the protoplasts of certain cells (SPORANGIA), and emerge through
openings in the wall of this (Figs. 225, 231 sp).

The asexual spores of the Thallophyta are in part adapted to
distribution by means of water, as in the case of many sporangial
spores of Algae and Fungi. These spores are naked, without a cell

196

BOTANY

PART I

wall, and as a rule able to move through the water by the aid of
cilia (Figs. 225, 229 A). They are termed SWARM SPORES or ZOO-
SPORES, and the receptacles in which they are formed are spoken of
as ZOOSPORANGIA (Green and Brown Algae, some Phycomycetes).

The spores in other Thallophyta are adapted to dispersal by
wind. Examples are afforded by many sporangial spores and all
conidiospores of the Fungi. They are very small and light, sur-
rounded by thick walls and resistant to drying. Such spores are
usually produced by organs which are exposed to the air ; in Fungi
living in or on solid substrata
they may be borne on aerial
hyphae (Fig. 224). They are
thus borne on CONIDIOPHORES or

SPORANGIOPHORES Or On FRUCTI-
FICATIONS.

FIG. 224.— Conidiophore of Aspergillus
herbariorum. (x 540. After KNY.)

FIG. 225. — Saprolegniamixta. Sporangium from
which the biciliate zoospores (s2) are escap-
ing. (After G. KLEBS.)

In the Bryophyta, Pteridophyta, and Spermatophyta the asexual
cells are always developed as endospores in special sporangia of more
complicated structure than in the Thallophyta. These sporangia are
multicellular structures, one or more outer layers of cells forming the
wall, and the enclosed cells constituting the sporogenous tissue
(Fig. 226 sg). When ripe, the sporangia have usually special arrange-
ments in the wall for opening and shedding the small and light
spores, which may be dispersed by wind or (in the case of many
Spermatophytes) by animals. The spores are always surrounded by
cell walls.

The spore capsules or SPOROGONIA of the Bryophyta attain the
most complicated structure. They are as a rule stalked and are
situated on the thallus or at the ends of leafy branches. The sporo-

D1V, I

MORPHOLOGY

197

gonium is not, as appears at first sight, a member of the moss-plant,
but lives on this like a parasite. It is, in fact, the spore-bearing
generation (sporophyte) which remains permanently attached to the
moss-plant (gametophyte).

In the Pteridophyta, on the other hand, the leafy plant is the
sporophyte and bears small and inconspicuous sporangia, usually on
leaves which are termed SPOROPHYLLS. These may resemble the
foliage leaves, but there is often a division of labour between the
sporophylls and the foliage leaves. The former are devoted mainly
or entirely to the production of sporangia and, therefore, differ from
the foliage leaves in the lack of expanded green surfaces. The
sporophylls are often associated in numbers at the ends of branches of

FIG. 226. — Diagram of the
sporangium of a Pterido-
phyte, the sporogenous
tissue (sgr) being enclosed
by a sterile wall.

FIG. 227. — Flower of Paeonia peregrina. k, Calyx ;
c, corolla ; a, stamens ; g, carpels. The nearer
sepals, petals, and stamens are removed to show the
pistil formed of two free carpels. (£ nat. size.
After SCHENCK.)

limited growth, as in Equisetum and Lycopodium (cf. Figs. 486, 491).
These differ in appearance from the vegetative shoots and die off
after they have served for reproduction. They are known as CONES
or FLOWERS. THE SIMPLEST FLOWER is THUS A PORTION OF A
SHOOT WHICH BEARS SPOROPHYLLS. The cones of Pteridophyta may
have a number of sterile scale leaves at the base.

In the Spermatophyta the sporangia are also formed in special
regions of the shoot or FLOWERS, all the members of which are
concerned with reproduction and not with the nutrition of the plant.
These flowers, which are homologous with those of the Pteridophyta,
are metamorphosed regions of the foliage shoots. They are the ends
of long or short shoots, the leaf primordia of which do not become
foliage leaves but develop as the crowded floral leaves. These have
the diverse forms of SEPALS, PETALS, STAMENS, and CARPELS.

The STAMENS produce the pollen or POLLEN GRAINS in the POLLEN
SACS, which are special sporangia with a many-layered wall. The

198 BOTANY PART i

pollen grains are spores (Fig. 32) which to begin with are single cells
but later become multicellular (Gymnosperms), or at least contain
more than one nucleus (Angiosperms). The CARPELS, which are free
in the Gymnosperms but form closed OVARIES in the Angiosperms,
bear the OVULES. These are shortly-stalked oval bodies of complicated
structure. In each ovule a single spore is permanently enclosed, pro-
tected by the sterile integuments.

The cone-like flowers of the Gymnosperms (97), composed of
numerous, spirally -arranged, scale -like stamens or carpels, closely
resemble the cones of the Pteridophyta. The flowers of the

Angiosperms (97) have usually a quite distinct
appearance (Fig. 227) owing to (1) the
limited number of the usually whorled floral
leaves, (2) the frequent differentiation of
the outer floral leaves into firm green sepals
and coloured delicate petals, (3) the char-
acteristic form of the stamens, and (4) the
union of the carpels to form the pistil. All
these parts of the flower are arranged
regularly. In the typical angiospermic

FIG. 228. -Diagram of a Liliaceous • flower, five whorls, each of five floral leaVCS,

2Ti*?i2^?£± regularly alternate (Fig. 228); the outer-

to which is the bract. (After most whorl is formed of the sepals which

STRASBURGER.) enclose and protect the other parts when

young, the second is formed of the petals,

the third and fourth of the stamens, and the fifth and highest by
the carpels (98). These foliar structures arose from the shortened,
and often flattened or hollowed, floral axis ; they are often united with
one another and with the axis in such a way as to require thorough
comparative and developmental study to ascertain the facts clearly.

(b) Sexual Reproductive Cells. Gametes. 1. Different Forms
of Sexual Cells and Sexual Organs. — A great variety in the methods
of sexual reproduction is shown by plants ; different as the extremes
are, however, they are connected by intermediate links.

Thallophyta. — In many of the lower Algae and Fungi all the
cells of the plant may simultaneously form sexual cells. With pro-
gressive organisation a division of labour is met with. As in the case
of the formation of asexual reproductive cells, certain cells or organs
with definite positions carry on the sexual reproduction. The parts
of 'the plant body which bear the sexual organs may be specialised in
relation to this.

In the simplest types of sexual reproduction met with in the
lower Algae and Fungi, the sexual cells or GAMETES are usually
naked protoplasts of similar size and structure ; these resemble the
asexual swarm spores but conjugate with one another (ISOGAMY, Fig.
229 B). They develop, singly or in numbers, from the protoplasts

DIV. I

HORPHOLOQY

199

of certain cells termed GAHETANGIA, the process resembling the origin

of the swarm spores. The product resulting from the conjugation of

the gametes is called a ZYGOTE or ZYGOSPORE (Fig. 229 B 4). The

facts are in favour of regarding the gametes as homologous with the

swarm spores, from which they often differ

only in their smaller size, and the game-

tangia as homologous with sporangia. By

this is meant that the gametes and game-

tangia have been derived phylogenetically

by the modification of swarm spores and

sporangia. Such gametes are capable of

active movement^ by means of cilia ; they

seek one another in the water and unite

in pairs (Fig. 229 B).

The gametes, however, frequently

FIG. 229.— Ulothrix zonata. At Asexual
swarm spore; Bl, a gamete; B2,
B3, conjugating gametes \Rkt zygote
resulting from conjugation, (x 500.
After STKASBURGER.)

differ in size in the Algae and Fungi ; the
larger gametes, which contain abundant
reserve materials, are female ( ? ) and the smaller are male ( $ ). The
female gamete may be non-motile when it is known as an egg-cell. In
this case the small SPERMATOZOID seeks out and fertilises the large EGG-
CELL (OOGAMY). In the case of oogamy the gametangia are usually

FIG. 230.— Monoblepharis sphaerica. End of filament with terminal oogonium (o) and an antheridium
(a). 1. 'Before the formation of the egg-cells and spermatozoids. 2. Spermatozoids (s) escaping
and approaching the opening of the oogonium. 3. osp, ripe oospore, and an empty antheridium.
(x 800. After CORNU, from VON TAVEL, Pilze.)

different. The cells in which the small naked spermatozoids arise
in large numbers are termed ANTHERIDIA (Figs. 230, 2 a; 231 a),
while those within which one or more egg-cells are formed are the
OOGONIA (Figs. 230, 2; 231 0,, <?„). The egg-cell (OOSPHERE), which is
usually naked, frequently remains in the oogonium, in the wall of
which an opening forms (Figs. 230, 2 ; 231 o,, 0,,, o). Fertilisation of

200

BOTANY

tART I

the receptive oosphere results from spermatozoids, which have been
liberated into the surrounding water in an actively motile condition,
being chemotactically attracted by substances excreted from the
egg-cells.

Numerous transitions between the two conditions show clearly
that oogamy has been derived phylogenetically from isogamy. From
this it follows that the antheridia and oogonia are homologous with
one another, and also with the sporangia (cf. also Fig. 231).

It is not until after the entry of a spermatozoid that the egg-cell
becomes capable, either at once or after a resting period, of developing

further. As a rule, after becom-
ing surrounded by a thick wall
it separates from the parent
plant as a unicellular oospore
(Fig. 230, 3 osp), and only com-
mences its independent develop
ment later with the bursting of
its wall. In other cases, while
still attached to the parent plant,

FIG. 231.— Diagrams founded on Algae. sp,\ Spor- . , . . \ J

angium with spores; a, antheridium with sperma- it develops into a multicellular

tozoids; o/, oogonium with several and o,, with and more or less segmented

a single egg-cell ; o, the pore in the cell wall. body which produces unicellular

asexual spores ; these spores are
then set free from the parent plant as the true reproductive bodies.

Bryophyta, Pteridophyta. — Oogamy is the rule in these groups.
The male and female sexual organs are of more complicated structure
than in the Thallophyta. They are not single cells but have walls
composed of a layer of sterile cells. In the case of the multicellular
antheridia (Fig. 232, 1) this encloses a larger or smaller number of
cells with abundant protoplasm (the SPERMATOGENOUS TISSUE), from
each of which a spermatozoid will be formed. In the flask-shaped
female sexual organ, which is known as an ARCHEGONIUM, there is
only one egg-cell surrounded by the wall formed of a layer of cells
(Fig. 232, 2). The archegonia and antheridia are homologous
structures. They have special arrangements for opening at maturity.
In the Bryophyta they are borne on the thalloid or leafy gametophyte.
In the Pteridophyta the sexual organs are not borne on the leafy
plant (which has been seen to be reproduced by spores) but on the
prothallium, which is the sexual generation or gametophyte living
independently of the sporophyte.

In the Bryophyta and Pteridophyta the oosphere after fertilisation,
which takes place in the same way as in the Thallophyta, develops
forthwith into the EMBRYO which becomes the SPOROPHYTE (the
stalked capsule in Bryophyta, and the leafy plant in the Pteridophyta).

Spermatophyta. — In this group also the sexual reproduction is
exclusively oogamous, but the sexual organs have come to differ

DIV. 1

MORPHOLOGY

201

widely from the simpler types. The gametes are formed in greatly
reduced or unrecognisable archegonia and antheridia ; these are pro-
duced in extremely reduced prothallia, often consisting of only a
few cells, that are enclosed in the pollen grains and ovules of the
flowers. The pollen grains contain the male sexual cells,
while one or more egg-cells are contained in the ovule.

The peculiar method of fertilisation in spermato-
phytes is connected with the fact that the egg-cell
remains enclosed within the ovule in the flower. The
pollen grains after being shed from the pollen sac require
to be carried to the ovules in the case of Gymnosperms,
or to a special receptive portion of the ovary called
the STIGMA in the Angiosperms.
This is the process of POLLINATION.
Most of the manifold modifications
of the flowers of Angiosperms are
adaptations to the method of pollina-
tion ("), which always involves special
means of transport of the pollen.
When, as is often the case, male
and female organs are present in
the same flower, i.e. in hermaphrodite
flowers, it might be assumed that no
special arrangements would be neces-
sary to bring the pollen to the stigma.
More accurate investigation has, how-
ever, shown that such adaptations
exist in abundance and are often of
the most detailed nature. They do

, . , FIG. 232.— 1. Antheridium, with wall of sterile

mply aim at the conveyance cells enclosing the spermatogenous tissue.

2. Archegonium, with corresponding wall

and an egg-cell. Both based on a Liverwort.

of the pollen to the stigma of the
same flower ; often they render such
SELF-POLLINATION (autogamy)
impossible and effect CROSS-POLLINATION (allogamy), i.e. the con-
veyance of pollen to the stigma of another flower on the same plant
(geitonogamy) or on another individual (xenogamy). The transport
of the pollen may be by wind, water, or the agency of animals
attracted to the flowers by their colour, scent, or nectar ; thus most
flowers can be classed as ANEMOPHILOUS, HYDROPHILOUS, or ZOIDIO-
PHILOUS (cf. the Special Part). Most spermatophytes have thus
become independent of the presence of water for the purpose of
fertilisation and are in a special sense land plants.

In addition to plants which show allogamy there are others which have arrange-
ments leading to autogamy, either when cross-pollination does not succeed, or
primarily as in cleistogamous flowers (cf. the Special Part).

After pollination the pollen grain grows out into a POLLEN TUBE,

202 BOTANY PART i

which in Angiosperms makes its way by means of the style to the
cavity of the ovary and through the outer layers of sterile cells of
an ovule to the egg-cell. When an open connection has been estab-
lished between the pollen tube and the egg-cell, the latter is fertilised
by a nucleus from the pollen tube. The fertilised egg develops
within the enlarging ovule to a multicellular embryo, which becomes
segmented into the COTYLEDONS, RADICLE, and PLUMULE. The ovule
becomes the SEED, the outermost tissues giving rise to the seed-coat.

THE SEED, WHICH IS SHED WHEN RIPE AND SERVES TO MULTIPLY THE
PLANT, IS THUS A FURTHER DEVELOPED OVULE ENCLOSING AN EMBRYO.

The ovary also develops further after fertilisation and gives rise to
the FRUIT. When this remains attached to the plant it opens when
mature by splits, pores, or the separation of a lid," in order to liberate
the seeds (capsule). Often the whole fruit enclosing the seed is
separated from the plant, as in the case of berries, nuts, and stone-
fruits.

The seeds or the detached fruits are adapted for dispersal (10°)
like other reproductive bodies. This is effected by the same means
as the transport of pollen, by currents of air or water, by means of
animals, and sometimes by special constructions or movements of the
plant. The construction of seeds and fruits shows adaptation to the
mode of dispersal (cf. the Special Part).

On the seeds being thus sown, GERMINATION (101) commences after
a longer or shorter time. As a rule the root of the embryo emerges
first, rupturing the seed-coat. Since this is often very hard, special
regions for the exit of the root may be present in it (e.g. in the Coco-
nut). In the further development of the shoot of the seedling, mani-
fold differences become apparent in different kinds of plants ; these
will be described in the Special Part. The seedling at first grows
at the expense of food materials provided by the parent plant and
stored in the seed.

A peculiar type of asexual reproduction (apogamy) occurs in some flowering
plants and replaces the sexual reproduction. Within the ovule and replacing the
suppressed egg cell, asexual embryos are developed from other cells (95). The seeds
thus include no product of sexuality but have become organs of vegetative repro-
duction. This formation of adventitious embryos is commonly associated witli
POLYEMBRYONY, i.e. the formation of a number of embryo plants in a single seed
(Funkia ovata, Citrus aurantium, Caelebogyne ilicifolia, etc.).

2. The Process of Cell-Fusion in Fertilisation and its Results.—

The actual process of fertilisation in its simplest form can be best
observed in those lower organisms with similar gametes (Fig. 229).
In these it can be easily shown that not only the cytoplasm of the
two cells but sooner or later the nuclei also fuse. When the male
cell possesses chromatophores, which in many Algae (Florideae, Chara,
etc.) is not the case, they do not fuse with those of the female cell.
They either coexist in the fertilised cell or, when a constant number

DIV. i MORPHOLOGY 203

of chromatophores is maintained, disappear. In Angiosperms, so far
as our present knowledge goes, only a male nucleus, without cytoplasm
or chromatophores, enters the oosphere. From this it has been
concluded THAT THE ESSENTIAL ELEMENT IN FERTILISATION is THE

PASSAGE OF THE MALE NUCLEUS INTO THE EGG-CELL.

In the typical process of nuclear divisioji it has been seen that
the nuclei of an individual possess a constant number of chromosomes
characteristic of the species. The male gamete thus contributes as
many chromosomes as the female gamete. These chromosomes do
not fuse in the conjugation of the sexual nuclei, so that the nucleus
of the zygote has double the number of chromosomes possessed by
the sexual cells {l02). It is DIPLOID and contrasts with the HAPLOID
nuclei of the gametes.

The nuclei resulting from the further division of the nucleus of
the zygote are as a rule diploid ; in each there are as many chromo-
somes derived from the male as from the female nucleus. When
the chromosomes of the haploid cells are characterised by differences
in size which are apparent at each nuclear division, the diploid
nuclei show pairs of chromosomes of each size. These chromosomes
of equal length, the one derived from the male and the other from
the female parent, as a rule lie in pairs in the nuclear plate (Fig. 1 4).

Since the nuclei of the sexual cells of all the individuals of a
race are always haploid, while the conjugation nucleus and as a rule
the products of its division are diploid, there must be a change from
the diploid to the haploid condition at some point in the developmental
history of the individual. Were this not so, the number of chromo-
somes would double with each generation. The change is effected
at the REDUCTION DIVISION (103), which is a peculiar nuclear division
in which there is a separation to form the daughter nuclei of entire
chromosomes, and not half-chromosomes resulting from longitudinal
splitting. This occurs at a definite point in the development, which,
however, differs in different organisms. Thus a regular alternation
of the haploid and diploid phases of the nucleus is characteristic of
the ontogenetic development of sexual organisms.

Frequently, but not always, the alternation of nuclear phase
is connected with the alternation of generations, as in many Algae,
Fungi, the Bryophyta, Pteridophyta, and Spermatophyta. The
sporophyte arising from the fertilised egg is diploid, and the reduc-
tion division precedes spore formation. As a result the spores, the
gametophytes developed from them, and the sexual cells are haploid.

In many Algae, however, the first division of the nucleus of the zygote is the
reduction division, so that all the cells of the organism, including the sexual cells,
with the exception of the fertilised egg, are haploid. In others, such as Fucus,
the reduction takes place at the formation of the sexual cells, so that the opposite
case is presented of all the cells with the exception of the gametes being diploid.

There are certain remarkable cases in which the one generation develops from

204

BOTANY

PART I

the vegetative cells of the other without change in the number of chromosomes.
In Athyrium filixfoemina clarissima, Jones, the fern plant arises without nuclear
fusion from vegetative prothallial cells with diploid nuclei ; without any production
of spores, or the occurrence of a reduction division, the diploid cells of the leaf
margin produce diploid prothallia (APOSPORY). According to YAMANOUCHI (in
Nephr odium molle) a haploid prothallial cell may, without nuclear fusion, give rise

FIG 233.-Pollen.mother.cell of a -Lily in division, somewhat diagrammatic. Fixed with chrom-
atic acid and stained with iron haematoxylin. The chromatophores are not visible 1 The
f the chromosomes. Further description in text. (After STRASBURGER.)

to a haploid fern-plant. Further, it is possible to obtain experimentally, on the
regeneration f cut portions of the stalks of moss capsules, a diploid moss plant
i.e. a diploid gametophyte ; this produces diploid sexual cells that are capable of
fertilisation. Tetraploid moss capsules are the result, and from these again by
regeneration tetraploid moss plants have been obtained. It is evident, therefore,
that there is not a direct connection between the chromosome number and the
construction of the two generations (95).

In some plants the reduction division is omitted so that diploid egg-cells are

DIV. I

MORPHOLOGY 205

formed (95). Such eggs, which already have the double number of chromosomes
usually only attained on fertilisation, proceed to develop without fertilisation.
This is the case for the unfertilised egg-cells of the Sperm atophyta, Marsiliaceae,
and Chara, mentioned on p. 193, while in other Algae the haploid egg-cell
develops parthenogenetically into a new plant. When diploid sexual cells proceed
to develop without fertilisation, it is usual to speak of apogamy (cf. p. 202) and not
of parthenogenesis.

The reduction division in contrast to the typical division is termed HETERO-
TYPIC, and is also spoken of as MEIOSIS. It is characteristic of this, that
in the prophase the nuclear contents become for a period contracted together at
one side, at least in fixed preparations (SYNAPSIS, Fig. 233, 2, 3). It is
further characteristic of the succeeding stages that the paternal and maternal
chromosomes become associated or united in pairs or GEMINI. The number of
these GEMINI is half as great as the number of chromosomes in [the tissue cells
of the same plant, since two chromosomes are represented by each segment. The
paired chromosomes become shorter and thicker and are distributed around
the periphery of the nucleus ; this is the condition that has been termed
DIAKINESIS (5, 6). At this stage kinoplasmic filaments are becoming applied to
the nuclear membrane (6) ; the latter disappears, and the nuclear spindle, which
is at first multipolar (7) but ultimately becomes bipolar (8), originates from the
kinoplasmic fibres. The paired chromosomes become attached to the fibres of the
spindle and arranged in an equatorial nuclear plate (8). Shortly afterwards the
separation of the chromosomes, until now united in pairs, takes place (9). IN

THIS PROCESS, IN WHICH THE ESSENTIAL OF THE REDUCTION DIVISION IS EFFECTED,
IT IS NOT LONGITUDINAL HALVES OF CHROMOSOMES BUT ENTIRE CHROMOSOMES

WHICH SEPARATE FROM ONE ANOTHER. The result of this is that each daughter
nucleus receives only half as many chromosomes as were found in the tissue cells
of the same plant, and that these chromosomes may be male or female. Since
chromosomes of corresponding lengths are always associated in the gemini, one
being derived from the male and the other from the female parent, and these
chromosomes separate from one another in the reduction division, each haploid
daughter nucleus must inherit some chromosomes from the father, and others
from the mother. Which chromosomes come from the one or other parent appears
to be determined by chance. The formation of the daughter nuclei is completed
(10) as in an ordinary division, but following promptly on the first reduction
division, which is also known as the HETEROTYPE division, comes a second or
HOMOTYPE division, which in all essentials follows the typical course (11, 12).
Thus two rapidly-succeeding nuclear divisions are characteristic of most cases of
reduction. In the homo ty pic division longitudinal halves of chromosomes separate
as in the typical division. A difference from the latter is that the chromosomes
are not split longitudinally in the prophase of the homotypic division itself, but,
as it seems, were already split in the prophase of the preceding reduction division
without the halves thus formed separating.

The fundamental difference between the typical and somatic nuclear division
and the reduction division may be made clearer by means of a diagram. Fig. 234
A represents a somatic division with longitudinal splitting of the Chromosomes.
In A a six longitudinally split chromosomes, distinguished by the different
shading, are shown arranged to form the nuclear plate. The two middle ones are
seen from the end, the others from the side. In A b the separated halves of these
chromosomes are shown on their way to the poles of the spindle in order to form
the daughter nuclei. In Fig. 234 B the reduction division is diagrammatically
represented. The six chromosomes of Fig. 91 A are shown in B a similarly

206

BOTANY

PART I

shaded and united in three gemini. The two lateral gemini are seen from the
side, the middle one from the end. The latter one shows the longitudinal split in
the component chromosomes and the orientation of the plane of fission. In B b
the chromosomes of each geminus have separated and are moving towards the poles
of the spindle to form the two daughter nuclei. The two halves of each chromo-

FIG. 234. — Diagrammatic representation of ordinary nuclear division (A) and of the reduction
division (B). (After STRASBURGER.)

some thus go to the same daughter nucleus. This division results in a reduction
of the chromosome number from six to three. In contrast to this reduction
division, which, because whole chromosomes separate, results in a definite differ-
ence of the products of division, may be placed the somatic nuclear division.
This, since the longitudinal halving of the chromosomes gives rise to completely
equivalent products of division, may be termed equation division.

Opinions are divided as to how and when the chromosomes in the reduction
division become associated in pairs, or temporarily united in a single structure.
It is possible that the scheme of the reduction division is not always the same.
Usually the chromosomes appear placed side by side in the pair (parasyndesis),
but in some cases they appear to be placed end to end (metasyndesis).

SECTION IV

THE THEORY OF DESCENT AND THE ORIGIN OF NEW SPECIES

A. The Theory of Descent (104). — How the organic forms living
on the earth with their morphological peculiarities have arisen is one
of the most important theoretical questions in morphology. The
assumption once made that the kinds of plants were independently
created (theory of special creation) has become gradually abandoned
in favour of a theory of evolution, especially owing to the deepen-
ing of morphological knowledge and the influence of CHARLES
DARWIN. This has already been referred to in the Introduction.
The theory of evolution regards the existing organisms as developed
from other and frequently more simply-constructed forms which lived
in earlier periods of the earth's history (cf. p. 1 ff.). This fundamental
biological theory now permeates morphological investigation so
completely that it is indispensable for the morphologisfc to be
acquainted with the evidence for it. Evidence is afforded by classifica-

DIV. I MQRPHOLOGY 207

tion, morphology, the geographical distribution of plants and animals,
and by palaeontology.

1. EVIDENCE FROM CLASSIFICATION. — According to the theory
of special creation the various species of plants were created inde-
pendently and are essentially constant. They were supposed to be
so little subject to change that one species could not arise from
another ; at most a species could give rise to more or less inheritable
varieties. This view thus assumes that there are sharp limits between
the species, and also that there is an essential difference between
species and varieties. As the student of classification proceeds to
examine any group of organic forms he finds that there are no
characters to be relied on to distinguish varieties from species. The
amount of morphological difference between the species of a genus,
the varieties of a species, or between species and varieties, is quite
undetermined. It has also come to be recognised that species are
not independent morphological units but in many cases are compre-
hensive groups of forms or petites espkces (e.g. in the genera
Erophila, Rubus, Bosa, Hieracium, Quercus). The sharp differentiation
of such species from other species, i.e. other groups of forms, is
frequently difficult or scarcely possible. The constant small species
often differ less than do many so-called varieties. It thus becomes
a matter of taste or "systematic sense" whether a particular form
should be regarded as a species or a variety and how a species should
be delimited. The rule formerly relied upon, that crosses between
two independently created species would be sterile while those
between two varieties of a species would be fertile, has proved
untrustworthy ; fertile and sterile hybrids are known both between
two varieties and two species. There are not only transitions
between species but between genera and even families, so that in
these cases also the limits have to be drawn at the discretion of the
systematise All these facts only become comprehensible if it is
assumed that species were not independently created but are capable
of heredity with variation, so that new species can be derived from
others by inherited changes, while more marked changes give rise to
new genera or families. On any other assumption it remains incon-
ceivable why organisms can be placed in groups of lower and higher
order (species, genera, families, classes, etc.), which are in part co-
ordinate (like the species of a genus or the genera of a family) and
in part subordinated to others (like the species to the genus or the
genera to the family) ; further, that the groups of extinct organisms
which lived in earlier geological periods can as a rule be naturally
placed in the same classification as the existing forms. All these
difficulties disappear when organisms are regarded as blood relations,
and the natural system as expressing their nearer or more distant
relationship, and thus, in a certain degree, as a genealogical tree of
living beings.

208

BOTANY

PART I

2. MORPHOLOGICAL EVIDENCE. — Certain facts are inexplicable on
the theory of special creation, while they are naturally explained on
the theory of descent. The common morphological plan of construction
exhibited by the members of a systematic group, such as a genus, a
family, or a class, is of this nature. It extends in a sense to all
organisms as shown in the cellular structure and the nature of proto-
plasm. On the other hand, the theory of evolution may explain the
unexpected occurrence of certain features in a group when the plan
of construction would not have led us to anticipate them (e.g. the
spermatozoids in the pollen-tube of the Cycadeae). The great groups

of the Bryophyta, Pteridophyta, and
Gymnosperms, with all their morpho-
logical differences, are essentially
similar in the course of development
and alternation of generations, and
in the construction of their sexual
organs. Only on the assumption of
a blood relationship can one under-
stand how organs of different species,
that appear completely different and
perform different functions, prove on
morphological investigation to be
homologous, or that the organs of
one and the same organism are so
frequently homologous in spite of
their diverse structure and functions.
For example, thorns and tendrils are
F'^:^±»fl^ "transformed" leaves, stipules, sterns,

purpurea ; C, Gratiola officinalis ; D, Or TOOtS ; the Cotyledons, SCalc-leaVCS,

Veronica Chamaedrys. The sterile stamens "bracts, sepals, petals, Stamens, and
are represented by black dots, and the . f ,,

position of completely aborted stamens by Carpels Ot a plant are all

crosses. (D after EICHLER.) formed" foliage leaves. All these

metamorphoses of organs have evi-
dently taken place during the phylogenetic development. In the
same way reduced functionless organs found in some plants have been
derived from plants in which the corresponding organs are still well
formed. In the family of the Scrophulariaceae (Fig. 235) the number
of stamens ranges from five in Verlascum to two in such forms as
Calceolaria ; in the genus Scrophularia one stamen of the five is present
in a reduced condition, while this stamen is wanting in Digitalis ; in
Gratiola two fertile and two reduced stamens are present, in Veronica
two fertile stamens only, and in Calceolaria only two half-stamens.
Useless reduced organs are difficult to understand on the theory of
special creation. Occasionally an unfamiliar character appears in a
plant which can only be regarded as a reversion to a long-lost feature
of its ancestors ; examples are afforded by the occasional fertility of

DIV.

MORPHOLOGY 209

reduced stamens or the appearance of reduced or fertile stamens in
positions where fertile stamens were present in the ancestry. The
similarity of the embryos of very different organisms, which is most
strikingly shown in the animal kingdom, is a further indication of
genetic relationship. So also is the fact that occasionally the embryos
are more highly organised than the mature organism (in some reduced
organisms, e.g. many parasites). The juvenile leaves on the seedlings
of some plants which are adapted to extreme conditions of life may
resemble the ordinary leaves of less specialised species of the same
genus (e.g. in Acacia, Fig. 136). Not infrequently a species repeats
more or less completely in its ontogenetic development what we assume
on other grounds to have been the course of its phylogenetic
development (BIO<?ENETIC LAW).

3. EVIDENCE FROM GEOGRAPHICAL DISTRIBUTION. — Geographical
limits which hinder free migration (e.g. high mountains, and seas in
the case of land plants and masses of land in the case of marine
organisms) stand in striking correspondence with differences in the
fauna and flora of particular habitats, countries, continents, or oceans.
The assemblages of organisms found in two continents differ as regards
their families, genera, etc., in proportion to the degree of present and
former isolation because the forms in each region have continued
their phylogenetic development independently. The easier the
exchange of forms between two regions the more numerous will be
those which are common to both. It is a general rule that the
inhabitants of any region are most closely related to those of the
nearest region from which migration may be assumed, on geological
and geographical reasons, to have taken place. This holds, for
example, for the Cape Verde Islands and the African mainland, and
for the Galapagos islands or Juan Fernandez and the neighbouring
regions of America. The more a habitat, such as an island, is isolated
from the rest of the world the richer will it tend to be in peculiar
forms (ENDEMISM) ; these often differ only slightly from other non-
endemic forms from which they have evidently originated, though
further dispersal has been impossible.

4. PALAEONTOLOGICAL EVIDENCE. — Palaeontology shows that in
the history of the earth species have become extinct and others
appeared ; that not infrequently the forms in successive geological
strata can be arranged in series showing progressive organisation ;
and that the groups which are regarded as most highly organised
appeared relatively late in the history of the earth (e.g. the Angio-
sperms in the Cretaceous period). It has also made us acquainted with
extinct intermediate types between genera, families, and classes.
That such cases are not more frequent evidently depends on the
incompleteness of the geological record. In Botany the most important
of these synthetic groups is that of the Pteridospermeae or Cycadofilices,
which are plants of the Carboniferous period connecting the Ferns

210 BOTANY

and the Cycadeae ; they have leaves like the former but seeds like
the latter, while anatomically they present resemblances to both.

5. DIRECT EVIDENCE OF THE VARIABILITY OF SPECIES. — All the
preceding sources of evidence gain in significance from the direct
observation of the inconstancy of some species. Careful observation
establishes the appearance, both under natural conditions and, more
frequently, in cultivation, of inheritable deviations which would have
the systematic rank of varieties or species. It has also been possible
in various ways to experimentally produce new forms the characters
of which are inherited. The importance of such observations is that
they give some insight into the problem of the formation of species
and the origin of new morphological characters.

B. Formation of Species and the Origin of Adaptations. — All
observations have so far shown that the inheritable changes in
organisms may concern this or that character, may be larger or smaller,
and are irregular in origin. This serves to elucidate the great variety
in organic forms. These abrupt changes may be harmful, indifferent,
or useful to the organism. If they are so injurious that the life of
the organism is scarcely possible, the variety will disappear as quickly
as it originates (e.g. seedlings that have lost the power of forming
chlorophyll). To what extent such inheritable changes arise under
the influence of external conditions has yet to be determined in
particular cases ; it will be treated of in the physiological portion of
this text-book.

Since the acceptance of a theory of evolution it has been evident
that the origin of the ADAPTIVE CHARACTERS of organisms called for
special explanation. The recognition that living beings vary in all
directions does not afford insight into the striking fact that organisms
are in many ways adapted to their environment, and organs more or
less adapted to their functions, while the reactions of the organisms are
beneficial. This condition of adaptation or inherited adaptedness
must in some way have originated phylogenetically. As to how it
arose, observations and experiments have to the present given no
direct answer. Explanations have been sought in a different way,
the two most important hypotheses being known as Lamarckism and
Darwinism.

1. Lamarekism (105). — This hypothesis starts from the fact that
some organisms assume a different form according to the surroundings
in which their germ cells develop to the mature organism, without
losing the power of developing differently in another environment.
Thus there are plants which can live both on land and in the water
(amphibious), assuming different forms according to the environment.
When grown on land they have the form and internal structure of
typical land plants ; when cultivated in water they resemble typical
aquatic plants. Some plants under dry conditions of cultivation
produce xerophilous characters, while when grown in moist air they

DIV. I

MORPHOLOGY 211

are hygrophilous. This power of reacting to different environments
by the development of different characters is known as the capacity
of modification. Such MODIFICATIONS (cf. Physiology, p. 322) are
not inheritable in the sense that the seeds of, for example, an am-
phibious plant which has developed in water to a water plant will
produce the aquatic form if they are sown on land. On the contrary,
the land form is always produced on land and the aquatic form in water
whether the seeds have been taken from the one form or the other.

These influences of the environment have been regarded as direct
adaptations on the part of the plant which has the power of thus
modifying itself. The power has further been attributed to the
organism of responding by a useful reaction to every external influence,
even to those not met with under natural conditions. Such a power
of adaptation would apply to new functions as well as to external
factors ; the need of an organ would bring about its formation. It is
further assumed by Lamarckism that every modification, especially
those resulting from external factors or the needs of the organism, is
inheritable, or at least can become inheritable in the course of time.
Thus when a plant has been for generations directly adapted to aquatic
life, to life in the shade, or at the expense of another organism, the
acquired peculiarities of structure gradually become fixed, i.e. they
also appear when the occasion for them is no longer present.
Regarding this view it must first be remarked that the assumption
"a need for an organ can bring about its formation" is not clear, and
also that nothing is known of the inheritability of those effects of
external conditions that have been termed modifications above. For
these reasons alone Lamarckism must be given up. Further, it is
difficult to conceive that the organism should react usefully in
anticipation of particular external factors. As a matter of fact we
not uncommonly meet with reactions to new unaccustomed stimuli
which appear quite indifferent or even harmful. Thus the tentacles
of Drosera become curved at a high temperature just as if they were
in contact with an insect. Leaves cut off from a plant may continue
to live for years by producing roots even when they are unable to
form shoots. When there appears to be direct adaptation to various
stimuli (e.g. water, light, air, shade, etc.), to which particular
organisms are exposed in their habitats, the result may be otherwise
explained. It may be assumed that such organisms already possess
the capacity or the factors which enable them to follow this or that
course of development according to the external conditions. The
external conditions would not produce the factors but only determine
their becoming manifest or not. How these factors have historically
come about, and why some organisms possess them and others not,
why, for example, only some plants are adapted to live in water as
aquatic plants or as land plants on the land, remains still unexplained.
On this question Lamarckism throws no light.

212 BOTANY PART i

2. Darwinism (104' 106). — DARWIN starts from the fact that the
limited conditions for life on the earth do not permit of unlimited
increase in the number of organisms. Nearly every living being
produces during its individual existence so many germs that were all
to grow the whole earth would in a short time be overpopulated.
That so few descendants of an individual survive is due to many
being destroyed at all stages from the germ cell onwards. They are
overcome in the STRUGGLE FOR EXISTENCE with the environment, in
which other organisms of the same or different species are included.
Were all the offspring alike, accident only would decide which should
survive, and such accidents do play a great part. Since, however,
inheritable differences occur among the offspring, those individuals
will as a rule be favoured in the struggle for existence which by
their peculiarities are capable of maintaining themselves, or are more
capable than the others in the particular situation to which chance
has brought them. Thus a process of selection (NATURAL SELECTION)
comes about. If, further, the selected variants hand on their
properties to their descendants, and the variation and the struggle
for existence is repeated, the process must lead to the selection of
still better adapted forms. Organisms may arise with any sort of
characters, useful, indifferent, or harmful. Since, however, those
with injurious qualities promptly disappear, those that remain are
better adapted than those that perish. Usefulness which was not
explained by Lamarckism (where the useful capacity of reaction in
relation to new conditions of the environment was assumed) comes
about according to Darwinism from the preservation of new inheritable
properties which contribute to the success of the organism in the
struggle for existence. It is in this that the great advance made by
DARWIN'S theory, as compared with Lamarckism, consists. It is
supported, as has been seen, by the observations hitherto made on
the origin of new inheritable characters in organisms, although the
assumptions of Darwinism leave various difficulties to be overcome.

DIVISION II
PHYSIOLOGY

213

DIVISION II
PHYSIOLOGY (^

THE object of Physiology is to describe the phenomena of life, to
study their dependence on external factors, and so far as possible to
trace them back to their CAUSES. Physiology, like Chemistry and
Physics, is concerned with inquiries into the causes of what takes
place. It must, however, also take into consideration the significance
to the organism of what happens. In its methods as well as in its
problems Physiology agrees with Physics and Chemistry ; its methods
are EXPERIMENTAL.

The main results of physiological investigation are the following :

1. There is no fundamental distinction between the vital pheno-
mena of animals and plants. This is not surprising, since plants
and animals are only morphologically distinct in their more advanced
representatives. In the physiological sphere it becomes more and more
clear, as investigation proceeds, how similar the course of life in the
two kingdoms is. The physiology of organisms is thus really a single
subject. A text-book of botany has evidently only to give an account
of the physiology of plants, but, where this is useful, analogous pheno-
mena in the animal kingdom will be mentioned.

2. In some respects the behaviour of the living plant does not differ
from that of non-living bodies. In spite of the large amount of water
which it contains, the plant is as a rule solid, and has the physical
properties of such a body. Weight, rigidity, elasticity, conductivity
for light, heat, and electricity are properties of the organism as they
are of lifeless bodies. However important these properties may be to
the existence and the life of the plant, they do not constitute life itself.

3. The ESSENTIAL PHENOMENA OF LIFE are strikingly different from
the processes met with in non-living bodies. They are intimately
connected with the protoplasm and depend on the peculiar fashion
in which this substance reacts to influences of the outer world, i.e.

Upon its IRRITABILITY and CAPACITY OF REGULATION.

(a) Irritability. — In the reactions of the organism the con-
nection between the causal influence and the effect induced by it
is not so apparent as it is in chemical or physical processes. This

215

216 BOTANY PART i

depends on the part always taken by the protoplasm, so that the
reaction observed is not the direct effect of an external cause, but a
very indirect result. Further, according to the condition of the proto-
plasm, the same factor may produce different effects. An example
will make this clear.

If the free end of a flexible rod is placed horizontally, it will bend downwards
to a definite point as the result of its weight. A part of a plant will behave
similarly, and if dead, as for instance a withered stem, will remain in the position
it thus assumes. If, however, a living growing stem has been used in the experi-
ment it will exhibit an effect of gravity which is very surprising in comparison
with the purely physical effect. The growing portion of the stem curves, and by
its own activity becomes erect again ; it thus moves against the force of gravity.
If the experiment is made with a tap-root, this will curve vertically downwards
much further than its own weight would cause it to do. A rhizome (e.g. of Scirpus],
on the other hand, will place its growing tip horizontally when it has sunk by
its own weight out of the horizontal plane. In these three experiments the
physical conditions are the same. The weight of the earth acts on a horizontally-
placed portion of a plant. The results in the three cases are as different as
possible.

The explanation of this remarkable behaviour of the plant is to
be sought in the fact that, while to begin with gravity influences it as
it would influence an inorganic structure — giving weight to the mass
— this primary physical change then acts as what is called a stimulus.
This liberates inner activities of the plant which have neither quantita-
tively nor qualitatively a recognisable connection with the force of
gravity. Such relations become clearer if the organism is compared
with a mechanism. The connection between the light pressure of the
finger on the trigger of a gun and the flight of the bullet is not a
simple one. The pressure first liberates a trigger ; the energy thus
obtained drives the hammer on to the percussion-cap ; this explodes
and causes the powder to explode ; the gases liberated by the explosion
force the projectile from the barrel. It is clear that the force of the
hammer bears no relation to that of the pressure of the finger of the
marksman, and there is just as little connection between the amount of
force generated by the expansion of the powder and that exerted by
the hammer of the gun. There are energies present, those of the
trigger and powder, which are set free. Such liberations of energy,
especially when they follow in order and constitute a chain of
processes, are of very frequent occurrence in the organism. They are
known as phenomena of irritability, and the factor which starts them
is termed the stimulus. They are always found when the specific
phenomena of life are concerned.

Just as the action of a machine is only comprehensible when its
construction is known, a knowledge of the external form and internal
structure of the plant is a necessary preliminary to its physiological
study. It has been seen, however, that it is not possible to under-
stand the function from the structure to the same degree in the case

DIV. ii , PHYSIOLOGY 217

of the plant as it is in that of a machine. In the organism we
are concerned not with the mechanical interaction of parts but with a
succession of chemical reactions. While it is true that the phenomena
of life cannot as yet be thoroughly explained, this does not negative
the conviction that they only differ from the processes in inorganic
bodies by their much greater complexity ; in principle a physico-
chemical explanation of vital phenomena can be attained.

(b) Capacity of Regulation. — The study of machines not only
assists in the comprehension of a liberating stimulus but further
renders clear the second widely-spread property of organisms, i.e. their
regulative power. As in a machine the speed may be automatically
maintained at a particular level, so in numerous processes in a plant
there is an element which controls the result both as regards quality
and quantity. Though self-regulated processes are not wanting in
the inorganic world, they do not occur abundantly as they do in
the organism. ON THIS ACCOUNT THE POWER OF REGULATION MAY

BE REGARDED, TOGETHER WITH THE IRRITABILITY, AS A SPECIALLY
IMPORTANT CHARACTERISTIC OF LIVING BEINGS.

4. So long as the organism is actively living, an unbroken chain
of changes can be recognised in it which are exhibited in the three
following ways :

(i.) An organism, which appears to us as an individual, does not
consist of the same unchanged material, even when no further growth
in size is taking place. While its external form remains constant,
progressive changes go on internally. New substances are taken
up from without, are transformed within the plant, and are again given
off from it. The organism has a METABOLISM. Inorganic nature
offers us no process analogous to this.

(ii.) As a rule, however, metabolism does not proceed so that the
absorption and giving-off of material are equal, but more is absorbed
than is given off. The mass of the organism is increased, it GROWS.
Growth is also known in the cases of chemical precipitates or deposits,
and of crystals. In these cases it tends to proceed in such a way
that no essential change of shape takes place (crystals), or that the
changes in shape are accidental and irregular (precipitates). The
organism, on the other hand, by changes of its form assumes quite
definite shapes, which follow in regular order. It passes through a
DEVELOPMENT which leads sooner or later to the production of new
organisms or daughter individuals ; REPRODUCTION takes place.
Growth, development, and reproduction are processes highly charac-
teristic of living beings.

Some precipitates have a certain external similarity to plants under certain
conditions. If some sulphate of copper to which sugar has been added is intro-
duced into a solution of ferrocyanide of potassium and common salt containing
gelatine, a precipitate of ferrocyanide of copper is formed. This to all appearance
grows, and in its form recalls that of plants. This "artificial plant" lacks, however,

218 BOTANY PART i

not only the internal structure of a true plant, but especially the power of repro-
duction and of regular development.

(iii.) Lastly, organisms' exhibit powers of MOVEMENT; they either
change their positions bodily, or they bring larger or smaller parts of
their bodies into other positions. Since inorganic bodies and dead
organisms may exhibit movements, it is only the kind of movement
and the means by which it is brought about that are characteristic
of living beings.

In nature the three processes mentioned above, metabolism,
development, and movement, usually go on simultaneously. Meta-
bolism without movement of the substances concerned is impossible ;
development is bound up with metabolic changes and with movements ;
and, lastly, movements cannot occur without metabolism. Neverthe-
less, we may for descriptive purposes consider the three processes
separately, and thus divide Physiology into the following sections :

(1) The study of metabolism or chemical physiology, which may

also be termed the physiology of nutrition.

(2) The study of development or the physiology of form, changes

of shape, and the mechanism of development.

(3) The study of movement.

5. The full vital activity of the plant is only attained when a number
of conditions, which may be divided <into internal and external, are
fulfilled (2). The internal causes of life are connected with the
protoplasm. Its structure and organisation not only determine that
the changes which take place in the organism have a vital character,
but that the organism shows specific differences depending on the
descent of its protoplasm. Thus the most fundamental condition of
life is the presence of a living mass of protoplasm. All other condi-
tions of life can be created or removed at will. The protoplasm, on
the other hand, cannot be artificially synthesised, and only arises in
the organism by the activity of existing protoplasm.

The protoplasm can, however, only carry on its activity by con-
tinual interaction with the surrounding world. The influence of the
latter is threefold. It provides the material from which the body of
the plant is built up ; it acts as the source of liberating stimuli
(p. 216) ; it provides the plant with the necessary energy either in the
chemical energy of substances absorbed from without or as vibrations
of the ether.

In the external factors that are of importance for the life of a
plant, a distinction must be drawn between the necessary and the
inessential factors. Indispensable conditions of vital activity are a
certain temperature and the presence of certain substances, as well as
the absence of others that act injuriously or fatally (poisons). On the
other hand, light is not in such a general sense a necessary condition
for life. Some plants require direct sunlight, at least for their
aerial organs, while others avoid this and seek the shade (shade

DIV. ii PHYSIOLOGY 219

plants) ; others can pass through their whole life-history in complete
darkness.

The necessary factors must further be present within certain
definite limits. An excess (above the maximum) or too little (below
the minimum) is alike injurious, and at a certain intensity (optimum)
the best results are obtained. MINIMUM, OPTIMUM, and MAXIMUM are
recognisable in the dependence of every vital phenomenon on an
external factor, and are called the CARDINAL POINTS of the influence
of this factor. They are by no means constants ; they differ for
particular organisms and particular vital phenomena ; they change
with the duration of the influence of the factor, and they depend on
the condition of the plant, and on other external factors.

Every transgression of the minimum, or the maximum, for an
external factor leads sooner or later to death. This may result from
too high a temperature or from too low a temperature, from too
much or too little light, or from an excess or an insufficiency of
some substance. Thus when too little water is given a plant dries
up, or when a substance is present in excessive and injurious amount
a plant may be poisoned.

Most plants are killed by being frozen (3) at sufficiently low temperatures.
Nearly all are killed by high temperatures that are far below the boiling point
of water. Only some Cyanophyceae can endure the very high temperature of
certain hot springs.

Susceptible plants, especially those of a tropical climate, are killed even at
temperatures above 0° C. Others are killed by the formation of ice in the tissues,
while some may be frozen hard in winter without suffering any harm. Cochlearia
fenestrata in Northern Siberia endures a temperature of - 46° C. without injury,
and some forest trees can stand even - 60° C. The resistance of lower organisms
to extreme cold is noteworthy. Thus in PICTET'S experiments Diatoms endured for
a long time a temperature of - 200° C.

By increase of the intensity of light any cell can be killed ; in different cases
the action of the light may be either mainly chemical or mainly thermal. Many
Bacteria are killed even by bright daylight ; on this depends the important
hygienic effect of light in houses and dwelling-rooms.

The need of light not only changes from one species of plant to another, or from
individual to individual, but the optimum effect of light may change for the same
individual as it develops. Many of the cultivated plants of the tropics, e.g.
Coffee and Cocoa, require shade when young, and need to be at first protected by
shade-giving trees (species of Albizzia, Musa) planted for this purpose. When older
they bear or even require exposure to the full tropical sun.

Among the influences of particular substances that of WATER is especially
evident. When light and temperature are at the optimum, as is the case in the
tropics, the development of plants depends above all on the supply of water. In
regions with a large rainfall, uniformly distributed throughout the year, a most
luxuriant vegetable growth occurs as in the formation of the TROPICAL RAIN
FOREST. A regularly recurrent dry period determines DECIDUOUS FOREST, a lesser
rainfall permits of the formation of SAVANNAHS, and still more reduced precipita-
tion leads finally to a DESERT (4). %.

Few plants can bear prolonged drying and the associated loss of water. Often

220 BOTANY

death at low temperatures results, not from the direct influence of the cold, but
from the insufficient absorption of water, the roots being unable to take from the
cold or frozen soil enough water to make good the transpiration from the sub-aerial
organs.

6. Death does not necessarily at once result when the minimum
or maximum for external factors is overstepped. The organism has
frequently passed into a condition of LATENT LIFE, and this may also
come about from internal causes. It is often difficult to decide from
inspection whether an organism is in the condition of ACTIVE LIFE, of
LA.TENT LIFE, or of DEATH. Latent life has this in common with
death, that all vital activities are arrested ; but while active life can
be resumed from latent life, this is impossible when the organism
is dead.

Many resting stages of plants, such as seeds and spores, pass into the state of
latent life. They are then as a rule far more resistant to desiccation, heat, and
cold than organs in an active condition. Thus spores of Bacteria can bear a moist
heat of 100° C. and more, and the same holds for some seeds, such as those of species
of Medicago. On the other hand, spores and seeds in the dry condition resist a low
temperature even of - 253° C. (5)

SECTION I

METABOLISM («)

I. The Chemical Composition of the Plant (7)

Any consideration of the metabolic changes in the plant requires
a knowledge of its chemical composition. This is studied by chemical
methods.

Water and Dry Substance. — Some insight into the composition of
the plant can be obtained without special means of investigation.
Every one who has dried plants for a herbarium knows that the plant
consists of water and dry substance. He also knows how the removal
of the water influences such fundamental physical properties of the
plant as its rigidity and elasticity. By means of weighing it is
easy to show how large is the proportion of water in the total weight
of the plant. For this purpose it is not sufficient to expose the plant
to the air, for when air-dried it still retains a considerable proportion
of water, which must be removed by drying in a desiccator or at a
temperature of over 100° C. It can thus be ascertained that the
proportion of water is very considerable ; in woody parts some 50 per
cent, in juicy herbs 70-80 per cent, in succulent plants and fruits
85-95 percent, and in aquatic plants, especially Algae, 95-98 per cent,
of the weight of the plant consists of water.

DIV. ii .PHYSIOLOGY 221

Ash. — While we can thus distinguish by drying between the water
and the dry substance of the plant, we are able by burning to dis-
tinguish between the combustible or organic material and the incom-
bustible substance or ash. The fact that the plant leaves an ash is
evident in the burning of wood or in the smoking of a cigar; the
microscope further shows that even minute fragments of cell wall or
starch grains leave an ash on burning. Information as to the quantita-
tive relations of the ash is afforded by analysis, which shows especially
that the various organs of a plant differ in this respect; leaves, for
example, tend to contain more than stems. It has thus been found
that the dry substance of the leaves of Brasdca rapa contains about
20 per cent of ash, while the stems have only 10 per cent (cf. p. 238).

The constituents of the ash also vary according to the nature of
the soil and other external influences. On the other hand, distinct
species may accumulate different quantities of mineral substances, even
when exposed to the same external conditions.

While the majority of the more common elements occurring in
the earth are found in the ash of plants, only a few elements are
present in sufficient amount to be quantitatively estimated. These
are the non-metals Cl, S, P, Si, and the metals K, Na, Ca, Mg,
and Fe.

Organic Substance. — Chemical analysis is not needed to show
that the plant contains carbon in a combined form. Every burning
log or match shows by its charring that it contains carbon. The
examination of a piece of charcoal in which the finest structure of the
wood is retained, shows further how uniformly the carbon is distributed
in the plant, and how largely the substance of the plant consists of this
element. Accurate weighing has shown that carbon constitutes about
one-half of the dry weight of the plant. On combustion of the dry
plant the organic substance is changed, and passes off in the form of
carbon dioxide and water, ammonia or free nitrogen. It contained
the elements H, 0, N, and C chemically combined ; some of the
elements mentioned as occurring in the ash may also occur in organic
compounds.

Source of the Materials. — There are thus only the following
thirteen elements found in considerable quantity in the plant :

H, Cl, 0, S, N, P, C, Si and Na, K, Mg, Ca, Fe.

When the plant is growing their amount is continually increasing
in the plant, and they must therefore be continually absorbed from
without.

As a rule, only gases and liquids can enter the plant; solid
substances have to be brought into solution before they can pass
through the firm cell walls. When, however, cell walls are absent, as
in the Flagellates and Myxomycetes, the naked protoplasm is able
to surround and thus to absorb solid particles.

222 t BOTANY PAET i

The chemical composition of animals is essentially similar to that
of plants. The absorption of food in animals takes place by means
of the digestive system. The contrast is, however, not so great as
appears at first sight, for as a rule the food materials are converted
into a fluid condition before they are absorbed by the cells.

II. The Nutrient Substances : their Absorption and their
Movement within the Plant

The materials taken into a plant may be necessary, unnecessary, or
harmful. In any particular case this can only be decided experi-
mentally, for it would lead to erroneous conclusions to assume that
all substances constantly present in a plant are necessary. It has
indeed been found that only ten of the thirteen elements mentioned
above are indispensable. They enter the plant not as elements but
as compounds. We can distinguish as the three main groups of
nutrient substances — (a) water, (b) salts dissolved in water, (c) gases.

A plant cannot exist without a continual supply of nutrient sub-
stances. This is evident in the case of a growing plant in which the
increase in size of the body is at the cost of the material absorbed
from without. The fully-grown portions of the plant also require a
steady supply of new material, since their metabolism involves a
constant loss of substance.

(a) Water

All the chemical changes which take place in the metabolism of
the plant are carried out in WATERY SOLUTIONS. For this reason

WATER IS AN INDISPENSABLE CONSTITUENT of the plant. All portions

of the plant are permeated with water, and the protoplasm, the basis
of life, always contains 75 per cent or upwards of water. The plant
can only carry on its life fully when in this condition of saturation
with water. Any considerable diminution in the amount of water
either destroys the life permanently, or at least so greatly diminishes
the manifestations of life that they can no longer be observed.

With the exception of some succulent plants wl^ch are uninjured by the loss
of nine-tenths of their water, plants as a rule have their activity impaired by the
loss of water in withering, and are killed by complete desiccation. It is always to be
regarded as due to some special provision or exceptional quality when entire plants,
or their reproductive bodies which have been dried, can be again brought to life
by a supply of water. Thus, for example, some epiphytic Ferns, some Algerian
species oflsoetes, and the Central American Selaginella lepidophylla, can withstand
droughts of many months' duration, and on the first rain again burst into life and
renew their growth. In like manner many Mosses, Liverworts, Lichens, and
Algae growing on bare rocks, tree-trunks, etc., seem able to sustain long seasons
of drought without injury.

Seeds and spores after separation from the parent plant can as a rule endure

DIV. ii PHYSIOLOGY 223

drying and remain productive for a long time. In this case also all vital manifesta-
tions cease in the dry condition.

Many seeds lose their power of germination after having been kept dry for only
one or a few years ; others even after a few days ; and others again cannot endure
drying at all. It must not be forgotten that in all these instances a certain amount
(about 9-14 per cent) of hygroscopic water is retained by plants even when the
air is quite dry. Over the sulphuric acid of the desiccator seeds retain for weeks
6 per cent or more of their weight of water. Even drying at 110°, or the action
of absolute alcohol, can be borne by some spores and seeds.

Absorption of Water

Absorption of Water by the Cell. — All parts of a plant and all
the parts of its individual cells are saturated with water. The cell
membrane has the water so freely divided between its minute particles
that the water and the solid substance are not distinguishable under
the highest magnification. If the water is allowed to evaporate, air-
filled cavities do not appear in its place, but a contraction of the
cell wall takes place. On the other hand, the absorption of water by
dry or not fully saturated cell walls causes a swelling of the latter.
The increase in volume which a body undergoes as the result of the
introduction of fluid is termed IMBIBITION (8) ; the amount taken up
is limited for a particular temperature. There are substances which
swell in alcohol or xylol ; the vegetable cell wall, however, swells in
water. The walls of lignified cells absorb about one-third of their
weight of water, while those of many Algae and some seed-coats
and pericarps absorb several times their weight. This takes place
with considerable energy, and can therefore overcome considerable
resistance.

The air-dry protoplasm of many seeds and spores imbibes water
and swells just as does the cell wall. Like gum arabic, however, it
loses the characters of a solid body and passes into a colloidal solution.
This is the condition of the protoplasm, as a rule, in the actively
living cell, though certain portions may have a firmer consistence.
Colloidal solutions have, indeed, always the tendency to pass from
the fluid (sol) condition to the gel condition.

The cell sap is always a molecular solution of crystalloids in
water, but may also contain colloids.

Only a cell which is not completely saturated for water can
withdraw water from its surroundings. It is thus necessary to be
clear as to what is meant by a cell being saturated for water. For
the cell wall the answer is simple ; the wall is saturated when the
maximum of swelling has been reached. It is much more difficult to
determine the limits of water capacity for the protoplasm and cell sap.
Taking the latter first, it may be assumed for the sake of simplicity
that it is a solution of crystalloids, and that it is enclosed by the
cell wall only without an intervening layer of protoplasm. If a tube

224 BOTANY PART i

of cellulose is filled with a solution, for instance of common salt, and
placed in water, a process of DIFFUSION will commence. Water
passes into the tube while salt passes out from it. Although the wall
of the cell offers greater resistance to the passage of the salt than of
the water, the diffusion if continued long enough will result in the
same concentration being attained at all points both within and
without the cell. A partition which is permeable to both water and
salts thus only affects the process of diffusion by diminishing its
rapidity. When the wall consists of a substance which is readily
permeable to water but quite •impermeable to the salt, the course of
diffusion is essentially different. If such a SEMI-PERMEABLE MEM-
BRANE is employed, there is no question of a diffusion of the salt, but
the conditions permit of a diffusion of water
inwards. Since within the semi -permeable
membrane a portion of the space is occupied
by the molecules of .salt, the water is here less
concentrated than outside. A diffusion from
the more concentrated to the less concentrated
-^ water, therefore, takes place. Such a one-sided
diffusion is termed OSMOSIS (9), and it results in
a condition of pressure (OSMOTIC PRESSURE)
within the cell.

A physical apparatus may, in the first
instance, be employed to demonstrate and
measure the osmotic pressure. Since semi-
Fio.m-osmometer.r.ciay permeable membranes are mostly delicate, they

cell with the precipitation l TIT

membrane (N) ; B, mano- are Supported by a Solid but pOrOUS Substratum ;

meter with mercury (Q) -, they may be deposited on the walls of cells of

z, sugar solution, unglazed clay. Such a cell (Fig. 236) may,

for instance, have a semi-permeable membrane

of ferrocyanide of copper deposited on its inside. The cell is then
filled with a solution of sugar, closed, provided with a m.ercury
manometer, and immersed in water. The osmotic pressure is indicated
by the rise in height of the mercury. It has been found that a
1 per cent solution of cane sugar can give rise to a pressure of f atmo-
sphere. Assuming that the semi-permeable membrane is impermeable
to the dissolved substance, the effect of all solutions of crystalloids is
nearly proportional to the number of molecules and ions present.
Solutions that produce the same osmotic pressure are termed isosmotic ;
thus, for example, 0'58 per cent NaCl, 27 per cent grape sugar, and
5'13 per cent cane sugar, are isosmotic with 1 per cent potassium
nitrate.

The clay cell corresponds to the cell wall and the ferrocyanide of
copper membrane to the protoplasm. In the vegetable cell itself the
cell wall is completely permeable apart from some special cases (9a).
The layer of protoplasm applied to it, on the other hand, is more or

DIV. II

PHYSIOLOGY

225

less semi-permeable, at least so long as it is living. As a result of
this there is a one-sided passage of water into the vacuole without
any corresponding passage outwards of salts. A further result is
the pressure of the cell contents on the protoplasmic sac and through
it on the cell wall. The protoplasm becomes stretched under this
pressure (turgescence, osmotic pressure) without much resistance, but
the cell wall, by virtue of its elasticity, exerts a considerable counter-
pressure. This puts a limit on the absorption
of water by the cell. It ceases when the
amounts of water entering and forced through
the distended membrane in a unit of time are
equal.

It is not necessary to go further into the
question of the water-content of protoplasm.
It is also necessarily limited, since the proto-
plasm is under pressure on the one side from
the cell sap, and on the other from the cell
wall.

The distension of the cell wall is often con-
siderable and depends on the amount of the
internal pressure and the elastic properties of
the cell wall. In many cases the cell wall is
stretched by the pressure some 10 per cent to
20 per cent, in extreme cases even 50 per cent,
and it contracts when the pressure ceases.
When the cell is pricked or the protoplasm
killed, the pressure is removed and the wall con-
tracts (Fig. 237). By the distension the cell
wall becomes more rigid, just as a thin india-
rubber balloon when air is forced into it resists
changes of shape. The increase of rigidity of
the plant, by reason of the turgor pressure or
turgescence, is very important ; it is the simplest,
and in many cases the only way, in which the
cell becomes rigid. This is dependent naturally
upon the presence of a sufficient supply of water ;
if a distended cell is taken from the water and

allowed to give up water in the air, the stretching of the wall disappears,
and with this the rigidity ; the cell wilts. With a fresh supply of
water the turgescent condition can be restored. So long as a cell does
not possess its maximum water-content it acts as a suction-pump, the
degree of suction depending on the deficiency in water. Under such
circumstances it will be evident that cells with highly-concentrated cell
sap will develop the greatest power of suction.

Many chemists regard every molecular watery solution as having
a definite osmotic pressure, whether this is actually effective towards

FIG. -J37.— Internodal cell of
Nitetta. F, Fresh and tur-
gescent ; p, with turgor
reduced, flaccid, shorter
and narrower, the proto-
plasm separated from the
cell walls in folds ; ss,
lateral segments. ( x circa
6. After NOLL.)

226

BOTANY

PART I

the outside or not. A wilted cell which has lost water has more
concentrated cell sap, and in the chemist's sense the osmotic pressure
has increased. On the other hand, the pressure acting on the mem-
brane has diminished or is completely eliminated. This latter pressure,
i.e. the externally effective osmotic pressure, may be distinguished as
TURGOR PRESSURE, since it brings about the stiffness or turgescence of
the plant. A statement that a cell has a certain osmotic pressure
thus tells nothing as to the height of the turgor pressure ; this will
vary according to the water supply. Given a sufficient supply of
water it is true that the whole osmotic pressure will be expressed as
turgor pressure.

The phenomenon known as PLASMOLYSIS serves to determine the
osmotic pressure. If a turgescent cell is placed in a salt solution
which has a higher osmotic pressure than the cell sap, the pressure on

FIG. 238. — A young cell from the cortical parenchyma of the flower-stalk of Cephalaria leucantha.
m, .Cell wall ; pi, protoplasm ; v, vacuole. 7, In water ; II, in 4 per cent potassium nitrate
solution ; 777, in 6 per cent solution ; IV, in 10 per cent solution. (After DE VRIES.)

the membrane is removed and there is a shortening of the cell
followed by a separation of the protoplasm from the wall ; this
begins at the angles and ultimately leads to the rounding off of the
protoplast within the cavity of the cell (Fig. 238). It is immaterial
what substance is employed to produce plasmolysis, but the proto-
plasm must be impermeable to it and not injured by it. The reason
why the solution withdraws water from the cell sap is readily under-
stood. Since the external solution contains more molecules and ions
than the internal solution, the water in it is less concentrated ; water
therefore passes from the higher concentration to the lower until
the concentration within and without is the same. If the solution
employed for plasmolysis just effects the separation of the protoplasm
at the angles of the cell, it can be regarded as isosmotic with the cell
sap. Since the osmotic pressure of the solution is known from
physical investigations, we thus arrive at the osmotic pressure in the
cell. Plasmolytic determinations have shown that in ordinary cells

DIV. TI PHYSIOLOGY 227

this amounts to 5-10 atmospheres, but can sometimes be 100 or more
atmospheres. It tends to be unequal even in neighbouring cells,
and may show periodic variations in connection with external
conditions (10).

The separation of the protoplast from the cell wall does not take place so
smoothly as shown in Fig. 238. The protoplasm tends to remain connected to the
wall by fine strands which rupture later.

On transference to pure water the turgescent condition will be regained, if
the protoplasm has not been injured by the solution. If the protoplasm is killed,
however, it has become completely permeable, and the necessary condition for a
one-sided pressure has disappeared. Fresh living slices of the Sugar Beet and of
the Beet Root when placed in pure water do not allow the colouring matter to
escape from the uninjured cells. If the protoplasm is killed, the pigment passes
into the surrounding water.

High osmotic pressures are found in cambium cells (25 atmospheres), nodes of
grasses (40 atmospheres), and certain -desert plants (100 atmospheres). The
highest pressures are met with in plants, which like those of the sea and sea-
shore live in solutions of common salt, or like some Fungi succeed in sugar solu-
tions. In these cases also the osmotic pressure of the cell always exceeds that of
the surrounding solution ; it is adapted and capable of regulation in relation to
the medium, and is therefore not always the same (n). It is easy to understand
why cells with such high osmotic pressures burst when transferred to less con-
centrated solutions or to pure water, in which their turgor pressure is greatly
increased.

The Absorption of Water by more Complex Plants. — In many
lower plants all the living cells take part in the absorption of water.
In more complex plants only the
superficial cells are in contact with
the supply of water in the environ-
ment, and absorption of water is
limited to them. In the cormus,
at least in the typical land plants,

the absorption of water is limited Fl(, o39._Tip-of a root-Lair with adhering
to the epidermal Cells of the rOOtS. particles of soil, (x circa 240. After NOLL.)

The suVaerial parts of the plant,

covered with a more or less strongly-developed cuticle, cannot under
natural conditions absorb sufficient water for the needs of the plant.
The root, on the other hand, is highly specialised for this purpose,
both as regards its external form and the structure of its limiting
layer. Since the water in ordinary soils is finely subdivided and held
firmly by the particles of the soil, a large surface must be exposed
by the absorbing root. This is attained by the extensive branching
of the root-system and by the presence of root-hairs which become
attached to the finest particles of the soil (Fig. 239).

The plant is connected to the soil by the numerous lateral roots
and their root-hairs, and can thus obtain the water held by capillarity
in the soil, as soon as by loss of water a power of suction has arisen

228 BOTANY PART i

in the root-hairs. A plant can extract water even from a soil which
appears dry. As absorption from such a soil continues the plant
begins to wilt, but even in this state absorption is still taking place,
though it does not go so far as to obtain the last traces of water from
the soil. The process continues further in desert plants according to
FITTING, since their cell sap is highly concentrated and can develop
a very strong osmotic suction (12).

Following SACHS, BRIGGS and SHANTZ have determined the water-content of
the soil at the moment of wilting. This they term the coefficient of wilting and
express it as a percentage of the dry weight of the soil. They find that it has
nearly the same value in different plants, but differs widely in different soils.
Thus the coefficient of wilting in coarse sand is 0'9, in fine sand 2 '6-3 '6, in sandy
loam 9 '9, and in clayey loam up to 16'5.

Other Types of Absorption of Water. — Some plants do not obtain their water
from the soil. They belong chiefly to two distinct ecological groups, the
EPIPHYTES and the WATER PLANTS. The morphological and anatomical pecu-
liarities found in relation to the absorption of rain and dew by -the sub-aerial
organs have already been dealt with on p. 184.

Movement of Water in the Plant

That a movement of water from the roots to the aerial parts of the
plant must take place follows from the fact that water is required in
the development of new cells in the growing regions. The plant,
however, requires far more water than is needed for its construction,
because it gives off large quantities of water in the form of vapour,
and a less amount in the liquid form from its aerial portions. The
former process is known as TRANSPIRATION, the latter as EXUDATION.

Transpiration (13)

The vegetable cell, like every free surface of water or substance
swollen with water (e.g. gelatine, mucilage), must give up water to the
air so long as the latter is not completely saturated. Under certain
conditions the loss of water from some parts of plants (e.g. roots, sub-
merged portions, shade plants) is very great. Such objects exposed to
dry air, especially in the sun, lose so much water that they become
collapsed, limp, and wilted, and ultimately dried up. The leaves borne
on ordinary land plants behave otherwise. At first sight no loss of
water is perceptible from them ; but they also wilt during a drought,
which renders absorption of water from the soil difficult. If the supply
of water to them is interrupted completely, as by cutting them off,
the wilting occurs more speedily. That they as a rule do not wilt
when in position on the plant evidently depends on the fact that water
is supplied from below in equal amount to that evaporated from above.
The giving off of water can be demonstrated by simple methods.

DIV. ii PHYSIOLOGY 229

1. If a transpiring part of a plant is covered with a bell-jar that has been pre-
viously cooled, the water vapour given off from the plant will be deposited in the
liquid form on the inside of the bell-jar, just as the aqueous vapour in our breath
condenses on a cold window pane. 2. Transpiration can be very strikingly
demonstrated by the change in colour of cobalt paper ; filter-paper soaked in a
solution of cobalt-chloride has when completely dried a blue' colour which changes
to red on the presence of water. If a small piece of this cobalt paper is laid on
a leaf and protected from the dampness of the atmosphere by a slip of glass, the
change in colour to red, that commences at once, indicates the transpiration ;
conclusions as to the quantity of water given off may be drawn from the greater
or less rapidity of the commencement and progress of the change in colour.
3. Exact information on this point can only be obtained by weighing experiments.
These show that the loss of water vapour by a plant is usually so great as to be
recorded as a common balance without great difficulty in the course of a quarter of
an hour. No general statement can be made as to the amount of transpiration
from a unit area of transpiring surface, for this depends on many external factors,
e.g. temperature, light, supply of water, etc., as well as on the structure of the
plant.

The process of transpiration takes place in this way. An
epidermal cell exposed to the air will lose some of the imbibition
water of its cell wall by evaporation; this would go on until the
cell wall was dried by the air if a reserve of water were not obtainable
from within the cell. This is in fact obtained from the protoplasm,
from which the cell wall, no longer fully saturated, withdraws imbibi-
tion water, and the protoplasm in turn makes good its loss from
the vacuole. The movement of the water affects the interior of
the cell, and brings about a concentration of the cell sap. Thus the
conditions are established for the cell to absorb water from an adjoin-
ing cell which is not itself transpiring, and the loss of water is thus
conducted from the superficial cells where evaporation is taking place
into the depths of the tissue. The amount of transpiration primarily
depends on the permeability to water of the cell wall. If the cell
wall is an ordinary cellulose membrane the amount of transpiration
will be large ; when the wall is covered with wax or cuticle, or
impregnated with cuticular substance, it gives off little water. Com-
parative investigations on suitable objects, by means of cobalt paper,
show how the transpiration diminishes with the increase in thickness
of the cuticular layers until it ultimately becomes practically non-
existent. Corky walls behave in the same way as cuticularised
layers. In their outer covering of cork, cuticle, and wax, plants
possess a protection from a too rapid loss of water. A pumpkin, with
its thick cuticle and outer coating of wax, even after it has been
separated from its parent plant for months, suffers no great loss of
water. A potato or an apple is similarly protected by a thin layer
of cork from loss of water by evaporation. The green organs of
plants, on the other hand, which must be able to get rid of the
surplus water in order to secure the concentration of the nutrient

230 BOTANY PAET i

salts and to reduce their temperature, make little use of such pro-
tective coverings. On the contrary, it has been seen (p. 168) that
they are provided, besides the adaptations to regulate the transpiration,
with special contrivances for promoting evaporation. Their great surface
extension may be specially mentioned.

Transpiration is not, however, limited to the cells which are directly
in contact with the atmosphere ; an enormous number of internal cells
can get rid of water vapour when they abut on intercellular spaces.
The air-filled intercellular spaces would clearly become after a short
time completely saturated with water vapour were they completely
closed. Communications exist, however, as we have seen, between
the atmosphere and the intercellular spaces, the most important
being the stomata (p. 51). The aqueous vapour can escape by these,
and thus the condition of saturation of the air in the intercellular
spaces is not complete. The water vapour escaping from the stomata
is readily recognised by means of cobalt paper. If pieces of this are
laid at the same time on the upper and lower surface of a leaf that
has stomata only on the lower side, a change of colour will take place
in the cobalt paper on this side, while no appreciable giving off of
water will be shown for the upper side.

It is usual to distinguish stomatal and cuticular transpiration, and
we may thus say that only the stomatal transpiration is of importance in
the typical land plant. In plants inhabiting damp localities the cuti-
cular transpiration becomes considerable. Though the openings of the
stomata are extremely small (the breadth of the pore being 0*007 mm.
and less) so that neither dust nor water can pass through them into the
plant, they are usually present in such enormous numbers and so suitably
distributed that their united action compensates for their minuteness.
When it is taken into consideration that, as NOLL has shown, a medium-
sized Cabbage leaf (Brassica oleracea) is provided with about eleven
million, and a Sunflower leaf with about thirteen million stomata,
it is possible to estimate how greatly evaporation must be promoted
by diffusion through these fine sieve-like perforations of the epidermis
and of the cuticular membrane which allows practically no water to
pass. BROWN and ESCOMBE have shown that the movement of
diffusion through this perforated membrane is as rapid as if no cuticle
were present. If this is correct the question presents itself, why
the plant has constructed such a complicated apparatus instead of
allowing free transpiration from unprotected cells. The explanation
lies in the fact that the stomata not merely facilitate transpiration,
but can stop it; they serve to REGULATE the transpiration, which
a cuticle cannot do. The width of the pore of the stoma can be
altered by changes in the guard cells. When the pore is fully opened
transpiration is maximal, and when it is completely closed transpira-
tion sinks to zero. Since the opening and closing of the pore take
place in accordance with the needs of the plant, the stomata are

DIY. ii PHYSIOLOGY 231

organs which react in a wonderfully purposive fashion. Opening
is caused by illumination and by a certain degree of humidity of
the air; on the other hand, darkness or dry air effect a closing
of the pore.

The movements of the guard cells are movements of irritability
and are brought about by changes in turgescence. As a consequence
of the peculiar thickening of the elastic cell walls of the guard cells
(p. 52), an increase of the turgor pressure intensifies the curvature
of the cells and a diminution of turgor lessens the curvature. The
former change leads to the opening of the pore and the latter to its
being closed, as will be evident from Fig. 240 without further descrip-
tion (cf. also Figs. 47-49).

The stomata are mainly present on the leaves, which are thus to
be regarded as organs of transpiration (and of assimilation, p. 249).

FIG. 240. — Storua of Hdleborus sp. in transverse section. The darker lines show the shape assumed
by the guard cells when the stoma is open, the lighter lines when the stoma is closed. (After
SCHWENDENER.) The cavities of the guard cells with the stoma closed are shaded, and are
distinctly smaller than when the stoma is open.

The amount of water evaporated from the leaf surfaces is surprising (14).
For instance, a strong Sunflower plant, of about the height of a
man, evaporates in a warm day over a litre of water. It has been
estimated that an acre of Cabbage plants will give off two million
litres of water in four months, and an acre of Hops three to four
millions. For a Birch tree with about 200,000 leaves and standing
perfectly free, YON HOHNEL estimated that 300-400 litres of water
would be lost by evaporation on a hot dry day ; on an average the
amount would be 60-70 litres. A hectare of Beech wood gives off on
the average about 20,000 litres daily. It has been calculated that
during the period of vegetation the Beech requires 75 litres and the
Pine only 7 litres for every 100 grammes of leaf substance. For every
gramme of dry, solid matter produced, 250-900 grammes of water
are evaporated on the average.

It is evident from these and similar experiments that more water is evaporated
in a given time from some plants than from others. These variations are due to

232 BOTANY PART i

differences in the area of the evaporating surfaces and to structural peculiarities
(the number and size of the stomata, presence of a cuticle, cork, or hairy covering,
etc.). But even in the same shoot transpiration is not always, uniform. This is

attributable to the fact that, both from internal
and external causes, not only the size of the
openings of the stomata varies, but also that
transpiration, just as evaporation from a surface
of water, is dependent upon external con-
ditions. Heat, as well as the dryness and
motion of the air, increases transpiration for
purely physical reasons; while light, for
physiological reasons, also promotes it. From
both physical and physiological causes, tran-
spiration is more vigorous during the day than
night. Plants like Impatiens parviflora, which
droop on warm days, become fresh again at the
first approach of night. Information as to the
condition of opening (15) of the stomata can be
obtained by the use of cobalt paper (cf. p. 230)
or by the method of infiltration. If the stomata
are open, fluids such as petroleum, alcohol, etc.,
easily penetrate and inject the whole system
of intercellular spaces ; the leaf thus becomes
translucent. If a strip of black paper is laid
across a leaf the underlying stomata close. On
treatment with alcohol the appearance repre-
FIG. 241 .-A leaf of Lilac darkened in the sented in Fig. 241 is then obtained. The open
middle while the ends were exposed to condition of the stomata may also be demon-
light. Only the illuminated stomata .
remain open and allow the absolute strated by the method of gaseous diffusion.
alcohol to enter. (After MOLISCH.) If a red leaf containing anthocyan with its

stomata open is placed in air containing

ammonia, a blue colour develops in a few seconds ; this does not take place if
the stomata are closed.

Plants of dry habitats which require to economise the absorbed
water show numerous arrangements which protect them against
excessive transpiration (cf. p. 168). In plants living in very damp
situations, on the other hand, arrangements to further transpiration
are found. When the leaf is able, either by absorption of heat from
without or by the production of heat within itself (p. 276), to raise
its temperature above that of its surroundings, transpiration is still
possible even in an atmosphere saturated with aqueous vapour. In
the process of exudation the plant has a further means of giving off
water even after transpiration has completely stopped.

Exudation (16)

The discharge of water in a liquid state by direct exudation is
not of so frequent occurrence as its loss by transpiration, but is found

DIV. ii PHYSIOLOGY 233

under special conditions, viz. when the plant is saturated with water
and the air is saturated with water vapour. Early in the morning,
after a warm, damp, but rainless night, drops of water may be
observed on the tips and margins of the leaves of many of the plants
of a meadow or garden. The drops gradually increase in size until
they finally fall off and are again replaced by smaller drops. These are
not dew-drops, although they are often mistaken for them ; on the
contrary, these drops of water exude from the leaves themselves.
The drops disappear as the sup becomes higher and the air warmer
and relatively drier, but can be induced artificially if a glass bell-jar
be placed over the plant, or the evaporation in any way diminished.
The excretion of jlrops from the leaves
can be brought about by artificially forcing
water into cut shoots.

The drops appear at the tips of the leaves
in Grasses, on the leaf -teeth of Alchemilla,
and from the blunt projections of the leaves in
Tropaeolum (Fig. 242). They come from so-
called WATER -STOMATA (p. 113) or through
ordinary stomata, or they are secreted by small
pits or hairs (sometimes by stinging hairs).
All such water- excreting organs are termed

HYDATHODES.

The excretion of liquid water is far more
common in moist tropical forests than in tem-
perate climates. Such exudations of water are
particularly apparent on many Aroids, and drops
of water may often be seen to fall, within short
intervals, from the tips of the large leaves. From Fl(; L>42. -Exudation of drops of water
the leaves of Colocasia nymphaefolia the exuded from a leaf of Tropaeolum majus.
drops of water are even discharged a short dis- (After NOLL.)
tance, and 190 drops may fall in a minute from

a single leaf, while ^ litre may be secreted in the course of a night. Again,
in unicellular plants, especially some Moulds, the copious exudation of water is very
evident. The water in this case is pressed directly through the cell walls, and
in some cases also, as is the case in water plants, through the easily permeable
cuticle.

Since the excretion of water in the liquid form can occur when
the conditions are unfavourable to transpiration, especially in sub-
merged water plants, it may in a sense take the place of transpiration
in maintaining the current from the water-absorbing organs. Its
physiological significance is not, however, the same as transpiration,
since the expressed water always contains salts, and sometimes also
organic substances in solution. In fact, the quantity of salts in water
thus exuded is often so abundant that after evaporation a slight
incrustation is formed on the leaves (the lime-scales on the leaves of
Saxifrages and the masses of salt in some halophytes, p. 240). In
some instances, also, the substances in solution in the water may play

234

BOTANY

PART I

the main physiological part in the process as in the case of the

secretions of the NECTARIES, of the DIGESTIVE GLANDS of insectivorous

plants (p. 258), and of the STIGMATIC FLUID.

Bleeding. — Exudation of water may often be observed after a

plant has been wounded ; it is regularly seen in trees and shrubs

when cut in the spring, and is especially
well marked in the Vine. In shrubs cut
off a short distance above the ground, the
extrusion of water from the wound is
readily demonstrated. In this weeping
or bleeding of wounds the water comes
from the vessels 'and tracheides, and is
pressed out with considerable force (ROOT
PRESSURE).

If a long glass tube be placed on the root-
stump and tightly fastened by rubber tubing,
the exuded fluid will be forced up the glass tube
to a considerable height. How great the force of
this pressure is may be shown by attaching to
the stump a manometer (Fig. 243). The column
of mercury will in some cases be forced to a
height of 50 or 60, and under favourable con-
ditions to 140 cm. or more (in the Birch). These
pressures would be sufficient to raise a column of
water 6, 8, and 18 metres high. The amount of
water extruded is greater when the soil is kept
moist and warm ; it continues under such con-
ditions, according to the kind of plant and its
stage of development, some days or even months.
°f The water may amount to many litres : up to

FIG. 243. — Vigorous exudation

water as the result of root-pres- l litre per day in the Vine, 5 litres in the Birch,
sure from a cut stem of Dahlia. , , ., _, -,..17 . _. .

The smoothly-cut stem sis joined and 1Q-15 lltres m_ Palms. In parts of plants

to the glass tube g by means that continue bleeding for some time a certain

of the rubber tubing c. The water periodicity in the amount is noticeable ; more is

W, absorbed by the roots from extruded by night than by day.

The outflowing sap often contains, in addition

the soil, is pumped out of the
vessels of the stem with a force

sufficient to overcome the resist- to mineral salts, considerable quantities of organic

ance of the column of mercury Q.
(After NOLL.)

substances (dissolved albuminous matter, as-
paragin, acids, and especially carbohydrates).
The amount of saccharine matter in the sap of

some plants is so great that sugar may be profitably derived from it. The sap of
the North American sugar maple, for example, contains J per cent of sugar, and a
single tree will yield 2-3 kilos. The sap of certain plants is also fermented and
used as an intoxicating drink (birch wine, palm wine, pulque, a Mexican beverage
made from the sap of Agave, etc.). One inflorescence of Agave will yield 1000
litres of sap in from four to five months.

Causes of the Excretion of Water (17). — The excretion of drops of water from
intact plants is in part due to an active excretion of water from superficial cells.
In other cases water is forced into the vessels, and finds a way out at the points of

DIV. ii PHYSIOLOGY 235

least resistance (p. 114). In the phenomenon of bleeding, also, water is forced from
parenchymatous cells into the cavities of the vessels ; although this process takes
place especially often in roots, it is not always absent in the cases of stems and
leaves.

Thus, when fully analysed, all the phenomena described show a one-sided
excretion of fluid from living cells. That this does not always result from the
same cause is indicated by what was stated above, since the fluid is sometimes
nearly pure water, at other times more or less concentrated sap.

1. The conceptions which have been formed regarding the one-sided excretion
of pure water from a cell cannot readily be summarised here.

2. When the excreted fluid contains dissolved substances in considerable
quantity, for example in nectaries, two possibilities present themselves. Either
these substances come from within the cell and the protoplasm must have become
permeable in one direction to them ; or they have been formed from the outer
layers of the wall and withdrawn water from the cell sap osmotically. It appears
that both possibilities are realised.

Conduction of Water (18)

The water, which is partly given off in the form of vapour,
especially from the leaves, and in part exudes in the liquid form from
hydathodes and wounds, has, as a rule, been absorbed by the roots.
It has thus to traverse a path which, even in annual plants, may
amount to some metres, and in the giants of the vegetable kingdom
may be more than 100 m. ; the stems of Eucalyptus amygdalina
are 100 m., those of Sequoia gigantea 95 m. in height. Osmotic
passage from cell to cell would bring about the movement of this
water far too slowly to cover the loss. The movement of water for
this purpose, or, as it is called, the TRANSPIRATION STREAM, is prac-
tically confined to the woody portion of the vascular bundles, e.g. the
wood of trees. This is shown by a classical experiment repre-
sented in Fig. 244. At Z in the branch b all the tissues external
to the slender column of wood have been removed. Since the leaves
of this branch remain as fresh as those of the branch c, it is evident
that the transpiration current must pass through the wood and not
through the cortical tissues. On the other hand, when a short length
of the wood is removed from a stem without at the same time unduly
destroying the continuity of the bark, the leaves above the point of
removal will droop as quickly as in a twig cut off from the stem.
This experiment can be performed either on intact plants or on cut-
off branches placed in water ; the latter for a time, until changes
have taken place at the cut surface, absorb water as actively as
does the intact plant by its roots. When a branch is cut off and the
cut surface is placed in a solution of gelatine, which penetrates for
some distance into the vessels and can then be allowed to solidify,
the wood will be found to have lost its power of conducting water.

236

BOTANY

PART I

This shows that the cavities of the vessels are essential for water
conduction. In the living plant, however, the vessels and tracheides
always contain air in addition to water, at least when transpiration
is active.

In water plants and succulents, in which little or no transpiration takes place,
the xylem is correspondingly feebly developed. On the other hand, the transpiring

leaf-blades have an extraordinarily rich

h supply of vascular bundles ; these anasto-

mose freely, so that any particular point
is sure to obtain sufficient water. The
illustration (Fig. 126) gives some idea of
this irrigation system of a leaf-blade, but,
since the finest bundles are only visible
with the help of the microscope and are
not represented, the system is even more
complex. The conducting tracts in the
stem leading to the leaves form, especi-
ally in trees which grow in thickness, a
wonderfully effective conducting system.
All the wood of a thickened stem does
not seive this purpose ; water conduction
is limited to the more recently developed
annual rings. When a heart -wood (p.
158) is formed this takes absolutely no
part in the process.

There is still uncertainty as to
the forces which give rise to the
transpiration stream. It is natural
to think of a pressure acting from
below, or a suction from above,
and to regard the former as due to

FIG. 244.-HALES' experiment to show the ascent roOt-presSUre, the latter to the prO-

of the sap in the wood. Although the cortex r £ . „,

has been entirely removed at Z, and the wood C6SS Ot transpiration. I here are,

alone left, the leaves of the branch b remain however, a number of reasons

as fresh as those on the uninjured branch c ; againgt ascribing the movement of

x, vessel containing water. Facsimile of the o

illustration in HALES' Vegetable Statics, 1727. the Water to rOOt-preSSUre, and

whether the suction force exerted

by transpiration is sufficient to continuously raise water to the summit
of a high tree appears doubtful. No generally accepted solution of
the much -discussed problem of the ascent of water has yet been
attained.

The following points have to be considered as regards the root-pressure. In
many plants the root-pressure actually observed is very slight or absent. Even
in plants with a powerful root-pressure the -amount of water thus supplied in a
given time is considerably less than that lost in transpiration. With somewhat
more active transpiration, therefore, the root- pressure is not manifested in the
way described above. When an actively transpiring plant is cut across above the

DIV. ii PHYSIOLOGY 237

root, no water is at first forced from the stock ; but, on the other hand, if water is
supplied to it the cut surface absorbs it greedily (negative pressure). Only after
it is fully saturated does the forcing-out of water commence. In nature root-pressure
thus only comes into play when transpiration is greatly lessened, for instance at
night when the air is damp and cool. The most, favourable conditions for this
phenomenon occur in spring when, on the one hand, the wood is richest in water,
and, on the other, the transpiring foliage is not fully developed. On wounding
the xylem the sap then oozes in drops out of the vessels and tracheides. A positive
root-pressure in trees with foliage appears only to occur in tropical forests.

That transpiration induces a suction from cell to cell has been pointed out
above, and it is clear that this suction will be continued from the parenchymatous
cells into the vessels. This suction force can be readily demonstrated.

A cut shoot placed with its lower end in water shows by remaining fresh that
it is able to raise the water to its uppermost twigs. This does not fully exhibit the
amount of suction force which the shoot can exert, for if the latter is connected with
a long tube filled with water it can support a water column of 2 metres or more in
height. If the end of the tube is dipped into mercury even this heavy fluid will
be lifted to a considerable height. Strong and otherwise uninjured branches of
Conifers are able to raise the mercury to the height of the barometric column, and
even higher, without showing signs of wilting. The connection between the end
of the shoot and the glass tube must of course be air-tight. Necessary conditions
for such a suction are on the one hand an air-tight closing of the water-conducting
tracts such as is actually found in the plant, and on the other hand a considerable
cohesive power of the fluid to be raised, which is also found to "exist in practice.
The conception is thus reached of a pull exerted by transpiration being conducted,
owing to the cohesion of the water, to the tips of the roots of a plant. Very
considerable traction forces have been demonstrated in the conducting tracts of
transpiring plants as is assumed by the COHESION THEORY (19). This theory is,
however, not yet proved. To transmit the suction downwards, the vessels would
require to be continuously filled with water, while, in practice, columns formed
alternately of air and water are found. When a pull took place the air bubbles
would expand, and in practice air under diminished pressure is found in the
vessels of actively-transpiring branches. When such vessels are cut across under
mercury, this is forced for a considerable distance into the cut vessels by the
force of atmospheric pressure. The supporters of the cohesion theory therefore
assume that other tracts completely filled with water are present, and that those
containing air merely serve as a magazine of water. It is not out of the question
that the living elements always present in the neighbourhood of the vessels and
tracheides may play a part in the raising of the water.

(b) The Nutrient Salts

The nutrient salts which are absorbed by a plant are almost all
met with in the ash ; only the compounds of nitrogen are wanting
Thus the following table of the nature of the ash of a number of
cultivated plants affords some insight into the amount and the dis-
tribution of the nutrient salts.

It is seen from this table that the ash - constituents are very
generally distributed but occur in varying proportions in different

238

BOTANY

PART I

plants and different parts of the same plant. The difference brought
out by the table in the proportions of the more important phos-
phoric acid and of the less essential silica and lime contained in
Rye and Pea seeds, as compared with the amounts of the same
substances in the straw, is worthy of notice. The Potato contains
much K20 and little CaO, while the wood of Spruce shows the
opposite condition.

Ash in

100 parts of ash contain

Plants

100 parts of

dry solid

matter.

K20

Na20

CaO

MgO

Fe203

Mn3O4

P205

SO3

Si02

Rye (grain) . .
Rye Cstraw) . .

2-09
4-46

32-10
22-56

1-47
1-74

2-94
8-20

11-22
3-10

1-24
1-91

47-74
6-53

1-28
4-25

1-37

49-27

0-48
2-18

Pea (seeds) . .

2-73

43-10

0-98

4-81

7-99

0-83

35-90

3-42

0-91

1-59

Pea (straw) . .

5-13

22-90

4-07

36-82

8-04

1-72

8-05

6-26

6-83

5-64

Potato (tubers).

3-79

60-06

2-96

2-64

4-93

1-10

16-86

6-52

2-04

3-46

Grape (fruit) . .

5-19

56-20

1-42

10-77

4-21

0-37

15-58

5-62

2-75

1-52

Tobacco (leaves)

17-16

29-09

3-21

36-02

7-36

1-95

14-66

6-07

5-77

6-71

Cotton (fibres) .

1-14

36-96

13-16

17-52

5-36

0-60

10-68

5-94

2-40

7-uO

Spruce (wood) .

0-21

19-66

1-37

33-97

11-27-

1-42

22-96

2-12

2-64

2-73

0-07

In the preceding table the figures do not express absolutely constant proportions,
as the percentage of the constituents of the ash of plants varies according to the
character of the soil.

The mineral substances which form the ash were at first regarded
as accidental impurities of the organic substance of the plant. But
every attempt to obtain a plant free from mineral substances shows
that they form essential constituents.

It was first asserted by BERTHOLLET (1803), and afterwards
emphasised by KARL SPRENGEL (1832), and later by LIEBIG, that the
mineral salts contained in plants were essential constituents of plant
food. Conclusive proof of this important fact was first obtained in
1842 by the investigations of WIEGMANN and POLSTORFF.

This conclusion can be reached by two methods, which at the
same time show whether all or only certain of the substances in
the ash are necessary. The first method is to cultivate the plant
in an artificial soil composed of insoluble substances such as platinum,
pure carbon, pure quartz, with which the substances to be investi-
gated can be mixed. The second method, that of WATER CULTURE,
is more convenient. Many plants are able to develop their root-system
in water instead of in the earth. It is thus possible to add to the
water the elements found in the ash in various combinations, and so
to ascertain which elements are necessary and which superfluous. As
Fig. 245, /, shows, the plant (Buckwheat) succeeds well in such a
food solution if of suitable composition ; it can form roots, shoots,
flowers, and fruits, and increase its dry weight a hundredfold or a
thousandfold, just as if it were growing in the soil. In distilled

DIV. II

PHYSIOLOGY

239

water, on the other hand, while the plant begins to grow normally,
the growth soon ceases entirely, and only a very dwarfed plant is
produced.

Culture solutions of various composition are used (19°). KNOP'S solution
contains — water 1000, calcium nitrate 1, magnesium sulphate 0'25, acid potassium
phosphate 0'25, potassium nitrate 0'25, and *

a trace of ferric chloride. The solution of
v. D. CROXE, with almost completely insoluble
compounds of phosphoric acid and iron, appears
in some cases to give better results (water
1000, potassium nitrate 1, potassium sulphate
0-5, magnesium sulphate 0'5, tertiary potassium
phosphate 0'25, ferrous phosphate 0*25).

From such water cultures it results
that the typical land plant succeeds satis-
factorily if supplied with the elements
K, Ca, Mg, Fe, and H, O, S, P, N, if
in addition 0 and C (the latter as carbon
dioxide) are available in the atmosphere.
There are thus in all ten elements
which must be regarded as indispensable
food -materials. Of these the seven
which remain after excluding H, O, and
C concern us here, since the plant obtains
them as nutrient salts from the soil or
water. Six of these seven are found in
the ash, while the nitrogen escapes on
combustion in the form of volatile com-
pounds. That these seven elements are
completely indispensable is shown by
the fact that if a single one is wanting
its loss cannot be made good by an
excess of the others, or by the presence
of a related element.

FIG. 245.— Water cultures of Fagopyrum

'turn. I, In nutrient solution

containing potassium ; II, in nutrient

solution without potassium. Plants

reduced to same scale. (After XOBBE.)

Thus, for example, potassium cannot, as
a rule, be replaced by sodium, lithium, or
rubidium. Lower organisms (Algae, Bacteria,
Fungi) are able to do without Ca. The absence
of a single necessary element is shown either
by the feeble and dwarfed development of the

plant (Fig. 245, //, absence of potassium) or by characteristic changes in the plant.
The best known of these is the effect of absence of iron, in which case the plant
does not become green (chlorosis). Injurious effects of poisoning are shown when
calcium is lacking.

More accurate consideration shows that it is not correct to speak
of definite elements which are indispensable to the plant. Just as a

240 BOTANY PART I

mixture of the elements H and 0 is not a substitute for water, it is
not sufficient to supply the plant with the elements contained in the
nutrient salts either as elements or in any of their combinations.
Thus metallic potassium or pure sulphur are of no use. The plant
requires particular salts or, since these in part dissociate in water,
particular ions. Necessary kations are K+, Ca++, Mg++, Fe++ (or
Fe+++), while S04~ ", H2P04~ arid N03~ are necessary anions. While
phosphorus and sulphur can only be utilised in these combinations,
the nitrogen can also be obtained, although not always so usefully in
the form of the kation NH4+.

The method of water culture has not only shown the necessity for
certain salts, but also that many substances, especially sodium, chlorine,
and silicon, which the plant usually absorbs can be done without.

Even in halophytes, in which it is present in greatest quantity, sodium is not
indispensable. These plants live in soils rich in sodium chloride not because this
substance is necessary to them but because they bear it better than other plants
do. The concurrence of these in such localities is thus prevented. The character-
istic succulent construction of halophytes (Fig. 195) is more or less completely lost
in the absence of common salt. Sodium appears to be indispensable to the Diatoms
and some Seaweeds (<2°).

Silicon is not indispensable to Equisetum and Grasses which contain considerable
quantities of Si02 ; on the other hand, it is requisite to the Diatoms, the cell walls
of which are almost entirely composed of silicic acid, and owe their permanence
to this. The cell walls of Diatoms form considerable geological deposits of siliceous
earth or kieselguhr. Aluminium (21), while generally distributed in small quantities,
is only absorbed in considerable amount by a few plants (e.g. species of Lycopodium) ;
whether useful or indispensable to these is not established. On the other hand,
although scarcely a trace of iodine can be detected by an analysis of sea-water,
it is found, nevertheless, in large quantities in seaweeds, so much so that at one
time they formed the principal source of our supplies of this substance. Whether
it is essential to these plants is not known.

The substances which, as culture experiments show, are not indispensable for
the life of the plant are, however, of use in so far as they can replace for some
purposes (such as the neutralisation of free acids, etc.) essential elements of plant
food. The latter are thus available for the special purposes for which they
are indispensable. Thus K can be partially replaced by Na, and Mg by Ca.
Certain other substances, although not indispensable, are of use in the plant
economy and of advantage to growth. For example, Buckwheat flourishes
better when supplied with a chloride, and the presence of silica is advantageous
as contributing to the rigidity of the tissues. It has also been found that the
presence of certain substances which are not of direct use may inhibit the poisonous
action of other substances some of which are necessary.

Absorption of Nutrient Salts. — The nutrient salts can only be
absorbed by the superficial cells of the plant when in solution. The
question has to be considered in what way the dissolved substances
reach the vacuole through the cell wall and the protoplasm. It was
seen in connection with plasmolysis (p. 226) that the protoplasm is
semi-permeable, i.e. permeable to water but not to dissolved substances.

DIV. ii PHYSIOLOGY 241

If the protoplasm were really quite impermeable to the salts that
have been considered above, not even traces of them could enter the
cell cavity. Practically, however, the impermeability of the protoplasm
is perhaps not absolute for any substance ; there are all grades, from
substances that pass through the protoplasm as easily as water, to
those that are almost incapable of passing through it. Alcohol, ether,
chloral hydrate, numerous organic pigments, and, lastly, very dilute
acids and alkalies, diffuse with special rapidity.

The permeability of the protoplasm is not always the same, and
may be regulated according to the requirements of the cell (22). The
salts of alkalies, for example, determine an increasing impermeability
as regards themselves, and the salts of the alkaline earths can also
diminish permeability for the alkaline salts. The absorption or not of
a substance is determined not by the whole protoplasm but by its
external limiting layer. In the further passage of the substance, from
the protoplasm into the cell sap, the wall of the vacuole exercises a
similar power of selection. The cause of the SELECTIVE POWER, by
reason of which different cells can appropriate quite distinct con-
stituents or substances in different amounts from the same soil, is to
be sought in this most important property of the limiting layers of the
protoplasm.

From the same soil one plant will take up chiefly silica, another lime, a third
common salt. The action of Seaweeds in this respect is especially instructive ;
living in a medium containing some 3 per cent of common salt and poor in
potassium salts, their cells, nevertheless, absorb relatively little common salt, but
accumulate potassium salts.

Every substance to which the limiting layers of the protoplasm
are permeable must ultimately reach the same concentration in the
vacuole as in the solution outside the cell when its absorption would
cease. Practically it often enters in much greater amount than this.
Thus, for example, only a trace of iodine is present in sea- water,
but may be accumulated in such quantities in seaweeds for these to
become a source from which it is commercially obtained. The cell
has not only a selective power, but is also able to store up materials
by converting them into insoluble or indiffusible forms.

Certain organic pigments (23) such as methylene blue are especially suited to
demonstrate the entrance and accumulation. Many cells contain tannins in their
vacuoles, and these substances form with the entering pigment a compound which
is indiffusible or quite insoluble. For this reason the vacuole becomes deeply
coloured or has blue precipitates, though the solution of methylene blue employed
is extremely dilute. It is noteworthy that the protoplasm itself remains un-
stained and is not in any way injured ; the pigment would be accumulated iu
dead protoplasm.

Under natural conditions some plants absorb the nutrient salts
from water as do the plants in a water-culture experiment. This is

242 BOTANY PART I

the case in many water plants in which the whole external surface is
of use in absorption. Since the salts only exist in very dilute solution
in the water, the need of an extended surface for this purpose is
readily understood; this in part explains the frequent occurrence of
finely divided leaves in water plants. The salts dissolved in the water
are not, however, sufficient for all aquatic plants; many absorb
substances from the soil underlying the water by means of their roots,
and do not succeed when deprived of roots.

As a rule in the higher plants the salts are absorbed from the soil.
The salts contained in the nutrient solution described above, or similar
compounds, are constantly present in the water of the soil ; some of
them, however, in such small amount as only to suffice for the growth
of plants for a short period. Other sources of supply of the food-salts
must exist when such growth continues. In fact, the amount of salts
dissolved in the soil-water is no measure of the fertility of the soil.
The soil always contains food-salts, partly in an absorbed condition,
and partly in mineral form which the plant has to render accessible.
This is effected mainly by the excretion of carbonic acid from the root-
hairs. Many substances are much more readily soluble in water con-
taining carbonic acid than in pure water.

The solution of solid rock by the plant may most readily be shown by allowing
the roots to grow against smooth polished slabs of marble ; the course of the roots
is indicated by the etching of the surface.

There are other cases in which stronger acids than carbonic acid excreted by
the plant are concerned in bringing minerals into a soluble form. This can hardly
be doubted when felspar and mica are dissolved by certain Lichens (24). Fungi
and Bacteria also frequently produce and excrete solvents of this kind during their
metabolism, and may have a similar effect on insoluble substances in the soil.

Some soils, especially those containing much clay, lime, or humus, have the
property of retaining potassium and ammonium salts, and in less degree salts of
calcium and magnesium, as well as phosphates ; these substances are not easily
washed out of the soil but can be obtained by plants. This is spoken of as the
power of absorption of the soil for the substances in question. This does not hold
for all salts ; thus, for instance, sulphates and nitrates are not absorbed. Absorp-
tion is completely wanting in a pure sandy soil.

When the substratum contains, in addition to water and nutrient
salts, dissolved organic substances, these may be absorbed in the same
way. Water cultures show, however, that at least the typical green
plant is not dependent on such substances. It is otherwise with the
Fungi and other plants which resemble them in metabolism (p. 255).^

In addition to water and nutrient salts dissolved gases may also be
absorbed by the roots. As a rule only oxygen need be considered.
The main source from which gases are absorbed is the atmosphere.

Transport of the Nutrient Salts. — The salts do not remain in
the epidermal cells of the root or shoot but pass from the place of
absorption through the whole plant. This takes place in two ways,

DIV. ii PHYSIOLOGY 243

by DIFFUSION and by CONDUCTION. Necessary conditions for diffusion
are that the cell wall and protoplasm should be permeable for the
substance in question, and that there should be a difference in its
concentration between the starting place and termination. In the
transport from one vacuole to that of the neighbouring cell the
substances must first pass into the protoplasm, then into the cell
wall, then again into the protoplasm, and finally into the vacuole.
The cell walls, at all events when thick, appear to offer special
difficulty in the process. On this account all thickened cell walls
are provided with thin places (pits), and the pit membranes are
traversed by fine protoplasmic threads (plasmodesms, p. 44). In
the sieve -tubes the pit membrane is absorbed, and thus coarser
strands of protoplasm connect the one cell with its neighbour. The
investigations of BROWN and ESCOMBE have shown that a finely per-
forated septum, if the perforations are a certain distance apart, offers
no obstacle to diffusion (25).

Movements of diffusion may also take place within a cell if dissolved
substances are not at the same concentration throughout the cell.
Movements of diffusion proceed quite slowly. The rapidity with
which mixing occurs may be greatly hastened if a movement in
mass be added to that due to diffusion. In common life and in the
laboratory this is effected by shaking the solution, and within a cell
the same result may be obtained, e.g. by the protoplasmic movements.
The greater the length of a cell the more suitable is it for conducting
material through the plant, since the slow diffusion movement need
only take place at long intervals, i.e. at the ends of the cell • in the
intermediate portion movements of mixing play a large part.

When a plant requires more rapid transport of materials the
nutrient salts are conveyed in the plant by the transpiration current.
It is thus not merely water but a very dilute food-solution that is
conducted by the vascular bundles, and the use of transpiration is, in
the first place, to concentrate this nutrient solution and, in the second,
to bring it quickly to the proper parts of the plant. Apart from this
result it would be difficult to understand the process of transpiration,
and the plant would certainty have found means of limiting it. When
it is actually checked (cf. p. 168), we have to do with plants which
grow slowly on account of the poor supply of salts, and also it is true
of carbonic acid.

Nutrient Salts and Agriculture. — Since the plant thus continues
to absorb nutrient salts from the soil, this must become poorer in the
particular substances unless the loss is repaired in some way. In
nature this results from the fallen and dead parts of plants returning
to the soil, and the salts contained in them becoming available for
further life. In agricultural practice, however, a large proportion of
the vegetation is removed in the crop, and the salts it contains are
thus lost to the ground ; at the most a fraction may be returned to

244 BOTANY PART I

the soil in the dung of grazing animals. The effect of manure in
increasing growth, which has for ages been known to practical men,
depends at least in part on the salts contained in it. Since, however,
the amount of salts thus returned to the soil is insufficient to meet the
loss, artificial manuring is required in agricultural practice (26). The
first place among manures must be given to those which contain
nitrogen, potassium, and phosphoric acid. Nitrogenous substances
which are used besides guano (which also contains phosphoric acid)
are Chili saltpetre, ammonium sulphate, calcium cyanamide, and
calcium nitrate ; the two last have recently been, artificially prepared
from atmospheric nitrogen. Potassium is present in the Stassfurt
waste salts, of which kainite is the most important since it also
contains MgS04. As an important source of phosphorus, the so-called
Thomas slag may be mentioned ; this substance is formed in working
ores containing phosphorus, and consists of triple phosphate of calcium.
It can only be utilised by plants when in a state of very fine sub-
division, as what is known as " Thomas-meal." Superphosphate is
obtained by the treatment of potassium phosphate with sulphuric acid.
The Soil and Plant Geography. — From what has been said it
might be concluded that a soil capable of supporting one kind of plant
must be able to support any other species. Plant geography (27),
however, shows that the composition of the soil exerts a great influence
on the distribution of plants. This depends, on the one hand, on the
fact that different plants make different demands on the amount and
solubility of the essential food-materials, and, on the other, upon the
presence in the soil of substances other than the indispensable salts ;
the influence of these non-essential substances is different upon different
species of plants. For example, CaCo3 has a poisonous effect on some
plants, and NaCl upon others, while other plants can endure large
doses of these substances.

The effect of the soil upon the distribution of plants does not depend merely
upon its chemical nature. The physical properties of soils play an important role.
Further, a plant may be absent from a locality, which, so far as the nature of the
soil is concerned, would be suitable, because its seeds have never been brought to
the spot.

(e) Gases

While water and salts are, as has been seen, as a rule absorbed from
the soil, the air contains substances which are necessary to the success-
ful existence of the plant, and must be termed food-materials. These
are carbon dioxide and oxygen. They are, as a rule, obtained from
the atmosphere. Only submerged water plants obtain them from the
water, in which case they are absorbed in the same way as other
dissolved substances.

Oxygen. — When a plant is deprived of oxygen, all vital manifesta-

DIV. ii PHYSIOLOGY 245

tions usually cease. Since oxygen is also essential to the human
organism, this fact does not seem surprising (cf. p. 273).

Carbon Dioxide. — It appears at first sight much less self-evident
that carbon dioxide should be indispensable to the plant, and yet
this is the case. While no source of carbon is offered to the plant
in a water culture, it grows in the food-solution, and accumulates
carbon in the organic compounds of which it consists ; the only
possible conclusion is that the plant has utilised the carbon dioxide of
the atmosphere. Carbon dioxide is present in ordinary air in the pro-
portion of 0'03 per cent. If such air is passed over a green plant
exposed to bright light, it can be shown that the carbon dioxide
diminishes in amount or disappears. Colourless parts of the plant, or
organisms like tjie fungi which are not green, behave differently ; they
absorb no carbon dioxide. If a green plant is placed in a bell-jar and
supplied with air freed from carbon dioxide, its growth soon stops, and
increase in dry weight ceases completely. Carbon dioxide is thus an
indispensable food-material, and is evidently the source from which the
plant obtains its carbon. The small proportion of this gas present in
the atmosphere is quite sufficient for the nutrition of plants (p. 251).
A supply of. organic compounds of carbon in the soil or culture solution
does not enable a plant to dispense with the carbon dioxide of the air ;
in any case CO., is the best source of carbon for the green plant which
we are at present considering. Neither is it sufficient to supply such
a plant with carbonic acid in the soil or culture solution ; it requires
to be supplied directly to the leaves.

Other Gases. — Oxygen and carbon dioxide are the only gases
which are necessary to the plant. For most plants the nitrogen of
the atmosphere is of no use (cf. p. 259).

Absorption of Gases. — Carbon dioxide and oxygen in part enter
the epidermal cells, and partly pass by way of the stomata into the
intercellular spaces, from which they reach the more internal tissues.

There are no air-filled canals or spaces in the cell wall or the
protoplasm through which gases could diffuse into the cell. Thus
absorption of gases is only possible in so far as they are soluble in
the water permeating the protoplasm and wall. The gases behave
like other dissolved substances and diffuse into the cell. They
diffuse through cell walls more easily the richer in water these are.
The ordinary cell wall, when in a dry condition, hardly allows gases
to diffuse through it (28) ; in nature, however, the cell wall is always
more or less saturated with water. The cuticle, on the other hand, has
very little power of imbibing water, and places considerable difficulty
in the way of any diosmotic passage of gases ; it is not, however, com-
pletely impermeable.

The gaseous diffusion takes place rather through the substances
with which the cell wall is impregnated than through the substance
of the wall itself. Since carbon dioxide is much more readily

246

BOTANY

PART I

soluble in water than is oxygen, it will be evident that it will
pass more rapidly through a cell wall saturated with water than
oxygen will. In all probability this holds for the cuticle as well.
Since, however, the partial pressure of the oxygen in the air is
relatively considerable, while that of carbon dioxide is very slight,
oxygen can pass in sufficient quantity through the cuticle, but carbon
dioxide cannot ; on this account we find that all organs which only
require to absorb oxygen are unprovided with stomata, while organs
which absorb carbon dioxide always have stomata.

In the soil as well as in the air, plants, as a rule, find so much oxygen that this
gas is able to pass through the epidermis. Organs which live in swampy soil

which is poor in oxygen form an exception to this.
In marsh plants, which stand partly in the air, the
large intercellular spaces form connecting canals
through which the atmospheric oxygen without
being completely used up can reach the organs grow-
ing deep in the swampy soil and cut off from other
supplies of oxygen. In some cases (especially in
Palms and Mangroves) the need of a supply of oxygen
to such roots is met by specialised roots (PNETJMATO-
PHORES) which project vertically from the muddy
soil (Fig. 188), and absorb oxygen from the air.
The efficiency of the stomata in gaseous exchange
varies with the width to
which the pores are open.
The closure of the pores of
the stomata, which may be
brought about in maintain-
ing a sufficient supply of
water, not only arrests
FIG. 246.-Diagram of an experiment to demonstrate the transpiration, but also pre-

inovement of air through the stomata. vents the entrance of C02

into the plant.

It has been seen in considering the giving off of water vapour that the stomata
in spite of their small size facilitate diffusion on account of their enormous
numbers and their distribution. This also applies to the absorption of carbon
dioxide. Thus, for example, a square metre of the surface of a Catalpa leaf absorbs
about two-thirds the amount of carbonic acid gas taken up in an equal time by the
same area of potash solution freely exposed to the air.

The Movement of Gases from cell to cell and their interchange
between the cells and the intercellular spaces takes place by diffusion.
In the intercellular spaces movements in mass due to pressure are
concerned. Unequal pressure is set up by the warming or cooling
of the air in the intercellular spaces, or by movement of the part of
the plant leading to changes of shape. The intercellular spaces form
a highly-branched system of cavities communicating with one another
and with the atmosphere. The communication with the outside is
effected in the first instance by the stomata, and also by the lenticels

DIV. ii PHYSIOLOGY 247

and organs of similar function (p. 59) ; both diffusion and move-
ments in mass of the gases go on through these openings.

- That the intercellular spaces were in direct communication with each other, and
also with the outer atmosphere, was rendered highly probable from anatomical
investigation, and has been positively demonstrated by physiological experiment.
It is, in fact, possible to show that air forced by moderate pressure into the inter-
cellular passages makes its escape through the stomata and lenticels ; and con-
versely, air which could enter only through the stomata and lenticels can be drawn
out of the intercellular passages. The method of conducting this experiment can
be seen from the adjoining figure (Fig. 246). The leaf-stalk of an uninjured leaf
of Nymphaea is introduced into a glass cylinder which has been filled with and
inverted in water. The leaf- blade is under atmospheric pressure ; the pressure
on the cut end of the petiole is less than this by a fe.w centimetres of water. This
difference is, however, sufficient to maintain an active current of air from the cut
petiole. That this air enters by the stomata is shown by the stream ceasing when
the upper surface of the leaf is submerged and the stomata thus cut off from the air.
Intercellular air-spaces are extensively developed in water and marsh plants
(cf. p. 165), and may form two-thirds of their volume. The submerged portions
of water plants unprovided with stomata thus secure a special internal atmo-
sphere of their own, with which their cells maintain an active interchange of
gases. This internal atmosphere is in turn replenished by slow diffusion with the
gases of the surrounding medium. As regards the rest of their gaseous interchange,
these plants are wholly dependent on processes of diffusion, since stomata, etc., are
wanting. Plants which possess these organs may also obtain gases by diosmosis
if the cuticle of their epidermis is permeable to gases.

III. The Assimilation of the Food-Materials

The plant grows and continues to form new organs ; for these
purposes it continually requires fresh supplies of food-materials. The
materials of the food become changed after their absorption, and the
substance of the plant is built up from them. They are said to have
been ASSIMILATED. By assimilation is understood the transformation
of a food-material into the substance of the plant. Those pro-
cesses of assimilation in which profound changes take place, e.g. the
change from inorganic to organic compounds, are especially interesting.
This is particularly the case when we are still unable to experimentally
bring about the reaction outside the organism.

A. ASSIMILATION OF CARBON
1. Assimilation of Carbon Dioxide in Green Plants

The assimilation of carbon dioxide by a green plant is a process of
the kind referred to in which organic substance containing carbon is
derived from carbon dioxide. In the assimilation of carbon dioxide,
soluble carbohydrates such as grape-sugar are formed in the chloro-
plast under the influence of sunlight. If we assume that the carbonic

248

BOTANY

PART I

acid gas of the atmosphere (carbon dioxide, C02) becomes on its solu-
tion in the cell H2C03, the formation of sugar would take place in two

stages. In the first, oxygen would
be given off and formaldehyde (28a)
formed :

H2COS

H2CO

02.

In the second stage the aldehyde
is polymerised to sugar :

In any case, for every volume
of carbon dioxide which disappears
an equal volume of oxygen makes
its appearance. It has been shown
by eudiometric measurements that
this is the case (WILLSTAETTER).
The oxygen given off can, how-
ever, even when it is only detected
qualitatively, be used as an indi-
cator of the decomposition of the
carbonic acid. Thus, when a plant
is enclosed along with phosphorus
in a space free from oxygen and
exposed to light, the formation
of oxygen is shown by the white
fumes given off from the phos-
phorus. Another means of draw-
ing conclusions as to the production
of oxygen by a green plant is
afforded by the movements of
certain Bacteria which previously
lay motionless in the water (p.
331). The clearest demonstration
of assimilation is obtained by using
certain water plants such as Elodea or Potamogeton. If cut shoots or
leaves of these plants are submerged in water and exposed to light, a
brisk continuous stream of bubbles comes from the cut surface. If the
gas is collected in considerable quantity in a suitable apparatus, e.g. in
a test-tube (Fig. 247), it can be shown to consist not of pure oxygen
but of a mixture of gases rich in oxygen ; a glowing splinter bursts
into flame in the gas.

The appearance of the bubbles of oxygen is explained in this way. The carbon
dioxide dissolved in the water enters the green cells of the plant by diffusion and is
there decomposed. The oxygen given off is much less soluble than carbon dioxide
and therefore appears in the gaseous form. It passes into the intercellular spaces,

FIG. 247. — Evolution of oxygen from assimilating
plants. In the glass cylinder C, filled with
water, are placed shoots of Elodea canadensis ;
the freshly-cut ends of the shoots are intro-
duced into the test-tube R, which is also full
of water. The gas bubbles B, rising from the
cut surfaces, collect at S. H, stand to sup-
port the test-tube. (After NOLL.)

DIV. ii PHYSIOLOGY 249

causing there an increase of the pressure, and this is the cause of the appearance of
bubbles of gas at every wounded surface.

The foundations of our knowledge of the assimilation of carbon
dioxide by the green plant were laid, in the end of the eighteenth
and beginning of the nineteenth centuries, by PRIESTLEY, INGEN-
HOUSS, SENEBIER, and TH. DE SAUSSURE. The discovery is of
extraordinary significance, for THE FORMATION OF ORGANIC MATERIAL

FROM CARBON DIOXIDE BY THE GREEN PLANT IS THE PROCESS WHICH
KKNDERS POSSIBLE THE LIFE OF ALL OTHER ORGANISMS AND IN
PARTICULAR OF ANIMALS UPON THE EARTH (cf. p. 255).

By means of the gas-bubble method it is easy to bring proof of
the statement made above that only the green parts of plants, and
these only in light, are able to assimilate C02. Thus the stream
of bubbles from an Elodea which goes on briskly at a brightly-lit
window becomes slower as the plant is brought into the middle
of the room, and ultimately ceases when the intensity of the light is

400

FIG. 248. — Absorption spectrum of chlorophyll according to GR. KRAUS. The Fraimhofer lines
(B, C, etc.) are indicated above and the wave-lengths (700 /t^-400 /&/*) below. The black and
shaded regions are those where the light is absorbed or weakened.

still such as to allow our eyes to read. Within certain limits
assimilation increases in proportion to the intensity of the light.
Similar experiments may be carried out using artificial sources of
light. They show that all the methods of illumination in common
use may be effective in the assimilation of C02. The rays of different
wave-length are by no means of equal use in assimilation.

The ultra-red and ultra-violet rays have very little effect, and the assimilatory
activity is almost entirely limited to the rays of a wave-length from about 0'4 p
to 0 '8 ft which are perceived by our eyes. "Within these limits light of a wave-
length of about 0'68 /* has undoubtedly the greatest effect ; this is the wave-length
at which the maximum absorption of light by chlorophyll occurs (Fig. 248). In
other regions of the spectrum also, according to URSPRUXG, there is a correspondence
between the absorption of light and assimilatiou. It is true that the assimilation
in blue and violet light is not so great as the absorption bands would suggest ;
according to UKSPUUXG this depends on secondary causes.

Since sunlight is in nature an indispensable factor in C02 assimila-
tion it becomes at once clear why certain organs of the plant, the
foliage leaves, have a flat expanded shape. Their large surface fits

250 BOTANY PART i

them to absorb the light. If their function of C02 assimilation is
to be well performed the foliage leaves must not only have a large
surface but also be thin. Practically it appears that light which has
passed through one or two foliage leaves is unable to exert any further
assimilatory effect. The leaves must, however, contain a very large
number of chlorophyll grains. Their dark green colour shows that
this is the case, and microscopical examination confirms this. Stems
have far fewer chloroplasts than the leaves, and the roots and other
subterranean organs have none at all.

Every investigation shows that organs without chlorophyll are
quite unable to assimilate carbon dioxide. This holds not only for
the organs of the plant but for the parts of the cell. The colourless
protoplasm and the nucleus of the cell give off no oxygen when
exposed to sunlight ; this can readily be proved by the bacterial
method (p. 248). The chloroplasts alone are the active organs in C02
assimilation, and only when they contain chlorophyll ; etiolated or
chlorotic chloroplasts are not functional.

In the red-leaved varieties of green plants, such as the Purple Beech and Red
Cabbage, chlorophyll is developed in the same mariner as in the green parent
species, but it is hidden from view by a red colouring matter in the epidermis or
in deeper-lying cells. In the Red Algae, on the other hand, the chromatophores
themselves have a red colour ; after death a red pigment (phycoerythrin) becomes
free, leaving the chloroplasts green. Regarding the pigments in the Phaeophyceae
and the Diatomeae cf. p. 19.

In studying the effect of different kinds of light upon assimilation, it is custom-
ary either to use the separate colours of the solar spectrum, or to imitate them by
means of coloured glass or coloured solutions. SCHOTT and others have employed
red and blue glasses or double-walled bell-jars filled with suitably-coloured
solutions.

Only a relatively small percentage of the light which falls on the
leaf and is absorbed is utilised in the assimilation of C02 (29). That,
however, light must disappear as such in C02 assimilation is clear, for
from what other source than the energy of light could the energy be
obtained that is stored up in the organic substance formed in assimila-
tion ? This potential energy of the organic substance of the plant
serves to maintain the vital processes. The force exerted by our
steam-engines is also to be traced to the assimilatory activity of the
plants, the wood or the carbonised remains of which are burnt
beneath its boiler. In the combustion of the reduced carbon com-
pounds to carbon dioxide the energy, which was previously required
to transform carbon dioxide into the combustible materials, again
becomes free.

The assimilatory activity of a chloroplast, like every vital function,
is dependent on a number of internal and external factors. To the
internal factors belong the presence of the pigment chlorophyll and
its situation in a living chloroplast. Chlorophyll itself, separated from

DIV. ii PHYSIOLOGY 251

the plant, is as little able to decompose the carbon dioxide as is a
chloroplast which for any reason has not developed the characteristic
pigment (chloroplasts developed in the dark or in the absence of iron,
leucoplasts of subterranean parts or of epidermal cells) or has lost it
(chromoplasts). Since, however, assimilation is not proportional to the
amount of chlorophyll, it is necessary to assume with WILLSTAETTER (30)
that in addition to the pigment another factor is essential, whether
this is the protoplasm of the chloroplast or an enzyme which it contains
(p. 264).

Among external factors sunlight as referred to above must be
mentioned first, and next the presence of carbon dioxide. Since the
latter is only present in small proportion in the air, the life of plants,
and with this tl\e existence of all organisms, would ultimately cease
were not fresh supplies of carbon dioxide continuously produced.
Estimating the amount of carbon dioxide in the atmosphere at 2100
billion kilogrammes and the annual consumption by green land plants
at 50-80 billion kg., the supply would be used up in some thirty
years (30a).

The air is continually receiving new supplies of carbonic acid through the
respiration and decomposition of organisms, through the combustion of wood and
coal, and through volcanic activity. An adult will exhale daily about 900 grammes
C0.2 (245 grammes C). The 1400 million human beings in the world would thus
give back to the air 1200 million kilos of C02 (340 million kilos C). The C02
discharged into the air from all the chimneys on the earth is an enormous amount.
In Germany alone in 1911, besides 73 million tons of brown coal, 161 million
tons of coal were used ; the latter would produce some 400,000 million kg. of
carbon dioxide, which is about 1/5000 of the total amount in the atmosphere.
Animals produce large amounts of carbon dioxide in respiration, as also do plants,
including fungi and bacteria (especially the bacteria of the soil).

The fixation of carbon dioxide by green plants and the production of carbon
dioxide in the ways referred to are approximately equivalent. The amount of
carbonic acid gas contained in the air varies at different times and places. It
has been found that in 10,000 litres of air it was 27 to 2'9 litres in July, 3 '0-3 '6
litres in the winter ; close to the ground 12-13 litres were present in the same
volume. The average amount is about 3J-3£ litres in 10,000 litres of the
atmosphere. This weighs about 7 grammes, of which T8T is oxygen, and only T3T
carbon. Only 2 grammes of carbon are thus contained in the 10,000 litres of air.
In order, therefore, for a single tree having a dry weight of 5000 kilos to acquire its
2,500,000 grammes of carbon, it must deprive 12 million cubic metres of air of their
carbonic acid. From the consideration of these figures, it is not strange that the
discovery of INGENHOUSS was unwillingly accepted, and afterwards rejected and
forgotten. LIEBIG was the first in Germany to again call attention to this discovery,
which to-day is accepted without question. The immensity of the numbers just
cited are not so appalling when one considers that, in spite of the small percentage
of carbonic acid in the atmosphere, the actual supply of this gas is estimated at
about 2100 billion kilos, in which are held 560 billion kilos of carbon. The
whole carbon supply of the atmosphere is at the disposal of plants, since the C02
becomes uniformly distributed by constant diffusion.

Submerged water plants absorb the C02 dissolved in water. Its amount varies

252 BOTANY PART i

considerably according to the temperature. At 15° C. a litre of water contains about
as much C02 as a litre of atmospheric air. The dissolved bicarbonates also play
an important part in the supply of carbon to aquatic plants (31).

Artificially conducting carbonic acid through the water increases, to a certain
degree, the evolution of oxygen, and the assimilatory activity. Similarly an
artificial increase of carbonic acid in the air is followed by increased assimilation.
Whether and to what extent an artificial enriching of the air in C02 would be of
advantage in horticulture or agriculture cannot be said (32).

The C02 assimilation, like all vital processes, is dependent on the
temperature. It begins at a temperature a little above zero, reaches
its maximum at about 37° C., and again stops at about 45° C.

These cardinal points not only have different positions in different plants but
do not remain constant for any particular plant. This is especially true of the
optimum which in the course of a few hours may sink from 37° C. to 30° C. In bright
warm weather assimilation does not reach its full possible value since the supply of
carbon dioxide is then insufficient.

Other less important factors need not be considered in detail. It may be
mentioned, however, that many substances can bring about a temporary, or
ultimately a permanent, limitation or arrest of the assimilatory process.

Products of the Assimilation of Carbon Dioxide. — It was assumed
above that sugar was formed from the carbon dioxide, and analysis
in fact shows that the amount of sugar in a foliage leaf is increased
after exposure to sunlight. It is true that grape-sugar is neither
always nor only shown to be present ; usually other more complex
carbohydrates appear. These can all, however, be traced back to
hexoses like grape-sugar, and arise by the union of two or more
molecules of hexose and the loss of the elements of water. Prominent
among them are cane-sugar (C12H22On) and starch (C6H1005)n. The
occurrence of starch in the chloroplasts of illuminated foliage leaves is
very common, but by no means general. When the leaves are placed
in darkness for some time the starch disappears. When on the other
hand a part of the plant from which the starch has been removed is
exposed to sunlight, new starch grains often form in the chloroplasts
in a surprisingly short time (5 minutes) ; these soon increase in size
and ultimately exceed in amount the substance of the chloroplast itself.
Since starch is stained blue by iodine the commencement of assimila-
tion can be readily demonstrated macroscopically (SACHS* method).

Leaves which have been in the light have their green colour removed by means
of alcohol, and are treated with a solution of iodine ; they take on a blue colour.
If the amount of starch is greater the colour is a deeper blue or almost black. The
depth of the coloration thus affords a certain amount of information as to the
quantity of starch present. To demonstrate smaller amounts of starch the
decolorised leaves are placed, before staining with iodine, in a solution of potash or
of chloral hydrate in order to swell the starch grains. This method of demonstrat-
ing assimilation can also be used to show that the starch only appears in the
illuminated portions of the leaf. If a stencil of opaque material from which, for
instance, the word "Starke " has been cut is laid on the leaf, the word " Starke "

IHV. II

PHYSIOLOGY

253

will appear blue on a light ground, as in Fig. 249, when the leaf after being
illuminated is treated with iodine. Instead of a stencil a suitable photographic
negative can be used, as MOLISCH has shown ; after illumination and subsequent
treatment with iodine a positive photograph is obtained (Fig. 250).

In some plants (many Monocotyledons) no starch is formed in the chloroplasts,
but the products of assimilation pass in a dissolved state directly into the cell
sap. Starch is formed, however, where there is a surplus of glucose, sugar, and
other substances, as, for example, in the coloured plastids of flowers and fruits.
The guard cells of the stomata and the cells of the root-cap of these Monocoty-
ledons also contain starch. In other cases only a fraction of the product of
assimilation appears as starch (in Relianthus, for example, only £), while the rest
remains as sugar or is otherwise
made use of. It is thus clear that
the amount of starch formed cannot
always be taken as*a measure of
the assimilation.

Starch formation can be induced
to take place in the dark by float-
ing leaves on a sugar solution ot
suitable concentration. This shows
that the formation of starch does

FIG. -_>49. — Assimilation experiment
with the leaf of Arivpsis peltata.
(Reduced.)

'.— The positive photoyraph obtained by cover-
ing a leaf of Tropaeolum which has been freed of
starch by the negative and exposing it to the sun.
After assimilation the leaf has been treated with
iodine. (After MOLISCH.)

not stand in direct connection with the assimilation of carbon dioxide but is only
the result of the accumulation of sugar in the cell.

In some Algae neither sugar nor starch but other products of assimilation are
formed, e.g. Floridean starch.

The nature of the "fat-drops" which frequently appear in assimilating cells
and their connection with this process is still uncertain (32°).

The Quantity of the Assimilated Material depends on the one
hand upon the kind of plant and on the other upon the external
conditions to which it has been exposed. It can be said that a square
metre of leaf of an actively assimilating plant under optimal external
conditions produces between 0'5 and 1 gramme of dry substance per
hour. When it is considered how many square metres of leaf surface
are daily assimilating, a conception can be formed of the huge produc-
tion of organic substance in this largest of all chemical factories.
SCHRODER estimates the amount formed annually by land plants

254 BOTANY PART i

as about 35 billion kg. The German harvest alone contained in 1912
some 9 milliards kilos of assimilated material in the cereals (rye,
wheat, spelt, barley).

There are two methods (33) in use for determining the amount of assimilation.
The method invented by SACHS is as follows. In the morning portions of
leaves, usually halves, are removed ; their siiperficial area is measured and they
are then dried and weighed. In the evening equally large portions (the remaining
halves) of the leaves which have been exposed to light throughout the day are
similarly dried and weighed. The increase of weight indicates the gain to the
plant by the assimilation of carbon. This is SACHS' half-leaf method. A quite
distinct method of quantitatively determining the assimilation of C02 is that of
KREUSLER which has been used by GILTAY and BROWN. A leaf still attached to
the plant is placed in a closed chamber through which a constant current of air
passes ; the amount of C02 removed from the air by the leaf is determined. The
amount of sugar or starch which could be formed from this amount of C02 can
then be easily calculated.

2. The Gain in Carbon by Bacteria (34)

Certain Bacteria, which will be described in another part of this
text-book, are characterised by the power of increasing their substance
in a purely inorganic food-solution ; they do this in the dark and
without chlorophyll so long as carbonates are present. This has been
determined for the Nitrite- and Nitrate-bacteria, the Sulphur-bacteria,
and for the Bacteria which oxydise methane and hydrogen. Some of
them depend entirely on C02, while others can also utilise organically-
combined carbon.

Nothing is known at present of the products of carbon assimilation
in these Bacteria. The gain in organically-combined carbon is slight.
Only a quite minimal fraction of the organic carbon compounds which
at any moment exist on the earth owes its origin to these Bacteria.
The fact of their carbon assimilation remains none the less interesting,
especially since it takes place in an essentially different manner to the
assimilation of the green plant. Some other source of energy must
take the place that sunlight does in assimilation in a green plant to
build up the organic substance ; this energy is obtained by oxidation
of ammonia, nitrites, oxide of iron, sulphuretted hydrogen, methane,
and hydrogen (p. 274). .We may therefore term the formation of
organic material in green plants PHOTOSYNTHESIS, and in these Bacteria

a CHEMOSYNTHESIS.

3. The Gain in Carbon in Heterotrophie Plants

While the gain of carbon from carbon dioxide is to be considered
as the typical carbon assimilation of plants, it is by no means the only
method found in the vegetable kingdom. Since it depends — leaving
the Bacteria mentioned above out of account — on the presence of

DIV. ii PHYSIOLOGY 255

chlorophyll and of sunlight, it cannot "come into consideration in sub-
terranean parts of plants, in all plants that are not green, and in the
case of all animals. All these are in fact dependent on organically-
combined carbon which has been derived directly or indirectly by the
assimilatory activity of green parts of plants. All organisms which
in their nutrition are dependent on the activity of" green plants are
termed heterotrophic ; the green plants and also the Nitro-bacteria are
termed autotrophic. Autotrophic plants also depend on other organisms.
It will be seen that life is only continuously maintained on the earth
by the changes in substances effected in one direction by particular
organisms being balanced by the activity of other organisms. Hetero-
trophic organisms show by their mode of life, and especially by the
situations in which they live, that they make other demands on food-
material than do autotrophic plants. They occur either as parasites
on living plants and animals, or they live as saprophytes on dead
organisms or substances derived from organisms.

The demands which heterotrophic plants make on a source of carbon
can be best studied in saprophytic Bacteria and Fungi. These
organisms can be cultivated on various complex substrata, and 'con-
clusions can be drawn from their growth as .to the nutritive value of
the compounds supplied as food. The nutrient solution must as a
rule contain, in addition to the indispensable mineral substances and
a source of nitrogen (usually a salt of ammonia), sugar as a source
of carbon. It should have a slightly acid reaction for mould fungi and
be weakly alkaline or neutral for bacteria, and -is often converted into
a solid medium by mixture with gelatine or agar-agar. The sugar
can, in many cases, be more or less suitably replaced by other organic
substances such as other carbohydrates, fats, albumen and derived
substances, organic acids, etc. While these sources of carbon can
be placed in order as regards their nutritive value for any particular
organism, this cannot be done generally ; there are many saprophytes
which are adapted to quite peculiar conditions and use in preference,
as a source of their carbon supply, compounds, which for the majority
of other plants have scarcely any nutritive value (e.g. formic acid,
oxalic acid).

Even the saprophytes which succeed on very various compounds of carbon
(omnivorous saprophytes) are capable of distinguishing between them. Thus from
ordinary tartaric acid Penicillium only utilises the dextro-rotatory form, and Bacillus
subtilis only the laevo-rotatory form. Aspergillus growing in a mixture of glucose
and glycerine utilises the former first ("election" of nutritive materials). If the
glycerine alone is given, it is completely utilised.

The power possessed by many Fungi of utilising such organic
compounds as starch, cellulose, etc., which are insoluble in water, is
very remarkable ; these substances can only be absorbed after a process
of transformation and solution. The Fungi and Bacteria in question

256 BOTANY PART i

excrete enzymes (cf. p. 264), which have the power of rendering the
substances soluble.

Saprophytes are thus characterised by the nature of their
assimilatory activity ; they are unable to carry out the first
step in the assimilation of carbon which is effected so easily by the
green plant with the help of light. On the other hand, there is
probably no difference between them and autotrophic plants in
the further steps of assimilation, in the construction from simple
organic compounds of the more or less complex compounds which
compose the body of the plant.

Among phanerogamic plants also some heterotrophic forms, that at
first sight appear to be saprophytes, occur. This is the case for certain
orchids which grow in humus (Neottia, Coralliorrhisa, Epipogon) and
for Monotropa. The absence of chlorophyll and, except for the
inflorescence, the subterranean mode of life indicate the heterotrophic
nature of these forms. The obvious assumption that they obtain
their supply of carbon from the humus of the soil of woods is, however,
very improbable. Since all these plants harbour a fungus in their roots
or rhizomes, the absorption of food material is probably due to the
fungus. The flowering plants probably lead a parasitic life upon the
fungi in their roots (mycorrhiza ; cf. p. 261).

These plants thus lead us to the consideration of PARASITES,
numerous examples of which are found in the Fungi and Bacteria ;
parasitic forms also occur among Algae, Cyanophyceae, and the higher
plants.

That these parasites, or at least many of them, absorb nutrient
materials from the host upon which they live is often evident
from the condition of the latter ; the host may be seriously injured
and even ultimately killed by the parasite. What the particular
substances are that the parasite absorbs and requires for successful
growth is, however, difficult to determine. Since frequently only
organisms of a definite natural group (family, genus, species) are
attacked by one species of parasite, it may be assumed that the latter
makes quite specific demands as to the quality or quantity of its
nutriment. This assumption is supported by the fact that we are
unable to cultivate most parasites apart from their hosts.

B. ASSIMILATION OF NITROGEN

Since a green plant obtains its carbon from carbon dioxide, which
is only present in a very small proportion in the air, it might be
assumed that the enormous supply of nitrogen in the air would form
the primary and the best source of this element of plant food.
Every water culture, however, shows clearly that atmospheric nitrogen
cannot be utilised by the typical green plant. If combined nitrogen
is omitted from the nutrient solution the plant will not grow.

DIV. ii PHYSIOLOGY 257

In the food -solution given above nitrogen was supplied as a
nitrate, and this form is most suitable for the higher plants. But
compounds of ammonia, so long as they are not injurious to the plant
owing to an alkaline reaction, can also be utilised. Organic com-
pounds of nitrogen also, such as amino-acids, acid amines, amines, etc.,
Avill serve for food, though none of them lead to such good results as
are obtained with nitrates. Nitrites can also serve as a source of
nitrogen, but in too high concentrations are injurious.

"\Ve are not nearly so well acquainted with the assimilation of
nitric acid and of ammonia as we are with that of carbon dioxide.
We do not know accurately the place in which the assimilation
takes place, we know less of the contributory external conditions,
and lastly, we jare not clear as to the products of assimilation.
Ultimately, of course, albumen is formed, a far more complex substance
than a carbohydrate, containing always, besides C, H, and 0, some
15-19 per cent of N, besides S and in some cases P. The methodical
study of the products of the breaking down of albumen gives some
insight into the structure of the proteid molecule. This shows that
in albumen a large number of amino-acids are combined with loss of
water. Since EMIL FISCHER has obtained albuminous substances
(polypeptides) by a union of amino-acids followed by polymerisation,
it is probable that in the plant also such amino-acids are first
formed and then unite further. If the simplest amino-acid, glycocoll,
XH0 • CH2 • C0.7H (which, it is true, is not of wide occurrence in
plants), is considered, it is evident that this can be derived from
acetic acid by replacing an atom of H with the NH2 'group. Nitric
acid, HN03, must therefore be reduced when its nitrogen is to
be employed in the construction of proteid. This reduction is
independent both of sunlight and chlorophyll, so that nitric acid can
be assimilated in darkness and in colourless parts of the plant.
Indirectly, of course, chlorophyll and light are of importance in the
synthesis of proteids in so far as compounds containing carbon are
required, and these are formed in sunlight with the help of chlorophyll.
On account of their rich supply of carbohydrates the foliage leaves
are specially fitted for the production of proteid, but they are not
" organs of proteid formation " in the same degree as they are organs
for the formation of carbohydrates. Only in a few plants (nitrate
plants, e.g. Chenopodium, Amarantus, Urtica) can the nitric acid be
recognised in the leaves ; in most plants it appears to be transformed
soon after its absorption by the root.

We know as little of the steps in the assimilation of ammonia as
of those of nitric acid. Since no preliminary reduction is required,
ammonia might be regarded as more readily assimilable than nitric
acid. When ammonia is found to be less favourable in a water
culture than nitrates, this may be due to certain subsidiary harmful
effects of the former substance.

s "

258 BOTANY PARTI

The hypothetical intermediate products between the nitrogenous
compounds absorbed and the completed proteids, i.e. various amino-
acids and related substances, are present in all parts of the plant.
Leucin, tyrosin, and asparagin are especially common. It can,
however, rarely be determined whether these substances have been
synthesised from ammonia or nitric acid or whether they have arisen
by the breaking down of albumen (cf. p. 266).

Nitrogen is present not only in proteids but in LECITHINS and in
ORGANIC BASES. The former are complex esters in which glycerine is
combined with two molecules of fatty acid, one molecule of phosphoric
acid, and the nitrogen -containing base, cholin. They are never
absent from living protoplasm. The majority of organic bases
(alkaloids) are probably by-products of the assimilation of nitrogen
and are not further utilised.

While it can be said that the typical autotrophic plant can
assimilate nitrogen as well or better as nitric acid than as ammonia,
this does not hold for the majority of Fungi. Only a few of these
prefer nitric acid; as a. rule ammonia is the best nitrogenous food.
Some Fungi lack the power to construct the more complex substances
of the plant from such simple nitrogenous compounds, or at least
the latter are formed more rapidly and certainly from organic sub-
stances. Further, in these Fungi there are various types ; some
succeed best with amino- acids, others with peptone, while others
prefer proteid. They' are all heterotrophic as regards their nitro-
genous food.

The so-called INSECTIVOROUS or CARNIVOROUS PLANTS must be
referred to here (35) (cf. p. 185). These are plants provided with
arrangements for the capture and retention of small animals, especially
insects, arid for the subsequent solution, digestion, and absorption of
the captured animals by means of enzymes. All these insectivorous
plants are provided with chlorophyll ; the explanation of their peculiar
mode of life can hardly be to obtain organic compounds of carbon.
It is further known that they can succeed without animal food, but
the moderate supply of an animal substance has a distinctly beneficial
effect manifested in increased production of fruits and seeds. It is
very probable, though by no means established, that the carnivorous
habit is a means of obtaining nitrogen. Whether the nitrogen in the
peat or water in which insectivorous plants often grow is insufficient
in quantity, or whether its quality is not optimal, must be left
undetermined. It is doubtless possible that organically-combined
nitrogen is specially advantageous to these plants. This does not
exclude the possibility that the insectivorous habit is related not only
to the supply of nitrogen, but to that of other nutrient salts, especially
of potassium and phosphoric acid. Whether these salts are utilised
in organic combinations or are transformed in the digestive process to
the inorganic form is unknown. In the latter case the use of the

DIV. II

PHYSIOLOGY 259

insectivorous habit would have to be sought in the provision of more
nutrient salts than are afforded by the soil.

The insectivorous plants strike the ordinary observer as deviating
from ordinary plants in the direction of the animal kingdom. Like
animals they utilise solid food which has to be rendered fluid by
enzymes before it is absorbed into the cells. The similarity between
animals and these plants appears to be increased by a comparison of
the stomach and the pitchers, etc., of some insectivorous plants. It
should be recognised, however, that some Fungi and Bacteria stand
physiologically closer to animals. They can obtain all their food by
the digestion of solid organic material, while the insectivorous plants
are autotrophic, at least as regards their supply of carbon.

In relation t<^ insectivorous plants certain phanerogamic parasites
may be considered which were omitted above (p. 254), since they
possess green leaves and are evidently autotrophic as regards their
supply of carbon. In spite of this, however, the plants only develop
normally, when their root-system is in connection with the foots of
other plants by means of disc-shaped haustqria. They may even (as
is also the case with Cuscuta) enter into this relation with other
individuals of the same species. Thesium, belonging to the Santalaceae,
and the following genera of the Rhinanthaceae, Bhinanthus, Euphrasia
Pedicularis, Bartsia, and Tozzia, may be mentioned as examples of
plants showing these peculiar conditions. In Tozzia the parasitism is
well marked in the earliest developmental stages. The Mistletoe
(Viscum album), although strictly parasitic, possesses, like many of the
allied foreign genera of the Loranthaceae, fairly large leaves well
supplied with chlorophyll, and quite able to provide all the carbo-
hydrates required. By its reduced root-system it obtains, however,
from the host plant (as has also been shown to be probable in the
case of the Rhinanthaceae (36)) its supply of water and dissolved salts.

In contrast to these plants, which are either demonstrably or probably
supplied with organically-combined nitrogen, there are certain micro-
organisms which are strikingly autotrophic as regards nitrogen, while
they are heterotrophic as regards their carbon assimilation. These
organisms are able to utilise the nitrogen of the atmosphere. Their
existence was first established at the end of last century by the work
especially of WIXOGRADSKI, HELLRIEGEL, and WILFARTH (3T).

In the first place there are certain Bacteria, such as Clostridium
Pasteurianum and related forms and Azotobader chroococcum, which live
independently in cultivated soil and in water under very various
external conditions. They fix free nitrogen and thus possess a
very important power both for their own success and for that
of many other organisms ; this property is of the greatest importance
in agriculture. An increasing number of the lower Fungi have been
shown by recent researches to have the same power though in less
degree. In addition to these free-living forms there are micro-organisms

260

BOTANY

PART I

which occur parasitically in higher plants and have the same property.
The best investigated among these are the various forms of Bacillus
radicicola, which infest the roots of Leguminosae and frequently give
rise to enormous numbers
of gall-like tubercles upon
them (Figs. 251, 252).
The Leguminosae thus
appear to differ from all
other green plants in their

FIG. 251.— A root of Vicia Faba,
with numerous root -tubercles.
(Reduced. After NOLL.)

FIG. 252. — 1, Young tubercles (1C) on a root (IF) of Vicia Faba,
B, large-celled tissue filled with masses of Bacteria, M, the
"meristem" of this. T, tracheides. (x 60.) 2, A cell of
the tubercle filled with thousands of Bacteria, and beside
it some un-infected cells, (x 320.) 3, An infected root-
hair containing the "infection hypha." (x 320.) U, Bacteri-
oids. 5, Unaltered Bacteria, (x 1200. After NOLL.)

mode of accumulating nitrogen (38) ; this was -first established by
GILBERT and LAWES in England and ScHULTZ-LuPiTZ in Germany.

The rod-shaped bacteria penetrate through the root-hairs into the cortex of the
roots, and there give rise to the tubercles. These tubercles become filled with
a bacterial mass, consisting principally of swollen and abnormally-developed
(hypertrophied) BACTEIUOIDS, but in part also of bacteria, which have remained
in their normal condition. While the bacteria live on carbohydrates and at first

DIV. ii PHYSIOLOGY 261

also on albuminous substances supplied by the host plant, the latter profits by
the power of fixing free nitrogen possessed by the bacterioids. The bacterioids
furnish a steady supply of combined nitrogenous substance to the leguminous
plant. It has been calculated that Lupins are able in this way to obtain 200 kg.
of nitrogen per hectare. The agricultural importance of this natural fixation of
nitrogen will be evident. It has been attempted to further it by infecting fields
with soil rich in the bacteria, or with pure cultures of specially active forms
( " nitragin "). A marked increase in the crop of Serradella is obtained in this way.
If the soil in which a Leguminous plant is grown contains a sufficiency of nitrates,
the plants may live at their expense ; since the presence of nitrates exerts an
injurious influence on Bacillus radicicola, practically no nodules are formed under
such circumstances.

Besides the Leguminosae, Elaeagnus and Alnus are able to utilise free atmo-
spheric nitrogen when their roots bear nodules ; these are due to infection by
another of the lower organisms. A species of Podocarpus which has a mycorrhiza
can also utilise atmospheric nitrogen. It is thus not improbable, though as yet
unproved, that other mycorrhizas may have a similar significance. The roots
not only of the phanerogamic plants without chlorophyll, referred to on p. 256,
but also of most green plants living in the humus soil of woods and heaths,
especially the trees, stand in close relation to Fungi (").

The fungal hyphae are sometimes found within the root occurring in tangled
groups in the cells of definite cortical layers, while individual filaments extend into
the soil. In other plants the hyphae invest the outer surface of the young roots
with a closely-woven sheath. The former is called endotrophic, the latter ecto-
trophic mycorrhiza, but the extreme forms are connected by intermediate conditions.
The fungi of the endotrophic mycorrhiza are in part digested by the cells of the
root, and thus all the substances liberated will be available for the phanerogamic
plant. This is not known in the case of ectotrophic mycorrhiza. STAHL regards the
significance of fungal infection of the flowering plant to lie in the active absorption
of nutritive salts from the soil by the fungus. The advantage to the fungus is
obviously, at least in the cases in which it infects green plants, the provision of
carbohydrates which it obtains. It is probable that the consortia of Fungi and
Algae which are called Lichens can be ranked here as regards their physiology of
nutrition (39a).

More recently swellings which are due to infection by bacteria have been dis-
covered in the leaves of tropical plants belonging to the Rubiaceae and Myrsinaceae.
While, however, in the case of the Leguminosae the infection always depends on
accidental meeting of the bacteria and the flowering plant, in these families the
bacteria are present in the embryo of the plant. When they are artificially kept
from the egg-cell the development of Ardisia is abnormal. It is quite probable
that in these cases also an assimilation of free nitrogen takes place C40).

C. ASSIMILATION or OTHER SUBSTANCES

Sulphuric acid most nearly resembles nitrogen since it also is used
in the construction of proteids which contain about J-1J per cent
of S. It is still uncertain where and under what conditions its
assimilation occurs ; we only know that a reduction of acid radicals
must take place in the process. In some plants sulphur is combined
in other substances besides proteids.

262 BOTANY PART i

Phosphoric aeid is connected with sulphuric acid in so far as it
is employed in the construction of at least some proteid substances,
especially the nucleo-protein of the cell nuclei; it forms from 0'3 to 3
per cent of this. In entering into the molecule of this substance the
phosphoric acid, unlike sulphuric acid, is not reduced. Lecithin (cf.
p. 258), which is present in all plants, also contains phosphorus, and
this is also the case for phytin, which occurs especially in seeds.

The Metals. — As may -be shown by the method of water culture,
potassium, calcium, magnesium, and iron are just as essential as any
of the substances hitherto mentioned. It is very probable, at least
for potassium and magnesium, that they take part in the construction
of certain compounds that are essential for the existence of the plant.
Probably protoplasm contains these elements. Other substances also
may contain them ; thus, for instance, a considerable amount of
magnesium has been shown to exist in chlorophyll. It was formerly
believed that chlorophyll contained iron because the chloroplasts
remained yellow when iron was omitted from the food solution. It
is now known that chlorophyll does riot contain iron and that iron is
also necessary for plants that are not green. This supports the assump-
tion that protoplasm itself contains iron, and that the " chlorosis "
which occurs when iron is wanting is a result of a diseased condition
of the protoplasm.

Since potassium, magnesium, and iron thus pass into the substance
of the plant they must be assimilated, but we know nothing of how
or where this happens. The case of calcium is somewhat different ;
it is not invariably essential, for some Algae can succeed without it.
In other plants it has a protective function, preventing the poisonous
effects which result from iron, magnesium, potassium, and sodium, and
also from phosphoric acid, sulphuric acid, nitric acid, and hydrochloric
acid. It is, however, improbable that the indispensability of calcium
in the case of the higher plants is merely due to this protective
function.

In speaking of insectivorous plants and of certain green parasites it
was mentioned that they might perhaps obtain their mineral food-
materials in organic compounds ; nothing certain is known on this
point.

Water. — We know that water is essential to the plant. When it
is taken into the plant as water without undergoing chemical change
we do not speak of its " assimilation." This is the case, for example,
in the water which fills the vacuoles of cells or that which permeates
the protoplasm and cell wall. It is different where the water is
chemically combined. This necessarily takes place when carbohydrates
are formed from carbon dioxide, and probably in other cases also.
In these cases there is the same justification for speaking of the
assimilation of the water as of the assimilation of carbon dioxide.

DIV. II

PHYSIOLOGY 263

IV. Translocation and Transformation of Assimilates

The assimilates serve primarily .for the construction of new
substance of the plant and the growth of new cells. They are also
employed as reserve materials and as substances in course of trans-
location, while some are used up in the metabolism and others in the
production of excretions and secretions.

It is only rarely, however, that growth takes place where the work
of assimilation is effected. Thus the assimilation of carbon dioxide goes
on mainly in fully-grown foliage leaves while the growing points are
more or less distant from the leaves. The assimilatory activity and
the formation of new organs also do not coincide in time. Many
plants have periods of active assimilation when but little growth is
taking place and, alternating with these, periods of active growth
associated with little or no assimilatory activity. Our trees lose their
leaves in autumn and herbaceous plants lose all the above-ground
organs. In both cases new organs of assimilation must be formed in
spring before assimilation can be resumed ; in the growth of these
organs the plant utilises stored assimilates. Every germinating seed-
ling also lives at first wholly at the expense of assimilates of a preced-
ing generation. Such stored -up assimilates are termed RESERVE
MATERIALS ; they may be deposited where they are formed or may be
carried to secondary places of deposit. Every foliage leaf which in
the evening of a bright summer's day is gorged with starch is an
illustration of the first condition. The second is seen in seeds where
reserve materials are stored in the endosperm or the cotyledons. It
is also found in vegetative organs, which may even show by their form
that they are places for storage of reserve materials; examples of
these are the swollen leaves of bulbs, swollen stems (e.g. potato), or
swollen roots (e.g. turnip). In order that assimilates should reach
these storage places they must be capable of TRANSLOCATION, and they
have also to be conveyed through the plant when they are removed
from, the place of storage and employed in the development of new
organs. Many reserve materials or assimilates occur in a solid form
which does not allow them to pass from cell to cell ; starch is an
example of this. Others are, it is true, soluble, but have such large
molecules that they only diffuse with difficulty. For these reasons
reserve substances have usually to undergo a change before they can
be conveyed through the plant.

A. MOBILISATION OF RESERVE MATERIALS

In the mobilisation of reserve materials we have usually a not very
profound change of the nature of a hydrolysis, i.e. a splitting of the
substance into smaller molecules with the absorption of water.

264 BOTANY PART I

This must be separately considered for the three main types of
reserve material, the carbohydrates, the fats, and the albuminous
substances.

1. Hydrolysis of Carbohydrates

Starch is one of the most important reserve materials in
plants. It not infrequently forms the main part of the reserve
substance in seeds as well as in tubers and bulbs. In the potato
tuber 25 per cent arid in the grain of wheat 75 per cent of the
fresh weight consists of starch. It is also present in considerable
amounts in the pith, the xylem parenchyma, the medullary rays, and
the rind of trees. The starch has to be broken down in order to
allow of its translocation. This is effected technically by treatment
with acids ; the grape-sugar of commerce is obtained by treating
potato-starch with sulphuric acid. The molecule of starch is split up
into numerous molecules of dextrose according to the formula

In the plant this hydrolysis is effected not by means of acids but by
a special organic substance called diastase. Diastase can be extracted
from the organs by water or glycerine, precipitated by means of
alcohol from the extract and again dissolved, without any essential
change in its properties. On the other hand, diastase is very suscep-
tible to high temperatures, and is rendered permanently inactive by
heating to about 75° C. It has not yet proved possible to obtain
chemically pure diastase; it is always mixed with proteids and was
therefore for long regarded as of this nature. .Remarkable views which
have more recently been formed as to its chemical nature and its
formation still require confirmation (40a).

Diastase has the same effect 'on starch as sulphuric acid has ; they
both act as catalysators. The name catalysators is given to sub-
stances which influence the rapidity of a chemical reaction. We are
mainly concerned with the acceleration of reactions. The usual
method in the chemical laboratory of accelerating a reaction is the
application of heat ; the fact that the life of the organism is confined
to a narrow range of temperature limits this method. A second
method is by the use of inorganic catalysators. Many of these, such
as sulphuric acid mentioned above, injure the protoplasm ; it is thus
easy to understand why the organism should form special catalysators
that are not injurious. These are termed ENZYMES (41) and occur in
both plants and animals. While many inorganic catalysators influence
very various chemical processes, the influence of organic catalysators
is quite specific ; thus diastase only acts on starch. Since the cataly-
sator either does not enter into the reaction or at least does not do
so permanently, a small amount of it is able to hydrolyse a large

D1V. II

PHYSIOLOGY -

265

quantity of the substance acted on, if the products of the reaction
are continually removed.

Diastase is found in many parts of the plant, especially in those
which contain much starch, such as foliage leaves and germinating
seeds. The amount of diastase in an organ is not constant, but is
regulated according to the needs of the plant ; further, its action
can be arrested by the formation of other enzymes (anti-enzymes).
This is one of the many regulatory processes so characteristic of the
organism.

In the plant diastase acts on the starch grains. These are corroded
under its influence; they are dissolved away from without inwards, but
this proceeds as a rule irregularly, so that the shape of the grain changes.
At particular spots the diastase
eats more quickly into the
grain and, using pre-existing
splits and canals, breaks it up
into smaller portions which
then dissolve further (Fig.
253). Outside the plant the
action of diastase can best
be shown on thin starch
paste : on adding diastase to
this the characteristic iodine
reaction is lost after a few
minutes or a quarter of an
hour. The blue colour given

. n . ° , FIG. 253.— Different stages of the corrosion shown by

at first, Changes tO a Wine-red the starch grains of germinating Barley. (After NOLL.)

tint, and ultimately a yellow

colour is given. Dextrin is an intermediate product between the starch

and the maltose.

Cellulose is also of frequent occurrence as a reserve substance. In
the endosperm of many seeds the cell walls are very strongly thickened
and the thickening layers are dissolved in the process of germination.
Such thickened walls are beautifully shown in many palm seeds, e.g. in
the Vegetable Ivory Palm. The solution of the thickening is due to
an enzyme, the so-called cytase, which, however, does not act on every
variety of cellulose. Typical cellulose (p. 38) is not attacked by it,
but only reserve cellulose, which differs in its chemical structure.

Inulin, which is found especially in Compositae and Campanulaceae,
is related according to its empirical formula (C6H1005)n with cellulose
and starch, but is distinguished from these substances by always
occurring in plants in the dissolved form. In spite of this it is
incapable of translocation on account of the size of its molecule, and
is broken down on germination by an enzyme into a sugar of the
formula C6H1206. The sugar in this case is, however, levulose.

Cane Sugar, which occurs for example in the sugar-cane and sugar-

266 BOTANY PART i

beet, may be connected with inulin. It is converted by the widely-
spread enzyme " invertin " into equal parts of dextrose and levulose.

2. The Fats

Though we are unable to manufacture the reserve carbohydrates
mentioned either from dextrose or levulose, we can understand that
it is as easy for the plant to build them up as to break them
down. It is much more difficult to understand in what way the
plant is able to form fats (glycerine esters of various fatty acids ; cf.
p. 30) from carbohydrates. Fats are always present in living proto-
plasm ; the general distribution of lecithin which is derived from fats
has already been mentioned. Fats occur in relatively large amounts
as reserve materials, but not in the assimilating foliage leaves. They
occur in large amount in many ripe seeds, where they are formed
at the expense of carbohydrates. At germination they are decomposed
by the enzyme lipase into fatty acids and glycerine. The fatty acid
is capable of passing through the water-saturated cell wall more readily
than the fat, but does not usually travel as such for any considerable
distance in the plant ; it is usually quickly converted into a carbo-
hydrate. A fatty oil sometimes occurs in the succulent portions of
fruits, e.g. in the oil-palm and the olive, and then does not enter again
into the metabolism of the plant.

3. Albuminous Substances

Albumen occurs in the storage places for reserve materials partly
in a crystalline and partly in an amorphous form. The crystals occur
free in the cytoplasm, nucleus, or in the chromatophores ; in seeds
they are" found especially in the aleurone grains, where they are
associated with globoids. The latter then contain Ca, Mg, and
phosphoric acid in an organic compound (cf. p. 31).

The products of the hydrolytic breaking down of albuminous
substances are mainly amino-acids, the wide distribution of which in
the plant has already been referred to. When seeds rich in proteid
such as Eicinus, Pinus, etc., are germinating, the abundant amino-
acids may be regarded as derived from the proteid. Amino-acids
occurring in other situations may have arisen in the synthesis of
proteids. The proteid-molecule does not produce at once or ex-
clusively amino-acids ; the breaking down of the ver}T large molecule
is a gradual one, in which the bodies which appear first have many
properties in common with proteids ; first comes albumose, then
peptone, and only then amino-acids. With the latter appear ammonia,
also products of decomposition containing sulphur and phosphorus,
and generally carbohydrates also.

DIV. II

PHYSIOLOGY 267

This Jiydrolytic breaking down of proteids takes place under the
influence of " proteolytic " enzymes (proteases) which very probably
are closely similar to corresponding enzymes in the animal body. We
should therefore have to distinguish

1. Pepsin, which only breaks down the proteid molecule to
albumoses and peptone.

2. Erepsin, which transforms peptone into amino- acids. It is
uncertain whether in addition there should be added

3. Trypsin, which transforms proteids directly into amino-acids.

The decomposition products of albumen quickly undergo changes in the plant,
and therefore the mixture of nitrogenous organic compounds which one obtains
from a plant kept in the dark is not identical with the products of the hydrolysis
of albumen outsid^ the plant. In the plant syntheses take place after the primary
decomposition, and these lead to the formation of such substances as amides, the
most widely spread of which is asparagin. This dominates in Gramineae and
Leguminosae (15 g. are present in a litre of sap from bean seedlings) ; it is
replaced in Cruciferae and Cucurbitaceae by glutamin, while in the Coni ferae
arginin, a di-amino-acid, appears to play the same part. The syntheses proceed
still farther in light, when proteid may again be formed from the products of
decomposition of albumen.

B. TRANSPORT OF THE MOBILISED RESERVE MATERIALS

When the reserve materials have been brought by the aid of the
proper enzymes into the soluble form, or have been transformed into
substances with smaller molecules, they are capable of being
transported; we may speak of them as being mobilised. Their
movements are governed by the general principles of translocation of
substances. It is especially necessary that a diffusion current should
be established and maintained. This is brought about by the active
growth of cells at a greater or less distance from the place of storage
of the reserve material. As long as this lasts each molecule on
its arrival at the place of growth is promptly transformed (e.g. sugar
into starch or cellulose), and thus room is made for the molecules that
follow. In non- growing organs also (e.g. cotyledons, endosperm) a
gradient of diffusion is established by the cells to which the current
passes, having a greater power of condensing the sugar (forming
starch) than the others. A diffusion current can also be artificially
established where a storage structure under proper conditions is
placed in relation on one side with a large amount of water. It is thus
possible to bring about artificially an emptying of seeds, bulbs, etc.

When substances have to be transported for considerable distances,
the movement of diffusion, since it goes on slowly, is replaced by
movement in mass. Thus in spring the reserve materials deposited
in the wood of our trees are carried up by the ascending current of
water in these vessels ; at this season the fluid in the vessels contains

268 BOTANY PART I

abundant glucose. In the other direction a stream of mobilised
reserve material can pass downwards from the foliage leaves by way
of the sieve-tubes (42). While, however, the mechanical causes of the
transpiration stream are at least partially understood, so far as they
depend upon the evaporation of water, we do not know the forces
concerned in movements in mass in the sieve-tubes.

Another example of translocation is afforded by leaves shortly
before they are shed. In many but not all cases the useful materials
in the leaf are transferred to the stem and thus are not lost to the
plant. Phosphoric acid, potassium, and nitrogenous substances are thus
transferred to the stem, but the cell walls, a protoplasmic layer, and
osmotically-active substances in the vacuole remain so that the leaf
falls in a turgescent condition (43).

C. FURTHER METAMORPHOSES OF SUBSTANCE

Regeneration of Reserve Materials. — Sooner or later the reserve
materials mobilised by the help of enzymes are again converted into
substances with large molecules. This occurs at any rate at the end
of their transport, whether they are again deposited as reserve
materials or are employed as constructive substances. Thus, for
example, glucose formed in a leaf may pass to a seed or a tuber and
be there transformed into starch or cell wall. When the transport
is for a considerable distance the formation of reserve material may
go on by the way and not only at the end of the journey. This is
specially well seen in the case of starch. Along the routes of sugar
transport so-called transitory starch may be formed in every cell.
This starch formation diminishes the concentration of the solution,
and thus helps to maintain the continued motion of the diffusion
current.

Other Products of Metabolism (*4). — Only a small proportion of
the substances met with in plants have been enumerated above. It
will be sufficient to mention here the organic acids, ta.nnins, glucosides,
alkaloids, colouring matters, ethereal oils, resins, gum-resins, caoutchouc
and gutta-percha among the legion of substances which are derived
from the products of assimilation. The organic acids will be referred
to later (p. 271); the origin and physiological significance of the
others are too little known for them to be dealt with. It is known
that as a rule they are not further utilised after their formation. They
are probably, therefore, by-products of the metabolism of the plant.
They need not, however, for this reason be useless, and it is believed
that some bitter or poisonous substances protect the plant from being
eaten by animals ; some pigments are of use in the attraction of
animals which distribute pollen, seeds, and fruits, or frighten away
injurious animals (warning colours). Resin and latex when they
exude and harden may assist in the closing of wounds.

DIV. ii PHYSIOLOGY 269

The Ripening of Succulent Fruits. — A striking transformation of substances
takes place in the ripening of succulent fruits. The relatively rare case of the
formation of fats has already been mentioned. Much more frequent is the change
of starch into sugar associated with the disappearance of organic acids and tannins.
The fruits thus become sweet-tasted instead of acid or bitter, and are eaten by
animals which distribute the seeds. The significance of these chemical changes
is thus ecological.

V. Respiration and Fermentation

In the higher plants all the organic substance produced in
assimilation is not used for construction and storage purposes ;
a part of it is always broken down and returns to the state of
inorganic compounds. The significance of this process, which is
usually associated with the absorption of oxygen and is termed
respiration, does not lie in the substances formed but in the libera-
tion of energy which is essential for the life of the plant. In certain
lower plants the necessary supply of energy may be obtained in other
ways. Usually organic substances are absorbed from the substratum
and broken down without being first assimilated. The decomposi-
tion may be effected by oxidation, reduction, or dissociation ; all these
processes are grouped togejther as fermentation. Other lower organisms
can utilise the energy set free in the oxidation of certain inorganic
compounds. Transitional forms occur between the various methods
of obtaining the necessary energy.

A. RESPIRATION

By respiration in its typical form is understood the oxidation of
organic material to carbon dioxide and water; this involves the
absorption of oxygen from without (cf. p. 244).

In the higher animals the process of respiration is so evident as
not easily to escape notice, but the fact that plants breathe is not at
once so apparent. Just as the method of the nutrition of green plants
was only discovered by experiment, so it also required carefully-
conducted experimental investigation to demonstrate that PLANTS
ALSO MUST BREATHE IN ORDER TO LIVE; that, like animals, they
take up oxygen and give off carbonic acid. The question had already
been thoroughly investigated by SAUSSURE, and by DUTROCHET in
the years 1822 to 1837, and its essential features correctly interpreted.
Later the existence of respiration in plants was doubted owing to
the demonstration of their power of decomposing carbon dioxide and
giving off oxygen ; it seemed impossible that both processes could go
on at the same time. The correct view was then formulated by
SACHS. ASSIMILATION AND RESPIRATION ARE TWO DISTINCT VITAL
PROCESSES CARRIED ON INDEPENDENTLY BY PLANTS. WHILE IN THE

PROCESS OF ASSIMILATION GEEEN PLANTS ALONE, AND ONLY IN THE

270 BOTANY PART i

LIGHT, DECOMPOSE CARBONIC ACID AND GIVE OFF OXYGEN, ALL PLANT
ORGANS WITHOUT EXCEPTION BOTH BY DAY AND BY NIGHT TAKE UP
OXYGEN AND GIVE OFF CARBONIC ACID. Organic substance, obtained
by assimilation, is in turn lost by respiration. That green plants
growing in the light accumulate a considerable surplus of organic
substance is due to the fact that the daily production of material by
the assimilatory activity of the green portions is greater than the
constant loss which is caused by the respiration of all the organs.
Thus, according to BOUSSINGAULT'S estimates, in the course of one
hour's assimilation a plant of Sweet Bay will produce material
sufficient to cover thirty hours' respiration. If assimilation is sup-
pressed by keeping the plant in darkness, it loses considerably in
dry weight.

Plants produce in twenty-four hours about five to ten times their own volume
of carbonic acid. In shade plants this is usually reduced to twice the plant's
volume, while the commonly-cultivated Aspidistra produces only one-half of its
own volume, and can therefore succeed even under conditions which are unfavour-
able to assimilation.

In order to demonstrate the existence of respiration either the
absorption of oxygen or the giving off of carbon dioxide by the plant
may be employed. If a handful of soaked seeds is placed at the
bottom of a glass cylinder, the top of which is closed for a day by a
glass plate, the oxygen in the space is used up by the germinating seeds;
a candle will be extinguished if it is introduced into the cylinder. If
germinating seeds or flower- heads of Compositae (B, Fig. 254) or
young mushrooms are placed in a flask and prevented from falling
out when the flask is inverted by means of a plug of cotton-wool (W),
the mouth of the flask can be dipped under mercury (S) and some
solution of caustic potash (K) be introduced above this. The carbon
dioxide formed is then absorbed by the caustic potash and the
mercury rises (Fig. 254). When this experiment is carried out
quantitatively it is found that a fifth of the volume of air disappears,
so that all the oxygen has been absorbed. Since, however, when no
potash is present, the volume of gas is not altered by the respiration
of the plants, an equal volume of carbon dioxide must be formed for
each volume of oxygen that is absorbed. The respiratory coefficient
or ratio between the absorbed oxygen and the excreted carbon dioxide

is equal to unity ( Q 2= 1 \ If we assume that sugar is the substance
respired, this must take place according to the formula
°6Hi2°6 + 602 = 6C02 + 6H20.

This is an exactly opposite process to the assimilation of carbon dioxide.
It is not so easy to demonstrate the formation of water in typical
respiration as it is to show the utilisation of oxygen and the pro-
duction of carbon dioxide. Quantitative estimates of the loss of dry

DIV. II

PHYSIOLOGY

271

weight and of the carbon dioxide formed show that the latter does
not account completely for the former ; a part of the dry substance
must thus have been transformed into water.

The volume of air does not under all circumstances remain
unchanged by the respiration of the plant ; the carbon dioxide pro-
duced is not always equal in
volume to the oxygen which dis-
appears. Small deviations from
this ratio occur in all plants,
and considerable ones in, for
instance, the germination of fatty
seeds, and in the leaves of cer-
tain succulent plants (Crassu-
laceae). This is connected
with the fact that in these seeds
fats, which are much poorer in
oxygen than carbohydrates, are
used in respiration ; and that
in the Crassulaceae certain
organic acids are produced from
carbohydrates instead of carbon
dioxide and water. In other
plants also similar acids, though
not in so great amount, are
formed. They probably arise
mainly in the respiratory pro-
cess, but may also be produced
in constructive metabolism.

In the germination of fatty seeds
far more oxygen is absorbed than
carbon dioxide is given off ; this may
go so far that in the first days in the
dark, in spite of continual respiration,
an increase in the dry weight takes FlG- 254.— Experiment to demonstrate respiration

place. The respiratory quotient is

,, , ,, ,-»r <• i

thus less than 1. Most of the oxygen

is used in the transformation of fats,
which are poor in oxygen, into carbo-
hydrates, and only a'small proportion
is used in respiration.

In the Crassulaceae a large proportion of the carbohydrate is changed into
organic acids in the process of respiration. The oxidation is thus incomplete ;
it does not lead to the formation of C02, so that less of this gas is formed than the
amount of oxygen absorbed would lead us to expect. The respiratory quotient is
less than 1. This peculiar respiratory process which is connected with an accumu-
lation of acids in the cell sap, as can be recognised by the taste, is not without
ecological significance for succulent plants. The acids formed (especially malic and
oxalic acids) give off C02 in the light. This can be again employed in assimilation,

inver^ *"*, (S •'" P*rtia'\f ed, with
flowers which are held in place by the plug of
cotton (r) Owing to the absorption of the

carbon dioxide exhaled in respiration by the
solution of caustic potash (K), the mercury (Q)
rises iu the neck of the flask- <After XOLL-)

272 BOTANY PART i

while, in typical respiration at least, the C02 formed during the night escapes, and
is lost to the plant. The succulents thus economise their supply of C, which is
probably connected with the fact that they do not so readily obtain carbon dioxide
from the air as other plants, owing to the diminution of gaseous exchange on account
of the limitation of transpiration.

As has been mentioned, respiration is of general occurrence
in the higher plants. It not only occurs in the parts of plants which
do not possess chlorophyll and are commonly used in experiments
on respiration, but can be demonstrated also in cells which contain
chlorophyll. In this case the respiration in the light is masked by
the quantitatively greater process of assimilation ; it appears only as a
diminution in the products of assimilation. If the light is diminished
assimilation ultimately ceases and the respiration becomes evident.

Though respiration goes on in every cell its intensity varies greatly
in different organs and under various external conditions. Actively-
growing parts of plants, young fungi, germinating seeds, flower-buds,
and especially the inflorescences of Araceae and Palms, exhibit very
active respiration. In some Bacteria and Fungi this exceeds, as
compared with the body-weight, the respiration of the human body.
In most cases, however, especially in parts of plants composed wholly
or mainly of full-grown tissues, the consumption of oxygen and
production of carbon dioxide is considerably less than in warm-blooded
animals. Among external conditions which have an important
influence on the intensity of respiration the temperature and the
amount of oxygen must be especially mentioned. An increase of
temperature accelerates respiration as it does all the vital processes.
The production of carbon dioxide is about doubled or trebled by a
rise of 10° C., just as other chemical processes outside the plant
are. With continued rise of temperature, however, the respiration
diminishes. In contrast to other like phenomena the fall in the
respiratory curve is exceedingly steep, so that the optimum and
maximum almost coincide.

Respiration is commonly spoken of as a process of combustion.
Were this correct it might be .expected that the amount of available
oxygen would be of fundamental importance ; in particular it
might be anticipated that respiration would be greatly increased in
pure oxygen and completely suspended in a space free from oxygen.
Neither of these assumptions is true. Respiration is not markedly
increased in pure oxygen, and only at a pressure of 2-3 atmospheres
of oxygen does an increase in the respiration become perceptible ;
this is soon succeeded by a decrease in the respiration indicating the
approach of death. Even more striking is the fact that plants in the
absence of oxygen continue to produce carbon dioxide. In this case
one cannot speak of a process of combustion ; the phenomenon is termed
INTRAMOLECULAR RESPIRATION (45) because the carbon dioxide which is
formed owes its origin to a rearrangement of the atoms in the molecule

DIV. ii PHYSIOLOGY 273

of the sugar which serves as the material for respiration. The molecule
of sugar breaks down and forms, in addition to carbon dioxide, other
reduced compounds. Sometimes, for example, alcohol according to
the formula

If this empirical formula is replaced by the structural formula

COH . CHOH . CHOH . CHOH . CHOH . CH2OH
- C02 + CH3 . CH2OH + CH3CH2OH + CO,,

it will be seen that the molecule of sugar has broken down into four
portions, two of which are poorer and two richer in oxygen than the
molecular groups from which they are derived. In this type of
respiration certain molecular groups withdraw the combined oxygen
from others.

It may be assumed that oxygen -respiration and intramolecular
respiration are expressions of one and the same property of the plant ;
in other words, that on withdrawal of oxygen normal respiration passes
over into intramolecular respiration. If this is true, it follows that the
essence of respiration does not consist in an oxidation process but in a
breaking down of organic substance in which products arise that readily
take up oxygen. The materials which are respired in the plant, such as
carbohydrates and proteid, are not easily oxidisable at ordinary tempera-
tures. Fats, it is true, which may also serve as material for respiration,
are oxidisable, but in this case we know that they are transformed
into carbohydrates before they are used for respiration by the plant.
The plant must thus have at its disposal special means in order to
carry on the oxidation and the preceding decompositions that are
involved in respiration. It is scarcely to be doubted that enzymes are
concerned in this, but we have at present no insight into their precise
action (46).

At first sight respiration appears a contradictory process, since in
it organic material which has been built up in assimilation is again
broken down. Its meaning only becomes evident when, turning
from the changes of substance, those of energy are considered. It
is not the production of CO., and H20 that is important, but only
the liberation of energy. This is effected on the breaking down of
such substances as carbohydrates, for the construction of which,
as has been seen, a supply of energy is requisite. On this liberated
energy the plant is dependent for the driving force in many of
its vital phenomena. Movement of protoplasm, growth, and move-
ments due to stimuli cease on the withdrawal of oxygen from the
plant. All these vital phenomena begin again on the restoration of
a supply of oxygen, if this is not too long delayed. It might have
been expected that the organism would possess arrangements by the
help of which the external energy of light or heat could be employed

274 BOTANY PART i

as driving power. Practically, however, it is found that the plant
proceeds to store up the energy of the sun's rays in the form of
potential chemical energy, and then utilises this at need.

In intramolecular respiration also energy is set free ; this does not,
however, suffice in most organisms to maintain the driving force for
the vital processes. Some seeds can remain alive for many hours or
days with intramolecular respiration, and some even continue to give
off the same amount of carbon dioxide as in ordinary respiration.
In most cases, however, the amount of C02 rapidly diminishes.
In other plants death soon occurs, probably owing to the reduced
compounds acting as poisons. The value of intramolecular respiration
is in these cases only slight. On the other hand it has a" very great
importance in certain organisms which will be referred to later.

B. OXIDATION OF INORGANIC MATERIAL (47)

While most plants use organic compounds, especially carbohydrates,
in respiration, certain Bacteria utilise other sources of energy. Thus,
the nitrite bacteria which commonly occur in the soil oxidise ammonia
to nitrous acid, and the associated nitrate bacteria further oxidise the
nitrous acid to nitric acid. By the help of the energy thus obtained
they can then — as has already been pointed out on p. 254 — assimilate
carbon dioxide ; the chemical energy takes the place in them of the
sun's energy for the typical autotrophic plant. There is no breaking
down of organic material so that the whole of the assimilated nutri-
tive substance is retained, and the working of these organisms is very
economical. Since, however, only a limited amount of ammonia is
available, and this is derived from other organisms, they cannot take
the dominant place in nature which the green plants do.

With the nitro bacteria the so-called sulphur bacteria may be associated ; these
oxidise sulphuretted hydrogen to sulphuric acid, sulphur being an intermediate
product, and being stored in the body of the plant. In the same way as the
sulphur bacteria utilise the energy set free in the oxidation of sulphuretted
hydrogen, the iron bacteria obtain usable energy by the oxidation of ferrous to
ferric oxide, other bacteria by the oxidation of methane to carbon dioxide and water,
and yet others by that of hydrogen to water.

G. FERMENTATION (48)

With the removal of oxygen intramolecular respiration begins, but
this cannot supply the necessary energy to maintain life in the higher
plants, although it may do so in lower organisms. Many Bacteria,
Fungi, and certain Algae (Characeae) are notably independent of a
supply of oxygen ; they succeed with slight traces of this gas, or they
avoid it altogether and live in situations where oxygen is absent.

DIV. ii PHYSIOLOGY 275

Such organisms are called anaerobes or anaerobionts in contrast to
the typical aerobes or aerobionts. All intermediate stages connect the
two extremes. The true anaerobionts decompose large amounts of
organic substances, and this decomposition, which is in principle the same
as the process of intramolecular respiration, is termed FERMENTATION.
As in intramolecular respiration, these processes are concerned with
obtaining combined oxygen.

The prototype of fermentation is the alcoholic fermentation brought
about by the yeast fungus. In this sugar is split up into alcohol
and carbon dioxide, and the process has great technical importance
in the production of beer, wine, and brandy. The chemical process
is the same as that of intramolecular respiration in a green plant;
in contrast to this the yeast plant obtains in the fermentation a
complete substitute for respiratory activity. It is, however, only
independent of oxygen when it is supplied with a suitable ferment-
able material (sugar). In the absence of sugar, oxygen is indis-
pensable, and normal respiration takes place. When both sugar
and oxygen are supplied, respiration and fermentation go on simul-
taneously ; part of the sugar is transformed into C2H6O and C02 and
another part into H20 and C02. Obviously, the transformation of
sugar into alcohol and carbon dioxide will provide much less energy
than the complete combustion to carbon dioxide and water. It is
thus easy to understand that yeast utilises enormous quantities of
sugar. Only about 2 per cent of the sugar in the nutrient solution is
used in the construction of the substance of the plant, i.e. is assimilated;
the rest is fermented. For effecting this extensive decomposition of
the sugar, yeast employs a specific enzyme (zymase), the existence of
which was demonstrated by E. BUCHNER (49).

Many other carbohydrates undergo fermentations, and this also
* holds for proteids. In the latter case the process is termed putre-
faction when it takes place in the absence of oxygen, and decay when
oxidation is possible. In nature aerobic bacteria occur first in the
fermentation of albuminous substances, and these prepare the way for
anaerobic forms, so that a sharp distinction between decay and putre-
faction is impossible. In all cases the proteids are first hydrolytically
dissociated with the production of the substances already mentioned,
especially amino-acids. These are further changed, first by the separa-
tion of XH2, and then more profoundly ; ill-smelling substances such as
indol and skatol are often, but not in all cases of proteid fermentation,
formed. It is impossible to draw a sharp line between those decom-
positions which go on without the assistance of atmospheric oxygen
and those in which oxygen plays a part. We are obliged to class as
fermentations all those metabolic processes by which energy is obtained,
which differ from typical oxygen respiration. In this sense the oxida-
tion of alcohol to acetic acid effected by the acetic acid bacteria and
also the production of acids in the higher plants, especially in succulent

276 BOTANY PART i

plants (p. 271), would be fermentations. Lastly, the processes of de-
nitrification and of reduction of sulphates, in which anaerobic bacteria —
probably in order to obtain oxygen — reduce nitrates to free nitrogen
and sulphates to sulphuretted hydrogen, cannot be excluded from
fermentations.

Many fermentations have another significance besides that of
obtaining energy. The products of fermentation such as alcohol,
acids, etc., are poisons ; they are, as a rule, more injurious to other
organisms than they are to those which produce them. On this
account they are suited to exclude other organisms from the supply
of food-material. It is true that a fermentation organism in a pure
culture on a definite substratum renders, by the products of its meta-
bolism, the latter not only unsuitable to concurrent organisms but
sooner or later for itself. When organic material, as is the case in
nature with the remains of dead organisms, is the prey of various
micro-organisms these co-operate in their action ; metabolic products
of one kind of micro-organism are further decomposed by others until
the organic compounds are converted into inorganic or mineral sub-
stances. The final products are water, hydrogen, methane, ammonia,
nitrogen, and sulphuretted hydrogen.

Circulation of Material. — All these end-products of fermentation
can be utilised by other organisms. Leaving C02 and H90 aside as
having been sufficiently dealt with, it may be noted that hydrogen,
methane, ammonia, and sulphuretted hydrogen are all oxidised by
particular bacteria, while others assimilate nitrogen. It is only by
this co-operation of all organisms that life is maintained on the earth
and substances again brought into circulation. If only one type
of organism existed, it would in a short time have destroyed the
possibility of its own existence by its one-sided metabolism.

D. PRODUCTION OF HEAT AND LIGHT IN RESPIRATION
AND FERMENTATION

Heat (50). — Since typical respiration is a process of oxidation, it is
easy to understand that it is accompanied by an evolution of heat. That
this evolution of heat by plants is not perceptible is due to the fact
that it is not sufficiently great, and that considerable quantities of heat
are rendered latent by transpiration, so that transpiring plants are
usually cooler than their environment. In some fermentations, e.g.
alcoholic fermentation, a considerable quantity of heat is evolved.
The heat of rotting manure is well known and employed in the con-
struction of hot-beds.

The spontaneous evolution of heat is easily shown experimentally, if tran-
spiration and the loss of heat by radiation are prevented and vigorously-respiring
plants are selected. A quantity of germinating seeds (peas) shows under proper

DIV. ii PHYSIOLOGY 277

conditions a rise in temperature of 2° C. The greatest spontaneous evolution of
heat manifested by plants has been observed in the inflorescences of the Araceae,
in which the temperature was increased by energetic respiration 10°, 15°, and
even 20° C. Also in the large flower of the Victoria regia temperature varia-
tions of 15° C. have been shown to be due to respiration. One gramme of the spadix
of an Aroid exhales, in one hour, up to 30 cubic centimetres C02 ; and half of
the dry substance (all the reserve sugar and starch) may be consumed in a few
hours as the result of such vigorous respiration. These high temperatures in
flowers and inflorescences attract insects that are of use in pollination. Specially
high temperatures are obtained by cutting up living leaves in large quantity and
ensuring a sufficient supply of oxygen. Under these conditions the temperature
to 40°-50° C., and the leaves perish. After their death a further rise of
temperature is due to the action of micro-organisms.

In the healing of wounds in plants, respiration and also the production of heat
are markedly increased ; the contrary ^s seen in conditions of starvation.

In the fermentation of tobacco also a considerable rise in temperature takes
place. This is still more marked when damp hay or cotton wool is piled up in
large quantity and left undisturbed ; by the formation of easily inflammable gases,
this may lead to the spontaneous combustion of the material. MIEHE has most
recently investigated the spontaneous heating of hay. First by the respiratory
activity of Bacillus coli the temperature is raised to 40° C. ; then a number of
thermophilous Moulds and Bacteria become established, among which Bacillus
calfador raises the temperature to 70° C. Ultimately all the organisms perish
owing to the temperature to which they have given rise and the hay becomes
sterile.

Phosphorescence (51). — Under the same conditions as those of respiration a
limited number of plants, particularly Fungi and Bacteria, emit a phosphorescent
light. The best-known phosphorescent plants are certain forms of Bacteria which
occur in the sea, and the mycelium, formerly described as "Rhizomorpha," of the
Fungus Armillaria mellea. Harmless phosphorescent Bacteria (Microspira photo-
ycna, Pseudomonas lucifera] occur on phosphorescent fish or meat. According
to MDLISCH Bacterium phosphoreum (Micrococcus phosphoreus] usually occurs on
meat which has been moistened with a 3 per cent solution of common salt and
kept at a low temperature. The most important plants, in addition to many
animals, taking part in the phosphorescence seen in the sea are Pyrocystis noctiluca,
belonging to the Gymnodiniaceae and certain Peridineae.

This phosphorescence at once disappears in an atmosphere devoid of oxygen,
only to reappear on the admission of free oxygen. On this account the phos-
phorescent Bacteria, according to BEYEUINCK and MOLISCH, afford a delicate test
for the activity of assimilation. All the circumstances which facilitate respiration
intensify phosphorescence ; the converse of this is also true. According to the
results of investigations concerning the phosphorescence of animals, from which
that of plants does not probably differ in principle, the phosphorescence is not
directly dependent upon the respiratory processes. Xo use is known for the
phenomenon of phosphorescence.

278 BOTANY PART i

SECTION II
DEVELOPMENT (52)

DEVELOPMENTAL PHYSIOLOGY, which is also spoken of as the
MECHANISM OF DEVELOPMENT, will be treated here under three heads.
A few introductory remarks will in the first place render more vivid
some facts that have already been mentioned in the morphological part.
On this follows developmental physiology in the proper sense, the
object of which is to understand causally the successive processes in
development arid to modify these at will. As yet the results
obtained do not reach far towards Uiis goal ; the problems are more
numerous than the solutions. These problems require to be presented
from two points of view : in the second sub-section the factors which
influence development will be considered, while in the third sub-section
the presentation will be based on the developmental processes them-
selves.

I. Introductory Remarks

Development accompanied by changes of form due to growth is
one of the most general and striking of the vital phenomena of the
plant. A mere increase in volume does not necessarily imply growth,
for no one would say that a dried and shrivelled turnip grows when
it swells in water. Only permanent and irreversible increase of size
can be termed growth, and this whether the plant as a whole is gain-
ing or losing in substance. Usually growth is associated with gain of
material, but in the case of potatoes sprouting in a dark cellar loss
takes place by transpiration and respiration, and yet the shoots
exhibit growth.

1 . The Measurement of Growth.

Total Elongation. — The rate of growth of a plant, or the total
elongation in any unit of time, may be directly measured by means of
a scale in the case of some quick-growing organs, e.g. the inflorescences
of Agave and the shoots of Bambusa. Usually it is necessary to magnify
in some way the actual elongation for more convenient observation.
This may be effected by means of a microscope, which magnifies the
rate of growth correspondingly with the distance grown. For large
objects, the most convenient and usual method of determining the
rate of growth is by means of an AUXANOMETER.

The principle of all auxanometers, however they may differ in construction, is the
same, and is based upon the magnification of the rate of growth by means of a
lever with a long and short arm. In Fig. 255, at the left, a simple form of auxano-

DIV. II

PHYSIOLOGY

279

meter is shown. The thread fastened to the top of the plant to be observed
is passed over the movable pulley (r) and held taut by the weight (g), which
should not be so heavy as to exert any strain on the plant. To the pulley there
is attached a slender pointer (z), which is twenty times as long as the radius
of the pulley, and this indicates on the scale (S) the rapidity of the growth
magnified twenty-fold.

Self -registering auxanometers are also used, especially in making extended
observations. In Fig. 255, at the right, is shown one of simple construction.
The radius of the wheel (-ft) corresponds to the long arm, and the radius of the
small wheel (?•) to the short arm of the lever, in the preceding apparatus. Any
movement of the wheel, induced by the elongation of the shoot, and the con-
sequent descent of the weight (</), is recorded on the revolving drum (CO by the
pointer attached to the weight Z, which is in turn balanced by the counter- weight

FIG. 255.— Simple and self-registering auxanometers. For description see text.

( IV]. The drum is covered with smoked paper, and kept in rotation by the clock-
work (U). If the drum is set so that it rotates on its axis once every hour, the
perpendicular distances between the tracings on the drum will indicate the propor-
tional hourly growth.

The rate of growth in plants is usually too slow to allow of the
result being directly observed after a short time. Only some fungal
hyphae and the stamens of some Gramineae grow so rapidly that
their elongation is evident, even to the naked eye. The fructifica-
tion of the Gasteromycetous fungus Didyophora grows in length to the
extent of 5 mm. per minute (A. MOLLER), and according to AsKENASY
an increase in length of T8 mm. a minute has been observed in
the stamens of Triticum (Wheat). This approximately corresponds to
the rate of movement of the minute-hand of a watch. In comparison
with these the next most rapidly-growing organ known is the leaf-

280 BOTANY PART

sheath of the Banana which shows an elongation of I'l mm., and a
Bamboo shoot, with an increase in length of 0'75 mm. per minute ; a
strong shoot of Cucurbita grows 0*1 mm. per minute, the hyphae of
Botrytis grow 0'034 mm., while most other plants, even under favour-
able circumstances, attain but a small rate of elongation (0'005 mm.
and less per minute).

The rate of growth of an organ never remains uniform ; even
under constant external conditions it gradually increases from very
small values to a maximum and then decreases to zero. This pheno-
menon is known as " the grand period of growth." An example will
illustrate its course.

For the first internode of the stem of the Lupine, growing in the dark at a
constant temperature, the daily growth observed, measured in tenths of a milli-
metre, was :

8, 9, 11, 12, 35, 43, 41, 50, 51, 52, 65, 54, 43, 37, 28, 18, 6, 2, o.

The grand period is not always so regular as in this example ;
frequently deviations due to abrupt changes in the growth are
apparent.

Distribution of Growth (6S). — As a rule any part of a plant is
not growing throughout its whole extent but consists of both fully-
grown and still growing portions. The latter also are not elongating
uniformly but are composed of zones, passing gradually into one
another, in which the rates of growth differ. The length and position
of the growing zones is not the same in different organs. The grow-
ing zone is longer in aerial roots and in extreme cases may amount to
1 m. In roots it is situated at the tip and occupies a length of 5
to 10 mm. The behaviour of stems varies. Those without sharply-
defined nodes have a single zone of growth of considerable length
(frequently extending to *5 m.). They thus resemble the aerial roots.
In many shoots, especially those divided into nodes and internodes,
there are a number of zones of growth separated by fully -grown zones.
This is termed intercalary growth and is beautifully shown, for
example, in the haulms of grasses, where a growing zone is found
at the base of each internode. At the bases of many leaves also,
especially of Monocotyledons, an intercalary growing zone is found.

The distribution of growth in any member of the plant is ascertained by
periodically measuring the distance between certain natural or artificial marks.

Thus, for example, the tip of the root in Fig. 256 7 is marked with lines of
india-ink at intervals of 1 mm. The marks start from the growing point of the
root (0) just behind the root-cap. Twenty-two hours later the marks had been
separated from one another as is shown in Fig. 256 //. The elongation has been
unequal in the different zones ; at the upper and lower ends of the marked
region it diminishes and thus leads to the fully-grown region on the one hand
and the embryonal region at the tip on the other. Between these and nearer to
the apical end is a zone where the maximal growth has taken place. If the
growth of one transverse zone such as that between 0 and 1 is followed on

DIV. II

PHYSIOLOGY

281

successive days it is found that it grows at first slowly, then rapidly, and then
again slowly. In other words, every division of the growing zone exhibits the
grand period of growth. The millimetre zones marked off from the apex are
thus in different stages of their grand periods ;
the two first are on the ascending side of the
curve, 3 and 4 are at the summit, and the
others are on the descending slope of the curve.
Other organs give corresponding results.

Distinct periods of growth separated by an
interval of time occur in the scapes of the Dande-
lion, the first period in relation to the develop-
ment of the flowers, the second to that of the
fruits. A similar behaviour is found in other
organs whose function after a time becomes
altered (flower or fruit stalks in Linaria cymba-
laria, and Arachis hypogaea).

Rate of Growth. — From the fact that
in different organs zones of different
length are in a growing condition, it
follows that such results as to the total
growth of an organ as were described on
p. 279 do not give the true rate of growth,
i.e. the growth of a unit of length in unit
time. Thus in the shoots of the Bamboo
the growing zone is many centimetres
long, while in Botrytis it is only 0'02 mm.
in length. While Bambusa shows twice
as much growth per minute as Botrytis

does, itS rate Of growth is really much FIG. 256.— Unequal growth of different

less. To express the rapidity of growth

it is necessary to express the elongation

per minute as a percentage of the growing

zone. This gives a rapidity of growth

of 83 per cent in Botrytis, and of only

1*27 per cent in Bambusa. The maximum

growth observed is 220 per cent in some

pollen tubes, while some shoots which are still clearly growing have a

rate of only 0'5 per cent.

Size of the Plant. — We can only determine the definite elongation
of a part of the plant when, in addition to the rate of growth and the
length of the growing region, the duration of growth is known. The
size of the plant, which, as is well known, depends in various ways on
external conditions and yet is a specific character, is determined by
variations in these factors. A definite size belongs to the specific pro-
perties of an organism just as much as the form of its leaves, etc. ;
further, the whole organisation of the plant is such that it involves a
particular size. The stems of twining plants are particularly long,

o J

regions of the root-tip of Vina, Faba.
I, The root-tip divided by marking
with india-ink into 10 zones, each
1 mm. long. //, The same root after
twenty -two hours ; by the unequal
growth of the different zones the
lines have become separated by un-
equal distances. (After SACHS.)

282 BOTANY PART i

while "rosette plants," in which the leaves are separated by hardly
recognisable internodes, stand in striking contrast to them.

2. The Phases of Growth

In the simplest plants, such as the lower Algae, Fungi, or Bacteria,
development consists merely in growth of the cell followed by cell
division. These cases have been sufficiently dealt with in the morpho-
logical section. In more complex plants growth and division of cells
are also found, but these processes appear subordinated to the growth
of the whole. Three distinct processes can be distinguished in this,
though they are not always separated in time. These are the stage of
FORMATION OF EMBRYONIC ORGANS, that of ELONGATION, and the stage
of INTERNAL DEVELOPMENT (54).

(a) Embryonic Rudiments. — The embryonic growth takes place
normally at the growing1 points, and new growing points arise as a
rule directly from the latter. Only in the case of roots is the forma-
tion of the growing points of lateral branches somewhat delayed and
takes place from remains of the growing point which have retained
the embryonic character. The main features of the formation of
organs at the growing points have been dealt with in the section on
Morphology. SYMMETRY and POLARITY have been considered on
p. 74 ff.; these are often manifested even at the growing point. The
contrast of base and apex which constitutes polarity is determined in
the egg-cell in higher plants, and is as a rule maintained when once
established. It must be pointed out here that all growing points do
not arise from pre-existing similar ones. Development of the plant
can proceed by restitution as well as by the normal organogeny.

By Restitution (55) is understood the new formation of organs
which as a rule follows the mutilation of a plant, and can take place
in situations where no active growth would have been manifested in
an uninjured plant. The types of restitution may be distinguished
as regeneration and reparation.

REPARATION is when the lost organ is again formed from the
wounded surface. This kind of restitution, though not uncommon
in lower plants such as Algae and Fungi, is of very restricted occurrence
in the higher plants. Only tissues that are meristematic or embryonic,
and by no means all of these, are capable of reparation. It is most
frequently seen in the growing point of roots ; when the tip is removed
by a transverse cut, if this is not more 'than 0'5 mm. from the tip,
it may be again formed. A longitudinally-split root-tip tends to com-
pletion by reparation, so that a root thus treated may obtain two
growing points. True reparations do not occur at the growing points
of shoots ; they are rare in the case of leaf-primordia.

REGENERATION, on the other hand, is wide-spread among plants.
In this case an organ which has been lost is replaced either by the

DIV. II

PHYSIOLOGY

283

formation of a new one in the vicinity of the wound or the out-
growth of one which was in a rudimentary condition. Examples
of this type of restitution are afforded by the Algae and Fungi, and
especially by Bryophyta. These can only be mentioned here, and
consideration will be limited to the Flowering Plants. The capacity
to form roots is especially wide-spread. In Geraniums, Willows,
and many 'other plants, roots can be induced to form at any point
by cutting off the shoots. In other plants the roots develop at
particular places such as the older nodes. After roots have developed,
the stem gives rise to a complete plant either by the unfolding of
axillary buds or by the development of new growing points of shoots.
Separated leaves are often able to form
roots, though the power of giving rise
to a new shoot is rarely connected
with this. Even separated roots, when
they are able to give rise to shoots,
may regenerate new plants. Regenera-
tive buds may also arise on tendrils,
flowers, and fruits. When in regenera-
tion the production of shoots is not
provided for by existing growing
points, new ones may
be developed. If the
growing point of a
seedling is destroyed
a new growing point
may be developed from
the meristem above
the youngest leaf-

\A hile FIG. 257. — Transverse section of the leaf of Begonia showing the
the regeneration is development of an adventitious shoot from an epidermal cell,
a, The epidermal cell has divided once ; 6, a mnlticellular
nere restricted to men- meristem has been produced, (x 200. After HANSEN.)

stematic cells, in other

cases older fully-grown cells may recommence to grow and divide
and thus return to the meristematic condition. A special tissue, called
CALLUS, is thus first formed at the wounded surface, and new shoots
may form within this. In yet other cases fully-grown epidermal or
parenchymatous cells may give rise to growing points directly, i.e.
without the formation of callus. Fig. 257 shows the origin of a
regenerative shoot from an epidermal cell of a leaf of Begonia.

Tissues may also be regenerated from mature parenchymatous cells. Thus
when the conducting tracts are interrupted new vessels may be formed from the
parenchyma and re-establish the connection. The tissues which have been removed
or interrupted are, however, not always formed anew ; frequently substitutionary
growth takes place. Thus, as a rule, an epidermis is replaced by cork, and it is
exceptional for a true epidermis with stomata to be regenerated (56).

284 BOTANY PART I

The new formation of epidermis, which occurs in the normal course of develop-
ment in certain Araceae with perforations in their leaves, may be referred to here.
In Monster a deliciosa particular limited regions of the laminae of quite young leaves
die. Around these spots the mesophyll divides and forms from the outermost
layer of cells a secondary epidermis, clothing the perforations and connecting with
the primary epidermis of the upper and lower surface of the leaf. In the normal
development of plants many processes which can be regarded as regenerative take
place such as repeated cork-formation (p. 163).

In addition to the fact that regeneration occurs, the question as
to where this takes place is of interest. The polarity which exists
in the intact plant is frequently manifested in regeneration. Thus
shoots tend to appear at the apical end and roots at the basal end
of portions of stems, while the opposite distribution is found in roots.
In more lowly-organised plants polarity is often apparent in the re-
generative process, as when each of the single cells separated from a
Cladophora forms a colourless rhizoid at the base and a green filament
at the apical end.

This contrast of base and apex does not appear in regeneration
from foliage leaves ; this may be connected with the fact that the
regenerating leaf is not included in the new formation. Frequently
a new plant arises at the base of the leaf, which then dies off. Some-
times regeneration proceeds from the general surface of the leaf
(Torenia\ but frequently the place of regeneration can be determined
by cutting the lamina, the new plants forming above the incisions
(Begonia, Fig. 258).

The phenomena of regeneration have great importance in horticulture, since
they allow of plants being rapidly multiplied without the aid of seeds. In
artificial reproduction detached pieces of plants are made use of for the purpose of
producing fresh complete plants. In many cases this is easily done, but in others
it is more difficult or even impossible. The favourite and easiest method is by
means of CUTTINGS, that is, the planting of cut branches in water, sand, or earth, in
which they take root (Oleander, Pelargonium, Tradescantia, Fuchsia, Willow, etc.).
Many plants may be propagated from even a single leaf or portion of a leaf, as,
for instance, is usually the case with Begonias. In other cases the leaves, while
still on the parent plant, have the power to produce adventitious buds, and in
this way give rise to new plants. The Dandelion possesses the capability of
developing from small portions of the root, and to this peculiarity is due the
difficulty with which it is destroyed.

(b) Elongation. — The meristematic primordia require to enlarge
and unfold before they can become functional, and this increase of
size is effected in a peculiar and economical fashion. It results
mainly from absorption of water from without. Organic material
is of course required for the extension of surface of the cell walls,
but there is no need of an increase in protoplasm during the enlarge-
ment. There is a great difference in this respect between the growth
of a plant and a typical animal ; nothing corresponding to this " phase
of elongation " is met with in the latter.

DIV. ii PHYSIOLOGY 285

The meristematic cells of the growing point contain considerable
amounts of imbibed water in the wall and protoplasm. As absorp-
tion of water from without continues, a distinction becomes evident
between the fully-saturated protoplasm and the vacuoles filled with
a watery solution ; this leads ultimately to the single large central
vacuole or sap-cavity surrounded by the peripheral layer or sac of
protoplasm (cf. p. 12, Fig. 3). It has been already seen (p. 225)
that the vacuole is the seat of osmotic forces ; the turgidity of the
cell is essential to the growth in surface of the cell wall.

FIG. 258.— Leaf of Begonia used as a cutting and bearing regenerative shoots. (After STOPPEL.)

Cells in which the turgescence has been destroyed by plasmolysis (p. 226)
exhibit no further growth, and it might be concluded from this that the mechanical
distension of the wall assists or renders possible its growth. No clear corre-
spondence between distension and growth can, however, be assumed to exist. More-
over, the pressure of turgescence cannot be replaced by mere mechanical stretch-
ing of the wall. The protoplasm plays the main part in the growth in surface
of the cell wall, and in connection with this it can be understood how the walls
of cells that are only slightly distended may grow rapidly.

Regarding the processes in the growth of cell wall which are termed apposition
and intussusception, svhat is necessary has been stated on p. 35. In growth in
surface due to plastic stretching without addition of material, followed by the
addition of new layers to the wall, the stretching due to turgor appears as a
natural preliminary to the growth. In the case of growth by intussusception the
turgor pressure appears less necessary.

With the increased absorption of water following on the growth of the wall

286 BOTANY PART i

the cell sap must become more dilute. This does not actually occur owing to the
power of the growing cell to regulate the osmotic pressure of the cell sap. The
pressure can be increased by the transformation of sugar into organic salts ; thus,
for example, by a change of glucose into oxalic acid the osmotic pressure can be
trebled. On the other hand, the pressure can be lessened, e.g. by complete
combustion of sugar in respiration.

Besides the expansion in the longitudinal direction, expansion in
a transverse plane (growth in thickness) has to be considered. The
diameter of the mature root or stem is often considerably greater than
that immediately behind the growing point. As has been seen on
p. 140, a distinction is drawn between primary and secondary growth
in thickness. Only the primary growth in thickness is a phenomenon
of the kind that is here being considered. In secondary growth new
meristematic cells are formed from an intercalary meristem or cambium,
and only later pass into a phase of expansion.

TISSUE TENSIONS. — The expansion of the cells in length and
breadth does not always take place uniformly and simultaneously in
the whole cross -section of an organ. It is usual to find that, in
growing stems for instance, the pith strives to expand more strongly
than the peripheral tissues. Since no breach of continuity between
the two regions is possible, a state of tension (tissue tension) results.
The pith expands the cortical tissues and these compress the pith ;
the actual length of the organ is the resultant of these antagonistic
tendencies. If the tissues are artificially separated, each assumes its
own specific length ; the pith elongates and the cortex contracts and
the tension disappears.

The tissue tensions which occur generally in growing organs may be demon-
strated in this way. In a sunflower shoot the pith is separated for some
distance from its connections to neighbouring tissues by means of a cork-borer.
On withdrawing the cork-borer the cylinder of pith projects for some distance from
the cut surface of the stem (Fig. 259, 1). If a similar shoot is split longitudinally
the two halves curve outwards owing to the elongation of the pith and the
contraction of the epidermis. Even in the case of hollow shoots such as the stalk
of the inflorescence of the Dandelion (Taraxacum} a tension exists between the
outer and inner tissues which is expressed by curvatures when the stalk is split
longitudinally (Fig. 259, 2a). If the stalk after this treatment is placed in water
the curvature increases considerably (Fig. 259, 2V).

Tissue tensions also occur in leaves and roots. The tensions need not be in the
longitudinal direction alone ; there are also transverse tensions. Thus, for example,
the rind of trees which increase in thickness by secondary growth is considerably
stretched in the tangential direction. On being separated from the wood it there-
fore contracts.

The tissue tensions gradually arise at some distance from the
growing point when the expansion of cells is commencing, and as a
rule they again disappear in the fully-grown zone, though they persist
in the case of some organs. They are of great importance for the
rigidity of growing tissues ; they increase the rigidity given by the

D1V. II

PHYSIOLOGY

287

turgescence of the individual cells. The tissue tension presents a certain
resemblance to the turgescence of the cell ; this is most evident in the
typical stem. Just as the cell sap distends the cell wall by its osmotic
pressure, the expanding pith stretches the cortical tissues. Increased
resistance to deformation and increased rigidity result from the
stretching of the cortex, just as they do in the cell from the stretching
of the wall.

The tissue tension ceases as all the cells attain the permanent
mean length dictated by the size of the organ. Sometimes, however,
certain cells after attaining their greatest
length exhibit a considerable contraction
associated with an alteration in shape.
This occurs often in roots when the tissues
of the cortex £nd of the central portion
are thrown into folds by the contraction
of the tissue that lies between them. The
significance of this contraction of roots,
which may lead to a shortening of the
fully-grown structure by 10-70 per cent,
is very great. Thus it is due to it that
the leaves of many " rosette plants," in
spite of the continued growth in length
of the stem, remain always appressed to
the soil. It determines and regulates the
penetration of many tubers and bulbs to
a definite depth in the soil. It increases
the fixation of the plant in the soil, since
greater stability results from tense than
from slack roots.

(c) Internal Differentiation. — The
cells of the typical growing point maintain
their power of growth and division ; they
are termed meristematic cells. All organs
composed of such cells have in principle

the capacity for unlimited growth. Embryonic tissue is found not only
at the growing points, but in the secondary meristems (p. 47).

A portion of the meristematic tissue, or the whole of it in the case
of organs of limited growth, becomes transformed into the somatic
cells of the permanent tissues ; in these growth and cell division cease,
and sooner or later death ensues (p. 309).

The internal development of an organ commences close behind the
growing point and lasts for a longer or shorter time. While the full
development of hairs is frequently very rapid, the definite form and
structure of the internal tissues is often only completed after the phase of
elongation is ended. When secondary growth in thickness takes place
there is no termination to the internal development. The development

FIG. 259. — 1, Shoot of Helianthus
annuus with the leaves removed
and the pith separated from the
peripheral tissues by means of a
cork -borer. 2, Stalk of the in-
florescence of Taraxacum, split
longitudinally by two incisions at
right angles to one another ; a,
just after splitting ; b, after im-
mersion in water.

288 BOTANY PART i

of the " permanent tissues " from the primary and secondary meristems
has been described in the morphological section. Here it is only
necessary to recall the fact that the following processes are con-
cerned ; in the first place the formation of cells by cell division which
takes place in the embryonic tissues and at the commencement of
elongation ; following on this the separation of cells which gives rise
to intercellular spaces ; the independent growth of the individual cells ;
thickening and chemical changes of the cell walls ; modifications (and
eventually in some cases the complete disappearance) of the cell
contents ; and lastly fusions of cells (cf. p. 44).

In the arrangement of the tissues the same symmetry, which is
apparent in the external form of the organs of the plant, is seen ; the
internal structure of the organs is thus radial, bilateral, or dorsiventral.

II. The Factors of Development

In attempting to determine the factors which influence development
it is necessary to treat of examples which show in characteristic fashion
the effect of particular factors. Completeness, either in the enumera-
tion of the factors or as regards their influence, is out of the question.
It is advisable to select the simplest influences when possible, since
more complicated cases require further investigation. As in other
cases the factors may be divided into the two groups of external and
internal factors.

A. External Factors

All the forces and substances which have been seen to be
physiologically effective in the metabolism, or which play a part in
movements, are among the external factors of development.

Certain external factors were mentioned on p. 218 as general
conditions of life ; without these it is evident that no development
would take place. These, and other factors which are not necessary,
exert a profound influence on growth. Quantitative and even quali-
tative changes in the organs of plants may be educed by variation in
the intensity, quality, or direction of such factors. These influences,
in which the connection between cause and effect is always compli-
cated and involves stimulation of the protoplasm, are termed
formative.

1. Temperature. — As in the case of metabolism it is found that
a certain temperature is a necessary formal condition of growth.

There is complete cessation of growth at a temperature less than
0° or higher than 40°-50°. Between the MINIMUM and MAXIMUM
temperatures, at which growth ceases, there lies an OPTIMUM tem-
perature at which the rate of growth is greatest. This optimum

mv. it

PHYSIOLOGY

temperature usually lies between 22° and 37° C. Plants inhabiting
different climates exhibit considerable differences in regard to the
cardinal points for temperature (cf. p. 219).
That the different individuals of the same
species may show great differences in the
dependence of the phase of elongation on tem-
perature is seen in the unequal development of 1L I
the buds of the Horse-chestnut, etc., in spring.
Even in the same individual the processes of
growth in the different organs are variously
influenced by the temperature.

In tropical plants the minimum temperature may be
as high as + 10° C., while those of higher latitudes,
where the first plants of spring often penetrate a covering
of snow, as well as those of the higher Alps and polar
regions, grow vigorously at a temperature but little
above zero. Many of our spring plants show that the
opening of their flowers can take place at a lower tempera-
ture than the unfolding of the foliage leaves.

2. Light. — -The growth of a plant is rarely
so strictly limited to a particular illumination as
to a particular temperature. There are, however,
some organs in which growth commences only
after a certain intensity of light has been experi-
enced; some seeds (p. 305) and all parts of plants
which are normally exposed to light can only
continue their development when this is present.
Long-continued darkness produces an abnormal
growth, in that the normal correlation between
different organs is disturbed ; the growth of

certain organs is unduly favoured, and of others FIG. 260.— TWO seedlings of
^ i 11 • °' — -" ""• — * — ' —

greatly retarded. In darkness the yellow pig-
ment of the chloroplasts but not the chlorophyll
is formed. The stems of Dicotyledons, in such
cases, become unusually elongated, also soft and
white in colour. The leaf-blades are small and
of a bright yellow colour, and remain for a long time folded in the bud
(Fig. 260 E). A plant grown under such conditions is spoken of as

ETIOLATED.

The elongation of certain organs and simultaneotts reduction of others has
an ecological significance in nature in the case of seedlings and rhizomes which
are growing in the dai'k. The parts which are functional only in the light remain
at first undeveloped, and the constructive material for them and especially for
the chlorophyll is economised. The great elongation of the other organs which
is mainly dependent on an accumulation of water brings the parts that need it
as soon as possible into the light.

Sinapis alba of equal age.
E, Grown in the dark,
etiolated ; N, grown in
ordinary daylight, normal.
The roots bear root-hairs.
(After XOLL.)

290 BOTANY PART i

Comparison of an etiolated plant with one grown in the light shows
that the influence of light is not the same on all organs ; it may
either increase or arrest the growth. While, however, the action
of light in arresting the growth of the stem increases with the
intensity, the increase of the growth of leaves due to the light has
a limit ; the leaf attains its maximal size in light of moderate intensity.
It is a one-sided view of the growth in length of the stem, and the
resulting height .of the plant that is expressed by the statement,
"the effect of illumination is to retard growth." In these organs,
and in others that behave similarly, the effect of light is found
to be much less simple. It appears rather, as is shown by the
accurately -investigated case of the coleoptile of Avena, that light
first accelerates and then retards growth, and that both influences
increase with the intensity of the light. With every increase in
the illumination there is first acceleration and then retardation of
growth, while on darkening the plant there is retardation followed by
acceleration (57).

The effect of the component rays of white light appears to be still
less simple. When light is arresting the elongation of the stem it is
the blue and violet rays of short wave-length that are effective, while
the red rays behave in the same way as darkness. Other processes
of growth, however, are influenced differently. The germination of
the spores of certain ferns is accelerated by red light, while blue
light hinders it even more than darkness. Spores germinated in red
light produce greatly elongated cells which only become divided by cell
walls in blue light (57a). The complicated nature of the phenomena
is in part explained by light acting both as a stimulus to growth and
as a source of energy. Ultra-violet light injures the plant ; radium-
and Rontgen-rays retard, but, like poisons (p. 29 4), may when in
small quantity promote growth (58).

In addition to the intensity and the quality of the light, its
direction greatly influences the form of the plant body. The
curvatures due to one-sided illumination (phototropism) will be dealt
with later in connection with the phenomena of movement. The
illumination may also influence the polarity and symmetry of the
plant. Thus in some simply-organised plants the more strongly
illuminated side of the cell from which development starts becomes
the apex and the other side the base. In other cases an originally
radial growing point becomes bilateral or dorsiventral under one-
sided ^Humiliation. Lastly, an organ which has passed the embryonic
stage may become dorsiventral, as in cases where roots form on the
shaded side only. When it is possible to experimentally transform
the external symmetry the internal structure is also as a rule altered,
the connection between the two being very close.

In the germination of the spores of Equisetum, the first division wall, and with
this the distinction of apex and base, is determined by the direction of the light.

DIV. ii PHYSIOLOGY 291

A similar influence of light on the polarity is shown by the egg-cells of Fucus and
Dictyota.

Antithamnion cruciatum, one of the Florideae, forms decussately-arranged
branches when in diffused light ; on one-sided illumination the branches all stand
in one plane at right angles to the direction of the rays. Further examples of
dorsiventrality induced by one-sided illumination are afforded by the branches of
' many Mosses, the thalli of most Liverworts, and the prothalli of Ferns ; these
structures in the absence of such illumination are sometimes radial and in other
cases bilaterally symmetrical. In fern prothalli and the thallus of Marchantia
the dorsal side is determined by the stronger illumination. In the case of the
prothalli, when the lower side is illuminated, the new growth is adapted to the
altered direction of the light and the former upper side becomes the lower ; in the
Marchantiaceous thallus, on the other hand, the dorsiventrality once induced
cannot be changed. The shoots of Ivy and other root-climbers in which the
climbing roots are produced on the shaded side may be cited as an example of
dorsiventrality induced by light in the higher plants.

Comparison of an etiolated and a normal plant shows that influence of the
intensity of the light under which the plant has grown extends to the internal
structure. The tissues of the etiolated plant are less differentiated and thickened
cells are wanting. A less complete contrast than between light and darkness
may be effective. Shade-leaves (59) have a very different structure from the leaves
of the same species developed in full sunlight. They are thinner, their palisade
cells narrow below,»leaving wide intercellular spaces between them, and form only
a single layer ; in sun-leaves the palisade cells are longer and form several layers.

Alpine plants, the illumination of which differs in duration, intensity, and
composition from that in the plains, differ in their whole habit from lowland
plants. Their vegetative organs are contracted, while the flowers are large and
brightly coloured. Other factors than light are concerned in this change.

3. Gravity. — A plant can readily be removed from the light but
gravity is always acting upon it. It is only possible to change the
direction of its action. When the direction of the action of gravity
coincides with that of the main shoot and root of the plant no effect
is perceptible ; when it forms an angle with the line of these organs
curvatures are produced (see Geotropism), as in the case of illumina-
tion from one side. Apart from these curvatures an action of
gravity on the polarity of the plant is established ; this does not
amount, however, to inversion or to the transformation of the shoot
into a root. There is no case of the polarity of the undifferentiated
egg- cell being altered by gravity; this is always determined by
internal causes, though gravity may have a modifying influence.

If twigs of Willow are cut and suspended in a moist chamber roots form near
to the lower end, while only the buds situated near the other end expand into
shoots (Fig. 261, 1). If the twig is hung in the inverted position it is the
corresponding buds at the end which is now lowest which still give rise to shoots,
while the strongest roots are produced near to the lower end which is now upper-
most (Fig. 261, 2). This experiment shows that internal causes mainly determine
the contrast of the two poles. Since, however, in the inverted position there is a
displacement downwards of root-formation and upwards of the unfolding of the

U 1

292

BOTANY

PART I

buds gravity must also play a part. It has, however, in no case proved possible
to effect a complete and lasting inversion of the polarity of a plant in this way ;
while such inverted plants may live for a considerable time, they exhibit serious
disturbances in their anatomical construction (*").

An effect of gravity on the internal disposition is also seen in the case of
obliquely or horizontally placed branches. The tendency of the internal disposition
is to cause the uppermost buds to develop and give rise to long
shoots. On branches displaced from the vertical the basal buds are
favoured and the more apical buds arrested. When the branch
is curved the strongest branches arise at the highest point of the

curve. In the cultivation of vines
and fruit trees this peculiarity is
utilised to produce shorter and
weaker shoots (short shoots),
which experience has shown are
those that bear the flowers.

4. Mechanical In-
fluences. — Pressure and
traction exert a purely
mechanical influence upon
growth, and also act as
stimuli upon it. External
pressure at first retards
growth ; it then, however,
stimulates the protoplasm
and occasions the distension
of the elastic cell walls, and
frequently also an increase
of turgor. As a consequence

of this increased turgtfT, the

COunter-resistailCe to the CX-
• • A •« j

ternal pressure is intensified.
If the resistance of the body exerting the pressure cannot be overcome,
the plasticity of the cell walls renders possible a most intimate contact
with it; thus, for instance, roots and root-hairs which penetrate a
narrow cavity fill it so completely that they seem to have been poured
into it in a fluid state. It would be natural to suppose that the effect
of such a tractive force as a pull would accelerate growth in length by
aiding and maintaining turgor expansion. But the regulative control
exercised by the protoplasm over the processes of growth is such that
mechanical strain first acts upon growth to retard it, but then causes
an acceleration of even 20 per cent.

Other actions of mechanical influences as stimuli may be mentioned. Lateral
roots arise only from the convex sides of curved roots (Fig. 262), the cause lying
probably in the DIFFERENCES OF TENSION between the two sides. The primordia
of the haustoria of Cuscuta and the adhesive discs on the tendrils of some species
of Parthenocissus are caused to develop by the STIMULUS OF CONTACT.

FIG. 261.— Twigs of Willow : 1, in the -normal position ; 2,
in the inverted position growing in a moist chamber.
(After VOCHTING.)

D1V. II

PHYSIOLOGY

293

If mechanical effects lead to wounding the result may be the
phenomena of healing (p. 164) or restitution (p. 282).

5. Chemical Influences. — The presence of the necessary nutrient
substances in sufficient quantity and the absence of poisonous
substances are formal conditions for growth. While it is known that
particular, essential, nutrient materials are not replaceable by an
excess of others, some substances may be of special importance in
particular processes. Since elongation is essentially due to the
introduction of water, the signifi-
cance of the water supply to a
growing plant is obvious. Growth
often ceases when there is not
sufficient water in the soil. Even
a diminution in the humidity of
the air may arrest growth by
increasing transpiration. Some
plants, however, can store water,
and are therefore more inde-
pendent of its direct absorption.
They grow at the expense of the
stored water, and can often with-
d raw the water from older portions
so that these wither while growth
goes on at the apex, as is shown
by potatoes sprouting in a dark
cellar. Plants in damp situations
are usually larger than those
grown in dry places, and in fact
may differ from them in their

whole habit and mode of growth. FlG- 262. -Young plant of Lupine, the main root of

P • , -i which has become curved. The lateral roots

A local excess of water in the have arisen on the convex faces of the curves.

plant, such as may be brought (After NOLL.) .

about by arresting transpiration

by a coating of paraffin oil, may lead to various departures from the

normal structure (596).

A striking stimulus -effect results from permanent contact with
liquid water in such plants as can endure this. This is doubtless the
result of the combined effect of a number of factors and not simply to
the material effect of the water. Thus both the arrest of transpiration
and the change in the illumination are of importance.

Amphibious plants, that is such as are capable of living both upon land and
in water, often assume in water an entirely different form from that which they
possess in air. This variation of form is particularly manifested in the leaves,
which, so long as they grow in water, are frequently linear and sessile or finely
dissected, while in the air their leaf-blades are much broader and provided with
petioles (cf. Fig. 128). The leaf-stalks and internodes also often exhibit a very

294 BOTANY PART I

different form in air and water, and undergo the same abnormal elongation as in
darkness.' This is especially noticeable in submerged water plants, whose organs
must be brought to the surface of the water (stem of Hippuris, leaf- stalk of
Nymphaea). Such plants are enabled by this power of elongating their stems or
leaf- stalks to adapt themselves to the depth of the water, remaining short in
shallow water and becoming very long in deep water.

The water-forms also differ from the land-forms in their internal structure.
Thickened cell walls are frequently absent from the stem, and the vascular bundles
are reduced; the leaves resemble shade -leaves. The most marked contrast to
water plants is presented by such land plants as are exposed to insufficient water
supply or too active transpiration. In these the vascular bundles are strongly
developed, while the epidermis has the arrangements which have been considered
under the means of protection against excessive transpiration.

In addition to the true nutrient materials which are employed
in the construction of the substance of the plant, oxygen requires to
be mentioned. Although its entry into the plant is connected with a
loss of organic substance, it is quite indispensable for growth on
account of the need of respiration. In aerobic plants at least, growth
ceases completely on the withdrawal of oxygen ; a diminution or
increase of the proportion of oxygen in the air also influences growth.

Stimuli of the most various kinds proceed from substances acting
on the plant.

Poisons must first be mentioned ; these are substances which in very dilute
solutions arrest growth and ultimately life. Thus even in a dilution of 1 in
25,000,000 copper sulphate kills such Algae as Spirogyra and also peas in water
cultures. It is a striking fact that many poisons when in extreme dilution have
a stimulating effect on growth. Chemical stimuli due to other substances play a
large part in the germination of many seeds, spores, and pollen grains, and in the
development of fruits. Some pollen grains only germinate when they obtain traces
of substances which are present on the stigma. Many parasitic fungi and also
parasitic Phanerogams (Orobanche, Lathrea) are stimulated to develop by unknown
substances proceeding from their hosts. In Algae and Fungi high concentration
of some food materials may give rise to striking changes in form.

6. Influence of Foreign Organisms. — Fungi and Bacteria living
parasitically in flowering plants often cause profound deformations
that are known as GALLS (60). In the simplest cases there is merely a
hypertrophy of cells, while in more complex ones there are qualitative
changes in the organ. Still more striking gall-formations are caused
by animals, especially insects. Outgrowths form, which serve the
parasites for protection and food. The structure of the gall appears
purposive when considered from the side of the parasite, the protective
layers and nutritive layers of the gall being without significance for
the plant.

Euphorbia Cyparissias, when attacked by a rust fungus (Aecidium Euphorbiae),
becomes sterile, remains unbranched, has shorter and broader leaves, and in its
whole appearance is so changed as scarcely to be recognisable. Plant lice some-
times cause a flower to turn green, so that instead of floral leaves green foliage-like

DIV. II PHYSIOLOGY 295

leaves appear. Another peculiar example of abnormal growths is afforded by the
GALLS or CECIDIA produced on plants by Fungi, or more frequently by insects,
worms, and arthropods. The effect of these formations on the normal development
of the tissues of a plant is more or less disturbing, according to their position,
whether it be in the embryonic substance of the growing point, in the tissues still
in coarse of differentiation, or finally in those already developed. Galls which are
products of abnormal tissue formation are termed HISTOID, while ORGANOID galls
depend on the transformation or new formation of members of the plant body.
The latter are especially instructive. The larvae of Cecidomyia rosaria live in the
growing points of Willow stems, and occasion a malformation of the whole shoot
by the production of galls, known as " willow -roses," which are composed of
modified leaves and axes. Flies (Diptera) often deposit their eggs in the tissues of
partially-developed leaves, in consequence of which the leaves become, according
to their age when attacked, more or less swollen and twisted. After the leaves of
the oak have attained their full growth they are often stung by a gall-wasp of the
genus Cynips. The poison introduced by the sting, and also by the larvae hatched
from the eggs deposited at the same time, occasions at first only a local swelling of
the leaf tissue, which finally, however, results in the formation of yellow or red
spherical galls on the lateral ribs on the under side of the leaf.

Symbionts, i.e. associated, mutually-beneficial organisms, neither
of which can be regarded as the host, may influence one another
formatively. This is seen, for example, in Lichens.

It is probable that chemical substances play an important part in
the influences exerted by one organism on another. It is true that
only in rare cases have deformations resembling galls been brought
about by the action of dead substances extracted from the normal
inhabitant of the gall. Parasites which do not give rise to galls
probably act on the host plant by poisonous substances. On the other
hand, the host plant by forming anti-bodies may injure the parasite or
prevent its entrance. Thus HEINRICHER has shown that some kinds
of pear-tree are readily infected by the mistletoe and others only with
difficulty ; he has also shown that probably one infection by the
parasite renders the host more resistant to artificial infections. There
are thus PHENOMENA OF IMMUNITY in the vegetable kingdom, though
they have not been nearly so thoroughly investigated as in the case of
animals (60a).

7. Pupposiveness of the Reactions to External Factors. — It has
been seen that the form and structure of the plant is influenced in a
regular fashion by many external factors. While some of the resulting
changes are without importance to the plant or, as in the case of galls,
are only of use to the organism causing the change, the majority of
reactions to external stimuli are remarkably purposive, i.e. they are
of use to the plant. Examples are afforded by the elongation in
etiolation, the characteristic development of amphibious plants in
water and on land, the increase of protections against transpiration
with the greater dryness of the atmosphere, etc. ; these purposive
reactions are termed ADAPTATIONS. How it comes about that the

296 BOTANY PART i

plant frequently reacts in a purposive fashion will not be considered
here (cf. p. 212).

B. Internal Factors

When a change occurs in an organism while all the external factors
remain constant it must be referred to internal factors. The latter
cannot be so readily analysed as the external factors, so that the
reference of many phenomena to internal factors is frequently little
more than a statement of our ignorance.

1. Determinants. — The determinants which a plant has derived
from its parents are the first internal causes to be mentioned ; it is
these that lead to the regular origin of a fungus from a fungal spore
or of a bean-plant from a bean-seed. In particular they determine the
agreement of all the individuals of any species, when under the same
external conditions, in such characters as the colour of the flower,
form of the leaf, size, etc. It is not as a rule possible to experimentally
alter the determinants possessed by a species, and they cannot be
ascertained by direct observation On this account further considera-
tion of them may be deferred until heredity is treated later.

2. The Phenomena of Correlation (61). — While external factors
have a profound influence on the internal structure of plants the
differentiation of tissues proceeds under quite constant external con-
ditions ; it is thus determined by internal causes. We do not know
what is the nature of the particular causes that force a meristematic
cell into a definite course of development. Only one thing is certain ;
from every cell of the growing point everything might arise, all the
cells agreeing in their determinants. It is the mutual connections or
correlations between the cells that lead to the lines of development
followed by this and that cell. When these connections are removed
it has been seen in the phenomena of reparation (p. 282) how cells
exhibit quite other capacities than those they had previously shown
when in connection with one another. This applies to mature as well
as meristematic cells when their connection with neighbouring cells is
interfered with. Thus in the process of regeneration (p. 282) it has
been seen how fully-grown cells that would soon have perished again
become young, and how, for example, from a single epidermal cell all
the various cells characteristic of the particular plant can be derived.
It is clear that an organism in which such mutual action of the cells
was lacking could not exhibit the division of labour that is customary
in the higher plants. In other words, correlations must be reckoned
among the " regulations " without which the organism is inconceivable.

Such correlations exist between the externally visible organs of
a plant as well as between its cells. This, if not as a rule evident,
becomes apparent when an organ is removed and the reactions of the
isolated organ and of the plant from which.it was taken are studied,

DIV. ii PHYSIOLOGY 297

or when an organ is experimentally brought into a position it did not
previously occupy.

The first result of the removal of an organ may be the appearance
of so-called COMPENSATIONS ; other remaining organs become larger.
The leaves which arise at the growing point prevent older leaves
attaining their maximal size, and if the growing point is removed the
size of the leaf may be increased (e.g. in the tobacco plant). The
active development of some of the axillary buds hinders that of many
others ; if the dominant shoot is removed the resting buds commence
to grow. The conclusion may be drawn that even in normal develop-
ment the size of the organs is determined by correlative influences
from neighbouring organs. In other cases a QUALITATIVE effect
follows the removal of an organ. If the tip of a Pine is removed, its
place is taken by one of the adjacent lateral branches, which assumes
the erect position and shows the same leaf arrangement as the original
main shoot. It appears that the usual oblique position and dorsi-
ventral arrangement of the foliage on the lateral branches comes
about under the influence of the main shoot. In this and many other
cases of correlative influence it is not necessary that the organ should
be removed ; as a rule it is sufficient to interfere with its normal
action, as for example by embedding it in plaster of Paris.

It has been shown in treating of restitution (p. 282) that new
roots or shoots may be produced on isolated organs. Thus the
members of the plant, like every cell, are originally capable of further
development in a number of directions. It is their mutual influence
that serves to control this.

The effect of correlation is also shown when an organ is trans-
planted to a new position. By methods of transplantation, which
have been derived from horticultural practice, it is easy in the case of
many plants to make a separated part grow in relation to a wounded
surface. The separated part is termed a graft, while the plant upon
which it is inserted is called the stock. The graft may be of the same
species as the stock, or from a related kind of plant. One correlative
influence which is apparent is the suppression of regeneration on the
part both of the stock and the graft. The latter adopts the root-
system of the stock, while the stock in turn adopts the shoot-system
of the graft ; there is no necessity for the formation of new organs.

Artificial GRAFTING, like artificial propagation, plays an important part in
horticulture. Separated shoots bearing buds serve as the grafts or scions, and are
caused to unite with a rooted plant as the stock. In this way it is possible to
obtain examples of considerable size of a race or species more rapidly than by
seeds or by artificial propagation. In practice several different methods of insert-
ing grafts are in use, but only the more important can be mentioned here.
GRAFTING is the union of a shoot with a young and approximately equally-
developed wild stock. Both are cut obliquely with a clean surface, placed
together, and the junction protected from the entrance of water and fungi by
means of grafting wax (Fig. 263 II}. Cleft or tongue grafting is the insertion of

298

BOTANY

PART I

weaker shoots in a stronger stock. Several shoots are usually placed in the
cut stem of the stock, care being taken that the cambial region of the different
portions are in contact, and that the cortex of the shoots is in contact with that of
the stock. In other methods of grafting, the cut end of the shoot is split longi-
tudinally and the cut shoot is inserted in the periphery, or a graft may be inserted
in the cortex or in the side of the stock. In grafting in the cortex the flatly-cut
shoot is inserted in the space cut between the bark and the splint wood (Fig. 263
/). In lateral grafting, the shoot, after being cut down, is wedged into a lateral
incision in the stock.

FIG. 263.— Different modes of grafting. I, Crown grafting ; II, splice grafting ; III, bud grafting.
W, Stock ; E, scion. (After NOLL.)

A special kind of grafting is known as BUDDING (Fig. 263 III}. In this process
a bud (" eye ") and not a twig is inserted under the bark of the stock. The " eye "
is left attached to a shield-shaped piece of bark, which is easily separated from
the wood when the plants contain sap. The bark of the stock is opened by a
T-shaped cut, the "eye" inserted, and the whole tightly covered. Occasionally
some of the wood may be detached with the shield-shaped piece of bark (budding
with a woody shield). In the case of sprouting buds, the budding is made in
spring ; in dormant buds, which will sprout next year, in summer.

The union is accomplished by means of a callus (p. 164), formed by both the
scion and the stock. Vessels and sieve -tubes afterwards develop in the callus,
and so join together the similar elements of the two parts. Such an organic union
is only possible between very nearly related plants : thus, for example, of the
Amygdalaceae, the Plum, Peach, Almond, and Apricot may readily be grafted one
upon the other ; or of the Pomaceae, the Apple with the Quince ; but not the
Apple with the Plum, nor (as has been asserted) with the Oak.

DIV. 11 PHYSIOLOGY 299

The polarity which is noticeable in phenomena of regeneration also influences
the practice of grafting. Unlike poles of a plant may readily be induced to grow
together, while like poles may only be brought to do so with difficulty, and then
do not develop vigorously.

The stock and graft influence one another in a variety of ways.
For example, portions of annual plants grafted on perennials attain an
extended period of life ; the opposite effect, a shortening of the life
of the graft, may also result from grafting. Qualitative changes may
also be brought about and may go so far as to lead to a vegetative bud
of the graft becoming transformed into a flowering shoot. The specific
properties of the two components are, however, maintained in cases of
transplantation. Certain cases known as chimaeras appear at first
sight to constitute an exception to this statement ; fuller investigation,
however, shows that while externally they appear intermediate forma-
tions between the symbionts in the graft, no mingling of the specific
characters has taken place.

Chimaeras (61a). — Some plants grown in Botanic Gardens under
the names Laburnum Adami and Crataegomespilus suggest in a number
of ways comparison with hybrids (p. 317), but have undoubtedly not
arisen by sexual reproduction. Laburnum Adami (Fig. 264) is inter-
mediate between Laburnum vulgare and Cytisus purpureus ; it frequently
develops branches which can only be regarded as " reversions " to
Laburnum vulgare, and less commonly others that completely resemble
Cytisus purpureus. Certain intermediate forms between Crataegus
monogyna and Mespilus germanica are known as Crataegomespilus or
Bronveaux hybrids. The origin of these is known. The intermediate
forms, of which several are known differing from one another, arose in
the region of a graft of Mespilus on Crataegus in a garden at Bronveaux
near Metz. It can be regarded as certain that the origin of Laburnum
Adami was similar. Both plants have therefore been regarded as
graft hybrids, i.e. as hybrids not resulting from the union of sexual
cells, but by some influence of vegetative cells on one another.

More recently HANS WINKLER has produced such " graft hybrids "
experimentally. He grafted Solanum nigrum, the Woody Nightshade,
on Solanum Lycopersicum, the Tomato, and after union had taken place
cut the stem of the stock transversely at the level of the graft.
Among the adventitious shoots which developed from the region of
junction of the two components there occurred well-marked inter-
mediate forms. In the first instance there were forms which were
composed of longitudinally-united halves with the characters of the
grafted plants ; these were termed chimaeras by WINKLER. Later
there were obtained other intermediate forms, externally uniform
(Fig. 265), which appeared to be the desired graft hybrids. Closer
investigation showed, however, that these also were to be regarded
as chimaeras, since they consisted of parts of the Tomato and the
Nightshade intimately united in growth but otherwise unchanged.

FTG. 264.— Laburnum Adami, Poit (Cytisus Adami, Hort), with atavistic branches showing the
characters of the two parental forms, Laburnum vulgare to the left and Cytisus purpureus to
the right. (After NOLL.)

300

DIV. ii PHYSIOLOGY 301

They were not longitudinally-united halves, however, but inner and
outer layers of the growing point were formed of tissues of the two
different species (cf. pp. 307 and 86). These have therefore been termed
periclinal chimaeras in contradistinction to the sectorial chimaeras in
which longitudinal segments are evident.

Cytisus Adami and the Crataegomespili are also periclinal chimaeras.
True graft hybrids in which a mingling of the specific characters in a
single cell has resulted from grafting are as yet unknown.

Solanum tubinyese has the dermatogen of the Tomato, while the internal
tissues are those of the Nightshade. The converse is the case for Solanum Kolreu-
terianum. In S. proteus the two outer layers are. from the Tomato and .the
remainder from the Nightshade, while S. Gaertnerianum affords the converse
condition (Fig. 265). In a corresponding fashion the dermatogen in Cytisus
Adami is derived Ifrom Cytisus purpureus and the internal tissues from Laburnum
vulgar e. In one of the Bronveaux hybrids (the form Asnieresii} a core of Crataegus
is covered by the epidermis of Mespilus ; the other form (Dardari) has two or
more enveloping layers from Mespilus. When adventitious shoots are developed
from a single layer, these have the pure specific characters proper to the layer
without any trace of admixture with the other symbiont.

Nothing is known with certainty of the mode of origin of periclinal chimaeras,
but it can hardly be doubted that the growing points of these adventitious shoots
are composed of cells derived from the two components, the one forming the core
and the other the surface layers. WINKLER'S contention that there were also
true graft hybrids is doubtful, and this author's own investigations show that
the change in chromosome number in these plants is susceptible of another
explanation. Further, the association of specifically different nuclei in the one
cell, so long as they do not fuse, does not constitute a true hybrid but only a
chimaera. Such a mixo-chimaera, which can again separate into its components
vegetatively, has been experimentally produced in Phycomyces nitens by
BUUGEFF (616).

III. The Course of Development and its Dependence
on External and Internal Factors

The course of development consists of a succession of processes
which tend to be repeated in the same order in any particular kind of
plant. Observations in nature suffice to show that this succession
must be capable of modification. Deviations from typical form which
are spoken of as monstrosities are not uncommonly met with. It is
one of the objects of developmental physiology to ascertain the causes
of such monstrosities, to produce them experimentally, and thus to
arrive at some insight into the causes of normal development.

Although there are at present few of the phenomena of develop-
ment which can be controlled experimentally, the results obtained force
the conclusion upon us that THE TYPICAL COURSE OF DEVELOPMENT

IS ONLY ONE AMONG A NUMBER OF POSSIBILITIES, THE OCCURRENCE
OF WHICH IS DETERMINED BY A PARTICULAR COMPLEX OF CAUSES.

302

DIV. ii PHYSIOLOGY 303

Every departure from this complex of causes will also find its ex-
pression in the form of the plant.

Alterations of the normal form tend to be more extreme the
younger the cells are which are influenced. When the embryonic
substance of a growing point is diverted from its normal course of
development, a quite different structure may replace the one which
was anticipated ; in other cases intermediate forms of more or less
monstrous appearance are developed. The embryonic substance of a
growing point is still capable of giving rise to all the primordia which
are included in the range of form of the species, and thus a vegetative
shoot may arise in place of a leaf ; in exceptional cases even the
growing point pf a root may continue its development as a shoot.
On the other hand, the alteration of leaves that have commenced to
develop is mainly restricted within the limits of the metamorphosis of
the leaf ; thus, for example, petals may be formed in place of stamens
or carpels. The later the transforming influence takes effect on the
primordium, the more incomplete will be its transformation.

All anomalous formations and functions of plants constitute the province of
PHYTOPATHOLOGY (62) ; pathological morphology is concerned with the former.
Monstrosities of external form are treated of under VEGETABLE TERATOLOGY (63)
and the pathological alterations of the shape and contents of cells and tissues in
the pathological anatomy of plants (M).

The development of an organism does not proceed always with the
same activity or in continuous uniform growth. Usually periodic
alterations are evident, resting periods alternating with others of
active growth. During the latter, cell divisions periodically take
place, various forms of leaves and shoots arise, and reproductive organs
are developed ; periodically also larger and smaller parts of the
organism die off.

A. Resting Condition and the Commencement of Growth (65)

Attention has already been directed to the fact that three distinct
states may be recognised in the plant : active life, latent life, and
death. It was further pointed out that all the manifestations of life
are at a standstill in the condition of latent life ; the activities
of metabolism, even respiration, are suspended, and there are no
indications of growth and movement. The capacity of development
still remains, however, and this distinguishes latent life from death.

Resting Condition. — The condition of latent life is met with in
seeds, in the spores of some lower plants, and in many fully-grown
parts and buds of plants during unfavourable periods of the year (cold
periods, dry periods). It cannot be endured indefinitely by plants ;
even seeds and spores in which it is most complete lose sooner or later
the capacity of development and die. In other cases, as in the

304 BOTANY PART I

unfertilised egg-cell, growth is suspended, but all vital activities are
not suppressed.

At first sight it appears as if the resting condition during an
unfavourable season was caused thus. As a matter of fact, however,
periodic cessations of growth are found in many tropical trees ; while
temperature arid water-supply continue favourable, the leaf formation
does not proceed continuously, but is interrupted by resting periods,
so that there are several periods of active growth in the course of the
year. In our native plants also the entry upon a resting period is
in no way determined by the low temperature. The unfolding of the
leaves of many trees ceases completely in May or June. Further, our
trees, when transferred to a tropical climate, frequently exhibit a
periodicity similar to the native plants of the new locality. These
phenomena are not interpreted in the same way by all investigators.
On the one hand it is assumed that every periodicity in the growth
of a plant is determined by a periodicity in the environment which
need not be in the supply of moisture and warmth, but may concern,
for example, the absorption of nutrient salts. On the other hand it
may be assumed that plants possess a periodicity depending on
internal causes, and that they become adapted to the seasonal
changes in countries where such occur ; with us the resting period
is the winter, while in other countries it occurs in the dry period.
This does not hold for all plants, however. In our climate there are
some herbs, such as Senecio vulgaris, which continue to grow throughout
the whole year if the external conditions permit, and in the tropics
plants which grow continuously also occur.

The Oak, Beech, Apple, and Pear retain their resting period in the sub-tropical
climate of Madeira, while under uniformly favourable conditions in the mountain
regions of Java the periodicity may be disturbed in particular individuals. This
even occurs in the several branches of the same tree, which may then bear leafy
and leafless boughs at the same time (Oaks, Magnolias, Fruit, and Almond trees,
together with some endemic species). Other trees gradually accustom them-
selves to the new conditions, as the Peach, for instance, which in Reunion has
become nearly evergreen in the first generation and completely so in the second.
It does not appear to be known how the periodicity of the unfolding of its buds
has been affected.

Commencement of Development. — The termination of the resting
condition and the resumption of growth often depends only on the
establishment of general conditions for growth. In other cases the
resting condition is more fixed but may be sometimes shortened by
particular stimuli.

The germination of seeds takes place as a rule when the general
conditions for growth are present, especially the necessary temperature,
supply of oxygen, and water ; but examples are not wanting in which
special stimuli are requisite. Such special stimuli, usually provided

PHYSIOLOGY 305

in the process of fertilisation, are also concerned in removing the
inhibitions on the growth of egg-cells.

Some seeds pass through a prolonged resting period before they commence to
germinate. They may lie for years in the soil, while others of the same age have
germinated long before ; this in part depends on the hardness of the seed-coat and
the consequent difficulty of swelling. This also appears to be the main reason
why the seeds of many aquatic plants (6e) will not germinate in pure water,
but do so on the addition of acids or alkalies. In some cases fully swollen
seeds are unable to germinate except in the LIGHT (67). The red and yellow rays
are usually more effective than more highly refractive rays, and a surprisingly
short exposure to illumination may suffice (Lythrum salicaria, -^ second, at
Hefner-Kerze intensity of illumination 730). Not uncommonly the illumination
may be replaced by a particular high temperature or by chemical stimuli. The
latter play the chief part in the case of certain parasites which only germinate
in the vicinity of their host plants (Orobanche, Tozzia). In other cases (e.g.
AiiKirantus] light hinders or delays germination, and darkness is an advantage.

In the case of spores also germination may begin on the establishment of the
formal conditions of growth or may require special stimuli.

A striking and fixed resting condition is seen in deciduous trees.
At a certain season of the year, in the autumn or earlier, their buds
can in no way be induced to expand. Later, however, a considerable
shortening of their resting period may be caused not only by a higher
temperature but by a number of stimuli such as frost, heat, dryriess,
darkness, illumination, ether vapour, acetylene, tobacco smoke, wound-
ing, injection of water, etc. .

The awakening from the resting state (68) is most readily effected shortly before
the normal resumption of activity, but almost as readily at an early period shortly
after the period of rest has begun. In the intervening period of complete rest,
attempts at removing the inhibition on growth are usually without effect. These
relations have to be taken into consideration in the forcing of plants in horti-
cultural practice.

The Stimulus of Restitution (69). — The causes of the commencement
of growth in the case of restitutions have also to be considered. The
answer appears simple, since the phenomena as a rule follow on
wounding. The fact, however, that processes that resemble restitu-
tions are met with in the course of normal development shows that
circumspection is required. Thus, for example, young plants are
developed in the indentations of the leaves of Bryophyllum, and in the
case of certain Begonias shoots are developed from the intact as well
as from the incised leaf-blade. It has been shown experimentally that
for many true restitutions it is not the removal of an organ but
the interruption of its functions that is required to start the new
growth (p. 297).

. Polarity. — The fertilised ovum of the flowering plant, when the
inhibition on its growth is removed, forms two distinct growing
points for the shoot and root respectively. A corresponding polar

306 BOTANY PART i

differentiation with the distinction of apex and base is met with also
in more simply-constructed plants. While cases have been already
referred to in which this distinction is determined by an external
factor, in all higher plants the polarity is specific and depends on
internal causes. We can neither cause growth with polarity in
a spherical apolar Alga, nor induce a higher plant that possesses
polarity to become apolar.

The polarity once it has been defined in the egg- cell is on the
whole maintained throughout growth. In some plants, however, it
can be seen to be altered from internal causes.

Thus in species of Platycerium and Adiantum among the Ferns and in
Neottia nidus avis among the Orchids, shoots are formed directly from the growing
points of roots. In the Adder's-tongue Fern (Ophioglossum] the vegetative repro-
duction depends entirely on the formation of buds close to the growing points of
the roots. The apex of some fern leaves also (e.g. Adiantum Edgeworthii] may
grow directly into a shoot.

Symmetry. — Every growing point effects in a characteristic fashion
the further construction of the organ to which it belongs, and also
provides the primordia of lateral organs, the distribution of which as
they appear is definitely determined, and may be radial, bilateral, or
dorsiventral. Thus a certain symmetry already exists in tjie growing
point, and, at least in many cases, is determined by purely internal
causes ; in others external factors have a preponderating effect.

B. Growth and Cell Division

Growth, once started, does not always proceed uniformly. Some
Algae such as Vaucheria or Fungi like Saprolegnia continue to extend
the cell by apical growth. In the great majority of cases, however,
there is a limit to this, and when a certain size has been exceeded
the normal mass of the cell is regained by division. There is no
regular rule, since the process depends not only on external conditions
but in great part on internal. Thus, for example, divisions proceed
rapidly at the growing point while they become less frequent later,
though growth still proceeds. In accordance with this the size of
the cells as a rule increases considerably on passing from the growing
point to the region composed of permanent tissue behind. The
volume of the nuclear mass is also of importance in the question
of the size of the cell. It has been possible in some instances to
obtain a nuclear mass twice or four times that of the normal nucleus
in a cell ; all the cells derived from such a cell proved to be consider-
ably above the normal in size (70).

A mean volume or mass of the cell can always be regarded as one
of the hereditary characters of a species. When species of different
sizes are compared, the range in size of cell is not found to be as great
as that in the size of the plant as a whole. In other words, large

DIV. II

PHYSIOLOGY

307

plants are mainly (but not entirely) determined by a large number of
cells (T1).

Little is known as to the particular causes of cell division (72).
It doubtless depends on a very complicated succession of phenomena ;
these concern not only the protoplasm but the nucleus which initiates
the process. In the growing point of the shoot in higher plants, and
also in some Algae, a certain periodicity is evident in the cell division
which occurs more frequently at night than during the day ; it is
evident that light has an inhibiting effect, but unknown external and
internal factors must co-operate. Not merely the fact that a new
cell wall is formed but the direction in which it arises is a problem
of developmental physiology. It has long been observed that the
position of the new cell walls
shows a striking similarity to
the behaviour of weightless
liquid films such as those of
soap bubbles. The latter tend
to contract to the least possible
surface, and therefore are in-
serted as nearly as possible at
right angles on the walls already
present. In spite of the great
similarity between the arrange-
ment of cell walls on the one

, , , . ,. . . . , FIG. 266.— Diagrammatic representation of a growing

hand and of surfaces of minimal po^t. (After SACHS.)

area on the other, it would be

unsafe to conclude that the same causes determine the position in

the two cases, for the cell wall is never fluid.

The principle of the rectangular intersection of cell walls is strikingly shown
in the growing points of phanerogamic plants. In these, as is shown in SACHS'
diagram (Fig. 266), the cell walls form two systems of parabolas which have a
common focus and intersect at right angles. The one system (Fig. 266 I-VI] runs
more or less parallel to the surface of the growing point ; these cell walls are
termed PERICLINAL. The walls at right angles to these (1-11 ) are termed

ANTICLINAL.

C. Further Periodic Changes in Vegetative Form

Other periodic phenomena often occur while growth is active,
There are, for example, periodic changes in the form of the leaves and
stem, which are not only quantitative but qualitative ; foliage leaves
alternate with scale leaves or bracts, or leafy shoots with rhizomes,
the transitions being either gradual or abrupt. The correlation of
growth, already considered (p. 296), is concerned in these phenomena.
The existence, or rather the activity, of a certain quantity of foliage
exerts an influence on the primordia forming at the growing point

308 BOTANY PART i

and causes them to develop as bud-scales. If the foliage leaves are
removed in early summer these primordia develop as foliage leaves
instead of scale leaves. In a similar fashion the removal of leafy
shoots may affect a subterranean rhizome, and cause it to grow out of
the soil and form foliage leaves instead of scale leaves.

Another kind of heterophylly is met with in some plants in
which the form of leaves produced during youth differs from those
borne on the older plant. It is sometimes possible to bring about
a return to the juvenile form when the external conditions under which
this arises are again established. Thus in the case of Campanula
rotundifolia round leaves can be developed on plants which have
formed the subsequent linear leaves by diminishing the intensity of
the illumination. In some aquatic plants the submerged leaves belong
to the juvenile form, and the floating or aerial leaves to the later
adult form. Here also the juvenile form can be induced. This is not
always the case, however, for sometimes the growing point has been
so profoundly changed that it can only produce the later adult type
of foliage.

The stem also may undergo far-reaching transformations. It may
be erect in the case of leafy shoots or creep horizontally on or
in the soil ; in twining plants the internodes are greatly lengthened,
while they are very short in rosette plants ; there are wide differences
in the growth in thickness, in extreme cases the stem becomes a
tuber. All these various forms or modes of growth result from
definite influences, and can, in part at least, be obtained experimentally
even at times and places where they would not occur in the " normal "
course of development.

The formation of tubers in the Potato affords an example of the
plasticity of the stem. As is represented in Fig. 203, the tubers
usually form at the ends of horizontal stolons which arise from the
lower region of the foliage shoot where it is embedded in the soil.
The tuber forms by marked growth in thickness of the end of the
stolon, and cessation of its growth in length. If, however, the leafy
shoot is removed at the proper time, the ends of the stolons grow into
erect branches which emerge from the soil and bear foliage leaves.
The typical development of the Potato can thus be modified so that
no tubers are formed. On the other hand, tubers can be caused to
form at other places : for example, at low temperatures the main
axis of a particular kind of Potato will remain short, and be trans-
formed into a tuber ; in other varieties tubers are produced near the
summit of the aerial leafy shoots when the tip of the shoot is
darkened. Boussingaultia baselloides is even more plastic than the
Potato ; any bud can be induced to form a tuber, and when buds are
lacking, internodes or roots may swell into tubers. Apparently the
production of a certain amount of reserve material acts as a stimulus
leading to the formation of a storage organ.

DIV. ii PHYSIOLOGY 309

D. Duration of Life

We have further to consider the periodic alternation expressed in
the duration of life of the plant as a whole. There are plants, such
as Stellaria media and Senecio tulgaris, which in a few weeks go through
their whole development from the germination of the seed to the ripen-
ing of their seeds. Since each seed can germinate at once, several
generations may be developed within the year. The individual plant
dies on producing a certain number of seeds, but the seeds ensure the
maintenance of the type of plant. Many annual plants are similar
though their life is more closely connected with the seasons of the
year. With these may be placed other plants which only fruit once
(monocarpic) but in which seed-formation is preceded by two or
many years of purely vegetative growth, with or without resting periods.
Probably in all these cases the development of fruit is the cause of
the death of the vegetative organs, for their life can be considerably
prolonged by preventing seed-formation. In contrast to these plants,
others, such as our native trees, fruit repeatedly, the existence of
the individual not being terminated by seed-formation. All perennial
types exhibit another periodicity besides that due to the seasons.
A tree in its first year when it is a seedling has less intensity of
growth than many annual plants ; the intensity of growth increases
gradually and its growth in length, its growth in thickness, and even
the elementary organs of the wood continue to increase in size until
a maximum is attained. Some trees attain a great age and are
capable of unlimited growth. From a certain point of maximum
development, however, the annual shoots become smaller, apparently
on account of the increased difficulty of exchange of materials between
the roots and leaves. Ultimately the tree dies for this reason, or
owing to the attacks of parasites or other disturbing external effects.
If care is taken to ensure the production of new roots near the
growing points of shoots, the latter will continue to grow \vith
the same intensity, and no termination of the growth is to be
anticipated. This experiment cannot be performed on every tree,
since some do not readily give rise to roots ; it is easily done
with the Willow, however, by using branches as cuttings. Long
before the whole individual perishes, however, single parts of it
have died. Thus the leaves have been shed after persisting for
one or several years. In some cases whole branches are shed, though
often they perish without being thrown off and gradually break up
while still attached to the plant. All the older tissues of the stem
also die ; the peripheral tissues are transformed into bark and either
fall off or form a protective covering to the parts within. In the
centre the wood is transformed into heart-wood in which the remain-
ing living elements die. In an old tree only the growing points,
whether apical or intercalary, and the youngest tissues derived

310 BOTANY PART I

from them remain alive. Thus we see that every cell which has
lost its embryonic character dies after a longer or shorter time.
Though this cannot as a rule be prevented, we cannot say that the
death is necessary. It is because certain cells develop that others
die, and their death is a phenomenon of correlation. In plants that
are capable of restitution the removal of the growing point before
the permanent tissue has become too old leads to fully-grown cells,
which would normally die, becoming embryonic again and continuing
to live.

The longevity of trees (73) having an historical interest isnaturally best known and
most celebrated, although, no doubt, the age of many other trees, still living, dates
back far beyond historical times. The celebrated Lime of Neustadt in Wurtemberg
is nearly 700 years old. Another Lime 257 m. in circumference had 815 annual
rings, and the age of a Yew in Braburn (Kent) which is 18 m. in circumference is
estimated at 2880 years. Sequoia gigantea, the giant tree of California, attains
according to H. MAYE, the age of 4000 years. An Adansonia at Cape Verde, whose
stem is 8-9 m. in diameter, and a Water Cypress (Taxodium mexicanum) near
Oaxaca, Mexico, are also well-known examples of old trees. The celebrated
Dragon tree of Orotava, which was overturned in a storm in 1868, and afterwards
destroyed by fire, must have been some 600 years old. Bryophytes also may
attain a great age ; the apically-growing mosses of the calcified Gymnostomum
clumps, and the stems of the Sphagnaceae, metre-deep in a peat-bog, must
certainly continue to live for many centuries.

E. Reproduction

Cell division, especially when the two resulting cells separate, can
be regarded as a process of reproduction. In more complex organisms
also vegetative growth often passes gradually into reproduction.
Only those forms of reproduction require special consideration in
which special organs are formed (reproductive organs, germs) which
separate from the parent plant and, at the expense of a supply of
reserve material, commence a new life. In this way young organisms
originate which then repeat the development of the parent organism,
its gradual increase in strength, and its later decay. Often these
reproductive organs have the further duty of carrying the organism
over a period of cold or drought ; they thus constitute a resting
stage. With favourable conditions their growth recommences, they
germinate.

Reproduction is concerned, however, .not merely with the continua-
tion of the parent organism, but at the same time with an increase
in the number of individuals (p. 192). For the continuance of the
species it is not only necessary that numerous germs should be
produced, but that they should be widely distributed ; as a rule there
will be no room for new individuals to grow in the place where the
plant which bears the seeds is growing.

DIV. ii PHYSIOLOGY 311

It will be seen in the Special Part how various are the arrange-
ments to ensure the formation of reproductive bodies in the vegetable
kingdom. The division of the latter into classes, orders, etc., is
mainly based on this variety. Two types of reproduction can, how-
ever, be readily recognised throughout. These are vegetative and
sexual reproduction, and may also be termed monogenic and digenic
respectively, since only one organism is concerned in vegetative and
two in sexual reproduction.

The organs which serve for reproduction have been treated in
the section on Morphology. In this place the conditions and the
significance of the phenomena have to be considered and the properties
of the offspring discussed.

1. The Conditions of Reproduction (74)

In nature reproduction appears to follow vegetative growth with
some degree of necessity. It commences as a rule when the vegetative
growth is slackening and the plant has attained a certain age. It
can, however, be shown that this succession is not obligatory, and that
the natural course of development is determined by quite definite
conditions, and can be greatly modified by other influences.

Thus the question arises, under what conditions does vegetative
growth and under what conditions the formation of reproductive
organs respectively take place ? Since these problems have as yet
been relatively little studied, it is not easy to give a general answer
to this question. We must, therefore, confine ourselves to making clear
the essential facts by means of some examples.

Lower Plants. — The fungi belonging to the genus Sapi'okgnia
have a non-septate, branched mycelium without chlorophyll. They
occur commonly in nature on dead insects which have fallen into water,
and their thallus first grows through the body of the insect. After a
time, however, it grows out and forms a radiating growth around the
insect. The end of each of the radiating hyphae becomes as a rule
cut off by a septum, and its contents divide up into numerous swarm-
spores ; these emerge, move about, and finally germinate to give rise
in another place to a new individual of Saprolegnia. Later eggs and
sperm-cells are formed on the older plant and, at least in some species,
the former only develop after being fertilised. With the production
of fertilised eggs the activity of the Saprolegnia plant tends to cease ;
it gradually perishes.

G. KLEBS has shown that it is possible to completely change this
course of development of Saprolegnia ; KLEBS has succeeded in direct-
ing the development in the following ways among others :

1. The mycelium can continue for the whole year to grow vege-
tatively when supplied continually with fresh and suitable nutritive
material.

312 BOTANY PART i

2. Such a well-nourished mycelium on being transferred to pure
water proceeds completely and at once to form sporangia.

3. In solutions of leucin (O'l per cent) and haemoglobin (O'l per
cent) at first a strong growth develops and then sexual organs are
formed. Swarm-spores are not formed ; they appear, however, after
the sexual organs, when a more dilute solution (O'Ol per cent) of
haemoglobin is employed.

It is thus clear that quite definite conditions exist for vegetative
growth, others for the formation of sexual organs, and yet others for
the appearance of asexual reproduction.

Conditions of the Formation of Flowers. — In the Phanerogams
asexual reproduction by means of bulbils, etc., is much less prominent
than the sexual reproduction which is connected with the flower.
The question of the causes of the development of flowers is of
special interest. Observations in nature and experimental work
show that in this case also sexual reproduction is not absolutely
essential to the maintenance of the species, and that the formation
of flowers only takes place under quite definite conditions. The
results which KLEBS obtained with Sempervivum Funkii can be sum-
marised thus :

1. With active carbon -assimilation in bright light and rapid
absorption of water and nutrient salts, the plant continues to grow
purely vegetatively.

2. With active carbon -assimilation in bright light, but with
limitation of the absorption of water and salts, the development of
flowers takes place.

. 3. With a moderate absorption of water and nutrient salts it de-
pends on the intensity of the illumination whether vegetative growth
or the production of flowers takes place. With weaker intensity of
light, and when blue light is used, only growth takes place ; with
stronger illumination or with red light flowering occurs.

KLEBS distinguished three phases in the formation of the flowers
of Sempervivum. 1. The establishment of the condition of readiness for
flower-development. 2. The formation of the primordia of flowers
recognisable under the microscope. 3. The enlargement of the in-
florescence. These three phases are connected with wholly different
conditions and depend therefore in different ways on external factors.
The initial condition is determined by a preponderance of carbon-
assimilation over processes in which carbohydrates are consumed, such
as respiration and vegetative growth. Since a high temperature
increases the respiration and nutrient salts promote vegetative growth,
a low temperature and a limited supply of nutrient salts are necessary
in addition to good illumination to render the plant ready to develop
flowers. This condition when once attained may be destroyed by a
high temperature, while it may be preserved for a long while, even
in darkness, by a low temperature. While in this respect 'light

DIV. ii PHYSIOLOGY 313

apparently acts only in determining the assimilation of C02, in the
second phase it has another significance • a certain period of illumina-
tion is quite indispensable for this, and only the rays of greater wave-
length are effective, those of short wave-length even destroying the
state reached in the first phase. In nature the first phase is attained
in autumn, but a sufficiently long and intensive illumination is wanting.
Under continuous illumination by an Osram lamp, the light from which
is rich in red rays, the formation of flowers may be hastened by
months ; the earlier in winter this is done the longer is the illumina-
tion required, and the period is shortened by increasing the intensity
of the illumination. Interruptions in the illumination must not be
too prolonged or the influence of the illuminated period is lost. The
third phase of elongation is, like the first, dependent on the nutritive
effect of light ; in accordance with this, if the preceding nutrition has
been sufficient it may, in part at least, be carried out in the dark.

Similar thorough analyses of the conditions of flowering are not available as
yet for other cases, but numerous observations and experiments indicate that
light, temperature, and the nutrient salts are of primary importance in the forma-
tion of the flowers. Since these factors are also indispensable for the vegetative
life of the plant, it is the amount in which they are available and especially their
relative proportions which determine whether a particular bud shall form a flower
or grow vegetatively.

The importance of light in the formation of flowers is shown by the well-known
fact that the Ivy only flowers when growing in a well-illuminated situation and
not in the shade of woods, although it grows well in the latter habitat. VOECHTING'S
experiments on Mimulus Tilingii gave the same result. At a certain low
intensity of light, which is quite adequate for vegetative -growth, this plant
produces no flowers. KLEBS has made corresponding experiments with Veronica
Chamaedrys, and he states that in all plants which do not contain any great amount
of reserve materials a diminution of light leads to the suppression of flower-
formation. He regards the carbon-assimilation resulting from the illumination as
the primary cause of this influence on the development of flowers. At a certain
intensity of light, which is insufficient for the development of normal flowers,
cleistogamous flowers are produced.

Temperature also obviously plays a part. A continuous high temperature
hinders flowering. Thus plants of our climate eventually become vegetative in the
tropics (Cherry), and native perennial plants, such as the Beet or Foxglove,
can be prevented from flowering in their second year if they are kept warm and
allowed to grow on during the winter. In this way KLEBS succeeded in keeping
the Beet in a purely vegetative state for several years. Glechoma and Sempervi-vum
also, if their winter rest is prevented, grow vegetatively for years.

Lastly, the nutrient salts have to be considered. By removing the supply of
salts, seedlings can often be converted into dwarf starved plants in which, after a few
minute foliage leaves have been formed, the development of flowers begins at once.
Experiments of MOEBIUS have shown that Grasses and Borago flower better if the
supply of salts is limited than if well manured. The increase of fertility
which results from root-pruning in fruit trees may depend upon a limitation of
the absorption of nutrient salts. That, however, all nutrient salts do not act in the
same way has been pointed out by BENECKE, who showed both from the literature

314 BOTANY PART i

and from his own experiments that nitrogenous food ,led to a diminution arid
phosphorus to an increase in the development of flowers.

If after the formation of flowers has commenced the conditions for vegetative
growth are re-established, a shoot already predisposed to flower- formation may
again become vegetative. Thus when Mimulus Tilingii is brought into conditions
of poor illumination the flower-buds already laid down remain undeveloped and
resting buds in the axils of bracts develop into leafy shoots. The whole appearance
of the plant is thus greatly altered.

Determination of Sex (75).— Most flowers are hermaphrodite and produce both
male and female sexual cells. In other cases unisexual flowers are produced either
only or in addition to the hermaphrodite flowers. The fact that the female
flowers are developed as a rule in different situations from the male flowers indicates
that each of the two forms has its special conditions of development ;• what these
conditions are is, however, unknown.

The determination of sex thus becomes a problem of developmental physiology
especially when dioecious plants (i.e. those which have male and female individuals)
are concerned. Generally the two forms occur in about equal proportions in
nature, and this relation cannot be altered experimentally. It is also not possible
by means of external influences of any sort to cause a seed to develop into the one
or other sexual form. The sex is already determined in the seed as a result of
internal causes which will not be further considered here ; these have already
acted in the sexual cells or at fertilisation.

Fertilisation. — The product of fusion of the egg and sperm-cell
surrounds itself, as a rule, with a cell wall. In the lower plants an
oospore or zygospore is thus formed which germinates, usually after first
undergoing a period of rest. In the higher plants growth and cell
division take place forthwith ; an embryo is produced which in Bryo-
phyta and Pteridophyta continues its further development, while in
the Phanerogams it soon enters on a period of rest. Before this, how-
ever, a number of stimuli have proceeded from the development of
the embryo ; these are especially complex in the Angiosperms. The
ovule in which the embryo is enclosed commences to grow ; it enlarges
and assumes a characteristic structure. It has developed into the seed,
and this as a rule is liberated from the ovary and, after a resting
period, germinates. The ovary also grows actively after fertilisation
and develops into the fruit. The variety in fruits cannot be entered
upon in this place. (Cf. Special Part.)

These formative processes of growth in the ovules, ovary, and ultimately also in
other parts of the flower, are to be regarded as phenomena of correlation. When
fertilisation does not take place, all those changes which lead to the development of
a ripe fruit from the flower do not usually occur. Instead another correlative
influence arises which leads to the casting off of the now useless organ as a whole.
Some few plants, especially such as have been long cultivated, are to some extent
an exception to this. In nearly all varieties of the Banana, in the seedless Orange,
and in the Sultana Raisin, no embryo is formed, but in spite of this the fruits
develop. The stimulus to this development can proceed either from the mere
pollination of the stigma or from the fertilisation of the ovules, which then sooner
or later cease to develop without arresting the development of the fruit. In some

DIV. ii PHYSIOLOGY 315

cases, however, "barren " fruits develop wholly without the stimulus of pollination
(parthenocarpic (76) fruits of the Fig, Cucumber, and certain species of Apple and
Pear).

Influences which affect parts at a distance also proceed from the pollen-grains and
pollen-tubes on the stigma. Thus after the stigma of an orchid is pollinated the
stigma and the gynostemium swell, and the perianth is promptly arrested in its
growth and withers. As FITTING (77) showed, this influence proceeds from soluble
organic substances which withstand heating, and can be readily separated from the
mass of ungerminated pollen.

Whether a simple spore or a complex embryo is the result of
fertilisation it is always distinguished from the cells which gave
rise to it by exhibiting nuclei which contain the diploid number of
chromosomes (p. 203). On this account a reduction division which
restores the normal number of chromosomes is sooner or later the
necessary sequel to fertilisation.

2. The Significance of Sexual Reproduction

The significance of sexual reproduction is not at once evident.
Many plants occur in nature or under cultivation without being
sexually reproduced, and succeed with vegetative reproduction only.

Lower plants which have not attained to sexual reproduction have already been
referred to. Of higher plants which no longer produce descendants sexually the
cultivated Bananas, some Dioscoreaceae, some forms of Vine, Oranges, and Straw-
berry may be mentioned. The Garlic, which forms small bulbils in place of flowers,
the White Lily, and Ranunculus Ficaria, which has root-tubers, only rarely produce
fertile seeds if allowed to form their vegetative organs of reproduction. Under
certain conditions, as for instance on cut inflorescences, seeds may be produced,
though as a rule these plants are multiplied entirely vegetatively. ISTo degeneration
such as was formerly held to be unavoidably associated with purely vegetative
multiplication is to be observed in these cases (78).

If thus the monogenic reproduction suffices to maintain the species
digenic reproduction must serve some further purpose not effected by
the former. Otherwise it would be inconceivable why digenic repro-
duction had arisen, and why the arrangements to effect it are far more
complicated and less certain than in the case of vegetative reproduction.

Were the Algae and Fungi alone taken into consideration it might
be supposed that sexual reproduction led to the formation of specially
resistant germs which could endure a longer period of rest under
unfavourable conditions — as a matter of fact the zygospores and
oospores are much more resistant than the swarm-spores and conidia.
But even in the Pteridophyta this relation is inverted, for the fertilised
egg-cell requires to develop forthwith, or else it perishes, while the
asexual spores can endure a long resting period.

It is the rule in digenic reproduction that the sexual cells are
individually incapable of development; this takes place only after the
sexual cells have united. Thus one use of fertilisation lies in the

316 BOTANY PART i

remo.val of an arrest of growth, though it cannot be said that this was
its original and essential significance. It is much more probable that the
sexual cells have gradually lost the capacity of independent development
since in this way the possibility of fusion was increased. If every
sexual cell commenced to grow at once, this would in most cases take
place before fusion with another sexual cell could be effected

This assumption is supported by the behaviour of some Algae, in which
the sexual cells can often germinate independently ; the egg-cells especially may
develop without fertilisation. From the analogy with similar cases in the animal
kingdom this phenomenon has been termed PARTHENOGENESIS. In the primitive
Algae parthenogenesis is possible, because in them the incapacity of development
of the egg-cell has either not been acquired or is easily removed under special con-
ditions. Thus for example in the Alga Protosiphon parthenogenetic development
is induced by a high temperature, and the same happens in the case of the ova
of some lower animals (Echinoderms) on treatment with solutions of a certain
concentration. . It may perhaps be assumed that in the cases in which development
only takes place after fertilisation the stimulus to development is given by some
substance contained in the sperm-cell.

Among the higher plants also phenomena to which the name parthenogenesis (79)
has been applied occur ; they are better termed apogamy. Thus the egg-cells of
some Compositae, and also of Alchemilla, Thalictrum purpurascens, Wickstroemia
indica, Ficus hirta, Marsilia Drummondii, and Chara crinita develop without
previous fertilisation. These cases are distinguished from those just described by
the egg-cells in question having retained the number of chromosomes characteristic
of vegetative cells. They are diploid cells (p. 203) and not fitted for fertilisation.

We thus arrive at the conclusion that the essential of sexual repro-
duction cannot consist in the removal of the arrest to development
of the sexual cells. This leads us to consider THE FUSION OF THE

SUBSTANCE OF THE TWO CELLS AND THE MINGLING OF PATERNAL AND
MATERNAL CHARACTERS WHICH FOLLOWS FROM THIS. This brings

out the chief distinction between the two modes of reproduction ; the
vegetatively produced progeny are due to no such mingling of
characters. The complex of characters in vegetative multiplication
does not differ as a rule from that in the parent form. As a matter
of fact, we preserve by vegetative multiplication all the varieties and
races of our cultivated plants, even when these do not come true from
sexually produced seed. In contrast to the vegetative progeny the
sexually produced descendants, as a rule, cannot completely resemble
the mother plant, but must combine the characters of both parents.
The more these differ from each other, the more striking will be the
visible effect of fertilisation.

F. Heredity, Variability, Origin of Species

Heredity (80). — By inheritance is understood the familiar pheno-
menon that the properties of the parents are repeated in their
progeny. This phenomenon is presented to us in the division of a

DIV. ii PHYSIOLOGY 317

cell, which is the simplest form of reproduction, as well as in the
more complicated process of sexual reproduction. That the daughter
cells resemble the parent cells requires no explanation. The problem
of heredity appears when descendants are derived from the GERMS,
which are small portions of a complicated parent organism, by a
process of DEVELOPMENT. It is assumed that such germs possess
DETERMINANTS or GENES, which determine that an organism shall
react in a definite specific way to external factors. It appears
probable that these determinants are associated in the chromosomes of
the nucleus, but we know nothing as to the way in which they
influence the course of development.

Such determinants must be present in the sexual cells of the
higher plants, ^and both in the male and the female cells. The
fertilised egg - cell must thus possess a double number of these
though a single organism is derived from it. That, originally at
least, the same determinants are present in all cells of the plant and
not only in the germ cells is shown by the phenomena of restitution.

The problems of inheritance are of greatest interest in sexual
reproduction, in which the part played by the two parents in the
organisation of the progeny comes into prominence. These problems
can only be attacked by a consideration of hybrids, since the
individuals of a pure species have the same determinants.

Hybrids (81). — The union of two sexual cells is, as a rule, only
possible when they are derived from individuals of the same species ;
it is only then that they fuse together in the act of sexual repro-
duction. Occasionally, however, the sexual cells of different varieties,
species, or even genera have been shown to be able to unite and
produce descendants capable of development. Such a union is termed
HYBRIDISATION, and its products HYBRIDS. They are also spoken of
as HETEROZYGOTES or individuals derived from two dissimilar sexual
cells, in contrast to HOMOZYGOTES, which have arisen from the
union of sexual cells with identical determinants. Hybrids are as
a rule obtained more readily the closer the parent forms are to one
another, but this is not a rule without exceptions.

Some families exhibit a tendency to hybridisation (Solanaceae, Caryophyllaceae,
Iridaceae, etc.) while in others hybrids are obtained with difficulty or not at all
(Papiliouaceae, Coniferae, Convolvulaceae, etc.). The behaviour of related genera
and species also is frequently very different. Thus species of Dianthus, Nicotiana,
Vefbascum, and Geum readily hybridise with one another, while those of Silene,
Solanum, Linaria, and Potentilla are difficult to hybridise. Hybridisation of
closely related species may frequently fail when more distant species can be
crossed.

Hybrids also occur in nature, especially in the genera Salix, Rubus, Hieracium,
and Cirsium. That such natural hybrids do not occur oftener is due to the lack
of an opportune time or space for their development, and also to the Jact that in
the case of pollination of flowers with different kinds of pollen, that of their own
species seems as a rule more effectual in effecting fertilisation.

FIG. 267.— 1. Sorbus aiicuparia. 2. Sorbui aria. 3. The hybrid between these.
(After SCHLECHTENDAL, LANGETHAi, and SCHENK. Flora v. Deutschlund, 5th ed. by HALLIER.)

318

DIV. ii PHYSIOLOGY 319

Hybrids are often recognisable by having the characters of inter-
mediate forms between the two parents. They may either be truly
intermediate, e.g. Nicotiana rustica $ x Nic. paniculata $ and Sorbus
aria x S. aucuparia (Fig. 267), or may in some characters resemble more
closely the male parent and in others the female parent. In exceptional
cases a hybrid may, even to minute characters, resemble the male
parent (some hybrids of the Strawberry) or the female parent. In
the great majority of cases it is all the same which plant is taken as
the male and which as the female parent. In some cases, however,
the hybrid A ? x B $ is clearly different from A $ x B 9 .

The mingling of characters is often complete. Had one species simple and
the other compound leaves, their hybrid would have leaves more or less cleft
(Fig. 267) ; or were, the flowers of one parent species red and those of the other
yellow, the hybrid frequently bore flowers which were orange-coloured. If an
early blooming form were crossed with a late bloomer, the hybrid would flower at
a time intermediate between the two. Another type of hybrid which is less
commonly met with is that of the MOSAIC HYBRIDS. In this parts with maternal
characters are mingled with others which have the characters of the male parent.

Xew characters appear in hybrids such as diminished fertility, a
greater tendency to the formation of varieties, and frequently a more
luxuriant growth.

The fertility is often so enfeebled that the hybrids either do not flower
(Rhododendron, Epilobium), or are sterile and do not reproduce themselves
sexually. This enfeeblement of the sexuality increases the more remote is the
relationship of the ancestral forms. Other hybrids such as those of Salix and
Hieracium remain fertile.

Hybrids, particularly those from nearly related parents, frequently produce
more vigorous vegetative organs, they bloom earlier, longer, and more profusely
than the uncrossed plants, while at the same time the flowers are larger, more
brilliant, and exhibit a tendency to become double. The luxuriance of growth and
the increased tendency to produce varieties displayed by the hybrids have made
the whole subject of hybridisation one of great practical as well as theoretical
importance.

Inheritance in Hybrids (82). — By the experimental study of
hybridisation, the sexuality of plants, for a long time doubted, was
indisputably proven. With this object in view, hybrids were raised
in great numbers by KOLREUTER as early as 1761. It is now the
problems of ' inheritance connected with hybridisation that are the
main centres of interest. For the study of heredity, however,
hybrids between species are far too complicated. It was by using
closely related forms that GREGOR MENDEL at Briinn discovered in
1866 certain laws, which, however, did not attract attention or
influence the progress of investigation till after 1900. At this
date they were re-discovered simultaneously by DE VRIES, CORRENS,
and TSCHERMAK. In order to obtain these laws or rules MENDEL
required to follow the behaviour of the hybrids through a number of

320

BOTANY

PART I

generations, taking account of all the individuals that result and
breeding from them.

1. SEGREGATION OF CHARACTERS. — This is the most generally
applicable of the laws or rules discovered by MENDEL and will be best
illustrated by an example. If a red-flowered Mirabilis jalapa be
crossed with a white-flowered individual one obtains a generation of
hybrids with uniformly rose-coloured flowers If these are fertilised
from one another a second generation is obtained, bat the individuals
of this are not uniformly coloured ; in addition to rose-coloured plants
pure red-flowered and white-flowered plants occur in the proportion
per cent of 50 : 25 : 25, i.e. in the ratio 2:1:1 (Fig. 268). When

FIG. 2(i8.— Mirahilis jalapa, alba and rosea. With the hybrid between thpm in the first
and second generations. (Diagram. After COBRENS.)

fertilised from one another the pure red-flowered plants produce a red-
flowered progeny and the white-flowered plants also breed true ; they
have returned to the pure parent forms. The 50 per cent of rose-
coloured plants again segregates in the next generation, and .like the
former generation yields 25 per cent pure red, 25 per cent pure white,
and 50 per cent rose-coloured plants. The proportion of hybrid
plants thus continually becomes lessened by the return to the red and
white types; in the eighth generation only 0*75 per cent of hybrids
remain, and this small remainder continues to segregate further on
breeding. These results are theoretically explained since MENDEL'S
investigations by assuming that the sexual cells of the rose-flowered
hybrids are not themselves of hybrid nature, but are already segre-

Gen;

DIV. ii PHYSIOLOGY 321

gated into pure red and pure white sexual elements. In the process of
fertilisation the union producing a hybrid, red x white (white ? x red $ ,
red 9 x white $ ), will occur twice as frequently as the union red x red
or white x white, which give rise to pure forms.

2. RULE OF DOMINANCE. — The characters in which the parents
differ do not, however, always blend so that the hybrid exhibits
an intermediate character. More usually the hybrids completely
resemble in this respect either the paternal or maternal parent, the
character of the one parent being dominant in the hybrid while the

A urtica A

^••^ Dodartii + pilulifera £J Ik

iP A ™

pilulifera ^fl B^ Dodartii

J| IfcGen.
^^^^^ i

^/^^ "^^^ *^^^^^ ^^^^

ill) lit) iiii ilil

FIG. 269.— The hybrid between Urtica pilulifera and Urtica Dodartii in three generations.
(Diagram. After COBHEXS.)

other remains latent. This is the case, for example, in hybrids
between Urtica pilulifera with serrate leaves and U. Dodartii (Fig.
269). The hybrids have all serrate leaves like U. pilulifera. so
that in the second generation the proportion of serrate-leaved to
entire-leaved individuals is per cent 75:25 (3:1). Only 50 per
cent of the serrate-leaved individuals are, however, of hybrid nature
and continue to show a similar splitting of characters in the next
generation ; 25 per cent have become pure U. pilulifera. It is
impossible to predict which characters will prevail in any cross, and
the question can only be settled by experiment ; usually the phylo-
genetically younger character appears to be dominant.

With regard to the above example of dominance CORRENS (83) has

Gen.

322 BOTANY

recently shown that, at least in a particular stage of development, the
homozygous plants of Urtica pilulifera can be distinguished from the
heterozygotes. Nevertheless it may be said that two plants possessing
different determinants may be apparently similar, while on the other
hand two organisms possessing the same determinants may appear
distinct owing to diverse action of the environment. The nature of
the determinants which are contained in a plant can thus not be
discerned from its appearance but only by breeding experiments.

3. AUTONOMY OF CHARACTERS. — When the parents differ in two
characters instead of only one, monohybrids instead of dihybrids
result. It then appears that the several characters are independ-
ently transmitted and distributed in the descendants (autonomy of
characters). Thus new combinations of characters may come about, a
fact of great importance in plant-breeding. From the crossing of
peas with yellow, wrinkled seeds, and those with green, smooth seeds,
among other possible combinations of the characters the new ones
yellow-smooth and green- wrinkled appear. Many characters, however,
tend to remain associated together (coupled characters).

It is not possible to enter in this place into the complicated
phenomena of the production and segregation of dihybrids and
polyhybrids.

Validity of the Mendelian Rules. — These rules are not limited
to hybrids in the narrow sense of the word, but have an extensive
application to inheritance in both the animal and vegetable kingdoms.
It cannot be said that there are not other laws followed in inheritance,
for there are already well-investigated cases which do not conform to
the Mendelian rules (84). On the other hand, it is noteworthy that
many phenomena which at first appeared to contradict these rules
have proved on further investigation to be consistent with them.

Variability (85). — By variability is understood the fact that the
individuals belonging to any species are not all alike. Frequently
the variability is only apparent, the species not having been properly
defined. Thus in Rosa, Bubus, Draba verna, etc., there are many
species that closely resemble one another. The impression given of a
" varying " species is in these cases a completely false one ; each
of the "ELEMENTARY SPECIES," of which the "COLLECTIVE SPECIES"
is composed, proves to be constant and does not exhibit transitions to
the other elementary species.

Such cases are to be left out of consideration here. We are
concerned with the most strictly limited species, if possible with the
descendants of a single self-fertilised plant constituting what is known
as a pure line (JoHANNSEN). It is found that these also vary. The
process of variation and the varieties can be traced to two causes
and are therefore distinguished as MODIFICATIONS and MUTATIONS.
To these must be added the combinations originating from crossing.

MODIFICATIONS. — This name is given to variations which have

D1V. II

PHYSIOLOGY

323

been produced by external factors. It has already been pointed out
(p. 288 ff.) in what way innumerable external factors influence the form
of the plant. The differences that characterise the land and water
forms of an amphibious plant or the forms of one species growing in

FIG. 270. — Taraxacum ojficinale. 1, cultivated in the plains ; 2, in the Alps. (Both similarly reduced.

After BONNIER.)

the plains and on mountains are considerable. The plants represented
in Fig. 270 are portions of one and the same individual; 1 was
grown in the plain and 2 on a mountain. In order to ascertain the
full capacity for modification of any plant it is necessary to cultivate
it under all conditions under which it can exist. Such investigations
have been carried out with success by KLEBS. If it were possible to

324

BOTANY

PART I

grow two plants of the same origin under completely identical
conditions they would necessarily be indistinguishable. In practice
this is never possible, and therefore the homozygotic individuals of a
pure line show many quantitative differences even under the most
uniform cultivation possible. For example, the seeds of a pure line
of Bean can be sorted into a number of groups according to their
weights, and the number in each group or category ascertained. The
result of such an investigation is the curve in Fig. 271, which shows
that the weight- categories that occur most frequently are those

closest to the average weight, and
that the farther a category is
from the average the fewer are
the individuals belonging to it.
Practically all statistical investi-
gations of variation conform to
this result. The VARIATION
CURVES thus obtained agree more
or less closely with the so-called
curve of chance. This is readily
understood, for there are always
several external factors acting
which may result in either an
increase or diminution of the
size, number, or weight under
consideration. Only chance de-
cides which effect takes place.
Thus only rarely will all the
factors make for diminution or

. , J11 the *™*0™ for increase ; more

of a pure line (JOHANNSEN'S Line K). (After frequently the factors Will be

BAUR.) combined so as to determine an

intermediate result.

If a seed of a pure line is sown it is indifferent whether one
starts from a small, medium, or large specimen. The variation curve
of the next generation will not differ from that of the generation to
which the seed belonged. Similarly the changes resulting from
cultivation in alpine regions (Fig. 270) are not inherited. Such
modifications persist only as long as, or but little longer than, the
action of the causes giving rise to them.

Practical experience seems at first sight to contradict this
result. In the process of SELECTION a plant with special properties
is chosen from a large number and the same characters appear
to recur frequently in its descendants. This depends on the fact
that in this case a single pure line has been isolated from what
was really a mixture of a number of different races or lines. The
characteristic properties of the selected line are continued in the

FIG. 271,-Variation curve of the weights of Beans

DIV. II

PHYSIOLOGY

325

descendants. If the material to begin with is really pure, selection
has no effect.

COMBINATIONS. — When a plant originates not from self-fertilisation
but from a cross, this may be termed a hybrid even if its parents
belonged to very nearly related races. In this sense in every cross
between two individuals heterozygotes must appear. The descend-
ants of a hybrid will have the characters of the one parent or of
the other or of both, and will thus appear diverse. This form of
variation is superficially not to be distinguished from modification,
for it can also show the curve of chance. It is, however, essentially
different since it is inheritable. The descendants vary according to
the Mendelian rules. This form of variation is termed combination.

FIG. 272.— Habit of 1, Chelidonium majus; 2, Chelidonium majus laciniatum. (After LEHMANN.)

MUTATIONS (S6) are variations that are distinguished from com-
binations in not having arisen by hybridisation, but resemble them in
being inherited. Mutations can only be recognised with certainty
under experimental conditions, when in the descendants of a pure line
individuals appear which possess a new character or are wanting in
a character of the parent organism, the departure being maintained
in their offspring. The appearance of such mutations has been
observed in experiments both with seedlings and with buds. It is also
highly probable that many variations met with in nature should be
regarded as mutations. Thus, for example, Chelidonium laciniatum, a
mutation of Chelidonium majus with incised leaves, was found at
Heidelberg in 1590 (Fig. 272). Fragraria monophylla, which was first
noticed in 1761, differs from the ancestral form of the Strawberry
in having simple instead of trifoliate leaves. The remarkable

326 BOTANY PART i

Nicotiana tabacum virginica apetala, which arose in a culture of KLEBS,
must be placed here. In many plants reddish - leaved forms have
arisen as mutations. All these forms are distinguished from the
parent form in a single character. Once they have arisen they have
remained constant in all their descendants.

Nothing certain is known as to the causes of mutations. If they
should prove in certain cases to be determined by external factors they
would still be sharply distinguished from modifications. In the mutation
a change in the determinants has occurred ; either old determinants
have been lost or new ones have made their appearance. The latter case
must, however, be rare. Mutations do not appear only in relation to
sexual reproduction. Thus in some Bacteria which increase in number
by repeated division mutations have been found. In higher plants also
single buds are known to have become changed and their new characters
have persisted. These cases are spoken of as bud mutations. Doubt is
often expressed as to whether in the Bacteria and in the moulds there
is any sharp distinction between mutations and modifications.

Origin of Species. — Various lines of evidence, dealt with on
p. 206 ff., have led to the view that the organisms which inhabit the
earth at the present time have developed from others that existed
in previous ages. This hypothesis, which is known as the THEORY^OF
DESCENT (87) and is of great importance, assumes that the " species "r is
not constant but liable to change. In addition to what has been said
earlier (p. 206 ff.) it is only necessary to state here that only mutations
and combinations among the variations yet observed could play a
part in the origin of a new species. Latterly the indications that
hybridisation has been of importance in the production of species
have multiplied. Certain species of Oenothera behave like hybrids
the parents of which are no longer in existence.

SECTION III
MOVEMENT

Phenomena of movement are met with in the living plant not less
generally than those of metabolism and development. Metabolism is
associated with a continual movement of the raw food-materials, which
are absorbed, and of the elaborated assimilates and excreted sub-
stances. These movements cannot be directly observed, but are not
less certainly established ; they have already been dealt with. In
addition there exist a number of visible alterations of position exhibited
either by the whole plant or by its several organs ; these movements
are, it is true, often very slow but sometimes are quite sudden.

PROTOPLASM itself is capable of different movements. Naked
protoplasmic bodies almost always show slow movements resulting in

DIV. ii PHYSIOLOGY 327

a gradual change of position ; but cells enclosed by cell walls possess
also the power of INDEPENDENT LOCOMOTION, often indeed to a con-
siderable extent, Multicellular plants, however, as a rule ultimately
attach themselves, by means of roots or other organs, to the place of
germination, and so lose for ever their power of locomotion, except in
so far as it results from growth.

Many perennial plants do not reappear in exactly the same spot.
Since new parts arise by growth while old portions die off, such plants
change their place gradually. A good example is afforded by plants
with rhizomes growing forward at the tip while the hinder region is
decaying. In trees the main axis continues alive, but the growing
points are changing their position ; thus the growing point of a giant
Australian Eucalyptus moves from the level of the soil to a height
of 110m.

Geophytes (p. 177) moving forward in a straight line in the ground come to
new places, the food materials of which have not been used up by them. This
movement is especially evident in those in which the rhizome remains short, owing
to the former year's growth soon decaying. The annual movement in Listera ovata
is only 3-5 mm., in Arum maculatum 1-3 cm., and in Paris quadrifolia 6-8 cm.
The change of place is more marked in the case of plants provided with special
off-shoots or runners. The movement is not really wanting in geophilous plants
which continue in the same spot (Ophrydeae), because the direction of elongation
regularly alternates, or as in Colchicum because the new shoots in their expansion
have to force their way through the remains of the previous year's growth. In the
latter case the corms may be laterally distant, 5-7 cm., from the foliage leaves and
connected with these by means of an S-shaped curved stem.

v In addition to these movements, occasioned by a growth in length,
plants firmly established in the soil also possess the power of changing
the position and direction of their organs by means of CURVATURE.
Not only unequal growth but other processes also take part in these
changes of form. In this way the organs are brought into positions
necessary or advantageous for the performance of their functions.
By this means, for example, the stems are directed upwards, the roots
downwards ; the upper sides of the leaves turned towards the light,
climbing plants and tendrils twined about a support, and the stems
of seedlings so curved that they break through the soil without injury
to the young leaves.

Movements of locomotion and movements of curvature have thus
to be distinguished.

I. MOVEMENTS OF LOCOMOTION (88)
A. Mechanism of Movements of Locomotion

In a fuller consideration of changes of position we can leave on
one side the carriage forward in a straight line by means of growth of
the growing point, since this has been dealt with in the chapter on

328 BOTANY PART I

development. We thus confine ourselves to the protoplasmic move-
ments among which the AMOEBOID MOVEMENT, the CILIARY MOVE-
MENT, and the MOVEMENT OF PROTOPLASM IN CELLS WITH CELL WALLS
may be distinguished.

The creeping movements of naked protoplasts, such as are shown
by an amoeba or plasmodium, in the protrusion, from one or more
sides, of protuberances which ultimately draw after them the whole
protoplasmic body, or are themselves again drawn in, are distinguished
as AMOEBOID MOVEMENTS. These movements resemble, externally, the
motion of a drop of some viscous fluid on a surface to which it does
not adhere, and are chiefly due to surface tension, which the proto-
plasm can at different points increase or diminish by means of its
quality of irritability.

By means of local changes of surface-tension similar amoeboid movements
are also exhibited by drops of lifeless fluids, such as drops of oil in soap solution,
drops of an oily emulsion in water, or drops of mercury in 20 per cent solution of
potassium nitrate in contact with crystals of potassium bichromate.

In the SWIMMING MOVEMENTS BY MEANS or CILIA (89), on the con-
trary, the whole protoplasmic body is not involved, but it possesses
special organs of motion in the form of whip-like FLAGELLA or CILIA.
These may be one, two, four, or more in number, and arranged in
various ways (Figs. 216, 219). They extend through the cell wall when
this is present and move very rapidly in the water, imparting con-
siderable velocity to the protoplast, often giving it at the same time
a rotary movement. The minute swarm-spores of Fuligo varians tra-
verse 1 mm. (sixty times their own length) in a second, those of Ulva
0'15 mm., while others move more slowly. The Vibrio of Cholera,
one of the most rapidly moving bacteria, takes 22 seconds to traverse
a millimetre.

Diatoms and Desmids exhibit a different class of movements. The Diatoms
which have a slit or raphe in the siliceous cell wall glide along, usually in a line
with their longitudinal axis, and change the direction of their movements by
oscillatory motions. From the manner in which small particles in their neigh-
bourhood are set in motion, it is concluded that there exists a current of proto-
plasm, which bursts through the raphe ; this, according to 0. MULLEK, is the
cause of the movement (90). The cells of Desmidiaceae effect their peculiar
movements by local fluctuations in the mucilaginous excretion. The Oscillarieae
appear to behave similarly (91).

In addition to such changes of place of whole cells there are also
movements of the protoplasm within the cell wall. Of these move-
ments rotation and circulation (cf. p. 1 3) have to be distinguished.

In these movements the outermost layer of protoplasm in contact witli the cell
wall remains at rest ; the movement cannot thus be compared to that of an
amoeba enclosed in a cell. The movement continues when the protoplasm has
been detached from the cell wall. Its cause must be looked for in surface
tensions between the protoplasm and the cell sap.

PHYSIOLOGY 329

The streaming movements of protoplasm were discovered by CORTI in 1772.
Favourable examples for their demonstration are the hairs of many plants, the
cells of the leaves of some water plants, and the long cells of the Characeae and
Siphoneae.

B. The Conditions of Locomotion

Since these movements are due to protoplasm and its organs it
will be readily understood that they depend on the general conditions
for the life of the protoplasm.

The existence and the activity of all these movements thus depend
especially on a favourable temperature, and in aerobic plants on the
presence of free oxygen. The protoplasmic movement can, however,
continue for we^ks in the absence of oxygen in the case of facultative
anaerobes like Nitella. Certain Bacteria that are obligate anaerobes
lose their motility on the entrance of oxygen ; on the other hand,
aerobic Bacteria which have ceased to move in the absence of oxygen
resume their movement when a supply of this gas is available (p. 248).

On overstepping the minimum or the maximum for these factors
a loss of motility or a condition of rigor results. Thus we speak of
cold-rigor, heat-rigor, etc. This condition can be removed by a return
of the favourable conditions, but if it lasts long enough will ultimately
lead to death. In some cases it is sufficient that these general con-
ditions of life should be present, but in others the movement only
results on the application of a special stimulus.

Thus it is known that protoplasmic movement often only appears on wounding
the plant, or is increased by this. In certain Bacteria movement is started by
the stimulus of light or by a particular concentration of the substratum. Other
external influences may lead to a loss of- motility, while movement also ceases in
temporarily motile objects^ such as swarm-spores or spermatozoids, as the result
of internal causes .

In giving a definite direction to movements of locomotion,
external stimuli play a very special part. In the absence of such
directive stimuli plasmodia move without a destination, the direction
of swimming or circulatory movements may frequently be reversed,
and only the rotation-stream is characterised by a constant direction.

C. Tactic Movements

The main directive stimuli are one-sided illumination, and dissolved
substances unequally distributed through the water. The directive
movements brought about by such factors are termed tactic; that
effected by light is phototaxis, and that by dissolved substances
chemotaxis. Other less widespread tactic movements will be omitted
here.

The resulting movements bring the freely motile plant or the
motile organ of a cell either towards or away from the stimulus ; in

330 BOTANY PAKT i

the former case the taxis is positive, and in the latter negative. The
nature of the reaction frequently depends not only on the object, but
on the external conditions.

1. Phototaxis (92)

Phototactic movements may be best observed when a glass vessel
containing water in which are Volvocineae, Chlamydomonadinae, or
swarm-spores of Algae is exposed to one-sided illumination from a
window. After a short time the uniform green tint of the water
disappears, since the motile organisms have all accumulated at the
better-illuminated side of the vessel. If the latter is turned through
an angle of 180° the Algae hasten to the side which is now illuminated.
If, however, a stronger light, such as direct sunlight, is allowed to fall
on the vessel the same organisms which till now have reacted positively
become negatively phototactic and swim away from the source of light.
Other external factors may have the same effect.

In some organisms, such as the plasmodia of Myxomycetes, we find a negative
reaction even to a light of low intensity. There are also colourless organisms
which have a positive phototactic reaction. In nature phototactic movements
usually bring the organism into a position of optimal illumination.

There are two distinct kinds of phototaxis. In the one (TOPOPHOTOTAXIS)
the organism places itself in the direction of the rays of light, and moves towards
or away from the source of light. In other cases (PHOBOPHOTOTAXIS) the organism
reacts on the passage from light to darkness by a sudden movement that brings it
back into the light ; it thus remains fixed in the illuminated spot.

A very striking example of phototaxis is afforded by the chloro-
plasts within the cell (93). These movements have the result of bringing
the chlorophyll grain into such a position that it can obtain an optimal
amount of light. This object is sometimes attained by rotation of the
chloroplast, and sometimes by its movement to another position in
the cell.

In the cylindrical cells of the filamentous Alga Mesocarpus, the chloroplasts, in
the form of a single plate suspended length -wise in each cell, turn upon their
longitudinal axes according to the direction and intensity of the light. In light of
moderate intensity they place themselves transversely to the source of light, so that
they are fully illuminated (transverse position) ; when, on the other hand, they are
exposed to dii-ect sunlight, the chlorophyll plates are so turned that their edges
are directed towards the source of light (profile position).

In the leaves of mosses and of the higher plants and in fern prothalli a similar
protection of the chloroplasts against too intense light, and their direct exposure,
on the other hand, to moderate illumination, is accomplished, where they are of
a different form and more numerous, by their different disposition relatively to the
cell walls. In moderate light the chlorophyH bodies are crowded along the walls,
which are at right angles to the direction of the rays of light (Fig. 273 T). They,
however, quickly pass over to the walls parallel to the rays of light as soon as the
light becomes too intense, and so retreat as far as possible from its action (Fig. 273 S).

DIV. II

PHYSIOLOGY

331

In darkness or in weak light tlie chloroplasts group themselves in still a third way
(Fig. 273 JV), the advantage of which is not altogether clear.

The form of the chlorophyll grains themselves undergoes modification during
changes in their illumination ; in moderate light they become flattened, while in
light of greater intensity they are smaller and
thicker. As a special mode of protection
against too intense light, the chloroplasts of the
Siphoneae and Diatomeae (and the same thing is
observed in many plants) become balled together
in separate clumps.

In correspondence with the changes in the
position of the chloroplasts, the colouring of
green organs naturally becomes modified. In
direct sunshine they appear lighter, in diffused
light a darker green.

2. Chemotaxis (94)

Chemotaxis results, as mentioned
above, from the unequal distribution
of substances dissolved in water. Posi-
tive chemotaxis leads to the irritable
plants accumulating in the region of
higher concentration of the chemotactic
material.

Such substances are of definite
nature. Thus, for example, many bac-
teria are "attracted" by particular
organic or inorganic food materials,
e.g. peptone, sugar, meat-extract, phos-
phates, etc., while they are " repelled "
by other substances such as acids and
alkalies. While the chemotaxis here
serves the process of nutrition, its use
is different in the case of spermatozoids ;
these male sexual cells are thus attracted
to the egg -cells. Nuclei and chloro-
plasts may also show chemotactic move-
ments.

The spermatozoids of the Ferns are attracted by malic acid or malates to the
neck of the archegonium ; in the case of the spermatozoids of Lycopodium, citric
acid, in Mosses, cane sugar solution, and in the Marchantieae proteid substances
are the respective attractive substances. Often extremely minute quantities of the
substance will bring about active irritable movements ; thus even a O'OOl per cent
solution of malic acid will attract the numerous spermatozoids of a Fern swimming
in pure water. In chemotaxis as in phototaxis we can distinguish phobic and topic
modes of reaction.

Aerotaxis determined by oxygen is found in the case of Bacteria ;

PIG. 273.— Varying positions taken by the
chlorophyll grains in the cells of
Lemna trisulca in illumination of differ-
ent intensity. T, in diffuse daylight ;
S, in direct sunlight; N, at night.
Tho arrows indicate the direction of
the light. (After STAHL.)

332

BOTANY

PART I

on this account these organisms have been used to demonstrate the
assimilation of carbon dioxide (p. 248).

The phenomenon of hydrotaxis, a directive movement due to the
unequal distribution of water -vapour in the air, may be associated
with chemotaxis. A positive hydrotaxis is shown by the plasmodia of
Myxomycetes, and this passes into negative hydrotaxis at the time of
spore-formation.

II. MOVEMENTS OF CURVATURE

The kinds of curvature which may take place in the organs of
attached plants are illustrated by Fig. 274. A four-angled prism

is of equal length along
each of its angles. If it is
bent in one plane the angles
of the concave side must
become markedly shorter
than those of the convex
side. An elongation of
one side or a shortening of
the other side or simultane-
ous lengthening of one side
and shortening of the oppo-
site side must lead to curva-
ture. When in this process
of bending the column
remains in one plane, it is
spoken of simply as curved.
When, however, it passes
out of the one plane so
that the bending follows a
line oblique to the longitu-
dinal axis it is spirally wound (IV). Lastly, when the column remains
as a whole straight but its angles follow spiral lines, it is termed
twisted (III). The torsion comes about by a difference in length be-
tween the middle line and the angles ; all the latter are of equal length.
Ways in which Curvatures are produced. — In the production of
curvatures we are always concerned, as has just been shown, with
changes in the dimensions of an organ due to unequal lengthening or
shortening. In bringing about these changes in dimension the follow-
ing means are employed by the plant.

1. Growth. This can only lead to elongation.

2. Osmotic pressure. This can effect an elongation or a shortening

according as it is increased or diminished.

Variations in the amount of water in the cell wall or in dead
cells. These also can effect either elongation or shortening.

FIG. 274. — Four-angled prism. I, Straight; //, curved
III, twisted ; IV, spirally wound.

DIV. ii PHYSIOLOGY 333

According to the means employed in altering the dimensions, the
curvatures of plants may be divided into GROWTH-CURVATURES,

VARIATION MOVEMENTS DEPENDING ON TURGESCENCE, and HYGROSCOPIC
MOVEMENTS. Since growth and osmotic pressure are vital phenomena,
i.e. are essentially influenced by the living protoplasm, they will be
treated below along with the locomotory movements which are
dependent on the living substance of the plant. The hygroscopic
movements, on the other hand, are not vital phenomena ; they occur
in dying or dead organs and are brought about exclusively by
external factors. The protoplasm only plays a part in these move-
ments in that it has led to such a construction of the organs that
changes in the amount of water present produce curvatures and
not a simple change in length.

A. Hygroscopic Movements

Two quite distinct types of movement are included in the
hygroscopic movements. In the first, which are termed IMBIBITION
MECHANISMS (95), the cell walls increase in size on swelling or contract
on shrinking.

The swelling or shrinking depends on the fact that the water of
imbibition is not contained in cavities like those in a porous body
(such as a sponge or a piece of plaster of Paris) that contain the
capillary water, but in being absorbed has to force apart the minute
particles of the cell wall. Conversely these particles approach one
another again when the imbibition water evaporates. When on
different sides of an organ there are unequally well-developed layers,
or layers that swell with unequal rapidity, or when opposite layers
differ in the direction of their greatest extension on swelling,
curvatures must take place every time the organ is moistened or dries.
Though we are here dealing with purely physical phenomena, they
may possess great importance for the plant.

The rupture of ripe seed-vessels, as well as their dehiscence by the opening of
special apertures, is a consequence of the unequal contraction of the cell walls due
to desiccation. At the same time, by the sudden relaxation of the tension, the
seeds are often shot out to a great distance (Euphorbia, Geranium, etc.). This
dehiscence on drying is termed XEROCHASY, and is contrasted with the opening of
the fruits and dispersal of the seeds in some desert plants when they are moistened
(HYGROCHASY). The best example of this is the fruit of Mesembryanthemum
linguiforme. The behaviour of the " Rose of Jericho " (Anastatica hierochuntica)
is similar. The whole plant when fruiting dries up, and owing to the unequal
shortening of the upper and under sides of the branches becomes contracted into a
spherical mass. On the addition of water, the plant resumes its original form, its
fruits open and shed the seeds which are thus under favourable conditions for
germination. With Anastatica some other plants (e.g. Odontospermum) may be
mentioned, to some of which the name Rose of Jericho is also applied. In certain
fruits not only curvatures but torsions are produced as the result of changes in the

334

BOTANY

PART

amount of water they contain, e.g. Erodium gruinum (Fig. 275), Stipa pennata,
Avena sterilis ; by means of these, in conjunction with their stiff barb-like hairs,
the seeds bury themselves in the earth.

The opening or closing of the moss sporogonium is, in like manner, due to the
hygroscopic movements of the teeth of the peristome surrounding the mouth of
the capsule. In the case of the Equisetaceae the outer walls of the spores them-
selves take the form of four arms, which,
like elaters, are capable of active move-
ments.

In order to call forth imbibition move-
ments the actual presence of liquid water
is not necessary, for the cell walls have the
power of absorbing moisture from the air.
They are hygroscopic, and are used to
estimate the humidity of the air in hygro-
meters and weather-glasses.

The mechanisms which depend
on the cohesive power of water are
distinguished from those depending
on imbibition. The COHESION MECHAN-
ISMS were previously confounded with
the latter, from which they differ in
that, even during the movement, the
cell walls remain saturated with
water. It is the lumen of the cell
which diminishes in size when the
loss of water, on which the move-
ment depends, occurs. A good ex-
ample is afforded by the movements
of the sporangium of the Polypo-
diaceae on drying. The sporangia
are stalked, biconvex bodies contain-
ing the spores within a wall composed
of one layer of cells. While the rest
of the wall is composed of thin
walled cells, one row of peculiarly thickened cells forms a vertically
placed semicircle (Fig. 276 R). The cells of this ANNULUS have their
outer walls thin, the lateral walls increasingly thickened from the
outside inwards, and the inner walls thick. On exposure to dry air
the cells of the annulus gradually lose the contained water. The
watery contents do not, however, separate from the cell wall nor
does a rupture occur in the liquid, since the adhesion to the wall and
the cohesion of the molecules of water is very great, amounting
to hundreds of atmospheres (96). A deformation of the cell wall,
therefore, follows the diminishing water- content ; the thin outer
wall (Fig. 276, 3) is pulled inwards, thus approximating the thickened
lateral walls. There thus comes about an energetic one-sided shortening

FIG. 275. — Partial fruit of Erodium gruinum.
A, in the dry condition, coiled ; B, moist
and elongated. (After NOLL.)

DIV. II

PHYSIOLOGY

335

of the annulus which leads to the opening of the sporangium and the
shedding of the spores.
With further loss of
water the contained
water ultimately tears
apart from the wall, an
air-filled space appears,
and the cells of the
annulus resume their
original form. Since
this occurs suddenly, the
majority of the spores
are forcibly thrown out,
as the sporangium again
closes. The sporangia of
other Vascular Crypto-
gams and the walls of FlG 276.— 1. Sporangium of Polypodium falcatum. (After CAMP-
polleil-SaCS afford in their BELL.) 2. Cells of annulus in original position. 3. After

orjeninp- other examnles partial evaP°ration of the water filling them 0") > the "Pi**

cell wall (o) is curved in, while the lower \(u) retains its
Of Cohesion-mechanisms. original length. (2, 3 after NOLL.)

Many hygroscopic

curvatures also depend on the co-operation of movements depending
on imbibition and on cohesion.

B. Movements of Curvature in the Living Plant

As in the case of plants which exhibit active locomotion, the
phenomena of movement in attached plants may occur when all
the general conditions of vital phenomena are present, but sometimes
only when a particular factor (stimulus) is acting. The latter deter-
mines either the amount of the curvature only or its direction also.
Movements which take place without such specific external stimuli
are termed AUTONOHIC, while the others are termed INDUCED or
PARATONIC movements.

1 . Autonomie Movements of Curvature

As stated above, a sufficient intensity of the external factors with
which life is associated (p. 218) is sufficient to call forth these move-
ments. Beyond a certain minimum and maximum a condition of
rigor in which the plant is motionless occurs. Thus, states of rigor
due to heat, cold, darkness, dryness, etc., are known.

Thus also the growth of the shoot or root in a straight line (with
the characteristic grand period of growth, dependent, as has been
shown, wholly on internal causes) is an autonomic movement. A
number of growth curvatures or nutations are associated with this

BOTANY

growth, and it might almost be said that there is hardly such a thing
as growth in a straight line. The tips of the organs describe extra-
ordinarily irregular curves in space ; they exhibit " circumnutations,"
as was discovered by DARWIN. While these curvatures are usually so
slight as not to be perceptible without the aid of special methods, cases
exist in which organs exhibit very conspicuous, striking, and regular
autonomic growth curvatures.

The unfolding of most leaf and flower buds, for example, is a nutation move-
ment which, is induced by the more vigorous growth of the upper side of the young
leaves (epinasty). The same unequal growth, in this case of the under side, mani-
fests itself most noticeably in the unrolled leaves of Ferns and many Cycadeae
(hyponasty). The stems of many seedlings are, on their emergence from the seeds,
strongly curved, and this aids them in breaking through the soil. By the nuta-
tion of the shoots of the Wild Vine (Parthenocissus quinquefolia) a curvature is
produced which continuously advances with the increased growth.

When the unequal growth is not confined "to one side, but occurs alternately on
different sides of an organ, the nutations which result seem even more remarkable.
Such movements are particularly apparent in the flower-stalk of an Onion, which,
although finally erect, in a half-grown state often curves over so that its tip touches
the ground. This extreme curvature is not, however, of long duration, and the
flower-stalk soon becomes erect again and bends in another direction.

If the line of greatest growth advances in a definite direction around the
stem, the apex of the latter will exhibit similar rotatory movements (REVOLVING
NUTATION). This form of nutation is characteristic of the tendrils and shoots of
climbing plants, and facilitates their coming in contact with a support.

Besides these nutations which result from growth, autonomic
variation movements are also met with, though less commonly. They
are almost confined to foliage leaves, and indeed to those which have
pulvini at the base of the petiole and of its further ramifications.
Pulvini occur especially in Leguminosae and Oxalideae, also in Marsilia,
and are characterised by a structure which fits with their particular
function.

In the ordinary parenchymatous cell the cell wall, owing to its
growth in thickness, ceases to be stretched ; on plasmolysis it therefore
does not in full-grown cells contract in the same degree as it does in
growing cells (cf. Fig. 237). Conversely on an increase of the in-
ternal pressure the wall only becomes slightly stretched. In some
cases, however, and the pulvinus is an example, the cell walls even
in their fully-grown state are considerably distended by the osmotic
pressure. This is shown not only by their behaviour on plasmolysis,
but also by the persistence of marked tissue-tensions.

A pulvinus of one of the Leguminosae, such as the Kidney Bean, has the
vascular bundle and the sclerenchyma, which are peripherally arranged in the leaf-
stalk, united to form a central and easily-bent strand ; this is surrounded by a
thick zone of parenchyma (Fig. 277, 3). If from a pulvinus isolated by two
transverse sections the middle sheet of tissue is cut out (Fig. 277, 1), the bulging of
the cortical parenchyma both above and below shows the considerable tension. On

DIV. ii PHYSIOLOGY 337

splitting the portion of the pulvinus longitudinally as in Fig. 277, 2, the tendency
towards expansion of the parenchyma, especially of its middle layers, is very
clearly shown.

It will now be readily seen that an increase in turgescence on all
sides will increase the tension between the vascular bundle and the
parenchyma and thus increase the
rigidity of the pulvinus. On the
other hand, an increase of turges-
cence on one side or a diminution
on the other side, or the occurrence
of both these changes together, will
cause a lengthening of the one side

and a Shortening, of the Other Side FIG. 27".— Pulvinus of Phasedus (after SACHS).

Which naturally Curves the pulvinus. *• ***** cut longitudinally from the middle

m, i r ji • -i of the pulvinus ; 2, the same cut up ; 3,

The Vascular bundle IS passively transverse section, g, Vascular bundle.

bent, and undergoes no alteration

in length. The passive movement of the part of the leaf attached to

the pulvinus is due to the curvature of the pulvinus.

Autonomic variation movements are probably present in all leaves
provided with pulvini, but only attain a striking degree in a few
plants.

Thus the small lateral leaflets of Desmodium gyrans move uniformly or move
interruptedly in elongated ellipses. At higher temperatures (30-35° C.) the move-
ment is very rapid, the course being completed in half a minute. The movement
of the leaflets of Oxalis hedysaroides is still more rapid, the tip moving through
O'5-l'o cm. in one or a few seconds. While the autonomic movements of these
two plants do not appear to be affected by light, those of Trifolium pratense are
completely suppressed in light. In the dark, however, the terminal leaflet
exhibits oscillatory movements with an amplitude that may exceed 120° ; these are
regularly repeated in periods of two to four hours.

2. Paratonie Movements (Stimulus Movements) (97)

In the induced or paratonic movements an external factor always acts
as a stimulus and starts the movement. By means of these movements
attached organisms bring their organs into the positions in which
their functions can be best carried out. If the organs of a seedling
continued to grow on in the directions which have been accidentally
brought about on sowing the seed, the root would often grow into the
air and the shoot into the soil.

Light, heat, gravity, and chemical or mechanical influences of the
most various kind enable the plant to orientate itself in its environ-
ment. The different organs of a plant often show quite different re-
actions to the same external stimulus. Thus the stem and root, while
both tending to place themselves in the direction of the rays of light,
grow towards or away from its source respectively ; the leaves, on the

BOTANY PART i

other hand, place their flat surfaces at right angles to the incident
rays. The mode of reaction is not determined once and for all, but
can be profoundly modified. The tone of the plant is thus altered,
the change being brought about by either internal or external factors.

The condition of receptiveness to stimuli in the plant is common to all
irritable movements and indeed all irritable phenomena. It largely depends on
external factors. The same factors that give rise to the stimulus may also
intensify or weaken the receptiveness. Other substances, such as the narcotics so
well known in animal physiology, may blunt the receptiveness. The stimulus
must give rise to definite changes in the plant ; the protoplasm must react to these
changes in such a way that the characteristic externally visible reaction ultimately
takes place. Between this result and the reception of the stimulus there doubt-
less intervene many and complicated processes which are at present but little
understood. The places where the stimulus is received and perceived are termed
sense organs or, better, organs of perception. There is particular reason to
distinguish organs of perception, when it can be shown that the place where a
stimulus is received is separated in space from the part where the movement is
effected. In such a case a conduction of the stimulus must take place.

The power of perception or of sensation in the plant can be spoken of without
implying any subjective perception, will, or thought, as in the complicated human
psychology. This is unfortunately sometimes done by modern sensational writers.
The existence of a "soul " in the plant can neither be denied nor asserted ("). No
conclusion in this respect can be drawn from the fact that certain features of
stimulus movements take place in a similar way to our perceptions. These
regularities, which will be later referred to as showing a relation between the
intensity of the stimulus and the excitation (p. 347) are, however, of the'greatest
interest.

Those movements which bring about a particular position with
regard to the direction of action of the stimulus may be grouped
together as MOVEMENTS OF ORIENTATION or TROPISMS. The other
movements of curvature, leading to the assumptions of definite posi-
tions with respect to the plant and not to the direction of the stimulus,
are termed NASTIC movements.

(a) Tropisms

In the movements of orientation we have to distinguish ortho-
tropous (parallelotropous) and plagiotropous organs. The former
place themselves in the direction of the stimulus and approach the
source of the stimulus (positive reaction) or move away from it
(negative reaction). Plagiotropous organs place themselves at right
angles to the direction of the stimulus or obliquely to its direction.
The mode of reaction of any particular organ may be changed by
external or internal factors. The movements of orientation are
distinguished as phototropic, geotropic, etc., according to the stimulus
bringing them about.

The tropisms of attached plants correspond to the tactic movements of motile

DIV. ii PHYSIOLOGY 339

plants. As in the case of the latter, their significance lies in the attainment of
favourable conditions of life. The effective stimulus, the positive and negative
modes of reaction, and the alternation from one to the other are completely
analogous to the phenomena already described in relation to tactic movements.

1. GEOTROPISM (")

It is a matter of experience that the trunks in a Fir wood are
all vertical, and therefore parallel to one another ; the branches and
leaves of those trees, on the other hand, take other positions. If,
instead of a tree, we consider a seedling, for example of the Maize,
\ve find that, at any rate to begin with, the organs stand in the
vertical line. At the same time we here observe more readily than
in the case of a ,tree the totally different behaviour of the roots and
the stem, the former growing vertically downwards and the latter
upwards. If we bring the seedling from its natural position and
lay it horizontally we find that a curvature takes place in both
organs ; the root curves downwards, and the shoot of the seedling
upwards. Since these curvatures are not effected at the region
where the root passes into the shoot, but in the neighbourhood of
the apices of the two organs, a region of variable length remains
horizontal, and only the two ends of the plant are brought by
the curvature back into their natural directions, and continue to
grow in them. That this vertical growth of the main root and main
stem is due to gravity is apparent from direct observation, which
shows that these organs are similarly oriented all over the globe, and
lie in the direction of radii of the earth. The only force acting
everywhere in the direction of the earth's radius that we know of is
gravity. Not, however, as a result of this line of thought, but from
the experiments of KNIGHT (1806), was this knowledge introduced
into our science. KNIGHT'S experiments rest on the following
consideration. It is evident that gravity can only cause the root to
grow downwards, and the stem to grow upwards, if the seed is at
rest and remains in the same relative position to the attractive force
of the earth. From this KNIGHT conjectured "that this influence
could be removed by the constant and rapid change of position of
the germinating seed, and that we should further be able to exert an
opposite effect by means of centrifugal force."

He therefore fastened a number of germinating seeds in all
possible positions at the periphery of a wheel, so that the root on
emerging would grow outwards, inwards, or to the side, and he
caused the wheel to rotate round a horizontal axis. Since this
rotation was very rapid, not only was the one-sided action of gravity
excluded, but at the same time a considerable centrifugal force was
produced, which in its turn influenced the seedlings. The result of
the experiment was that all the roots grew radially away from, and
all the shoots radially towards the centre of the wheel. Thus the

340 BOTANY PART i

centrifugal force determined the orientation of the seedlings as gravity
does normally.

In another experiment KNIGHT allowed gravit}^ and centrifugal
force to act simultaneously but in different directions on the seed-
lings. The plants were fastened on a wheel which rotated round a
vertical axis. When the distance of the plants from the centre and
the rapidity of rotation were so adjusted that the mechanical effects
of the centrifugal force and of gravity were equal, the roots grew out-
wards and downwards at an angle of 45° and the stem inwards and
upwards at the same angle. As the rapidity of rotation increased, the
axis of the seedlings took a position approximating more to the
horizontal. It results from these experiments that the plant does
not discriminate between gravity and centrifugal force, and that the
one can be replaced by the other. Both these forces have this in
common, that they impart to bodies an acceleration of mass.

An essential addition to the fundamental researches of KNIGHT
was given much later (1874) by the experiments of SACHS. In these
the plants were rotated round a horizontal axis as in KNIGHT'S first
experiment, but the rotation was slow, taking ten to twenty minutes
to effect one complete rotation. This is so slow that no appreciable
centrifugal force is developed. Since, however, by the continual
rotation any one-sided influence of gravity is eliminated, the roots and
shoots grow indifferently in the directions which they had at the
beginning of the experiment. In this experiment SACHS employed
a piece of apparatus termed the KLINOSTAT.

The property of plants to take a definite position under the
influence of terrestrial gravity is termed GEOTROPISM. It has been
seen that there are not only orthotropous organs which place them-
selves in the direction of gravity, and grow positively geotropically
(downwards) or negatively geotropically (upwards), but also plagio-
tropous organs which take up a horizontal or oblique position. The
positions assumed by the lateral organs are also — though as a rule
not exclusively — determined by gravity.

All vertically upward -growing organs, whether stems, leaves
(Liliiflorae), flower-stalks, parts of flowers, or roots (such as the
respiratory roots of Amcennia (Fig. 188), Palms, etc.), are negatively
geotropic. When such negatively geotropic organs are forced out of
their upright position, they assume it again if still capable of growth.
In negatively geotropic organs, growth is accelerated on the side
towards the earth ; on the upper side it is retarded. In consequence
of the unequal growth thus induced, the erection of the free-growing
extremity is effected. The actual course of the directive movement
of geotropism, as will be seen from the adjoining figure (Fig. 278),
does not consist merely of a simple, continuous curvature. The
numbers 1-16 show, diagrammatically, different stages in the geotropic
erection of a seedling growing in semi -darkness and placed in a

DIV. II

PHYSIOLOGY

341

horizontal position (No. 1). The. growth
in the stem of the seedling is strongest
just below the cotyledons, and gradually
decreases towards the base. The curva-
ture begins accordingly close to the coty-
ledons, and proceeds gradually down the
stem until it reaches the lower, no longer
elongating, portions. Owing to the down-
ward movement of the curvature, and
partly also to the after effect of the
original stimulus, the apical extremity
becomes bent out of the perpendicular
(No. 7), and in ^this way a curvature in
the opposite direction takes place. For
two reasons this excessive curvature must
again diminish (13-16); the stem is now
exposed to another geotropic stimulus in
the opposite direction to the first, and this
is combined with a tendency to straighten,
which is termed AUTOTROPISM (10°).

Every geotropic curvature flattens out or dis-
appears when the plant, before full growth has
taken place, is caused to revolve on the klinostat.
Since in this case the geotropic stimulus is want-
ing, some other cause must underlie the straighten-
ing. It appears, in fact, that every change in
the condition of curvature of an organ, whether
resulting from geotropism or from some other
cause, acts as a stimulus. The plant works
towards a restoration of the original condition,
and this tendency is termed autotropism. An
organ which was originally straight thus tends
by autotropism to return to this condition when
curved in any way, either by growth or by
mechanical bending. Similarly a curved organ
tends to regain its original form when this has
been for any cause lost.

In some cases negatively geotropic curvatures
may take place in full-grown (I01) shoots, i.e. in
such as no longer exhibit growth in length when
not geotropically stimulated. Thus in woody
stems and branches the growth in length of the
cambium of the lower side may bring the organ
into the erect position as a result of geotropism.
The greater the resistance of the parts which
have to be passively bent the more slow and in-
complete will this response be. The so-called
nodes of grasses, which in reality are leaf-cushions,

FIG. 278. — Different stages in the pro-
cess of geotropic movement. The
figures 1-16 indicate successive
stages in the geotropic curvature of
a seedling grown in semi-darkness :
at 1, placed horizontally ; at 16,
vertical. For description of inter-
mediate stages see text. (After
NOLL. Diagrammatic.)

342

BOTANY

PART

can also be stimulated by geotropism to further growth. If the stimulus acts on
all sides, as when the node is horizontally placed and rotated on the klinostat, all
the parenchymatous cells exhibit a uniform elongation. If the node is simply
placed horizontally the growth is limited to the lower side while the upper side is
passively compressed (Fig. 279). By means of such curvatures in one or several
nodes grass haulms laid by the wind and rain are again brought into the erect
position.

Positive geotropism is exhibited in tap-roots, in many aerial roots,
and in the leaf-sheaths of the cotyledons of some Liliaceae and in the
rhizome of Yucca. All these organs,
when placed in any other position,
assume a straight downward direc-
tion and afterwards maintain it.
Positively geotropic, like negatively
geotropic, movements are possible

FIG. 279. — Geotropic erection of a grass-haulm
by the curvature of a node. 1, Placed hori-
zontally, both sides (u, o) of the node being
of equal length ; 2, the under side (u)
lengthened, the upper side (o) somewhat
shortened ; as a result of the curvature the
grass-haulm has been raised through an
angle of 75°. (After NOLL.)

FIG. 280. — Geotropic curvature of the roots
of a seedling of Vicia Fdba. I, Placed
horizontally ; 77, after seven hours ; 177,
after twenty-three hours ; Z, a fixed index.
(After SACHS.)

only through growth. The power of a downward curving root-tip
to penetrate mercury (specifically much the heavier), and to overcome
the resistant pressure, much greater than its own weight, proves
conclusively that positive geotropism is a manifestation of an active
process. Positive geotropic curvature is due to the fact that THE

GROWTH OF AN ORGAN IN LENGTH IS PROMOTED ON THE UPPER
SIDE, AND RETARDED ON THE SIDE TURNED TOWARDS THE EARTH.

Fig. 280 represents the course of the geotropic curvature in a root.

Most lateral branches and roots of the first order are plagiogeotropic, while
branches and roots of a higher order stand out from their parent organ in all direc-
tions. THESE ORGANS ARE ONLY IN A POSITION OF EQUILIBRIUM WHEN THEIR

LONGITUDINAL AXES FORM A DEFINITE ANGLE WITH THE LINE OF THE ACTION OF

GRAVITY. If forced from their normal inclination they return to it by curving.
A special instance of plagiogeotropism is exhibited by strictly horizontal organs, such
as rhizomes and stolons, which, once they have attained their proper depth, show a
strictly TRANSVERSE GEOTROPISM (diageotropism). Should the proper depth not be

DIV. ii PHYSIOLOGY 343

attained, the plant tends towards it by upwardly or downwardly directed movements,
and then takes on the horizontal growth. The oblique position naturally assumed
by many organs is in part the result of other influences.

A special form of geotropic orientation is manifested by dorsiventral organs, e.g.
foliage leaves, zygomorphic flowers (p. 72). All such dorsiventral organs, just as
radial organs that are diageotropic, form a definite angle with the direction of
gravity, but are only in equilibrium when the dorsal side is uppermost. In the
orientation of dorsiventral organs, not merely simple curvatures but torsions are
concerned.

The rotation of the ovaries of many Orchidaceae, of the flowers of the
Lobeliaceae, of the leaf-stalks on all hanging or oblique branches, of the reversed
leaves (with the palisade parenchyma on the under side) of the Alstroemeriae,
and of Allium ursinum, all afford familiar examples of torsion regularly occur-
ring in the process of orientation.

The foliage leaves which possess pulvini must again be specially mentioned
among dorsiventral organs since they can change their position by geotropic
variation movements in the fully-grown state.

Twining" Plants (102), which are found in the most various families
of plants, have shoots which require to grow erect but are unable to
support their own weight. The erect stems of other plants, which
often secure their own rigidity only by great expenditure of assimi-
lated material (in xylem and sclerenchyma), are made use of by
stem-climbers as supports on which to spread out their assimilatory
organs in the free air and light. The utilisation of a support pro-
duced by the assimilatory activity of other plants is a peculiarity they
possess in common with other climbers, such as tendril- and root-
climbers. Unlike them, however, the stem-climbers accomplish their
purpose, not by the help of lateral clinging organs, but by the
capacity of their main stems to twine about a support. The first
internodes of young stem-climbers, as developed from the subterranean
organs which contain the reserve food material, as a rule stand erect.
With further growth the free end curves energetically to one side and
assumes a more or less oblique or horizontal position. At the same time
the inclined apex begins to revolve in circles like the hand of a watch.
This movement continues from the time of its inception as long as the
growth of the shoot lasts, and as a rule takes place in a definite direc-
tion. In the majority of twining plants the circling movement as seen
from above is in the direction opposite to that of the hands of a watch
(towards the left as we commonly express it). The Hop and the
Honeysuckle twine to the right, in the direction of the hands of a
watch. In Bowiea volubilis and Loasa lateritia a rotation alternately to
the right and left has been observed. The plants that circle to the
left are also left-handed climbers, i.e. the spiral which their stems
form (Fig. 281 /) mounts from the left to the right and, as seen
from above, against the direction of the hands of a watch. Similarly
the plants that circle to the right are right-handed climbers. There is
thus a close relation between the revolving movement and the twining.

344

BOTANY

PART I

The revolving movement is regarded by some authors as purely autonomic
(p. 336) ; on the other hand, it is held that gravity has a determining influence
upon it. This disputable question is still unsettled.

The commencement of the revolving movement does not by itself
determine a twining movement. This only begins when the shoot

meets a more or less vertical and
not too thick support. This is
enclosed in loose and at first very
horizontal spirals which gradually
become more erect and steeper. The
straightening results from negative
geotropism and leads under other-
wise favourable conditions when the
support is subsequently removed to
a complete obliteration of the spiral
coils, the straightened stem appearing
twisted. If the support is not re-
moved it leads to tightening of the
spiral and increased pressure on the
support. The twining movement
thus comes about by the revolving
movement together with negative
geotropism. The support plays a
part in that it prevents the other-
wise inevitable straightening. It
must stand more or less vertically,
because otherwise it would not be
continually grasped by the overhang-
ing tip of the shoot.

FIG

The twining is further assisted by the
shoots of the twining plant having to begin
with elongated internodes while the leaves
remain small. In this respect these shoots
resemble those of etiolated plants ; the

». 281.-I, Sinistrorse shoot of Pharbitis. d } d unfoldi Of the leaves allows of
II, Dextrorse shoot of Myrsiphylhim J

asparagoides. (After NOLL.) the regular circling of the tip which might

otherwise be interfered with by the leaves

encountering the support. The firm hold on the support is frequently increased
by the roughness of the surface of the stem owing to hairs, prickles, ridges, etc.
Torsions also, the causes of which cannot be entered into here, have a similar
effect.

Although STARK has recently shown that twining plants are not insensitive to
contact with the support (cf. p. 354), it still holds good that the result of this
contact does not determine the twining movement.

Alteration of the Geotropie Position of Rest. — The position
assumed by an organ as a result of a definite geotropic stimulation

DTV. II

PHYSIOLOGY

345

is not determined once and for all, but is liable to change owing to
internal and external influences. There is thus a " change of tone "
as regards geotropic stimulation. A certain " tone " is thus regarded
as the normal one, and the resulting reactions are expressed in the
distinction of orthotropous and plagiotropous, and positively and
negatively geotropic organs respectively.

Among the external factors which influence the geotropic tone,
light, temperature, oxygen, and gravity itself may be mentioned, and
as an internal factor the developmental phase of the organ.

The alteration of geotropic reaction by the illumination has an important
influence on the depth at which rhizomes occur. When the tip of a rhizome of
Adoxa growing on a slope becomes exposed to the light, its transverse geotropism

FIG. 282.— Rhizome of Polygonatum. The dotted Hue marks the surface of the soil. The aerial
shoots are cut off. Rhizome 1 was planted too high ; its continuation is downwards, only
the terminal bud which will form a flowering shoot being directed upwards. Rhizome 2 was
planted erect and too deep ; its continuation is obliquely upwards. (After RAUNKIAER.)

becomes altered to positive geotropism, and this leads to the rhizome again enter-
ing the soil. Frequently the influence of light on the parts of the plant above
ground suffices to direct the subterranean rhizome. If the rhizome of Polygonatum
is planted too high in the soil, although covered by earth and in the dark, the
new growth turns obliquely downwards ; if planted too deeply it turns upwards
(Fig. 282). At the correct depth the rhizome is transversely geotropic. Light
also acts strongly on the geotropism of lateral roots ; when illuminated the lateral
roots of the first order approach the orthotropous position of rest much more
closely than they do in the dark.

An effect of temperature may be observed on the stems of some spring plants ;
these often lie on the ground at temperatures in the neighbourhood of 0° C. and
only become orthotropous at higher temperatures. With lack of oxygen many
roots and rhizomes become negatively geotropic, and thus reach regions where more
oxygen is available.

Changes of tone due to internal causes are seen, for instance, in rhizomes, which

346 BOTANY PART i

at a certain stage of development change from the diageotropic position and
become orthotropous, or in inflorescences which become positively geotropic after
fertilisation. In this way the fruits of Trifolium subterraneum and of Arachis
hypogaea become buried in the soil. In twining stems also a change of tone has
been noted ; while young they do not twine.

Geotropism as a Phenomenon of Irritability. — The discoverer
of geotropism, KNIGHT, attempted to explain the geotropic move-
ments on purely mechanical lines ; this did not seem difficult,
especially for positively geotropic organs. He regarded them as
simply following the attractive force of gravity till a condition of
rest is attained. Later HOFMEISTER advanced similar views. The
correct assumption that we are concerned with complicated stimulus
mechanisms in which terrestrial gravity only plays the part of the
liberating factor depends on the work especially of DUTROCHET,
FRANK, and SACHS. Even the single fact that the root can carry out
its geotropic curvature against the resistance of mercury is sufficient
to call in question every purely mechanical explanation.

Only in recent times has the attempt been made to determine
what is the primary effect of gravity in the plant (103). There is
no doubt that we are concerned with an effect of pressure ; the fact
that gravity can be replaced by centrifugal force is in favour of this.
This effect of pressure only comes into action in the case of ortho-
tropous organs in proportion as it acts at right angles to the longi-
tudinal axis, and thus in relation to the vertical component when
the organ is placed obliquely. Lastly, it is clear that the pressure
must act within the cells, and is in no way replaceable by external
influences.

It is not known whether this pressure is determined by the entire cell-contents
and acts on the protoplasm as a whole, or whether special organs are concerned
in its production and reception. Various hypotheses on this question have been
advanced. F. NOLL first elaborated the idea that there must be some bodies in
the cells of greater specific gravity than the surrounding protoplasm, and capable,
under the influence of gravity, of exerting a one-sided pressure on the protoplasm ;
on this taking place the protoplasm directs the processes of growth in accordance
with the direction of the force of gravity. NEMEC and HABERLANDT then sug-
gested that these specifically heavier bodies (statoliths) might be found in certain
starch grains which show relatively rapid movements of falling in the cells. They
found such starch grains in the endodermis of the stem and in the cells of the
root -cap. They assume that the stimulus of gravity can only directly affect
portions of the plant provided with such starch grains, but that it may be con-
ducted from these points to others. As a matter of fact the attempt had
previously been made to show that only the tip of the root can receive the
gravitational stimulus. Even at the present time this question is not decided,
and not a few investigators assume that all cells — though in various degrees — are
geotropically sensitive. Thus fungi, in which statoliths are not found, are
geotropic. The hypothesis of NfeMEC and HABERLANDT, though there is much
in its favour, is not fully established. HABERLANDT himself states that in certain

DIV. ii PHYSIOLOGY 347

cases (moss-rhizoids) geo-perception is still possible after the disappearance of
starch. If, however, the investigations of ZOLLIKOFEB, are confirmed, according
to which, after disappearance of the starch, the power of geotropic reaction is
lost, while growth and phototropic reactions continue, the statolith-hypothesis
would have received the long-sought support.

As a rule we can only infer the geotropic irritability of an organ
from the curvatures that take place, but in some cases it can be
done independently of this reaction. Thus, for example, in some
grass seedlings (Paniceae) that have a well-developed iuternode be-
neath the sheathing leaf, the latter becomes full grown and no longer
capable of curvature ; it is, however, still geotropically sensitive, since
on the sheath being exposed to the one-sided action of gravity the
internode below, which is not itself sensitive to the stimulus, becomes
curved. The geolropic stimulus must have been conducted from the
sheathing leaf to the internode. In other grass seedlings (Poaeoideae)
it has been observed that the tip of the sheath is much more sensitive
to the geotropic stimulus than the zone of maximal growth, and a
similar diminution of the sensibility on passing backwards from the
tip holds for roots. It is possible with special apparatus to stimulate
geotropically in opposite directions the apex and growing zone of
such objects by centrifugal force, and to show that the curvature
of the growing zone is then determined by the stimulated tip. There
is thus a conduction of the stimulus in the basal direction which
overcomes the direct stimulation of the growing zone. In such cases
a clear separation of three processes is evident, the reception of the
stimulus (perception), the conduction of the stimulus and the reaction.
An organ may be perceptive without being able to react or conversely.
We are justified in assuming that these three parts of the process
must be distinguished in cases where they are not so evident.

It can be inferred from these experiments that the degree of
geotropic curvature and the rapidity with which it is produced in
no way measures the amount of the stimulus, since they are largely
dependent on the capacity for growth. The degree of geotropic
stimulation depends both on the specific receptivity of the stimulated
organ and on the amount of stimulus which it has received. For
any given organ it is directly proportional to the amount of stimulus.
By this is understood the product of the intensity of the stimulus
and the duration of its action. Thus, it is the same so far as result
is concerned, whether a high centrifugal force for a short time or a
less force for a correspondingly longer time be employed.

This law (104) holds good only within certain limits. It has been
shown that an orthotropous organ, when laid horizontally under
constant external conditions, begins to curve after a definite time.
The period from the commencement of stimulation to the commence-
ment of the reaction is termed the REACTION-TIME. To obtain a
geotropic reaction, however, it is not necessary to stimulate an organ

348 BOTANY

PART I

during the whole reaction-time. A much shorter period of stimulation
is sufficient to obtain a geotropic curvature as an after effect from the
organ which has been replaced in the vertical position. The minimal
period of stimulation after which a visible curvature results is termed
the PRESENTATION-TIME. The law of amount of stimulus only applies
to stimuli which last as long or somewhat longer than the presentation-
time ; the presentation-time is thus inversely proportional to the
intensity of the stimulus. No corresponding increase of geotropic
curvature follows larger amounts of stimulus.

Stimuli below the presentation time are not without effect. On
repetition they are summed up and result in a curvature when the
sum of separate stimuli amounts to the presentation-time, if the
intervals between the separate stimuli have not been too great. A
lower limit for the duration of separate stimuli has not as yet been
determined.

The law of amount of stimulus also applies when the centrifugal
force or gravity acts obliquely on an orthotropous part of a plant.
The effect of gravity diminishes in proportion to the sine of the angle
of incidence; if at 90° it = 1, it will be = 0'5 at 30°. Thus only the
pressure at right angles to the long axis is effective.

2. PHOTOTROPISM (HELIOTROPISM) (105)

A good opportunity for the observation of heliotropic phenomena
is afforded by ordinary window-plants. The stems of such plants do
not grow erect as in the open, but are inclined towards the window,
and the leaves are all turned towards the light. The leaf- stalks and
stems are accordingly ORTHOTROPIC and POSITIVELY PHOTOTROPIC.
In contrast to these organs the leaf -blades take up a position at
right angles to the rays of light in order to receive as much light as
possible. They are DIAPHOTOTROPIC, or TRANSVERSELY HELIOTROPIC,
in the strictest sense. If among the plants there should be one
with aerial roots, Chlorophytum for instance, an example of NEGATIVE
PHOTOTROPISM will be afforded, as the aerial roots will be found to
grow away from the window and turn towards the room. In Fig.
283 the phototropic curvatures which take place in a water culture
of a seedling of the White Mustard are represented.

Sensibility to phototropic influences is prevalent throughout the vegetable
kingdom. Even organs like many roots, which are never under ordinary
circumstances exposed to the light, often exhibit phototropic irritability. Positive
phototropism is the rule with aerial vegetative axes. Negative phototropism is
much less frequent ; it is observed in aerial roots, and sometimes also in climbing
roots (Ficus stipulate*,, Begonia scandens), in the hypocotyl of germinating
Mistletoe, in many, but not all, earth roots (Sinapis, Helianthus), in tendrils
(chiefly in those with attaching discs), and in the stems of some climbers. By
means of their negative heliotropic character, the organs for climbing and attach-

DIV. II

PHYSIOLOGY

349

ment, and the primary root of the Mistletoe, turn from the light towards, and are
pressed firmly against, their darker supports.

For more exact investigation of phototropic movements it is neces-
sary to be able to control more accurately the source and direction
of the light. This can be best accomplished by placing the plants in
a room or box, lighted from only one side by means of a narrow
opening or by an artificial light.
It then becomes apparent that
the direction of the incident rays
of light determines the photo-
tropic position ; every alteration
in the direction of the rays
produces a change in the position
of the phototropic organs. The
apical ends of many positively
heliotropic organs will be found
to take up the same direction
as that of the rays of light.

The exactness with which this is
done is illustrated by an experiment
made with Pilobolus crystallines (Fig.
284). The sporangiophores of this
fungus are quickly produced on moist
horse or cow dung. They are posi-
tively phototropic, and turn their
black sporangia towards the source
of light. When ripe these sporangia
are shot away from the plant, and
will be found thickly clustered about
the centre of the glass over a small
aperture through which alone the
light has been admitted ; a proof Fi<;. 283.— A seedling of the White Mustard in a

that the sporangiophores were all
previously pointed exactly in that
direction.

water culture which has first been illuminated
from all sides and then from one side only. The
stem is turned towards the light, the root away
from it, while the leaf blades are expanded at
right angles to the incident light. KK, Sheet of
cork to which the seedling is attached. (After
XOLL.)

The positive phototropic
curvatures are brought about

by THE SIDE TURNED TOWARDS

THE LIGHT GROWING MORE SLOWLY, AND THAT AWAY FROM THE LIGHT

MORE ACTIVELY, THAN UNDER ILLUMINATION FROM ALL SIDES. The

converse distribution of growth is found in negative phototropism.
As a rule CURVATURES ONLY TAKE PLACE IN THE REGION WHICH is

STILL IN A GROWING CONDITION, THE SHARPEST CURVATURE BEING AT
THE REGION OF MOST ACTIVE GROWTH.

The course of phototropic. curvature shows a complete correspondence with
geotropic curvature (p. 341). A. ENGLER has recently demonstrated phototropic

350

BOTANY

PART I

curvature even in trees where growth in length had ceased. It was formerly held
that the increased growth of the shaded side in positive phototropism was produced
by the beginning of etiolation, and that the diminished growth on the illuminated
side was due to the retarding effect which light exerts upon growth in length
(p. 289). This view has for some time been abandoned for good reasons ; it
cannot be maintained even in the modified form in which it has been recently
stated by BLAAUW (106). The fact that in many cases the curvature is far removed
from the region stimulated by light (p. 351) is especially opposed to this explanation.

It is evident from these considerations that it is not the difference
in the intensity of the light which causes the heliotropic curvatures,

but the direction in which
the most intense rays of
light enter the organs.
LIGHT ACTS AS A MOTORY
STIMULUS WHEN IT PENE-
TRATES AN ORGAN IN ANY
OTHER DIRECTION THAN
THAT WHICH CORRESPONDS
WITH THE POSITION OF
HELIOTROPIC EQUILIBRIUM.
Only one-sided illumination
can thus cause curvature in
a plant. If, without altering
the direction or the inten-
sity of the illumination, the
plant is kept in constant
rotation, around a vertical
axis, by means of clock-

FIG. 284.— Pilobolus crystallinus (P), abjecting its sporangia WOrk, the phototropic
towards the light. G, Sheet of glass ; B, opaque case , • i • , . f^

with a circular opening at F; M, vessel containing Stimuli acting on

horse-dung. (Of. description in text. After NOI.L.) different sides neutralise

one another and no cur-
vature takes place. This apparatus is known as a KLINOSTAT.

The phototropic curvatures are most strongly produced, just as in the case of
the heliotactic movements of freely moving swarm-spores, by the blue and violet
rays, while red and yellow light exerts only a much slighter influence. When a
plant receives on one side red light, and on the other side blue light, it turns
towards the latter, even when the red light is of greater intensity.

TRANSVERSE PHOTOTROPISM is confined almost solely to leaves and
leaf-like assimilatory organs, such as Fern prothallia and the thalli of
Liverworts and Algae. In these organs transverse phototropism, in
conformity with its great utility for assimilation, predominates over
all other motory stimuli. Such organs become placed at right angles
to the brightest rays of light to which they are exposed during their
development ; in this process torsions of the leaves or internodes
are combined with the simple curvatures.

DIV. ii PHYSIOLOGY 351

In very bright light the transverse position of the leaves may become changed to
a position more or less in a line with the direction of the more intense light rays.
In assuming a more perpendicular position to avoid the direct rays of the midday
sun, the leaf-blades of Lactuca Scariola and the North American Silphium laci-
niatum and the leaf- like shoots of some Cacti take the direction of north and south,
and so are often referred to as COMPASS PLANTS. The foliage leaf has thus, like
the chloroplast of Mesocarpus, the power of assuming either a profile or a full-
face position, and thus regulating the amount of light received.

A number of foliage leaves possess pulvini (Fig. 132) at the base of
the petiole, and also at the bases of secondary and tertiary branchings ;
variation movements are effected by the aid of these. In this way
these leaves are able to change their position throughout life, and at
any moment to assume the position which affords them the optimal
supply of light. " *rhey do not have a fixed light-position determined
by the strongest illumination during their development, but they
sometimes expose their edges and sometimes their surface to the light.

ALTERATION OF TONE (10T). — A particular part of a plant does not
react always in the same way to one and the same stimulus ; the mode
of reaction may be altered by age or other influences. In this sense
the terms " tone " and " change of tone " are used.

The flower-stalks of Linaria cymbalaria are at first positively phototropic.
After pollination, however, they become negatively phototropic, and as they
elongate they push their fruits into the crevices of the walls and rocks on which the
plant grows (p. 281).

Among external factors that alter the tone the amount of illumination itself is
particularly important. Small amounts of light falling from one side on Avena
produce without exception a positive phototropic curvature ; larger amounts give
a weaker positive soon followed by a negative curvature ; still larger amounts give
a purely negative reaction. With further increase in the illumination a positive
reaction is again obtained, and later a weakened positive if not a negative reaction.
How far the intensity of the illumination also influences the results cannot be
discussed here.

Phototropism, like geotropism, is a PHENOMENON OF IRRITABILITY (108).
In it the perception, conduction, and reaction of the stimulus can also
be distinguished ; there are also presentation-time and reaction-time.
Further, the law of amount of stimulus holds, and separate stimuli
which are individually ineffective can be added together to produce a
reaction.

Localisation of Phototropic Perception.— Often the stimulus of light is received
at the same place that the movement is effected. In certain leaves, however, the
lamina is able to perceive a phototropic stimulus without being able to carry out
the corresponding movement ; this takes place only after the stimulus has been
conducted to the leaf-stalk. It is true that the leaf-stalk can also react to direct
stimulation, but as a rule the dominant impulse proceeds from the lamina. Still
more striking relations are met with in the seedlings of certain Grasses ; in some
Paniceae only the tip of the so-called cotyledon can be phototropically stimulated,
and only the hypocotyledonary segment of the stem, separated by some distance

352 BOTANY PART i

from the tip of the cotyledon, is capable of curvature. In this case there is a well-
marked distinction between a perceptive organ and a motile organ ; the similarity
to corresponding phenomena in geotropism and in the animal kingdom is very
striking. There is an essential difference, however, in the method of transmission
of the stimulus; "Nerves" are completely wanting in the' plant, and the
stimulus is conveyed from cell to cell (109).

There is no doubt that the perception of light by the plant is closely connected
with photochemical processes. As to how the plant perceives the direction of the
light we are, however, ignorant (109°).

3. CHEMOTROPISM (no)

In the same way as light and gravity, heat and electricity, when
their action is one-sided, may bring about directive movements of the
plant. Since, however, these movements play no great part in nature
they need not be further considered. Those directive movements
which are brought about by the unequal distribution of dissolved or
gaseous substances in the neighbourhood of the plant are of much
greater importance ; these movements are termed chemotropic.

In the case of fungi and of pollen-tubes, chemotropic movements
have been demonstrated which bring the organism into a certain
concentration of particular substances ; this concentration is the
optimal one. With the same organism and the same stimulating
substance these movements are sometimes positive and sometimes
negative ; positive when they lead towards a higher concentration of
the substance, and negative in the converse case. In the case of
pollen-tubes sugar is the chief substance that acts as a stimulus ;
in fungi, in addition to sugar, peptone, asparagin, compounds of
ammonia and phosphates. There are also substances such as free
acids which always have a repellent influence even in extremely weak
concentration. Chemotropic irritability has also been demonstrated
in roots, though it cannot be said that it plays an important role in
their life.

In the examples of chemotropism given above, the stimulating
substances were solid substances in solution. When on the other
hand the plant is induced to perform directive movements by the
unequal distribution in a space of aqueous vapour or gases, a distinct
name has been required, though no distinction of principle can be
drawn. Irritable movements caused by differences in moisture are
termed HYDROTROPIC, while those brought about by gaseous differences
are termed AEROTROPIC. Aerotropism has been proved for pollen
tubes, roots, and shoots, and hydrotropism for roots and moulds.
Thus roots are positively hydrotropic and seek out the damper spots
in the soil by reason of this irritability. The sporangiophores of the
Mucorineae are negatively hydrotropic and thus grow out from the
substratum. These reactions may be so energetic as to overcome other
(e.g. geotropic) stimuli.

DIV. II

PHYSIOLOGY

353

4. HAPTOTROPISM (THIGMOTROPISM) (ni)

A curvature inwards on one-sided contact is found especially in
climbing plants which seek by such grasping movements to .encircle
the touching body and utilise it as a support. The arrangement
thus resembles what was seen in the case of twining plants, but the
movements are not in any sense geotropic. In the case of tendril-
climbers, the attachment to the support is effected, not by the main
axis of the plant, but by lateral organs of various morphological
character (cf. p. 182). These may either retain, at the same time, their
normal character and functions (as foliage leaves, shoots, or inflores-
cences), or, as is usually the case, become modified and as typical

tendrils serve solely as climbing
organs. Contact with a solid body
quickly induces an increase in the
growth of the opposite side of the
organ, and this, without any retarda-
tion of growth on the touched side,
leads to a sharp curvature of the
tendril which coils it about the

FIG. 285. — Surface views of cells from the
sensitive side of the tendril of CucurUta
Pepo, showing tactile pits, s. (x 540.
After STRASBURGFR.)

FIG. 286.— Transverse section through similar
cells to those in Fig. 68 ; a small crystal of
calcium oxalate (s) is present in the tactile
pit. (x 450. After STRASBURGER.)

support. The more slender the tendrils and the stronger their
growth, the more easily and quickly this process occurs. Owing to the
tendency of the curvature to press the tendrils more and more firmly
against the support, deep impressions are often made by them upon
yielding bodies, soft stems, etc.

According to PFEFFER'S investigations, it is of great importance to
the tendrils in the performance of their functions that they are not
induced to coil by every touch, but only through CONTACT WITH THE
UNEVEN SURFACE OF SOLID BODIES. Rain-drops consequently never
act as a contact stimulus; and even the shock of a continued fall
of mercury produces no stimulation, while a fibre of cotton-wool
weighing 0 '000 25 mgr. is sufficient to stimulate the tendril. Probably
the so-called tactile pits (Figs. 285, 286) favour the reception of such
weak stimuli. These are pits in the outer epidermal walls which

2 A

354

BOTANY

PART

widen outwards and are filled with protoplasm. They are found, for
instance, in the Cucurbitaceae, but may be wanting from some very
irritable tendrils (e.g. in Passiflora).

The tendrils of some plants (Cobaea, Eccremocarpus, Cissus) are
irritable and capable of curving on all sides ; others (tendrils of
Cucurbitaceae and others with hooked tips) are, according to FITTING,
sensitive on all sides but only curve when the under side is touched ;
if the upper surface is at the same time stimulated, curvature is
arrested. Some tendrils, only sensitive on one side, have the tactile

pits confined to this. In
some cases the tendrils
quickly grasp the support
(Passijiora, Sicyos, Bryonia) ;
while in other tendrils the
supports are very slowly
grasped (Smilax, Fit-is).

In the more typically de-
veloped tendrils the curvature
does not remain restricted to the
portions directly subjected to
the action of the contact stimu-
lus. Apart from the fact that,
in the act of coiling, new portions
of the tendril are being continu-
ally brought into contact with
the support and so acted upon
by the stimulus, the stimulation
FIG. 287.— Portion of a stem of Sicyos angulatus, one of the to curvature is also transferred
Cucurbitaceae, with tendril. The branch-tendril has to the portions of the tendril
grasped the upright support on the right and the not in contact with the support.
free portion has become spirally wound, x, Point of

reversal in the coiling of the tendril. (After NOLL.) Through the action of the propa-
gated stimulus, not only is the

free apex of the tendril twined more quickly around the support, but a tendency
to curvature is imparted to the portion of the tendril between the support and
the parent shoot. As this intervening part is extended between two fixed points,
this tendency causes it to coil spirally, like a corkscrew. With the spiral coiling
a torsion is produced, and since, on account of the fixed position of the two end
points, it cannot be exerted in one direction only, the spiral, for purely mechanical
reasons, coils partly to the left and partly to the right. POINTS OF REVERSAL (x)
thus occur in the windings which, in equal numbers to the right and to the
left, equalise the torsion (Fig. 287). By the spiral coiling of the tendrils the
parent-stem is not only drawn closer to the support, but the tendrils themselves
acquire greater elasticity and are enabled to withstand the injurious effects of a
sudden shock.

Advantageous changes also take place in the anatomical structure of the tendrils
after they are fastened to the supports. The young tendrils, during their rapid
elongation, which under favourable conditions may amount to 90 per cent of their
length, exhibit active nutations, and thus the probability of their finding a support
is enhanced. During this time they remain soft and flexible, while the turgor

DIV. ii PHYSIOLOGY 355

rigidity of their apices is maintained only by collenchyma. In this condition they
are easily ruptured, and have but little sustaining capacity. As soon, however, as
a support is grasped, the coiled-up portion of the tendril thickens and hardens,
while the other part lignifies and becomes so strengthened by sclerenchymatous
formations that the tendril can finally sustain a strain of many pounds. When
the tendrils do not find a support they usually dry up and fall off, but in some
cases they first coil themselves into a spiral.

Tendril -climbers are not, like twining plants, restricted to nearly vertical
supports, although, on account of the manner in which the tendrils coil, they can
grasp only slender supports. A few tendril-climbers are even able to attach them-
selves to smooth walls. Their tendrils are then negatively phototropic, and

FIG. 288. — Lophospermum scandens climbing by means of its tendril-like petioles.
(After NOLL.)

provided at their apices with small cushion-like outgrowths, which may either
develop independently on the young tendrils, or are first called forth by contact
irritation. These cushions become fastened to the wall by their sticky excretions
and then grow into disc-like suckers, the cells of which come into such close
contact with the supporting wall that it is easier to break the lignified tendrils
than to separate the holdfasts from the wall. Fig. 210 represents the tendrils of
Parthenodssus tricuspidata. The suckers occur on its young tendrils in the form
of knobs. In other species of Wild Vine the suckers are only produced as the
result of contact, and the tendrils of these plants are also able to grasp thin
supports.

Sometimes, as in the case of Lophospermum scandens (Fig. 288), the leaf-stalks,
although bearing normal leaf -blades, are irritable to contact stimuli and
function as tendrils. Of leaf-stalks which thus act as tendrils, good examples are
afforded by Tropaeolum, Maurandia, Soldnum jasminoides, Nepenthes, etc. In
other cases the midribs of the leaf-blades themselves become prolonged, and assume
the function of tendrils (Gloriosa, Littonia, Flagellaria}. In many species of
Fumaria and Corydalis, in addition to the leaf-stalks, even the stalks of the

356 BOTANY PART i

leaflets twine around slender supports, while the parasitic shoots of Cuscuta (Fig.
221) are adapted for both twining and climbing. In many tropical plants
axillary shoots are transformed into tendril-like climbing hooks. Climbing parts
of the thallus occur in some Thallophyta (Florideae).

More recent investigations have shown that haptotropism is more widespread
than was previously supposed. Etiolated seedlings are always haptotropic, and
this holds frequently for older shoots of green plants, especially of twining and
climbing plants. No use appears to attach to this power (112). The roots of
seedlings are only exceptionally irritable to contact.

(b) Nastie Movements (113)

In the tropistic and tactic movements of irritability, the direction
of the stimulus stands in direct relation to the direction of the move-
ment; the nastic movements, on the other hand, are either brought
about by diffuse stimuli with no definite direction or are not influenced
by the direction of the stimulus. The direction of the movement
always depends on the reacting organ and not on the environment,
the movements are not movements of orientation such as those we
have hitherto considered.

Typical nastic movements of variation are shown by stomata ; the structural
relations of these determines the opening or closing of the pore by changes in the
curvature of the guard-cells brought about by variations in their turgescence. It is
frequently assumed that the closing on loss of water and the opening on illumina-
tion are purely mechanical results. Loss of water will have as its direct result a
diminution of the osmotic pressure, and illumination will increase the pressure by
increasing the production of assimilates. It cannot, however, be doubted that in
addition to purely physical influences true stimulus-movements also take place.
Thus light and some other factors also may act as stimuli directing the production
of osmotic substances by the protoplasm in particular directions.

In other nastic movements, as in the case of the stomata, light and
heat, chemical substances, and sometimes also vibrations, may play the
part of stimuli. Often the movement of a particular organ results
from several of these stimuli in the same or in different ways.

1. NYCTINASTIC MOVEMENTS (m)

Many foliage leaves and floral leaves assume different positions by
day and by night. According as the change from the one position to
the other is brought about by variations in the intensity of light, in
the temperature, or in both factors at once, we distinguish between
photonasty, thermonasty, and nyctinasty. The movements are carried
out partly as growth-movements, partly as variation-movements.

1. THERMONASTY. — Growth - movements due to variations in
temperature are found especially in flowers, e.g. Crocus, Tulip,
Ornithogalum, Cokhicum, and Adonis. These flowers on a rise of
temperature exhibit a sudden and limited acceleration of the growth

DIV. ii

PHYSIOLOGY

357

of the inner side of their perianth-leaves or petals. The flowers
consequently open. On the other hand, they close on a fall in the
temperature.

The flowers of the Tulip and Crocus are especially sensitive to changes of
temperature. Closed flowers brought from the cold into a warm room open in a
short time ; with a difference of temperature of from 15°-20° they open in two to
five minutes. Sensitive flowers of the Crocus react to a difference of £° C. ; those of
the Tulip to 2°-3° C.

2. PHOTONASTY. — In a similar fashion other flowers (Nymphaea,
Cacti) and also the flower heads of Compositae (Fig. 289) open on
illumination and close on darkening. The night-flowering plants
such as Silene noctiftora and
Victoria regia behave in an
opposite manner.

The significance of these move-
ments must lie in only exposing the
sexual organs when insect- visits may
be expected ; at other times they are
protected against injury by rough
weather, especially by rain. These
plants are adapted to pollination by
moths.

3 NYCTINASTY _ Manv ^IG' ^* — Flower-head of Leontodon hastilis, closed
, . i M '• • when kept in darkness, open when illuminated.

foliage leaves exhibit nyctl- (From DETMER'S Physiol. Pract.)

nastic movements which are

usually influenced more by light than by temperature. In some
cases (e.g. in Chenopodiaceae, Caryophyllaceae, Balsamineae, and some
Compositae) these movements are entirely growth-movements as in
the floral leaves ; in the Leguminosae, Oxalideae, and other plants
provided with pulvini, variation-movements are found. The former
are naturally of short duration and cease when the leaves are full-
grown. The latter, however, continue for a long period. In the
movements of variation an increase of turgor probably takes place
in darkness in both halves of the pulvinus, but more weakly or
slowly on the concave side. The night- or sleep-position is always
characterised by a vertical position of the laminae, the leaf-stalk or
the pulvinus curving either upwards or downwards; the laminae
themselves have thus either their under or upper faces turned out-
wards. In the day-position the surfaces stand horizontally or at right
angles to the incident light (p. 351) (Fig. 290)..

That these phenomena are not due to phototropism is shown by the day-position
being assumed whether the under or the upper side is more strongly lighted or
when the illumination is equal. The same holds for the effect of darkness.

The significance of the vertical position assumed by foliage leaves at night is
regarded by STAHL as consisting in the diminution of the formation of dew and the

358

BOTANY

consequent favouring of transpiration. The fact that the stomata lie on the surface
protected in the sleep-position may be noted with regard to the furthering of
transpiration.

Excessively high temperature or illumination causes the leaves to depart from
the usual day-position and to assume a different one ; this is either externally

FIG. 290.— Amicia zygomeris, showing diurnal and nocturnal position of leaves.

similar to the night-position or is diametrically opposite to this. Thus the leaflets
of fiobinia are bent downwards at night, in diffused daylight they are spread out
flat, while in the hot mid-day sunlight they stand vertical. This so-called diurnal
sleep is only found in leaves with pulvini and is brought about in a different way
to the evening change of position ; there is no increase of turgescence but a condition
of flaccidity, which is unequal on the two sides of the pulvinus.

PERIODIC MOVEMENTS (115)

When a plant has carried out regular nyctinastic movements for a long period
under the influence of the alternation of day and night, the periodic movements con-
tinue for some days in constant light or constant darkness. In some plants it is
possible to bring about experimentally a shorter or longer period of change than the
usual one of twenty-four hours ; this new periodicity also shows an after effect.

On the other hand it is established that, in certain flowers (Calendula] and
leaves (Phaseolus), there are also movements with a period of 24 hours, determined
not by the rhythm of light and darkness or their after effect. The possibility
that these movements are antonomous is excluded. Their cause is unknown
but there is much in favour of the view of STOPPEL that variations in the electrical
conductivity of the atmosphere are of importance in determining them. It is
true that there is no exact basis for this view.

2. CHEMONASTY (116)

Chemonasty bears the same relation to chemotropism as photonasty
does to phototropism. From whatever side a chemical stimulus (such as
the vapour of ether, chloroform, or ammonia) acts on a sensitive tendril
the same side of the latter always becomes concave ; this is the side
which is especially sensitive to haptotropic stimulation.

DIV. ii PHYSIOLOGY 359

These chemonastic curvatures of tendrils are evidently of no use to the plants.
The same is the case for the nastic movements of tendrils which take place on
wounding and on rise of temperature (traumatonasty, thennonasty). On the
other hand, chemonastic movements play an important part in some insectivorous
plants.

Very striking chemonastic movements are exhibited by the tentacles
of Drosera (Fig. 214). On chemical stimulation these curve so that
their upper sides become concave and the glandular heads are thus
brought towards the centre of the circular leaf. Such substances as
albumen, phosphates, etc., which Drosera can use as food, serve as stimuli
(p. 258) ; so also can indifferent and even poisonous substances. Often
minimal traces of these substances (e.g. 0'0004 mgr. of ammonium
phosphate) suffice to bring about the irritable movement ; when the
stimulus is applied to the summit of the tentacle it leads to the
curvature at the base of the latter. There is thus in this case as in
certain phototropic curvatures, but even more clearly than in these,
a separation between the organ of perception which receives the
stimulus and the motile organ that effects the movement. The
stimulus received by the head of the tentacle must be conducted to
the base of the latter.

An insect that has settled on a marginal tentacle will be brought
by this curvature to the centre of the lamina. The short -stalked
tentacles borne here send a stimulus to all the marginal ones, causing
them to curve inwards. The insect is thus surrounded by many
glands and covered with their digestive secretion.

The curvature resulting from growth is carried out in the same way as in
tendrils. After curvature the tentacle has become considerably longer. When
growth ceases, the motility of the tentacles is ended so that they can only close
over a limited number of times. Further, the tentacles of Drosera in common with
tendrils can exhibit thigmonastic, traumatonastic, and thermonastic reactions.
Doubtless, however, their chemonastic irritability is the main and most important
one. Chemical stimuli are concerned in the movements of other insectivorous
plants, e.g. Dionaea and Pinguicula.

3. SEISMONASTY (m)

In Dionaea the two halves of the leaf -blade (Fig. 217) close
together not only as a result of chemical stimuli but also owing to a
mechanical stimulus. In contrast to the haptotropic movements of
tendrils or of Drosera resulting from contact with solid bodies, in the
case under consideration every disturbance resulting from a mechanical
shock acts as a stimulus ; the movement can thus be brought about
by rain-drops. These movements are termed seismonastic.

The most familiar example of seismonastic movements is furnished
by Mimosa pudica, a tropical leguminous shrubby plant, which owes
its name of sensitive plant to its extreme sensitiveness to contact.

360 BOTANY PART i

The leaves of this plant are doubly compound (Fig. 291). The
four secondary leaf - stalks, to which closely crowded leaflets are
attached left and right, are articulated by well-developed pulvini with
the primary leaf-stalks ; while they, in turn, as well as the leaflets,
are similarly provided with motile organs. Thus all these different
parts are capable of independent movement, and the appearance of
the entire leaf becomes, in consequence, greatly modified. In their
unirritated, light position (Fig. 291, on the left) the leaf -stalk is
directed obliquely upwards, while the secondary petioles with their
leaflets are extended almost" in one plane. Upon any vibration of

FIG. 291.— Mimosa pudica, with leaves in normal, diurnal position ; to the right, in the position
assumed on stimulation ; B, inflorescences.

the leaf, in favourable conditions of temperature (25°-30° C.) and
moisture, all its parts perform rapid movements. The leaflets fold
together, and, at the same time, move forward, the secondary petioles
lay themselves laterally together, while the primary leaf-stalk sinks
downwards (Fig. 291, on the right). Leaves thus affected, if left
undisturbed, soon resume their former position.

The behaviour of the leaves is still more remarkable when only a
few of the leaflets are acted upon by the stimulus. This is easily
demonstrated by holding a burning match near the leaflets of one of
the pinnae. The leaflets directly affected by the flame fold quickly
upwards, and this movement is performed successively by each pair of
leaflets of the pinna until the articulation with the primary leaf-
stalk is reached. The stimulation is then conveyed to the other
pinnae, the leaflets of which go through the same movement in the

DIV. ii PHYSIOLOGY 361

reverse order ; finally, the secondary petioles themselves draw together.
Suddenly, when the whole process seems apparently finished, the
main leaf -stalk in turn makes a downward movement. From this
leaf the stimulus is able to travel still farther through the stem, and
it may thus induce movement in leaves 50 cm. distant. The stimulus
can also be conducted from the roots to the leaves. In this case we
are dealing with a wound -stimulus which has far-reaching effects.
On otherwise disturbing the plant we also find a conduction of the
stimulus which, it is true, is not so extensive. '

The rate of conduction of the stimulus (118) may attain after wounding 10 cm.
and after contact 3 cm. per second, and thus be of considerable rapidity. It is,
however, greatly below the conduction of tlie stimulus along human nerves.
While it is not yq£ known with certainty how the stimulus is conducted in
Mimosa, it is clear that the process differs both from the conduction along nerves
and from that in other cases in plants. The stimulus can certainly be carried
across killed regions ; it probably passes along the tracheides of the xylem and
depends on the movement of water. Mimosa, thus reacts not only to the stimulus
of shock but to that of wounding, and the same movements of the leaves follow on
electric shocks, sudden changes of temperature, and chemical stimuli.

The position of a disturbed leaf is externally similar to its sleep- or night-position,
but the conditions of tension in the pulvinus which lead to the two positions differ.
The seismonastic, like the sleep-position, is caused by variations in turgor, but
depends on a diminution of the osmotic pressure and a flaccid condition of the half
of the pulvinus that becomes concave. This condition can be most clearly recog-
nised in the irritable under side of the main pulvinus of the leaf ; it is connected
with an escape of liquid from the cells into the adjoining intercellular spaces.

Many Leguminosae and Oxalideae are similar but less irritable. Thus Robinia
pseudaeacia and Oxalis acetosella exhibit slight movements on strong mechanical
stimuli. These are much less considerable than in Mimosa. Movements of the
leaves in response to wounding also are not confined to Mimosa.

The power of reaction to stimuli in Mimosa evidently depends
on external factors, and each of these when in excess or lacking may
lead to a state of rigor. Whenever the temperature of the surround-
ing air falls below a certain level (15°), no movements take place, and
the whole plant passes into a condition known as COLD RIGOR, while,
on the other hand, at a temperature of about 40°, HEAT RIGOR occurs.
DROUGHT RIGOR is induced, just before withering, by an insufficient
supply of water, and a DARK RIGOR by a prolonged retention in
darkness. In a vacuum, or on exposure to hydrogen and other gases
—chloroform vapour, coal gas, etc. — movement also ceases, partly on
account of insufficient oxygen, and partly from the actual poisonous
action of the gases themselves. If the state of rigor is not continued
too long, the original irritability will again return on the restoration
of normal conditions. Similar conditions of rigor are met with in
other cases of irritability.

The variation-movements exhibited by the staminal leaves of some Berberi-
daceae (Berberis, Mahonia} and Compositae, especially beautifully by Centaurea

362

BOTANY

PART I

americana, bear a certain relation to those of foliage leaves. The bow-shaped fila-
ments of the stamens of the Compositae straighten upon mechanical irritation. As

they frequently contract 10-20 per cent
of their length, the style becomes ex-
tended beyond the anther-tube (Fig.
292). The reduction in the length of
the filaments is accompanied by a moder-
ate increase in their thickness, due to the
elastic contraction of the cell walls, and
the consequent expulsion of water into
the intercellular spaces. The stamens
of Berleris and Mahonia are only sensi-
tive to contact on the inner side near the
base, and as their contraction occurs only
on the inner side, the anthers are thus
brought into contact with the stigma.

The two lips of the stigmas of Mimu-
lus, Goldfussia, Marty nia, Torenia, and
other plants close together when touched.
In a short time they open and are again
seismonastically sensitive. Opening
also takes place when pollen has been
brought to the stigma and germinated
on it. The destructive effect of the
pollen leads, however, to a closing

movement which is not a phenomenon

.. ., , .,.,
of irritability.

FIG. 292. — A single- flower of Centaurea jacea with
perianth removed. A, Stamens in normal
position; B. stamens contracted; c. lower
part of tubular perianth; ,, stamens; a,
anther - tube ; g, style ; P, pollen. (After
PFEFFER, enlarged.)

While SClSttlOnasty IS a peculiar

form of irritability, it is also the
extreme form of haptotropism. There are plants which exhibit a
perception intermediate between irritability to contact and to shock.
This applies to certain etiolated seedlings, the haptotropism of which
was mentioned above ; a jet of water or gelatine is sufficient to
stimulate them, though more weakly than stroking with solid
bodies (119).

PART II
SPECIAL BOTANY

DIVISION I
THALLOPHYTA. BEYOPHYTA. PTERIDOPHYTA.

SPECIAL BOTANY

SPECIAL Botany is concerned with the special morphology, physiology,
and ecology of plants. While it is the province of general botany to
ascertain the laws that hold for the structure, vital processes, and the
adaptations in the whole vegetable kingdom, it is the task of special
botany to deal with the separate groups of plants. It is the endeavour
of special morphology to obtain some insight into the PHYLOGENY OF
THE VEGETABLE KINGDOM by morphological comparison of the manifold
types of plants. The solution of this problem would provide the key
for the construction of a NATURAL SYSTEM of classification of plants
based upon their actual relationships. Such a system must necessarily
be very imperfect, as it is not possible to determine directly the
phylogenetic connection of different plants, but only to infer their
relationships indirectly from morphological comparisons.

Such a natural system, founded on the actual relationship existing
between different plants, stands in direct opposition to the ARTIFICIAL
SYSTEM, to which has never been attributed more than a practical
value in grouping the plants in such a manner that they could easily
be determined and classified. Of all the earlier artificial systems,
the sexual system proposed by LINNAEUS in the year 1735 is the
only one which need be considered.

LINNAEUS, in establishing his classification, utilised characteristics which referred
exclusively to the sexual organs, and on this basis distinguished twenty-four classes
of plants. In the last or twenty-fourth class he included all such plants as were
devoid of any visible sexual organs, and termed them collectively CRYPTOGAMS.
Of the Cryptogams there were at that time but comparatively few forms known, and
the complicated methods of reproduction of this large group of plants were absolutely
unknown. In contrast to the Cryptogams, the other twenty-three classes were dis-
tinguished as PHANEROGAMS or plants whose flowers with their sexual organs could
be easily seen. LINNAEUS divided the Phanerogams, according to the distribution
of the sexes in their flowers, into such as possessed hermaphrodite flowers (Classes
I. -XX.), and those in which the flowers were unisexual (XXI. -XXIII.). Plants
with hermaphrodite flowers he again divided into three groups : those with free
stamens (I. -XV.), which he further distinguished according to the number, mode
of insertion, and relative length of the stamens ; those with stamens united with
each other (XVI. -XIX.) ; and those in Avhich the stamens were united with the
pistil (XX.). Each of the twenty-four classes was similarly subdivided into

365

366 BOTANY PART n

orders. While some of the classes and orders thus constituted represent naturally
related groups, although by the method of their arrangement in the artificial
system they are isolated and widely removed from their proper position, they
include, for the most part, plants which phylogenetically are very far apart.

LINNAEUS himself (1738) felt the necessity of establishing natural
families in which the plants should be arranged according to their
"relationships." So long, however, as the belief in the immutability
of species prevailed, the expressions relationship and family could
have no more than a hypothetical meaning, and merely indicated a
supposed agreement between plants having similar external forms.
A true basis for a natural system of classification of organisms was
first afforded by the theory of evolution.

The system adopted as the basis of the following description and
systematic arrangement of plants is the natural system of ALEXANDER
BRAUN, as modified and further perfected by EICHLER, ENGLER,
WETTSTEIN, and others.

The vegetable kingdom may be divided into the following four
main groups :

1. Thallophyta.

2. Bryophyta.

3. Pteridophyta.

4. Spermatophyta.

DIVISION I
THALLOPHYTA. BRYOPHYTA. PTERIDOPHYTA

Since the time of LINNAEUS the Thallophytes, Bryophytes, and
Pteridophytes have been termed collectively Cryptogams in contrast
to the Phanerogams or Spermatophyta. These two main divisions are,
however, of unequal systematic value, for the lower Phanerogams
approach the Pteridophyta, from which they have originated, more
closely than these most highly developed Cryptogams approach the
Bryophyta. The Bryophyta and the Thallophyta agree in being
composed of more or less uniform cells, and are contrasted as CELLULAR
PLANTS with the VASCULAR PLANTS comprising the Pteridophyta and
Spermatophyta. Since, however, the Bryophyta and Pteridophyta
agree in many respects, and appear to have diverged from a common
source, the distinction of cellular and vascular plants must not be too
strongly insisted upon.

The Spermatophyta are distinguished by their distribution by
means of SEEDS from the Cryptogams, which form SPORES. Spores

DIV. i THALLOPHYTA 367

are unicellular structures which become separated from the parent plant,
and form the starting-point of the development of a new individual.
The Cryptogams might, therefore, be termed spore-bearing plants. The
seed-plants also produce spores, but the sporangium and contained spore,
which as a special structure develops into the seed, continues its
development while still connected with the parent plant, the seeds
being ultimately separated from this.

The distinctions between the Thallophytes, Bryophytes, and
Pteridophytes are briefly the following :

The THALLOPHYTA include a great variety of plants, the
vegetative portion of which may consist of one or many cells in the
form of a more or less branched thallus. Reproduction is both
sexual and asexual, but there is usually no definite succession of the
two modes of reproduction. An alternation of generations only
appears in the higher forms.

The BRYOPHYTA and PTERIDOPHYTA exhibit a regular alternation
of two generations in their life-history. The asexual generation forms
spores, and is called the SPOROPHYTE. From the spore the sexual
generation or GAMETOPHYTE develops; this bears sexual organs of
characteristic construction, the male organs being called antheridia,
and the female organs archegonia. From the egg-cell contained in
the latter, after fertilisation, the sporophyte again arises.

In the BRYOPHYTA the plant body is always a thallus, although in
the higher Mosses there is a segmentation into stems and leaves. The
Bryophytes possess no true roots, and their conducting bundles, when
present, are of the simplest structure. The sporophyte is a stalked
or unstalked capsule, which lives semi-parasitically on the sexual plant.

The PTERIDOPHYTA have small thalloid gametophytes ; the sporo-
phytes exhibit a segmentation into stems, leaves, and roots, and also
possess true vascular bundles ; they thus resemble the Spermato-
phyta in structure.

The Bryophyta and Pteridophyta are united as the Archegoniatae on account
of the structural agreement in their female reproductive organs or archegonia.
These organs are also present in a somewhat simplified form in the lower Spermato-
phyta (in most Gymnosperins), so that a sharp line cannot be drawn between the
Archegoniatae and higher groups of plants.

I. THALLOPHYTA (^

It was formerly customary to divide the Thallophyta into
Algae, Fungi, and Lichens. The Algae are Thallophytes which
possess chromatophores with pigments, particularly chlorophyll ;
they are, therefore, capable of assimilating and providing inde-
pendently for their own nutrition (autotrophic). The Fungi, on the
other hand, are colourless and have a saprophytic or parasitic mode

BOTANY PART ii

of life (heterotrophic). There are also Algae which are not strictly
autotrophic but can in greater or less degree employ organic substances
in their metabolism ; these mixotrophic forms succeed well in impure
water. 'Such a method of classification, however, although possessing
a physiological value, has no phylogenetic significance, as it does not
express the natural relationships between the various groups. In
the Lichens (Lichenes), which were formerly regarded as simple
organisms, the thallus affords an instance of a symbiosis of Algae
and Fungi. From a strictly systematic standpoint, the Fungi and
Algae composing the Lichens should be classified separately, each in
their own class ; but the Lichens, among themselves, exhibit such a
similarity in structure and mode of life, that a better conception of
their characteristic peculiarities is obtained by their treatment as a
distinct class in connection with the Fungi.

The phylogenetic connections of the fourteen classes into which
the Thallophyta are divided are expressed, so far as is possible, in
the following scheme :

^Bacteria, Bacteria.
Cyanophyceae, Blue-green Algae.

Myxomyeetes, Slime-Fungi.
mm^Dinoflagellatae, Dinoflagellates.
Diatomeae, Diatoms.
Conjugatae, Conjugates.
iHeterocontae.

•Chlorophyceae, Green Algae.

I~JL U 7 O

1*+mRhodophyceae, Ked Algae.

•Eumycetes, Fungi.
•Phycomycetes, Algal Fungi.
*Phaeophyceae, Brown Algae.
tCharaceae, Stone-worts.

The Bacteria and Cyanophyceae are among the most simply organised Thallo-
phyta ; they are closely connected and are often grouped together as the Schizo-
phyta. They occupy an isolated position in contrast to the remaining simple
Thallophytes, which with greater or less probability may be derived from the
Flagellatae. The Flagellatae used to be (and frequently still are) placed with the
lowest animals. As a matter of fact they combine plant and animal characteristics,
and may also be regarded as the starting-point of the lower animals. The
Myxomycetes may also have sprung from them as a group of colourless saprophytes.
The Peridineae are a further developed branch of the Flagellatae. The simplest
forms among the Heterocontae, the Green Algae, and the Phaeophyceae connect
directly with the Flagellata ; on the other hand, a direct connection of the latter
with the Conjugatae and Diatomeae presents greater difficulty.

The Phycomycetes have branched off from the main series of the Chlorophyceae.
The origin of the Red Algae and the Eumycetes, which appear to have sprung from
a common stock, is still in doubt. The Characeae occupy a quite isolated and very
advanced position, and have usually been regarded as the most highly developed

DIV. i THALLOPHYTA 369

of the Green Algae ; they appear to be connected in important characters with
the Brown Algae.

The Thallophytes are commonly multiplied and distributed by
asexually produced SPORES, the mode of development of which differs
in the several groups. In many cases the spores arise by a process
of cell division within certain cells, which are known as SPORANGIA ;
in other cases they arise by modification and separation of cells of
the thallus or by a process of cell-budding. When the spores possess
cilia and are able to move actively in the water, they are known as
swarm-spores (zoospores) ; when they do not bear cilia they are
termed aplanospores. In the latter case the spores if distributed
by water may be naked, or they may be provided with a cell wall
and suited for distribution in the air.

Sexual reproduction is also of widespread occurrence. It
consists, in the simplest cases, in the production of a single cell,
the ZYGOSPORE or ZYGOTE, by the union or conjugation of two
similarly formed sexual cells or gametes (iSOGAMY). The organs in
which the gametes are formed are termed GAMETANGIA ; planogametes
are provided with cilia while aplanogametes are non-ciliated. In
many of the more highly developed forms, however, the gametes are
differentiated as small, usually ciliated, male cells or SPERMATOZOIDS,
arid as larger non-ciliated female cells, the egg-cells or OOSPHERES.
The spermatozoids are formed in ANTHERIDIA, the oospheres in OOGONIA.
The zygote which results from the fertilisation of an oosphere by a
spermatozoid is known as an OOSPORE when it passes into a resting
condition ; it may, however, in certain groups commence its develop-
ment at once. It must be assumed that the sexual cells have been
derived in the phylogeny of plants from asexual spores. The
gametangia, oogonia, antheridia, and sporangia of the Thallophyta
are homologous structures. The sexual reproduction has originated
independently in several distinct groups.

While the reproduction of some Thallophyta is exclusively asexual, and of others
exclusively sexual, in many others both forms of reproduction occur. In the latter
case this may occur on the one plant, or separate successive generations may be
distinguishable. Generally speaking, there is, however, no regular succession of
asexual and sexual generations in Thallophytes, the mode of reproduction being to
a great extent under the influence of external conditions (2). Only in some Brown
Sea-weeds, in the Red Sea-weeds, and some Fungi is there an alternation of a
sexual generation (gametophyte) with an asexual (sporophyte), such as is found
in all Bryophytes and Pteridophytes.

In the union of the two sexual cells the fusion nucleus obtains the 'double
number of chromosomes ; it becomes DIPLOID while the sexual cells always have
HAPLOID nuclei. A REDUCTION DIVISION of the diploid nucleus to the haploid
must therefore occur in the course of the ontogenetic development and a distinc-
tion can thus be made between a haploid and a diploid phase in the life-history
of the plant. The reduction division in many groups of Thallophyta takes place
in the germinating zygote. It may, however, occur at different stages even in the

370 BOTANY PART n

same natural group and is thus not necessarily connected with the commencement of
a new generation. In certain Brown Algae and in all Archegoniatae the reduction
takes place in the sporangia so that the gametophyte is regularly haploid and
the sporophyte diploid. The nuclear difference cannot, however, be regarded as
determining the specific structure of the alternating generations.

The reproductive cells (swarm-spores, gametes) of the classes of Thallophyta
which can be derived from the Flagellata are in many cases ciliated, naked proto-
plasts resembling the cells of Flagellates. Even in the Bryophyta and Pterido-
phyta, and also in the Cycadeae and Ginkgoaceae, the male gametes, though
also secondarily modified, exhibit this return during the ontogeny to the phyletic
original form.

CLASS I
Bacteria (l> 3-9)

Bacteria are unicellular or filamentous organisms of very simple
construction. Chlorophyll is wanting in them, and their mode of
life is usually a parasitic or saprophytic one. A large number
of species exist distributed over the whole earth, in water, in the
soil, in the atmosphere, or in the bodies of dead or living plants and
animals. They are often termed Fission Fungi, or Schizomycetes,
since the multiplication of the unicellular forms takes place by a
division into two and the separation of the segments. This mode
of multiplication is also found in other unicellular plants.

The cells of the Bacteria are surrounded by a thin chitinous
membrane, and contain a protoplasmic body, which is usually
colourless, and can be made to contract away from the membrane
by plasmolysis. The protoplasm may contain one or more vacuoles.
One or several granular structures are also present in the protoplast ;
these so-called chromatin bodies may be deeply coloured by stains,
and have been regarded as nuclei by various authors. Since, as yet,
undoubted karyokinetic division has not been observed in these
bodies, the presence of nuclei in the bacterial cell cannot be regarded
as certainly established.

For the most part the Bacteria are extraordinarily minute organ-
isms, and probably include the smallest known living beings. The
spherical cells of the smallest forms are only 0*0008 mm. in
diameter; the rod-shaped cells of the tubercle bacillus are only
0*0015-0*004 mm. long, while most species are about 0*001 mm.
broad and 0*005 mm. long.

The simplest forms of Fission Fungi are minute spherical
cells, COCCI. Forms consisting of rod-shaped cells are designated
BACTERIUM or BACILLUS. Kod-shaped forms with a slight spiral
curvature are called VIBRIO, and those more strongly curved SPIRILLUM.
The unicellular cocci, rod-shaped forms, and vibrios may also remain
united in chains after the cell division. Frequently the cell membranes

DIV. I

THALLOPHYTA

371

undergo a mucilaginous swelling, the cells or cell-rows being embedded
in the gelatinous mass. This stage of development is termed ZOOGLOEA.

In contradistinction to these unicellular HAPLOBACTERIA the
TRICHOBACTERIA form filaments which as a rule are simple (Leptothrix,
Beggiatoa, Crenothrix). In Cladothrir, however, they exhibit what is
termed false branching. This comes about by the distal portion of
the filament being left on one side while the original line is continued
by the division of the cell behind the break.

Many Bacteria are motile. Their independent movements are
due to the vibration and contraction of fine protoplasmic cilia (*°)m
These cilia, according to A. FISCHER, are either distributed over
the whole surface of the cells (peritrichous) (e.g. Bacillus subtilis, Fig.
295 a, d • Bacillus typhi, Fig. 293 c; Bacillus tetani, Fig. 298 e), or

FIG. 2i'3.— Types of arrangement of flagella. a,
Vibrio cholerae ; b, d, Spirillum undula ; d,
development of a new bunch of cilia in divi-
sion ; c, Bacillus typhi ; e, Bacillus subtilis.
(x 22oO. After A. FISCHER.)

FIG. 294. — Cladothrix dichotoma. Formation
of swarm-cells from the .cells of the fila-
ment, (x 1000. After A. FISCHER.)

they spring from a single point either as a single flagellum (mono-
trichous) or as a group (lophotrichous). A single, polar flagellum
occurs in Vibrio cholerae (Fig. 293 a) ; a polar terminal tuft of
flagella in Spirillum undula (Fig. 293 b, d) ; a lateral tuft in the
swarm-spores of Cladothrix (Fig. 294). The ciliary tufts may become
so closely intertwined as to present the appearance of a single thick
flagellum. The cilia are never drawn within the body of the
cell, but undergo dissolution before the formation of spores takes
place, or under unfavourable conditions (Fig. 293 e).

Multiplication of the individual is accomplished vegetatively by
the active division or fission of the cells ; the preservation and dis-
tribution of the species by the asexual formation of resting spores.
These arise as endospores (Figs. 295 c, 296 e, j) in the middle or
at one end of a cell by the inner portion of the protoplasm separat-
ing itself from the peripheral, and surrounding itself with a thick
membrane. The membrane of the mother cell becomes swollen and

372

BOTANY

PART II

disintegrated when the spore is ripe. Spores are not found in all
species.

Order 1. Haplobaeteria. UNICELLULAR BACTERIA

This includes the great majority of the species.

Although the cycle of forms passed through in the life-history of a Bacterium
is a very simple one, the individual species, which can often be barely dis-
tinguished by morphological characters, show great variety in their metabolic
processes and in their mode of life. The majority of Bacteria require oxygen for
their respiration, and are therefore aerobic ; many can, however, develop without

this gas, while some species, e.g.
the butyric acid bacterium and the
tetanus bacillus, are strictly anae-
robic and only succeed in the absence
of oxygen. Some bacteria produce
by their respiration considerable
heat ; this is the explanation of
the spontaneous heating of damp
hay, dung, tobacco, and cotton-wool.
In such substrata Bacillus calfactor
develops ; it is adapted to live at
high temperatures (above 40°) and
is still motile at over 70° C. (cf. p.
277).

Saprophy tic and parasitic species
are distinguished, although a sharp
separation is often impossible. In
cultures the parasitic forms can be
made to lead a saprophytic life on
suitable substrata.

Bacillus suUilis, the Hay bacillus
FIG. 295.— Bacillus subtilis. a, d, Motile cells and (Fig. 295), which appears as a rule
chain of cells ; Z>, non-motile cells and chains of jn the decoction obtained by boiling
cells ; c, spores from the zoogloea e (a-dx 1500 ; h . t m ff rf example
e x 250. From A. FISCHER, Varies, uber Bac- * '

terien ) °* ™e "fe-liistory of a bacterium.

The spores of this species, which

withstand the effect of the boiling water, produce on germination rod-shaped
swarming cells with cilia on all sides ; these divide and may remain connected
in short chains. At the surface of the fluid these swarming cells change into non-
motile cells without cilia ; these divide up, giving rise to long intertwined chains
of cells. These are associated together in the pellicle covering the surface
(zoogloea stage). Spore formation occurs when the nutritive substances in the
fluid are exhausted.

The zymogenous 'or fermentation Bacteria and the saprogenous or decomposi-
tion Bacteria are other saprophytic forms. The former oxidise or ferment carbo-
hydrates. The latter decompose nitrogenous animal or vegetable substances
(albumen, meat, etc.) with the liberation of ill-smelling gases.

The acetic acid bacteria (Fig. 296 a, b, c) oxidise alcohol to acetic acid. The
transformation of sugar into lactic acid is brought about by the rod-like cells of
Bacillus acidi lactici (Fig. 296 d). Clostridium butyricum (Fig. 296 e} forms
butyric acid from various carbohydrates in the absence of oxygen, while certain

••-'

DIT. I

THALLOPHYTA

373

marsh bacteria (Fig. 296 /) in the absence of oxygen form marsh-gas and hydrogen
from cellulose. Bacillus protcus is the most common cause of decomposition of
meat, albumen, etc.

Streptococcus (Leuconostoc) mesenterioides (Fig. 297) causes fermentation of
beet-sugar. It forms large mucilaginous masses like frog-spawn, the bead-like
rows of cells being surrounded by a gelatinous investment. The latter is not
formed in media from which sugar is absent.

The Purple Bacteria, which develop in water containing decomposing organic
matter in the absence of oxygen and the presence of light, contain, according to
MOLISCH (4), a green and a red pigment (bacterio-chlorin and bacterio-purpurin).
Other bacteria secrete pigments in their cells or around them. The latter is
the case with Bacillus prodigiosus, •the ellipsoid peritrichous rod-shaped cells of
which form fuchsin - red colonies on milk or bread, and so have given rise
to the miracle of the bleeding Host.

Fio. 296.— Bacteria of fermentation, a-c, Vinegar bacteria ; o, Bacillus aceti ; b, Bac. Pasteurianus ;
c, Bac. Kittzingianus; cl, Bac. acidi lactici, lactic acid bacillus; e, Clostridium butyricum,
butyric acid bacillus ; /, Plectridium paludosum, fermentation bacterium from marsh water.
(x 1000. From A. FISCHER, Varies, iiber Bacterien.)

The photogenic bacteria produce within their cells a substance which becomes
phosphorescent on oxidation. The most widely spread of these phosphorescent
bacteria (5) is Bacterium phosphoreum, which occurs on meat.

Certain soil-bacteria (Clostridium Pasteurianum, Azotobacter chroococcum) and
marine bacteria are able to assimilate free nitrogen. To these nitrogen-fixing
forms also belong Bacillus (Rhizobiuni) radicicola and Bacillus Beijerinckii which
live symbiotically in the root-nodules of the Leguminosae (Figs. 251, 252).
Mycobacterium Rubiacearum is similarly symbiotic in the leaves of tropical Rubia-
ceae and produces analogous bacterial galls (6). On the other hand, de-nitrifying
bacteria, which decompose nitrates and nitrites with liberation of free oxygen,
occur both in the soil and in the sea (cf. p. 276).

The parasitic bacteria inhabit both animals and plants causing bacterioses.
Bacillus turncfaciens, discovered by Smith, gives rise to the cancer-like tumours
of Crown-gall on the higher plants. This organism is also pathogenic to man.
Another example is Bacillus phytophthorus, which attacks the potato (7).

The numerous pathogenic Bacteria are the most important causes of infectious
diseases. Their injurious influence on the tissues and blood of men and animals

374

BOTANY

PART II

is brought about by the excretion of poisonous substances, to which the name
toxins has been given. The following forms may be mentioned. Staphylococcus
pyogenes (Fig. 298 a), the cocci of which form irregular or racemose masses, is

the most common cause of suppuration,
while Streptococcus pyogenes (Fig. 298 &),
with cocci united in chains, occurs in ery-
sipelas and other suppurative lesions.
Micrococcus (Diplococcus) gonorrhoeae (Figs.
298 c, 299 a) has somewhat flattened cocci
arranged in pairs, and causes gonorrhoea.
Bacillus anthracis (Figs. 298 d, 299 c)
was found by R. KOCH in the blood and
organs of animals suffering from splenic
fever. The relatively large rod -shaped
cells may be united in short chains ; they
form endospores in cultures in the same
way as the Hay bacillus. Bacillus tetani
(Fig. 298 e] occurs in the soil, and is the
cause of tetanus. Its straight rod-shaped
cells are ciliated, and grow only in the
wound itself; their spores are formed in
the swollen end. Bacillus influenzae, short,
slender rods ; Bacillus pestis, small, stout,
non-motile rods. LOFFLER'S Bacillus diph-

theriae (Fig. 298 /) consists of small rod-shaped cells sometimes thickened at one
end. KOCH'S Mycobacterium tuberculosis (Figs. 298 g, 299 6), which is found in all
tuberculous lesions and secretions, and in the sputum, is a slender, slightly curved
rod ; branched forms also occur. It is non-motile and does not form spores. For

FIG. 297. — Streptococcus mesenterioides. A, Iso-
lated cells without gelatinous sheath ;
B, C, formation of chain of cells with
gelatinous sheath ; D, portion of mature
zoogloea ; E, formation of isolated cells in
the filaments of the zoogloea. (x 520.
After VAN TIEGHEM.)

FIG. 298. — Pathogenic Bacteria, a, Pus cocci ; &, erysipelas cocci ; c, gonorrhoea cocci ; d, splenic
fever bacilli ; e, tetanus bacilli ; /, diphtheria bacilli ; g, tubercle bacilli ; h, typhoid bacilli ;
i, colon bacilli ; k, cholera vibrios, (x about 1500. From A. FISCHER, Vorles. uber Bacterien.)

these reasons it is grouped with some other species in a special family, the
Mycobacteriaceae (8). Typhoid fever is caused by the ciliated cells of Bacillus
typhi (Fig. 298 h) ; Bacillus coli (Fig. 298 i), the colon bacillus, which is as a
rule harmless and always occurs in the human intestine, closely resembles the
typhoid bacillus. The comma bacillus of Asiatic cholera, Vibrio cholerae (Fig. 298 &),

DIV. I

THALLOPHYTA

375

was discovered by R. KOCH. It occurs in the intestine as short curved rods with
a single polar flagellum, and sometimes in longer spirally-wound chains.

FIG. 299. — Stained preparations from Ziegler's Text-book of Pathology, a. Gonococci in the
gonorrhoeal discharge, mucus and pus corpuscles with cocci (methylene blue and eosin), x 700 ;
b, tubercle bacilli in sputum of phthisis (fuchsin and methylene blue), x 400 ; c, splenic fever
bacilli in the pustule of the disease (methylene blue and vesuvin), x 3-30. (From A. FISCHER,
Varies, fiber Bacterieit.)

Besides the above injurious parasites there are others which are more or less
harmless occurring on the mucous membranes, in the mouth (Fig. 80), or the
intestine. Sarcina ventriculi, which
occurs as packets of cocci in the stomach
and intestine of man, will serve as an
example of these.

In addition to saprophytic and para-
sitic Bacteria, there are others which,
though possessing no chlorophyll, obtain
their food from inorganic compounds
only. These are the Nitrite Bacteria
(Nitrosomonas) and the Nitrate Bacteria
(Nitrobactcr), which live in the soil. The
former oxidises ammonia to nitrous acid,
and the latter oxidises the nitrous to

nitric acid. They both obtain their carbon from carbonic acid, and thus derive
their food independently of any organic food-supply (Fig. 300, cf. p. 254).

FIG. 300.— Nitrifying bacteria, after WIXO<;RAD-
SKY. o, Nitrosomonas europaea, from Zurich ;
b, Nitrosomonas jai-anensis, from Java ; c,
Nitrobucter, from Quito, (x 1000. From
FISCHER, Vorles. iiin-r Bactfricn.)

Order 2. Triehobacteria. FILAMENTOUS BACTERIA (9)

The filamentous bacteria comprise only a few genera. They approach in their
organisation the filamentous Cyanophyceae and may, in part at least, have been
derived from these as colourless forms. The majority live saprophytically in water
but some are autotrophic.

The widely distributed Cladothrix dichotoma is morphologically the highest
among these. It is found in stagnant water, and consists of falsely - branching

2 Bl

376 BOTANY

delicate filaments attached to Algae, stones, and woodwork, and forming a slimy
coating over them ; the filaments are composed of rod-shaped cells. Reproduction
is effected by ciliated swarm-cells, which originate by division from cells of the
filament and are set free by the swelling of the sheath (Fig. 294). The swarm-
cells come to rest after a time and grow into new filaments.

Another very common form is Crenof.hrix polyspora, which consists of un-
branched filaments attached to the substratum, but easily broken, and can
accumulate hydrated oxide of iron in its sheaths. It often forms masses in the
cavities of water-pipes, blocking them up and rendering the water und linkable.
The reproduction of Crenothrix is effected by small, round, non-motile cells, which
arise by subdivision of the cells of a filament enclosed by its sheath.

The numerous kinds of Sulphur Bacteria, of which Beggiatoa alba is the most
widely distributed, are found in sulphurous springs and at the bottom of pools
where sulphuretted hydrogen is being formed by decomposition of organic
material. The sulphur bacteria can thus live autotrophically, without organic
food, utilising in their metabolism salts of ammonium and carbon dioxide. These
bacteria oxidise sulphuretted hydrogen into sulphur, and store the latter substance
in the form of rounded granules within their cells, ultimately oxidising it to
sulphuric acid. Some Haplobacteria also belong to this physiological group
(cf. p. 276).

Cklainydothrix (Leptothrix) ochracca, the so-called Iron- Bacterium, oxidises oxide
•of iron to the hydrated oxide of iron which it accumulates in tho sheaths of its
filaments. It occurs in ditches and swampy places in meadows. It can thus exist
with only a trace of organic food, but on the other hand succeeds well without iron
in organic food-solutions.

Other iron -bacteria such as Spirophyllum fcrruyineum according to LIESKE
are purely autotrophic. They only succeed in water containing in addition to
small quantities of inorganic salts some carbonate of iron. They oxidise the
ferrous oxide to the hydrated oxide of iron which they accumulate. This oxida-
tion process supplies the energy for the assimilation of carbon dioxide.

CLASS II
Cyanophyeeae, Blue green Algae (!> 10)

The Cyanophyeeae are simply organised unicellular or filamentous
Thallophytes of a bluish-green colour ; the cells or filaments are
frequently united into colonies by the gelatinous swelling of the cell
walls. The numerous species, which are distributed over the earth,
live in water, or form gelatinous or filamentous growths on damp
soil, damp rocks, or the bark of trees. Like the pure green Algae,
they are autotrophic.

The protoplast of each cell possesses a peripheral chromatophore of the form of
a hollow cylinder or hollow sphere ; in addition to chlorophyll this contains a
hlue-green pigment (phycocyau) from which the name of the class is derived, and in
some species also a red pigment (phycoerythrin). Tho product of assimilation
is glycogen. The centre of the cell is occupied by the colourless central body,
which corresponds to a nucleus and contains chromosome-like structures. As
definite inclusions of the cells may be mentioned the cyanophycin granules,

DIV. 1

THALLOPHYTA

377

which are of proteid nature and are situated within the chromatophore. The
cell wall consists of cellulose and pectic substances.

Reproduction is exclusively vegetative by cell division. In many forms resting
spores arise by the enlargement of single cells, the walls of which become greatly
thickened (Fig. 302). This process differs from that in the Bacteria.

Just as the Bacteria are designated Fission Fungi (Schizomycetes), the Blue-
green Algae may be termed Fission Algae (Schizophyceae), since the reproduction
of both depends on fission. The two groups would form the class of fission plants
Schizophyta. The Bacteria and the Cyanophyceae have much in common, but
the cilia and eudospores of the former are unknown in the latter group.

The simplest Cyanophyceae consist of spherical cells ; this is the case with
species of Chroococcus. In Gloeocapsa (Fig. 35), found on damp rocks and walls,

lefts.*? -•'-' «*J-™ "

Fn;. 301. — -4, OsciUari'i j. ,••</<<•< j/.s : a, terminal portion of a
filament : h and c, portions from the middle of a filament
properly tixed and stained ; t, cells in division (x 1080).
B. Os<-illa,'ia Froellch.il (x 540). (After STRASBURGER.)

FIG. 302. — Nostoc Linckii. A species
that floats freely in water. A,
Filament with two heterocysts
(h) and a large number of spores
(sp) ; B, isolated spore beginning
to germinate ; C, young filament
developed from spore, (x 650.
After BORKET.)

the cells remain connected together after division in a gelatinous mass, forming
a multicellular colony.

The species of Oscillaria, which occur everywhere in water or on damp soil,
are the simplest of the filamentous forms which may be unbranched or exhibit
false branching (Fig. 86). The filament, which is usually provided with a thick
sheath, consists of similar flattened cells (Fig. 301). It can separate into pieces
(hormogouia), which become free owing to the pressure of the sheath, and grow
into new filaments. In other filamentous Cyanophyceae specially modified cells
with their contents degenerated occur in the filament. The significance of these
HETKPwOCYSTS is not yet clear. The species of Nostoc (Fig. 302), whose bead-
like filaments are united by the swelling of the cell walls into more or less
spherical gelatinous colonies living on damp soil or in water, afford an example
of this.

The filamentous Cyanophyceae, especially the Oscillarieae and the hormogonia
of Xostoc and some related genera carry out creeping movements on a solid

378

BOTANY

I- ART II

substratum and are both phototactic and cheniotactic. These movements
are effected by the swelling of an anisotropous mucilage excreted by the cells.
The main axis of swelling of this forms an acute angle with the long axis of the
filament, so that the latter is moved forwards without rotating on its axis(IO°).

Some Cyanophyceae take part with the Fungi in the formation of Lichens.
Some species also are endophytic and inhabit cavities in other plants, e.g.
Anabaena in Azolla, Nostoe in some Liverworts, in Lemna, and in the roots of
Cycas. Nostoe punctiforme occurs as a facultative parasite in the rhizome of
Gunner a (106).

CLASS III

Flagellata (Flagellates) (

The Flagellata are a group of unicellular, aquatic organisms
exhibiting a wide range of form ; they combine animal and vegetable
characteristics, and may be regarded
as the starting-point on the one side
of unicellular Thallophytes, on the
other of the Protozoa.

The protoplast exhibits con- '
tractile or amoeboid movements, and
is limited by a denser protoplasmic
layer and not by a definite cell
wall. One or more cilia (flagella)
are present as motile organs. The

Fio. 303. — Chrysamoeba radians. Occurs in fresh
water und has a single cilinm and two brown-
ish-yellow chromatophores. 1, Ordinary form ; Fn;. 3U4. — Diuobryon Sertuhma. Occurs in
2, amoeboid condition with radiating pseudo- fresh-water plankton and forms invested
podia. (After KLEBS.) colonies, (x 600. After SENN.)

protoplast contains a nucleus, a pulsating vacuole, and in many species
well -formed green, yellow, or brownish -yellow chromatophores. A
red eye -spot is frequently present. The assimilation product is
usually oil, but starch and other carbohydrates also occur. Other forms
are colourless and are saprophytic or obtain their food like animals.
The protoplast of some Flagellates, especially of the colourless forms,

DIV. I

THALLOPHYTA

379

may take on an amoeboid condition in which it exhibits changes in
form and creeping movements. In other cases slender processes or
pseudopodia may be put out and again
withdrawn as in the Rhizopoda. These
assist in the absorption of solid particles
of food (Figs. 303, 309).

Most representatives of the group live
as naked, free cells ; others form more or
less complicated cell-colonies held together
by mucilage, or they possess peculiar
stalked or unstalked firm investments
sometimes with siliceous or calcareous
skeletal structures.

Sexual reproduction is wanting. Multi-
plication takes place by longitudinal divi-
sion, and in many species thick -walled
resting spores or cysts are produced. On
the germination of these, after division of Flo> m5._HydrUrus foetidu*.

the Contents, a number of daughter Cells of a branch of the colony enclosed
may be liberated (Fig. 308 B). * mucilage. (After BEBTHOI.D.)

B, Swarm -cell. (After KLEBS.)

The Chrysomonadinae are an important group (From PASCHER, Flagellaten.)
of the Flagellata, to which belong Chrysamoeba

(Fig. 303) and the colonial form, Dinobryon (Fig. 304). They are characterised by
their radial structure and by their chromatophores which are usually brownish
yellow, less commonly red or blue green, and form a special carbohydrate

FIG. 306. — A, Distephanus speculum. (After BORGERT.) B, C, Calyptrosphaera insignis from
the Adriatic ; B is in optical section and C in surface view, (x 1600. After SCHILLER.)

(leucosin). Hydrurus foetidus (Fig. 305) is an example of a more complex
member of the Chrysomonadinae. Its cells are associated in colonies as long
branched mucilaginous filaments which may be 30 cm. in length and are attached
to stones in running water. Numerous cells without cilia are embedded in the

380

BOTANY

PART II

mucilage of the filament and increase in number by longitudinal division. From
these are derived uniciliate swarm-cells, which escape from the filament and ulti-
mately become attached and produce new filaments. In other related Flagellates
also such alga -like resting stages predominate, while the motile cells serve for
reproduction and dispersal. Two peculiar families of small organisms found
in the plankton of the sea can be placed along with the Chrysomonadinae.
These are the Silicon1 agellatae (12°) which have perforated siliceous skeletons
(Fig. 306 A} and the Coccolitho-
phoroideae (12&) which have a wall
composed of calcareous plates or rods
and reproduce by producing usually
four swarm -spores (306 B}. The
Diatomeae and the Heterocontae
appear to have been derived from
the neighbourhood of the Chryso-
monadinae, so that these three groups
might be associated together as the
Chrysophyta.

The Cryptomonadinae are rather
more highly organised than the
Chrysomonadinae and differ from
them in the dorsiventral protoplast
obliquely truncated at the anterior
end where two cilia of unequal length
arise from a depressed furrow (Fig.
307). Chrysidella (Zooxanthella)
belongs to this group. They are
symbiotic with various marine animals
(Radiolariae, Actiniae, etc.), in the

FIG. 308. — Euglena gracilis. A, Form with green
chromatophores (ch) ; n, nucleus ; v, vacuole and
red eye-spot ; g, flagellum. B, Hemi-saprophytic
form with small green chromatophores. C,
Colourless saprophytic form occurring in nutrient
solution in absence of light. D, Resting cyst of
the form C ; r, red eye-spot. E, Germination of
the resting cyst of the form A by division into
four daughter cells which later escape. (A, C x
630 ; B x 650; D, E x 1COO. After ZUMSTEIN.)

FIG. 307.— Cryptomonas erosa.
(x 650. After STEIN.)

protoplasm of the cells of which their yellow resting cells lie. From these the
protoplast later emerges in the form of a ciliated Flagellate. The Dinoflagellatae
are related to the Cryptomonadinae. Some other genera, such as Phaeocystis and
Phaeothamnion which form mucilaginous colonies during most of their life, may
also be placed here. They suggest comparison with the Brown Algae, but it is
doubtful whether they should be regarded as really leading to that group.

The starting-point of the Chlorophyceae is to be looked for among the Flagellates
provided with green chromatophores.

The Euglenineae (12c) are an advanced group of green Flagellates. Species of
JZuglena (Fig. 308 A] often form a green scum on ponds. There are nearly allied
but colourless saprophytic forms. Euglena gracilis can indeed be changed into a

DIV. I

THALLOPHYTA

381

hyaline form with leucoplasts when cultivated in organic solutions in the dark.
Sexual reproduction has been observed by GERTRAUD HAASE in Euglena sanguinea,

A * B C D

FIG. 309. — Mastigamoeba invertens. A, Free swimming. B, Amoeboid

i I .
(x 666. After LEMMERMAXN.)

. — asgamoea nverens. , ree swmmng. , moeoid condition, (x 1033.)
Dimorpha mutans, with retracted (C) and extended (D) pseudopodia. An ingested particle of
food is within a vacuole. 666. After LEMHERMAN

but this requires confirmation. It takes place in the spring at the bottom of the
pool, the cells throwing off their flagella and dividing into small amoeboid
gametes with one nucleus and two chromatophores ; these gametes then conjugate
in pairs. The zygote without undergoing a period
of rest then divides into four or eight cells which
grow into the normal individuals.

The numerous colourless Flagellates which have
saprophytic or animal-like nutrition must have been
derived from those with coloured chromatophores.
In some cases near relationship is indicated by
agreement in the structure of the cells.

In the Pantostomatineae particles of food are
ingested over the whole surface by means of pseudo-
podia (Fig. 309), in the Protomastiginae usually
at an oral opening, while two such spots are present
in the Distomatineae. To the second group belong
certain forms that live in the blood and the gut of
animals and give rise to some tropical diseases.
Thus Trypanosoma Brucei causes the Tsetse-disease
of cattle, and T. gambiense (Fig. 310) the sleeping
sickness in man ; both are conveyed by flies belong-
ing to the genus Glossina.

It may be assumed that the Myxomycetes arose
from colourless Flagellates and also that the lower
Protozoa (Rhizopoda) can be placed in relation to them as a lower group.

FIG. 310. — Trypanosoma gambiense.
A, From the blood of an infected
monkey, the flagellum forming
an undulating membrane. B,
From the fly Glo?sina with the
flagellum internal. (After
MIXCHIN.)

CLASS IV
Myxomyeetes (Slime Fungi) (*> 13> l4' 15)

The Myxomycetes form an independent group of lower Thallophytes;
in certain respects they occupy an intermediate position between plants

382

BOTANY

PART I

and animals, and have in consequence also been termed Mycetozoa or
Fungus - animals. They are represented by numerous species, and
are widely distributed over the whole earth. In the first instance
the behaviour of the most comprehensive Order, the Myxogasteres,
may be considered. In their vegetative condition these Slime Fungi
consist of naked masses of protoplasm, the PLASMODIA, containing
numerous small nuclei but utterly devoid of chlorophyll. Glycogen
occurs as a reserve substance, while starch is not found. The plasmodia
(Fig. 4) are found most frequently in woods, upon soil rich in humus,
upon fallen leaves, and in decaying wood. They creep about on the
substrata, changing their form at the same time, and thrust out
processes or pseudopodia, which may in turn coalesce. They feed
by taking up solid particles and reach favourable situations for their

nutrition owing to their capacity
of chemotactic, hydrotactic, and
negatively phototactic move-
ments. At the period of spore-
formation the plasmodium
creeps out from the substratum
towards the light and air, and,
after coming to rest, is con-
verted into a single or into
numerous and closely contiguous
fructifications, according to the
genus. On the periphery of each
fructification an outer envelope

FIG. 311.— Ripe fructifications, after discharge of the T>T?RmTTTTu ia WTYIO^ • wlii'la

spores. A, Stemonitis fnsca (x 10); B, Arcyria <
punicea(x 12); C, Cribraria rufa (x 32). internally the Contents of the

fructification separate into

SPORES, each of which is provided with a nucleus, and enclosed by an
outer wall. In many genera, part of the internal protoplasm within the
SPORANGIUM or spore-receptacle is utilised in the formation of a CAPIL-
LITIUM (Figs. 311 A, B, 312 B\ consisting of isolated or reticulately-
united threads or tubes. Upon the maturity of the spores, the
peridium of the sporangium becomes ruptured, the capillitium expands
(Fig. 311 B\ and the spores are dispersed by the wind, aided by the
hygroscopic movements of the capillitium. In the case of the genus
Ceratiomyxa, the process is somewhat simplified, as the fructification
is not enveloped by a peridium, and the spores are produced on the
surface at the ends of short stalks.

The germination of the spores (Fig. 313, Chondrioderma) takes place in water
or on a wet substratum. The spore wall is ruptured and left empty by the escaping
protoplast. After developing a flagellum or CILIUM as an organ of motion, the
protoplast swims about in the water, being converted into a SWARM-SPORE (Fig. 313
e-g) which resembles certain Flagellata, with a cell-nucleus in its anterior or ciliated
end, and a contractile vacuole in the posterior end of its body. Even within the

DIV. I

THALLOPHYTA

383

spore a division may take place, so that two swarm-spores are liberated. In some
species the swarm-spores can increase in number by fission. Eventually the

FIG. 312.— Trichia varla. A, Closed and open sporangia (x 6); B, a fibre of the capillitium
(x 240); C, spores (x 240). D, Leocarpus fragilis. Groups of sporangia upon a Moss.
(Nat. size.)

cilium is drawn in, and the swarm-spore becomes transformed into a MYXAMOEBA
(Fig. 313 i, Tc) ; these have the capacity of multiplication by division (Fig. 314 A, B}.
In conditions unfavourable for their development they surround themselves with
walls, and as MICROCYSTS pass into a state of rest, from which, under favourable

FIG. 313.— Chondrioder'mu di/orme. a, Dry, shrivelled spore ; b, swollen spore ; c and d, spores
showing escaping contents ; etf, g, swarm-spores ; 7i, swarm-spore changing to a myxamoeba ;
i, younger, k, older myxamoebae. Cf. Fig. 4. ( x 540. After STRASBURGER.)

conditions, they again emerge as swarm - spores. According to JAHN (14) the
myxamoebae fuse in pairs, their haploid nuclei uniting (Fig. 314 C).

The uninucleate amoeboid zygotes, which have thus resulted from a sexual
fusion, unite to_form larger multinucleate plasniodia. These take up additional

384 BOTANY PART n

haploid amoebae, but these are digested within vacuoles (Fig. 314 D}. Ultimately
the plasmodium proceeds to form 'the fructification. The diploid nuclei of the
plasmodium undergo repeated mitotic divisions (Fig. 314 E). Their last division
shortly before the delimitation of the spores is a heterotypic division, in which
the chromosomes are reduced to the half number. Each haploid nucleus thus
formed becomes the nucleus of a spore. The nuclei not employed in spore-
formation degenerate. In Ceratiomyxa the spores may include a degenerating
nucleus as well as the normal one. From the latter by two successive divisions
four nuclei are formed and are present in the ripe spore. Another division occurs on
germination, so that ultimately eight swarm-spores are produced from each spore.
In the structure of their swarm- spores and myxamoebae the Myxomycetes show
their derivation from organisms of the nature of the Flagellata. Plasmodial

fusions are also known among

/•'- - .. ^ Flagellates.

/ '* g ./K Very large plasmodia, often

\ over a foot in breadth, of a

yK bright yellow colour and creamy
"^JgflS*\\ consistency, are formed by Fuligo
f -"',' LJf varians (Aethalium septicum),

\-%S m and as the "flowers of tan" are

* £«;i often found in summer on moist

J^A tan bark. If exposed to desicca-

tion, the plasmodia of this Myxo-
mycete pass into a resting state,
and become converted into spheri-

*' -"jJ-K / 7 cal or strand-like SCLEROTIA, from

' / / which a plasmodium is again pro-

K, ^ / - duced on a further supply of

'. Q K - /^ ' " water. Finally, the whole plas-

\,, ^ modium becomes transformed

into a dry cushion- or cake-shaped

FIG. 314.— Physarum didermoides. A, B, Amoebae in fructification of a white, yellowish,
process of division ; C, conjugation of two haploid or brown colour. The fructifica-
amoebae ; kk, the two uniting nuclei; D. binucleate ,- . ,, . .

plasmodium with a haploid amoeba enclosed in a tion, m this instance, is enveloped
digestive vacuole ; E, plasmodium with six dividing "7 an outer calcareous crust or
nuclei (fcj) and with digestive vacuoles. (After JAHN.) rind, and is subdivided by numer-
ous internal septa. It encloses

numerous dark violet-coloured spores, and is traversed by a filamentous capillitium,
in which are dispersed irregularly-shaped vesicles containing granules of calcium
carbonate. A fructification of this nature, or so-called aethalium, consists, there-
fore, of a number of sporangia combined together, while in most of the Myxomy-
cetes the sporangia are simple and formed singly.

The structure and nature of the sporangia afford the most convenient means
of distinguishing the different genera. The usually brown or yellow sporangia are
spherical, oval, or cylindrical, stalked (Figs. 311, 312 D) or not stalked (Fig.
312 A}. They usually open by the rupture of the upper portion of the sporangium
walls, the lower portion persisting as a cup (Figs. 311 B, 312^4). In Cribraria
(Fig. 311 C) the upper part of the wall of the sporangium, which contains no
capillitium, becomes perforated in a sieve-like manner. In Stemonitis (Fig. 311
A] the whole peridium falls to pieces, and the capillitium is attached to a
columella, which forms a continuation of the stalk.

(ft

DIV. I

THALLOPHYTA

385

The order Plasmodiophoraceae (15) contains a few parasitic organisms, the
chief of which is Plasmodwphora Brassicae, which causes tuberous swellings on
the lateral roots of various species of Brassiea. Its myxatnoebae occur in
numbers in the cells of the hypertrophied parenchyma of these swellings ; after
the contents of the host-cell have been exhausted they fuse into plasmodia, and
these, after repeated nuclear divisions, give rise to the numerous spores, which are
set free by the disorganisation of the plant. In the plasmodium a reduction
division takes place, the resulting nuclei being those of the spores. The spores
germinate like those of Chondrioderma, and the myxamoebae penetrate the roots
of a young Cabbage-plant. The formation
of true sporangia, however, does not take
place, and this Slime Fungus represents a
more simply organised or, in consequence
of its parasitic mode of life, a reduced
Myxoiuycete.

The systematic position of this order is
still doubtful since it presents some cy to-
logical resemblances to the Chytridiaceae,
which are placed with the Phycomycetes.

The small order of the Acrasieae occupies
a lower position among the Myxomycetes.
There are no swarm -spores. Amoebae
arising from the spores increase in number
by division and then become associated
together, without fusion, to form an aggre-
gate plasmodium. In the simplest cases
this changes directly into a mass of spores.
In some genera (Didyostelium), however, a
stalk is formed from some of the amoebae
which remain sterile and are converted into
firm cells ; up this stalk other amoebae creep
and form the mass of spores.

With some reservation the Myxobac-
teriaceae (16) may b.^ placed here. Our
accurate knowledge of them is in the first
instance due to THAXTEI:, who grouped them
with the Bacteria, but according to VAHLE
they come nearer to the Myxomycetes.
They are widely distributed and live sapro-
phytically on the dung of animals, and in
habit resemble the Myxomycetes. In the vegetative stage they appear as swarms
of rod-shaped small cells connected together by the gelatinous substance secreted
by the cells, and exhibit slow creeping movements. Ultimately they form fructi-
fications that are usually brightly coloured ; these have the form either of definitely
limited masses of spores or of cysts which contain within a firm membrane the
numerous spores arising by a transformation of the rod-shaped cells. The cysts are
unstalked, or are raised singly or in groups on a stalk, formed, like the wall of
the cyst, of gelatinous material derived from the rod-shaped cells excluded from
spore formation. In germination the swarms of rod-shaped cells emerge from the
ruptured cysts (Fig. 315).

FIG. 315. — A, Myxococcus digitatus, bright red
fructification occurring on dung (x 120).
B, Polyangium primigenium, red fruc-
tification on dog's dung (x 40). C,
Chondromyces apiculatus, orange fructifi-
cation on antelope's dung. D, Young
fructification ( x 45). E, Single cyst ger-
minating (x 200)- (A, B after QUEHL ;
C-E after THAXTER.)

386

BOTANY

PART II

CLASS V
Dinoflagellatae (l> n> 17'19)

The Peridineae or Dinoflagellatae are connected as an independent
and further developed group with certain Flagellata. They occur as
unicellular, free-swimming organisms in fresh
water, but for the most part in the sea, where,
together with the Diatomeae, they constitute
an important constituent of the phyto-plank-
ton. Their cells are characterised by the pos-
session of two long cilia or flagella which
spring from the middle of the ventral surface
in a longitudinal furrow ; one of the cilia is
directed backwards, the other is thrown
into curves and lies in a transverse furrow
(Fig. 316). The protoplast contains a nucleus,
vacuoles of different sorts, and numerous
brownish-yellow chromatophores ; the latter
contain a mixture of several pigments. Starch
or oil is formed as the product of assimilation.
While the Gymnodiniaceae (Fig. 317 d)
have either naked cells or cells limited by
a uniformly thickened cellulose wall, the

typical Peridiniaceae have a wall composed of cellulose formed of
polygonal plates ; these are usually delicately sculptured and per-

PIG. 316.— Peridinium tabulatum.
(After SCHILLING.)

FIG. Zl7.—Cystodinium Steinii : a, cyst ; b, division into two swarm cells ; c, a cyst swelling ;
d, liberated swarm cell. ( x 480. After KLEBS.)

forated with pores. The transverse furrow is formed by one girdle-
shaped plate (Fig. 316).

In many Peridineae of the plankton the plates bear special wing-like expansions

DIV.

THALLOPHYTA

387

(Fig. 318) or the cells have long horn-like processes. These adaptations enable
the organisms to remain floating in the water (18).

In some Dinoflagellatae the chromatophores are only represented by colourless
leucoplasts. Such species live either as saprophytes or in the same way as
animals. Spirodinium hyalinum is a colourless, naked, fresh-water form, the
protoplast of which for the purpose of absorbing nourishment loses its cilia
and assumes the form of an amoeba ; in this condition it encloses and digests,
small Algae.

Some marine Peridineae (e.g. Ceratium tripos, Peridinium divergens) are
phosphorescent, and play a considerable part in the phosphorescence of the sea (5).

Reproduction is effected by division usually of the motile cells. In certain
genera (Peridinium, Cystodinium [Fig. 317]) the motile cells enter into a longer

FIG. 318. — Peridineae of the plankton. A, Ceratocorys horricla var. africana, Indian Ocean (x 250) ;
B, Ceratium tripos intermedium var. aequatorialis, Indian Ocean (x 62); C, Ceratium tripos
ciU'lterum, and D, Ceratium pal mat urn, Atlantic Ocean (x 62); E, Ceratium furca, Atlantic
Ocean (x 125). (After G. KARSTKN.)

or shorter resting stage and form non-ciliated cysts in which division takes place ;
the daughter cells emerge from the swollen cysts as swarm cells. Lastly the
motile stage may be completely suppressed and the two naked daughter cells
emerge from the swollen cyst as non-ciliated cells provided with their own cell
walls (Hypnodinium).

Some genera (Ceratium} form thick- walled resting-cysts within the old parent
membrane.

Sexual reproduction has not been demonstrated in the Dinoflagellatae (19).

CLASS VI
Diatomeae (Diatoms) (!< n> ™"23)

The Diatomeae (Bacillariaceae) constitute a very large class of
unicellular Algae. They occur, usually associated together in large
numbers, in both fresh and salt water, and also on damp soil.

BOTANY

The cells are either solitary or form colonies; they are free-
floating, or are attached by means of gelatinous stalks, excreted by
the cells themselves (Fig. 319). Sometimes the cells remain con-
nected and form bands or zigzag chains,
or, on the other hand, they are attached
and enclosed in gelatinous tubes, while
in the case of the marine genus Scliizo-
nema they lie embedded in large numbers
in a gelatinous branching thallus. The
cells also display a great diversity of
shape ; while generally bilaterally sym-
metrical, they may be circular or ellip-
tical, rod- or wedge-shaped, curved or
straight. The structure of their cell
walls composed of pectic substance that
is silicified is especially characteristic ;
it is formed of two halves or VALVES,
one of which overlaps the other like

FIG. 319. — Licmophora flabellata.
Colony of Diatoms with branched
gelatinous stalks. (After SMITH,
from GOEBEL'S Organographie.)

FIG. 320.— Planktoniella sol. Atlantic Ocean. A disc-
shaped plankton diatom with a hollow floating wing
arising from the girdle side. The protoplast con-
tains a nucleus and numerous chromatophores.
(x 322. After G. KARSTKN.) .

the lid of a box. The cells thus present two altogether different
views, according to the position in which they are observed, whether
from the GIRDLE or VALVE SIDE (Fig. 79).

The lateral walls of the two valves are formed of the girdle pieces attached
beneath the margins. In some genera the girdle side is extended by the intro-
duction of annular or scale-shaped intermediate bands.

DIV. i THALLOPHYTA 389

The two valves are so strongly impregnated with silica, that, even
when subjected to intense heat, they remain as a siliceous skeleton,
retaining the original form and markings of the cell walls. The walls
of the cells, particularly on the valve side, are often ornamented with
numerous fine, transverse markings or ribs, and also with small
protuberances and pits. They are often perforated by open pores
which serve to give exit to the gelatinous secretion.

The cell has always a central nucleus (Fig. 79) and one or two to
four (Fig. 323) large, or numerous smaller chromatophores (Fig. 320)
embedded in its parietal protoplasm. These chromatophores are flat,
frequently lobed, and of a brownish -yellow colour. Pyrenoids are
often present. The pigments are chlorophyll and yellow phycoxanthin.
Globules of a fatty oil are also included in the cell contents, and
take the place of starch as an assimilation product.

The Diatomeae multiply vegetatively by longitudinal division
which always takes place in one direction. In this process the two
valves are first pushed apart from one another by the increasing
protoplasmic contents of the mother cell, which then divides longi-
tudinally in such a direction that each of the two new cells retains
one valve of the mother cell. After the division of the protoplasm of
the mother cell is accomplished, each daughter cell forms, on its naked
side, a new valve fitting into the old one. The two valves of a cell are
therefore of different ages. In consequence of this peculiar manner of
division, since the walls of the cells are silicified and incapable of dis-
tension, the daughter cells become successively smaller and smaller,
until finally, after becoming reduced to a definite minimum size, they
undergo transformation into AUXOSPORES. The auxospores are usually
two or three times larger than the cells from which they arise, and by
their further development they re-establish the original size of the cells.

The sexual reproduction consists of a conjugation of similar gametes.

The Diatoms include two orders, Centricae and Pewnatae.

The auxospores in the Centricae, which are characterised by the centric structure
of their valves, grow from vegetative cells without any previous process of conjuga-
tion. In the Pennatae, with a pinnate sculpturing of their valves, on the other hand,
the auxospores develop from the zygotes resulting from a conjugation of gametes.
The Pennatae have diploid vegetative cells, the reduction division taking place
in the formation of the gametes. The Centricae are haploid and the simple
chromosome-number has been attained at the division of the zygote, which so far
as is known is in them the result of the fusion of ciliated gametes. The two
groups of the Diatoms are thus sharply distinguished.

Order 1. Diatomeae Centricae

In these the valves are symmetrical about a centre, and have the sculpturing
radially or concentrically arranged. The great majority of the forms of this order
are marine, and play a large part in the composition of the plankton (18). The
plankton diatoms are provided with special arrangements for floating, e.g. horn-like
projections or wings of the cell wall such as are seen in Figs. 320 and 321.

2 Cl

390

BOTANY

The auxospore formation in the Centricae does not take place by the conjugation
of two gametes but by the protoplasmic body of a cell becoming free from the cell
walls arid increasing in size ; the enlarged cell is first surrounded by a weakly

FIG. 3-2l.—Corethron Valdiviae. From the Antarctic plankton, a, Cell with floating bristles and
tentacles ; b, Auxospore formation ; the protoplast after casting off one valve has emerged from
the other and, surrounded by the perizonium, has become four times its original size ; c, the
protoplast contracted within the perizonium and forming the new upper valve ; (/, the peri-
zonium having disappeared above, the auxospore forms the new lower valve and escapes from
the perizonium. (After KARSTEN.)

silicified membrane (perizonium), and in this the new valves are formed (Figs.
321, 322 £).

The Centricae further differ from the Pennatae by possessing a special method of

FIG. 322. — Biddulphia mdbiliensis. A, View from the girdle side ; B, auxospore formation ; C, cell
divided into two sporangia preparatory to the formation of microspores ; D, spore formation
in the sporangia ; E, swimming microspore. (A-D x 228, E x 570. After P. BERGON.)

reproduction by means of so-called microspores (21) ; the formation of these has been
accurately followed by BERGON in Biddulphia moUliensis. A cell first divides into
two daughter cells or sporangia, the contents of which round off and by repeated
division form many (32) microspores. These emerge as naked swarm-spores, each

D1V. I

THALLOPHYTA

391

provided with two long cilia with knob -like thickenings at the tip (Fig. 322
C-E). These swarm-spores appear to behave as gametes, for KAHSTEN" observed in
preserved material of Corethron valdiviae that the inicrospores conjugated in pairs
to form zygotes. The zygote increased in size and divided into two cells. Each
daughter cell had at first two nuclei, one of which later disappeared ; it grew
gradually into a mature individual of Corethron. The whole process may be
compared with that described above in Closterium among the Desmidiaceae.
The ciliated gametes or microspores which have been observed in other genera
indicate a phylogenetic relation of the
Diatomeae to the Flagellatae, especi-
ally to the Chrysomonadinae. y ^LA f]

Order 2. Diatomeae Pennatae

In shape these are elongated, ellip-
tical, or boat-shaped^but may be wedge-
shaped ; the valves have their sculptur-
ing pinnate (Figs. 319, 323, 324).- In
many of the Pennatae (Fig. 79) a longi-
tudinal line corresponding to an opening
in the cell walls, and exhibiting swollen
nodules at both extremities and in the
middle, is distinguishable in the surface
of the valves. Forms provided with such
a median suture or RAPHE are character-
ised by peculiar creeping movements, re-
sulting from the streaming protoplasm
in the longitudinal slit of the raphe.

The formation of the auxospores is
accomplished in various ways. The
process in Navicula, Pleurosigma, etc.,
may be taken as a starting point ; two
cells lay themselves side by side, and
secrete a mucilaginous sheath. The
nuclei of these cells undergo a reduction
division, into four nuclei, two of which
are large and two small. Each cell
then divides into two gametes, each
containing a large and small nucleus.
The gametes escaping from the cell

walls conjugate in pairs to form zygotes with four nuclei ; the two large nuclei
fuse, while the small nuclei disappear. Each zygote grows within a thin invest-
ment (perizonium) to form an auxospore several times the original size. This
secretes two new valves and commences to divide vegetatively (Fig. 323).

In Surirella and Cocconels (Fig. 324) the conjugating cells do not undergo
division, but unite directly with one another. The nuclei, however, divide ; in
the former genus two nuclear divisions occur in each of the conjugating cells,
resulting in one large and three small nuclei ; in the latter genus there is only
a single nuclear division giving one large and one .small nucleus. The large nuclei
fuse, the small ones degenerate.

In Achnanthes subsessilis the cell contents of a single cell divides into two
daughter cells, which escape, and then fuse together to form the auxospore.

2 C2

pr. 323. — Formation of auxospores in Navicula
i-iridv.la. A, Cell seen from the valve side. B,
Two cells lying alongside one another ; their
contents have divided into two daughter cells,
each of which possesses two nuclei. C, D,
Conjugation in pairs of the daughter cells to
form the auxospores, which at first contain
four nuclei. . E, The two full-grown auxospores.
(x 500. After KARSTEX.)

392

BOTANY

PAllT II

In some Pennatae the sexuality is lost and the auxospores arise apogamously. Jn
Synedra the mother cell divides into two cells which grow into auxospores ; the

nuclei of the daughter cells
L j,

undergo a division, but the
resulting nuclei again fuse.
In Rhabdonema arcuatum
the process is similar, but
the second nuclear division
does not occur.

Rhabdonema adriaticum
goes a step farther ; the
nucleus divides, but one of
the daughter nuclei is ex-
truded from the protoplast.
The undivided mother cell
develops into the auxospore.
Many Pennatae occur in
places where decomposing
substances are present in
abundance. 'Such species
can assume a saprophytic
mode of life, their chromato-
phores becoming colourless
and reduced in size. It has

1, Vegetative cell; «, pair of been shownthatsomecolour-
less species of Nitzschia
which occur in the sea are
exclusively dependent on
organic substances for food, the reduction of their chromatophores and pigment
being complete (^}.

Navicula ostrearia is a Diatom occurring in the oyster-beds of the French coast,
which serves as food for the oysters ; its protoplasm contains a sky-blue pigment
called marennin. This pigment is the cause of a green coloration of the oysters
in which the marennin undergoes alteration and is accumulated (23).

Diatoms occur also as fossils. Their silicified valves form a large part of the
deposits of SILICEOUS EARTH (Kieselguhr, mountain meal, etc.), and in this form
they are utilised in the manufacture of dynamite.

On account of the extreme fineness of the markings of their valves, it is
customary to employ certain species of Diatoms as test objects for trying the
lenses of microscopes. Pleurosigma angulatum is commonly used for this purpose.

FIG. 324. — Coccone/is placentula.

cells before conjugation ; 3, k, cells in process of conjuga
tion. gk, Large nucleus ; kk, small nucleus ; g, gelatinous
substance. (After KARSTUN, from OLTMANNS' Algae.)

CLASS VII
Conjugatae (T> u> 24'26)

This class of green fresh-water Algae includes unicellular and
simply filamentous forms, and is clearly distinct from that of the
Chlorophyceae. Their cells, which increase in number by cell division,
are uninuclear, and differ from those of the Diatoms in having a cell
wall which is not silicified, and in the presence of large green chloro-

DIV.

THALLOPHYTA

393

plasts of complicated structure. Asexual reproduction by swarm-spores
is wanting in them as in the Diatoms, with which they also show
points of agreement in their sexual reproduction. This consists in the
conjugation of two equivalent non-ciliated gametes to form a zygote or
zygospore.

The Conjugatae and Diatomeae were formerly united in one group called the
Zygophyceae, or on account of the non-ciliated gametes, the Acontae. This is no
longer regarded as a natural grouping. It has been seen above that some Diatoms
have ciliated gametes. The reduction divi-
sion in the Conjugatae occurs after conju-
gation in the germinating zygote, while in
the Pennatae it takes place at the formation
of the gametes. Tfee two groups have
evidently originated independently from
the Flagellatae.

1. The Mesotaeniaceae, the simplest
of the unicellular Conjugatae, include
only a few genera. They are distinguished
from the following order by the cell wall
of the shortly cylindrical cells not being
formed of two halves. The mode of con-
jugation presents some differences. In
Cylindrocystis (Fig. 325) the protoplasts
of two cells fuse to form the zygote ; the
nuclei unite while the four chloroplasts
persist. Before germination the zygote
undergoes successive division into four
cells, which then escape. Reduction is
effected in the first nuclear division. In

Spirotaenia the protoplasts of the conju- FlG. 3-25.-^, Cylindrocystis BreUsonii ; the
gating cells first divide and the daughter
cells unite in pairs to form the zygotes.
Only two individuals arise from a zygote,
the other two being suppressed.

2. The Desmidiaceae, which occur in
peaty pools, ponds, etc., are unicellular or

their cells are united in rows ; they are of great beauty and, like the Diatoms,
exhibit a great variety of form. Their cells are composed of two symmetrical
halves, separated, as a rule, from each other by a constriction. Each half
contains a large, radiate chromatophore or a chromatophore composed of a number
of plates. Within the chromatophores are disposed several pyrenoids, while the
nucleus lies in the centre of the cell in the constriction. The cells themselves
display a great diversity of form and external configuration, being sometimes
rounded (e.g. Cosuiarium, Fig. 326^4, £), sometimes stellate (Micrasterias, Fig. 326
D). The cell walls, which, as in the Diatoms, consist of separate halves, are
frequently beset with wart- or horn-like protuberances and often provided with
pores. In some genera there is no constriction between the two halves of the cell.
This is the case, for instance, in the crescent-shaped Closterium moniliferum (Fig.
327 F), whose two chromatophores are elongated conical ribbed bodies, while in
each end of the cell there is a small vacuole containing minute crystals of gypsum

nucleus is in the centre between two
large lobed chloroplasts with elongated
pyrenoids. J5, The zygote before, and C,
after the fusion of the nuclei. D, The
zygote before germination, with four
daughter cells. (After KACFFMANX.)

394

BOTANY

in constant motion (25). Many Desmids are characterised by heliotactic move-
ments ; they protrude fine mucilaginous threads through the cell walls at their
ends ; by means of these they can push themselves along, and take up a position in
a line with the direction of the incident rays of light.

Multiplication is effected by cell division. This is accomplished by the forma-

FIG. '326. — A, Cosmarivm coelatum, dividing. B, C,
Cosmarium botrytis. C\, Two cells at right angles
preparing for conjugation — the lower cell shows
the conjugation canal ; C%, gametes fused into the
young zygote ; C$, mature zygote ; D ,• Micrasterias
crux melitensis. (After RALFS ; C%, C% after DE
BARY.)

FIG. 327. — Closterium. A, Zygote before
germinatio.ii showing the two nuclei
not yet united ; B, germinating
zygote with the nuclei united ; C,
division into two cells each contain-
ing one larger and one smaller
nucleus ; Z>, further state of ger-
mination ; E, young plants escaping
from the cell-membrane ; F, Clos-
terium moniliferum, mature plant.
(A-E after KLEBAHN.)

tion of a partition wall across the middle of the cell after the nuclear division is
completed. Each daughter cell eventually attains the size and form of the mother
cell, by the outgrowth of a new half on the side towards the plane of division
(Fig. 326 A).

In conjugation two cells approach each other, and surround themselves with a

THALLOPHYTA

395

mucilaginous envelope. Their cell walls rupture at the constriction, and parting
in half allow the protoplasts to escape ; these then unite to form a zygospore.
The zygospores frequently present a very characteristic appearance, as their walls
are often beset with spines (Fig. 326 C). The four empty cell halves may be seen
close to the spore. In some Desmidiaceae the conjugating cells undergo a pre-
liminary division, the daughter cells uniting in pairs.

The two sexual nuclei in the zygote do not fuse until germination of the latter
is about to commence. The resulting nucleus then undergoes division, presum-
ably with reduction, into four nuclei, two large and two small. Only two cells
are formed from the zygote, each of which has thus two nuclei of different sizes ;
the smaller nuclei disappear (Fig. 327). The production of two cells on germina-
tion thus appears to be derived from the division into four cells seen in Cylindro-

8.— .4, Conjugation of Spirogyra quinina (x 240). B, Spirogyra longata(x 150) ; z, zygospoie.
<_', Cell of Spirogyra jugoJis ; k, nucleus ; ch, chromatophores ; p, pyrenoid (x 256).

cystis, and to stand to the latter as a reduced form. Two of the four chloroplasts
in the zygote disappear, while the other two undergo a division before germination.
3. Zygnemaceae. — In this family, all of which are filamentous in character,
the genus Spirogyra, with its numerous species, is the best known. It is
commonly found in standing water, forming unattached masses of tangled green
filaments. The filaments exhibit no distinction of base and apex, and are
composed of simple rows of cells, which vary in length in different species.
Growth results from the division and elongation of the cells in one direction
only. Each cell has a large nucleus and one or several spiral green band-like
chromatophores (Fig. 328 (7). The cells of Zygnema contain two star-shaped
chromatophores. The cells of the filament may separate under certain circum-
stances. The cell wall is smooth and without pores. The filaments can undergo
movements.

396

BOTANY

PART II

CONJUGATION, in the case of Spirogyra, is preceded by the development of
converging lateral processes from the cells of adjacent filaments. When two

processes from opposite cells meet (Fig. 328^4)
their walls become absorbed at the point of
contact, and the whole protoplasmic contents
of one cell, after contracting from the cell wall,
passes through the canal which is thus formed
into the opposite cell. The protoplasm and
nuclei of the conjugating protoplasts then fuse
together while the chloroplasts do not unite,
but those of the entering protoplast disorganise.
The resulting cell forms the zygospore in-
vested with a thick wall, and filled with fatty
substances arid reddish-brown mucilage spheres.
This form of conjugation, which' is the one ex-
hibited by most species, is described as scalari-
form (Fig. 328 A), as distinct from the lateral
conjugation of some species, in which two
adjacent cells of the same filament conjugate
by the development of coalescing processes,
which are formed near their transverse wall
(Fig. 328 £). In some genera the zygote is

formed midway in the conjugation tube.

J . d

The conjugation nucleus of the young zygo-

spore undergoes a tetrad division associated
with the reduction in number of the chromo-
somes. One of the four nuclei becomes that of
the young plant while the others appear as
small nuclei, which then degenerate (Fig. 329). The chloroplasts of the gamete
that passed across also degenerate. In this way one young plant arises which
protrudes from the zygospore as a tubular growth and forms a filament by cell
division (26).

FIG. 329. — Spirogyra longata : zygotes of
various age. ' A, The two sexual nuclei
before fusion ; B, after fusion ; C,
division of the nucleus of the zygote
into four haploid nuclei ; D, the
three small nuclei degenerating. The
chloroplasts are represented as cut
across against the wall. (After
TRO'NDLE.)

CLASS VIII

Heteroeontae (*> n> 27)

In the Heteroeontae a number of genera of green Algae are included which were
formerly placed in the Chlorophyceae but are now separated as an independent class
derived from the Chrysomonadinae.

They are characterised by the yellowish green colour of the discoid chroma-
tophores, which contain in addition to chlorophyll a yellow pigment which turns
blue with acids, and form oil and not starch as the product of assimilation. The
motile cells almost always have two cilia of unequal length attached rather to the
side. The cell wall, which contains pectin and is usually silicified, in many cases
consists of two overlapping halves. Some Heteroeontae are unicellular, others
form gelatinous colonies, while others are filamentous.

Reproduction is effected by swarm-spores, which in some genera are replaced
by endogenous aplanospores. Resting cysts are also formed, and these, like
the aplanospores, have a two-valved silicified membrane. In certain genera, in

DIV. I

THALLOPHYTA

397

addition to the swarm -spores, gametes which conjugate isogamously in pairs have
been observed.

The Heterocontae form part of the Marine plankton in which a number of
unicellular genera (Meringosphaera, Halasphaera) occur.

At the base of the class may
be placed such Flagellate -like
forms as Chloramoeba hetero-
morpha (Fig. 330), which lives in
fresh water. The naked, amoeboid
cell contains a nucleus and 2-6
yellowish-green chloroplasts ; at
the anterior end, just outside a
vacuole, two cilia are situated
which are of very unequal length.
It is this last feature jvhich gives
the name to the group. Chlora-
inoeba is one of those low green
organisms which become colour-
less and lose the power of inde-
pendent nutrition when cultivated
in a nutritive solution in the dark.
Thick -walled resting cells also
occur.

Among the higher Hetero-

FIG. 330. — Cliloramoeba heteromorpha : 1,
green form ; 2, colourless form ;
v, vacuole ; k, nucleus. 3, A resting
cell. (After BOHLIX, from OLT-
MAXXS' Algae.)

FIG. 331. — Conferva bombycina. 1, Filament ; 2, 3, forma-
tion of transverse wall (q) in cell division ; 5, forma-
tion of aplanospores by breaking down of the filament ;
10, Zoospores with cilia of unequal length. (After
GAY (1, 5), BOHLIX (2, 3), LUTHER (10). From
OLTMAXXS' Algae.)

contae the genus Conferva (Tribonema), which is widely spread in fresh water,
must be mentioned (Fig. 331). The plant consists of simple unbranched fila-
ments the cells of which have peculiarly-constructed walls ; the wall consists of
two parts separated by an oblique annular split at the middle part of the cell.
On cell division a new portion, H -shaped in longitudinal section, is intercalated.
One or two zoospores are produced from a cell of the filament. In addition to
zoospores thick -walled aplanospores arise by the separation by the cells of the
filament.

The majority of the Heterocontae have uninucleate, only occasionally binucleate
cells. But there are some genera with multinucleate cells in the class, e.g.
Ophiocytium and Sciadium.

398 BOTANY PART n

CLASS IX
Chlorophyceae (l> "• 28'38)

When the green Conjugatae and Heterocontae are separated there
remains the large natural group of the Chlorophyceae, including several
series of genera. The majority of these Algae live in fresh water
or in damp situations ; some large forms occur on the sea coast but
do not contribute to the plankton. Their characteristic chloroplasts
are of a pure green colour, frequently contain pyrenoids, and nearly
always form starch. The asexual swarm-spores are pear-shaped, and
in typical forms possess two or four cilia of equal length (on this
account the group is sometimes termed Isocontae) and a curved or
bowl -shaped chloroplast. In some genera the swarm -spores are
replaced by non-motile aplanospores, and in certain of the more
advanced genera (Oedogonium,, Vaucherici) the swarm-spores are of more
complicated structure, but can be derived from the typical simple
form.

The swarm-spores exhibit phototactic movements by means of which they
reach favourable conditions of illumination for their germination.

In all the orders sexual reproduction is usually effected by the
conjugation of gametes which resemble the zoospores. In all the
groups, except the Protococcales, isogamy is replaced by oogamy
in the higher forms. The reduction division so far as is known takes
place on the germination of the zygote.

Of the five orders included in the Chlorophyceae the Volvocales
stand nearest to the Flagellata and, as is also the case with the
Protococcales, include unicellular and colonial forms. The Ulotrichales
and Siphonocladiales are filamentous ; in the former the filaments are
composed of uninucleate, in the latter of large multinucleate cells.
The filaments are simple in the lower forms, but branched in the
more advanced ones. The thallus of the Siphonales is formed of a
single multinucleate cell.

Order 1. Volvocales

Typical representatives of this order are characterised by the cilia being retained
by thejr cells in the vegetative stage ; the plants are therefore motile. Each cell
has a nucleus and a chloroplast. The Volvocales thus resemble the Flagellata.

Chlarnydomonas (Fig. 333) and Haematococcus (Fig. 332) are widely distributed
forms consisting of free-swimming cells (29). In the former the cell membrane is
closely applied to the protoplast, at the anterior end of which two cilia and a red
eye-spot are situated ; in the latter genus the membrane is separated from the
protoplast by a gelatinous layer except at the anterior end. Haematococcus
pluvialis occurs commonly in puddles of rain-water, and, like Chlamydomonas
nivalis, which gives rise to "red-snow" and occurs on snow in the Alps, etc.,
is characterised by the presence of a red pigment (haematochrome) in the cells.

DIV. I

THALLOPHYTA

399

Reproduction is both asexual, by swarm-spores, 2-8-16 of which are formed in a
mother cell and are set free by rupture of the membrane, and sexual ; the sexual
reproduction is by conjugation of similar, small, biciliate gametes formed in large
numbers (to 64) in a
mother cell, and uniting
in pairs by their anterior
ends to form a zygote. In
Chid. ni ydomonas cocci-
feru, according to GORO-
SCHA.NKIN (M), there is
in contrast to the other
species a marked differen-
tiation in the sexual
cells. Single cells become
transformed into large,
non-ciliated, female
gametes or egg - cells ;
others divide and each

i : A, swarming cell ;

FIG. 332.— .4, B, Haematococcus pluvialis (x

B, formation of swarm -spores. C-G, Haematococcus Biitschlii :

C, formation of gametes (x400); D, gamete; E, conjugation of
two gametes ; F, G, zygotes (x 800). (C-G after BLOCHMANN.)

gives rise to 16 small,

biciliate male gametes. The transition to oogamy thus occurs in this group even

among the isolated unicellular forms.

Polytoma uvella, which resembles Chlamydomonas in structure, is a colourless

and saprophytic form (Fig. 333, 2).

Under certain conditions some Chlamydomonads lose their cilia and the cells

enclosed in swollen gelatinous walls
undergo divisions and form colonies.
This is termed the Palmella stage. The
cells can again become motile under
favourable conditions.

The biciliate cells of Pandorina,
Eiidorina, Volvox, etc., are united in
colonies or coenobia. In Volvox (Fig.
334), which may be regarded as the
highest form in the order, the free-
swimming colonies have the shape of a
hollow sphere. The component proto-
plasts are connected by fine processes,
so that the organism must be regarded
as constituting a single individual.

The sexual cells are differentiated into

j .j m, ,,

°™ "d ^matozoids. The egg-cells

anse bY tne enlargement of single cells
of the colony ; they are large, green,
non-motile cells surrounded by a muci-
laginous wall. The small spermatozoids

are elongated bodies of a bright yellow colour, provided with two cilia attached
laterally below the colourless anterior end ; they arise by the division of a cell
of the colony into numerous daughter cells. After fusing with a spermatozoid
within the cavity of the colony the egg-cell is transformed into the thick-walled,
resting oospore. The vegetative reproduction of Volvox takes place by the division
of single cells of the colony to form a new daughter colony ; this corresponds
to the formation of swarm-spores in other genera. Eudorina is also oogamous.

CUT

FIG. 333. — 1, Chlamydomonas angulosa (after
DILL); g, cilia; ,, vacuole ; *, nucleus; ckr,
chromatophores ; py, pyrenoid ; a, eye-spot.
2, Polytoma uvella (after DANOEARD). (From
OLTMANSS' Algae.)

400

BOTANY

PABT II

Order 2. Protococcales

These are unicellular green Algae, or their cells are united in colonies of various
form ; the vegetative cells have no cilia, and the cell or colony is consequently
non-motile. Usually each cell contains a nucleus and only one chloroplast.
Reproduction is by means of zoospores, in place of which in many genera non-

FKJ. 334. — Volvox globator. A, Colony showing various stages of development of ova and
spermatozoids (x 165). B, Bundle of spermatozoids formed by division from a single
cell (x 530). C, Spermatozoids (x 530). D, Egg-cell surrounded by spermatozoids in
the mucilaginous membrane (x 265). (After F. COHN.)

ciliated aplanospores are found. Sexual reproduction, when present, takes the
form of conjugation of similar gametes. It has only been demonstrated in certain
genera and appears not to have arisen in the simpler forms.

The simplest forms belong to the genera Chlorococcum and Chlorella (31- 32).
The cells of the former are spherical, and occur in fresh water and also on damp
substrata ; they frequently take part in the composition of Lichen thalli. Asexual
reproduction is by the production from a cell of a Dumber of biciliate zoospores
(Fig. 335) ; under certain conditions these are replaced by aplanospores without
cilia. Chlorella vulgaris (Fig. 336) is a widespread Alga, the small cells of which

DIV. I

THALLOPHYTA

401

formed cell walls. (After BEYERINCK, from
OLTMANNS' Algae.)

often live symbiotically in the protoplasts of lower animals (Infusoriae, Hydra,
Spongilla, Planariae) ; it is multiplied only by division of the cells into 2, 4, or 8
aplanospores which surround themselves with walls and grow to the full size.

The simplest type of cell colony, consisting of four cells, is found in the genus
Scenedcsmus, which is widely spread
in fresh water, and connects on to
Chlorella. The commonest form, Sc.
acutus, has spindle-shaped cells, while
the colonies of Sc. caudatus are dis-
tinguished by four long horn-like pro-
longations of the cell wall (Fig. 337).
In reproduction each cell divides in

the direction of its length into four ^ ^HHH^ ~ Wty 9

daughter cells, which on escaping from
the parent cell form a new colony. More FlG ^^^chlorococcum(Chlorosphaera) limicola. 1,
complicated cell colonies are met with Vegetative cell and cell divided into 8 zoospores;
in Pediastrum (Fig. 338), in which f, free zoospores ; 3, zoospores after they have
each cell-family forms a free-floating
plate, composed internally of polygonal
cells, while on the margin it consists of cells more or less acutely crenated. The
formation of asexual swarm-spores is effected in Pediastrum by the division of
the contents of a cell into a number (in the case of the species illustrated, P. granu-
latum, into 16) of naked swarm-spores, each with two cilia. The swarm-spores,
on escaping through the ruptured cell wall (Fig. 338 A, 6), are enclosed in a
common envelope. After first moving vigorously about within this envelope, they

eventually collect together and form a
new cell-family. Pediastrum also pos-
sesses a sexual mode of reproduction.
The gametes are all of equal size, and,
except that they are smaller and are
produced in greater numbers, are
similar to the swarm - spores. They
move freely about in the water, and
in conjugating fuse in pairs to form
zygotes. The further development of
the zygotes into cell-families is not yet
fully known.

Fio. 336.— Chlorella i-ulgaris. l, Cell ; », 3, division The life-history of the Water-net
into four aplanospores; *, 5, division into eight (Hydrodictyon utriculatuni) (*•**) is
aplanospores. (After GRINTZESCO.) , . ,, . ., T, . ,. ,,

essentially similar. It is one of the

most beautiful of the free-floating, fresh-water Algae, the hollow cylindrical colonies
being formed of elongated cells united together to form a many-meshed net.

The Protococcales like the Volvocales can be derived from .the Flagellata. In
contrast to the latter group the non-motile, non-ciliated condition of the cells has
become prevalent as it has throughout the higher Algae. In some genera of the
Protococcales even the spores do not develop cilia, although, as a rule, the repro-
ductive cells of the Algae tend to retain the Flagellate character. The loss of
motility is accompanied by a more complex external form of the cells.

Order 3. Ulotrichales

The Ulotrichales exhibit, as compared with the unicellular green Algae, an
advance in the external segmentation of the thallus. It is always multicellular,

402

BOTANY

PART II

and, in most of the genera, consists of simple or branched filaments. The
filaments are either attached by a colourless basal cell to the substratum
(Fig. 340 A) or float free. The thallus of the marine genus Ulva (Ulva lactuca,
SEA LETTUCE) has the form of a large, leaf-like cell surface, and is two layers
of cells thick (Fig. 81, young plant). In Enteromorpha (Fig. 339) the thallus is
ribbon-shaped, either cylindrical or flattened ; when young it is two-layered, but
later it becomes hollow, the wall thus consisting of one layer of cells. Although
the majority of the Ulotrichales live in fresh or salt water, a few aerial forms
(Chroolepideae) grow on stones, trunks of trees, and, in the tropics, on leaves.
To this family belongs Trentepohlia (or Chroolepus] Jolithus, often found growing
on stones in mountainous regions. The cell filaments of this species appear red
on account of the haematochrome they contain and possess a violet-like odour.

The cells have always only one nucleus
and also a single chloroplast. \

The asexual reproduction is accom-
plished by the formation of ciliated swarm-
spores. Sexual reproduction is effected
either by the fusion of planogametes, or

FIG. 337. — A, Scenedesmus acutus. B, The same,
undergoing division. C, Scenedesmus caudatus.
(x 1000. After SENN.)

Fio. 338.— Pediastrum granulatum. A, An old
cell-family : a, cells containing spores ; b,
spores in process of extrusion (the other
cells have already discharged their spores).
B, Cell-family shortly after extrusion of the
spores. C, Cell-family 4i hours later, (x 300.
After AL. BRAUN.)

the sexual cells are differentiated as non-motile egg-cells and motile 'sperm atozoids.
Ulothrix zonata (2) (Fig. 340 A) is one of the commonest filamentous Algae.
The filaments of Ulothrix exhibit no pronounced apical growth ; they are
unbranched, attached by a rhizoid cell, and consist of rows of short cells ; each
cell contains a band -shaped chloroplast. The asexual reproduction is effected
by means of swarm-spores, which have four cilia (C), and are formed singly or by
division in any cell of the filament. The swarm-spores escape through a lateral
opening (B} formed by absorption of the cell wall, and, after swarming, give rise to
new filaments. The sexual swarm cells, or planogametes, are formed in a similar
manner by the division of the cells, but in much greater numbers. They are
also smaller, and have only two cilia (JE). In other respects they resemble the
swarm-spores, and possess a red eye-spot and one chromatophore. By the con-
jugation of the planogametes in pairs, zygotes (F-H] are produced, which, after
drawing in their cilia, round themselves off and become invested with a cell wall.
Ulothrix is dioecious, for gametes derived from the same filament do not fuse, but
only those of distinct origin. After a shorter or longer period of rest the zygotes are

DIV. I

THALLOPHYTA

403

converted into unicellular germ plants («7), and give rise to several swarm-spores
(K), which in turn grow out into new filaments. Under some conditions the
planogametes can give rise to new plants parthenogenetically without conjugating.
Further, the filaments can, in addition to the swarm -spores with four cilia
described above, produce others of smaller size (micro-zoospores) which resemble
the gametes. These possess four or two cilia, and as a rule die if the temperature
of the medium is above 10° ; below this temperature they come to rest after a few-
days and proceed to germinate slowly. This Alga is thus of interest from the
incomplete sexual differentiation exhibited by its gametes.

The genera Oedogonium (**) and Bulbochaete may be quoted as examples of
oogamous Ulotrichales. While the thallus of the latter is branched, the
numerous species of Oedogonium
consist of unbranched filaments,
each cell of which possesses one
nucleus and a single parietal
chromatophore composed of
numerous united bands. The
asexual swarm -spores of Oedo-
gonium are unusually large, and
have a circlet of cilia around
their colourless, anterior ex-
tremity (Fig. 341 B). In this
case the swarm -spores are formed
singly, from the whole contents
of any cell of the filament (A),
and escape by the rupture of
the cell wall. After becoming
attached by the colourless end
they germinate, giving rise to a
new filament. For the purpose
of sexual reproduction, on the
other hand, special cells become
swollen and differentiated into
barrel- shaped oogonia. A single
large egg -cell with a colourless
receptive spot is formed in each oogonium by the contraction of its protoplasm,
while the wall of the oogonium becomes perforated by an opening at a point
opposite the receptive spot of the egg. At the same time, other, generally
shorter, cells of the same or another filament become converted into antheridia.
Each antheridium usually gives rise to two spermatozoids. The spermatozoids are
smaller than the asexual swarm-spores, but have a similar circlet of cilia. They
penetrate the opening in the oogonium and fuse with the egg-cell, which then
becomes transformed into a large firm -walled oospore. On the germination of
the oospore its contents become divided into four swarm-spores, each of which
gives rise to a new cell filament. In the adjoining figure (Fig. 342) a germinating
oospore of Bulbochaete with four swarm-spores is represented.

In some species of Oedogonium the process of sexual reproduction is more
complicated, and the spermatozoids are produced in so-called DWAUF MALES. These
are short filaments (Fig. 341 C, a) consisting of but few cells, and are developed
from asexual swarm-spores (ANDROSPOIIES) which, after swarming, attach them-
selves to the female filaments, or even to the oogonia. In the upper cells of the

FIG. 339. — Enteromorpha compressa. (5 nat. size.)

404

BOTANY

PART II

dwarf male filaments thus derived from the androspores, spermatozoids are pro-
duced which are set free by the opening of a cap-like lid (Fig. 341 Dt a).

The genus Coleochaete (35) is also oogamous (Fig. 343). The long colourless neck of
the flask-shaped oogonium opens at the tip to allow of the entrance of the spermato-

zoid. The spherical oospore increases
in size and becomes surrounded by
a single layer of pseudo-parenchy-
matous tissue derived from filaments
that spring from the stalk cell of the
oogonium and neighbouring cells.
In this way a fruit-like body is
formed. On germination the oospore
undergoes a reduction division and
divides into 16-32 wedge-shaped
cells, then breaks up and liberates
^ \ \ \\ a swarm-spore from each cell.

Order 4. Siphonocladiales

The Algae of this order are fila-
mentous and usually branched ;
they are distinguished from the
Ulotrichales by their large multi-
nucleate cells, the chloroplasts of
which are either solitary, large, and
reticulately- formed, or appear as
numerous small discs.

The genus CladopJiora, numerous
species of which occur in the sea
and in fresh water, is one of the
most important representatives of
the order. 01. glomerata (Fig. 84)
is one of the commonest Algae in
streams, often attaining the length
of a foot. It is attached by rhizoid-
like cells, and consists of branched
filaments with typical apical growth
which some other representatives
of the order do not show. The
structure of the cells is represented
in Figs. 7, 9, and 18. Branching
takes place from the upper ends of
the cells by the formation of a pro-
trusion which is cut off as the first cell of the branch. Asexual reproduction
is by means of biciliate zoospores (Fig. 344), which arise in numbers from the
upper cells of the filaments, and escape from these sporangia by a lateral opening
in the wall. The sexual reproduction is isogamous as in Ulothrix.

Only in the genus Sphaeroplea has the sexual reproduction become oogamous.
S. annulina consists of simple filaments and occurs in fresh water.

Many forms occur in the sea (e.g. Siphonocladus), and some have a highly
complicated thallus, which is always, however, formed of branched filaments ; by
calcareous incrustation some forms come to resemble coral. Acetabularia mediter-

FIG. 340.— Ulothrix zonata. A, Young filament with
rliizoid cell r (x 300) ; B, portion of filament with
escaping swarm-spores ; C, single swarm-spore ; D,
formation and escape of gametes ; E, gametes ; F, G,
conjugation of two gametes ; H, zygote ; J, zygote
after period of rest ; K, zygote after division into
swarm-spores. (B-K x 482. After DODEL.)

DIV. I

THALLOPHYTA

405

FTQ. 341. — A, B, Oedogonium. : A, escaping swarm-spores ; B, free
swarm-spore. C, D, Oedogonium dliatum : C, before fertilisa-
tion ; D, in process of fertilisation ; o, oogonia ; a, dwarf
males ; S, spermatozoid. (x 350. After PRINGSHEIM. )

FIG. 342.— Bulbochaete inter-
media. A, Oospore. B,
Formation of four swarm-
spores in the germinating
oospore. (x 250. After
PRINGSHEIM.)

ranea (Fig. 345) will serve as an example of such calcareous Algae. The thin stalk
of the thallus is attached by
means of rhizoids, while the
umbrella-like disc consists of
closely united tubular out-
growths, each of which is to
be regarded as a gametangium.
The contents of the latter do
not form the biciliate gametes
directly, but first divide into
a large number of firm-walled
cysts. These remain in the
resting condition throughout
the winter, and then give rise
to numerous gametes which
conjugate in pairs. Thezygotes
germinate promptly and grow
into new plants.

Order 5. Siphonales

The Siphoneae are distin-
guished from the preceding
groups of Algae by the struc-
ture of their thallus, which,
although more or less profusely
branched, is not at first divided
by transverse septa. The cell
wall thus encloses a continu-
ous protoplasmic body in which FlG- 343.— Coleochaete pulrinata. 1, Antheridium (a) and
numerous nuclei and small >'oun§ °°g°nium (°>- *. Oogonium shortly before open
,, , . ing. 3, Fertilised oogonium ; ek, nucleus of the ovum ;

green chloroplasts are em- sk> male nucleugi ^ Oospore enclosed to form the

bedded. The same type of « fructification." 5, Germinating oospore. (After
thallus is also met with in OLTMANSS.)

406

BOTANY

PART II

the Phycomycetes or Algal
Fungi.

The majority of the Siphoneae
inhabit the sea, and on account
of the complicated segmentation
of their thallus, afford one of
the most interesting types of
algal development. The genus
Caulerpa (36), represented by
many species inhabiting the
warmer water of the ocean, has
a creeping main axis. Increasing
in length by apical growth, the

FIG. 344. — Cladophora glomerata.
Swarm-spore. ( x 500. Alter STRAS-

BURQER.)

FIG. 345. — Acftabularia mediterranea.
(Nat. size. After OLTMANNS.)

FIG. 346. — Caulerpa prolifera. The shaded lines on the
thallus leaves indicate the currents of protoplasmic move-

stem-like portion of the thallus
gives off from its under surface
profusely-branched colourless
rhizoids, while, from its upper
side, it produces green thalloid
segments, which vary in shape
in the different species. In
Caulerpa prolifera (Fig. 346),
which occurs in the Mediter-
ranean, these outgrowths are
leaf -like and are frequently
proliferous. In other species
they are pinnately lobed or
branched. The whole thallus,
however branched and seg-
mented it may be, encloses
but one cell-cavity, which is,
however, often traversed by a
network of cross -supports or
trabeculae. Starch - forming
leucoplasts are present in the
colourless parts of the thallus.
The genus Bryopsis, on the
other hand, has a delicate, pin-
nately -branched thallus (37).
The thallus of Halvmeda, the

ment. a, Growing apex of the thallus axis ; b, b, young s
thallus lobes ; r, rhizoids. Q nat. size.)

of which occur in the
warmer seas, is composed of

DIV.

THALLOPHYTA

407

flattened segments, and resembles an Opuntia on a small scale. By incrustation
with lime it attains a hard, coral -like texture. The segments are formed of
branched tubular filaments.

In Bryopsis the biciliate, pear-shaped, conjugating gametes are differentiated
into a larger female cell with a green chromatophore and a smaller male cell,
three times smaller than the female and with a single yellow chromatophore ;

FIG. 347. —Tt" - A, Young sporangium. B, Zoospore with the sporangium from

which it has escaped. C, A portion of the peripheral zone of a zoospore. D, A young plant
with rhizoids developed from a zoospore. (A, B after GOTZ ; D after SACHS ; from OLTMANNS'

Algae. C after STRASBURGER.)

in J'aucheria and Dichotomosiphon oogamous reproduction is well marked (3S).
The latter Algae occur in fresh water or on damp soil. The thallus consists of a
single branched filamentous cell attached to the substratum by means of colour-
less rhizoids (Fig. 3-47 D).

The swarm-spores of l\m.cheriat which differ from those of the other Sipho-
nales, are developed in special sporangia, cut off from the swollen extremities of
lateral branches by means of transverse walls (Fig. 347). The whole contents of
such a sporangium become converted into a single green swarm-spore. The wall

2 D2

408

BOTANY

PART II

of the sporangium then ruptures at the apex, and the swarm-spore, rotating
on its longitudinal axis, forces its way through the opening. The swarm -spore
is so large as to be visible to the naked eye, and contains numerous nuclei
embedded in a peripheral layer of colourless protoplasm. It is entirely surrounded
with a fringe of cilia, which protrude in pairs, one pair opposite each nucleus.
Morphologically the swarm -spores of Vaucheria correspond to the total mass of
individual zoospores of an ordinary sporangium.

The sexual reproduction of Vaucheria is not effected, like that of the other
Siphoneae, -by the conjugation of motile gametes, from which, however, as the
earlier form of reproduction, it may be considered to have been derived. The
oogonia and antheridia first appear as small
protuberances, which grow out into short lateral
branches, and become separated by means of
septa from the rest of the thallus (Fig. 348 o, a).
At first, according to OLTMANNS and HEIDINGEK,
the rudiment of an oogonium contains numerous
nuclei, of which all but one, the nucleus of the
future egg-cell, retreat again into the main
filament before the formation of the septum.
In its mature condition the oogonium has on
one side a beak-like projection containing only

FIG. 348. — Vaucheria sessilis. Portion of a filament
with an oogonium, o ; antheridium, a ; ch, chro-
matophores ; n, cell nuclei ; ol, oil globules,
(x 240. After STRASBURGER.)

Fio. 349. — Botrydinm granulatum.
A , The whole plant. B, Swarm-
spore. (A x 28 ; B x 540. After
STRASBURGER.)

colourless protoplasm. The oogonium opens at this place, the oosphere rounding
itself off. The antheridia, which are also multinucleate, are more or less coiled (a],
and open at the tip to set free their mucilaginous contents, which break up into a
number of swarming spermatozoids. The spermatozoids are very small, and have
a single nucleus and two cilia inserted on one side. They collect around the
receptive spot of the egg-cell, into which one spermatozoid finally penetrates.
After the egg-cell has been fertilised by the fusion of its nucleus with that of
the spermatozoid, it becomes invested with a wall and converted into a resting
oospore. On germination the oospore grows into a filamentous thallus.

Botrydium granulatum (Fig. 349), which was formerly included in the Hetero-
contae, may be placed in the Siphoneae. This Alga is cosmopolitan and grows
on damp clayey soil, where it forms groups of green balloon-shaped vesicles about
2 mm. in size. These are attached to the soil by branched colourless rhizoids. The
whole plant corresponds to a single multinucleate cell ; its protoplasm contains
numerous green chloroplasts. The zoospores, produced in large numbers by the

Div. i THALLOPHYTA 409

division of the contents, escape by an opening at the summit. Each has a single
cilium and contains two chloroplasts. After swarming the spore surrounds itself
with a wall and grows into one of the balloon-shaped plants. Sexual reproduction
is not known (2).

CLASS X
Phaeophyeeae (Brown Algae) (J> "• 39'47)

The Phaeophyeeae, like the Chlorophyceae, can be derived from
Flagellata. They attain a higher grade of organisation in their
vegetative organs than do the Green Algae.

With the exception of a very few fresh- water species, the
Phaeophyeeae are^ only found in salt water. They attain their
highest development in the colder waters of the ocean. They
show great diversity in the form and structure of their vegetative
body. The simplest representatives of this class (e.g. the genus
Ectocarpus) have a filamentous thallus consisting of a branched or
unbranched row of simple cells. Some Phaeophyeeae, again, have a
cylindrical, copiously-branched, multicellular thallus (e.g. Cladostephus),
whose main axes are thickly beset with short multicellular branches
(Fie. 89) : while in other cases the multicellular thallus is ribbon-shaped

\ O / ' *

and dichotomously branched (e.g. Dictyota, Fig. 83). Growth in length
in both of these forms ensues from the division of a large apical cell
(Figs. 89 and 90). Other species, again, are characterised by disc-
shaped or globose thalli.

The Laminariaceae and Fucaceae include the most highly developed
forms of the Phaeophyeeae. To the first family belongs the genus
Laminaria found in the seas of northern latitudes. The large
stalked thallus of the Laminarias resembles an immense leaf ; it is
attached to the substratum by means of branched, root-like holdfasts,
developed from the base of the stalk.

In Laminaria digitata and L. Cloustoni (Fig. 351), a zone at the base of
the palmately-divided, leaf-like expansion of the thallus retains its meristematic
character, and by its intercalary growth produces in autumn and winter a new
lamina on the perennial stalk. The older lamina becomes pushed up and gradually
dies, while a new one takes its place and becomes in turn palmately divided by
longitudinal slits. The large size of their thalli is also characteristic of the
Laminarias ; L. saccharina (North Sea), for instance, has an undivided but
annually renewed lamina, frequently 3 m. long, and a stalk more than 1 cm. thick.

The greatest dimensions attained by any of the Phaeophyeeae are exhibited by
certain of the Antarctic Laminariaceae. Of these, Macrocystis pyrifera(^\g. 350) is
noted for its gigantic size ; the thallus grows attached to the sea-bottom at a depth
of 2-25 m., and, according to SKOTTSBERG (&), is at first dichotomously branched.
Single shoots of the thallus grow to the surface of the water, and floating there attain
a great length ; they bear on one side long flat lobes divided at their free ends,
and having at the base of each a large swimming bladder. In the Antarctic
SKOTTSBERG measured examples 70 m. long, while FRYE, RIGG, and CRANDALL

410

BOTANY

PART II

determined the length on the coasts of California as 457 m. Other noteworthy
forms are the Antarctic species of Lessonia. in which the main axis is as thick as
a man's thigh ; from it are given off lateral branches with hanging leaf -like
segments. The plant attains a height of several metres, and has a tree-like habit
of growth.

The Fucaceae (40), although relatively large, do not compare with the Lami-
nariaceae in size. As examples of well-known forms of this order may be cited

FIG. 35Q.—Macrocystispyrifem, Ag. «, Younger, b, older
thallus. (s'5 nat. size. After SKOTTSBERG.)

Fucus vesiculosus, which has a ribbon-shaped,
dichotomously - branching thallus with air-
bladders, Fucus platycarpus without bladders,
and Fucus serratus (Fig. 352) with a toothed
thallus. They are fastened to the substratum
by discoid holdfasts, and growing sometimes
over 1 metre long are found covering extended
areas of the littoral region of the sea-coast.
Sargassum, a related genus chiefly inhabiting
tropical oceans, surpasses the other Brown
Seaweeds in the segmentation of its thallus.
The thallus of Sargassum shows, in fact, a
distinction into slender, branched, cylindrical
axes with lateral outgrowths, which, according
to their function, are differentiated as foliage,
bracteal, or fertile segments, or as air-bladders.
The species of Sargassum which in the
warmer regions of the ocean often form large

yellowish-brown floating masses are worthy of note. In the Sargasso Sea of the
Atlantic Ocean there are according to BORGESEN two species (S. natans = S. bacci-
ferum and S. fluitans) which have this exclusively pelagic mode of life. They
have reproduced here for ages by vegetative budding, though originally coming
from attached species of the coasts of the West Indies and tropical America (41).
S. natans also occurs in the Pacific.

The cells of the Phaeophyceae (42) have usually but one nucleus.
They contain a larger or smaller number of simple or lobed, disc-

FIG. 351. — Laminciria Cloustoni, Xorth
Sea. (Reduced to J.)

DIV. 1

THALLOPHYTA

411

shaped, brown chromatophores, giving to the algae a yellowish-brown
or dark-brown colour. In addition to the pigments of chlorophyll

FIG. 352.— Fucus serratus. To the left the end of an older branch bearing conceptacles. (J nat. size.)

they contain a special yellow pigment, phycoxanthin (fucoxanthin). A
polysaccharid called laminarin arises as a metabolic product from glucose,
while in addition mannite is formed. Small vacuoles containing a
tannin-like substance called fucosan are generally distributed in the

412

BOTANY

PART II

cells ; this is a by-product of the process of assimilation. Among the
more highly developed forms the thallus exhibits a well-differentiated
anatomical structure. The outer cell layers, as a rule, function as
an assimilatory tissue, the inner cells as storage reservoirs. In the
Laminariaceae and Fucaceae structures closely resembling the sieve-
tubes of the cormophytes occur, and conduct albuminous substances.

Even in the largest Sea-weeds (including the Red Algae) intercellular spaces
containing air are wanting in the tissues. According to KNIEP the gaseous inter-
changes in assimilation, and especially in respiration, are on this account difficult

in the more massive Algae. On the other hand,
gases readily diffuse through algal cell walls.

Four orders of the Phaeophyceae may
be distinguished. The Phaeosporeae include
forms with simple structure of the thallus
which is frequently filamentous. They are
vegetatively reproduced by means of zoo-
spores and sexually by ciliated gametes.
They thus resemble the simpler Green Algae.
The Tilopteridaceae and Dictyotaceae stand at
a higher level, their sexual cells being differ-
entiated as large non-motile egg-cells and
small ciliated spermatozoids. Their sexual
cells are formed on special sexual individuals
or gametophytes. From the fertilised egg
the asexual generation or sporophyte is
FIG. 353. -.4, pieurodadia locust™, developed ; this is similar to the gametophy te,
Uniiocuiar sporangium with its but produces the asexual spores so that there
SStrrS.^ £ is a "^-marked alternation of generations
chromatophore. (After RLE- which is also apparent in some of the Phaeo-
BAHN.) B, Chorda fiium. Zoo- sporeae. In the Laminariaceae also there is

spores. (After REINKE.) (From i i, -• £

OLTMANNS' Algae.) oogamy and a regular alternation ot genera-

tions, but the sporophyte and gametophyte

are very unlike, the latter being a small filamentous dwarf plant.
The Fucaceae are also characteristically oogamous, but produce no spores
and thus lack an alternation of generations.

The zoospores, gametes, and spermatozoids are spindle-shaped and always have
a red eye-spot and two laterally inserted cilia, one directed forwards and the other
backwards. They have a great resemblance to certain brownish-yellow Flagellata.

Order 1. Phaeosporeae

In this order are included the majority of the Phaeophyceae. A sexual multi-
plication is effected by means of swarm -spores, which are produced in large numbers
in simple (unilocular) sporangia and germinate shortly after swarming (Fig. 353).

In addition to unilocular sporangia, multilocular sporangia are produced in the
Phaeosporeae (Fig. 354). Each cell of the multilocular sporangium produces a single
swarm-spore, rarely several. The conjugation of these swarm-spores has been
observed in some genera. On this account these swarm-spores must be termed

DIV. I

THALLOPHYTA

413

planogametes, and the corresponding sporangia gametangia. The degree of sexual
differentiation varies, and in some cases the swarm-spores produced in multilocular

FIG. 355. — Ectocarpus siliciilosus. 1, Female
garnet* surrounded by a number of male
gametes ; seen from the side. 2-5, Stages in
the fusion of gametes. 6, Zygote after 24
hours. 7-9, Fusion of the nuclei in conjuga-
tion, as seen in fixed and stained material.
(1-5 after BERTHOLD ; 6-9 after OLTMANXS.)

FIG. 354.— A, Ectocarpus siliculosns. Plurilocular
sporangium liberating its contents. (After
THURET.) B, C, D, Sphacelaria cirrhosa, de-
velopment of the plurilocular sporangium.
(After REIXKE.) (From OLTMANXS' Algae.)

FIG. 356. — A, Antheridium ; B, Oogonium of
Cutleria multifida. (x 400. After REIXKE.)

sporangia can germinate without conjugating, as was seen to occur in Ulothrix
among the Chlorophyceae.

Ectocarpus siliculosus (Fig. 354) will serve as an example of the mode of con-
jugation of gametes produced from multilocular gametangia. The gametes are
similar in form, but their different behaviour allows of their distinction into male
and female which are formed in distinct gametangia, borne on the same or different

414

BOTANY

TART II

plants. The female gamete becomes attached to a substratum, and numerous
male gametes gather around it (Fig. 355, 1). Ultimately a male gamete fuses
with the female to form a zygote (Fig. 355, 2-9). This contains after the fusion
a single nucleus, but two chrornatophores, and soon becomes attached and
surrounded by a cell wall ; it grows into a new plant.

In other Phaeophyceae the distinction between the two kinds of gametes is
expressed in their shape and size. The Cutleriaceae afford a particularly good
transition from isogamy to oogamy and a differentiation of the gametangia into
antheridia and oogonia (Fig. 356).

In certain Phaeosporeae, e.g. the Cutleriaceae (43), a regular alternation of genera-
tions is found. The haploid sexual plants alternate with diploid asexual individuals,

FIG. 357. — Dictyota dichotoma. Transverse sections of the thallus. 1, With tetrasporangia ;
with a group of oogonia ; 3, with a group of antheridia (after THURET). A, Spermatozoid
(after WILLIAMS). (From OLTMANNS' Algae.)

the reduction division taking place in the zoosporangia. In Zanardinia the two
generations are alike and have a disc-shaped thallus. In Cutleria, on the other
hand, they are unlike, the sexual plant having erect, dichotomously-divided shoots,
while the sporophytic plants (Aglaozonia) form flat, lobed, prostrate discs. The
alternation of generations is not always strictly maintained in Cutleria, since both
sporophyte and gametophyte may give rise to its like.

Order 2. Tilopteridaceae (44)

This order includes only a few forms which in vegetative, habit correspond
to the simpler Phaeosporeae such as Ectocarpus. A single large egg-cell is
produced in each oogonium, while the antheridia give rise to small biciliate
spermatozoids. In the asexual sporangia there is no division into spores, but the
contents become a single large monospore with four nuclei and enclosed by a cell
wall, while in the Dictyotaceae four free spores are formed.

DIV.

THALLOPHYTA

415

Order 3. Dictyotaceae (45)

Only a small number of forms belong to this family. The fan-shaped Padina
pavonia, which occurs in the Mediterranean, and Dictyota dichotoma, with a forked
ribbon-shaped thallus, which is widely spread in the European seas (Fig. 83), are
examples. The spores are formed as in the Red Algae in sporangia ; usually there
are four spores (tetraspores), less commonly eight. They have no cell walls and
are unprovided with cilia and must be termed aplanospores (Fig. 357, 1). The
tetrasporangia may be derived from the unilocular sporangia of the Phaeosporeae.
The oogonia and antheridia in Dictyota are grouped in sori (Fig. 357, 2, 3), and

D v; F

FIG. 358. — Laminaria digitata. A, Male gametophyte ; a, empty antheridia. B, C, D, Female
gametophytes (B is large, C small, while D is reduced to a single oogonium) ; og, oogonium ;
o, egg-cell. E, Young sporophyte, still seated on the empty oogonium. Ft Further developed
sporophyte with the rhizoids. (A x 600 ; B x 292 ; C x 322 ; D x 625 ; E X 322 ; F X 390.
After H. KYLIX.)

arise from adjacent cortical cells, each of which divides into a stalk cell and the
oogonium (or antheridium). The peripheral cells of the autheridial group remain
sterile and form a kind of indusium. Each oogonium forms a single uninucleate
oosphere ; the antheridia become septate, resembling the plurilocular gametangia,
and each cell gives rise to a spermatozoid. This, in contrast to the spermatozoids
of other Brown Algae, has a single long cilitim, inserted laterally. The zygote
germinates without undergoing a period of rest.

Dictyota is dioecious. The male and female plants arise from the asexually-
produced tetraspores ; from the fertilised ovum plants which bear tetraspores are
developed. In the tetrad division in the sporangia the number of chromosomes
becomes reduced from 32 to 16, and the reduced number is maintained in all the
nuclei of the sexual plants, the double number being again attained in fertilisation.
There is thus a true alternation of generations. The sexual generation (gametophyte)

416

BOTANY

PART II

and the asexual generation (sporophyte) do not, however, show differences in
structure.

Order 4. Laminariaceae (46)

The regular alternation of generations of these plants, which are the largest of the
Brown Algae, corresponds with that in Ferns in that the gametophyte in contrast to
the sporophyte is very small. The large sporophyte bears club-shaped or cylindrical
sporangia forming an extensive superficial layer. Each surface cell of the thallus is
prolonged as a club-shaped sterile cell or paraphysis beside which the sporangia arise
as shorter cells. The reduction division takes place in the sporangia. From the

biciliate swarm-spores minute fila-
mentous male and female gameto-
phytes develop (Fig. 358). The
former are abundantly branched, while
the latter consist of few cells and in
extreme cases may be reduced to a
single cell. The male gametophytes
bear the antheridia beside or behind
one another at the tips of the branches.
Each antheridium gives rise to one
spermatozoid. Any cell of the female
gametophyte may form an oogonium,
from an opening at the summit of
which the naked egg -cell emerges.
This remains in front of the opening
and after fertilisation (which has not
been observed) proceeds to grow into
the young sporophyte (Fig. 358 E. F].
The oogonia and antheridia are homo-
logous with the gametangia of the
Phaeosporeae.

PASCHEII has observed on culti-
vated young sporophytesof Laminaria.
saccharina an extremely early pro-
duction of sporangia. Thus the sporo-
phyte, which is usually of large size, may under particular external conditions
undergo profound reduction in size. A point of view is thus attained from which
the striking dimorphism of the two generations may be explained.

Order 5. Fucaceae (47)

Asexual reproduction is wanting in this order, while sexual reproduction is
distinctly oogamous. The oogonia and antheridia of Fucus are formed in special
flask-shaped depressions termed CONCEPTACLES, which are crowded together below
the surface in the swollen tips of the dichotomously-branched thallus (cf. F. scrratus,
Fig. 352). The conceptacles of F. platycarpus (rig- 359) contain both oogonia and
antheridia, while F. vesiculosus, on the contrary, is dioecious. From the inner wall of
the conceptacles, between the oogonia and antheridia, spring numerous unbranched
sterile hairs or PARAPHYSES, some of which protrude in tufts from the mouth of the
conceptacle (Fig. 359 p). The antheridia are oval in shape, and are formed in
clusters on special short and much-branched filaments (Figs. 359 a, 360, 1). The
contents of each antheridium separate into sixty-four spermatozoids, which are dis-

a o o

FIG. 359. — Fucus platycarpus. Monoecious con-
ceptacle with oogonia of different ages (o), and
clusters of antherid ia (a) ; p, paraphy ses. ( x circa
25. After THURET.)

DIV. I

THALLOPHYTA

417

charged in a mass, still enclosed within the inner layer of the antheridial wall (Fig.
360, 2). Eventually set free from this outer covering, the spermatozoids appear as

FIG. 360.— Fucus. 1, Group of antheridia. 2, Antheridia showing escaping spermatozoids. 3,
Oogonium, the contents of which have divided into eight egg-cells. U, Contents separated
from stalk (st). 5, Liberation of the egg-cells. 6, Oosphere surrounded by spermatozoids.
(After THURET. From On MANNS' Algae.)

somewhat elongated ovate bodies, having two lateral cilia of unequal length and
a red eye-spot. The oogonia (Figs. 359 o ; 360, 3) are nearly spherical, and are
borne on a short stalk consisting of a single cell. They are of a yellowish-brown
colour, and enclose eight spherical egg-cells which are formed by the division

418 BOTANY PABT n

of the oogonium mother cell and are separated by delicate cell walls. The eggs
are enclosed within a thin membrane when ejected from the oogonium. This
membranous envelope deliquesces at one end and, turning partly inside out,
sets free the eggs (Fig. 360, 4, 5). The spermatozoids then gather round the eggs
in such numbers that by the energy of their movements they often set them
in rotation (Fig. 360, 6). After an egg has been fertilised by the entrance of one
of the spermatozoids it becomes invested with a cell wall, attaches itself to the
substratum, and gives rise by division to a new plant.

In the case of other Fucaceae which produce four, two, or even only one egg 'in
their oogonia, the nucleus of each oogonium, according to OLTMANNS, nevertheless
first divides into eight daughter nuclei, of which, however, only the proper
number give rise to eggs capable of undergoing fertilisation. The other reduced
eggs, incapable of fertilisation, degenerate.

Since the Fucaceae have no asexual spore-formation the alternation of genera-
tions characteristic of Dictyota is wanting in them. The thallus of Fncus,
developed from the fertilised ovum, has diploid nuclei. Reduction takes place in
the first two divisions within the oogonium and antheridium, so that four haploid
nuclei result. In the oogonium one further division, and in the antheridium four
take place before the sexual cells are produced. Thus in Fucus, in contrast to
Dictyota, only a very short haploid stage can be recognised.

Economic Uses. — The dried stalks of Laminaria digitata and L. Cloustoni were
used as dilating agents in surgery. IODINE is obtained from the ash (varec, kelp)
of various Laminariaceae and Fucaceae, and formerly soda was similarly obtained.
Many Laminarias are rich in MANNITE (e.g. Laminaria saccharina), and are used in
its production, and also as an article of food by the Chinese and Japanese.

CLASS XI
Charaeeae (Stoneworts) (1( n> 48)

The Charaeeae or Charophyta form a group of highly organised green Thallo-
phytes sharply isolated from both simpler and higher forms. Their origin must
be looked for in the Chlorophyceae, but the complicated structure of their sexual
organs does not allow of any immediate connection with the oogamous Green Algae.
On the other hand, in certain characters they show some approach to the Brown
Algae, from which they differ in the pure green colour of the chromatophores.
They cannot be regarded as leading towards the Bryophyta although their karyo-
kinetic nuclear division exhibits a great agreement with that of the Archegoniatae.

The Charaeeae grow in fresh or brackish water, attached to the
bottom and covering extended areas with a mass of vegetation. Their
regular construction and habit is characteristic. In some species
the cylindrical main axes are over a foot in length, and are composed
of long internodes alternating with short nodes, from which short
cylindrical branches are given off in regular whorls with a similar
structure, but of limited growth (Fig. 361). The lateral axes are
either unbranched or give rise at their nodes to verticillate outgrowths
of a second order. From the axil of one of the side branches of each
whorl a lateral axis resembling the main axis is produced. The attach-
ment to the substratum is effected by means of colourless branched
rhizoids springing from the nodes at the base of the axes. The rhizoids

DIV. I

THALLOPHYTA

419

show a similar segmentation into long internodal cells and nodal cells
that are laterally displaced. Branching takes place at the nodes.

Both the main and lateral axes grow in length by means of an apical cell, from
which other cells are successively cut off by the formation of transverse walls.
Eacli of these cells is again divided by a transverse
wall into two cells, from the lower of which a long
interuodal cell develops without further division ;
while the upper, by continued division, gives rise
to a disc of nodal cells, the lateral axes, and also,
in the lower portion of the main axis, to the rhizoids.
In the genus Xitella the long internodes remain naked,
but in the genus Chara they become enveloped by a
cortical layer consisting of longitudinal rows of cells
which develop at the nodes from the basal cells of the
lateral axes. A corresponding construction is found
among other Thallophyta in certain Brown Algae (e.g.
Spertna tochnus).

Each cell contains one normal nucleus derived
from a karyokinetic division. As a result of
the fragmentation of its original nucleus, how-
ever, each internodal cell is provided with a
number of nuclei which lie embedded in an
inner and actively -moving layer of parietal
protoplasm. Numerous round chloroplasts are
found -in the internodal cells.

Asexual reproduction by means of swarm-
spores or other spores is unrepresented in the
Characeae. Sexual reproduction, on the other
hand, is provided for by the production of egg-
cells and spermatozoids. The female organs are
ovate. They are visible to the naked eye, and,
like the spherical red-coloured anthericlia, are
inserted on the nodes of the lateral axes. With T

FIG. 361.— Chara fragilis. End

the exception of a few dioecious species, the Of main shoot, (Nat. size.)
Characeae are monoecious. The fertilised egg-
cell develops into an oospore. The Characeae thus exhibit no altera-
tion of generations but a succession of gametophytes.

The male organs (Fig. 362 A) are developed from a mother cell
that first becomes divided into eight cells. Each octant by two
tangential walls gives rise to three cells. In this way are derived the
eight external tabular cells of the wall, the cavities of which are in-
completely partitioned by septa extending in from the cell wall ; the
eight middle cells form the manubria and become elongated ; the eight
innermost cells assume a spherical form as the primary head cells.
Owing to the rapid surface growth of the eight shield cells a cavity
is formed within the male organ into which the manubria bearing the

420

BOTANY

PART II

head cells project. The latter form 3-6 secondary head cells, and from
each of these arise 3-5 long unbranched spermatogenous filaments.
These are composed of disc-shaped cells from each of which a spirally-
wound spermatozoid with two cilia is liberated
(Fig. 362 C). The spermatogenous filaments
or antheridia may be compared morphologi-
cally to the plurilocular gametangia of the
Brown Algae. These, as in Stilophora for in-
stance, may consist of simple rows of cells and

FIG. 362. — Chara fragilis. A, Median longitudinal section through a lateral axis r, and the sexual
organs which it bears (x 60); a, antheridium borne on the basal nodal cell na, by the stalk
cell p ; m, manubrium ; db, an oogonium ; no, nodal cell ; po, the stalk cell ; v, pivotal cell
(Wendungszdle); c, the crown. B, A lateral axis ( x 6) ; a, antheridium; o, oogonium. C,
Spermatozoid ; k, nucleus ; cl, cilia; c, cytoplasm (x 540). (After STRASBURGER.)

be grouped together in sori. The male organ of the Characeae, which
as a whole is commonly spoken of as an antheridium, thus contains
eight groups of endogenously-formed antheridia and should on this
account be termed an antheridiophore.

The female organ (Fig. 362 ob) consists of an oogonium which
contains a single egg-cell with numerous oil-drops and starch grains.
To begin with, the oogonium projects freely, but later becomes sur-
rounded by five spirally-wound cells. These cells end in the corona,

DIV. i THALLOPHYTA 421

between the cells of which the spermatozoids make their way in
fertilisation. At the base of the oogoniurn there are small cells
(JFenchingszellen) cut off from the oogonial rudiment; in Cham there
is one, in Nitella three such cells. These divisions correspond to the
first divisions in the mother cell of the male organ. The female organ
may thus be regarded as an oogoniophore reduced to a single
oogonium.

The egg, after fertilisation, now converted into an oospore, becomes invested
with a thick colourless wall. The inner walls of the tubes become thickened
and encrusted with a deposit of calcium carbonate, while the external walls of
the tubes, soon after the fruit has been shed, become disintegrated.

In the germination of the oospore the nucleus, according to OEHLKERS and
ERNST, divides into four, the first division being heterotypic. The enlargement
of the zygote opens the membrane at its summit. While three nuclei remain in
the ventral portion of the zygote and there degenerate, the fourth nucleus enlarges
and passes into the apical protrusion, which is then cut off by a cell wall. From
this cell by further divisions a simple filamentous young plant consisting of a
number of segments is produced. From the first node of this plant rhizoids are
developed, while at the second some simple lateral axes arise as well as one or more
main axes. By the further growth and branching of the latter the adult plant
develops. The diploid stage in the Characeae is thus limited to the oospore, the
plant itself being throughout haploid.

The behaviour of Chara crinita is remarkable. According to ERNST the
haploid male and female individuals of this dioecious species only occur occasionally ;
their cells have twelve chromosomes. Diploid female plants with twenty-four
chromosomes are, on the other hand, widely spread. These, which appear to have
arisen by the crossing of Chara crinita with other species, are propagated
apogamously by means of diploid egg-cells. This is therefore an example of
apogamy and not, as was previously assumed, of parthenogeuetic development of
haploid egg-cells (48a).

The formation of tuber-like bodies (bulbils, starch-stars) on the lower part of
the axes is characteristic of some species of the Characeae. These tubers, which
are densely filled with starch and serve as hibernating organs of vegetative
reproduction, are either modified nodes with much-shortened branch whorls (e.g. in
Tolypellopsis stelligera, when they are star-shaped), or correspond to modified
rhizoids (e.g. the spherical white bulbils of Chara aspera).

CLASS XII
Rhodophyeeae (Red Algae) (^ n> 28' 49' 50)

The Rhodophyeeae or Florideae constitute an independent group
of the higher Algae, the phylogenetic origin of which is perhaps to
be sought among the higher Green Algae, but they also exhibit
connections with the Brown Algae. They are almost exclusively
marine, and specially characterise the lowest algal region on the
coasts of all oceans. A few genera (e.g. Batrachospermum, Lemanea)
grow in fresh- water streams.

2 El

422 BOTANY PART n

The thallus of the Red Algae exhibits a great variety of forms.
The simplest forms are represented by branched filaments consist-
ing of single rows of cells (e.g. Callithamnion). In other cases the
branched filamentous thallus appears multicellular in cross-section.
In many other forms the thallus is flattened and ribbon -like (e.g.
Chondrus crispus, Fig. 363 ; Gigartina mamillosa, Fig. 364) ; while
in other species it consists of expanded cell surfaces attached to a
substratum. All the Florideae are- attached at the base by means
of rhizoidal filaments or discoid holdfasts. One of the more com-

Fio. 363.— Chondrus crispus. (i nat. size.)

plicated forms is Delesseria (Hijdrolapathuni) sanguined (Fig. 88), which
occurs on the coasts of the Atlantic. The leaf-like thallus which
springs from an attaching disc is provided with mid-ribs and lateral
ribs. In the autumn the wing-like expansions of the thallus are
lost, but the main ribs persist and give rise to new leaf-like branches
in the succeeding spring. The thalli of the Corallinaceae, which
have the form of branch -systems or of flattened or tuberculate
incrustations, are especially characterised by their coral-like appearance,
owing to the large amount of calcium carbonate deposited in their cell
walls. The calcareous Florideae are chiefly found on coasts exposed
to a strong surf, especially in the tropics.

DIV. I

THALLOPHYTA

423

The Rhodophyceae are usually red or violet ; sometimes, however,
they have a dark purple or reddish-brown colour. Their chromato-
phores, which are flat, discoid, oval, or irregular-shaped bodies and
closely crowded together in large numbers in the cells, contain a red
pigment, PHYCOERYTHRIN, and in some cases a blue pigment (PHYCO-
CYAN) in addition. They are developed from colourless, spindle-
shaped leucoplasts in the apical cells and germ cells. True starch is
never formed as a product of assimilation, its place being taken by
other substances, very frequently, for example, by Floridean starch
in the form of spherical stratified
grains which stain red with iodine.
Oil-drops also occur. The cells
may contain one or several nuclei.

Reproduction is effected either
asexually by means of spores, or

FIG. 364.— Gigcrtina mamttlosa. s, Wart-shaped
cystocarps. (| nat. size.)

sexually by the fertilisation of
female organs by male cells.

The asexual SPOKES are of two kinds.
In the first case they are non-motile,
have no cilia, and are simply naked
spherical cells. They are produced,
usually, in groups of four, by the division
of a mother cell or sporangium. The
sporangia themselves are nearly spherical
or oval bodies seated on the tlialloid
filaments or embedded in the thallus.
The spores escape by a transverse rup-
ture of the wall of the sporangium. In
consequence of their usual formation
in fours, the spores of the Florideae
are termed TETRASPORES (Fig. 365).

They are analogous to the swarm-spores of other Algae ; similar spores are found
also in the Dictyotaceae among the Brown Algae. The tetrasporangiuni as a rule
has to begin with a single nucleus, which divides to give rise to the nuclei of the
four spores. In some cases (Martensia, Nitophyllum), however, they are to begin
with nmlrinucleate, but all the nuclei except one degenerate. The monosporangia
of the Nemalionaceae, which liberate only a single spore, and the polysporangia of
the Ceramiaceae, which form a number, are equivalent to the tetrasporangia.

The second form of asexual spore in the Red Algae is represented by the
CARPOSPORES (cf. p. 424), which are liberated singly from terminal carposporangia
as spherical and, to begin with, naked, non-ciliate protoplasts, and thus resemble
the monospores.

In the construction of the sexual organs, particularly the female, the Rhodo-
phyceae differ widely from the other Algae. £atrachospermum -monilifonne, a
fresh-water form, may serve as an example to illustrate the mode of their
formation. This Alga possesses a brownish thallus, enveloped in mucilage, and
consisting of verticillately- branched filaments. The sexual organs appear on the
branching whorls seated on closely-crowded, short, radiating branches.

The antheridia, also known as spermatangia (Fig. 366 A\ are produced

2 E2

424

BOTANY

PART II

usually in pairs, at the ends of the radiating branches. Each antheridium
consists of a single thin -walled cell, in which the whole of the protoplasm
is consumed in the formation of one uninucleate SPERMATITJM ; in Batracho-
spermum and Nemalion the nucleus of the spermatium divides into two. The
spermatia are nearly spherical, and are invested with a thin outer membrane
or cell wall. They are non-motile, unlike the ciliated spermatozoids of the
other Algae, and have therefore received a distinctive name. In consequence of
their incapacity for independent movement, they must be carried passively by the
water to the female organs, which are sjtuated near the antheridia at the ends
of other branches. The female organ is called a CARPOGONIUM (Fig. 367),
and consists of an elongated cell with a basal flask-shaped portion prolonged
into a filament, termed the TRICHOGYNE. The basal portion contains the
nucleus of the egg and the chromatophores, while the trichogyne functions

FIG. 365.—Callithamnioncorymbosum. A, Closed
sporangium; B, empty sporangium with
four extruded tetraspores. (After THURET. )

FIG. 366. — Batrachospermum monili-
forme. Branches bearing antheridia.
At s*, a free spermatium ; at s,
another just escaping ; at v, an
empty antheridium. (x 540. After
STRASBURGER.)

as a receptive organ for the spermatia, one or two of which fuse with it,
and the contents, escaping through the spermatium wall, pass into the carpo-
gonium. The sperm nucleus passes down the trichogyue and fuses with the
nucleus of the egg-cell. The fertilised egg, which becomes limited from the
trichogyne by a wall, does not become converted directly into an oospore, but,
as a result of fertilisation, numerous branching sporogenous filaments (GOXIMO-
BLASTS) grow out from the sides of the ventral portion of the carpogonium. At the
same time, by the development of outgrowths from cells at the base of the carpo-
gonium an envelope is formed about the sporogenous filaments. The whole
product of fertilisation, including the surrounding envelope, constitutes the
fructification, and is termed a CYSTOCARP. The profusely-branched sporogenous
filaments become swollen at the tips and give rise to spherical, uninucleate spores
known as CARPOSPORES, which are eventually set free from the envelope. In
the case of Batrachospermum the carpospores produce a filamentous protonema,
the terminal cells of which give rise to asexual unicellular spores. These spores
serve only for the multiplication of the protonema. Ultimately, however, one
of the lateral branches of the protonema develops into the sexually differentiated
filamentous thallus. The production of spores by the protonema is analogous to
the formation of tetraspores by other Florideae.

The homologies underlying the variously-constructed sexual organs of the Red

DIV. I

THALLOPHYTA

425

Algae can be recognised, according to N. SVBDELIUS, when their development is
taken into consideration and they are compared in the light of the first nuclear
division in the rudiment. The young carpogonium contains two nuclei, of which
that belonging to the trichogyne later degenerates. (The uninncleate carpogonium
of Batrachospermum is apparently an exception.) The trichogyne corresponds
morphologically to the spermatangium, and its ventral portion to the basal or
mother cell on which one or more spermatangia are situated. The trichogyne and
egg-cell are only separated by a cell wall after fertilisation (496).

The formation of the antheridia (49a) as well as of the frequently very com-
plicated cystocarps follows a variety of types in the Florideae. In all cases,
however, according to OLTMANNS, the carpospores are to be regarded as derived in
their development from the fertilised egg-cell.

Dudresnaya coccinea, which is found on the warmer coasts of Europe, has a

FIG. 367. — Batrachospermum moniliforme. A, Young carpogonium terminating a branch. B
Ripe carpogonium; t, trichogyne. C, Stage after fertilisation by the spennatium (s), the egg,
cell (o) containing the two sexual nuclei. D, Gonimoblasts (g) and investing filaments (h). E,
Some of the mature gonimoblasts with the carpospores (fc) ; these have emerged from ki and ^2-
(A-D x 960, .Ex 720. After H. KYLIN.)

branched, cylindrical thallus and will serve as an example of the more complicated
mode of origin of the spore -bearing generation (Fig. 368). The carpogonial
branches consist of about seven cells, the terminal one bearing a very long
trichogyne. After fertilisation the carpogonial cell grows out into a filament,
which elongates and becomes branched. This filament fuses with a number of
special cells, characterised by their abundant contents, the AUXILIARY CELLS. The
first of these lie in the carpogonial branch itself, the others in adjoining lateral
branches. All the nuclei of the sporogenous filament are derived by division from
that of the fertilised egg-cell. The successive fusions with auxiliary cells do not
involve nuclear fusions, but simply serve to nourish the sporogenous filament. A
second and third sporogenous filament may arise from the carpogonial cell. Two out-
growths now arise from each of the swollen cells of the sporogenous filament
which fused with auxiliary cells. By further division of these outgrowths the spherical
masses of carpospores, which subsequently become free, are derived.

In all Red Algae, as has been seen above, two generations can be distinguished,
the GAMETOPHYTE, which produces the egg -cells and the spermatia, and the
SPOROPHYTE, which proceeds from the fertilised egg and produces the; carpospores

426

BOTANY

PART II

asexually. The two differ from one another in form, the gametophyte being an

Fi(i. 368. — Dudresnaya coccinea. A, Carpogouial branch ; c, carpogonium ; t, trichogyne. B, Carpo-
gonium after fertilisation, grownsout into the sporogenous filament (s/). C, Fusion of the
sporogenous filament with the first auxiliary cell (u^. D, Branching of the filament and fusion
with six auxiliary cslls (ara6) ; the cells a3-a6 are borne on branches originating from the axis
ha (diagrammatic). E, Ripe cluster of carpospores originating from one branch. (A-D after
OLTMANNS ; E after BORNET. A-C x about 500 ; D x 250 ; E x 300.)

independent plant, while the sporophyte is morphologically more primitive and is
dependent in its nutrition and development upon the sexual plant.

DIV. i THALLOPHYTA 427

The spores produced in the tetrasporangia (or in the corresponding mono-
sporangia or polysporangia) represent a second form of asexual spore, by means of
which an increase in numbers of the sexual plants is effected. They may be
entirely wanting in some cases (Nemaliori).

In certain genera these sporangia occur only on the sexual plant itself. In the
majority of genera, on the other hand, plants are developed from the carpospores
which bear tetraspores only, and from these tetraspores the, usually dioecious,
sexual plants arise. The life -history then includes the three generations,
gametophyte, carposporophyte, and tetrasporophyte. A purely asexual generation
morphologically resembling the sexual generation has here been secondarily derived
from the latter. In some Red Algae with such a life-history a further complication
is introduced by the gametophyte bearing tetraspores, or equivalent monospores,
which again produce gametophytes.

The behaviour^of the nuclei and their reduction division has been investigated
in a small number of species and has revealed noteworthy differences in the distri-
bution of the haploid and diploid phases among the generations (&e).

In Scinaia the reduction division, according to SVEDELIUS, takes place in the
first division of the fertilised egg, so that this only is diploid while the carpo-
sporophyte, the carpospores, and the gametophyte proceeding from the latter
are all haploid. The gametophyte here reproduces itself asexually by haploid
monospores in place of tetraspores, which are wanting. Nemalion, according to
KYLIN, behaves similarly but has neither tetraspores nor monospores on the
gametophyte.

It may be anticipated that in all Red Algae with this simple alternation of
generations the reduction division will follow the Scinaia type, which can be
regarded as the most primitive.

In those Red Algae in which three generations occur in the life-history the
reduction division is relegated to the tetrasporangium, so that the gametophyte
proceeding from the tetraspores is haploid, while the carposporophyte, the
carpospores, and the tetrasporophyte developed from the latter constitute the
diploid phase. Polysiphonia, Griffithia, Delesseria, Nitophyllum, and Rhodomela
are known to behave in this way. If in such cases asexual spore-formation takes
place on the gametophyte this does not involve a reduction division. According to
SVEDELIUS the gametophyte of Nitophyllum punctatum is an example of this ; it
bears monospores in addition to the sexual organs. These monosporangia correspond
to the tetrasporangia of the tetrasporophyte, are at first multinucleate, but all
the nuclei except one degenerate. They produce, without any reduction, a single,
haploid monospore.

Harveyella mirabilis (50), one of the Florideae occurring in the North Sea, is of
special interest. It grows as a parasite on another red seaweed, Rhodomela sub-
fusca, on which it appears in the form of a small white cushion-like growth.
As a result of its parasitic mode of life the formation of chromatophores has been
entirely suppressed, and thus this plant behaves like a true fungus.

Economic Uses. — Gigartina mamillosa (Fig. 364), with peg -like cystocarps
2-5 mm. in length, and Chondrus crispus (Fig. 363), with oval cystocarps about
2 mm. long, sunk in the thallus and tetraspores in groups on the terminal segments
of the thallus. Both forms occur in the North Sea as purplish-red or purplish-
brown Algae ; when dried they have a light yellow colour, and furnish the official
CARRAGHEEN, "Irish Moss," used in the preparation of jelly. AGAR-AGAR, which
is used for a similar purpose, is obtained from various Florideae ; Sphaerococcus
(Gracilaria} lichenoides supplies the Agar of Ceylon (also called Fucus amylaceus),

428 BOTANY PART n

Eucheuma spinosum the Agar of Java and Madagascar, Gelidium corneum and
Gr, cartilagineum the Agar of Japan.

CLASS XIII
Phyeomyeetes (*• "• 52> 53'60)

In the structure both of their thallus and sexual organs the Phyeomyeetes exhibit
a close connection with the Siphoneae. The phylogenetic origin of most of the
Phyeomyeetes is probably to be sought in this group, though certain forms point
to a relationship with other Green Algae (e.g. Basidiobolus with the Conjugatae,
and the Chytridiaceae with Protococcales and Flagellata). They can only for the
present be regarded as a definite class, pending their separation into several series
derived from distinct classes of Algae.

In the simplest cases, as in the Chytridiaceae, the thallus consists
of a single cell which in its young stages is a naked protoplast.
In the higher forms the thallus consists of extensively -branched
tubular threads in which, as is the case in Faucheria, transverse septa
only form in connection with the reproductive organs. The con-
tinuous protoplasmic mass contains numbers of very small nuclei, but
chromatophores are entirely wanting in these colourless organisms.
The whole thallus of a fungus is spoken of as the MYCELUIM, the
individual filaments as HYPHAE. In the Phyeomyeetes the hyphae
are non-septate, their division into distinct cells only taking place
in a few cases. The plants are either saprophytes occurring on the
putrefying remains of animals or plants in water or on decaying
organic substances exposed to air, or they live parasitically in the
tissues of higher plants or of insects.

Asexual reproduction is effected by means of spores. These are
formed in the majority of the genera within sporangia, the protoplasm
of which splits into the numerous spores. The latter escape in the
genera which live in water as ciliated swarm-spores (Fig. 371) ; in the
forms which are exposed to the air the spores are enclosed by a cell
wall (Fig. 377). The conidia, which are sometimes found together
with sporangia, in other cases alone, are also adapted for dispersal in
air. They arise by a process of budding and abstriction from the ends
of certain hyphae which are usually raised above the substratum as
special conidiophores.

The sexual organs of the Phyeomyeetes are in many ways
peculiar, and the two groups of the Oomycetes and the Zygomycetes
are distinguished according to their nature. In the Oomycetes,
which stand nearest to the Siphoneae, oogonia and antheridia are
found ; the contents of the latter enter the oogonium by means of a
tubular outgrowth, and after fertilisation oospores are formed. In
Monoblepharis alone free spermatozoids are found. The sexual
organs of the Zygomycetes are alike, and on conjugation a zygospore

DIV. I

THALLOPHYTA

429

is produced. They are usually multinucleate, and thus are morpho-
logically comparable to a whole gametangium of an isogamous Alga.
In the Archimycetes sexual organs have been observed in a few
cases only in the form of antheridia and oogonia or of equivalent
gametes.

Multinucleate gametangia, oogonia, and antheridia, which fuse
directly with one another, without the separation and escape of the
individual gametes, are generally termed COENOGAMETES.

Order 1. Archimycetes (63)

The Chytridiaceae which belong here are microscopically small Fungi parasitic
on aquatic or land plants and in some cases on animals. The non-septate mycelium
is feebly developed, and is
frequently reduced to a single
sac -shaped cell inhabiting a
cell of the host. Asexual
multiplication is effected by
means of swarm -spores pro-
vided with one or two cilia
which enter the cells of the
host plant and at first have
no cell wall. A cell wall is
then formed and the parasite
becomes transformed into a
multinucleate sporangium
which liberates numerous uni-

nucleate swarm -spores by

,. i 1 vi FIG. 369.— Olpidium Brassicae. A, Three zoosporangia, the

means of a beak - like pro- contents £ Qne of which has escaped (x 160) ^ Zoo.

jection. Thick -walled spor- spores (x 520). C, Resting sporangia (x 520). (After
angia which only produce WORONIN.)
swarm -spores after a period

of rest are also developed. The life.- history of Olpidium Brassicae (Fig. 369),
which lives as a parasite in the stems of young Cabbage plants and causes their
death, is of this type. Synchytrium (Ghrysophlydis] endobioticum, the cause of
the wart disease of the Potato, has recently become widespread in Europe. It
gives rise to warty outgrowths on the stems and tubers ; these later break down
and decay. In summer it forms from the protoplast a sorus of 2-5 spherical,
thin-walled sporangia without beak-like projections, and also especially for the
winter rest, thick- walled, yellow, resting sporangia. These are at first uninucleate,
but on germinating in the moist soil form numerous uniciliate swarm -spores
which can enter the cells of the Potato.

Sexual reproduction as a preliminary to the formation of resting sporangia is
only known with certainty for a few forms. In Olpidium Viciae, which is
parasitic on Vicia unijuga, the uniciliate swarm-spores are in part asexual, pro-
ducing zoosporangia again a few days after entering a cell of the host. In part,
however, they behave as planogametes and conjugate in pairs to form naked
zygotes provided with two cilia. The zygote settles on the host plant, surrounds
itself with a cell Avail and passes its protoplast into the epidermal cell. Within
this the zygote develops into a resting sporangium, in which the delayed fusion of
the sexual nuclei takes place ; from this, numerous zoospores are developed.

430

BOTANY

PART II

In Olpidiopsis, which is parasitic in the hyphae of Saprolegnia, the method of
conjugation is different and more like that of the higher Phycomycetes. Larger
female and smaller male protoplasts lie side by side in the host cells, where they
grow, become multinucleate, and surround themselves with cell walls. The
contents of the male cell now pass into the female cell, which becomes a thick-
walled oospore. The nuclei appear to fuse in pairs. The further fate of this
oospore is not known. Olpidiopsis also multiplies by biciliate zoospores formed
in sporangia.

In other genera no sexuality has yet been demonstrated and no conjugation
precedes the development of the resting sporangia.

Order 2. Oomycetes

1. Only in the small primitive family of the Monoblepharideae (54) are free
ciliated spermatozoids liberated from the antheridia. In the other Oomycetes the

FIG. 370.— Monoblepharis sphaerica. End of filament with terminal oogonium (o) and an antheridium
a). 1, Before the formation of the egg-cells and spermatozoids. %t Spermatozoids (s) escaping
and approaching the opening of the oogonium. 3, osp, ripe oospore, and an empty antheridium.
(x 800. After CORNU.)

multinucleate contents of the antheridium do not divide into separate spermatozoids.

The species of Monoblepharis live in water upon decaying remains of plants.
Asexual reproduction is effected by means of uniciliate swarm-spores, formed in
large numbers in sporangia. The oogonium, which is usually terminal, contains
only a single egg-cell (Fig. 370). The antheridia, which resemble the sporangia,
liberate a number of uniciliate spermatozoids. On a spermatozoid reaching the
egg-cell through an opening in the tip of the oogonium an oospore is formed.
A spinous cell wall forms around the oospore.

2. The Saprolegniaceae (55), which connect on to the preceding family, live like
them saprophytically on the surface of decaying plants and insects and even on
living fishes. Asexual propagation is effected by club-shaped sporangia (Fig. 371)
which produce numerous biciliate swarm-spores. In Saprolegnia these swarm-spores
with terminal cilia withdraw the latter and become surrounded with a spherical
wall ; shortly afterwards, the contents again escape as bean-shaped zoospores
with the cilia inserted laterally. The sexual organs develop on older branches of

DIV. I

THALLOPHYTA

431

the mycelium (Figs. 372, 373). The oogouia give rise to a larger (as many as 50)
or smaller number of egg-cells, rarely only to a single one. At first the oogonium
contains numerous nuclei, most of which, however, degenerate ; the remaining
nuclei divide once mitotically into daughter nuclei, of which some again degenerate,
while the oospheres become delimited around the remaining nuclei. The egg-cells
are always uninucleate. The tubular antheridia, with a number of nuclei that undergo
one mitotic division, apply them-
selves to the oogonia and send
fertilising tubes to the egg-cells.
One male nucleus enters the egg-
cell and fuses with its nucleus.
The oospore after fertilisation
acquires a thick wall. The re-
duction division takes place on
the germi nation *of the oospore.
In some forms belonging to this

The

FIG. 371. — Xcii'i-oh'-jiiM m

biciliate zoospores, s-, are escaping
from the sporangium. (After G.
KLEBS.)

FK;. 372. — Saprolegnia mixta. Hyphae bearing the
sexual organs : a, antheridium which has sent
a fertilisation tube into the oogonium ; oi,
egg-cell ; o2, oospore enclosed in a cell wall ; op,
parthogenetic oospores ; g, young oogonium.
(After G. KLEBS.)

family, and also in some Peronosporeae, the formation of antheridia is occasionally
or constantly suppressed ; the oospores develop parthenogenetically without being
fertilised (Fig. 372 op).

3. The Peronosporeae (56) are parasitic fungi whose mycelium penetrates the
tissues of the higher plants. In damp climates certain species occasion epidemic
diseases in cultivated plants. Thus, the mycelium of Phytoplitliora infestans, the
fungus which causes the Potato disease, lives in the intercellular spaces of the
leaves and tubers of the Potato plant, and by penetrating the cells with its short

432

BOTANY

PART II

haustoria leads to the discoloration and death of the foliage and tubers. Sexual
reproductive organs have not as yet been observed in this species on the Potato
plant but have been produced when the fungus is cultivated on certain media.
Asexual, oval sporangia are formed on long branching sporangiophores which grow
out of the stomata, particularly from
those on the under side of the leaves
(Fig. 374), and appear to the naked
eye as a white mould. The sporangia,
at first terminal, are cut off by trans-
verse walls from the ends of the branches
of the sporangiophore, by the subse-
quent growth of which they become
pushed to one side, and so appear to
be inserted laterally. Before any
division of their contents has taken
place, the sporangia (B) fall off and
are disseminated by the wind ; in
this way the epidemic becomes wide-
spread. The development of swarm-
spores in sporangia is effected only in

water, and is consequently possible
only in wet weather. In this process
the contents of the sporangium divide
into several biciliate swarm -spores

FIG. 373.— Achlya polyandra. The fertilisation
of two egg-cells, o, of an oogonium by two
tubes from the antheridium, a ; ek, nucleus
of the egg-cell ; sk, sperm-nucleus ; in o2
the section has not passed through the egg-
nucleus. (After TROW.)

FIG. 374. — A, Surface view of the epidermis of a
potato leaf, with sporangiophores of Phyto-
phthora infestans projecting from the stomata
( x 90) ; B, a ripe sporangium ; C, another
in process of division ; -D, a swarm - spore.
(B-D x 540. After STRASBURGER.)

(C, D}. Each of these spores, after escaping from the sporangium, gives rise to a
mycelium, which penetrates the tissues of a leaf. The sporangium may also ger-
minate directly without undergoing division and forming swarm-spores. A similar
transformation of sporangia into conidia is also found in other Peronosporeae as a
result of their transition from an aquatic to a terrestrial mode of life.

Plasmopara viticola, an extremely destructive parasite, also produces copiously-
branched sporangiophores and occasions the "False Mildew " of the leaves and fruit
of the Grape-vine. Albugo Candida (=Cystopus candidus], another very common
species, occurs on Cruciferae, in particular on Capsella bursa pastoris, causing
white swellings on the stems. In this species the sporangia are formed in long

DIV. I

THALLOPHYTA

433

chains on the branches of the mycelium under the epidermis of the host plant,
and produce in water numerous swarm-spores.

The sexual organs of the Peronosporeae resemble those of the genus Vaucheria
(Fig. 348). They arise within the host plant— the oogonia as spherical swellings
of the ends of certain hyphae, the antheridia as tube -like outgrowths arising as
a rule just below the oogonia. Both are cut off by transverse walls and are multi-
nucleate (Fig. 375). The several species exhibit interesting differences as regards
the nuclear changes. In Peronospora parasitica, Albugo Candida, and A. Lepigoni,
Pythium, Plasmopara, and Scler'ospora, a single large central egg-cell or oosphere
becomes differentiated in the protoplasm of the oogonium ; this contains a

FIG. 375. — Fertilisation of the Peronosporeae. 1, Perono-
spora parasitica. Young multinucleate oogonium (og)
and aiitheridium (an). ~'. Albugo Candida. Oogonium
with the central uninucleate oosphere and the fertilis-
ing tube (a) of the antheridium which introduces the
male nucleus. 3, The same. Fertilised egg-cell (o)
surrounded by the periplasm (p). (x (566. After
WAGER.)

FIG. 376. — Rhizopus nigricans ( =
Mucor stolonifer). Portion of the
mycelium with three sporangia ;
that to the right is shedding its
spores and shows the persistent
hemispherical columella. (x 38.)

single nucleus in a central position, while the remaining nuclei pass into the
peripheral layer of protoplasm (periplasm). The antheridium now sends a process
into the oogonium, which at its apex opens into the oosphere and allows a single
male nucleus to pass into the latter. The oosphere then becomes surrounded with
a cell wall, and nuclear fusion takes place, while the periplasm is utilised in form-
ing the outer membrane of the spore (episporium). In Peronospora parasitica the
ripe oospore has a single nucleus, in Albugo it becomes multinucleate as a result
of nuclear division. In Albugo Bliti and A. portulacae there is also a central
oosphere surrounded by periplasm, but the oosphere contains numerous nuclei,
which fuse in pairs with a number of male nuclei entering from the antheridium.
A multiuucleate oospore thus arises from the compound egg-cell. The behaviour
of these two species can be regarded as primitive, the uninucleate oospheres of

434

BOTANY

PART II

the first -named forms having been derived from the multinucleate condition.
Albugo tragopogonis occupies an intermediate position in that its oosphere is at
first multinucleate, but later contains only one female nucleus, the others having
degenerated. The superfluous nuclei in the oogonia and antheridia may be
regarded as the nuclei of gametes which have become functionless, and are com-
parable with the superfluous egg-nuclei of certain Fucaceae. The oospores either
produce a mycelium directly or give rise to swarm - spores. The nuclei in the
oospore are diploid ; their first division, which may occur before germination, is
the reduction division.

Order 3. Zygomycetes

1. The Mucorineae (57) comprise a number of the most common Mould Fungi.
They are terrestrial and saprophytic, and are found chiefly on decaying vegetable
and animal substances. Asexual reproduction is effected by non-motile, walled
spores, which either have the form of conidia or arise endogenously in sporangia.

FIG. 377.— 1, Mucor Miicedo. A sporangium in optical longitudinal section ; c, columella ; m, wall
of sporangium ; sp, spores. 2, Mucor mucilagineus. A sporangium shedding its spores ; the
wall (m) is ruptured, and the mucilaginous substance (2) between the spores is greatly swollen.
(1 x 225, 2 x 300, from v. TAVEL, Pilze. After BREFELD.)

Sexual reproduction consists in the formation of zygospores, as a result of the con-
jugation of two equivalent coenogametes.

One of the most widely distributed species is Mucor Mucedo, frequently found
forming white fur-like growths of mould on damp bread, preserved fruits, dung,
etc. Mucor stolonifer ( — Rhizopus nigricans), with a brown mycelium, occurs on
similar substrata. The spherical sporangia are borne on the ends of thick, erect
branches of the mycelium (Fig. 376). From the apex of each sporangiophore a
single spherical sporangium is cut off by a transverse wall, which protrudes into
the cavity of the sporangium and forms a columella (Fig. 377). The contents
of the sporangium become divided by repeated cleavages into numerous spores.
These escape by the swelling of a substance which lies between the spores and the
bursting of the sporangial Avail. In Pilobolus, which occurs commonly on dung,
the sporangium is forcibly cast off from the turgid sporangiophore which bursts at
the columella (cf. pp. 349, 350). According to HARPER the spores of Pilobolus are
binucleate, while those of Sporodinia (Fig. 378) are multinucleate.

Under certain conditions, instead of asexual sporangia, organs of sexual repro-
duction are produced. The hyphae of the mycelium then give rise to lateral, club-
shaped branches. When the tips of two such branches come into contact, a
conjugating cell or coenogamete is cut off from each by a transverse wall (Fig. 379).
The two gametes thereupon coalesce, and fuse into a ZYGOSPORE, the outer wall of

DIV. i THALLOPHYTA 435

which is covered with warty protuberances. As regards the behaviour of the nuclei in
the process of conj ugation, only a few facts are known. In Sporodinia, Phycomyces,
and other genera the sexual nuclei in the zygospore fuse in pairs. After a period of
rest the zygospore germinates, developing a germ-tube, which may at once bear a
sporangium (Fig. 379,5). The reduction division in Phycomyces takes place, accord-
ing to BUKGEFF, in the young sporangium formed on the germ-tube of the zygo-
spore.

BLAKESLEE'S demonstration of the dioecious (heterothallic) nature of the
mycelium of most Mucorineae, for example Mucor Jlucedo and Rhizopus nigricans, is
of great interest. The formation of zygo-
spores only takes place when male and
female mycelia come in contact. In other
Mucorineae (homothallic, e.g. Sporodinia
grandis] the two conjugating gametes may
arise on the same mycelium. Exception-
ally in heterothallic species, such as Phyco-
myces nitens, a homothallic.. mycelium may
appear or a neutral mycelium which forms
sporangia only (57°).

"Within the group of the Zygomycetes
a reduction of sexuality can be seen. Thus,
in the case of certain Mucorineae, although
the conjugating hyphae meet in pairs, no FIG. S78.-Sporodinia grandis. Median section
fusion takes place, and their terminal cells of a ripe sporangium. The spores are
become converted directly into spores, multinucleate. ( x 425. After HARPER.)
which are termed AZYGOSPORES. In other

forms, again, hyphae-producing azygospores are developed, but remain solitary,
and do not, as in the preceding case, come into contact with similar hyphae.
There are also many species in which the formation of zygospores is infrequent.

Both the size and number of spores produced in the sporangia of Mucor Mucedo
are subject to variation. The sporangia of the genus Thamnidium are, on the other
hand, regularly dimorphic, and a large sporangium containing many spores is formed
at the end of the main axis of the sporangiophore, while numerous small sporangia,
having but few spores (sporangioles), are produced by its verticillately branching
lateral axes. The sporangia may at times develop only a single spore, as the
result of certain conditions of food-supply, and in this way assume the character of
conidia. This dimorphism is even more complete in the tropical genus Choanephora.
In this case, in addition to large sporangia, conidia are produced on special coni-
diophores. There are, finally, Zygomycetes (e.g. Chaetocladium) whose only
asexual spores are conidia. In this one group, therefore, all transitional forms,
from many-spored sporangia to unicellular conidia, are represented.

Rhizopus nigricans has a poisonous substance in its cell sap which has fatal
effects on animals (58).

2. The Entomophthorineae (59) is a small group of fungi which mostly live
parasitically iu the bodies of insects and caterpillars. The multinucleate mycelium
remains non-septate or later becomes divided into cells. Asexual multiplication is
effected by means of conidia which contain one or numerous nuclei. These arise
singly at the ends of branches of the mycelium and when ripe are forcibly abjected.
Sexual reproduction is by means of zygospores, in place of which azygospores
frequently arise.

The best-known example is Empusa inuscae (Fig. 380), which is parasitic on
house-flies. The conidia, which are multinucleate, form a white halo around the

436

BOTANY

PART II

body of
well

the dead fly which has been killed by the fungus. This is particularly
when the dead fly is adhering to the glass of a window.

3. Basidiobolaceae(60).—
Basidiobolus ranarum, a sapro-
phytic fungus growing on the
excrement of Frogs, must be
separated from the preceding
group. Each of the cells of its
septate mycelium contains one
large nucleus. Theconidia, which
arise singly on the ends of the
conidiophores and are abjected
when ripe, are uninucleate. The
mode of origin of the zygospores
is peculiar. Two adjoining cells

FIG. 379. — Mucor Mucedo. Different stages in the
formation and germination of the zygospore.
1, Two conjugating branches in contact ; 2,
septation of the conjugating cells (a) from the
suspensors (6) ; 3, more advanced stage, the
conjugating cells (a) are still distinct from one
another : the warty thickenings of their walls
have commenced to form ; 4, ripe zygospore (fc)
between the suspensors (a); 5, germinating
zygospore with a germ-tube bearing a sporan-
gium. (1-4 x 225, 5 x circa 60, from v. TAVEL,
Pilze. After BREFELD.)

FIG. 380. — Empusa muscae. A, Hypha
from the body of a fly. B, Young
conidiophore arising from the
mycelium and projecting from the
body of the insect. C, Formation
of the conidium into which the
numerous nuclei have passed from
the conidiophore. (x 450. After
OLIVE.)

conjugate after they have put out beak-shaped processes which are cut off as
transitory cells. In the zygospore the two sexual nuclei give rise to four, of which
two disorganise while the other two fuse. Both in this procedure and in the
nuclear structure there are evident resemblances to the Conjugatae.

CLASS XIV

Eurayeetes (1( 51) °2' 61~86)

When the Phycomycetes are excluded there remain two great
groups of Fungi, the Ascomycetes and the Basidiomycetes, regarding

DIV. i THALLOPHYTA 437

the classification and phylogeny of which there is still much un-
certainty. The attempt has been made to derive them from the
Phycomycetes. Not only is the construction of the thallus against
this, but the structure of the sexual organs and. the development of
the fruit in the Ascomycetes indicate on the other hand a connection
with the Red Algae. The Uredineae or Rusts, one of the simplest
orders of Basidiomycetes, appear to connect the latter group with
the Ascomycetes.

The saprophytic or parasitic thallus of the Eumycetes is, like that
of the Phycomycetes, composed of fine, richly-branched filaments or
hyphae which together form the mycelium (Fig. 66). The hyphae are,
however, in this case septate, consisting of rows of cells. The cell
membrane, which contains chitin, is usually thin. In the colourless
protoplasm there are usually numerous minute nuclei (Fig. 6),
while in other cases each cell has a pair of nuclei or only a single
nucleus. Chromatophores are wanting and true starch is never
formed ; the place of the latter is taken by glycogen, often in con-
siderable quantity, and by fat-globules. The hyphae of a mycelium are,
as a rule, either isolated or only loosely interwoven ; they spread
through the substratum in all directions in their search for organic
nourishment. In many of the higher Fungi, however, the profusely-
branching hyphae form compact masses of tissue. Where the fila-
ments in such cases are in intimate contact and divided into short
cells, an apparently parenchymatous tissue or PSEUDO-PARENCHYMA
is produced. Such compact masses of hyphal tissue are formed by
some species of Fungi when their mycelia, in passing into a vegetative
resting stage, become converted into SCLEROTIA, tuberous or strand-
like, firm, pseudo- parenchymatous bodies, which germinate under
certain conditions (Fig. 36). In the fructifications the hyphae are
also nearly always aggregated into a more or less compact tissue
(Fig. 37).

The two sub - classes are distinguished by their respective
methods of asexual spore-formation. The ASCUS is characteristic of all
Ascomycetes ; it is a club-shaped sporangium within which a definite
number of spores (usually 8) is formed in a peculiar way by free cell
formation (Fig. 381). The Basidiomycetes have in place of the
ascus a BASIDIUM of varying shape. It may either be four-celled or
a unicellular tubular structure from which the spores are abstricted by
a process of budding in definite numbers, usually four (Figs. 398, 403,
410).

Sub-Class L— Aseomyeetes (*> 51> 52> 61'74)

The Ascomycetes in their typical forms possess sexual organs,
the oogonia, which here go by the name of ascogonia or, as in the
Red Algae, of carpogonia, and antheridia. The sexual organs have

438 BOTANY

been accurately investigated in relatively few forms; a number of
distinct types are found.

1. In the Laboulbeniaceae (Fig. 396) the carpogonium with its
trichogyne, and the antheridia which produce spermatia, show a
striking correspondence with the structures of the same name in
the Red Algae.

2. The Ascomycetes which enter into the composition of Lichens
(Figs. 429, 430) approach most closely the preceding group. The
carpogonium is here a spirally- wound filament of cells terminating in
a trichogyne. The spermatia are formed in special flask -shaped
depressions of the thallus, the spermogonia. Similar reproductive
organs occur in some Ascomycetes which do not form parts of
Lichens.

3. Pyronema (69) (Fig. 390) and related genera, Ascodesmis
( = Boudiera CLAUSSEN) (69), Mon.ascus (C3), Aspergillus (66), exhibit a
distinct type. A multinucleate carpogonium which is provided with
a trichogyne is fertilised by a multinucleate antheridium, the two
structures being thus coenogametes (p. 429). Lachnea(Q4) may also be
placed here.

4. In the Erysibaceae (Fig. 382) a uninucleate antheridium unites
directly with a uninucleate oogonium.

Other genera exhibit transitions in the structure of the carpo-
gonia and antheridia from the type of the Lichen fungi to those
of Pyronema, and of the Erysibaceae. Thus the former may perhaps
be regarded as primitive Ascomycetes and the latter as reduced (62).

In some Ascomycetes the sexual organs are present, but no fertilisa-
tion of the carpogonium takes place, and in others they are more or less
completely reduced.

The carpogonium does not give rise to a resting oospore, but
remains in connection with the parent plant ; from it ascogenous hyphae
or cell-filaments grow out, branch, and ultimately form the asci at
the ends of branches. The ascogenous hyphae and asci proceeding
from a carpogonium, or in some cases from a group of carpogonia,
form a fruit-body or fructification. In the formation of this, vegeta-
tive hyphae, derived from the mycelium of the parent plant, and
sharply distinct from the ascogenous hyphae, take part. The sterile
hyphae grow between and invest the ascogenous filaments. The my-
celium which produces the sexual organs represents the sexual genera-
tion (gametophyte) ; the system of hyphae proceeding from the carpo-
gonium and ending in the asci corresponds to the asexual generation
(sporophyte).

Within or on the surface of the fructifications of some groups of
the Ascomycetes the asci stand parallel to one another in a layer
called the hymenium, and between them as a rule are paraphyses
borne on the sterile system of hyphae of the fructification.

In some orders of Ascomycetes the sexual organs and the

DIV. I

THALLOPHYTA

439

fructifications are completely wanting, probably owing to reduction.
The asci then arise directly from the mycelium.

The ASCUS originates from a single cell ; this to start with contains
two nuclei, which fuse, and the resulting nucleus by repeated division
gives rise to eight nuclei. By a process of free cell formation the spores
become limited by cell walls in the way shown in Fig. 21 (Figs. 381,
391). In contrast to the formation of
spores in the sporangia of Phy corny cetes
the cytoplasm of the ascus is not com-
pletely used up in the formation of the
ascospores. The spores usually form a
longitudinal row, embedded in the remain-
ing epiplasnvwhich contains glycogen, and
are ultimately ejected from the ruptured
apex of the ascus by the swelling of this.
The spores are adapted for dispersal in
the air.

p, paraphyses ; sh, subhymenial
tissue. ( x 240. After STRAS-
BURGER.)

In a few cases the eight nuclei before the
delimitation of the cells undergo further divisions ;
numerous free ascospores, e.g. 32 in TTiecotheus,
thus arise. More commonly divisions occur after
the spores are delimited, and result in the forma-
tion of eight bi- or multicellular bodies.

The behaviour of the sexual nuclei in and after
fertilisation of the carpogonium is only accurately

known in a few cases. For some Ascomycetes

-, ,, \-4--u FIG. 381.— Portion of the hymenium

(Pyronema and Monascus] it has recently been Qf ^^ es<nde^ \ Asci .

shown that the sexual nuclei do not fuse in the

carpogonium, but lay themselves side by side.

In the ascogenous hyphae the pairs of nuclei

divide conjugately, and only in the young ascus

do two nuclei, the descendants respectively of a male and a female sexual nucleus,

fuse together. Thus the conjugation of the sexual nuclei is here delayed from the

carpogonium to the development of the ascus.

So far as the results yet obtained allow of a conclusion being drawn, the
reduction division in the Ascomycetes happeus, just after the fusion of the two
nuclei in the ascus.

In the life-history of the Ascomycetes an asexual reproduction by means of
conidia often precedes the development of the fructification. The conidia are spores
provided with a cell wall which are budded off from the tips of simple or branched
hyphae, the conidiophores (Fig. 384).

According to the construction of the fructification we may dis-
tinguish in the first place the orders of the Erysibaceae, Plectascineae,
and Pyrenomycetineae, with closed or vase-shaped fruit-bodies (peri-
thecium), the Discomycetes with an open fructification (apothecium),
and the Tuberaceae with a fructification that is at first open but
becomes completely closed.

440

BOTANY

PART II

To these orders must be added the Exoasceae, in which the asci
arise from cells of the mycelium without the formation of any
fructification, and the very simple Saccharomycetes or Yeast Fungi.
These two groups can be regarded as reduced Ascomycetes.

The Laboulbeniaceae in which the asci are enclosed in small
perithecia occupy an isolated position.

The genetic connections of these orders are not yet clearly established.

Order l. Erysibaceae (Mildew Fungi) ("• 65)

The small spherical perithecia have a closed investment (peridium) which ulti-
mately opens irregularly and liberates the ascospores. The asci stand singly or
in a group in the centre of the fruit.

The Erysibaceae live as epiphytic parasites whose mycelium, somewhat

FIG. 382. — Sphaerotheca castagnei. Fertilisation and development of the perithecium. 1,
Oogonium (og) with the antheridial branch (as) applied to its surface ; 3, separation of
antheridium (an) ; 3, passage of the antheridial nucleus towards that of the oogonium ;
It, fertilised oogonium, in 5 surrounded by two layers of hyphae derived from the stalk cell (st) ;
6, the multicellular ascogonium derived by division from the oogonium ; the penultimate
cell with the two nuclei (as) gives rise to the ascus. (After HARPER.)

resembling a cobweb, and ramifying in all directions over the surface, particularly
the leaves, of higher plants, sends out haustoria which penetrate the epidermis
of the host. In some cases the mycelium also inhabits the intercellular spaces
of the leaf. The ripe ascus fructifications (perithecia) are small black bodies
provided with peculiar appendages. In the simplest forms (e.g. in the genus
Sphaerotheca} the spheroid perithecium encloses only a single ascus with eight
spores. It is enveloped by a covering of sterile hyphae, forming a sheathing
layer, two to three cells deep. The genera Erysibe and Uncinula, on the other
hand, develop several asci in each perithecium, and in Phyllactinia 12 to 25 asci are
present. Since all the eight nuclei are not utilised in spore formation the
number of spores in each ascus is usually 4, or only 2. The perithecia are
irregularly ruptured at their apices and the spores are thus set free. As HARPER
has shown, the first rudiment of the perithecium consists of an oogonium and

DIV. I

THALLOPHYTA

441

an antheridium. These are uninucleate cells, separated from the mycelium by

The male nucleus passes into the

partition walls, and stand close together,
oogoninm by an opening which forms in
the cell walls (Fig. 382, 1-4). After fertilisa-
tion the oogonium is surrounded by invest-
ing filaments which spring from its stalk
cell or from that of the antheridium (5),
and the oogonium itself becomes converted
into a multicellular structure (6). In Sphae-
rotheca the ascus containing eight spores
arises from the binucleate penultimate
cell, while in Erysibe and Phyllactinia this
cell exclusively or mainly produces asco-
genous hyphae which in turn give rise to
the numerous asci. Before entering upon
the formation of perithecia, the Mildew
Fungi multiply by means of conidia ab-
stricted in chains from special, erect hyphae,
from the tip downwards. These are distri-
buted by the wind. The Mildew Fungus
occurs on the leaves and berries of Vitis
in America and has appeared in Europe
on the Grape-vine since 1845. This fungus,
known as Oidium Tuckeri, is the conidial
form of Uncinula necator (-U. spiralis),
the small perithecia of which have append-
ages spirally rolled at their free ends and
are only rarely found (Fig. 383).

Order 2. Plectascineae

The spherical perithecia have a closed
peridium ; the asci are irregularly arranged
within this. *

1. Aspergillaceae (66). Fructification
small ; not subterranean. Here belong
two of the most common Mould Fungi,
Aspergillus (Eurotium) herbariorum and
Penidllium crustaceum, which live saprophytically on organic substances. Both
multiply extensively by means of conidia before they begin to form perithecia.

In the case of Aspergillus herbariorum, the conidia are abstricted in chains
from a number of sterigmata arranged radially on the spherical, swollen ends of
the conidiophores (Fig. 384). The conidiophores are closely crowded together,
and constitute a white mould, afterwards turning to a blue-green, frequently
found on damp vegetables, fruit, bread, etc. Some species of Aspergillus are
pathogenic in man and other mammals ; thus A. fumigatus, which lives in
fermenting heaps of hay at an optimum temperature of 40° C. (6~), causes mycosis
of the external ear, the throat, and the lungs.

In Penidllium crustaceum, another widespread blue-green mould, the erect
conidiophores (Fig. 384) are verticillately branched. The spherical perithecia of
Aspergillus and Penidllium are produced later on the mycelium, but only rarely
occur in the latter genus. They develop from the sexual organs consisting of

FIG. 383.— Uncinula necator. A, Conidial
stage ; c, couidium ; 5, conidiophore. B,
Hypha which has formed a disc of attach-
ment (a) and has sent a haustorium (ft) into
an epidermal cell. C, Perithecium with
appendages. (From SORAUEB, LINDAU,
and REH. Handb. d. Pflanzenkrankheiten,
ii. p. 194. 1906.)

442

BOTANY

PART IT

an antheridium and a carpogonium provided with a trichogyne. The walls of the
asci and the surrounding pseudo-parenchyma disappear in the ripe fructification
which opens irregularly by the rupture of the peripheral layer.

2. The Elaphomycetaceae have subterranean, truffle-like fructifications, the
peridium of which is sharply marked off from the powdery mass of spores derived
from the ascogenous hyphae. Elaphomyces granulatus (Boletus cervinus}, the
yellowish-brown fructifications of which are of the size of a walnut and have a
bitter taste, occurs commonly in woods in Europe. It is used in veterinary
medicine.

FIG. 384.— Conidiophores of Aspergillus herbariorum (to the^left) and Penicittium crustaceum

(to the right).

3. The Terfeziaceae are distinguished from the preceding group by the peridium
of the fructification not forming a sharply distinct layer. Species of Terfezia with
edible truffle-like fructifications occur in the Mediterranean region.

Order 3. Pyrenomycetes

The Pyrenomycetes comprise an exceedingly varied group of Fungi, some
of which are parasitic upon different portions of plants, and others are saprophytic
upon decaying wood, dung, etc., while a few genera occur as parasites upon the
larvae of insects. The flask-shaped fructifications or perithecia are characteristic
of this order. The perithecia are open at the top, and are covered inside, at the
base, with a hymenial layer of asci and hair-like paraphyses (Fig. 385). The
lateral walls are coated with similar hyphal hairs, the periphyses. The ascospores
escape from the perithecia through the aperture.

The simplest Pyrenomycetes possess free perithecia (Fig. 385) which are usually
small and of a dark colour, and grow singly on the inconspicuous mycelium (e.g.
Nectria, Sphaeria, and Podospora}. In other cases the perithecia are in groups
embedded in a cushion- or club-shaped, sometimes branching, mass of compact
mycelial hyphae having a pseudo-parenchymatous structure. Such a fructification
is known as a STIIOMA.

In the life-history of most Pyrenomycetes the formation of perithecia is pre-

DIV. I

THALLOPHYTA

443

ceded by the' production of various accessory fructifications, particularly of conidia,
which are abstricted in different ways, either directly from the hypliae or from
special conidiophores, and assist in disseminating the fungus. The conidiophores
are frequently united in distinct, conidial fructifications. A special form of such
fructifications are the PYCNIDIA produced by many genera. They are «mall
spherical or flask-shaped bodies which give rise to branched hyphal filaments from
the apices of which conidia, in* this case termed PYCNOSPORES or PYCNOCONIDIA,
are abstricted (Fig. 386). The structure of the pycnidia and pycnospores corre-
sponds to that of the spermogonia and spermatia of the Lichens, and they may

be regarded as the original male organs.

Claviceps purpurea, the fungus of Ergot,
is important on account of its official
value. It is parasitic in the young ovaries
of different members of the Gramineae,
particularly of Rye. The ovaries are in-
fected in early summer by the ascospores.
The mycelium soon begins to form conidia,
which are abstricted in small clusters from
short lateral conidiophores (Fig. 387 A}.

FIG. 385. — Peritbecium ofPodosporafimiseda
in longitudinal section, s, Asci ; a,
paraphyses ; e, periphyses ; m, mycelial
hypliae. (x 90. After v. TAVEL.)

FIG. 386.— 1, Conidiophore abstricting conidia,
from a pycnidium of Cryptospora hypodermia.
(x 300. After BREFELD.) 3, Pycnidium of
Stricter-id obducens in vertical section, (x 70.
After TULASNE.)

At the same time a sweet fluid is extruded. This so-called HONEY-DEW is eagerly
sought by insects, and the conidia embedded in it are thus carried to the ovaries of
other plants. After the completion of this form of fructification, and the absorption
of the tissue of the ovary by the mycelium, a sclerotium is eventually formed in
the place of the ovary from the hypliae of the mycelium by their intimate union,
especially at the periphery, into a compact mass of pseudo-parenchyma (Fig. 36).
These elongated dark-violet SCLEROTIA, which project in the form of slightly
curved bodies from the ears of corn, are known as Ergot, SECALE CORNUTUM
(Fig. 387 B}. The sclerotia, copiously supplied with reserve material (fat),
eventually fall to the ground, where they pass the winter, and germinate in
the following spring when the Rye is again in flower. They give rise to bundles
of hyphae which produce long-stalked, rose-coloured globular heads (C}. Over
the surface of the latter, numerous sunken perithecia (D, E) are distributed. Each
perithecium contains a number of asci with eight long, filiform ascospores, which
are ejected and carried by the wind to the inflorescences of the grass.

444

BOTANY

PART II

Nectria ditissima (68) is a very injurious parasitic fungus which inhabits the

FIG. 387. — Claviceps purpurea. A, Mycelial hypha witli com'dia; B, ear of Rye with several ripe
sclerotia ; C, a sclerotium with stromata ; D, longitudinal section of a fructification showing
numerous perithecia ; E, a single perithecium, more highly magnified ; F, ascus with eight
filiform spores ; G, a ruptured ascus with escaping spores ; H, a single spore. (A after
BBEFELD ; C-H after TULASNE ; B photographed from nature. OFFICIAL and Poisoxous.)

cortex of various trees and causes the canker of fruit trees. It forms in winter
and spring small red perithecia which are closely crowded together.
OFFICIAL. — Ergot is the sclerotium of Claviceps purpurea.

mv. i THALLOPHYTA 445

Order 4. Discomycetes C89)

The Discomycetes are distinguished from the other orders by their open apothecia,
which bear the hymenium, consisting of asci and paraphyses, freely exposed on
their upper surface (Figs. 381, 389). The different groups exhibit great diversity
as regards the manner of development of their fructifications.

The great majority of the Discomycetes, of which the genus Peziza may serve
as a type, grow on living or dead vegetable substances, especially upon decaying
wood, but sometimes also on humus soil. They produce saucer- or cup-shaped
fructifications of a fleshy or leathery consistency, and usually of small dimensions.
One of the largest forms, Peziza aurantiaca (Fig. 388), has irregularly bowl-shaped
fructifications, which may be seven centimetres broad and of a bright orange-red
colour, while in most of the other species they ar.e grey or brown. Such cup-
shaped fructifications are termed APOTHECIA.

FIG. 388.— Peziza aurantiaca.
(Nat. size. After KROMBHOLZ.)

FIG. 389. — Lachnea pulcherrima. Apothecium ruptured,
showing old and young asci between the paraphyses.
(After WORONIN, from v. TAVEL.)

The development of the apothecium may be described for Pyronema confluens,
in which it was first thoroughly investigated by R. HARPER. The fruit-body of
this species is about 1 mm. across, and of a yellow or reddish colour ; it often
occurs on spots where fires have been kindled in woods. The carpogonia are
especially large in this species, and several usually take part in the formation of
each apothecium (Fig. 390 A). The carpogonium or ascogonium consists of the
spherical, multinucleate oogonium, on the apex of which a multinucleate curved
cell, the trichogyne, is situated. The cylindrical, multinucleate antheridium
arises from a neighbouring hypha ; its apex comes into open communication with
the tip of the trichogyne by the breaking down of the intervening walls. The
male nuclei first wander into the trichogyne cell, and then, by the breaking down
of the basal wall of the latter, into the oogonium. The egg-cell then becomes
limited from the trichogyne by a new cell wall and sends out ascogenous filaments
containing the conjugate nuclei. These filaments branch and ultimately ter-
minate in asci (E), while the sterile hyphae and the paraphyses of the fructifica-
tion are derived from hyphae arising beneath the carpogonium. According to
HARPER. the male and female nuclei fuse in pairs with one another in the
carpogonium. More recent investigations by CLAUSSEN show that they only place

446

BOTANY

PART II

themselves side by side, and in the ascogenous hyphae divide conjugately, but
remain distinct from one another. The fusion of a descendant of a male nucleus

FIG. 390. — Pyronema confluen-s. A, Very young apothecium ; og, oogonia, with trichogynes (<) ; a,
antheridia (x 450). B, Fusion of the antheridium with the tip of the trichogyne (x 300). C,
The association in pairs of the male and female nuclei in the oogonium, which is cut trans-
versely ( x 1000). D, Passage of the paired nuclei into the ascogenous hyphae ( x 1000). E, Young
apothecium. The ascogenous hyphae springing from the oogonia have branched and are invested
by sterile hyphae (x 450). (B after HARPER. A, C, D, E after CLAUSSEN.)

with the descendant of a female nucleus does not take place till the development
of theascus (Fig. 391).

In many Discomycetes a reduction of the sexual organs has taken place
associated with a loss of sexuality. The antheridia are functionless or completely
suppressed, and in extreme cases the ascogonia are also wanting, only a tangle of
hyphae being recognisable in their position. The ascogenous hyphae in the
young fructification are, however, always present.

The asci develop in various ways at the ends of ascogenous hyphae. As a rule

DIV. I

THALLOPHYTA

447

the end of the ascogenous hypha when about to form an ascus becomes curved
into a hook-like shape (Fig. 391 A}. The two nuclei of the young ascus (a) lie
near to the bend, and on the formation of transverse walls are separated from
the uninucleate terminal cell (/&) and the stalk-cell (s), which also has a single
nucleus. The two nuclei of the young ascus fuse (C], and the resulting nucleus
gives rise by repeated division to the nuclei of the eight ascospores (D). The
terminal cell of the hook (h) and the stalk-cell (s) have their cavities continuous,
so that a binucleate fusion cell results which can proceed to form another young
ascus. In this way complicated systems of ascogenous hyphae arise.

The highest development is exhibited by the peculiar fructifications of the
Helvellaceae, the mycelium of which grows in the humus soil of woods. In the

FIG. 391.— Development of the Ascus. A-C,
Pyronema confluens. (After HARPER.)
D, Young ascus of Boudiera with eigkt
spores. ( After CLAUSSEX.) Explanation
in text.

FIG. 392.— Morchella esculenta.
(f nat. size.)

genus Morchella (Fig. 392) the fructifications consist of a thick erect stalk, bearing a
club-shaped or more or less spherical cap or pileus, which bears the hymenium,
with the eight-spored asci, on the reticulately-indented exterior surface (Fig. 381).
The Morchellas are edible (70), in particular 31. esculenta and M. conica. The former
has a yellowish -brown cap, ovately spherical in shape, and attains a height of
12 cm. ; the cap of the latter is conical and dark brown, and it reaches a height
of 20 cm. Gyromilra esculenta, with dark brown cap and white stalk, and others
are also edible. In their external appearance the fructifications of these highly
developed Discomycetes greatly resemble those of the Basidiomycetes.

Order 5. Tuberaceae (Truffles) (n)

The Tuberaceae or Truffle Fungi are saprophytic Ascomycetes, the mycelium
of which occurs in humus soil, particularly in woods. The ascus fructifications
familiar under the name of truffles are underground tuberous bodies, consisting
of a thick, investing layer, with passages opening to the exterior ; the walls of these
are lined with the hymenium composed of club-shaped asci (Fig. 393). The asci
contain only a small number of spores; in the case of the true Truffles (Tuber)
they are usually only four in number, and generally have a spinous or reticulately-

448

BOTANY

PART II

thickened epispore. They are set free iu the soil by the breaking down of the asci
and of the wall of the fructification.

The fructifications of many of the Tuberaceae are edible (70), and have an aromatic
odour and taste. They are, for the most part, obtained from France and Italy.

FIG. 393.— Tuber rufum. 1, A fructification in vertical section ( x 5) ; a, the cortex ; d, air-containing
tissue ; c, dark veins of compact hyphae ; h, ascogenons tissue. 2, A portion of the hymenium
(x 460). (After TULASNE, from v. TAVEL. Pihe.)

Of the edible varieties, the most important are the so-called black truffles
belonging to the genus Tuber, viz. Tuber brumale, melanosporum (Perigord Truffle),
aestivum, mesentericum. The fructifications of these species have a warty cortex of
a black, reddish-brown, or dark brown colour. The white truffle, Choiromyces
meandriformis, the external surface of which is pale brown, is also edible.

The fructifications when very young are open as in the Discomycetes. The
Truffles seem most nearly related to the Helvellaceae.

DIV.

THALLOPHYTA

449

Order 6. Exoasceae (r2)

The most important genus of this group of Ascomycetes is Taphrina (includ-
ing Exoascus), the species of which are parasitic on various trees. They develop,
in part annually, beneath the cuticle of the
leaves, causing discolorations of these organs ;
their mycelium persists during the winter in
the tissue of the host, so that a constant re-
currence of the disease takes place. The presence
of the mycelium in the tissues of the infected
part causes the abnormally profuse develop-
ment of branches known as WITCHES'-BROOMS.
Taphrina Carpini produces the abnormal growths
occurring on the ^Hornbeam ; Taphrina Cerasi
those on Cherry trees. Taphrina deformans
attacks the leaves of the Peach and causes them
to curl. Taphrina Pruni is parasitic in the
young ovaries of many species of Prunus, and
produces the malformation of the fruit known
as "Bladder Plums," containing a cavity, the
so-called "pocket," in the place of the stone;
the mycelium persists through the winter in
the branches. In the formation of asci, the
copiously-branched mycelium ramifies between
the epidermis and cuticle of the infected part.
The individual cells of the mycelium become
greatly swollen and grow into club-shaped tubes,
which burst through the cuticle and, after cutting
off a basal stalk-cell, are usually converted into
asci with eight spores (Fig. 394). As in other Ascomycetes the young ascus has
two nuclei which fuse, and the resulting nucleus undergoes three divisions to give
the nuclei of the eight spores. The numerous asci are closely crowded together.

The spores, which bud in water or sugar solution, frequently germinate whil
still enclosed within the asci (Fig. 394 «3, «4), and give rise by budding to yeast-
like conidia, e.g. in Taphrina Pruni.

The Exoasceae are perhaps to be regarded as reduced Ascomycetes, in which the
sexual organs have become completely suppressed.

FIG. 394. — Taphrina Pruni. Transverse
section through the epidermis of an
infected plum. Four ripe asci, olt ao
with eight spores, a3, 04 with yeast -
like conidia abstricted from the
spores ; gt, stalk-c^lls of the asci ; m,
filaments of the mycelium cut
transversely ; cvt, cuticle ; ep, epi-
dermis, (x 600. After SADEBECK.)

Order 7. Saccharomycetes (Yeast Fungi) (73)

The beer, alcohol, and wine yeasts included in the genus Saccharomyces are simple
unicellular Fungi which have the form of spherical, oval, or cylindrical cells contain-
ing a single nucleus. They increase in number by budding (Fig. 395). No mycelium
is formed, though sometimes the cells remain for a time united in chains. With free
access of oxygen and at a suitable temperature yeasts form asci when the nutrient
substratum is exhausted ; the asci externally resemble the yeast-cells, but contain a
few spores. In some yeasts a conjugation of two cells accompanied by a nuclear
fusion has been observed. In Saccharomyces Ludwigii the four spores in the ascus
germinate and fuse in pairs by means of a narrow conjugation-tube ; the latter
elongates into a germ-tube from which yeast-cells are abstricted. In the ginger-
beer yeast (Zygosaccharomyces} and in Schizosaccharomyces the yeast-cells conjugate

450

BOTANY

PART II

FIG. 395. — Saccharomyces cerevisiae. A, Yeast-cell ; B, C>
yeast -cell budding; D, ascus with four spores,
(x 1125. After GUILLIERMOND.)

by means of long tubes before spore-formation. These nuclear fusions possibly

correspond to those in the young asci of other Ascomycetes.

Physiologically these fungi are remarkable for their power of exciting, by means

of an enzyme (zymase), the fermentation of saccharine solutions, alcohol and

carbon dioxide being produced (cf. p. 274). The beer yeast (Saccharomyces

cerevisiae} is only known in the
cultivated form ; the wine yeast (S.
eUipsoideus}, on the other hand,
occurs regularly in the soil of vine-
yards in the spore-form ; the latter
is therefore always present on the
grapes and need not be added to
the grape-juice. Other genera, in
some of which a mycelium is de-
veloped, belong to this order.

No evidence is at present forth-
coming to show that the Yeasts are to be regarded as developmental forms of other

fungi. In various members of the

Exoasci and Ustilagineae, however,

yeast-like conidia which reproduce

by budding are known. Possibly

the Saccharomycetes are reduced

Ascomycetes, or they may represent

an independent group of very

simple fungi at the base of the

Ascomycetes.

Owing to their richness in

readily digestible substances,

especially proteids and glycogen,

but also fats, yeast has a consider-
able food- value. It is purified, dried

at 125° C., and sold for this purpose.

Order 8. Laboulbeniaceae (74)

The Laboulbeniaceae are a group
of minute fungi occupying an
isolated position ; our knowledge
of them is largely due to the work
of THAXTER. Their thallus con-
sists of two to a number of cells,
and is attached to the body of the
insect, most commonly a beetle,
on which it is parasitic by means FIG. 396. — Stigmatomyces Baerii. Description in text.

A, Spore. B-F, Successive developmental stages. D.
With spermatia escaping from the antheridia an. E.
With antheridia above and the lateral female organ,
F, Perithecium with developing asci. G, Ripe ascus
(After THAXTER.)

of a pointed process of the lowest

cell inserted into the chitinous

integument of the insect, or by

means of rhizoids which penetrate

more deeply. Stigmatomyces Baerii

which occurs on house-flies in Europe may be taken as an example. The

bicellular spore (Fig. 396 A), which has a mucilaginous outer coat, becomes

attached by its lower end (£}, and divisions occur in both cells (C). From

THALLOPHYTA 451

the upper cell an appendage is developed bearing a number of unicellular, flask-
shaped antheridia (D, an) from which naked spherical spermatia without cilia are
shed. The lower cell divides into four (D, a, b, c, d\ and the cell a projects and
gives rise to the multicellular female organ. The true egg-cell (E, ac], which is
called the carpogonium, is surrounded by a layer of cells. Above the carpogonium
come two cells (E, tp, t), the upper of which is the freely-projecting trichogyne or
receptive organ for the spermatia. After fertilisation the carpogonium becomes
divided into three cells, of which the uppermost disappears, the lowest (F, $t)
remains sterile, while from the middle cell the asci grow out. Each ascus (G)
produces four spindle-shaped, bicellular spores. The sexual nuclei become associated
in a pair in the carpogonium and divide conjugately. The nuclear fusion only
takes place in the young ascus. In certain species in which antheridia are wanting
a second nucleus, according to FAULL, is derived from the stalk -cell of the
trichogyne.

Sub-Class II.— Basidiomyeetes (l> 51> 52> 75^)

The Basidiomyeetes no longer possess sexual organs ; only in
the Uredineae or Rust Fungi are structures found which can be
regarded as persisting, though functionless, male organs, and cells
which appear to correspond to the carpogonia of Ascomycetes. In
place of asci, BASIDIA are present which produce by a process of
budding in most cases four BASIDIOSPORES. The basidia agree with
the asci in containing when young two nuclei, which fuse with one
another. The reduction division appears to follow on this nuclear
fusion or karyogamy. The resulting nucleus undergoes two
divisions, and the four resulting nuclei pass into the spores which
are budded off (Fig. 397).

The alternation of generations present in the Ascomycetes can no longer be
demonstrated in the Basidiomyeetes (with the exception of the Uredineae) owing
to the absence of the sexual organs. The union of sexual cells is replaced by
cell-fusions that result in binucleate cells. The pairs of nuclei correspond to
diploid nuclei, but fusion of the two haploid nuclei of the pair only takes place
in the young basidium. On the division of the truly diploid nucleus thus
produced, haploid nuclei again arise.

The basidia present three distinct types. In the orders Uredineae
and Auricularieae the upper portion of the basidium is divided by
transverse walls into four cells ; each cell bears a single spore on
a thin stalk (sterigma), arising near the upper end (Figs. 403, 408).
In the Tremellineae, on the other hand, the basidium is divided by
longitudinal walls into four cells, each of which continues into a
long tubular sterigma (Fig. 398). The basidium in the Exobasidiineae,
Hymenomycetes, and Gasteromycetes is unicellular, and bears as a
rule four spores at the summit ; these may be sessile or situated on
sterigmata (Figs. 397 ; 420, 2). The Ustilagineae are of interest, since
in one family of these fungi the basidia are divided, while in the
other they are undivided ; the number of spores produced is not a
definite one, but often very large.

2G1

452

BOTANY

In addition to basidia, the Basidiomycetes, like the Ascomycetes, produce
various forms of conidia as accessory fructifications in many species. The origin
of asexual spores by hyphal cells rounding off and developing a thick wall
and their ultimate separation is different from that of conidia (chlamydospores

FIG. 397.—Armillariamellea. A, Young
basidium with the two primary
nuclei ; B, after fusion of the two
nuclei. Hypholoma appendiculatum,
C, a basidium before the four nuclei
derived from the secondary nucleus
of the basidium have passed into the
four basidiospores. D, Passage of a
nucleus through the sterigma into
thebasidiospore. (After RUHLAND.)

FIG. 398. — Basidium of one of the
Tremellineae (Tremella lutescens) (after
BREFELD). (x 450. From v. TAVEL,
Pitee.)

according to BREFELD). These appear in the Ustilagineae as the smut-spores,
and as the rust -spores in the Uredineae. In the former the basidia arise
directly from spores of this kind (Fig. 400), in the latter from a definite type
of rust-spore (Fig. 403, 2). In other Basidiomycetes, if a few simple forms are
disregarded, the basidia are always borne upon or within more or less com-
plicated fructifications. The layer in which the basidia are associated together
is termed the hymenium. These fructifications correspond to those of the
Ascomycetes, but no sexual organs are concerned in their origin. The young
basidia, corresponding to the smut- and rust-spores, here arise from hyphae of
the fructification without the formation of chlamydospores.

Order 1. Ustilagineae (Smut Fungi) (76)

The Ustilagineae are parasites, and their mycelium is found ramifying in
higher plants, usually in definite organs, either in the leaves and stems, or in
the fruit or stamens. The Gramineae in particular serve as host plants ; certain
species of Ustilagineae are in a high degree injurious to cereals, and produce in
the inflorescences of Oats, Barley, Wheat, Millet, and Maize the disease known
as Smut.

The mycelium ultimately produces resting-spores by the formation of additional
transverse walls, and by the division of its profusely -branched hyphae into
short swollen cells. The cells become rounded off and converted into spores
within a gelatinous envelope, which, however, eventually disappears. The spores
then become invested with a new, thick, wall. In this way the mycelium is

DIV. I

THALLOPHYTA

453

transformed into a dark brown or black mass of spores. These smut-spores, brand -
spores, or resting-spores are scattered by the wind, and germinate only after an
interval of rest, producing the basidia in the succeeding spring ; the formation of
these is characteristically different in the two families of the Ustilaginaceae and
the Tilletiaceae.

The most important genus of the Ustilaginaceae is Ustilago. Ust. Avenae,
U. Hordei, and U. Tritici segetum, which were formerly united as U. Carbo, cause
the "smut" or "brand" of Oats, Barley, and Wheat. The mycelium penetrates
the ovary, and forms dark brown, dust-like masses of escaping resting-spores.
V. Maydis produces on the stalks, leaves, and inflorescences of the Maize tumour-
like swellings filled with bjand-spores in the form of a black powder. Other

FIG. 399.— Ustilago. A, Germinating smut-spore (cl), cultivated FIG. 400. — UstUago Scabiosae. A,

in nutrient solution ; t, transversely septate basidium
with lateral and terminal basidiospores (conidia) (c) (x
450). B, Germinating conidia, which are multiplying by
budding (x 200). C, An aggregation of budding conidia
(x 350). (After BREFELD, from v. TAVEL, Pilze.)

Young basidium with four nuclei
formed on germination of the
resting spore. B, Spore-forma-
tion on the 4-celled basidium.
(After HARPER.)

species live on the leaves of different grasses ; while U. antherarum, occurs in the
anthers of various Carophyllaceae (e.g. Lychnis, Saponaria}. In the case of female
flowers of Lychnis the presence of the fungus causes the development of stamens,
the anthers of which are filled with brand-spores.

The brand -spores of Ustilago fall to the ground, and after a period of rest give
rise, on germinating, to a short tube (promycelium) which becomes divided by
three or four transverse walls (Fig. 400 B}, and, functioning as a basidium,
produces ovate basidiospores (sporidia), both laterally from the upper ends of
the intermediate cells and also from the tip of the terminal cell. When abundantly
supplied with nourishment, as when cultivated in a nutrient solution, conidia are
continuously abstricted in large numbers (Fig. 399), and then multiply further by
budding. If the supply of nutriment in the substratum is insufficient, fusions
between conidia or between cells of the promycelium take place in many Smut Fungi
(Fig. 402). After the food-supply of the substratum is exhausted, the conidia grow
out into mycelial hyphae. The formation of the conidia in the damp manured soil
of the grain fields is accomplished during a saprophytic mode of existence, but the
hyphal filaments which are eventually produced become parasitic, and penetrate
the young seedlings as far as the apical cone where the inflorescence takes its

454

BOTANY

PART II

origin. The mycelium continues its development in the inflorescence, and
ultimately terminates its existence by the production of brand-spores.

In addition to the infection of young plants, either resting-spores or the conidia
resulting from their germination may be carried to the stigmas of the grass-flowers
and germinating there produce a mycelium which penetrates to the young seeds
and passes the winter in the embryo-plants. Such infection of the flowers may
alone take place as in Ustilago Tritici, U. Hordei, and U. antherarum, or the seed-
ling may more often be infected as in U. Avenae, U. Sorghi, U. Panici miliacei,
U. Orameri. The Smut of Maize can infect all parts of the plant while in a young
state and the disease is limited to the infected spots.

The life-history of the Tilletiaceae is similar to that of the Ustilaginaceae. The
best-known species are Tilletia Tritici ( = T. Caries) and Tilletia laevis, the fungi
of the stink-brand of wheat. The resting-spores fill the apparently healthy grains
and smell like decayed fish. In the first-named species the resting-spores are
reticulately thickened ; those of T. laevis, on the other hand, are smooth-walled.

FIG. 401. — Tilletia Tritici. A, The basidium developed from the brand-spore bearing at the end
four pairs of spores k (x 300). B, The dispersion of the spores which have fused in pairs
(x 250). C, One of the paired spores germinating and bearing a sickle-shaped conidium sk
(x 400). D, Mycelium with sickle-shaped conidia (x 350). (After BREFELD.)

Unlike the Ustilaginaceae, the germ -tube gives rise only at its apex to filiform
basidiospores, which are disposed in a whorl, and consist of four to twelve spores
(Fig. 401 A). The basidiospores also exhibit the peculiarity that they coalesce with
one another in pairs in an H-form. The filiform spores germinate readily, and
produce sickle-shaped couidia at the apex of the germ-tubes (Fig. 401 C). When
abundantly supplied with food material, the germ -tubes grow into large mycelia.
from which such sickle-shaped conidia are so abundantly abstricted that they
have the appearance of a growth of mould (D). Thus Tilletia, unlike Ustilago,
produces conidia of two forms ; but in other particulars the development of
both groups is the same.

As regards the behaviour of the nuclei, in the Ustilagineae the young spore
as a rule has two nuclei which then fuse. In the germination of the spore a
reduction division may therefore be anticipated. The cells of the promycelium
and the sporidia are uninucleate and mark the commencement of the haploid
phase. The binucleate condition is again attained in various ways. In U. Maydis
the parasitic mycelium consists of uninucleate cells until, shortly before the
formation of spores, neighbouring cells of the hypha fuse and thus the binucleate

DIV. I

THALLOPHYTA

455

cells which form the spores arise. On the other hand, V. Carlo and the majority
of the Ustilagineae attain the binucleate condition by a process of fusion between
pro-mycelial cells, sporidia, or the cells of the mycelium arising from these (Fig.
402). This also holds for Tilletia in which the sporidia before they are shed are
united in pairs, the nucleus from one sporidium passing into the other. The
hyphal cells and secondary sporidia and the cells of
the parasitic mycelium are therefore binucleate.

In the various Ustilagineae the haploid and diploid
phases do not exactly correspond.

Order 2. Uredineae (Rust Fungi) (77> 78)

The mycelium of the Uredineae lives parasitically
in the intercellular spaces of the tissues of the higher
plants, especially in the leaves, and gives rise to the
widely-spread diseases known as Rusts. Their more
varied spore-formation is a distinguishing feature as
contrasted with the Ustilagineae.

As in the latter order, the basidia are not produced
directly on the mycelium but on the germination of a
special type of spore, TELEUTOSPOKES or winter spores,
which are characteristic of all Uredineae. The teleuto-
spores arise in small clusters beneath the epidermis
of the diseased leaf from the ends of hyphae ; fre-
quently two or more form a short chain. They are
thick -walled resting -spores and persist through the
winter (Fig. 403, 1, 5 t). The group of spores usually
bursts through the epidermis. At first the spores, like
the cells of the mycelium which bears them, have two
nuclei, but the nuclei fuse before the spore is ripe.

In the germination of the teleutospore a BASIDIUM
(promycelium) grows from each cell (Fig. 403, 2) ; it

becomes divided by transverse septa into a row of four cells from each of which
a sterigma bearing a single uninucleated BASIDIOSPORE (sporidium) is produced.
The sporidia are dispersed by the wind and germinate in the spring on the leaves
of host plants (which may be of the same or different species from the one on
which the teleutospores were produced), giving rise to an intercellular mycelium,
all the cells of which are uninucleate. From this mycelium organs of two kinds
arise, spermogonia on the upper surface of the leaf and aecidia on the lower
surface.

The SPERMOGONIA (Fig. 404) are flask-shaped structures, the base of which is
covered with the projecting ends of hyphae ; from these are abstricted spermatia,
each of which has a single nucleus. Morphologically they are completely com-
parable to the similarly-named male sexual organs of some Ascomycetes ; among
the Basidiomycetes they persist only in the Uredineae, and even in them are no longer
functional and may be completely wanting. In nutrient solutions the spermatia
may put out short germ-tubes, but are not capable of infecting the host plant.

The AECIDIA (Fig. 405) are cup-shaped fructifications, which when young are
closed, but later open ; from the ends of the hyphae numerous closely-associated
chains of spores are abstricted. As a rule the enveloping layer or peridium of the
aecidium is formed of thick-walled cells corresponding to the sterilised peripheral
rows of spores. In Phraguiidium violaceum, which occurs on the leaves of the Black-

Fic. 402.— Ustilago Carbo. A,
Conjugating sporidia. B, The
two uppermost cells of a
promycelium fusing to give
rise to a binucleate cell. C,
Conjugation between two
promycelia. (x 1000. After
RAWITSCHER.)

456

BOTANY

PART II

berry, and has been fully investigated by BLACKMAN (78), the hyphae beneath the
epidermis when about to give rise to an aecidium first cut off a sterile cell, which
undergoes no further development, from their ends (Fig. 406 A}. The cell below
this increases in size ; it has at first>only a single nucleus, but becomes binucleate

FIG. 403.— Puccinia graminis. 1, Transverse section through a grass-haulin with group of teleuto-
spores. 2, Germinating teleutospore with two basidia. 3, Vegetative, It, germinating basidio-
spore ; the latter has formed a secondary spore, not having been able to infect a host plant.
5, A portion of a group of uredospores (u) and teleutospores (t) ; p, the germ-pores. 6, Germinat-
ing uredospore. (1, 2, 8, U after TULASNE ; 5, 6 after DE BABY. 1 x 150 ; % x circa 230 ;
3, k X 370 ; 5 x 300 ; 6 x 390. From v. TAVEL, Pilze.)

by the passage of a nucleus into it from an adjoining mycelial cell. The two
nuclei do not fuse. The binucleate cell undergoes successive divisions into a chain
of spore-mother-cells, each of which has a pair of nuclei ; and from each spore-
mother-cell an upper binucleate aecidiospore and a sterile intercalary cell, which
is also binucleate but soon shrivels up, are derived by a transverse division (B, C}.
According to CHRISTMAN (78) the development of the aecidiospores in Phrag-
midium speciosum (Fig. 407), which is parasitic on Rosa, proceeds somewhat

DIV. I

THALLOPHYTA

457

differently, and recent researches show that Puccinia and other genera agree.
Here also the ends of the hyphae (A} divide into a terminal sterile cell and a
lower fertile cell (£), but the
fertile cells fuse in pairs with
one another, the upper portions

of the separating walls breaking (\<

down ((7). The two nuclei lie
side by side and divide simul-
taneously (conjugate division).
Two of the daughter nuclei
remain in the lower part and two
pass to the upper portion of the
dividing cell, and this upper
portion is separated by a trans-
verse wall as fhe first spore-
mother-cell (D). In other re-
spects the formation of the
aecidiospores proceeds as de-
scribed above. A peridium is
not formed in Phragmidium,
but in Puccinia, etc. it arises
from the sterile peripheral chains
of spores and from the sterile terminal cells of the central rows of spores.

The ripe, binucleate aecidiospores (Fig. 406 D) are shed and infect a new host

FIG. 404. — Gymnosporangium davariaeforme. A spermo-
gonium rupturing the epidermis of a leaf of Crataegus ;
sp, spermatia ; p, sterile paraphy ses. (After BLACKMAN. )

FIG. 405. — Puccinia graminis. Aecidium on Berberis vulgaris ; ep. epidermis of lower surface of leaf ;
m, intercellular mycelium ; p, peridium ; s, chains of spores, (x 142.)

plant. Each spore gives rise to an intercellular mycelium which soon proceeds in
the summer to bear UREDOSPORES or summer spores. These appear in small circular
or linear groups and arise singly from the enlarging terminal cells of the hyphae

458

BOTANY

PART II

(Fig. 403, 5, 6). They have two nuclei like all the cells of the mycelium developed
from the aecidiospore. They serve commonly to ensure the spread of the fungus in
the summer. Later, either in the same or in distinct sori, the teleutospores are
formed and in these the fusion of the two nuclei to a single one takes place ; such
a fusion as a rule is found to take place in the young basidium.

The two types of cell fusion in the formation of the aecidium are also known in

other Uredineae, and must be regarded as replac-
ing a formerly existing method of fertilisation.
If we attempt to derive the Uredineae from the
Ascomycetes the spermatia must be regarded
as now functionless male cells, and the so-called
fertile cells in the young aecidium as corre-
sponding to carpogonia. Extending the com-
parison further the mycelium proceeding from
the aecidiospore in the Uredineae and the uredo-
spores and teleutospores borne on it, together
with the basidia, formed by the latter, would
together correspond to the diploid asexual
generation (sporophyte) of the Ascomycetes.
The basidiospores would thus correspond to the
ascospores, while the mycelium proceeding from
the basidiospores and ending in the production
of aecidia would be equivalent to the haploid
sexual generation (gametophyte). The agree-
ment between Ascomycetes and Uredineae is
also shown in the behaviour of the sexual nuclei
which only become associated in pairs to fuse
later in the yoimg ascus or the young basidium.
The three forms of spore borne by the sporo-
phyte show, according to CHUISTMAN, a certain
agreement in their development from the " basal
cell " from which they arise ; they may thus be
regarded as morphologically equivalent.

The life-history of the Rust Fungi is thus a
complicated one. The several forms of spore may
appear in the course of the year on the one
host, such Uredineae being termed autoecious.
On the other hand, the spermogonia and
aecidia may occur on one species of host plant,
and the uredosporesand teleutospores on another,
often unrelated, plant. In these heteroecious
species there is thus an alternation of host
plants. There are also pleophagous heteroecious Uredineae in which the aecidia
or the uredo- and teleuto-spores appear on a number of distinct host plants (79).

An example of an heteroecious Rust Fungus is afforded by Puccinia graminis,
the Rust of Wheat. It develops its uredospores and teleutospores on all the green
parts of Gramineae, especially of Rye, Wheat, Barley, and Oats. The aecidia
and spermogonia of this species are found on the leaves of the Barberry (Berberis
vulgaris). In the spring the hibernating double teleutospores give rise to trans-
versely septate basidia, from which the four basidiospores are abstricted (Fig.
403, 2). These are scattered by the wind, and if they fall on the leaves of the

PIG. IQG.—Phragmidium violaceum. A,
Portion of a young aecidium ; st,
sterile cell ; a, fertile cells ; at a%
the passage of a nucleus from the
adjoining cell is seen. B, Formation
of the first spore-mother-cell sw-i,
from the basal cell a of one of the
rows of spores. C, A further stage in
which from sm^ the first aecidiospore
(a) and the intercalary cell (2) have
arisen; sm^, the second spore-mother-
cell. D, Ripe aecidiospore. (After
BLACKMAN.)

DIV. I

THALLOPHYTA

459

Barberry they germinate at once. The germ -tube penetrates the cuticle, and
there forms a mycelium which gives rise to spermogouia on the upper side of the
leaf and to aecidia on the under side (Fig. 405). On the rupture of the peridinm
the reddish -yellow aecidiospores are conveyed by the wind to the haulms and
leaves of grasses, upon which alone they can germinate. The mycelium thus
developed produces at first uredospores (Fig. 403, 5). They are unicellular,
studded with warty protuberances, and provided with four equatorially-disposed
germ - pores. Their protoplasm contains reddish - yellow fat globules. The
uredospores are capable of germinating at once on the wheat, and thus the rust
disease is quickly spread. Towards the end of the summer the same mycelium
produces the dark brown, thick-walled teleutospores (Fig. 403, 1), which in this
species are always double, being united in pairs. Each teleutospore is provided
with one germ-pore, and on germination in the succeeding year the cycle is begun
afresh. The mycelium of the uredo-form may hibernate in winter wheat, and

FIG. 407. — Phragmidium speciosum. A, The first rudiment of au aecidium beneath the epidermis of
a leaf of Rosa. B, The division of the end-cell of a hypha into the upper, transitory, sterile cell
and the lower fertile cell. C, Conjugation of two adjoining fertile cells. D, Later stage in which
the first nuclear division is completed. E, Abstriction of the first aecidiospore mother-cell. F,
Chain of aecidiospores (aj, Oo) separated by intercalary cells (zj, z.£ ; sm, the last-formed spore-
mother-cell still undivided. (After CHRISTMAN.)

thus the rust may appear in the spring without the previous formation of
basidiospores or of aecidia (80).

All Uredineae do not exhibit so complicated a course of development as Puccinia
graminis. Rust fungi which produce all the forms of spore are termed eu-forms ;
those without uredospores, opsis- forms; those without aecidia, brachy - forms ;
those without aecidia and uredospores, micro-forms. In those Uredineae which
no longer possess aecidia and spermogonia, the cells of the vegetative mycelium
arising from the basidiospore are uninucleate, but subsequently, before the
formation of the teleutospores, binucleate cells are found. The binucleate
condition is attained, as has already been shown for several species, in the
preparation for the development of the first uredospores or, when these are
wanting, for the first teleutospores (e.g. in Puccinia Malvacearum). It results
from the conjugation of two cells, as has already been described for the developing
aecidium. This supports the homology of the three kinds of spore.

The genus Endophyllum (81), the species of which are parasitic on Sempervivum

460

BOTANY

PART II

and on Euphorbia, is simpler than the other Uredineae and forms neither
uredospores nor teleutospores. The mycelium proceeding from the basidiospore
consists of uninucleate cells and forms spermogonia and aecidia. The binucleate
condition is attained as in Phragmidium by cell-fusions of the cells that will then
give rise to the chains of aecidiospores. The mature aecidiospores behave like the
teleutospores of the other Uredineae ; their two nuclei fuse, and the spore germinates
to form a basidium bearing four uninucleate basidiospores. This is preceded by
a reduction division of the nucleus (Fig. 408). Possibly Endophyllum may be
regarded as a primitive form. Caeoma nitens behaves in the same manner (81a).

Order 3. Auricularieae

The basidia, as in the case of the Uredineae, are transversely septate, with
four spores. Only a few forms are included in this order. Among the most

Fio. 408. — Endophyllum Sempervivi.
A, Young aecidiospore, still bi •
nucleate. B, Mature uninucleate
spore. C, Germinating spore the Fio.
nucleus of which has divided to
form two. D, Aecidiospore which
has germinated to form a young
four-celled basidium. (After HOFF-
MANN.)

409. _ .Exobasidium Vaccinii. Transverse section
through the periphery of a stem of Vacdnium. ep,
Epidermis ; p, cortical parenchyma ; m, mycelial hyphae ;
b', protruding basidia without sterigmata ; b", with
rudimentary sterigmata ; b'", with four spores. ( x 620.
After WORONIN.)

familiar is Auricularia sambucina (Judas's ear), found on old Elder stems.
It has gelatinous, dark brown fructificatio'ns, which are shell-shaped arid bear
on their inner sides the basidial hymenium.

Order 4. Tremellineae

The basidia are longitudinally divided (Fig. 398). The hymenium is situated
on the upper surface of the fructifications, which are generally gelatinous and
irregularly lobed or folded. The few genera included in this order are saprophytic
on decaying wood and tree-trunks, on the surface of which the fructifications are
produced.

THALLOPHYTA

461

Order 5. Exobasidiineae

No distinctive fructifications are formed, and the basidia spring in irregular
groups directly from the mycelium. They bear four spores on slender sterigmata.
Exobasidium Vaccinii may be taken as a type of this form. The mycelium of
this fungus, which is widely spread in Europe, is parasitic on the Ericaceae,
especially on species of Vacdnium ; it causes hypertrophy of the infected parts.
The basidia are formed in groups under the epidermis, which they finally rupture
(Fig. 409). In this genus, as in many others, accessory fructifications are developed,
and spindle-shaped conidia
are abstricted from the my-
celium on the surface of the
host plant, before the forma-
tion of the basidia.

Order 6. Hymenomycetes (70)

The basidia are undivided,
and bear four spores at the
apices of slender sterigmata
(Fig. 410 sp). They are
produced on fructifications,
which bear definite hymenial
layers, composed, in addition
to the basidia, of paraphyses
(Fig. 410 p), and also of
sterile cystidia (c) or club-
shaped tubes characterised

by their larger diameter and

, ,, . , , ,, FIG. 410. — Russula rubra. Portion of the hymemum. sh,
more strongly thickened wall. Sub.hymenial layer : 5, basidia ; s, sterigmata ; sp, spores ; „,

The four spores are pro-
jected from the sterigraata
by means of the osmotic pressure of the basidium to a distance of about ^ mm. ;
they readily adhere to any surface. The paraphyses by separating the basidia
facilitate the free shedding of the spores. The cystidia, according to KNOLL, are
organs for secreting water and mucilage. They may have other functions in
particular cases ; thus in Coprinus they hold apart the gills and ensure the free fall
of the spores (82).

In the Hymenomycetes, as in the most nearly related orders, special sexual
organs are wanting and the basidia correspond to the asci of the Ascomycetes, and
like these have, to begin with, two nuclei which then fuse. The question thus
arises in what way the binucleate condition of the young basidium is brought
about and what homologies exist with Ascomycetes in the course of development (83).

More recent investigations, especially those of KNIEP, have shown that in many
Hymenomycetes a mycelium consisting of uninucleate cells is developed from the
uni- or bi-nucleate basidiospores ; that sooner or later before the formation of the
fructification the binucleate condition is attained ; that the pairs of nuclei show
conjugate division ; and that the binucleate condition is associated with the
peculiar formation of clamp connections until the formation of the basidia. The
clamp connections arise in the same way on the vegetative hyphae composed of
elongated cells and on the shorter and stouter hyphae from which the hymenium is
formed. In both cases a short protrusion forms about the middle of a terminal cell
of a hypha (Fig. 411, 1). One of the two nuclei passes into the protrusion

paraphyses ; c, a cystidium. (After STRASBURGER. x 540.)

462

BOTANY

PART II

and divides these (2, 3) simultaneously with the other nucleus of the pair. A
transverse wall then forms just beneath the protrusion. The upper nucleus
from the latter passes into the terminal cell of the filament, while the lower

protrusion. This
off from the
a wall and
beneath into

FIG. 411.— Armillaria mucida. Clamp formation and
development of the basidium. 1, Commencement
of clamp formation in the binucleate terminal cell.
2, One nucleus passing into the protrusion. 3,
Conjugate nuclear division. l+, Clamp -cell and
stalk-cell separated from the young basidium. 5,
Fusion of the two nuclei. 6, Basidium with single
nucleus resulting from fusion. 7, Young basidium
with the four basidiospore nuclei and the developing
sterigmata. (After H. KNIEP.)

remains in the
then becomes cut
terminal cell by
fuses with the cell
which the nucleus passes. By
means of this clamp connection
each of the two cells thus obtains
a pair of nuclei derived from the
original pair. It is possible that
the significance of this round-
about process lies in its ensuring
the distribution of the sister nuclei
to the two cells. The binucleate
terminal cell gives rise to the
basidium. The two nuclei fuse
with one another and the resulting
nucleus divides to give rise to the
four nuclei for the spores (Fig. 411,
5, 6, 7).

This clamp formation corre-
sponds, according to KNIEP, to the
hook-shape assumed in the develop-
ing ascus of many Ascomycetes ;
this is, however, limited to the
ascogenous hyphae. Both groups
contain forms without such arrange-
ments, the development of, the
basidium or the ascus proceeding
directly from the binucleate ter-
minal cell of a hypha.

In the case of some Basidio-
mycetes the nucleus of the basidio-
spore divides into two and the
mycelium with binucleate cells
proceeds directly from this without
any clamp formation. The genus
Hypochnus behaves in this simpler
fashion according to KNIEP.

The binucleate mycelium re-
presents the diploid phase. The

haploid stage commences in the
basidium. Its end is indicated by the commencement of clamp connections,
but in Hypochnus it is limited to the uiiinucleate stage of the basidiospore. As
a result of the suppression of the sexual organs an alternation of generations is
no longer present. It can at most be inferred from a phylogenetic point of view.

Most of the Hymenomycetes develop their profusely-branched mycelium
in the humus soil of forests, in decaying wood, or on dying tree trunks, and
produce fructifications, commonly known as toadstools, protruding from the

DIV. I

THALLOPHYTA

463

FIG. 412.— Clavaria botrytis. (Nat. size.)

substratum. The mycelium of the forms vegetating in the soil spreads farther
and farther, and dying in the centre as it exhausts the food material of the
substratum, occupies continually-widening, concentric zones. In consequence of
this mode of growth, where the development has been undisturbed, the fructifica-
tions, which appear in autumn, form the so-called fairy rings. A few Hymeno-
mycetes are parasitic, and vegetate
in the bark or wood of trees. " n '-'"//' i

The Hymenomycetes are
further classified according to the
increasing complexity exhibited
in the structure of their basidial
fructifications.

1. In the group of the Thele-
phoreae, distinctive fructifica-
tions of a simple fype are found.
They form on the trunks of trees
either flat, leathery incrustations
bearing the hymenium on their
smooth upper surfaces ; or the
flat fructifications become raised
above the substratum and form
bracket -like projections, which
frequently show an imbricated

arrangement, and bear the hymenium on the under side (e.g. Stereum Mrsutum,
common on the stems of deciduous trees). The edible Craterellus cornucopioides
has peculiar black funnel-shaped fructifications.

2. The fructifications of the Clavarieae form erect whitish or yellow-coloured
bodies, either fleshy and club-shaped or more or less branched, in a coral-like

fashion. The larger, profusely- branched
forms of this group are highly esteemed
for their edible qualities ; in particular,
Clavaria flava, whose fleshy, yellow-
coloured fructifications are often ten centi-
metres high, also Clavaria botrytis (Fig.
412), which has a pale red colour. Sparas-
sis crispa, which grows in sandy soil in
Pine woods, has fructifications half a metre
in diameter, with compressed, leaf- like
branches.

3. The Hydneae have fructifications
with spinous projections over which the
hymenium extends. In the simpler forms
the fructifications have the appearance
of incrustations, with spinous outgrowths
projecting from the upper surface ; in

other cases they have a stalk, bearing an umbrella-like expansion, from the under
side of which the outgrowths depend. The latter form is exhibited by the edible
fungi Hydnum imbricatum, which has a brown pileus 15 cm. wide, with dark scales
on the upper surface, and Hydnum repandum (Fig. 413), with a yellowish pileus.
4. In the Polyporeae, a group containing numerous species, the stalked or
sessile and bracket-shaped fructifications are indented on the under side with pit-

FIG. 413. — Hydnum repandum. (Reduced.)

464

BOTANY

PART II

like depressions, or deep winding passages, or covered with a layer of tubes, closely
fitted together and lined by the hymenium. To this family belongs the genus
Boletus, occurring on the soil of woods, which has a large, thick-stalked pileus,

FIG. 414-.— Boletus Satanas. (After KROMBHOLZ, A nat. size.) Poisonous.

covered on the under side with a layer of narrow dependent tubes. Although
many species of this genus are edible (e.g. B. edulis, B. badius, B. elegans, and
B. luteus), others are exceedingly poisonous, in particular B. Satanas (Fig. 414).

Fm. 415.— Femes igniarius. Section through an old FIG. 416.— Psalliota campestri* ( = Aga-

fructification, showing annual zones of growth, o, news campestris). Mushroom. To

Point of attachment. (£ nat. size.) the right a young fructification.

(Reduced.)

The stalk of the latter fungus is yellow to reddish-purple, or has red reticulate
markings, while the pileus, which may be 20 cm. wide, is yellowish-brown on its
upper surface, but on the under side is at first blood-red, becoming later orange-
red. B. felleus is unpleasant on account of its bitter taste ; it differs from B. edulis
in having bright rose - coloured tubes. Of the numerous species of the genus

DIV. I

THALLOPHYTA

465

, Polyporus officinalis, with an irregularly tuberous white fructification,
occurs on Larches in South Europe ; it contains a bitter resinous substance and
is also used in medicine. The mycelium of Fomes fomentarius, Touch-wood, is
parasitic in deciduous trees, especially the Beech, and produces large, bracket
or hoof-shaped, perennial fructifications, 30 cm. wide and 15 cm. thick. They
have a hard, grey, external surface, but inside are composed of softer, more loosely-
woven hyphae, and were formerly used for tinder. The narrow tubes of the
hymenium are disposed on the under side of the fructifications in successive annual
layers. Fomes igniarius (Fig. 415),
which is often found on Oaks, and
has a similar structure, has a rusty-
brown colour, and furnishes, since
it is much harder, a poorer quality
of tinder.

Many parasitic Polyporeae are
highly injurious to the trees at-
tacked by them ; thus Fomes annosus
often causes the death of Pines and
Spruce Firs. Merulius lacrymans (84),
the Dry Rot fungus, is an exceed-
ingly dangerous saprophytic species
only rarely found wild in woods, but
attacking and destroying the timber
of damp houses, especially coniferous
wood. The mycelium of this fungus
forms large, white, felted masses
with firmer branched strands which
serve to conduct water and food
substances. The hyphae have clamp
connections. It gives rise to out-
spread, irregularly -shaped, pitted
fructifications of an ochre or rusty-
brown colour, and covered with a
hymenial layer. Good ventilation
of the infected space and dryness

are the best remedial measures. Merulius sill-ester which occurs in woods is a
related form.

5. The Agaricineae, which include the greatest number of species, have stalked
fructifications, commonly known as Mushrooms and Toadstools. The under side of
the pileus bears a number of radially-disposed lamellae or gills which are covered
with the basidia-producing hymenium. In the early stages of their formation the
fructifications consist of nearly spherical masses of interwoven hyphae, in which
the stalk and pileus soon become differentiated. Many Agaricineae develop a
so-called VELUM, consisting of a thin membrane of hyphal tissue which extends
in young fructifications from the stalk to the margin of the pileus, but is after-
wards ruptured, and remains as a ring of tissue encircling the stalk (Fig. 416).
In Amanita (Figs. 417-419) the rudiments of the stalk and pileus are at first
enclosed in a loosely- woven envelope, the VOLVA. In the course of the further
development and elongation of the stalk the volva is ruptured, and its torn
remnants form a ring or sheath at the base of the stalk, and in many cases are still
traceable in the white scales conspicuous on the surface of the pileus.

FIG. 417.— Amanita muscarid. (i nat. size.) Poisoxocs.

466

BOTANY

I'AKT II

Many of the Mushrooms found growing in the woods and fields are highly
esteemed as articles of food. Of edible species the following may be named : the
common Field- Mushroom, now extensively cultivated, Psalliota campestris (Fig.
416), with whitish pileus and lamellae at first white, then turning flesh-colour,
and finally becoming chocolate-coloured ; Cantharellus cibarius, having an orange-
coloured pileus ; Ladaria deliciosa, which has a reddish-yellow pileus and contains
a similarly-coloured milky juice in special hyphal tubes ; Ladaria volema has a
brownish-red cap, a stout stalk, and white milky juice ; Tricholoma equestre has
the upper side of the pileus yellowish brown while elsewhere it is of a sulphur-
yellow colour ; Lepiota procera, whose white pileus is flecked with brown scales ;

FIG. 418.— Amanita phalloides. (£ nat. size.)
VERY POISONOUS.

FIG. 419. — Amanita mappa. (J nat. size.)

POISONO US.

Amanita caesarea with an orange pileus bearing a few white scales and yellow
lamellae. The brownish fructifications of Armillaria mellea are also edible.
This species is a very injurious parasite, especially in Pine woods ; its mycelium
is characterised by the production of photogenic substances which cause the
infected wood to appear phosphorescent in the dark (5). The mycelium forms, as
a resting stage, blackish branched strands (rhizomorphs) beneath the bark or
between the roots of the host plants.

Of the poisonous Agaricineae the following are best known : Amanita muscaria
(Fig. 417), with white lamellae ; Amanita phalloides (Fig. 418), often confounded
with the Mushroom, with lighter or darker green pileus ; A. verna, with white
pileus, and A. mappa (Fig. 419), yellow or yellowish white. All three have white

DIV. I

THALLOPHYTA

467

gills and a swollen base to the stalk, which in the two first -named species
bears a large lobed sheath. Russula emetica, with a red pileus and white
lamellae ; Lactaria torminosa having a shaggy, yellow or reddish-brown pileus
and white milky juice.

fiozites gongylophora, found in South Brazil, is of special ecological interest.
According to A. MOLLER, this species is regularly cultivated in the nests of the
leaf-cutting ants. Its mycelium produces spherical swellings at the ends of the
hyphae, which become filled with protoplasm, the so-called Kohl-rabi heads, and
serve the ants as food-material. The ants prevent the development of the accessory
conidial fructifications peculiar to this fungus, and thus continually maintain the
mycelium in their nests in its vegetative condition. The fructifications, which
rarely occur in the nests, resemble those of Amanita muscaria, with which Eozites
is nearly allied. According to HOLTERMAN, the mycelium of Agaricus rajab is
cultivated in their nests by termites in tropical Asia (85).

ECONOMIC USES. — Polyporus fomentarius (FUNGUS CHIRURGORUM). Polyporus
officinalis ( = Boletus laricis] gives AGARICUS ALBUS, AGARICINUM, and ACIDUM

AGARICINUM.

Order 7. Gasteromycetes (70)
The Gasteromycetes are distinguished from the Hymenomycetes by their closed

FIG. 420.— 1, Sderoderma vulgare, fructification. 2, Basidia of same. (After TULASNE.)
3, Lycoperdon gemmatum. U, Geaster granulosus. (1, 3, 4. nat. size ; 2, enlarged.)

fructifications, which open only after the spores are ripe, by the rupture of the
outer hyphal cortex or PERIDIUM. The spores are formed within the fructifications

2H1

468

BOTANY

PART II

in an inner mass of tissue termed the GLEBA ; it contains numerous chambers,
which are either filled with loosely-interwoven hyphae with lateral branches
terminating in basidia, or their walls are lined with a basidial hymenium.

The Gasteromycetes are saprophytes, and develop their mycelium in the humus
soil of woods and meadows. Their fructifications,
like those of the Hymenomycetes, are raised above
the surface of the substratum, except in the group
of the Hymenogastreae, which possesses subter-
ranean, tuberous fructifications resembling those of
the Tuberaceae.

The fructifications of Scleroderina vulgare (Fig.
420, 1) have a comparatively simple structure.
They are nearly spherical, usually about 5 cm.
thick, and have a thick, light brown, leathery
peridium which finally becomes cracked and rup-
tured at the apex. The gleba is black when ripe,
and contains numerous chambers filled witli inter-
woven hyphae which produce pear-shaped basidia
with four sessile spores (Fig. 420, 2). This species,
which is considered poisonous, is sometimes mistaken
for one of the Truffle Fungi.

The genera Bovista and Lycoperdon (Fig. 420, 3)
(Puff balls) have also spherical fructifications, which
are at first white and later of a brown colour. In
the last-named genus they are also stalked, and in
the case of Lycoperdon Bovista may even become half
a metre in diameter. The peridium is formed of two
layers ; the outer separates at maturity, while the
inner dehisces at the summit. The hymenial layer
of basidia, in the fungi of this group, lines the
chambers of the gleba. The chambers are also pro-
vided with a fibrous capillitium consisting of
brown, thick- walled, branched hyphae which spring
from the walls, and aid in distributing the spores.
The fructifications are edible while still young and
white. When mature they contain urea.

In the related genus Geaster (Earth-star) (Fig.
420, 4) the peridia of the nearly spherical fructifica-
tions are also composed of two envelopes. When
the dry fruit dehisces, the outer envelope splits into several stellate segments,
and the inner layer of the peridium becomes perforated by an apical opening.

The highest development of the fructifications is exhibited by the Phalloideae(86),
of which Ithyphallus impudicus (Stink-horn) is a well-known exam pie. -This fungus
is usually regarded as poisonous. It was formerly employed in a salve as a
remedy for gout. Its fructification recalls that of the discomycetous Morchella,
but it has quite a different manner of development. A fructification of this
species of Phallus is about 15 cm. high. It has a thick, hollow stalk of a white
colour and perforated with pores or chambers. Surmounting the stalk is a bell-
shaped pileus covered with a brownish-green gleba which, when ripe, is converted
into a slimy mass (Fig. 421). When young the fructification forms a white, egg-
shaped body, and is wholly enveloped by a double-walled peridium with an inter-

FIG. 421.— lihyphallus impudicus.
(£ nat. size.)

DIV. i THALLOPHYTA 469

mediate gelatinous layer. Within the PERIDIUM (also termed volva) the hyphal
tissue becomes differentiated into the axial stalk and the bell-shaped pileus, carry-
ing the gleba in the form of a mass of hyphal tissue, which contains the chambers
and basidial hymenium. At maturity the stalk becomes enormously elongated,
and pushing through the ruptured peridium raises the pileus with the adhering
gleba high above it. The gleba then deliquesces into a dropping, slimy mass,
which emits a carrion-like stench serving to attract carrion-flies, by whose agency
the spores embedded in it are disseminated.

CLASS XV
Liehenes (Lichens) (l> 51> 87 91)

The Lichens are symbiotic organisms; they consist of higher
Fungi, chiefly the Ascomycetes, more rarely Basidiomycetes, and uni-
cellular or filamentous Algae (Cyanophyceae or Chlorophyceae), living
in intimate connection, and together forming a compound thallus or
CONSORTIUM. Strictly speaking, both Fungi and Algae should be
classified in their respective orders ; but the Lichens exhibit among
themselves such an agreement in their structure and mode of life,
and have been so evolved as consortia, that it is more convenient to
treat them as a separate class.

In the formation of the thallus the algal cells become enveloped by the mycelium
of the fungus in a felted tissue of hyphae (Fig. 422). The fungus derives its

nourishment saprophytically from __^_^ -.

the organic matter produced by the n\''o°n°0'D l?S??ff *$*££$ j '/«'/(? "l
assimilating alga ; it can also send MW/®^
haustoria into the algal cells, and «

so exhaust their contents. The
alga, on the contrary, derives a
definite advantage from its con-
sortism with the fungus, receiving
from it inorganic substances and
water, and probably organic sub-
stances also.

The main advantage in this
mutualistic symbiosis is probably
on the side of the fungus. This is
especially the case in those Lichens Flf;- 42'2- — Cetraria islandica. Transverse section

which grow on bare rock, while in throu§h the thallus; "> cortical la>"er of upper
,, . , .n surface ; ur, of the lower surface ; m, medullary

those growing on humus soil or on layer containing the green cells of the Alga> chloro.

the bark of trees the fungus can, coccum humicola. (x 272.)
in part at least, derive its food sapro-
phytically from the substratum. The Alga, however, exhibits active multiplica-
tion, and both it and the -fungus can, as a result of the symbiosis, succeed in
situations where neither could live alone.

The numerous Lichen acids, which are wanting only in the gelatinous Lichens,
are products of metabolism peculiar to the group. Their production is due to the
mutual chemical influence of the alga and fungus. They are deposited on the

2H2

470 BOTANY PART n

surface of the hyphae in the form of crystals or granules. Their supposed use as
a protection against snails appears, according to ZOPF, not to hold generally (88).

The Lichens are distributed in numerous species over the whole earth. They
extend further than even the Mosses towards the poles and towards mountain
summits. They attain their maximum development in moist Alpine regions where
they sometimes cover the soil, rocks, and tree-trunks with a colonial vegetation
or hang in beard-like masses from the branches of the trees. In the Arctic regions
they may cover the soil and give rise to extensive tracts of Lichen tundra.

The simplest Lichens are the FILAMENTOUS, with a thallus con-
sisting of algal filaments interwoven with fungal hyphae. An example
of such a filamentous form is presented by Ephebe pubescens, which is
found growing on damp rocks, forming a blackish layer.

Another group is formed by the GELATINOUS Lichens, whose
thallus, usually foliaceous, is of a gelatinous nature. The algae
inhabiting the thalli of the gelatinous Lichens belong to the families
of the Chroococcaceae and Nostocaceae, whose cell walls are swollen,
forming a gelatinous mass traversed by the hyphae of the fungus.
The genus Collema is a European example of this group.

In both the filamentous and gelatinous Lichens the algae and
the fungal hyphae are uniformly distributed through the thallus,
which is then said to be unstratified or HOMOIOMEROUS.

The other Lichens have stratified or HETEROMEROUS thalli. The
enclosed algae are usually termed GONIDIA. They are arranged in a
definite GONIDIAL LAYER, covered, externally, by a CORTICAL LAYER,
devoid of algal cells and consisting of a pseudo-parenchyma of closely-
woven hyphae (Fig. 422). It is customary to distinguish the three
following forms of heteromerous Lichens : CRUSTACEOUS LICHENS,
in which the thallus has the form of an incrustation adhering closely
to a substratum of rocks or to the soil, which the hyphae to a certain
extent penetrate. FOLIACEOUS LICHENS (Fig. 426), whose flattened,
leaf-like, lobed or deeply-cleft thallus is attached more loosely to the
substratum by means of rhizoid-like hyphae (rhizines), springing either
from the middle only or irregularly from the whole under surface.
FRUTICOSE LICHENS (Fig. 424) have a filamentous or ribbon-like thallus
branched in a shrub-like manner and attached at the base. They are
either erect or pendulous, or may sometimes lie free on the surface of
' the substratum.

In nature the germinating spores of the Lichen Fungi appear to
be capable of continuing their further development only when they
are enabled to enter into symbiosis with the proper gonidia. For a
few genera of Lichens, however, it has been determined that the
fungi sometimes exist in nature without the presence of the algae ; it
has been shown that the tropical Lichen Cora pavonia (Fig. 431),
whose fungus belongs to the order Hymenomycetes, may produce
fructifications even when deprived of its alga ; these have a form
resembling those of the fungal genus Thelephora. Mycelia have

DIV. I

THALLOPHYTA

471

also been successfully grown from the spores of certain Lichen-
forming Ascomycetes, cultivated without algae and supplied with a
proper nutrient solution.

Many Lichens are able to multiply in a purely vegetative manner,
by means of loosened pieces of
the thallus, which continue their
growth and attach themselves to
the substratum with new rhizines.
The majority of the heteromerous
Lichens possess in the formation
of SOREDIA another means of
vegetative multiplication. In this
process, small "groups of dividing
gonidia become closely entwined
with mycelial hyphae and form
small isolated bodies which, on

the rupture of the thallllS, are FIG. VS.-Parmelia physodes.

scattered in great numbers by «, Formation of soredia ; 6, single soredium.

the wind and give rise to new

Lichens. Frequently the soredia arise in circumscribed receptacles

(Fig. 423).

The fructifications of the Lichens are produced by the fungi, not
by the algae, which are always purely vegetative.

1. Ascolichenes

Only a few genera of Lichens have flask-shaped perithecia, the fungus be-
longing to the Pyrenomycetes (Endocarpon, Vei-rucaria). Most genera produce, as
the ascus-fruit of their fungus, cupular or discoid apothecia, sessile or somewhat
sunk in the thallus. In structure they resemble those of the Discomycetes, and
bear on their upper side an hymenium of asci and paraphyses. One of the
commonest species of fruticose Lichens belonging" to this group is Usnea barbata,
the Beard Lichen, frequently occurring on trees and having large fringed apothecia
(Fig. 424). JRamalinaframnea, which has a broad ribbon-shaped branched thallus
and grows on trees, and the numerous species of Roccella found on the rocks of
warmer coasts, have similar apothecia. Cetraria islandica, Iceland Moss (Fig. 425),
occupies an intermediate position between the fruticose and foliaceous Lichens.
It has a divided, foliaceous, but partially erect thallus, which is of a light bluish-
green or brown colour, whitish on the under side, and bears the apothecia
obliquely on its margin. This Lichen is found in mountainous regions and in the
northern part of the Northern Hemisphere. The numerous species of Parmelia
(Fig. 426) are foliaceous Lichens growing on trees and on rocks. Graphis scripta
s a well-known example of the crustaceous Lichens ; its greyish-white thallus
occurs on the bark of trees, particularly of the Beech, on whose surface the
apothecia are disposed as narrow, black furrows resembling writing.

A peculiar mode of development is exhibited by the genus Cladonia, whose
primary thallus consists of small horizontal scales attached directly to the ground ;
from this thallus springs an erect portion, the PODETIUM, of varying form and

2H3

472

BOTANY

PART II

structure in the different species. In some cases the podetia are stalked and
funnel-shaped, bearing on the margin or on outgrowths from it knob-like apothecia,
which in C. pyxidata are brown, in C. coccifera (Fig. 427) bright red. In other

FIG. 424.— Usnea barbata. ap, Apothecium.
(Nat. size.)

FIG. 425.—Cetraria islandica. ap, Apothecium.
(Nat. size.) OFFICIAL.

species the erect podetia are slender and cylindrical, simple or forked ; in C. rangi-
ferina, Reindeer Moss, which has a world-wide distribution, particularly in the
tundras of the North, the podetia are finely branched (Fig. 428), and bear the smal

brown apothecia at the ends of the branches.
The primary thallus of this species soon dis-
appears.

The ascus fructifications (apothecia or
perithecia) of the Lichens originate, as
STAHL and, more recently, BAUR (89) have
shown, from carpogonia or female sexual
organs which are frequently present in
large numbers on young lobes of the thallus.
The carpogonium (Fig. 429) is here a multi-
cellular filament, the lower part of which
is spirally coiled, while it continues above
into a trichogyne composed of elongated
cells and projecting from the surface of
the thallus. All the cells are uninucleate
and communicate with one another by
means of pits. Those of the lower part of
the filament contain abundant protoplasm.
Apart from their multicellular nature these structures recall the carpogonia found in
the Florideae. The spermatia which originate in spermogonia (Fig. 430) are presum-
ably the male sexual cells. The spermatia develop in different ways (90). In some
cases the inner wall of the spermogonium is lined with simple or branched hyphal
branches from the ends of which the spermatia are abstricted (Peltigera, Parmelia).
In other cases the spermogonium is at first filled with a hypha] tissue in which

FIG

426. — Parmelia acetabulum ; grows on
trees. (After REINKE.)

Drv. i

THALLOPHYTA

473

cavities are formed later and the sperraatia arise on very small and thin stalks
from the cells lining the cavities (Anaptychia, Physcia, Stictd). The spermatia,
embedded in a slimy mass, are shed from the spermo-
goiimm and conjugate with the adhesive tip of the
trichogyne (Fig. 4295). After conjugation the
or y^/" spermatia appear empty and their nucleus has dis-

appeared. When this has taken place the cells

Fn ;. 427. — Cladonia cocci/era,
t, iScales of primary
thallus. (Nat. size.)

Fio. 428.— Cladvnia rangiferina. A, sterile ; B, with
ascus-fruits at the ends of the branches. (Nat.
size.)

FIG. 42'.'. — Collemacrispum. A,
carpogonium (c) with its
trichogyne (0 ( x 405). B,
apex of the trichogyne
with the spermatium (.s)
attached (x 1125). (After
E. BAUR.).'

FK.. 430. — Anaptychia ciliaris. Ripe spermogoniuin. The
dark round bodies within the thallus are the green algal
cells, (x 192. After GLUCK.)

of the trichogyne collapse, while the cells of the coiled carpogonium swell,
undergo divisions, and form the ascogonium. From the latter the ascogenous
hyphae which bear the asci are produced. The vegetative hyphae composing

474

BOTANY

PART II

the fructification and the paraphyses originate from hyphae which arise below the
carpogonium. The fructification may arise from one or from several carpogonia.
The behaviour of the sexual nuclei requires further investigation. Such carpogonia
have been shown to give rise to the fructifications in a large number of genera.
In other genera (Peltigera, Solerina] they are reduced, the trichogyne is wanting,
and the reproduction is apogamous. Spermogonia are as a rule not found in these
cases, or are, as in the case of Nephromium, clearly degenerating structures. It
has been shown by A. MOLLER that the spermatia of Lichens can germinate and
produce a mycelium ; but this is not inconsistent with their primitively sexual
nature.

The behaviour of Oollema pulposum is very remarkable. According to
F. BACHMANN the spermatia arise in the interior of the thallus in small groups
on the hyphae, and do not become detached. The elongated terminal cell of the
trichogyne remains in the thallus. but grows towards the spermatia and fuses
with them (9°a).

2. Basidioliehenes (Hymenolieehnes) (91)

The Hymenolichenes are represented by Corapavonia, of which the genera Dictyo-
nema and Laudatea are only special growth forms. This Lichen is widely spread

in the tropics, growing on the soil or on
trees. The fungus of this Lichen belongs
to the family Thelephoreae (p. 463) ; its
flat, lobed, and often imbricated fructi-
fications are also found entirely devoid
of Algae. In symbiosis with the uni-
cellular Alga Chroococcus it forms the
fructifications of Cora pavonia (Fig.
431), resembling those of the Thelephoras
with a channelled, basidial hymenium
on the under side. Associated sym-
biotically, on the other hand, with fila-
ments of the blue-green Alga Scytonema,
if the Fungus preponderates, it produces
the bracket-like Lichens of the Didyo-
nema form, found projecting from the
branches of trees with a semicircular
or nearly circular thallus, having the
hymenium on the under side. When
the shape of the thallus is determined by the Alga, a Lichen of the Laudatea
form occurs as felted patches of fine filaments on the bark of trees, with the
hymenium on the parts of the thallus which are turned away from the light.

OFFICIAL. — The only representative of the Lichens is Cetraria islandica
(LICHEN ISLANDICUS). Lobaria pulmonaria is also used in domestic medicine.

The Manna Lichen (Lecanora esculenta) is a crustaceous Lichen that often
covers the ground to a depth of 15 cm. in the Steppes and Deserts of Southern
Russia, Asia Minor, and North Africa. The thallus falls into pieces the size of a
pea, and is thus readily swept by the wind ; it is used by the Tartars, who prepare
earth-bread from it. Cetraria islandica also, when the bitter substances are
removed by washing, may, owing to the abundant carbohydrate material (Lichen
starch) it contains, be used to make bread as well as to prepare jelly. Cladonia

FIG. 431.— Cora pavonia. A, Viewed from above ;
B, from below ; hym, hymenium. (Nat. size.)

DIV. i BRYOPHYTA 475

rangiferina is important as affording food for the Reindeer, and after the re-
moval of bitter substances can be used as fodder for cattle. Alcohol is obtained
from it in Norway.

Some species particularly rich in Lichen acids are used in the preparation of
the pigments orseille and litmus ; there are in the first place species of Roccella
(especially R. Montagnei, £. tinctoria, £. fuciformis, and .K. phycopsis) which are
collected on the coasts of the warmer oceans, and the crustaceous lichen, Ochrolechia
tartarea, in North Europe and America.

II. BRYOPHYTA (MOSSES AND LIVERWORTS) (*> 92' 93111)

The Bryophyta or Muscineae comprise two classes, the Hepatkae or
Liverworts, aad the Musci or Mosses. They are as regards their
general segmentation Thallophyta, but are distinguished from them
by the characteristic structure of their sexual organs, ANTHERIDIA
and ARCHEGONIA, which are similar to those of the Pteridophyta.
The Bryophyta and Pteridophyta are accordingly, in contrast to the
Thallophyta, referred to collectively as Archegoniatae.

The Bryophytes as well as the Pteridophytes reproduce also
asexually by means of SPORES provided with cell walls and adapted
for dissemination through the air. These two modes of reproduction,
sexual and asexual, occur in regular alternation, and are confined to
sharply distinct generations : a sexual (gametophyte), provided with
sexual organs, and an asexual (sporophyte), which produces spores.
The sexual generation arises from the spore, the asexual from the
fertilised egg. The number of chromosomes in the nuclei of the
sporophyte is t\vice as great as in the nuclei of the gametophyte.
The double number is acquired in the fusion of the sexual nuclei,
while the reduction to one-half takes place in the division of the
spore -mother- cells. This regular ALTERNATION OF GENERATIONS is
characteristic of all Archegoniatae. In the Bryophyta the plant is
the haploid generation, while the stalked capsule is the diploid
sporophyte. In the Pteridophyta the gametophyte is a small thallus,
w-hile the sporophyte is a large cormophytic plant.

In the development of the SEXUAL GENERATION, the unicellular
spore on germinating ruptures its outer coat or EXINE, and gives rise
to»a germ-tube. In the case of the Hepaticae the formation of the
plant at once commences, but in most of the Musci a branched,
filamentous PROTONEMA is first produced, composed of cells containing
chlorophyll (Fig. 432). The green, filamentous protonema gives
rise to branched, colourless rhizoids (?•), which penetrate the sub-
stratum. The MOSS -PLANTS arise from buds developed on the
protonema at the base of the branches. Protonema and moss-plant,
in spite of the difference in appearance between them, together
represent the sexual generation. Many Liverworts possess a thallus
consisting of dichotomously-branching lobes (Figs. 446, 447), which

476

BOTANY

PART II

is attached to the substratum at its base or on the under side by means
of rhizoids, thus repeating the vegetative structure of many Algae. In

FIG. 432.— Funaria hygrometrica. A, Germinating spore ; ex, exine. B, Protonema ; kn, buds ;
r,' rhizoids ; s, spore. (Magnified. After MULLER-THURGAU.)

the higher Hepaticae, on the other hand, and in all the Musci, there
exists a distinct differentiation into stem and leaves (Figs. 449, 456).

Khizoids spring from the
lower part of the stem.
True roots are wanting
in the Bryophytes,
which thus do not attain
a higher grade of organi-
jr sation than the differenti-
ated thallus already met
with among the Brown
Algae, for example in
Sargassum. The stems
and leaves of Mosses are
also anatomically of a
simple structure; if

FIG. 433.— Marchantiapolymorpha. A, Nearly ripe antheridium Conducting strands are
in optical section; p, paraphyses. B, Spermatozoids. pregent they are COttl-
(A x 90, B x 600. After STRASBURGER.)

posed merely ot simple

elongated cells. The sexual organs (antheridia and archegonia) are
produced on the adult, sexual generation ; in the thalloid forms on
the dorsal side of the thallus ; in the forms with stem and leaves at
pthe apex of the stem or its branches.

DIV. I

BRYOPHYTA

477

The ANTHERIDIA (Fig. 433) or male sexual organs are stalked,
ellipsoidal, spherical, or
club-shaped, with thin /~~\
walls formed of one layer AT
of cells and enclosing
numerous small, cubical
cells, each of which
becomes divided diagon-
ally or transversely into
two sperma tozoid
mother cells (w). At
maturity the sperm a to-
zoid mother cells separ-
ate and are ejected from
the antheridium, which
ruptures at the apex. In
the case of the Musci
there is a terminal group
of one or more cells with
mucilaginous contents
which on swelling burst
the cuticle (Fig. 438 A)

Fi<;. 434.— Development of the antheridium in Fegatdla conica,
one of the Marchantiaceae. A, Unicellular stage. E, The
stalk-cell (st) cut off. C, D, Antheridium divided into a
row of cells which in turn are divided by longitudinal
walls. E, Cutting off of the layer of cells to form the wall
(w). F, Advanced stage of development. (A-E x 400 ;
F x 220. After BOLLETER.) s

111

the Liverworts the mucilaginous cells
separate irregularly from one another
and there is no denned cap of cells.
By the dissolution of the enveloping
walls of the mother cells the sperma-
tozoids are set free as short, slightly-
twisted filaments, bearing two long
cilia close to the anterior end (Fig.
433).

The antheridium is developed from a
single superficial cell ; it is only in the
case of Anthoceros (Fig. 443) that it is
formed endogenously. In the lower Liver-
worts (Marchantiales) this cell becomes
divided into transverse disc-shaped seg-
ments ; each of these is divided by walls
at right angles into four cells, and then
Fio. 435.— Development of the antheridium of tangential walls in these quadrants separate
a Moss. Funaria hygrometrica. A Primor- the peripheral cells of the antheridial wall
dinm of an antheridium divided into four h internal cells, which give rise

cells. B, Formation of the apical cell from "I

the uppermost cell. C, Division of the apical to" the spermatogenous tissue (Fig. 434
cell. D, The separation of the wall-layer and A-F]. In the higher Liverworts (Junger-
the cells that will give rise to the spermato- rnanniales) the original cell is first divided
genous tissue. E, Same stage in transverse iuto ft rQW of three b transverse walls ;
section. F, Older stage. (After D. CAMPBELL.) .. , : . ., , ,. ,

the uppermost cell divides by a vertical

wall, and in each of the two resulting cells two successively-formed walls separate

478

BOTANY

PART II

the wall and the cells which give rise to the spermatogenous tissue. In the Mosses
(Musci), on the other hand, the antheridium develops by the segmentation of a
two-sided apical cell, which is delimited by two oblique walls in the uppermost
cell of a short row. Each of its segments is later divided into wall cells and an
internal cell which contributes to the development of the spermatogenous cells
(Fig. 435 A-F).

The archegonia (Fig. 436) are short-stalked, flask-shaped organs in
which a venter and neck can be distinguished. The wall of the ventral

portion encloses a large
central cell, which divides
shortly before maturity
^4 to give rise to the egg-

^y^ cell and the ventral-

canal-cell. The latter if
situated at the base os
the neck, just below a
central row of neck-
canal-celfe, the number
of which is lower in
Liverworts (4-8) than in
Mosses (10-30). The
neck opens by the swell-
ing of the mucilaginous
contents of the upper-
most cells which rupture
the cuticle and often
become rolled back as
four lobes (Fig. 438 B)
(95). The canal-cells be-
come mucilaginous. Since
water is essential for the
process of fertilisation,

FIG. 436.— Marchantiapolymorpha. A, Young, B, mature arche- ^nis onV takes place in
gonium ; C, fertilised archegonium, with dividing egg-cell, laild-f OmiS after Wetting

k', Neck-canal-cell ; k", ventral-canal-cell ; o, egg-cell ; pr,
pseudo-perianth, (x 540. After STRA.SBURGER.)

!,„ rain Or dew The
* , ,

movement of the sperma-
tozoids towards the archegonia, and down the neck-canal to the egg-cell
is directed by particular substances diffusing from the archegonium.

The spermatozoids of Mosses are attracted by cane-sugar solution, those of the
Liverwort Marchantia also by proteid substances and by salts of potassium, rubi-
dium, and caesium (96) (cf. p. 331).

The archegonium develops from a single superficial cell. In Liverworts this
divides into a lower cell, which gives rise to the stalk, and an upper cell ; the
latter is divided by three longitudinal walls into three outer cells surrounding a
central cell. The central cell is then divided by a transverse wall into a cap-cell
and a completely enclosed internal cell. The outer cells give rise to the wall of

DIV. T

BRYOPHYTA

479

the venter and neck, while the inner cell divides to give rise to the egg -cell,
ventral-canal-cell, and neck -canal-cells (Fig. 437). In Mosses, on the other hand,
the original cell divides by inclined walls, and the segments of the resulting two-
sided apical cell form the stalk. The terminal cell is then divided by three oblique
walls and one transverse wall into a three-sided apical cell, truncated below ; a
central cell beneath this ; and
three peripheral wall-cells. The
central cell gives rise to the egg-
cell, ventral-canal-cell, and neck-
canal-cells ; the segments of the
apical cell produce the wall of
the neck and the uppermost neck-
canal-cells. According to MELIK
the Sphagnaceae occupy a middle
position in that tlie stalk arises

FIG. 437. — Development of thearchegoniumof a Liverwort.
A (longitudinal section) and B (transverse section)
showing the upper cell divided by three walls. C, The
central cell divided into cap-cell(d) and internal cell (0-

D, The internal cell divided into the cells which will give
rise to the neck-canal-cells Qik), and the ovum and
ventral-canal-cells (c) respectively; st, young stalk.
(After GOEBEL.)

as in the Mosses, while the body
of the archegonium is differenti-
ated without a three-sided apical
cell as in the Liverworts.

Antheridia and archegonia are homologous organs, as is shown by the occurrence
of structures intermediate in nature ; the ventral-canal-cell and neck-canal-cells
are to be regarded as gametes which have become functionless. The ventral -
canal-cell is as a rule smaller than the egg but may equal it in size. Occasionally
several egg-cells may be developed in an archegonial venter, e.g. 4 or more in
Sphagnum (93).

After fertilisation the zygote, without undergoing a period of rest,
proceeds to divide and give rise to the embryo (Fig. 436 C). The

embryo grows into the

Asporogonium which re-
A-«X\ „ — . ^^ presents the asexual

generation and remains
throughout its life con-
nected with the sexual
generation ; it obtains
food -materials from the
latter like a semi-para-
sitic plant. The sporo-
gonium is a round or
A B oval capsule, with a

FIG. 438.- A, Summit of the empty antheridium of Polytrichum longer Or shorter Stalk,
cut in half and showing the dehiscence cap. (After GOEBEL.) and COntainin0" niimer-
B, Opened neck of the archegonium of Mnium umlulatum. oug gpOres These as

in Pteridophyta and

Spermatophyta, arise in tetrads by the twice-repeated division of the
spore-mother-cells, which have previously separated from one another
and become rounded off.

In the Mosses the lower part of the embryo penetrates into the, often much
enlarged, tissue of the stalk of the archegonium and in some cases even into the

480

BOTANY

PART II

summit of the stem. This tissue along with the layer derived from the venter of
the archegonium forms an investment that is later broken through by the growing
embryo. The upper portion derived from the archegonial wall is carried up as
the calyptra, while the lower portion forms a sheath round the base of the
sporogonial stalk. The origin of the calyptra is similar in many Liverworts (e.g.
in the Marchantiales) ; in others, however, the base of the embryo grows more or less
deeply into the tissue of the thallus or stem below the archegonium. In special
cases the tissue adjoining the archegonia forms a pouch-like structure (marsupium)
enclosing the archegouium and embryo ; this often grows down into the soil and
represents a peculiar organ of protection and nutrition.

The development of the sporo-
gonium exhibits a remarkable
variety. In the lower Liverworts
(Marchantiales) the zygote divides
by transverse and longitudinal
walls into 8, then by further radial
walls into 16 cells, following on
which comes division into external
and internal cells by periclinal
walls (Fig. 439). The foot and
short stalk of the sporogonium
come from the lower half of the
embryo and the capsule from the
.upper half, the internal cells of
which form the archesporium and
give rise to the sporogenous tissue.
The cells of this become in part
spore -mother -cells, while others
FIG. 439.— Development of the Sporogonium of Corsinia remain sterile and serve at first
marchantioides, one of the Marchantiaceae. A, The ag nutritive cells to the developing
zygote divided into 16 cells B, The lower half of the ^ ^$ C). ^ th

embryo developing as foot, the upper as capsule ; w,

wall cells; ar, archesporium (x 170). C, Older sterile cells usually grow into
sporogonium. The archesporium has given rise to spindle-shaped structures with a
spore-mother-cells and small sterile cells which in spiral thickening of the wall
Corsinia do not develop further into elaters. (x 90.) (elaters) these on the opening of
(After K. MEYER.)

the capsule assist in the dispersion

of the spores. Only in the Ricciaceae do all the internal cells become spore-mother-
cells, the whole sporogonium being simplified to a spherical, unstalked capsule with
a wall of one layer of cells.

In the higher Liverworts (Jungermanniales) the zygote first undergoes a number
of transverse divisions ; the lowest cell becomes sometimes after a few divisions an
absorbent organ while the upper cells give rise to foot, stalk, and capsule. In
addition to the spores, sterile cells, which usually develop into elaters, are formed
from the sporogenous tissue.

The Anthocerotales are Liverworts which deviate considerably as regards the
construction of the capsule from those described above and in some respects
approach the Mosses (cf. p. 483).

In the Mosses the sporogonium has a columella which is an axile strand of sterile
tissue serving for the conduction of materials ; around this the archesporium is
arranged as a, usually single, layer of cells. In the Sphagnales (Fig. 452 C) and
the Andreaeales the archesporium extends as a dome over the summit of the

DIV. I

BRYOPHYTA

481

columella, while in the Bryales (Fig. 458) it constitutes an open cylinder around
the columella. The elongated embryo is composed of segments which in the
Sphagnales arise by transverse division of the zygote and in other Mosses are cut

FI<;. 440.— Development of the sporogonium of the Moss, Funaria hygrometrica. A, B, Longitudinal
sections showing first stages in the development from the zygote s, apical cell. C-E, Transverse
sections: C, division into enduthecium (e) and amphithecium (a); D, further divided stage;
E, older sporogonium, in the endothecium of which the outermost layer is distinct as the
archesporium (or) from the columella (c> (After CAMPBELL.)

off from a two-sided apical cell. In each transverse segment a longitudinal
division follows, and in the resulting quadrants there is a separation of outer cells
(amphithecium) from internal
cells (endothecium) (Fig. 440).
In the Sphagnales only, the
archesporium arises as the
innermost layer of the amphi-
thecium ; in all other Mosses
it is the outermost layer of the
endothecium. It gives rise
exclusively to spores, no sterile
cells being formed (Fig. 441).

The Bryophyta are char-
acterised by a great power of
regeneration from cut portions
of all the organs. Vegetative
reproduction by means of
gemmae, etc., is widespread ;
they arise on the thallus, on
stems, on leaves, and on the
protonema in a great variety of ways, becoming separated later (w).

There are difficulties in the way of the phylogenetic derivation of the Bryophyta
from any definite group of Algae. Fetween the Bryophytes on the one hand, and

2 l

--,
-

FIG. 441. — Funaria, hygrometrica. Transverse section
through the archesporium (A, su), and the groups of still
connected spore -mother -cells derived from it (B, sm).
(After GOF.BEL.)

482 BOTANY PART n

the higher Green Algae and Characeae on the other, no transitional forms are
known. Morphological comparison points rather to a connection between the
Bryophyta and the Brown Algae, the multilocular gametangia of which (in some
genera already differentiated into oogonia and antheridia) may be regarded as
homologous structures leading to the archegonia and antheridia of the Arche-
goniatae. Thus the antheridium of the lower Liverworts shows a cellular con-
struction in agreement with that of the gametangia of Brown Algae (cf. Figs. 434,
354, 356) ; it is distinguished by the possession of a sterile, protective layer of
cells forming the wall, and the differentiation of this can be regarded as an
adaptation to a terrestrial mode of existence. Further, among the Brown Algae,
in Dictyota. there is an alternation of generations agreeing with that of Bryophyta,
although the gametophyte and sporophyte are similar in their vegetative structure.
The tetrasporangia of the sporophyte of Dictyota correspond to the spore-mother -
cells of the sporophyte of the Bryophyta ; their endogenous position in the latter
may be related to the influence of a terrestrial mode of life. While the form of
the gametophyte in the thalloid Liverworts shows many points in common witli
the thallus of certain Brown Algae, the sporophyte of the Bryophyta proceeds
early to the development of its spores, and ceases growth without a .segmenta-
tion into vegetative organs. It thus becomes essentially different from the
gametophyte (98).

With the exception of a few forms which have secondarily assumed an aquatic
life, the Bryophyta in contrast to the Algae are land-plants and exhibit corre-
sponding adaptations in their structure. Thus all the above-ground parts are
covered with a cuticle. The small size of the Bryophyta as compared with
Pteridophyta stands in connection with their simple cellular construction from
which true vessels are absent. True roots are also wanting. Some are minute
plants, while the largest Mosses, represented by the Dawsonieae of New Zealand,
have leafy stems attaining a height of 50 cm.

The two very distinct classes of Bryophytes may be briefly charac-
terised as follows :

1. Hepaticae (Liverworts). — The sexual generation, with poorly
developed and generally not distinctly differentiated proton ema, is
either a dichotomously-divided thallus or is developed as a leafy and,
with few exceptions, dorsiventral shoot. In the majority of Hepaticae,
in addition to spores, the capsule produces also elaters ; only in one
order, Anthoceroteae, does the capsule have a columella.

2. Musci (Mosses). — The protonema of the sexual generation is
usually well developed and distinctly defined, and the moss plant is
always segmented into stem and leaves. The leaves are arranged
spirally in polysymrnetrical, less frequently in bisymmetrical, rows.
The capsule is always without elaters, but with a columella.

Fossil Bryophyta. — The Liverworts are more primitive in their organisation
than the Mosses and appear to be more ancient, since their fossil remains are
occasionally met with back to the Carboniferous period, while the earliest known
Mosses are from the Upper Cretaceous. Most fossil Bryophytes are from the
Tertiary rocks and closely resemble existing forms,

DIV. i BRYOPHYTA 483

CLASS I
Hepaticae (Liverworts) (!> «• 93> "-104)

Most Liverworts inhabit moist situations and have a corresponding hygrophilous
structure. True aquatic forms are, however, only sparingly represented. Some
delicate Jungermanniaceae grow among Mosses. Other less numerous forms live
in extremely dry habitats on the bark of trees, on rocks or on the ground ; these
have xerophilous structure and arrangements for the storage of water. Among
the epiphytes those that grow on leaves in tropical forests (epiphyllous liverworts)
are noteworthy. As a rule the Liverworts play an inconsiderable part in the
composition of cryptogamic plant- formations.

The rhizoids of many Liverworts, especially of the Jungermanniaceae, and the
non-chlorophyllous tissue of the thallus of some Marchantiaceae are frequently
inhabited by endophytic fungi (e.g. by hyphae of Mucor rhizophilus) ; these do no
serious injury but appear to be of no special benefit (10°).

The Hepaticae are divided, according to the structure of the
sporogonium and the segmentation exhibited by the sexual plant, into
three orders, the Anthocerotales and Marchantiales being exclusively
thalloid, while the Jungermanniales include both thalloid and dorsi-
ventral foliose forms and, in the group of the Haplomitrieae, radially-
constructed foliose forms.

Order l. Anthocerotales (101)

This isolated group, including only a few forms, may be regarded as a primitive
order of Bryophyta. The sporogonium is characterised by a more complicated
internal construction than in the other Liverworts, in which it has undergone
progressive simplification.

The gametophyte has the form of an irregular, disc-shaped thallus, which is
firmly anchored to the soil by means of rhizoids. The cells of the thallus contain,
in contrast to those of other Bryophyta, a single large chloroplast with a pyrenoid.
On the lower surface, and less commonly on the upper, stomata occur. The
antheridia arise singly or in groups of two to four, by the division of a cell
lying below the epidermis (Fig. 443) ; they remain enclosed in cavities beneath
the upper surface of the thallus until maturity. The origin of the antheridia
thus differs from what is the case in all other Archegoniatae in being endogen-
ous ; a superficial cell divides into an outer segment, forming the roof of the
cavity, and an inner one, which becomes the mother-cell of the autheridia. The
cavity opens at maturity by mucilage formation in the cells of the outer wall.
The archegonia are sunk in the upper surface of the thallus ; after fertilisation they
become covered over by a many-layered wall (marsupium) formed by the growth
of the adjoining tissue. This enveloping wall is afterwards ruptured by the
elongating capsule, and forms a sheath at its base. ~The sporogonium consists
of a swollen foot and a long, pod-shaped capsule ; it has no stalk. The superficial
cells of the foot grow out into rhizoid-like papillae. The capsule splits longitudi-
nally into two valves, and has a central hair-like columella formed of a few
rows of sterile cells (Fig. 442). The columella does not extend to the apex of
the capsule, but is surmounted by a narrow layer of sporogenous cells. Elaters
also occur ; they are multicellular, variously shaped, and often forked.' The

484

BOTANY

PART II

sporogonia, unlike those of all other Hepaticae, do not ripen simultaneously
throughout their whole length, but from the tips downwards, and continue to
elongate by basal growth after emerging from the archegonia. The wall of the

FIG. 442. — Anthoceros laevis.
sp, Sporogonium ; c, colu-
mella. (Nat. size.)

FIG. 443.— Anthoceros Pearsoni. Development of the
endogenous antheridium. d, Covering cells ; st,
stalk-cells ; a, young antheridium. • (After D.
CAMPBELL.)

sporogonium possesses stomata, which do not occur in other Liverworts ; chlorophyll
is present in its cells.

On the under side of the thallus, slit-like openings, formed by the separation
of the cells, lead into cavities filled with mucilage. • Nostoc filaments penetrate
into these cavities, and develop into endophytic colonies (101°).

Order 2. Marchantiales ("l02)

The Liverworts included in this order in many genera have a decidedly com-
plicated structure. Marchantia polymorpha, found growing on damp soil, may
serve as an example. It forms a flat, deeply-lobed, dichotomously-branched
thallus, about two centimetres wide, and having an inconspicuous midrib
(Fig. 445 A, Fig. 446 A). ' From the under side of the thallus spring uni-
cellular rhizoids, some of which have smooth walls and serve mainly to attach
the thallus, while others have conical thickenings projecting into the cell-
cavity (Fig. 31) ; these peg-rhizoids are collected to form a wick-like strand below
the midrib. The thallus is provided also with ventral scales, consisting of a
single layer of cells. The dorsiventrality of the thallus is further shown by its
complicated anatomical structure. With the naked eye it may be seen that the
upper surface of the thallus is divided into small rhombic areas. Each area is
perforated by a central air-pore leading into a corresponding air-chamber immedi-
ately below (Fig. 95 A, £). The lateral walls of the air-chambers determine the
configuration of the rhombic areas. The air-pore in the roofing wall of each
chamber is in the form of a short canal, bounded by a wall formed of several tiers of
cells, each tier comprising four cells. Numerous short filaments, consisting of rows
of nearly spherical cells containing chlorophyll grains, project from the floor of the
air-chambers and perform the functions of assimilating tissue. Chlorophyll
grains are found also in the walls and roof of the chambers, but only in small
numbers. The intensity of the illumination exercises a great influence on the
formation of air-chambers ; when the illumination is very weak they may not

DIV. I

BRYOPHYTA

485

occur at all. The epidermis on the under side of the thallus is formed of one layer
of cells. The tissue below the air-chamber layer is devoid of chlorophyll, and
consists of large parenchymatous cells, which serve as storage cells.

Small cup-shaped outgrowths, with toothed margins, the gemmiferous receptacles
or gemma-cups, are generally found situated on the upper surface of the thallus over
the midribs (Fig. 445 &). These contain a number of stalked gemmae, flat, biscuit-
shaped bodies of a green colour. The gemmae arise by the protrusion and repeated
division of a single epidermal cell (Fig. 444) ; at maturity they become detached
from the stalk (at x, Fig. 444 D}. They are provided with two growing points,
one at each of the marginal constrictions, from which their further development
into new plants proceeds. On cross-section (E] they are seen to be composed of
several layers of cells ; some of the cells are filled with oil globules (D, o), while

from other colourless cells rhizoids develop.
Cells containing oil are also present in
the mature thallus, and are of frequent
occurrence in all the Hepaticae. By
means of the abundantly - developed

FIG. 444. — Marchantia polymorpha. A-C,
Successive stages in the formation of a
gemma ; st, stalk-cell ; D, surface view ;
E, transverse section of a gemma ; x,
point of attachment to stalk ; o, oil cells ;
r, colourless cells with granular contents,
from which the rhizoids will develop.
(4-Cx275; D-Ex65. After KNY.)

FIG. 445. — Marchantia polymorpha. A, A male
plant, with antheridiophores and gemma-cups b
(nat. size). B, Section of young antheridiophore ;
a, antheridia ; t, thallus ; s, ventral scales ; r,
rhizoids. (Somewhat magnified.)

gemmae Marchantia is enabled to multiply vegetatively to an enormous extent.
The dorsiventrality of the plants developed from the gemmae is determined by the
influence of light.

The sexual organs, antheridia and archegonia, are borne on special erect branches
of the thallus. The reproductive branches, which are contracted below into a
stalk, expand above into a profusely-branched upper portion. In this species,
which is dioecious, the antheridia and archegonia develop on different plants.
The branches producing the male organs terminate in lobed discs, which bear the
antheridia on their upper sides in flask-shaped depressions, each containing an
antheridium (Fig. 445 B}. The depressions, into each of which a narrow canal
leads, are separated from each other by tissue provided with air-chambers. (The
structure of the antheridia and spermatozoids is illustrated by Figs. 433, 434,
and the accompanying description.) The spermatozoids collect in a drop of water
on the disc, the margin of which serves to retain the water.

The female branches terminate each in a nine-rayed disc (Fig. 446 A). The upper
surface of the disc, between the rays, becomes displaced downwards in the process of

486

BOTANY

PART IL

growth, and, as the archegonia are borne on these portions, they seem to arise from
the under side of the disc. The archegonia are disposed in radial rows between the

FIG. 446.— Marchantiu polymorpha. A, A female plant, with four archegoniophores of different ages;
b, gemma-cups (nat. size). B, Under side of receptacle ; st, rays ; h, sheath ; sp, sporogonium
(x 3). C, Half of a receptacle, divided longitudinally ( x 5). D, Longitudinal section of a young
sporogonium ; spf, the foot ; sp, sporogenous tissue ; kw, wall of capsule ; aw, wall, and h,
neck, of archegonium ; p, pseudo-perianth (x70). E, Ruptured sporogonium; k, capsule; s,
spores and elaters ; p, pseudo-perianth; c, archegonial wall (xlO). F, An elater. G, Ripe
spores (x315). I/, Germinating spore (s) ; vk, germ tube; k, germ-disc, with the apical cell v
and rhizoid rh ( x 100). (C, E after BISCHOFF ; B, D, F-H after KNY.)

rays, each row being surrounded by a toothed lamella or sheath (perichaetium)
(B, 0, h). For structure of the archegonia see Fig. 436 and description.

Fertilisation takes place during rain, the raindrops splashing the liquid on
the male discs which contains the spermatozoids, on to the female receptacles.

DIV. i BRYOPHYTA 487

The epidermal cells of the latter project as papillae and constitute a superficial
capillary system in which the spermatozoids are conducted to the archegonia.

The fertilised egg-cell gives rise to a multicellular embryo (Fig. 436 (7), and
this, by further division and progressive differentiation, develops into a stalked
oval SPOROGONIUM. The capsule of the sporogonium is provided with a wall con-
sisting of one layer of cells except at the apex, where it is two-layered ; the cell- walls
have thickened bands. The capsule ruptures at the apex, the lid falling off and
the wall splitting into a number of recurved teeth. The ripe capsule, before the
elongation of the stalk, remains enclosed in the archegonium wall (Fig. 446 D,
aw}, which, for a time, keeps pace in its growth with that of the capsule. As
the stalk elongates, the archegonial wall or calyptra is broken through and
remains behind, as a sheath, at the base of the sporogonium (E, c). The capsule
is surrounded also by the pseudo-perianth, an open sac-like envelope which
grows, before fertilisation, out of the short stalk of the archegonium (Fig. 436

FK;. 447. — A, lli> •••in fl.u.i.1" n* ; submerged floating form. B, Riccia natans; land .form. C,
Fdccia natans ; floating form with long ventral scales. (Nat. size. B after GOBBEL. C after

BlSCHOFF.)

C, pr ; Fig. 446 D, E, p). The capsule contains spores and elaters (Fig. 446
F, G}.

Marchantia was formerly used in the treatment of diseases of the liver ; this
fact explains the origin of the name Liverwort.

The Ricciaceae (103) exhibit an extensive simplification of the sporogonium and
connect on as reduced forms to the more simply constructed Marchantiaceae. The
dichotomously-lobed or cleft thallu.s forms small rosettes, and grows on damp or
marshy soil. Riccia natans (Fig. 447 C) is found floating, like Duckweed, on the
surface of stagnant water. Riccia fluitans, on the other hand, lives wholly sub-
merged, and has narrow, more profusely-branching, thalloid segments (Fig. 447
A). These two aquatic species can, however, grow on marshy soil, and then form
flat rosettes (Fig. 447 B}. The Riccias are provided with fine rhizoids springing
from the under side of the thallus, and possess, in addition, a row of transversely
disposed ventral scales, consisting of a single layer of cells, which also assist in
the absorption of nourishment. Both organs are wanting in the submerged form
of Riccia fluitans.

The antheridia and archegonia are sunk in the surface of the upper side of
the thallus. From the fertilised egg-cell is developed a spherical sporogonium
which has no stalk. The wall of the sporogonium consists of a single layer
of cells ; it becomes disorganised during the ripening of the spores, which are
eventually set free by the rupture and disintegration of the venter and the
surrounding cells of the thallus. There are no elaters.

488

BOTANY

PART II

Order 3. Jungermanniales

These are usually small forms which grow on the ground or on tree-trunks,
and in the tropics on the surface of living leaves. In the simplest forms of
this order the thallus is broadly lobed, similar to that of Marchantia (e.g. Pellia
epiphylla, frequently found on damp ground) ; or, like that of Riccia fluitans,
it is narrow and ribbon-shaped, and at the same time profusely branched (e.g.
Metzgeria furcata, Fig. 94). In other forms, again, the broad, deeply-lobed thallus
has an evident midrib, and its margins, as in the case of Blasia pusilla (Fig.
448), exhibit an incipient segmentation into leaf-like members. The majority of
Jungermanniaceae, however, show a distinct segmentation into a prostrate or ascend-
ing, dorsiventral stem and leaves (Fig.
449). The latter consist of one layer of
cells without a midrib, and are inserted
with obliquely directed laminae in two
rows on the flanks of the stem. Many

FIG. 448. — Blasia pusilla. s, Sporogonium ;
r, rhizoids. (x 2.)

FIG. 449. — Plagiochila asplenioides.
s, Sporogonium. (Nat. size.)

genera (e.g. Frullania Tamarisci, a delicately-branched Liverwort of a brownish
colour occurring on rocks and tree-trunks) have also a ventral row of small scale-
like leaves or amphigastria (Fig. 450). The dorsal leaves are frequently divided
into an upper and lower lobe. In species growing in dry places, like Frullania
Tamarisci, the lower lobe may be modified into a sac, and serves as a capillary
water-reservoir. The leaves regularly overlap each other ; they are then said to
be overshot, when the posterior edges of the leaves are overlapped by the anterior
edges of those next below (Frullania, Fig. 450), or undershot, if the posterior
edges of the leaves overlap the anterior edges of the leaves next below (Piagio-
chila, Fig. 449).

The long-stalked Sporogonium is also characteristic of this order ; it is already
fully developed before it is pushed through the apex of the archegonial wall by
the elongating delicate stalk. It has a spherical capsule which on rupturing
splits into four valves (Figs. 448, 449). No columella is formed in the capsule ;
but in addition to spores it always produces elaters. In some genera (Pellia
Aneura) there are special elaterophores which consist of groups of sterile cells re-
sembling the elaters. The wall of the capsule (usually two or several cells thick)
consists of cells with annular or band-like thickenings, or the walls are uniformly

BRYOPHYTA

489

thickened with the exception of the outermost walls. Dehiscence is dependent
on the cohesive power of the water in these cells pulling the outer walls into the
cavity.

According to the position of the sexual organs and sporogonium the Junger-
manniales are divided into groups. 1. In the Anakrogynae the apex is not
used up in the formation of the
archegonia, and the sporogonia are
situated on the dorsal surface and
are surrounded by a sheath-like out-
growth of the thallus forming a
perichaetium. To this group belong
the thalloid forms (Pellia, Metzgeria) ^^7 _^ -^ \

rc*

FIG. 450.— Part of a shoot of FrullaHia
Tamarisci, seen from below, o, Dorsal
leaves with the lower lobes (w$) modi-
fied as water-sacs ; a, arnphigastrium.
(x 35.)

Fio. 451.— Haplomitrium Hoolceri. a, Origin of
a new shoot ; r, rhizome ; o, lower limit of
the aerial shoot. (After GOTTSCHE.)

and others showing a transition to the foliose forms (Blasia}. 2. In the
Akrogynae, on the other hand, the archegonia and the sporogonium stand at the
end of the main stem or of a branch and are surrounded by a perianth formed of
modified leaves. To this group belong the dorsiventral leafy forms, e.g. Plagiochila,
Frullania, and Jungermannia, a genus with numerous species. 3. The Haplo-
mitrieae hold an isolated position, but appear to exhibit the closest connection with
the Anakrogynae. This order contains only two genera, Calobryum, occurring
in the tropics, and Haplomitrium. The single species of the latter genus, H.
Hoolceri (Fig. 451), occurs in Europe, and possibly is a survival of pre-glacial
Liverworts. The Calobryaceae differ from all other Liverworts in the radial con-
struction of their shoot, which bears three rows of leaves. The sexual organs form
terminal groups in Calobryum, in Haplomitrium they occur between the upper
leaves.

CLASS II
Musei (Mosses) (l> 92> 93' 104-110)

The Mosses include a large number of forms distributed in all parts of the
world. They grow on dry soil, in swamps, on rocks, on tree-trunks and in
tropical forests, also as epiphytes on the branches, and less commonly in water ;

490

BOTANY

their structure is correspondingly various. Close tufts or masses are especially
characteristic of dry habitats, while the typical inhabitants of the soil of woods
have a looser mode of growth. In the moist mountain forests of the tropics and
sub-tropics Mosses often grow in considerable masses surrounding the branches or
hanging in long veil-like masses from them (105).

The Bog-Mosses form extensive growths on moors, as also do others (especially
Polytrichum] on the moist soil in the arctic moss-tundras.

The profusely-branched protonema of the Mosses appears to the
naked eye as a felted growth of fine, green filaments (Fig. 432).

FIG. 452. — Sphagnum fimbriatum : A, A shoot with four ripe sporogonia. Sphagnum squarrosum:
B, A lateral shoot with a terminal sporogonium ; ca, ruptured calyptra ; (/., operculum.
Sphagnum acutifoliurn : C, a young sporogonium in longitudinal section ; ps, pseudopodium ;
ca, archegonial wall or calyptra ; ah, neck of archegonimn ; spf, foot of sporogonium ; k,
capsule ; co, columella ; spo, spore-sac with spores. (/J and 0 after W. P. SCHIMPER ; A, nat.
size ; the other figures magnified.)

The oblique position of the cell walls in the filaments is characteristic.
The young moss plants are developed on the protonema as small
buds which arise as protrusions of cells of the filament, usually from
the basal cell of one of the branches. The protrusion is cut off by a
transverse septum, and after the separation of one or two stalk-cells
the three-sided pyramidal apical cell of the moss plant is delimited
in the enlarged terminal cell (106). The moss plants are always
differentiated into stem and leaf. The Mosses may be readily dis-
tinguished from the foliose Jurigermanniaceae by the spiral arrange-

DIV.

BRYOPHYTA

491

ment of their small leaves, which are rarely arranged in two rows.

In Mosses which have prostrate stems the leaves, although arranged

spirally, frequently assume a somewhat outspread position, and all

face one way, so that in such cases

a distinction between an upper and V* «« a

a lower side is manifested, but in a

manner different from that of the

Liverworts.

The STEM OF THE Moss PLANT is formed
of cells which become gradually smaller
and thicker- walled towards the periphery.
In the stems of many genera (e.g. Poly-
trichum, Mnium, £ig. 96 and p. 82) there
is found a central, axial strand consisting
of elongated, conducting cells with narrow
lumina. These strands are not as highly
differentiated as the vascular bundles of
Pteridophytes. They have neither vessels

FIG. 453. — Andreaea petrophila. ps, Pseudopodiura ;
Spf, foot ; k, capsule ; c, calyptra, ( x 12.)

FIG. 454. — Polytrichum commune, rh, Rhi-
zoids ; s, seta ; c, calyptra ; ap, apophysis ;
d, operculum. (Xat. size.)

nor sieve-tubes, but serve for the conduction of water and organic substances.
They are wanting in the Sphagnaceae or Bog Mosses which grow in swampy
places. The stems of the Sphagnaceae show a peculiar development of the outer
cortical layers. The cells in these layers are devoid of protoplasm, and are
in communication with each other and the atmosphere by means of large, open
pores ; to secure rigidity, they are also provided with spirally- thickened walls.

492 BOTANY PART n

They have a remarkable power of capillary absorption, and serve as reservoirs
for storing and conducting water.

The LEAVES of the true Mosses have, as a rule, a very simple structure. They
consist usually of a single layer of polygonal cells containing chloroplasts and are
generally provided with a median conducting bundle of elongated cells. The
leaves of the Bog Mosses (Sphagnaceae) have no bundles, and instead are supplied
with capillary cells for the absorption and storage of water. These cells are devoid
of protoplasm, and are similar to those in the periphery of the stem, but larger
and more elongated ; their walls, which are perforated, are strengthened by
transverse thickening bands. Between them are other elongated, reticulately
united cells containing cbloroplasts. A similar differentiation of the leaf -cells
occurs in a few other Mosses (e.g. Leucdbryum glaucum}.

A more complicated structure of the leaves resulting from their adaptation to
the absorption of water and protection against drying is exhibited by Polytrichum
commune. In this Moss the leaves develop on their upper surface numerous,
crowded, vertical lamellae, one cell thick ; these contain chlorophyll and serve
as an assimilatory tissue, while the spaces between the lamellae serve as reservoirs
for the storage of water. In a dry atmosphere the leaves fold together, and thus
protect the delicate lamellae from excessive transpiration (107). Many Mosses can
endure desiccation without injury.

The RHIZOIDS (Figs. 454, 456), each of which consists of a branched filament of
cells without chlorophyll, spring from the base of the stem. In structure they
resemble the protonema, into which they sometimes become converted, and then
can give rise to new moss plants.

The SEXUAL ORGANS are always borne in groups at the apices
either of the main axes or of small, lateral branches, surrounded by the
upper leaves of the latter which frequently have a distinctive structure,
and are known as the PERICHAETIUM (Fig. 456). Between the sexual
organs there are usually present a number of multicellular hairs or
paraphyses. The moss plants may be monoecious, in which case both
kinds of sexual organs are borne on the same plant either in the same
or different receptacles ; or dioecious, and then the antheridia and arche-
gonia arise on different plants. The archegonia and antheridia of
Mosses differ in their development from those of other Archegoniatae
by being formed by the segmentation of a two- or three-sided apical cell.

The SPOROGONIUM of the Mosses (108) develops a capsule with an
axial COLUMELLA consisting of sterile tissue (Fig. 458). The spore-sac
surrounds the columella, which conducts and accumulates food material
and water for the developing spores. Elaters are never formed. In the
young sporogonium outside the spore-sac a well-developed assimilating
tissue is present; this is bounded by water-storage tissue and an
epidermis. In most Mosses stomata are found on the lower part
of the capsule. The ripe capsule exhibits a variety of peculiar
structures to facilitate the opening and the distribution of the spores.
The stalk or seta raises the capsules so that the spores are readily
dispersed by wind. Distinctive variations in the mode of develop-
ment and structure of the capsules are exhibited by the three orders
of the Musci : Sphagnales, Andreaeales, and Bryales.

DIV I

BRYOPHYTA

493

Order l. Sphagnales (109)

The Sphagnaceae, or Bog Mosses, are the only family and include only a single
genus, Sphagnum, containing many species. The Bog Mosses grow in swampy places,
and form large tussocks
saturated with water.
The upper extremities of
the stems continue their
growth from year to year,
while the lower portions
die away and become
eventually converted into
peat. Of the numerous
lateral branches arising
from each of the shoots,
some grow upwards and
form the apical tufts or
heads at the summits of
the stems ; others, which
are more elongated and
flagelliform in shape, turn
downwards and envelop pIG> 4tt.—Schistostega osmundacea. A, Sterile ; B, fertile plant,
the lower portions of the (x 5.) C, Protonema. (x 90. After NOLL.)

stem (Fig. 452^4). Every
year one branch below the apex develops as strongly as the mother shoot, so

FIG. 456. — Mu iu HI iindulatum. Orthotropous
shoot terminating in a male receptacle sur-
rounded by involucral leaves. The lateral
shoots are plagiotropous. (After GOEBEL.)

FIG. 457. — Scleropodium purum. (Nat. size.)

that the stem becomes falsely bifurcated. By the gradual death of the stem
from below upwards the daughter shoots become separated from it, and form

494 BOTANY PART n

independent plants. Special branches of the tufted heads are distinguishable by
their different structure and colour ; on these the sexual organs are produced.
The male branches give rise, near the leaves, to spherical stalked antheridia.
The archegonia are borne at the tips of the female branches. The sporogonium
develops a short stalk with an expanded foot (B,C), but remains for a time enclosed
by the archegonial wall or calyptra. Upon the rupture of the archegonium, the
calyptra persists, as in the Hepaticae, at the base of the sporogonium. The
capsule is spherical and has a dome-shaped columella, which in turn is overarched
by a hemispherical spore-sac (spo) ; it opens by the removal of an operculum.
The ripe sporogonium is borne upon a prolongation of the stem axis, the pseudo-
podium, which is expanded at the top to receive the foot of the stalk. Of the
peculiar structure of the leaves and stem cortex a description has already been
given above. The protonema of the Sphagnaceae is in some respects peculiar.
Only a short filament is formed on the germination of the spore, the protonema
broadening out almost at once into a flat structure on which the young moss
plants arise.

Order 2. Andreaeales

The Andreaeales comprise only the one genus, Andreaea, small, brownish,
caespitose Mosses growing on rocks. The sporogonium is also terminal in this
order. The capsule, at first provided with a calyptra, splits into four longi-
tudinal valves (schizocarpous), which remain united at the base and apex
(Fig. 453). The "stalk is short, and is expanded at the base into a foot (Spf),
which in turn is borne, as in Sphagnum, on a pseudopodium (ps), a stalk-like
prolongation of the stem resulting from its elongation after the fertilisation
of the archegonium. The protonema is ribbon-shaped.

Order 3. Bryales (no)

In this order, which includes the great majority of all the true Mosses, the
moss fruit attains its most complicated structure. The ripe SPOROGONIUM,
developed from the fertilised egg, consists of a long stalk, the SETA (Fig. 454 s),
with a FOOT at its base, sunk in the tissue of the mother plant, and of a
CAPSULE, which in its young stages is surmounted by a hood or CALYPTIIA.
The calyptra is thrown off before the spores are ripe. It consists of one or two
layers of elongated cells, and originally formed part of the wall of the archegonium ;
this, at first, enclosed the embryo, growing in size as it grew, until, finally
ruptured by the elongation of the seta, it was carried up as a cap, covering the
capsule. It consists of several layers of cells and, especially in forms which occupy
dry habitats, bears hairs that correspond to protonemal threads of limited growth.
In some Mosses (e.g. Funaria) the young calyptra is distended and serves as a
reservoir of water for the young sporogonium (in). The upper part of the seta,
where it joins the capsule, is termed the APOPHYSIS. In Mnium (Fig. 460 A, ap)
it is scarcely distinguishable, but in Polytrichum commune it has the form of a
swollen ring-like protuberance (Fig. 454 ap\ while in species of Splachnum it dilates
into a large collar-like structure of a yellow or red colour. The upper part of the
capsule becomes converted into a lid or operculum which is sometimes drawn out
into a projecting tip. At the margin of the operculum a narrow zone of epidermal
cells termed the ring or ANNULUS becomes specially differentiated. The cells
of the annulus contain mucilage, and by their expansion at maturity assist in
throwing off the lid. In most Mosses the mouth of the dehisced capsule bears

DIV. I

BRYOPHYTA

495

a fringe, the PERISTOME, consisting usually of tooth-like appendages, but in others
this is wanting.

The peristome of Mnium hornum (Fig. 460), which will serve as an example,
is double ; the outer peristome is formed of 16 pointed, transversely striped teeth
inserted on the inuer margin of the wall of the capsule. The inner peristome lies
just within the outer, and consists of cilia-like appendages, which are ribbed on
the inner side and thus appear transversely striped ; they coalesce at their base into

FIG. 458. — Mnium hornum. Median longi-
tudinal section of a half-ripe sporogonium.
o, Operculum ; p, peristome ; c, columella ;
s, spore-sac containing the spores ; i, air-
space; «_/), apophysis ; st, stomata. (x 18.
After STRASBTRGER.)

FIG. 459. — Mnium hornum. Transverse section
through the wall of the capsule in the region
of the ring, a, Cells of the ring ; 1-4, succes-
sive cell layers with the thickened masses of
the peristome, d', d" ; d"', transverse pro-
jecting ribs ; c, the coalesced cilia. ( x 240.
After STRASBURGER.)

a continuous membrane. Two cilia of the inner peristome are always situated
between each two teeth of the outer row.

The teeth and cilia of the peristome are formed in this instance of thickened
portions of the opposite walls of a single layer of cells next to the operculum (Fig.
459), the teeth from portions of the external wall, and the cilia from portions of
the internal walls of the same layer. On the opening of the capsule the un-
thickeued portions of this layer break away and the teeth and cilia split apart.
The transversely -ribbed markings on their surface indicate the position of the
former transverse walls.

In the Polytrichaceae the origin of the peristome teeth follows a peculiar type ;
they are composed of a number of elongated entire cells.

The structure of the peristome varies greatly within the Bryales. By its

496

BOTANY

PART II

peculiar form and hygroscopic movements the peristome causes a. gradual dis-
semination of the spores from the capsule.

Variations in the form of the capsule, peristome, operculum, and calyptra afford
the most irr-portant means of distinguishing the different genera. The Bryales
are divided into two sub-orders, according to the position of the archegonia or of
the sporogonia developed from them.

(a) In the Acrocarpi the archegonia, and consequently the sporogonia, are
terminal on the main axis. Mnium undulatum (Fig. 456) and hornum, Poly-
trichum commune (Fig. 454), and Funaria hygrometrica are common examples.
Schistostega osmundacea, a moss living in caves, has fertile shoots, which have
spirally-arranged leaves and bear stalked capsules devoid of peristomes, and also
other shoots that are sterile, with two rows of leaves (Fig. 455). The protonema
of this species is peculiarly constructed and gives out an emerald phosphorescent

FIG. 460.— Mnium hornum. A, Capsule with upper portion of seta ; ap, apophysis ; p, peristome:
d, the separated operculum. B, Three teeth of the outer peristome seen from the outside ; an,
annulus. C, Inner peristome seen from the inside ; w, broader cilia ; h, narrower cilia.
(A x 4 ; B, C x 60.)

light. In some minute Mosses (Archidium, Phascum, Pleuridium] the sporo-
gonium is considerably simplified, the formation of operculum, annulus, and
peristome being suppressed and the spores set free by decay of the capsule.

(6) In the Pleurocarpi the growth of the main axis is unlimited, and the
archegonia with their sporogonia arise on short, lateral branches (Fig. 457). In
this group are included numerous, usually profusely-branched species of large
Mosses belonging to the families Neckeraceae and Hypnaceae, which are among
the most conspicuous mosses of our woods, and also the submerged Water Moss,
Fontinalis antipyretica.

III. PTERIDOPHYTA (VASCULAR CRYPTOGAMS) (

1, 92, 112-131

The Pteridophytes include the Ferns, Water-Ferns, Horse-tails,
and Club Mosses, and represent the most highly developed Crypto-
gams. In the development of the plants forming this group, as in the
Bryophyta, a distinct alternation of generations is exhibited. The

DIV. I

PTERIDOPHYTA

497

B, Prothallium with young fern attached to it by its foot ;
b, the first leaf; w, the primary root, (x circa 8.)

sexual generation bears the antheridia and archegonia ; the asexual

generation develops from the fertilised egg and produces asexual,

unicellular spores. On

germination the spores in

turn give rise to a sexual

generation. Since the

reduction division takes

place on the formation of

the spores, the sexual

generation is haploid and

the asexual generation

diploid.

The SEXUAL 'GENERA-
TION is termed the PRO-
THALLIUM or GAMETO-
PHYTE. It never reaches
any great size, being at
most a few centimetres in

diameter; in some forms FIG. 46l.~Dryopteris(Aspidium)JUix mas. ^1, Prothallium seen

it resembles in appearance from **low '' ar' arches°nia ; «», antheridia ; rh,
a simple, thalloid Liver-
wort ; it then consists of
a small green thallus, attached to the soil by rhizoids springing
from the under side (Fig. 461 A). In other cases the prothallium

is branched and fila-
mentous ; sometimes it
is a. tuberous, colour-
less mass of tissue,
partially or • wholly
buried in the ground,
and leading a sapro-
phytic existence, in
symbiosis with an endo-
phytic fungus forming
a mycorrhiza, while in
certain other divisions
of the Pteridophyta it

Fir,. 46-2.— A, Pteris serrulata, embryo freed from the archegonium, Undergoes reduction

in longitudinal section (after KIENITZ-GERLOFF): 7, basal wall; anr] rpmainq mnrp nr

II, transverse wall dividing the egg-cell into quadrants ; rudi- f

ment of the foot/, of the stem s, of the first leaf b, of the root w. l6SS compJetely enclosed

B, Section of a further-developed embryootPteridiumaquUinum within the Spore.

(after HOFMEISTER); /, foot still embedded in the enlarged Qn 4.1^ nrothallia ar^P

venter of the archegonium aw ; pr, prothallium. (Magnified.) ^

the sexual organs,

antheridia (Figs. 468, 475), producing numerous ciliate, usually spiral
spermatozoids, and archegonia (Figs. 469, 476), in each of which is
a single egg-cell. As in the Mosses the presence of water is necessary

498

BOTANY

PART II

for fertilisation. The spermatozoids are induced to direct their motion
toward the archegonia by the excretion from the latter of a substance
which diffuses into the surrounding water. In Ferns, Salvinia,
Equisetum, Selaginella, and Isoetes, this substance is malic acid or one
of its salts, while in Lycopodium it is citric acid.

Other organic acids, some salts of the metals, and even some alkaloids may
serve as attractive substances. Differences exist in the behaviour of different
genera in this respect. The chemotactic sensibility of the spermatozoids may
exist for a number of substances (n3).

After the fertilisation of the egg-cell by a spermatozoid there is
developed from it, as in the Bryophyta, the diploid asexual genera-
tion ; this is the cormophy tic
fern-plant.

The asexual generation
or sporophyte is represented
by a plant possessing a highly
differentiated internal struc-
ture, and externally seg-
mented into stem, leaves,
and roots. In the majority
of Pteridophytes (Ferns,
Equisetum), the fertilised
egg-cell, while still in the
archegonium, surrounds it-
self with a cell wall and

FIG. 463. — Transverse section of the rhizome of Pteri- , , . . . n , . ,

dium aquilinum. f, Concentric vascular bundles; undergoes dlVlSlOIl, fiPgt IDtO
«, sclerenchymatous plates; sp, peripheral zone of tWO Cells, by the formation

of a basal wall, and then
into octants by two walls
at right angles to each other and to the basal wall. By the
further division of these eight cells a small mass of tissue is formed,
and from this are developed the stem apex, the first leaf, the
primary root, and an organ peculiar to the Pteridophytes, the so-
called FOOT (Fig. 462/). The foot is a mass of tissue/- by means
of which the young embryo remains attached to the parent prothallium
and absorbs nourishment from it, until, by the development of its
own roots and leaves, it is able to nourish itself independently. In
some Lycopodineae (Lycopodium, Selaginella) a suspensor consisting
of one or a few cells is formed and serves as an absorbent organ.
The prothallium usually dies after the development of the young
plant. The stem developed from the embryonic rudiment may be
either simple or bifurcated, erect or prostrate ; it branches without
reference to the leaves, which are arranged spirally or in whorls,
or occupy a dorsiventral position. Instead of rhizoids, as in the
Bryophyta, true roots are produced, as in the Phanerogams. The

sclerenchymatous fibres ; r, cortex ; e, epidermis,
(x 7.)

DIV. i PTERIDOPHYTA 499

leaves also correspond in structure with those of the Phanerogams.
The three primary organs in most Pteridophyta grow by means of
apical cells (Figs. 100, 101, 156). Such apical cells are not to be
recognised in Lycopodium and Isoetes, while Selaginella shows both
growth by an apical cell and the transition to growth by a number
of initial cells. Stems, leaves, and roots are traversed by well-
differentiated vascular bundles, and the Pteridophytes are, in conse-
quence, designated Vascular Cryptogams. The bundles of the great
majority of Pteridophytes are as a rule constructed on the concentric
and radial types (cf. pp. 99 ff., Figs. 463, 464). Secondary growth in
thickness, resulting from the activity of a special cambium, occurs only

FIG. 464. — Transverse section of stem of Lycopodium complanatum. ep, Epidermis ; re, li, pp, outer,
inner, and innermost parts of the primary cortex, surrounding the central cylinder composed
of xvlem and phloem regions ; sc, scalariform tracheides ; sp, annular and spiral tracheides ;
v, phloem, (x 26. After STRASBURGER.)

occasionally in existing forms, but it was characteristic of the stems of
certain extinct groups of Pteridophytes.

The course of the vascular bundles in the leaves (venation) provides important
characters for classification, especially in the Ferns (Fig. 465). While only a single
median nerve is present in the simple leaves of the Horse-tails and Club-mosses
the nerves of the leaves of Ferns branch in the most various fashion ; they may
be dichotomous or pinnate and either end freely or anastomose to form a system
of meshes. In these polygonal meshes the ultimate branches may end blindly.

The SPORES are produced in special receptacles termed SPORANGIA
(Fig. 466), which occur on the asexual generation, either on the
leaves, or less frequently on the stems in the axils of the leaves.
The leaves which bear the sporangia are termed SPOROPHYLLS. The

500

BOTANY

PART II

sporangium consists of a wall enclosing the sporogenous tissue, the
cells of which, becoming rounded off' and separated from each other
as spore-mother-cells, give rise each by a reduction division to four
tetrahedral spores (spore-tetrads). The cells of the innermost layer of

the sporangial wall are rich in proto-
plasm, and constitute the TAPETUM.
This layer persists in the Lycopo-
dineae, but in the case of the Ferns
and Equisetineae the walls of the
tapetal layer become dissolved. In
the course of the development of
the sporangium the tapetal cells
then wander in between the spore-
mother-cells, their nuclei dividing
amitotically, so that the spores
eventually lie embedded in a muci-
laginous protoplasmic mass, the

FIG. 465. — Venation of Ferns. A, Adiantum
capillus veneris (venatio cyclopteridis). B,
Asplenium adiantum nigrum (v. spheno-
pteridis). C, Asplenium esculentum (v.
goniopteridis). D, Polypodium serpens (v.
marginariae). E, Polypodium nereifolium
(v. goniophlebii). F, Onoclea sensibilis (v.
sageniae).

Fio. 466. — Development of the spor-
angium of Asplenium. A, First divi-
sions of the young sporangium which
has originated from a single superficial
cell. B, Division into the wall (w),
and the central archesporial cell (ar)
which has cut off one of the tapetal
cells (0- C, Older stage in which the
archesporial cell has given rise to the
tapetal cells and the sporogenous
tissue (sp). (x300. After SAD EBECK.)

PERIPLASM, from which they derive nourishment (114). The wall of
the mature sporangium is formed of one or a number of layers of
cells. The unicellular spores have cell walls composed of several
layers. The young spore on becoming isolated in the tetrad surrounds
itself with a cutinised membrane (exospore) within which a cellulose
layer (endospore) is deposited. In many cases a perispore is deposited

DIV. i PTERIDOPHYTA 501

by the periplasm upon the exospore (in Horse-tails, Hydropterideae,
and some Ferns).

The spores of the majority of the Pteridophytes are of one
kind, and give rise on germination to a prothallium, which produces
both antheridia and archegonia. In certain cases, however, the
prothallia are dioecious. This separation of the sexes extends in
some groups even to the spores, which, as MACROSPORES (megaspores),
developed in MACROSPORANGIA (megasporangia), give rise only to
female prothallia ; or as MICROSPORES, which are produced in
MICROSPORANGIA, develop similarly only male prothallia. In accord-
ance with this difference in the spores, a distinction may be made
between the HOMOSPOROUS and HETEROSPOROUS forms of the same
group ; but thte distinction has no systematic value in defining the
different groups themselves, as it has arisen independently in several
of them.

The correspondence in the structure of their antheridia, archegonia, and
spore-mother-cells is in favour of a relationship between the Bryophyta and the
Pteridophyta. Though both groups may have had their origin from a common
group of Algae (p. 482), an independence in the further course of development
must be assumed in the two cases. In particular, it is impossible to derive the
sporophyte of the Pteridophyta from the sporophyte or sporogonium of the Moss.
While the latter without attaining any vegetative complexity comes to an end early
with spore- formation, the Fern sporophyte becomes differentiated into stem, leaf,
and root. The vascular bundles appear as quite new structures, the possession of
which enables the sporophyte to proceed to the development of a large complicated
and sometimes tree-like terrestrial plant ; this contrasts with the Bryophyta, where,
owing to the simple cellular structure and the absence of special water-conducting
channels, no great size can be reached. The plant only proceeds at a late stage to
the production of spores. The spore-mother-cells are formed endogeuously in special
parts of the leaf; these are indeed called "sporangia," but are not homologous
with the sporangia of Thallophyta. On this account it would seem advisable to
use a new term (sporothecae) for the so-called sporangia of Pteridophyta. The
spore-mother-cells, which may be most closely compared with the tetrasporangia
of Brown and Red Algae, correspond, rather than the sporothecae, to the sporangia of
Thallophyta.

The gametophyte of the Vascular Cryptogams closes its development early by
the formation of sexual organs. The typical fern-prothallus hardly surpasses the
juvenile form of a thallus, while in the Bryophyta, on the other hand, the sexual
generation exhibits a progressive development (98).

The Pteridophyta are divided into the following Classes.*
1. Filicinae. — Ferns. Stem simple or branched, with well-
developed, alternate, often deeply-divided or compound leaves called

[* To these must be added the recently established Class of the Psilophytales. This
includes the most simply organised Vascular Cryptogams. In some (Rhynia, Hornea)
the plant is rootless and leafless, consisting of a rhizome, branched cylindrical aerial
stems, and large terminal sporangia. In Asteroxylon and Psilophyton the stems bear
small simple leaves. A full account of these simple Vascular Cryptogams of Early
Devonian age will be found in Scott's Studies in Fossil Botany, 3rd ed., vol. i.]

502 BOTANY TART n

fronds. Sporangia either on the under side of the sporophylls,
united in sori or free, or enclosed in special segments of the leaves.
Spermatozoids multiciliate.

Sub-Class ]. Filicinae eusporangiatae. — Kipe sporangia with firm
wall composed of several layers of cells. Homosporous.

Sub -Class 2. Filicinae leptosporangiatae. — Ripe sporangia with
walls one layer thick.

Order 1. Filices. — Ferns, in the narrower sense. Homosporous.
Order 2. Hydropterideae. — Water-Ferns. Heterosporous.

2. Equisetinae. — Horse-tails. Stem simple or verticillately branched,
with whorled, scale-like leaves forming a united sheath at each node.
Sporophylls peltate, bearing a number of sporangia on the under side,
and aggregated into a cone at the apex of each fertile shoot.
Spermatozoids multiciliate.

Order 1. Equisetaceae. — Horse-tails. Homosporous, herbaceous
plants.

Order 2. Calamariaceae. — Calamites. Homosporous or hetero-
sporous. Extinct arborescent plants.

3. Sphenopliyllinae

Order 1. Sphenophyllaceae. — Stem slender; leaves in whorls.
Sporophylls with 1-4 sporangia, borne in cones. Homo-
sporous. Extinct plants.

4. Lycopodinae. — Stem simple or dichotomously branched. Roots
dichotomous. Leaves alternate, simple. Sporangia with firm walls,
always borne singly in the axils of the sporophylls.

Order 1. Lycopodiaceae. — Club -mosses. Homosporous ; sper-
matozoids biciliate ; herbs with dichotomously branched
shoots.

Order 2. Psilotaceae. — Homosporous ; stem herbaceous, dichoto-
mously branched, with alternate, simple, or scale-like leaves ;
rhizomes in place of roots ; sporophylls forked, each bearing on
the adaxial face close to its base a 2- or 3-locular sporangium.

Order 3. Selaginellaceae. — Heterosporous ; Spermatozoids bicili-
ate ; herbs with dichotomous stems and small leaves.

Order 4. Isoetaceae. — Quill-worts. Heterosporous ; spermato-
zoids multiciliate ; stem tuberous, simple, with secondary
thickening ; leaves awl-shaped.

Order 5. Sigillariaceae. — Extinct. Heterosporous ; arborescent ;
stem simple or sparingly branched dichotomously.

DIV. I PTERIDOPHYTA 503

Order 6. Lepidodendraceae. — Extinct. Heterosporous ; re-
peatedly dichotomously branched trees.

5. Pteridospermeae. — Extinct plants with the habit of large ferns.
Heterosporous with microsporangia and seed-like macrosporangia.
Derived from Eusporangiate Ferns.

CLASS I
Filieinae (Ferns) (l> 92' 112> 115)

The great ^majority of existing Pteridophytes belong to the
Ferns, taking the group in a wide sense. Two sub-classes are
distinguished according to the structure of the sporangia. The
Eusporangiate Ferns are characterised by sporangia, the thick wall
of which consists of a number of layers of cells. They open by a
longitudinal split. The Leptosporangiate Ferns, on the other hand,
have sporangia which, when mature, have their wall formed of one
layer of cells, and dehisce transversely or longitudinally. Stipules,
which are found at the base of the frond in the former group, are
wanting in the Leptosporangiatae. Differences also, exist in the
prothallus and in the structure of the sexual organs. Only in some
groups of Leptosporangiatae is there a perispore deposited on the
outside of the exospore.

While in earlier geological periods the Eusporangiatae were abundantly
represented, they now include only two families, each with a few genera. They
appear to represent the more ancient type of Ferns and to stand nearest to the
forms from which the Filieinae have been derived. Along with them, even in
palaeozoic times we have the Leptosporangiatae, from which in later cretaceous
and tertiary times the Hydropterideae have branched off as a small group of
aquatic or marsh-growing Ferns. In the Hydropterideae only among Ferns the
spores are differentiated into microspores and macrospores.

Sub-Class I. Eusporangiatae
Order l. Marattiaceae (116)

This order, perhaps the most primitive of existing Ferns, includes about 20
stately tropical ferns with thickened tuberous stems and usually very large leaves
provided with two stipules at the base. The sporangia are situated in groups
(sori) on the under surface of the leaves, and are either free (Angiopteris) or united
to form an oval capsule-like body, the chambers of which are the sporangia. The
prothallium in contrast to that of the Ophioglossaceae is a green, heart-shaped
thallus, resembling that of a Liverwort and growing on the surface of the soil.
It is sometimes dichotomously branched. The sexual organs resemble those of
the following order but are developed on the lower surface of the prothallus. An
endophytic fungus occurs in the cells of the prothallus.

504

BOTANY

PART II

Order 2. Ophioglossaceae (m)

European examples of this order, which contains only a few species, are afforded
by Ophioglossum vulgatum, Adder's Tongue (Fig. 467 E), and Botrychium, Moon-
wort (Fig. 467 A], Both have a short stem, from which only a single leaf unfolds

FIG. 467.— A, Botrychium lunaria. Sporophyte. (£ nat. size.) B, Transverse section of the pro-
thallus ; an, antheridium ; ar, archegonium ; em, embryo; en, fungal hyphae (x 45). C,
Prothallus bearing two embryos, the roots of which have emerged (x 16). D, Embryo with
the first and second roots (wlt ic2) and foot (/) (x 16). E, Ophioglossum vulgatum. Sporophyte
showing the bud for the succeeding year. (£ nat. size.) F, Ophioglossum vulgatum.
Prothallus. an, antheridia ; ar, archegonia ; fc, young plant with the first root; ad,
adventitious branch; h, fungal hyphae. (x 15. B-D, F after BRUCHMANN.)

each year. The leaves in both cases are provided with leaf-sheaths. In Ophioglossum
the leaf is tongue-shaped, in Botrychium it is pinnate. These leaves bear on their
upper side a fertile segment arising near the upper end of the leaf-stalk. This
fertile segment in Ophioglossum is simple and cylindrical, with the sporangia sunk
in two rows ; in Botrychium, it is pinnately branched in the upper part, and

DIV. I

PTERIDOPHYTA

505

thickly beset on the inner side with large, nearly spherical sporangia. The course
of the vascular bundles and occasional reversions indicate that the fertile segment
is derived from the union of two basal pinnae.

Our knowledge of the peculiar monoecious prothalli of the Ophioglossaceae is
largely due to BRUCHMANN ; they are long-lived, subterranean, saprophytic,
tuberous bodies without chlorophyll but inhabited by a mycorrhizal fungus. In
Ophioglossum (Fig. 467 F) they are cylindrical and radially symmetrical, simple
or branched ; in Botrychium (Fig. 467 B, C] they are oval or heart-shaped and
dorsi ventral. The antheridia (Fig. 468) and archegonia (Fig. 469) are sunk in
the tissue of the prothallus. The antheridium encloses a large spherical mass of
spermatozoid mother-cells which are set free when mature by the swelling of the

FIG. 468.— Ophioglossum i-ulgatum. A-C, Stages
in the development of the antheridium from
a superficial cell ; the upper cell in C gives
rise to the cover-cells, the lower to the
mother cells of the spermatozoids. D,
Antheridium not yet opened ; d, cover-cells.
E, Spermatozoid. (After BRUCHMANN.)

Fie. 469. — Ophioglossum vulgatum. A • C, De-
velopment of archegonium. D, Mature opened
archegonium with two spermatozoids ($) in
front of the opening ; h, neck-cells ; hk, neck-
canal-cells ; o, egg-cell ; b, basal cell. (After
BRUCHMANN.)

contents and the breaking down of one of the central cells of the outer wall. The
spermatozoids have a spirally wound body and numerous cilia ; a small vesicle is
adherent to the spermatozoid (Fig. 468 E}. The antheridia originate from single
superficial cells (Fig. 468 A-C), as do also the archegonia (Fig. 469 A-C). The
slightly projecting neck of the latter opens after the neck canal-cell has swollen
and disintegrated ; the oosphere (o) remains in the sunken venter. In many species
the embryo leads a subterranean existence for several years. The primary root is
first formed and soon projects from the archegonium (Fig. 467 C, F, k) ; later
the first leaf and the apical cell of the stem are differentiated. In some species of
Botrychium the embryo forms an elongated multicellular suspensor at the end of
which the proper embryonic mass is formed. In this an agreement with the
Lycopodinae is evident (cf. Fig. 493 and Fig. 498), which do not in other respects
show any close relationship to the Eusporangiatae.

Sub-Class II. Leptosporangiatae
Order 1. Filiees

The Filiees, or Ferns, in the narrower sense of the word, comprise
a large number of genera with numerous species, being widely distri-

506

BOTANY

PART II

buted in all parts of the world. They attain their highest develop-
ment in the tropics. The Tree-Ferns (Cyathea, Alsophila, Dicksonia),
which include the largest representatives of the order, occur in
tropical countries, and characterise the special family of the Cyatheaceae.
The stem of a Tree-Fern (Fig. 470) is woody and unbranched : it bears
at the apex a rosette of pinnately-compound leaves or fronds, which are

FIG. 470. — Alsophila crinita. A Tree-Fern growing in Ceylon. (Reduced.)

produced in succession from the terminal bud, and leave, when dead,
a large leaf scar on the trunk. The stem is attached to the soil by
means of numerous adventitious roots. The majority of ferns, how-
ever, are herbaceous, and possess a creeping rhizome, terminating
usually in a rosette of pinnate or deeply-divided leaves. Such a
habit and growth are illustrated by the common Male Fern Dryopt&ris
(Aspidium) filix mas, the rhizome of which is official (Fig. 471). The

DIV. I

PTERIDOPHYTA

507

leaves of Polypodium vulgare are pinnate, and spring singly from

FIG. 471.— Dryopteris (Aspidium) filix mas (f nat. size). A, Sorus in vertical section, (x 20.
After KNY.) B, Pinna with young sori still covered by the indusia. C, Somewhat older sori
with withered indusia. (Slightly magnified.) OFFICIAL.

508

BOTANY

PART II

the upper side of the creeping branched rhizome. In other cases
the leaves may be simple and undivided, as in the Hart's-Tongue
Fern, Scolopendrium vulgare (Fig. 472). In the tropics many herbaceous
Ferns grow as epiphytes on forest trees (cf. p. 183). When young,
the leaves are coiled at the tips (Fig. 470), a peculiarity common to
the Ferns as a whole, and to the Water-Ferns. Unlike the leaves of
most Phanerogams, those of the Ferns continue to grow at the apex
until their full size is attained. Peculiar brownish scales (paleae,
ramenta), often fringed and consisting of a single layer of cells, invest
the stems, petioles, and sometimes also the
leaves of most Ferns.

The sporangia are generally produced in
large numbers, on the under side of the
leaves. The sporophylls, as a rule, resemble
the sterile, foliage leaves. In a few genera
a pronounced heterophylly is exhibited : thus
in the Ostrich Fern, Struthiopteris germanica,
the dark brown sporophylls are smaller and
less profusely branched, standing in groups
in the centre of a rosette of large foliage
leaves. Blechnum spicant is another example.
In the different families, differences in
the mode of development as well as in the
form, position, and structure of the SPORANGIA
are manifested.

The sporangia of the Polypodiaceae, in
which family the most familiar and largest
number of species are comprised, are united
in groups or SORT on the under side of the
leaves. They are borne on a cushion -like
projection of tissue termed the RECEPTACLE
(Fig. 471 A), and in many species are covered
by a protective membrane, the INDUSIUM,
which is an outgrowth of the tissue of the

FIG. 472. — Scolopendrium milgare.

(inat. size.) leaf (Fig. 471 B, C). Each sporangium

arises by the division of a single epidermal

cell (Fig. 466), and consists, when ripe (Fig. 473), of a capsule at-
tached to the receptacle by a slender multicellular stalk, containing a
large number of spores, which only in a few genera (Asplenium, Aspidium,
Acrostichum, etc.) are surrounded by a perispore. The wall of the
capsule is formed of a single layer of cells. A row of cells with strongly
thickened radial and inner walls, extending from the stalk over the
dorsal side and top to the middle of the ventral side of the capsule,
are specially developed as a ring or ANNULUS, by means of which the
dehiscence of the sporangium is effected. This type of annulus is
characteristic of the Polypodiaceae.

DIV. I

PTERIDOPHYTA

509

On drying of the wall of the sporangium the cohesion of the remaining
water in the cells of the anuulus draws in the thin outer walls of these cells ; this
causes the annulus to shorten and determines the dehiscence of the sporangium by
a tranverse slit between the broad terminal cells of the annulus. When the pull
exerted by the cohesive power of the water suddenly gives way, the annulus returns
by its own elasticity to its original position, thus effecting the dispersal of the
spores. The sporangium remains open owing to the drying and contraction of
the thin cell walls (1I8).

The form and insertion of the sori, the shape of the indusium when present,
or its absence, all constitute important criteria for distinguishing the different
genera. The sori of Scolopendrium (Fig. 472) are linear, and covered with a
lip- shaped indusium consisting of one cell- layer. They are so disposed in pairs
on different sides of every two successive nerves, that they appear to have a
double indusium opening in the middle. In the genus Dryopteris (Aspidium), on
the other hand, each sorus is orbicular in form and covered by a peltate or

FIG. 473. — Sporangia. A, Dryopteris (Aspidium) filij; mas; there is a glandular hair at the base.
B and C, Alsophila armata, seen from the two sides. D, Aneimia caudata. E, Osmunda
mjalis. (A-D x 70 orig. ; E x 40. After LURSSEN.)

reniforrn indusium attached to the apex of the placenta ; a glandular hair is
frequently present on the stalk of the sporangium (Fig. 471). The sori of Poly-
podium vulgare are also orbicular, but they have no indusia. In the common
Bracken, Pteridium aquilinum, the sporangia form a continuous line along the
entire margin of the leaf, which folds over and covers them.

Besides the Polypodiaceae the Ferns include other families, mainly represented
in the tropics, the sporangia of which differ in the construction of the annulus
and in the mechanism of their dehiscence. The sporangia of the Cyatheaceae, to
which family belong principally the Tree-Ferns, are characterised by a complete
annulus extending obliquely over the apex of the capsule (Fig. 473 By C).
The Hymenophyllaceae, often growing as epiphytes on Tree-Ferns, have also
sporangia, with a complete, oblique annulus. The sporangia of the Schizaeaceae
and Gleicheniaceae, on the other hand, have a transversely-placed annulus which,
in the former (Fig. 473 D), is close to the tip and in the latter above the middle
of the sporangium, while in the Osmundaceae, of which the Royal Fern, Osmunda
regalis, is a familiar example, the annulus is represented merely by a group of
thick-walled cells just below the apex of the sporangium (Fig. 473 E). In the
three last-named families the sporangia open by a median split ; in the three
preceding families the dehiscence is transverse or oblique. There are thus two

510

BOTANY

PART II

main groups of longicidal and brevicidal Leptosporangiatae, the Eusporangiatae
coming closer to the former (119).

All the members of the Filices are homosporous. The PRO-
THALLIUM has usually the form of a small, flat, heart-shaped thallus

FIG. 474. — Trlchomanes rigidum. Portion
of a prothallus with an archegoniophore
(A) to which a young plant is attached.
(After GOEBEL.)

FIG. 475. — Ay Mature antheridium of Woodsia
ilvensis ; the cuticle (c) is ruptured. B,
Open antheridium; d, cap-cell ; r, swollen
annular cells. (After SCHLUMBERGER.) C,
Spermatozoid of Struthiopteris germanica ;
k, nucleus ; d, cilia ; 6, vesicle derived from
the vacuole ; c, cytoplasm. ( x 850. After
SHAW.)

(Fig. -461), bearing the antheridia and archegonia on the under side
which is turned from the light.

In certain Hymenophyllaceae ( Trichomanes) the prothallium is filiform and
branched, resembling in structure the protonema of the Mosses, and producing
the antheridia and archegonia on special multicellular lateral branches (Fig. 474).

The ANTHERIDIA and ARCHEGONIA (12°) are similarly constructed in
nearly all Leptosporangiatae, and present differences from those of the
Eusporangiate Ferns. The antheridia are spherical projecting bodies
(Fig. 475), arising on young prothallia by the septation and further
division of papilla-like protrusions from single superficial cells. When
mature, each antheridium consists of a central cellular cavity, filled

DIV. 1

PTERIDOPHYTA

511

with spermatozoid mother cells, and enclosed by a wall formed of
two ring-shaped cells and a lid-cell. The spermatozoid mother cells
are produced by the division of the central cell. They are discharged
from the antheridium by the pressure exerted by the swollen ring
cells, and the consequent rupturing of the lid-cell. Each mother cell
thus ejected liberates a spirally coiled spermatozoid. The anterior
extremity of the spermatozoid is beset with numerous cilia, while
attached to its posterior end is a small vesicle which contains a
number of granules, and represents the unused remnant of the
contents of the mother cell.

The archegonia arise from the many-layered median portion of
older prothallia. They are developed from a single superficial cell,
and consist of a* ventral portion, embedded in the prothallium, and a
neck portion. The neck, which projects above the surface of the

FIG. 476. — Poly podium vuJgare. A, Young archegonium not yet open ; K', neck-canal-cell ;
K", ventral-canal-cell ; o, egg-cell ; B, mature archegonium, open. ( x 240. After STKASBURGER.

prothallium, consists of a wall composed of a single layer of cells
made up of four cell rows (Fig. 476); it encloses the elongated neck-
canal-cell. The ventral portion contains the large egg-cell and the
ventral-canal-cell immediately above it. As the archegonium matures,
the canal-cells become disorganised, and fill the canal with a strongly
refractive mucilaginous substance. This swells on the admission of
water, and, rupturing the neck at the apex, is discharged from the
archegonium, which is now ready for fertilisation. The development
of the embryo is represented in Fig. 462.

In certain ferns the sporopliyte may originate on the prothallus by a process of
budding or direct vegetative growth ; the sexual organs are not formed or they take
no part in the production of the plant (apogamy). Conversely the prothallus may
arise directly, without the intervention of spores, from the tissues of the leaf
(apospory).

OFFICIAL. — Dryopteris (Aspidiuni) filix mas, provides FILIX MAS.

The long silky brown hairs from the base of the leaf-stalks of various Tree-Ferns,
especially Cibotium Barometz, and other species of this genus, in the East Indies
and the Pacific Islands, are used as a styptic, and also for stuffing cushions, etc.

512

BOTANY

PART II

Order 2. Hydropterideae (Water-Ferns)

The Water-Ferns include only a few genera, which are more or less aquatic in
habit, growing either in water or marshy places. They are all heterosporous. The
macro- and micro-sporangia do not develop, like those of the Filices, on the under
side of the leaves, but are enclosed in special receptacles at their base, constituting
sporangial fructifications or sporocarps. The wall of the sporangium, which consists
of a single layer of cells, has no annulus. The spores are surrounded by a
specially developed perisporium.

FIG. 477. — A, Marsilia quailrifolia ; a, young leaf; s, sporocarps. B, Pilularia globulifera ;
s, sporocarp. (After BISCHOFF, reduced.)

The "Water-Ferns are divided into two families : Marsittaceae, including three
genera, and Salviniaceae, with two genera.

To the Marsiliaceae belongs the genus Marsilia, of which the European M.
quadrifolia (Fig. 477-4) may be taken as an example. This species has a slender,
creeping, branched axis, bearing at intervals single leaves. Each leaf has a long
erect petiole, surmounted by a compound lamina composed of two pairs of leaflets
inserted in close proximity. The stalked oval sporocarps (s) are formed in pairs
above the base of the leaf-stalk, or in other species they are more numerous. Each
of them corresponds in development to the quadripinnate sterile lamina, but is not
divided into pinnae. The young leaves, as in the Filices, are circinate.

Pilularia also grows in bogs and marshes. P. globulifera is found in
Britain. It differs from Marsilia in its simple linear leaves, at the base of which
occur the spherical sporocarps, which arise singly from the base of each sterile
leaf-segment ; the sporocarp corresponds to a segment of the leaf (Fig. 477 B}.

DIV. I

PTERIDOPHYTA

513

The Salviniaceae contains only free-floating aquatic plants belonging to the two
genera Salvinia and Azolla. In Salvinia natans, as representative of the first genus,
the sparingly-branched stem gives rise to three leaves at each node. The two
upper leaves of each whorl are oval in shape, and developed as floating foliage
leaves ; the third, on the other hand, is submerged, and consists of a number of
pendant, filamentous segments which are densely covered with hairs, and assume
the functions of the missing roots. The sporocarps have an entirely different mode
of development from those of the Marsiliaceae ; they are spherical, and are borne
in small groups on the submerged leaves at the base of the filamentous segments
(Fig. 478 A). The sporangia are produced within the sporocarp from a column-like
receptacle, which corresponds in origin to a modified leaf-segment. The envelope
of the sporocarp is equivalent to an indusium ; it arises as a new growth in the
form of an annular wall, which is at first cup-shaped, but ultimately closes over
the receptacle and its sorus of sporangia.

FIG. 478.— Salvinia natans. A, Seen from the side ; B, from above (after BISCHOFF, reduced). C,
An embryonic plant ; msp, macrospore ; p, prothallium ; a, stem ; 6j, 62, 63, the first three
leaves ; &1} the so-called scutiform leaf, (x 15. After PRINGSHEIM.)

The second genus, Azolla, is chiefly tropical, represented by small floating
plants, profusely branched, and beset with two-ranked closely crowded leaves.
Each leaf consists of two lobes, of which the upper floats on the surface of the
water, while the lower is submerged, and assists in the absorption of water. A
small cavity enclosed within the upper lobe, with a narrow orifice opening outwards,
is always inhabited by filaments of the Blue Green Alga, Anabaena azollae. From
the fact that hairs grow out of the walls of the cavity between the algal filaments,
the existence of a symbiotic relation between the two plants would seem to be
indicated. Azolla, unlike Salvinia, possesses long slender roots developed from
the under side of the stem. The sporocarps are nearly spherical, and produced
usually in pairs on the under side of the leaves of some of the lateral branches.

In the structure of the sporangia and spores, and in the development of the pro-
thallia, the Hydropterideae differ in some respects from the Filices. These differ-
ences may be best understood on reference to Salvinia natans (121) as an example.
The sporocarps contain either numerous microsporangia or a smaller number of
macros porangia (Fig. 479 A, ma, mi}. In structure both forms of sporangia
resemble the sporangia of the Leptosporangiate Ferns ; they are stalked, and have,

514

BOTANY

PART II

when mature, a thin wall of one cell-layer, but no annulus (B, D). The MICRO-
SPORANGIA enclose a large number of microspores, which, as a result of their
development in tetrads from the mother-cells, are disposed in groups of four (C),
and embedded in a hardened frothy mass filling the cavity of the sporangium.
This frothy interstitial substance is derived from the tapetal cells, which gradually
lose their individuality and wander in between the spore-mother-cells.

The microspores germinate within the microsporangium, which does not open ;
each germinating microspore puts out a short tubular male prothallium, which
pierces the sporangial wall. Two antheridia are developed in this by successive
divisions (Fig. 480). Each antheridium produces four spermatozoids, which are
set free by the rupture of the cell walls. Although the whole male prothallium is
thus greatly reduced, it nevertheless exhibits in its structure a resemblance
to the prothallia of the Filices.

The MACROSPORANGIA are larger than the microsporangia, but their walls

FIG. 479. — Salvinia natans. A, Three sporocarps in median longitudinal section ; ma, macro-
sporocarp ; mi, microsporocarp ( x 8) ; B, a microsporangium ( x 55) ; C, portion of the contents
of a microsporangium, showing four microspores embedded in the frothy interstitial substance
( x 250) ; D, a macrosporangium and macrospore in median longitudinal section ( x 55).
(After STBASBURGEK.)

consist similarly of one cell-layer (Fig. 479 D). Each macrosporangium produces
only a single large macrospore, which develops at the expense of the 32
spores originally formed. The macrospore is densely filled with large angular
proteid grains, oil globules, and starch grains ; at its apex the protoplasm is
denser and contains the nucleus ; the membrane of the spore is covered by a dense
brown exospore, which in turn is enclosed in a thick frothy envelope, the perispore,
investing the whole spore and corresponding to the interstitial substance of the
microspores, and like this formed from the dissolution of the tapetal cells. The
macrospore remains within the sporangium, which is eventually set free from the
mother plant and floats on the surface of the water. On the germination of the
macrospore, a small-celled female prothallium is formed by the division of the
denser protoplasm at the apex, while the large underlying cell does not take part
in the division, but from its reserve material provides the developing prothallium
with nourishment. The spore wall splits into three valves, the sporangial wall is
ruptured, and the green prothallium protrudes as a small saddle - shaped body.
On it three to five archegonia are produced, but only the fertilised egg-cell of one
of them develops into an embryo, the foot of which remains for a time sunk in

DIV. I

PTERIDOPHYTA

515

the venter of the archegonium (Fig. 481). The first leaf of the germ plant is
shield-shaped (Fig. 478 C] and floats on the surface of the water.

The development of Azolla (121a) proceeds in a similar manner, but the sporangia
and spores exhibit a number of distinctive peculiarities. The micro- and macro-
sporocarps at first develop alike ; in each a single macrosporangium is laid down
surrounded by the tubular indusium, and from the stalk of the macrosporangium the
microsporangia grow out. In the microsporocarp only the microsporangia develop ;
in the macrosporocarp, on the other hand, only the m Jtcrosporangium becomes mature.

p J*

FIG. 480. — Sodrinianatans. Development
of the male prothallium. A, Division
of the microspore into three cells
7-777 ( x 860) ; B, lateral view ; C, ven-
tral view of mature prothallium (x
640). Cell 7 has divided into the pro-
thallium cells a and p ; the latter is
the rhizoid cell; cell 77 into the
sterile cells ft, c, and the two cells s1?
each of which has formed two spenna-
tozoid mother-cells ; cell 777 into the
sterile cells d, e, and the two cells so.
The cells s^ and s.x<2 represent two
antheridia ; the cells b, c, d, e, their
wall cells. (After BELA.JEFF.)

FIG. 481. — Salnnia natans. Embryo in longitudinal sec-
tion ; pr, prothallium ; S, spore-cell ; e, exinium ; p,
perispore ; spw, sporangial wall ; ar, archegonium ;
embr, embryo ; /, foot ; W], Wo., ^s> the first three
leaves ; st, apex of stem, (x 100. After PRIXGSHEIM.)

The 64 spores of the microsporangia are aggregated into several nearly spheri-
cal balls or massulae, formed from the interstitial substance derived from the
protoplasm of the tapetal cells. Each massula, enclosing a number of spores, is
beset externally with barbed, hook-like outgrowths of the interstitial substance
(glochidia). On the rupture of the sporangia the massulae are set free in the
water, and are carried to the macrospores, to which they become attached. In
the macrosporangium 32 macrospores are laid down, but only one comes to maturity ;
in the course of its development it supplants all the other sporogenous cells, and
finally the sporangial wall itself becomes flattened against the inner wall of the
sporocarp, frequently undergoing at the same time partial dissolution. The
macrospore is enveloped by a spongy perispore, whose outer surface exhibits

516

BOTANY

PART II

numerous depressions and protuberances prolonged into filaments. At the apex of
the spore the perispore expands into three pear-shaped appendages. The massulae
become attached to the perispore. The wall of the sporocarp is ruptured at its
lower portion, the apical portion
remaining attached to the spore in
the form of an ampulla-like covering.
The formation of the prothallia is
effected in essentially the same way
as in Salvinia, except that only one

FIG. 482. — Marsilia salvatrix. A, Sporo-
carp ( nat. size) ; st, stalk. JJ, Sporo-
carp opening in water, showing the
emerging mucilaginous cord. C, The
mucilaginous cord (</) ruptured and fully
extended ; sr, soral chambers ; sch, hard
shell of the sporocarp. D, An immature
sorus ; 'ma, macrosporangia ; mi, micro-
sporangia. (After J. SACHS and J. HAN-
STEIN.)

FIG. 483.— Marsilia quadrifolia. Development of
the male prothallus from the spore. A, The
spore ; B, a small prothallial cell (p) is cut off
by the wall (1) ; C and D, further divisions, sj, §2,
the mother-cells of the spermatogenous tissue
in the two antheridia; E, mature condition, two
groups of 16 spermatozoids having developed from
sj and s2> ne *n the substance derived from the
breaking down of the peripheral sterile cells; Ft
a spermatozoid, highly magnified, showing the
cilia arising from the elongated blepharoplast
lying beside the spirally-wound nucleus. (After
LESTEK W. SHARP.)

antheridium with eight spermatozoids arises on each of the small male prothallia
protruding from a massula.

The sporocarps of the Marsiliaceae (122) have a more complicated structure : those
of Pilularia globulifera are divided into four chambers, each with a single sorus ; in
Marsilia they enclose numerous sori (14-18) disposed in two rows. The sori in both
genera contain both micro- and macro-sporangia. These arise as in many ferns from
superficial marginal cells and come to lie in cavities by the upgrowth of the sur-
rounding tissue. The outer layers of this become differentiated to form a hard coat.

DIV. I

PTERIDOPHYTA

517

After a period of rest the sporocarps germinate in water. In Pilularia the
tissue surrounding the sori swells, bursts the hard coat, and emerges as a
mucilaginous mass ; this contains the sporangia from which, by further swelling
of the walls, the spores become free. The development of the prothalli and
fertilisation take place in the mucilaginous mass that persists for some days. The
sporocarp of Marsilia, on the other
hand, opens as two valves. A car-
tilaginous cord of tissue lying
within the ventral suture of the
sporocarp swells greatly, and split-
ting the ventral suture emerges
bearing with it the sori, enclosed
by membranous investments (Fig.
482).

From the microspore a reduced
male prothallus is developed within
the spore -membrane. This when
mature contains two antheridia,
each with 16 spermatozoids, and
liberates these as cork-screw-like,
spirally-wound, motile spermato-
zoids bearing numerous cilia (Fig.
483).

The thick -walled macrospore
has, as in the case of Salvinia,
denser protoplasm at the summit.
This is cut' off from the large cell
enclosed in the spore-coat by a wall,
and develops into a small green
saddle-shaped prothallus composed
of a few cells. This only forms a
thus

FIG. 484. — Marsilia vestita. A, Macrospore with the
nucleus at the summit in the protoplasm from
which the female prothallus shown in B is derived ;
o, egg -cell of the archegonium, with the ventral-
canal-cell and neck-canal-cell above it; k, nucleus
of the large cell enclosed in the spore-membrane.

C, Young embryo in the archegonium showing the
first divisions ; 1, basal wall ; 2, quadrant walls.

D, Later stage ; to, young root ; b, first leaf ; st, stem ;
/, foot. (A x (60 ;' B x 360; C x 525; D x 260-
After D. CAMPBELL.)

single archegonium and is
greatly reduced (Fig. 484).

The embryogeny follows the

type of the Leptosporangiate Ferns, the egg-cell dividing first by a longitudinally -
placed basal wall and then by transverse walls into quadrants ; these then divide
to give the octants. The first leaf and the root arise from the two upper pairs of
octants ; the lower pairs give rise to the foot and the stem-apex (Fig. 484 C, D).

The prothallus grows for a time enclosing the embryo, and forms a few rhizoids
from its lower cells. If fertilisation does not take place, a somewhat longer-lived
prothallus results, which does not, however, form further archegonia.

An apogamous formation of the embryo has been shown to exist in certain
Australian species of Marsilia belonging to the group of M. Drummondii (123).

CLASS II
Equisetinae (Horse-tails)

Order 1. Equisetaceae

92- 112- 115- l24

The Equisetaceae include only the one genus Equisetum, comprising 20
species, found widely distributed over the whole world. The genus can be

518

BOTANY

PART II

traced back to the Triassic period. Developed partly as land, partly as swamp
plants, they may always be distinguished by the characteristic structure and
habit of the asexual generation. They have a branching, underground rhizome
on which arise erect, aerial haulms, usually of annual growth. The rhizome of
the common Horse-tail, Equisetum arvcnse, develops also short tuber -like
branches which serve as reservoirs of reserve material and hibernating organs
(Fig. 486). The aerial haulms remain either simple, or they give rise to branch
whorls, and these in turn to whorls of a higher order. All the axes are
formed of elongated internodes ; they have a central pith-cavity and a peripheral

series of smaller air channels. The col-
lateral vascular bundles form a single
circle, as seen in transverse section (Fig.
485).

At each node is borne a whorl of scale-
leaves pointed at the tips, and united
below into a sheath closely enveloping
the base of the internode. The lateral
branches are developed in the axils of the
scale-leaves, but not having space to
grow upwards they pierce the narrow
sheath. As a result of the reduction of
the leaf laminae, the haulms themselves
assume the function of assimilation, and
for that purpose their cortical tissue under
the epidermis is provided with chlorophyll.
The SPOKANGIA are borne on specially -
Fio. 4S5.-Equisctum arvense. Transverse sec- shaped leaves or sporophylls. The sporo-
tion through the stem, m, Lysigenic medul- phylls are developed in whorls, but are
lary cavity ; c, endodermis ; d, carinal canals closely aggregated at the tips of the erect
in the collateral bundles; vl, vallecular fertile shoots into a cone (Fig. 486), which
cavities ; hp, sclerenchymatous strands m .

the furrows and ridges ; ch, tissue of the ls sometimes spoken of as a flower, from
primary cortex containing chlorophyll ; st, the correspondence in its structure to
rows of stomata. (x 11. After STRAS- the male flower of the Conifers. The
BURGER.) lowest whorl is sterile, and forms a collar-

like protuberance. The sporophylls (Fig.

486 E, C) are stalked and have a peltate expansion, on the under side of which are
borne the (5-10) sac-like sporangia. In the young sporangium the sporogenous
tissue is surrounded by a wall consisting of several cell layers, but eventually the
tapetal cells of the inner layer become disorganised, and their protoplasm penetrates
between the developing spores, forming the periplasmcdium. At maturity the
wall of the sporangium consists only of the outermost of the original layers ; the
cells of this are provided with annular and spiral thickenings. The sporangia thus
resemble the homologous pollen-sacs of Phanerogams. The dehiscence is determined
by the cohesive force of the diminishing amount of water in the cells of the outer
layer and' the contraction of the thin parts of the cell walls on drying. The
sporangia split longitudinally, and set free a large number of green spores, which
are nearly spherical in shape, and have peculiarly constructed walls. In addition
to the endospore and exospore, the spores are overlaid with a perispore deposited
by the periplasmodium, and consisting of two spiral bands (elaters) which are
attached to the spores only at their point of intersection (Fig. 486 D). On drying,
the spiral bands loosen and become uncoiled ; when moistened they close again

PTERIDOPHYTA

519

around the spore. By means of their hygroscopic movements they serve to hook

FIG. 486.— Equisetum arvense. A, Fertile shoots, springing from the rhizome, which also bears tubers ;
the vegetative shoots have not yet unfolded. F, Sterile vegetative shoot. B, C, Sporophylls
bearing sporangia, which in C have opened. D, Spore showing the two spiral bands (elaters)
of the perispore. E, Dry spores showing the expanded spiral bands. (A, F, J nat. size.
B, C, D, E, enlarged.)

together the spores, and in this way assure the close proximity of the unisexual
prothallia which the latter produce (Fig. 486 E).

520

BOTANY

PART II

In certain species some of the aerial haulms always remain sterile, branching
profusely, while others which produce the terminal «ones either do not branch at
all, or only at a later stage, and then sparingly. This distinction between the
sterile and fertile haulms is most marked in Equisetum arvense and Equisetum
Telmateja, in both of which the fertile shoots are entirely unbranched and
terminate in a single cone (Fig. 486). ' Resembling in their mode of life a parasite
upon the rhizome, they are otherwise distinguished from the vegetative haulms by
their lack of chlorophyll and their light yellow colour.

Equisetum giganteum, growing in South America, is the tallest species of the

FIG. 487. — Equisetum pratense. I, Female prothallium from the under surface, showing the arche-
gonia (A). II, Male prothallium with antheridia (A) ; d, cover cells of antheridia. (/ x 17,
J/X12. After GOEBEL.) Ill, Equisetum arvense. Spermatozoid : fc, nucleus ; bl, cilia-forming
blepharoplast with cilia ; zyt, cytoplasm, (x circa 1250. After SHARP.) IV, Equisetum arvense.
Embryo : 1, 2, octant walls. The stem (si) and first leaf- whorl (b) arise from the upper half, and
the root (w) and foot from the lower half, (x 165. After SADEBECK.)

genus ; its branched haulms, supported by neighbouring plants, attain a height of
over twelve metres, and are about two cm. in diameter.

The spores are all of one kind, and on germination give rise to thalloid
PROTHALLIA which are generally dioecious (Fig. 487). The female prothallia are
larger than the male, and, branching profusely, are prolonged into erect ruffled
lobes at whose base the archegonia are produced. In structure the archegonia
resemble those of the Ferns, but the upper cells of the four longitudinal rows of
cells constituting the neck are more elongated and, on opening, curve strongly
outwards. The spermatozoids, like those of ferns, bear numerous cilia. The first
leaves of the embryo are arranged in a whorl and encircle the apex of the stem.
The growth of the embryo is effected by the division of a three-sided apical cell
(Figs. 487 IV, 100, 101).

DIV. I

PTERIDOPHYTA

521

FIG. 488.— 1, Archaeocalamites radiatus. (After STCB.) 2, Annularia stdlata. (After SEWARD.)
From LOTSY, Botan. Stammesgesvhichte.

FtQ. 489. — lt Calamostachys Binneyana, Cone in longitudinal section. 2, The same in transverse
section. 3, Calamostachys Casheana, Transverse section of a sporangiophore, showing the stalk
and three macrosporangia and one microsporangium. kt Palaeostachya, Longitudinal section
of cone with axillary sporangiophores. (After SCOTT and HICKLING. From LOTSY.)

522

BOTANY

PART II

The outer epidermal walls of the stem are more or less strongly impregnated
with silica. In Equisetum hiemale, and to a less degree in Equisetum arvense, the
silicification of the external walls is carried to such an extent that they are used
for scouring metal utensils and for polishing wood.

Poisonous substances are formed in some species of Equisetum, and hay with
which the shoots are mixed is injurious to cattle.

Order 2. Calamariaceae (132)

This extinct order was highly developed in the palaeozoic period, especially
in the Carboniferous, when it was represented by numerous species. The plants
resembled the Horse-tails in general habit, but in some cases attained the size of
trees 30 metres high ; the hollow stem, which bore whorls of branches at the
nodes, was covered with a periderm, and underwent secondary thickening.
The leaves (Annularia, Fig. 488) stood in alternating whorls ; their form
was narrowly lanceolate and at their bases they united into a sheath. In the
most ancient type, Archaeocalamites (Fig. 488), they were dichotomously divided,
and thus more fern-like. The cones or flowers had in this genus the same structure
as those of Equisetum ; in most cases they were more complicated, whorls of
superposed scale-leaves separating the whorls of specialised sporangiophores. Each
of the latter was a stalked peltate disc bearing, on its under side, four sporangia

(Fig. 489). In Calamostachys the
sporangiophores are placed some
distance above the corresponding
sporophylls, while in Palaeo-
stachya they stand in the axils of
the latter. They may be regarded
morphologically as special out-
growths of the scale-like sporo-
phylls. It is an interesting fact
that heterosporous as well as
homosporous forms occur among
the Calamarieae.

CLASS III
Sphenophyllinae (132)

This small class occupies an
intermediate position between the
Equisetineaeandthe Lycopodinae.

The Sphenophyllinae were
represented by two genera in
palaeozoic times. Cheirostrobus

from the Lower Carboniferous had
FIG. 490. — 1, Sphcnophyttum, showing the branched stein i ,. . .,

- with both Lear and wedge-shaped leaves and, on the COmf leX COlieS ofsimilar structure
right, an elongated cone. (After SCOTT.) 2, S. to those of the Galamarieae, but
emarginatum. (After SEWARD.) From LOTSY. approached Lepidodendron in

anatomical structure. The species

of Sphenophyllum which lived from the Devonian to the Permian periods were
herbaceous land-plants with elongated internodes. The stems, which underwent

DIV. i PTERIDOPHYTA 523

secondary growth in thickness, bore superposed whorls of, usually six, wedge-shaped
or dichotomously-divided leaves. The spike-like cones resembled somewhat those
of Equisetum ; each sporophyll bore one to four homosporous sporangia (Fig. 490).

CLASS IV
Lyeopodinae (Club Mosses) (l> 92» 112> 115)

The Lyeopodinae are sharply distinguished from the other Pteri-
dophyta, by their general habit and the mode of their sporangial
development.

They were abundantly represented in the palaeozoic period and
included arborescent forms belonging mainly to the extinct orders of
Sigillariaceae and Lepidodendraceae.

The numerous existing species are all herbaceous plants. The
most important genera, representing as many orders, are Lycopodium,
Selaginella, and Isoetes.

The dichotomous branching of the stem (Figs. 139, 141) and root and
the simple form of the leaves are characteristic of the sporophyte.
The two first-named genera have elongated stems and small leaves ;
Isoetes, on the other hand, has a tuberous stem and long awl-shaped
leaves. Unlike the fertile leaves of the Filicinae and Equisetinae,
which always bear numerous sporangia, the sporophylls of the
Lyeopodinae produce the sporangia singly, at the base of the leaves
or in their axils. Although in many cases scarcely distinguishable
from the sterile leaves, the sporophylls are frequently distinctively
shaped, and, like those of Equisetum, aggregated at the ends of the
fertile shoots into terminal spike -like cones or flowers. Compared
with the leaves, the sporangia are relatively large and have a firm
wall of a number of layers of cells. The innermost layer of the
sporangial wall, the tapetal layer, is not absorbed. On this account no
perispore is deposited on the spore-wall. The developing spores are
surrounded with a mucilaginous nutritive fluid. The sporangia have
no annulus. Except in the case of Isoetes, the spores of which become
free by the decay of the sporangial wall, the sporangia dehisce by longi-
tudinal slits, which divide the wall into two valves ; the slits occur
where rows of cells of the wall have remained thin. Lycopodium is
homosporous, while Selaginella and Isoetes are heterosporous. The hetero-
sporous forms produce only greatly modified and reduced prothallia ; in
the genus Lycopodium, on the other hand, the prothallia are well de-
veloped, and show certain resemblances to those of the Ophioglossaceae.
The simplified prothalli of Selaginella and Isoetes may be compared to
early stages of the prothalli of Lycopodium which have proceeded to
form gametes early without undergoing vegetative development.

The Lycopodiaceae and the Selaginellaceae agree in the segmentation of the
embryo, which in both is characterised by possessing a suspensor, and in the

524

BOTANY

PAET II

structure of the spermatozoids, which are biciliate. The Isoetaceae, on the other
hand, have multiciliate spermatozoids and the emhryo has no suspensor. On these
grounds the two sub-classes of Lycopodinae biciliatae and Lycopodinae pluri-
ciliatae may be distinguished. Herbaceous Lycopods which are the forerunners
of Lycopodium and Selaginella are known in the Carboniferous, while Isoetes is
only known with certainty from the Lower Cretaceous.

Order 1. Lycopodiaceae (125)

The numerous widely-distributed species of the genus Lycopodium (Club
Moss) are for the most part terrestrial plants ; in the tropics many pendulous

FIG. 491.— Lycopodium davatum. A, Old prothallus. B, Prothallus with young plant attached.
C, Antheridium in vertical section. D, Spermatozoids. E, Young archegonium, the neck
still closed. F, Open archegonium ready for fertilisation. G, Plant bearing cones (£ nat. size).
H, Sporophyll with an opened sporangium. J, K, Spores from two points of view. L, A young
subterranean sporeling still without chlorophyll ( x 10) ; /, foot ; w, root ; 6, scale-leaves.
(A-F and. L after BRUCHMANN.)

epiphytic forms also occur. In Lycopodium clavatum, one of the commonest
species, the stem, which is thickly covered with small, awl-shaped leaves,
creeps along the ground ; it branches dichotomously," and gives rise to ascending

DIV. I

PTERIDOPHYTA

525

lateral branches, while from the under side spring the dichotomously-branched
roots (Fig. 491). The cone -like flowers, consisting of the closely-aggregated
sporophylls, are situated in groups of two or more at the ends of the forked
erect shoots. The sporophylls are not like the- sterile leaves in shape ;
they are broader and more prolonged at the tip ; each bears a large reniform
sporangium on the upper side at the base. The sporangium opens into two

FIG. 492.— ,4, Germinating spore of Lycopodium annotinum; r, rhizoid cell; &, basal cell; s,
apical cell ; sp, spore-membrane (x 580). B, Older stage of the prothallus of the same species,
showing the endophytic fungus (p) in the lower cells, and the apical cell divided into three
meristematic cells (x 470). C, Lycopodium. complanatum. Prothallus with antheridia (an),
archegonia (ar), and a young embryo (fc) ( x 26). (After BRUCHMANN.)

valves and sets free numerous minute spores (Fig. 491 H). Lycopodium
Selago differs in habit from the other species ; its bifurcately-branched stems
are all erect, and the fertile are not distinct from the vegetative regions of the
shoots.

The spores of the Lycopodiums are all of one kind, and in consequence of their
formation in tetrads are of a tetrahedral though somewhat rounded shape. The
exospore is covered with a reticulate thickening (Fig. 491 J, K).

The prothallia developed from the spores show a remarkable variety in the

526

BOTANY

PART II

group. The prothallia of Lycopodium clavatum (Fig. 491 A, B) and the closely
related L. annotinum are small, white, tuberous structures, which live as sub-
terranean saprophytes. At first top- shaped, they become converted by the
continued marginal growth into cup-shaped lobed bodies, which may attain a size
of two centimetres. Long rhizoids spring from the lower surface, while the upper

surface bears numerous antheridia and
archegonia. The spores only germinate after
six to seven years, forming at the expense
of their reserve materials a prothallus of five
cells. Further development only takes place
when fungal hyphae enter the lowest cells
(Fig. 492 A, S). The endophytic fungus
is confined to the peripheral tissues of older
prothalli ; it may emerge through the special-
ised basal cells of the rhizoids and invest
the latter (125°). Only after twelve to fifteen
years is the prothallus sexually mature, so
that its life may last some twenty years. In
L. complanatum (Fig. 492 (7) the subterra-
nean prothalli are turnip-shaped, in L. Selago
rounded or elongated cylindrical and dorsi-
ventral. The prothalli of the latter may be
developed on the surface of the soil, in which
case they are green. In the case of L. inun-
datum, the prothalli of which are found on
damp peaty soil, and in the tropical L. cer-
nuum, with erect profusely-branched shoots,

the prothalli are poor in chlorophyll and are
FIG. 493.— Development of the embryo in

Lycopodium conplanatum. A, Embryo attached to the soil by rhizoids ; they have
showing the first divisions ; the basal the form of small, half-buried, cushion-like
wall / separates the suspensor (et) from masses of tissue, which give rise to green,
the body of the embryo; the transversal aedal thanoid lobes. The archegonia occur
walls II and /// (the latter being in the , ,-, •> c j-u i -U ii j-v • j • ^

plane of the section) together with the at the base of these lobes> the ^theridia also
transverse wall IV give rise to two tiers on their surface. All Lycopod prothalli have
of four cells ; the tier next the sus- fungal filaments forming a mycorrhiza in their
pensor gives rise to the foot, the ter- peripheral tissue.

minal tier forms the shoot, (x 112). E ^ prothallia are all monoecious. The
Embryo of medium age ; s, apex of

stem; b, rudiment of leaf ; /, foot (x antheridia are somewhat sunk in the tissue
112). C, Embryo shortly before break- (Fig. 491 C) and enclose numerous spermato-
ing out of the prothallus ; bb, the two zo[^ mother-cells, in which small oval spenna-
first leaves covering the apex of the tozoid with two cilia attached below the
stem; w, the first root (x 40). (After .

BRUCHMANN.) apex, are formed. The archegonia (Fig. 491

E, F) are constructed like those of the Ferns,

but the upper cells of the neck become disorganised on opening. The number
of neck-canal-cells differs in the various species (1, 3-5, or 6-10).

The embryo (Fig. 493) remains during its development enclosed in the
prothallus. It has a spherical, in L. complanatum club-shaped and irregular,
foot which serves as an absorbent organ for the sporeling. Beneath the foot the
young shoot forms ; the first leaves are scale-like, and from the basal portion of
the shoot the first root develops. The suspensor is situated between the shoot
and the foot ; it serves as the first absorbent and nourishing organ of the embryo.

DIV. i PTEEIDOPHYTA 527

The spores of Lycopodium davatum and other species are sometimes
used in pharmacy.

Order 2. Psilotaceae

The only representatives of this order are Psilotum (two tropical species) and
Tmesipteris (one Australian species). They show in some features relationship
with the Sphenophyllinae, but are most naturally placed with the Lycopodinae.
The complete absence of roots is noteworthy. The simple leaves are alternately
arranged on the dichotomous stems ; the fertile leaves near the tips of the branches
are always deeply divided and resemble a pair of leaves.

Order 3. Selaginellaceae (128)

To this order belongs the genus Selaginella, represented by numerous and
for the most part^ tropical species. They have, as a rule, profusely-forked,
creeping, and sympodially- branched stems, but occasionally erect branched
stems ; some form moss-like beds of vegetation ; others, climbing on adjacent
plants, possess stems several metres long. Certain xerophilous species (S.
lepidophylla in tropical America, etc.) can endure drying up for months or
even years, closing together their rosette - shaped shoots by a cohesion-
mechanism, expand again on the arrival of rain (127). In general the
Selaginellas are similar in habit to the Lycopodiums. They have small
scale-like leaves which usually exhibit a dorsiventral arrangement, such as is
shown, for example, in the alpine Selaginella helvetica (Fig. 494),. the stem of
which bears two rows of small dorsal or upper leaves, and opposite to them
two rows of larger, ventral, or under leaves. (Cf. also Fig. 134.) The
rhizophores (128) are organs that are peculiar to the plants of this order ; they
are cylindrical, leafless, shoot-like structures, which arise exogenously, usually
in pairs, from the stem at a bifurcation. At their ends a number of endogenous
roots are produced, but the rhizophores are able, when the normal shoots are
cut back, to continue their growth as shoots of ordinary construction. Even
below the first leaves of the seedling plant short rhizophores are formed,
from which the first roots arise endogenously. The leaves of Selaginella are
characterised by the presence at their base on the upper side of a small
membranous ligule. This serves as an organ for the rapid absorption of
water (rain-drops) by the leafy shoot (129). In many species of Selaginella the
epidermal assimilatory cells of the leaves possess, as in Anthoceros, only one large
chloroplast (13°).

The cones or flowers are terminal, simple or branched, radially symmetrical,
or less commonly dorsiventral. Each sporophyll subtends only one sporangium,
which springs from the stem above the leaf-axil. The same spike bears both
macrosporangia and microsporaugia. Each macrosporangium (Fig. 495 A -C)
contains only four macrospores, which are produced by the growth and division
of a single spore -mother-cell ; all the other mother-cells originally developed
ultimately disappear. On account of the increasing size of the spores the
spherical macrosporangia become nodular. Opening, which is due to a cohesion-
mechanism, occurs along definite lines of dehiscence, the wall splitting into two
valves, which curve back from a boat-shaped basal portion. The spores are
ejected by the pressure of the contracting boat-shaped part and the valves.
Numerous spores are formed in the flattened microsporangia. The mode of
dehiscence is similar in these also, but the boat-shaped portion of the wall is
smaller, the valves extending to the base.

528

BOTANY

PAET II

The microspores begin their development while still enclosed within the

FIG. 494.—^!, Selaginella helvetica (from
nature, nat. size). B, Selaginella Kraus-
siana, embryonic plant with macro-
spore still attached. (After BISCHOFF,
magnified.)

FIG. 495. — Selaginella helvetica. A, Macrospor-
angium from above showing the line of dehis-
cence (cl). B, Opened, seen from the side ; the
four macrospores, C, have been ejected. D,
Microsporangium in the axil of its sporophyll.
E, The same, opened. F, Microspores. (x
about 15.)

FIG. 496.— A -E, Selaginella stolonifera, successive stages in the germination of a microspore ;
p, prothallial cell; w, wall-cells of antheridium ; s, spermatogenous cells; A, B, D, lateral,
C, dorsal view. In E the prothallial cell is not visible, the disorganised wall-cells enclose
the spermatozoid mother cells ; F, sperm atozoids of Selaginella cuspidata. (A-E x 640,
F x 780. , After BELAJEFF.)

sporangium. The spore first divides into a small lenticular vegetative cell, which

DIV. I

PTERIDOPHYTA

529

corresponds to the rhizoid cell of Salvinia, and into a large cell, which divides
successively into eight sterile prothallial or wall cells and two or four central
spermatogenous cells (Fig. 496 A). By the further division of the central
cells, which represent a single antheridium, numerous spermatozoid mother cells
are formed (B-D}. The peripheral cells then break down and give rise to a
mucilaginous substance, in which is embedded the central mass of spermatozoid
mother cells (E}. The small prothallial cell (p), however, persists. The whole
male prothallium is up to this stage still enclosed by the wall of the microspore.
This ultimately ruptures, and the mother cells are set free and liberate the club-
shaped spermatozoids. Each of these has two long cilia at its pointed end.

The macrospores in some species similarly begin their development within
the sporangia. After the division of the nucleus into daughter-nuclei and their
distribution in the apical cytoplasm, the formation of cell walls begins. In this

FIG. 497,—SelagineUa Martensii. A, Ruptured macrospore seen from above showing the prothallus
with three groups of rhizoids and several archegonia (x 112). B, Longitudinal section of
the prothallus showing two archegonia in which embryos are developing (x 112). (After
BRTCHMAXN.)

way, progressing from apex to base, the spore becomes filled by a process of
multicellular formation, with large prothallial cells. At the same time, and
proceeding in the same direction, there begins a further division of these cells
into smaller cells. In some species the apical disc of tissue is formed first, and is
separated by a thickened wall or diaphragm from the rest of the cavity of the
spore ; cell- formation occurs in this later. In the tissue at the apex, consisting of
small cells, the rudiments of a few archegonia appear, often even before the
formation of the prothallium has been completed. The archegonia are usually
not formed until the spores have been discharged from the sporangium, but in
some cases even fertilisation takes place on the parent plant.

The wall of the spore eventually bursts at the apex, and the prothallium
becomes partially protruded ; it forms a number of rhizoids on three projections
of its tissue. The fertilisation of one or two archegonia, which then takes place,
is followed directly by the segmentation of the fertilised egg-cells and the forma-
tion of the embryos (Fig. 497).

530

BOTANY

PAKT II

The development of the embryo, in which a suspensor consisting of one or
several cells, the apex of the stem with the first leaves, the first rhizophore and
the foot are distinguishable, proceeds in a great variety of ways in the genus.

The first division in the fertil-
ised egg-cell is transverse. In
S. Martensii, spinulosa, hel-
vetica, etc. , the upper hypobasal
cell gives rise to the suspensor
only, the main portion of the
embryo being derived from the
lower cells (Fig. 498) ; in S.
denticulata the upper cell forms
the foot and rhizophore as well
as the suspensor. The apex
of the shoot with the first pair
of leaves grows upwards and
the root downwards ; the young
plant remains attached to the
prothallus in the megaspore by
the foot (Fig. 494 £). In

FIG. 498.— Selaginella Martensii. Embryo before becoming S0me species (S. rubricaulis,
free from the prothallus in longitudinal section ; /, foot; spinulosa) the archegonia re-
main closed and the egg de-
velops apogamously into the
embryo. In S. Kraussiana and related forms the suspensor, according to Bruch-
mann, is reduced, but replaced functionally by a special embryonic tube proceeding
from the wall of the mother cell of the ovum ; the embryo is delimited in this
and comes into relation with the nutritive tissue.

wt, rhizophore; et, suspensor; fc, cotyledons with their
ligules. (x 150. After BRUCHM ANN.)

Order 4. Isoetaceae (1S1)

The isolated genus Isoetes must be regarded as a persistent branch of an
ancient group of plants, which in earlier geological periods was more richly
represented. The species of Isoetes are perennial plants, growing either on
damp soil or submerged in water. The stem is short and tuberous, rarely
dichotomously branched, terminating below in a tuft of dichotomously-branch-
ing roots, and above in a thick rosette of long, stiff, awl-shaped leaves
(Fig. 499). The stem is characterised by a secondary growth in thickness by
means of a cambium ; this produces to the outer side cortex (without phloem)
and to the inner side secondary phloem and xylem. The leaves are traversed
longitudinally by four air-passages, and expand at the base into a broad sheath.
On the inner side of the leaves, above their point of insertion, is an elongated
pit, the fovea, containing a large sessile sporangium. A ligule, in the form of
a triangular membrane, is inserted above the fovea. Isoetes thus differs greatly
in habit from the other genera, but resembles Selaginella in the development of a
ligule. On this account Isoetes and Selaginella are termed Ligulatae ; the extinct
Sigillariaceae and Lepidodendraceae also belong to this group.

The macrosporangia are situated on the outer leaves of the rosette ; the micro-
sporangia on the inner. Both are traversed by transverse plates of tissue or
trabeculae, and are in this way imperfectly divided into a series of chambers. In
contrast to Selaginella numerous macrospores are formed in each macrosporangium.
The spores are set free by the decay of the sporangial walls.

DIV. I

PTERIDOPHYTA

531

The development of the sexual generation is accomplished in the same way as
in Selaginella. The reduced male prothallium (Fig. 500) arises similarly within

Fio. 4i»t». — Isoetes lacustris. (i nat. size.)

FIG. 500. —A-F, Isoetes setacea (x 640). A, Microspore
seen from the side. B-D, Segmentation of the spore ;
p, prothallial cell ; wt the four cells of the wall ;
spennatogenous cells. E, The four spermatozoid
mother cells are surrounded by the disorganised cells
of the wall ; surface view. F, The same in side view.
G, Isoetes Mcdinverniana, spermatozoid (x 780)i
(After BELAJEFF.)

the spore, by the formation of a small, lenticular, vegetative cell '(p\ and a larger
cell, the rudiment of a single antheridium. The larger cell divides further into

cot

FIG. 501. — Isoetes echinospora. A, Female pro-
thallium ; ar, archegonium ; o, egg-cell. B, C,
Development of the archegonium from a super-
ficial cell ; h, neck-cells ; hk, neck-canal-cell ;
b, ventral canal-cell; o, egg -cell, (x 250.
After CAMPBELL.)

FIG. 502. — Isoetes echinospom. Embryo before
breaking out from the prothallus in longi-
tudinal section ; cot, cotyledon ; I, ligule ; v,
sheath at the base of the cotyledon in the axil
of which the apex of the stem arises ; w,
root ; /, foot. ( x 200. After CAMPBELL.))

four sterile peripheral cells, which completely enclose two central spermatogenous
cells. From each of the latter arise, in turn, two spermatozoid mother cells, four
in all, each of which, when liberated by the rupture of the spore wall, gives rise

532

BOTANY

PART II

to a single, spirally-coiled, multiciliate spermatozoid. The female prothallium
(Fig. 501), just as in Selaginella, also remains enclosed within the macrospore, and
is incapable of independent growth. It shows similarly an approach to the
Conifers, in that the nucleus first divides into numerous, parietal daughter-nuclei
before the gradual formation of the cell walls, which takes place from the apex of
the spore to the base. As a result of this process the whole spore becomes filled
with a prothallium, at the apex of which the archegonia are developed. The
embryo (Fig. 502) has no suspensor and thus differs from other Lycopodinae.

Order 5. Sigillariaceae (132)

The Sigillarias, found from the Culm onwards, are most numerous in the
Carboniferous period, and persist to the Bunter Sandstone. They were stately

FIG. 503. — 1, Lepidodendron. Recoustruction (after POTONIEJ. ..', L. Ac>iJ<-ntinii. cast of stem
surface (after STERNBERG). 3, k, Lepidodendron, leaf-cushions (after POTOME). 5, Piece
of cortex (after SEWARD). (From LOTSY, Botan. Siammesgeschichte.)

trees, with but little-branched, pillar-like stems, which grew in thickness. They
had long narrow leaves with a ligule, which when they fell off left longitudinal
rows of hexagonal leaf-scars on the surface of the stem. Long-stalked, cone-

DIV. I

PTERIDOPHYTA

533

like flowers were borne on the stem ; the sporangia were borne singly on the
sporophylls. Heterosporous.

FIG. 504. — Lepidostrobus Vdtheimianus. 1, Transverse section of cone with microsporangia ; tetrads
to right below. 2, Cone in longitudinal section showing microsporangia above and macro-
sporangia below. 8, Transverse section of cone with macrosporangia. A, Macrospore in
longitudinal section. 5, Macrospore, probably opening in course of germination. (1-5 after
SCOTT, KIDSTON, BIXKEY.) From LOTSY.

Order 6. Lepidodendraceae (132- I33)

The Lepidodendrons extend from the Devonian to the Rothliegende, but
are best developed in the Carboniferous period. They were tree-like plants
attaining a height of some 30 metres with dichotomously-branched stems which
grew in thickness. The leaves, which attained a 'length of 15 cm., were spirally
arranged and seated on rhombic leaf-cushions (Fig. 503). The cone-like flowers
(Lepidostrobus) were borne on the ends of branches or sprang from the stem
itself ; each sporophyll bore a single sporangium, which contained either macro-
spores or microspores (Fig. 504). The number of spores in the macrosporangium
was larger than in Selaginella. A prothallus was formed in the spore and
resembled that of the existing genus.

The discovery of seed-like structures borne by some of the palaeozoic
Lycopodinae (Lepidocarpon, Miadesmia) is of special interest. In them the
macrosporangium was surrounded by an integument leaving only a narrow slit-
like opening ; the sporophyll also took part in enclosing the sporangium. Only
one macrospore attained full development. As in Isoetes the prothallium re-
mained within the spore. The macrospores were produced on sporophylls
resembling those of Lepidostrobus. Probably pollination occurred while the

534

BOTANY

PART II

sporangia was still attached to the parent plant from which later the niacro-
sporophyll, together with its sporangium, separated as a whole.

FIG. 505. — Lyginodendron. Frond. (Sphenopteris Hoeninghousii.) (Reduced ^. After POTONI£.)

CLASS V
Pteridospermeae (132' 134)

So far as our knowledge goes the Equisetinae, Sphenophyllinae,
and Lycopodinae are branches of the Pteridophyte stock which have
undergone no further development in the direction of the more highly
organised plants. From the Filicinae, on the other hand, the first
seed-plants had arisen even in palaeozoic times. These are the
Pteridospermeae, which stand on a higher level than all other
Pteridophytes and connect the Ferns with primitive Gymnosperms

DIV. I

PTERIDOPHYTA

535

(Cordaiteae, Cycadeae) ; they have thus great importance in the

FIG. 506.— Lyginodendron oldhamium. Transverse section of stem, (x 2£. After SCOTT.)

FIG. 507.— Lyginodendron oldhamium. A, Microsporangia (OossoMeca). B, Macrosporangium
(Lagenostoma). Reconstruction. The open cupule bears stalked glands. (After SCOTT.)

phylogeny of the higher plants. They became extinct in the Permian
period.

In their vegetative organs the Pteridospenns resembled especially the

536 BOTANY PAHT n

Marattiaceous ferns. Their fronds (tiphenopteris, Fig. 505 ; Neuropteris) were
highly compound, the main rachis dividing dichotomously above the base. The
stem had axillary branching (Lyginodendrori) and underwent secondary thickening
by means of a cambium ; this cut off radially-seriated xylem elements to the
inside and phloem to the outside (Fig. 506). The leaf-trace bundles met with
in the cortex traverse the zone of wood to unite with the strands of primary
xylem at the periphery of the pith. The roots also underwent secondary
thickening.

The Pteridosperms were heterosporous ; the sporangia were borne on fronds
that resembled those of ordinary ferns. The microsporangia (Crossotheca, Fig.
507 A) showed resemblances to Matattiaceae ; the macrosporangia (Lagenostoma,
Fig. 507 B), on the other hand, were surrounded by a cupule and resembled in
construction the ovules of the Cycadeae ; the macrosporophylls were not, however,
arranged in cones.

DIVISION II

SPERMATOPHYTA

537

DIVISION II
SPERMATOPHYTA

The Transition from the Pteridophyta to the Spermatophyta (1).—
The Pteridophyta are characterised by the type of alternation of
generations they exhibit. The spore gives rise to the independently
living, haploid gametophyte. This is the short-lived prothallus, from
the fertilised egg -cell of which the physiologically independent
diploid sporophyte arises and forms the Fern, Horse-tail, or Club-
moss. The appearance of heterospory leads to a further reduction of
the prothallus, which ceases to produce both kinds of sexual organs.
In the germination of the microspores only a single, vegetative pro-
thallium-cell is to be recognised, the remainder of the small prothallium
representing one or more antheridia. The female prothallium, which
in Salvinia still becomes green and emerges from the macrospore, in
Selaginella and Isoetes has lost the power of independent nutrition.
The prothallium begins its development while still within the macro-
sporangium of the parent plant, and the macrospore, after being set
free, only opens in order to allow of the access of the spermatozoids
to the archegonia. From the fertilised egg the embryo develops
without a resting period into the young sporophyte.

The simplest Spermatophyta are only distinguished by inessential
differences from these most highly differentiated Archegoniatae.

The MACROSPORE, which in the Spermatophyta is termed the
EMBRYO-SAC, remains enclosed in the MACROSPORANGIUM or OVULE
(Fig. 508). The latter consists of the NUCELLUS (n), from the base of
which (the CHALAZA (ch)) one or two INTEGUMENTS (ii, ia) arise ; these
grow up as tubular investments of the nucellus and only leave a small
passage, the MiCROPYLE (m), leading to the tip of the latter. The
ovule is attached to the MACRO-SPOROPHYLL or CARPEL by a stalk or
FUNICULUS (/), which is often very short. The region to which one
or more ovules are attached is called the PLACENTA. If the nucellus
forms the direct continuation of the funiculus the ovule is termed
straight or ATROPOUS. More frequently the funiculus is sharply
curved just below the chalaza, so that the ovule is bent back alongside
its stalk (ANATROPOUS ovule). The line of junction of the funiculus

539

540

BOTANY

PART II

with the outer integument is still recognisable in the ripe seed, and
is termed the RAPHE. Lastly the ovule itself may be curved, in which
case it is spoken of as CAMPYLOTROPOUS. The three types are dia-
grammatically represented in Fig. 508 A-C.

As a rule only one embryo-sac is contained in an ovule. In the
same way as the four macrospores originate by the tetrad division in
the macrosporangium of Selaginella, in the macrosporangium (ovule) of
the Spermatophyta there is usually a single embryo-sac mother cell
which divides into four daughter cells ; three of these do not develop
further, while the fourth becomes the embryo-sac. The embryo-sac
of the simplest Spermatophyta also resembles the macrospore in
becoming filled with prothallial tissue, here termed the endosperm ;
one or more archegonia with large egg-cells are developed at the
summit of this. The fertilised ovum develops into the embryo while

FIG. 508.— A, Atropous ; B, anatropous ; C, campylotropous ovules. Diagrammatic and magnified.
Modified from SCHIMPER. Description in the text.

still enclosed within the macrospore and at the expense of the parent
plant. When the embryo has reached a certain stage in its develop-
ment, which is different and characteristic in different plants, its growth
is arrested, and after the separation from the parent plant it under-
goes a period of rest. It is still surrounded by the other portions of
the macrosporangium, viz. the prothallium or endosperm, the nucellus
(if this still persists), and the seed coat formed from the integuments.

THE COMPLETE STRUCTURE DERIVED FROM THE OVULE IS TERMED A
SEED, AND THE FURTHER DEVELOPMENT OF THE UNOPENED MACRO-
SPORANGIUM TO FORM A SEED, THE FIRST ORIGIN OF WHICH WAS SEEN

IN THE PTERIDOSPERMEAE (p. 534), is CHARACTERISTIC OF ALL

SEED-PLANTS OR SPERMATOPHYTA.

The MICROSPORES of the Spermatophyta are called POLLEN GRAINS.
They are formed in large numbers within the MICROSPORANGIA or
POLLEN SACS, which are borne singly or in numbers on the MICRO-
SPOROPHYLLS or STAMENS. The part of the stamen which bears the
pollen sacs is usually clearly distinguishable and is called the ANTHER.

DIV. n

SPERMATOPHYTA

541

The development of the pollen sac (Fig. 509) commences with
divisions parallel to the surface taking place in cells of the hypodermal
layer; this separates the cells of the primary archesporium from an
outer layer of cells. The latter divides to form three layers of cells.
The outermost layer of the wall in Gymnosperms and the hypodermal
layer in the Angiosperms gives rise to the fibrous layer and the inner-
most layer to the tapetum. The archesporium after undergoing a
number of divisions forms the pollen-mother-cells, each of which divides
as in Bryophytes and Pteridophytes into four daughter cells. These

FIG. 509. — Hemeroccdlis fulva. A, Transverse section of an almost ripe anther, showing the loculi
ruptured in cutting ; p, partition wall between the loculi ; a, groove in connective ; /, vascular
bundle ( x 14). B, Transverse section of young anther ( x 28). C, Part of transverse section of a
pollen sac ; pm, pollen-mother-cells ; t, topetal layer, later undergoing dissolution ; c, inter-
mediate parietal layer, becoming ultimately compressed and disorganised ; /, parietal layer of
eventually fibrous cells; e, epidermis (x 240). D and E, Pollen-moth er-cells of Alchemilla
speciosa in process of division (x 1125). F, Mature tetrad of Bry&nia dioica ( x 800). (After
STRASBURGER).

are the pollen grains, and are spherical or ellipsoidal in shape and
provided with a cell wall ; an external cutinised layer (the EXINE),
and an inner cellulose layer, rich in pectic substances (the INTINE),
can be distinguished in the wall.

While the male sexual cells of all archegoniate plants are depend-
ent on water for their conveyance to the female organs, the transport
of the pollen grains to the egg-cells is brought about in Spermatophytes
by means of the wind or by animals. However far the reduction of
the male prothallium has proceeded — and even in the case of the
heterosporous Pteridophyta only a single sterile cell was present — two
constituent parts are always distinguishable in the germinating pollen
grain ; these are a VEGETATIVE CELL which grows out as the POLLEN-

542 BOTANY

PART II

TUBE, and an ANTHERIDIAL MOTHER CELL which ultimately gives rise
to two GENERATIVE CELLS. The pollen-tube, the wall of which is
continuous with the intine of the pollen grain, ruptures the exine
and penetrates, owing to its chemotropic irritability, into the tissue
of the macrosporangium (cf. p. 352). The antheridial mother cell
passes into the pollen-tube and sooner or later gives rise to two
generative cells which reach the embryo sac and egg-cell by passing
along the pollen-tube. The name Siphonogams has been applied to
the seed -plants on account of the common character of the group
afforded by the formation of a pollen-tube.

The results reached by the above survey may be summarised by
saying that the Phanerogams continue the series of the Archegoniatae
and agree with the latter in exhibiting an alternation 'of generations
(cf. the Scheme on p. 543). While the asexual generation becomes
more complex in form and more highly organised, there is a
corresponding reduction of the sexual generation. The female sexual
generation is enclosed, throughout its whole development, in the
asexual plant, and only becomes separated from the latter in the seed,
which further contains as the embryo the commencement of the
succeeding asexual generation.

The investigations made of recent years into the phenomena of the
reduction division (cf. p. 204) in the spore-mother-cells of Archegoniates
and Spermatophyta have resulted in a confirmation of the limits of the
two generations in the latter (2). The number of chromosomes char-
acteristic of any plant is diminished to one-half, during the divisions
that lead to the origin of the sexual generation, and the full number
of chromosomes is not again attained until fertilisation takes place.
The asexual generation has always the double number, the sexual
generation the single number of chromosomes. The gametophyte is
haploid, the sporophyte diploid.

The Spermatophyta are divided into two classes which differ in
their whole construction: (1) the Gymnosperms, with naked seeds;
(2) the Angiosperms, with seeds enclosed in an ovary.

The names of these classes indicate the nature of one of the most
important differences between them. THE CARPELS OF THE ANGIO-
SPERMS FORM A CLOSED CAVITY, THE OVARY, WITHIN WHICH THE
OVULES DEVELOP. SUCH AN OVARY IS WANTING IN THE GYMNO-
SPERMS, THE OVULES OF WHICH ARE BORNE FREELY EXPOSED ON
THE MACROSPOROPHYLLS OR CARPELS.

The Gymnosperms are the phylogenetically older group. Their
construction is simpler and in the relations of their sexual generation
they connect directly with the heterosporous Archegoniatae ; they
might indeed be treated as belonging to this group.

The Angiosperms exhibit a much wider range in their morpho-
logical and anatomical structure. The course of their life-history
differs considerably from that of the Gymnosperms, and without the

Haploid Sexual Generation
=Gametophyte.

Diploid Asexual Generation
= Sporophyte.

543

544

BOTANY

PART II

intermediate links supplied by the latter group the correspondence
with the life-history of the Archegoniatae would not be so clearly
recognisable.

These conclusions are confirmed by the evidence afforded by
Palaeobotany. Gymnosperms or forms resembling them are found
along with what appear to be intermediate forms between the Gymno-
sperms and the Pteridophyta in the fossiliferous rocks of the Devonian,
Carboniferous, and Permian formations. The Angiosperms are, on
the other hand, first known from the Cretaceous formation.

Morphology and Ecology of the Flower (3)

1. Morphology. — The flowers of the Gymnosperms are all
unisexual and diclinous. The macrosporophylls form the female, the

N^V;

FIG. 510. — Pin-us montana. A, Longitudinal section of a ripe male flower (x 10). B, Longitudinal
section of a single stamen ( x 20). C, Transverse section of a stamen ( x 27). D, A ripe pollen
grain of Pinus sylvestris ( x 400). (After STRASBURGER.)

microsporophylls the male flowers. The two sexes are found either
on the same individual (MONOECIOUS), or each plant bears either male
or female flowers (DIOECIOUS). Leaves forming an envelope around
the group of sporophylls are only found in a few flowers of the
Gymriospermae (Gnetaceae).

The MALE FLOWERS are shoots of limited length, the axis of which
bears the closely crowded and usually spirally arranged sporophylls.
The scales which invested the flower in the bud often persist at the

DIV. n

SPERMATOPHYTA

545

base of the axis (Fig. 510). The microsporangia are borne on the
lower surface of the sporophylls, two or more being present on each.
Their opening is determined as in the sporangia of the Pteridophyta
by the peculiar construction of the outer layer of cells of the wall
(exothecium). The pollen grains are spherical, and are frequently
provided with two sacs filled with air, which increase their buoyancy
and assist in their distribution by the wind (Fig. 510). On germina-
tion the outer firm layer of the wall of the pollen grain (exine) is
completely lost, being fractured by the increase in size of the proto-
plasmic body.

In many Gymnosperms the FEMALE FLOWERS or CONES resemble
the male flowers in being composed of an axis bearing numerous
* spirally-arranged sporophylls.

In other cases they differ
A from this type in various

ways, which will be described
below (pp. 589 ff.).

FIG. 511. — Flower of Paeonia peregrina, iu longitudinal
section, k, Calyx, and c, corolla, together forming
the perianth ; «, androecium ; g, gynaeceum. The
anterior portion of the perianth has been removed,
(i nat. size. After SCHENCK.)

Fio. 512.— Flower of Acorus Calamus,
pg, Perigone ; a, androecium ; g,
gynaeceurn. (Enlarged. After
ENGLKR.)

In Angiosperms, on the other hand, a union of micro- and macro-
sporophylls in the one flower, which is thus HERMAPHRODITE, and the
investment of the flower by coloured leaves (differing in appearance
from the foliage leaves), forming a PERIANTH, is the rule (Figs. 511,
512). The Querciflorae afford an example of an exception to these
statements. In contrast to the UNISEXUAL or DICLINOUS flower with
the sporophylls arranged spirally on an elongated axis, which is
characteristic of the Gymnosperms, the perianth leaves and sporo-
phylls in the Angiosperms are usually borne in whorls on a greatly
shortened axis. THE ARRANGEMENT OF THE FLORAL LEAVES IN

WHORLS, THE COLOURED PERIANTH, AND THE HERMAPHRODITE NATURE
OF THE FLOWERS ARE THUS CHARACTERISTIC OF ANGIOSPERMS, although

these features do not apply without exceptions to all angiospermic
flowers. These differences depend on the important factor of the
MEANS OF POLLINATION. When, as is the case with the Gymnosperms

546 BOTANY PART n

and the catkinate flowers of Angiosperms, this function is performed
by the wind, the elongation of the axis and the absence of an invest-
ment of leaves around the female receptive organ are advantageous.
When, on the other hand, pollination is effected by insects or birds,
the conspicuousness given by the presence of a perianth and other
attractions, such as scent or sweet-tasting substances, are necessary.
The form of the flower, the arrangement of the sporophylls in it, and
the place at which nectar is secreted must be adapted to the body-
form or the habits of the visiting animals. It is to this that the
variety of form and colour exhibited in the flowers of Angiosperms
must be ascribed.

The association of hermaphrodite and unisexual flowers on the same plant
leads in certain Angiosperms to what is known as POLYGAMY. When herma-
phrodite and unisexual flowers are distributed on distinct individuals we have
andro- or gyno-dioecism ; when on the same individual andro- or gyno-monoecism.

The perianth usually consists of two whorls of members : these
may be similar in form and colour (e.g. Lilium), when the name
PERIGONE is given to them, or may be differentiated into an outer
green CALYX and an inner whorl of coloured leaves, the COROLLA (e.g.
Rosa). In every complete flower two whorls of stamens or micro-
sporophylls come next within the perianth, and within these again a
whorl of carpels or macrosporophylls. The whorls alternate regularly
with one another. The stamens collectively form the ANDROECIUM,
the carpels the GYNAECEUM.

Each stamen consists of a cylindrical stalk or FILAMENT and of
the ANTHER ; the latter is formed of two THECAE or pairs of pollen-
sacs joined by the continuation of the filament, the CONNECTIVE (Fig.
513). According to whether the thecae are turned inwards, i.e.
towards the whorl of carpels, or outwards, the anther is described as
INTRORSE or EXTRORSE. The opening of the ripe theca depends as a
rule (except in the Ericaceae) on the peculiar construction of the
hypodermal layer of the wall of the pollen sac. This is called the
fibrous layer or ENDOTHECIUM. On the other hand, in the Gymno-
sperms (excluding Ginkgo,'cL p. 591), as in the Ferns, the dehiscence
is effected by means of the external layer of cells (exothecium) (p. 545).
As a rule the septum between the two pollen sacs breaks down, so
that they are both opened by the one split in the Vail (Fig. 509 A).
The microspores in anemophilous plants are smooth, dry, and light,
and adapted for distribution by the wind. In entomophilous flowers,
on the other hand, the exine is frequently sticky or provided with
spiny projections, and the pollen grains are thus enabled to attach
themselves better to the bodies of the insect visitors. They also
differ from the pollen grains of the Gymnosperms in having more or
less numerous spots in the wall prepared beforehand for the emission
of the pollen-tube (Fig. 514). Sterile stamens which do not produce
fertile pollen are termed STAMINODES.

DIV. n

SPERMATOPHYTA

547

The flower is terminated above by the GYNAECEUM. The CARPELS
composing this may remain free and each give rise to a separate fruit

FIG. 513.— ,4 and B, Anterior
and posterior view of a sta-
men of Hyoscyamus niger ;
f, the filament ; p, anther ;
c, connective (magnified).
(After SCHIMPER.)

FIG. 514. —Pollen grain of Malm sylvestris.
S, Spinous projections of the exine ; s,
vertically striated layer of the exine ;
p, the same seen from above ; a, places
of exit of pollen-tubes. (After A.
MEYER.)

(APOCARPOUS GYNAECEUM) (Figs. 515a, 517 A\ or they unite together
to form the ovary (SYNCARPOUS GYNAECEUM) (Fig. 5156). The
carpels, as a rule, bear the
ovules on their margins, on
more or less evident out-
growths which are termed

PLACENTAS (Fig. 515rt, p).

In apocarpous gynaecea the
ovules are thus borne on the

Fi'.. 51""'. — Delphinium <-on-
tfolida. Cross-section of the
ovary, showing the ovules
on the placenta Q/). (Alter
EXGLER and PRAXTL.)

FIG. 5li>b. — Sumlittmis ni<jm. Longitudinal sec-
tion of flower, s. Ovule ; n, stigma. (After

Tsi HIROH-OsTERLE.)

united margins of the carpels, each margin bearing a row of ovules.
This is termed the VENTRAL SUTURE, while the midrib of the carpel
forms the DORSAL SUTURE. In syncarpous ovaries the ovules are
similarly borne on the margins of the coherent carpels (Fig. 516 pi).

548

BOTANY

PART II

The placentation is termed PARIETAL when the placentas form projections
from the inner surface of the wall of the ovary (Fig. 516 D}. If the margins of
the carpels project farther into the ovary, and divide its cavity into chambers or
loculi, the placentas are correspondingly altered in position, and the placentation
becomes AXILE (Fig. 516 B}. In contrast to such TRUE SEPTA, formed of the
marginal portions of the carpels, those that arise as outgrowths of the surface or

FIG. 516. — Transverse sections of ovaries. A, Lobelia • B, Diapensia ; C, Rhododendron ;
D, Passiflora ; pi, placenta ; sa, ovules. (After LE MAOUT and DECAISNE.)

sutures of the carpels, as in the Cruciferae, are called FALSE SEPTA (Fig. 656). By
the upgrowth of the floral axis in the centre of the ovary what is known as FREE
CENTRAL PLACENTATION comes about (e.g. Primulaceae). The projecting axis
cannot be sharply distinguished from the tissue of the carpels. The septa, which
were originally present, are arrested at an early stage of development or com-
pletely disappear, so that the ovules are borne on the central axis covered with
carpellary tissue and enclosed in a wall formed by the outer portions of the carpels.

FIG. 517. — Different forms of gynaecea. A, Of AconUum Napcllus ; B, of Linum usitatissimum ;
C, of Nicotiana rustica ; D, style and stigma of Achillea miUefolium ; /, ovary ; g, style ;
n, stigma. (After BERG and SCHMIDT, magnified.)

Each carpel in an apocarpous gynaeceum is usually prolonged above
into a stalk-like STYLE terminating in a variously-shaped STIGMA. The
stigma serves as the receptive apparatus for the pollen, and in relation
to this is often papillate or moist and sticky (Fig. 517 D). When

DIV. n

SPERMATOPHYTA

549

the gynaeceum is completely syncarpous, it has only one style and
stigma. In Fig. 517 an apocarpous (A) and a syncarpous gynaeceum
(C) are represented, together with one in which the carpels are coherent
below to form the ovary while the styles are free (B).

The POSITION OF THE OVULES WITHIN THE OVARY may be erect,

FIG. 518. — Ovary of Con i urn macidatum with
pendulous ovules, in longitudinal section.
Raphe ventral. (After TSCHIRCH-OSTERLE.)

FIG. 519. — Ovaries containing basal ovules
shown in longitudinal section. A, Fago-
pj/rnmescwie?i?iun(atropous); B, Armeria
maritima (anatropous). (x 20. After

DOCHARTRE.)

pendulous, horizontal, or oblique to the longer axis (Figs. 518, 519).
In anatropous ovules the raphe is said to be ventral when it is turned
towards the ventral side of the carpel, and dorsal if towards the
dorsal side of the carpel.

The differences in the form of the floral axis, which involve changes
in the position of the gynaeceum, lead to differences in the form of
the flower itself. Some of the commonest cases are diagrammatically
represented in Fig. 520 A-C. The summit of the floral axis is usually

FIG. 520.— Diagram of (A ):hypogynous, (B, B1) perigynous, and (C) epigynous flowers.
(After SCHIMPER.)

thicker than the stalk-like portion below ; it is often widened out
and projecting, or it may be depressed and form a cavity. If the
whorls of members of the flower are situated above one another on a
simple, conical axis, THE GYNAECEUM FORMS THE UPPERMOST WHORL

AND IS SPOKEN OF AS SUPERIOR, WHILE THE FLOWER IS TERMED

550 BOTANY PART n

HYPOGYNOUS (Fig. 521, 1). If, however, the end of the axis is
expanded into a flat or cup-shaped receptacle (hypanthium), an interval
thus separating the androecium and gynaeceum, the flower is termed
PERIGYNOUS (Figs. 520 B, B', 521, 2). When the concave floral axis,
the margin of which bears the androecium, becomes adherent to the
gynaeceum, the latter is said to be INFERIOR, while the flower is
described as EPIGYNOUS (Fig. 521, 3).

The regions of the axis, or of other parts of the flower which
excrete a sugary solution to attract the pollinating animal visitors,
are called NECTARIES. Their ecological importance is considerable.

In a typical angiospermic flower the organs are thus arranged in
five alternating whorls, of which two comprise the perianth, two the
androecium, while the gynaeceum consists of one whorl. The flower
is PENTACYCLIC. The number of members is either the same in each

FIG. 521. — Flowers in longitudinal section. 1, Ranunculus sceleratus with numerous apocarpous
carpels on a club- shaped receptacle; hypogynous flower. (After BAILLON, magnified.)
2, Alchemilla alpina, perigynous ; 3, Pyrus Mains, epigyuous. (After FOCKE in Nat. Pflanzen-
familien, magnified.)

whorl (e.g. three in a typical Monocotyledon flower, or five in a typical
Dicotyledon flower), or an increase or decrease in the number takes
place. This is especially the case with the whorls composing the
androecium and gynaeceum. Further, as is shown in the androecium,
a whorl may be entirely omitted or the number of whorls may be
increased. Flowers with only one whorl in the androecium are
termed haplostemonous, and those with two whorls diplostemonous.
When the outer whorl of the androecium (and in correspondence with
this the carpels) does not alternate with the corolla but falls directly
above this, the androecium is obdiplostemonous.

A diagram (cf. p. 88) of a pentacyclic Monocotyledon flower, so
oriented that the cross-section of the axis of the inflorescence stands
above and that of the subtending bract (cf. p. 121) below, is given in
Fig. 522, and that of a Dicotyledon flower in Fig. 523.

Both these floral diagrams are spoken of as empirical diagrams. A theoretical
diagram, on the other hand, is obtained when not only the organs actually
present are represented but also others the former presence of which must be

DIV. n

SPERM ATOPHYTA

551

assumed on phylogenetic grounds. Thus in the Iridaceae, which are closely
related to the Liliaceae, only one whorl of stamens (the outer) is present ; the inner
whorl which might have been expected has been lost (Fig. 524). When the
position of the missing members is marked by crosses in the empirical diagram the
theoretical floral diagram of the Iridaceae is obtained.

A FLORAL FORMULA gives a short expression for the members of a flower as shown
in the floral diagram. Denoting the calyx by K, the corolla by C (if the perianth
forms a perigone it is denoted by P), the androecium by A, and the gynaeceum
by G, the number of members in each case is placed after the letter. When
there is a large number of members in a whorl the symbol oo is used, denoting
that the number is large or indefinite. Such a formula may be further made to
denote the cohesion of the members of a whorl by enclosing the proper number
within brackets ; by placing a horizontal line below or above the number of
the carpels the superior or inferior position of the ovary is expressed.

FIG. 522.— Diagram of^
a pentacyclic mono- —
co\yledonous flower ^-,
(Lilium). (After"
SCHEXCK.)

FIG. 523.— Diagram of
a pentacyclic dico-
tyledonous flower
(Viscaria). (After
EICHLER.)

FIG. 524.— Theoretical dia-
gram of the flower of
Iris. The missing
whorl of stamens is
indicated by
(After SCHESCK.)

The floral diagrams in Figs. 522 and 523 would be expressed respectively
by the floral formulae, P3 + 3, A3 + 3, G(3) for the Monocotyledon, and K5, C5,
A5 + 5, G(5) for the Dicotyledon. __0ther examples are Ranunculus, K5, C5,
A oo, G»_; Hemlock, Ko, C5, A5, G(2) ; Artemisia, Ko, C(5), A(5), G(2).

By displacement of the floral members, by inequalities in their
size, or by the suppression of some of them, the original radial
(actinomorphic) construction (Fig. 525 A] is modified (cf. p. 72);
either dorsiventral (zygomorphic) flowers (Fig. 525 B) or completely
asymmetrical flowers (Fig. 525 C) may result. In the floral formula
0 indicates an actinomorphic and 4" a zygomorphic flower, e.g.
Laburnum, ^ Ko, Co, A (5 + 5), Gl. Zygomorphic flowers always
tend to assume a definite position in relation to the vertical. Radial
monstrosities of normally dorsiventral flowers are termed peloric.

2. Ecology. Pollination of Flowers (4) (cf. p. 201).— Many
differences in the structure of flowers and in the arrangement of
their organs which would otherwise be doubtful are explained when
brought into relation to the functions performed by the flower.
All flowers have the function of producing progeny sexually ; the

552

BOTANY

PART II

methods leading to this common end are, however, very various. In
contrast to the Bryophyta and Pteridophyta in which the union of the
sexual cells is effected by the aid of water, the Spermatophyta, which do
not separate a motile male gamete, and have the egg-cells permanently
enclosed in -the tissues of the parent plant, are forced to adopt other
methods. Arrangements to convey the microspores, enclosing the
male sexual cell, to the macrospores, enclosed in the macrosporangia
and containing the egg-cells, become necessary.

A large number of Spermatophyta make use of the wind to convey
the microspores, i.e. the pollen, to its destination. Examples are all
the Conifers, and also the majority of our native deciduous trees such
as the Elm, Oak, Beech, Hornbeam, and further our Grasses and
cereals. Simple as the relations in this case appear to be, various

FIG. 525. — A, Actinomorphic flower of Geranium sanguineum. B, Zygomorphic flower of Viola
tricolor. 0, Asymmetrical flower of Canna indica.

necessary preliminaries are required for successfully effecting this
method of pollination.

It is especially necessary that such ANEMOPHILOUS plants should
produce a very large quantity of pollen, since naturally only a small
fraction of what is shed will reach its destination. Thus at the
season when our coniferous woods are in flower large quantities of
pollen fall to the ground, constituting what is known as sulphur showers.

Anemophilous plants exhibit some characters in common which
stand in definite relation to wind-pollination. The male inflorescence
has usually the form of a longer or shorter catkin (Fig. 526) which
bears a large number of microsporophylls ; these are so oriented that
after the sporangia have opened the pollen can be readily carried away
by the wind. Examples are the catkins of the Oak (Fig. 610), Birch
(Fig. 604), Alder, Hazel, Hornbeam, and Walnut ; the catkins of the
last-named plant (Fig. 602) are especially long. The male flowers of
the Coniferae (Fig 510) are similar. The mode of attachment of the

DIV. n SPERMATOPHYTA 553

anthers of Gramineae on long slender filaments has the same significance.
The pollen grains of anemophilous flowers also have characteristic
features. They are light and smooth, and in some Conifers are even
provided with two wing-like sacs (Fig. 510 D), which enable them
to remain suspended longer in the air. Some Urticaceae (Pilea,
Urtica) scatter the pollen on the opening of the elastically-stretched
wall of the pollen sac as a light cloud of dust.

The female flowers are usually not brightly coloured and do not
develop nectaries. The stigmas, which catch the pollen, are strongly
developed and provided with long feathery hairs (Fig. 527), or their
form is brush-like, pinnate or elongated, and filamentous. In many
Gymnosperms (e.g. Taxus) the macrosporangium excretes a drop of
fluid in which the pollen grains are caught ; on drying up of the drop
the pollen is drawn down on to the tip of the
nucellus. In other cases the pollen grains glide
down between the carpellary scales of the cones
till they reach the moist micropyles of the
ovules and adhere to them.

Lastly, the time of flowering is not without
importance. The Elm flowers in February and
[March long before its leaves develop, and the
same holds for the Hazel, Poplar, and Alder.
In the Walnut, Oak, Beech, and Birch the
flowers open when the first leaves are unfolding,
and flowering is over before the foliage is fully
expanded. Were this not so, much of the
pollen would be intercepted by the foliage leaves,
and even more pollen would need to be produced
than has to be done to ensure fertilisation. In ^ 526 _Catkin of Corylus

the Conifers the foliage presents less difficulty, americana. (After DUCHARTRK.)

but here the female cones are borne at the

summit of the tree (Abies) or high up (Picea), while the male flowers are
developed on lower branches. The pollen grains are shed in warm
dry weather, and carried up in the sunshine by ascending currents
of air till they reach their destination on the female cones situated high
above the male flowers.

Only a small number of Phanerogams make use of the agency of
water for effecting their pollination, and are, on that account, termed
HYDROPHILOUS PLANTS. This applies only to submerged water plants
which do not emerge from the medium, e.g. Zostera, Seawrack.

The great majority of Phanerogams are dependent upon animals,
especially on insects, for the transference of their pollen. Plants
pollinated by the aid of insects are termed ENTOMOPHILOUS.

Since KONRAD SPRENGEL in his famous work, Das entdeckte
Geheimnis der Xafnr im Ban und in der Befruchtung der Blumen, 1793,
revealed the mutual relations between the forms and colours of flowers

554

BOTANY

PART II

and the insects that frequent them, no other department of biology
has been more actively studied than floral ecology. It is the more
remarkable that no one had put the question whether the colours seen
by our eyes were also perceived by the insects in the same way. It
was difficult to think of the display of colour in meadow or orchard
otherwise than as an apparatus of attraction for the visiting insects
seeking the food provided by the nectaries of the flowers. We owe
the opening up of this question to C. HESS (5). In the light of his

exact demonstration that bees
are colour-blind the earlier
views require to be revised.

HESS bases his argument on the
comparison of the behaviour of bees
with colour-blind human beings,
and shows that they, like all in-
vertebrate animals that have been
investigated, react quite similarly
to the stimuli of colour. Their
brightness -maximum lies in the
green-yellow region ; red appears
dark, and blue on the other hand
light. The attraction of flowers
for bees must accordingly depend
on the contrast effects of different
degrees of brightness.

In this demonstration there
appears to be wanting the answer
to the question at what distances
the eyes of the bee are able to per-
ceive strong contrasts in bright-
ness. An orchard in flower, apart
from any colour-sense on the part
of bees, would be more readily seen
by them at a distance on account
of the bright flowers contrasting with the dark background of foliage. To this
would be added the tendency of bees, at least of the same colony, to collect
together, so that when one bee has found a source of food, a crowd of others will
follow.

The facts regarding the pollination of flowers by insects which
SPRENGEL discovered still hold, although the particular question as to
how the apparatus rendering the flowers conspicuous affects the
eyes of insects, and how the conspicuousness has come about, is open
to reconsideration. It must be borne in mind that without any
relation to insect-pollination the Firs, Larch, and other Coniferae
exhibit intensely -coloured female cones, as do the male flowers of
the Pine when seen in mass. It would appear to be frequently of
importance to plants for their reproductive organs to have some colour-
other than green. The greater absorption of heat-rays may be con-

FIG. 527.— Anemophilous flower of Festuca elatior.
(After SCHENCK.)

DIV. n SPERMATOPHYTA 555

nected with the red stigmas of the early-flowering Hazel, and perhaps
also in the case of the cones of Coni ferae. Deeper investigation may
perhaps disclose further connections of this nature.

The relation between flowers and insects depending on the sense of
form and scent of the latter remains unquestioned, and has been more fully
investigated for bees by v. FRISCH. What explanation of the strong
scent, increasing towards evening, of Lonicera, Philadelphia, etc., can be
given except that it serves as an attraction to night-flying insects, such
as Hawk-moths, which are led by the scent to find their food ? How
could the existence of nectaries and the excretion by the plant of an
important reserve food substance be accounted for, if the guests which
greedily consume it were not indispensable to the flowers'! How,
lastly, could the*construction of a dorsiventral flower, such as that of
Salci'i. or of Orchis, be understood if we did not relate it to the insects
which visit the flower in search of nectar, and in doing so effect pollina-
tion 1 The mutual adaptations between the form of flowers and the
bodies of insects are so numerous, and the experimental fact that plants
removed from their native country, though growing healthily, remain
sterile owing to the lack of the pollinating insects to which they are
adapted, is so well established, that no doubt can be entertained on the
mutual adaptations of flowers and insects. Usually the position of the
nectaries is such that the hairy body of the visiting insect must carry
away pollen from the flower ; often the pollen will be deposited on
special regions of the insect's body and, when another flower is visited,
will be deposited on the stigma. It is of importance that the pollen of
such entomophilous plants differs from that of the anemophilous
flowers described above. Pollen grains provided with spiny pro-
jections, or with a rough or sticky surface, are characteristic of
entomophilous plants ; the grains may remain united in tetrads or in
larger masses representing the contents of a whole pollen-sac (Orchis,
Asdepias). The pollen itself forms a valuable nitrogenous food for
some insects such as bees ; these form " bee-bread " from it.

An example of a very close relation between floral construction and
the body of the visiting insect is afforded by the pollination of Salvia
pratenais by Humble Bees. Fig. 528, 1, shows a flower of Salvia with a
Humble Bee on the lower lip in search of nectar. The flower has
only two stamens, the two halves of each anther being quite differently
developed, and separated by an elongated connective ; the one half-
anther is sterile and forms a projection in the throat of the corolla-
tube, the other at the end of the long arm of the connective is fertile
and lies beneath the hood formed by the upper lip of the corolla.
The connective thus forms a lever, with unequal arms, movable on
the summit of the short filament. When the bee introduces its
proboscis it presses on the short arm of the lever; the fertile half-
anther is thus by the movement of the connective (c) on its place of
attachment to the filament (/) brought down against the hairy dorsal

556 BOTANY PART n

surface of the insect's body (Fig. 528, 1, 3). On visiting an older
flower the insect will meet with the stigma projecting further from the
upper lip on the elongated style (Fig. 528, 2). The stigma is then in the
position corresponding to the depressed half-anthers, and will receive
with certainty the pollen deposited from them on the back of the bee.

In addition to the stimulus of hunger, plants utilise the reproductive instinct
of insects for securing their pollination. Not a few plants (Stapetta, Aristolochia,
and members of the Araccae), by the unnatural colour of their flowers combined
with a strong carrion-like stench, induce carrion-flies to visit them and deposit
their eggs ; in so doing they effect, at the same time, the pollination of the flowers.
In the well-known hollow, pear-shaped inflorescences of the Fig (Ficus carica,
Fig. 614) there occur, in addition to long-styled female flowers that produce seeds,
similar gall-flowers with short styles. In each of the latter a single egg is laid by
the Gall- wasp (Blastophaga], which, while doing this, pollinates the fertile flowers
with pollen carried from the male inflorescence (the Caprificus). The large white

* 2

FIG. 528. — Pollination of Salvia pratensis. Explanation in the text. (After F. NOLL.)

flowers of Yucca are exclusively pollinated by the Yucca moth (Pronula). The
moth escapes from the pupa in the soil at the time of flowering of Yucca and
introduces its eggs into the ovary by way of the style ; in doing this it carries
pollen to the stigma. The larvae of the moth consume a proportion of the ovules
in the ovary, but without the agency of the moth no seeds will be developed, as
is shown by the sterility of the plant in cultivation.

ORNITHOPHILY plays a much less important part than entomophily ; the bird-
visitors are confined to the American Humming-birds and the Honey Birds of the
Old World. A specially remarkable case of adaptation of this kind is afforded by
Strelitzia reginae, which is often cultivated in greenhouses (Fig. 529). Its three
outer perianth segments (t) are of a bright orange colour ; the large azure-blue
labellurn (p) corresponds to one of the inner perianth leaves, while the other two (p)
remain inconspicuous and roof over the passage leading to the nectary. The
stamens (st) and the style (</) lie in a groove, the margins of which readily
separate, formed by the labellum, while the stigma (q) projects freely. The similarly-
coloured and showy bird (Nectarinia afro) flies first to the stigma and touches it,
then secures pollen from the stamens, which it will deposit on the stigma of the
flower next visited.

The structure of the pendulous inflorescence of Marcgrama is just as remarkable
(Fig. 530) ; in this the bracts form receptacles containing the nectar. Numerous
insects fly around these nectaries, and the darting Humming-birds, either in pursuit

DIV. II

SPERMATOPHYTA

557

of the insects or themselves in search of nectar, get dusted with pollen from the
flowers, which face downwards, and carry it to other flowers. On the investiga-

FIG. 529.— Ornithophilous flower of Strelitzia reainae and a cross-section of its large labellum (p);
t outer, and p inner perianth leaves ; g, style and stigma ; st, stamens. (From SCHIMPER, Plant
Geography.)

tions of HESS referred to above, it is easy to understand why the majority of
ornithophilous flowers (Aloe, Clianthus, epiphytic Loranthaceae, etc.) are red, since
this colour has the same value to the eyes of day-flying birds as to our own.

Besides these ORNITHOPHILOUS plants there are a few visited by Bats

558 BOTANY PART n

(CHIROPTEROPHILOUS) ; thus the dioecious Pandanaceous plant Freycinetia of
the Malayan Archipelago is pollinated by a Flying Fox (Pier opus], which eats the
inner bracts.

Pollination in some cases is effected by means of snails (MALACOPHILOUS
PLANTS). To their instrumentality the flowers of Calla palustris, Chryso-
splenium, and also the half-buried flowers of the well-known Aspidistra owe their
pollination.

It would seem remarkable that such manifold and various adapta-
tions for the conveyance of pollen should exist while the majority of

FIG. 530.— Inflorescence of Marcgravia umbdlata adapted for pollination by Humming-birds.
(From SCHIMPER, Plant Geography.)

angiospermic plants have hermaphrodite flowers ; it is known, however,
that the pollination of a flower with its own pollen may result in
a poorer yield of seed (Rye) or be without result (self-sterility in
Cardamine pratensis. Lobelia fulgens, Corydalis cava, etc.).

Cross-pollination (allogamy) must take place when the pollen can
only germinate if the stigma is rubbed as in the case of Laburnum
vulgare. The insect visit, which as a rule will bring foreign pollen,
prepares the conditions for germination and excludes the action of the
flower's own pollen. In the Orchids the flower's own pollen has a
directly injurious influence, and when applied to the stigma causes the
flower to wither.

Even when there is no self-sterility there are many and various
conditions which render the self -fertilisation of hermaphrodite flowers

DIV. n

SPERMATOPHYTA

559

impossible and favour cross-pollination. It is obvious that dioecism
completely prevents self-fertilisation, and that monoecism at least

FIG. 531. — Flower of Anthriscus sylvestris. Slightly magnified. 1, In the male,
2, in the female condition. (After H. MOLLER.)

hinders the pollination of the flowers with pollen from the same plant.
A similar result is brought about when the two kinds of sexual organs
of a hermaphrodite flower mature at different
times. This very frequent condition is known
as DICHOGAMY. There are obviously two
possible cases of dichogamy. Either the
stamens mature first and the pollen is shed
before the stigmas of the same flower are
receptive ; the plant is known as PROTAX-
DROUS. On the other hand, the style with
its stigma may ripen first, before the pollen
is ready to be shed; the plant is PROTOGYNOUS.
PROTANDRY is the more frequent form
of dichogamy. It occurs in the flowers of the
Geraniaceae, Campanulaceae, Compositae,
Lobeliaceae, Umbelliferae (Fig. 531), Gerani-
aceae, Malvaceae (Fig. 664), etc. The anthers,
in this case, open and discharge their pollen
at a time when the stigmas of the same flowers
are still imperfectly developed and not ready

for pollination. In Salda also (Fig. 525) FIG. 532.— Inflorescence of Plan

protandry is the necessary preliminary to the
cross-pollination.

In the less frequent PROTOGYNY the female
sexual organs are ready for fertilisation before
the pollen of the same flowers is ripe, and
the stigma is usually pollinated and withered

before the pollen is shed (Scrophularia nodosa, Aristolochia dematitis,
Helleborus, Magnolia., Plantago, Fig. 532).

tago media with protogynous
flowers. The upper, still closed
flowers (9) have protruding
styles ; the lower ( $ ) have
lost their styles, and disclose
their elongated stamens. (After
F. NOLL.)

560

BOTANY

PART II

The effect of HETEROSTYLY discovered by DARWIN is similar.
According to TlSCHLER this condition can be altered by the conditions
of nutrition. A good example is afforded by Primula sinensis (Fig.
533). Comparison of the flowers on different individuals shows that
they differ as regards the position of the stamens and stigma. There
are long-styled flowers, the stigma standing at the entrance to the
corolla-tube, while the anthers are placed deep down in the tube ; and
short-styled flowers, the stigma of which stands at the height of the
anthers, and the stamens at the height of the stigma of the long-styled
flower. An insect will naturally only touch organs of corresponding
height with the same part of its body and thus carry pollen between
the male and female organs of corresponding height. Thus cross-
pollination is ensured. The relative sizes of the pollen grains and
stigmatic papillae agree with this cross-pollination.

FIG. 533.— Primula sinensis: two heterostyled flowers from different plants. L, Long-styled,
K, short-styled flowers ; G, style ; S, anthers ; P, pollen-grains, and N, stigmatic papillae of
the long-styled form ; p and n, pollen-grains and stigmatic papillae of the short-styled form.
(P, N, p,n,x 110. After NOLL.)

The same DIMORPHIC HETEROSTYLY is exhibited by Pulmonaria,
Hottonia, Fagopyrum, Linum, and Menyanthes. There are also flowers
with TRIMORPHIC HETEROSTYLY (LyiJirum salicaria, and some species of
Oxalis) in which there are two circles of stamens and three variations
in the height of the stigmas and anthers.

In a great number of flowers self-pollination is made mechanically
impossible, as their own pollen is prevented by the respective positions
of the sexual organs from coming in contact with the stigma
(HERCOGAMY). In the Iris, for example, the anthers are sheltered
under the branched petaloid style. The pollinia of Orchis are retained
in position above the stigma ; in Asdepias the five pollinia are attached
in pairs to swellings of the style by adhesive discs (cf. Fig. 746).

Sometimes hercogamy and dichogamy occur together. The flowers of
Aristolochia clematitis (Fig. 534) are protogynous. The conveyance of pollen

DIV. n

SPERMATOPHYTA

561

from the older to the younger flowers is effected by small insects. The flowers at

first stand upright with a widely-opened mouth (Fig. 534 I), and in this condition

the insects can easily push past the

downwardly - directed hairs which

clothe the tubular portion of the corolla

and reach the dilated portion below.

Their exit is, however, prevented by

the hairs until the stigma has withered

and the anthers have shed their pollen.

When this has taken place (Fig. 534 II)

the hairs dry up, and the insects

covered with pollen can make their

way out and convey the pollen to the

receptive stigmas of younger flowers.

All these varied and often highly
specialised arrangements to ensure
crossing indicate a tendency to favour
the union of sexual cells which differ
in their hereditary characters more
widely from one another than would
be the case if derived from the same
flower. The progeny from allogamous
fertilisation tend to be stronger than
from autogamous fertilisation.

In certain plants in addition to the
large CHASMOGAMOUS flowers, pollin-
ated by wind or insects, small incon-
spicuous flowers occur which never open
and only serve for self- fertilisation ;
these CLEISTOGAMOUS flowers (6) afford
a further means of propagating the plant, while the plants have the opportunity
of occasional cross-pollination owing to the presence of the large chasmogamous
flowers. Cleistogamy is of frequent or regular occurrence in species of Impatiens,
Viola, Lamium, and Stellaria, in Specularia perfoliata, Juncus bufonius, etc.
Polycarpon tetraphyllum has only cleistogamous flowers.

Development of the Sexual Generation in the Phanerogams

A. In the Gymnosperms (") a prothallium consisting of a few cells
is formed on the germination of the MiCROSPORE. This lies within the
large cell, which will later give rise to the pollen-tube, closely
applied to the cell wall ; the nucleus of this cell is marked k in Fig.
536 A, The first-formed cell (p) corresponds to the vegetative cells of
the prothallium. The SPERMATOGENOUS CELL (sp), which is cut off
last, divides later into the MOTHER CELL OF THE ANTHERIDIUM (Fig.
536 B, m), and a STERILE SISTER CELL (s) adjoining the prothallial
cell. It is by the breaking down or the separation of the sterile
sister cell that the antheridial mother cell becomes free to pass into
the pollen-tube. There, or before its separation, it divides into two
daughter cells ; these are the GENERATIVE CELLS or MALE SEXUAL CELLS.

FIG. 534. — Flowers of Aristolochia dematitis cut
through longitudinally. /, Young flower in which
the stigma (N) is receptive and the stamens (S)
have not yet opened. II, Older flower with the
stamens opened, the stigma withered, and the
hairs on the corolla dried up. (x 2. After
F. NOLL.)

562

BOTANY

PART II

(a) Cyeadeae

In the Cyeadeae and in Ginkgo these male cells still have the
form of spermatozoids, and thus connect directly with the hetero-
p sporous Archegoniatae. Their mode of development
is shown for Zamia in Fig. 536. The description
of the figure deals with the details. As is further
shown in Fig. 537 (a) the two spermatozoids remain
for a time back to back attached to the sister cell of
FIG 535.-Poiien.grain the antheridium ; after their separation (b) they round

of Ginkgo biloba still . . .•,•,•/ J . ,,

within the micro- °"» the anterior end being provided with a spirally-
sporangium. (x arranged crown of cilia by means of which they
are capable of independent movement (Fig. 538).

The female cones of Zamia bear numerous sporo-
phylls, the hexagonal shield-shaped terminal expansions (Fig. 583) of
which fit closely together. Each sporophyll bears a pair of macro-

300. After STRAS-

BURGER.)

FIG. 536. — Formation of spermatozoids in Zamia floridaiia. A, Mature pollen -grain (x 800);
v, vegetative prothallial cell— the dark streak at its base indicates the position of another
crushed cell ; fc, nucleus of the pollen-tube ; sp, spertnatogenous cell. B, C, D, Stages in the
development of the antheridium (B, C x 400 ; D x 200) ; v, persisting vegetative cell growing
into the sterile sister cell of the antheridium (s) ; m, mother cell of the antheridium, i.e.. mother
cell of the spermatozoids; e,exine. Inthemother cell the large blepharoplasts (W) which form the
cilia are visible ; in B and C they are star-shaped, while in D they are composed of small granules,
which will form the cilium-forming spiral band. Starch-grains are present in the pollen-tube,
and in C they are appearing in the vegetative cell and the sister cell, both of which in D are
packed with starch. In D the two spermatozoids (sp) derived from the mother cell are seen
divided from one another by a wall. (After H. J. WEBBER.)

sporangia. The macrosporangium consists of the nucellus and an
integument. The micropyle forms an open canal above the tip of

DIV. n

SPERMATOPHYTA

563

the nucellus. At the period during which the male cones are shedding

their pollen, the macrosporophylls become slightly separated from

one another so that the wind-

borne pollen -grains can readily

enter. A more or less extensive

cavity (POLLEN -CHAMBER, Fig.

539) has by this time been formed

at the apex of the nucellus, while

the disintegrated cells, together

perhaps with fluid excreted from

the surrounding cells of the

nucellus, have given rise to a

sticky mass which fills the micro-

pylar canal and forms a drop at FlG- ssr.-Upper end of the pollen-tube of z

™, ,, r . floridana, showing the vegetative proth

its entrance. The pollen-grams
reach this drop and, with the
gradual drying up of the fluid,
are drawn through the micropylar
canal into the pollen-chamber.

During the development of
the pollen-tube (Fig. 510) and the formation of the motile spermato-
zoids, the embryo-sac filled with the prothallial tissue is increasing in
size within the nucellus. As in the Coniferae the embryo-sac arises
by the tetrad division of an embryo-sac mother cell which usually

floridana, showing the vegetative prothallial
cell (<•), the sterile sister cell (s), and the two
spermatozoids. o, Before movement of the
spermatozoids has commenced ; b, after the
beginning of ciliary motion ; the prothallial cell
is broken down and the separation of the two
spermatozoids is taking place, (x circa 75. After
H. J. WEBBER.)

FIG. 538.— Zamia floridana. Mature, free-
swimming spermatozoid. (x 150. After
H. J. WEBBER.)

FIG. 539. — Longitudinal section of
a young macrosporangium of
Ginkgo biloba. m, Micropyle ; i,
integument ; p, pollen-chamber ;
e, embryo-sac ; w, outgrowth of
sporophyll. (x 35. After
COULTER and CHAMBERLAIN*.)

crushes the other sporogenous cells, as in the case of the macro-
sporangium of Selaginella. As it crushes the tissue of the upper
portion of the nucellus it approaches the base of the pollen-chamber.

2oi

564

BOTANY

PART II

At the apex of the embryo-sac are found the archegonia, usually four
in number, and separated from one another by some layers of cells.

Fie. 540. — Dioon edule. Upper portion of the nuceilus at the period of fertilisation. The pollen-
tubes have grown down from the pollen-chamber through the nuceilus after becoming
attached by lateral outgrowths. They have reached the archegonial chamber and two of
them have already liberated their contents. Two large archegonia with projecting neck-cells
are present. (After CHAMBERLAIN.)

Each archegonium has a neck, and ultimately cuts off a canal-cell.
The archegonia are situated at the base of a depression in the pro-

DTV. TI

SPERMATOPHYTA

565

thallium, the archegonial chamber (Fig. 540), which in Dioon is about
1 mm. in depth and 2 mm. across. The pollen-tubes grow into this
depression and liberate their spermatozoids together with a drop of
watery fluid in which they swim. The spermatozoids require to
narrow considerably in order to pass through the space between
the neck-cells. The spermatozoid strips off the ciliated band on enter-
ing the protoplasm of the egg, and its nucleus fuses with that of the
latter. The nucleus of the fertilised ovum (Fig. 541) soon divides,
and the daughter nuclei continue to divide rapidly, until after the
eighth division there are about 256 free nuclei within the cell. These

FIG. 541. — Zamiafloridana. An ovum im-
mediately after the fusion of the nucleus
of a spermatozoid with the female
nucleus has taken place. The ciliary
band of the spermatozoid remains in
the upper portion of the protoplasm
of the ovum. A second spermatozoid
' has attempted to enter the ovum,
(x 18. After H. J. WEBBER.)

FIG. 542. — Two young pro-embryos
of Dioon edule showing their
relation to the archegonial
chamber. S, suspensor ; e, em-
bryo. (After CHAMBERLAIN.)

are crowded towards the lower end of the fertilised egg, where cell
walls commence to form between them.

The so-called PRO-EMBRYO is thus formed (Fig. 542), at the
growing end of which the embryo develops from relatively few cells.
The cells farther back elongate greatly and as a SUSPENSOR carry the
embryo into the prothallus. This in Spermatophytes is termed the
ENDOSPERM and serves as a nutritive tissue for the growing embryo.
The latter ultimately develops, at the end directed into the prothallus,
two large COTYLEDONS between which is the rudiment of the apical
bud or PLUMULE. The region of the stem below the cotyledons is
termed the HYPOCOTYL ; it passes gradually into the main root or
RADICLE, which is always directed towards the micropyle.

202

566

BOTANY

PART II

(b) Coniferae

The development of the microspores of the Coniferae when they
germinate differs from the process described above. The prothallial

— - If

FIG. 543. — Development of the pollen-tube. A, B, Pinus laricio (x 300. After COULTER and
CHAMBERLAIN). C, Picea excelsa (x 250. After MIYAKE). p, Remains of the prothallial cells ;
up, spermatogenous cell ; m, antheridium mother cell ; s, its sterile sister cell ; g, generative
nuclei of unequal size in a common protoplasmic body ; A:, pollen-tube nucleus.

cells, the number of which in the ancient genus Araucaria is larger

than in the other Coniferae and the
Cycadeae, soon collapse (Fig. 543
A, B\ and the generative cells never
have the form of spermatozoids.
The gap between the Coniferae and
the Pteridophyta is thus a wider
one.

The Abietineae have two genera-
tive nuclei of unequal size in the
one protoplasmic body ; only the
larger nucleus which goes first is
fertile (Fig. 543 (7, g).

FIG. 544.— Taxus baccata. Longitudinal section In Araucaria the prothallial tissue is
through the sporogenous tissue, showing an highly developed. The spermatogenous
embryo-sac mother cell which has under- cell gives rise to the sterile cell and the
gone the tetrad division ; three of the facul- antheridium mother cell. From the latter
tative macrospores are degenerating, while , , . , . , . , , . . ,

the fourth is undergoing further develop- ^vo generative nuclei, which to begin With
ment. (x 250. After STRASBUROER.) are ot equal size, are produced ; they are

enclosed in a common protoplasmic mass.

In many cases one of the two nuclei appears to gradually diminish in size.

DIV. n

SPERMATOPHYTA

567

Araucaria thus stands nearest to the Abietineae. In the Cupressineae two equal
generative cells are found throughout. Taxus has a single generative cell ; the
sister cell produced on the division of the antheridium mother cell is greatly
reduced.

As a rule the macrosporophylls bear two macrosporangia. The
single mother cell undergoes a tetrad division (Fig. 544), and of the

four resulting cells only one
develops into an embryo-sac
(macrospore). This, as it in-
creases in size, first crushes
its sister cells and later the
whole sporogenous complex of
cells. Meanwhile, by the re-
peated division of the nucleus
and protoplasm, the macro-
spore becomes filled with the

Fio. 545.— Median longitudinal section of an .ovule of
Picea excelsa at the period of fertilisation, e, Em-
bryo-sac filled with the prothalliura ; a, archegonium
showing ventral (a) and neck portion (c) ; o, egg-cell ; FIG. 546. — Archegonium of Pinus laricio
n, nucleus of egg-cell ; nc, nucellus; p, pollen-grains ;
t, pollen-tube; i, integument; s, seed -wing, (x 9.
After STRASBUROER.)

before the separation of the ventral-
canal-cell, (x 104. After COULTER and
CHAMBERLAIN.)

tissue of the prothallium (Fig. 545). The archegonia are formed at
the apex of the prothallium ; each consists of a large ovum and a
short neck. As in the Pteridophytes a small ventral canal-cell is cut
off from the egg-cell shortly before fertilisation (Fig. 546). The
development of the embryo from the fertilised ovum presents great
differences in the several orders and even genera, and the following
description applies to the species of Pinus (Fig. 547 D-K).

By two successive divisions of the nucleus four nuclei are formed
which pass to the base of the egg-cell, where they arrange themselves

568

BOTANY

PART II

in one plane and undergo a further division. Cell walls are formed
between the eight nuclei of this eight-celled pro-embryo. The cells
form two tiers, those of the upper tier being in open communication
with the cavity of the ovum. The four upper cells then undergo
another division (G\ and this is followed by a similar division of the
four lower cells (H). The PRO-EMBRYO thus consists of four tiers, each
containing four cells, the cells of the upper tier being continuous with

FIG. 547.— Picea excelsa (A-C). Pinus laricio (Z)-A~). A, Mature ovum with its nucleus (cm) and the
ventral-canal-cell (d). B, The male nucleus (sri) within the ovum. C, Fusion of the male
and female nuclei. D-K, Description in text ; s, suspensor. (A-C x 55, after MIYAKE ;
D-H x 200, after KILDAHL ; 7, A" x 104, after COULTER and CHAMBERLAIN.)

the remaining portion of the ovum. In the further development of
the three lower tiers the middle tier elongates to form the SUSPENSOR
(K, s), pushing the terminal tier from which the embryo will arise into
the tissue of the prothallium or endosperm ; the cells of the latter are
filled with nutritive reserve material.

In other genera a separation of the four rows of cells takes place,
and each bears a young embryo. As a rule, however, only a single
embryo continues its development in each macrospore, although several
archegonia may have been fertilised. The embryo is formed of the

DIV. II

SPERMATOPHYTA

5t>9

same parts as the embryo in the Cycadeae, but the number of cotyle-
dons is frequently greater than two.

(e) Gnetineae

The last order of Gymnosperms, the Gnetineae, exhibit a peculiar and
isolated course of development. The microspores in their development and

,.\\-

FIG. 548. — Apex of the embryo-sac of Gnetum Rumphianum shortly before the development
of the.female cells, u-k, Female nuclei ; mk, male nuclei ; PK, pollen-tube nucleus ; ps, pollen-
tube, (x 500 )

germination show no essential differences from those of other Gymnosperms ; the
separation of the generative cells is, however, less clear and sometimes wanting
in that two similar nuclei lie in the common protoplasmic investment. The
macrospores show more marked peculiarities. The macrospores of Ephedra and
Welwitschia have well-developed prothallia. Ephedra forms archegonia which on.
the whole resemble those of the Coniferae. Wdwitscliia has elongated cells with
2-5 nuclei which grow from the summit of the prothallus into the tissue of the
nucellus towards the entering pollen-tubes. Their significance as archegonia is
not clear. In Gnetum (Fig. 548) no prothallium is formed, but the embryo-sac

-.70

BOTANY

PART II

becomes filled with protoplasm in which are numerous nuclei. Each of the two
generative cells from the pollen-tube fuses with a female nucleus. Of all the
fertilised cells resulting from the penetration of a number of pollen-tubes to the
embryo-sac only one develops into an embryo.

B. Angiosperms (8)

(a) The MICROSPORES of Angiosperms before they are shed from
the pollen-sac form an antheridial mother cell (Fig. 549 m) which is

Fia. 549. — Pollen-grain of Lilium Martagon and its germination, k, Vegetative nucleus of the
pollen-grain ; m, antheridial mother cell ; </, generative nuclei, (x 400. After STBASBURGKR.)

clearly delimited from the large pollen-tube cell, but is not enclosed
by a cell wall. When the pollen grain germinates on the stigma the
antheridial cell passes into the pollen tube, and its nucleus sooner or
later divides into two generative nuclei (g) which lie free in the proto-
plasm within the pollen-tube without being enclosed in a common
mass of protoplasm. They are of an elongated oval or ellipsoidal

DIV. n

SPERM ATOPHYTA

571

shape and pass one after another down the pollen-tube. The nucleus
of the pollen-tube (k) is usually visible in the neighbourhood of the
generative nuclei. The absence of the small prothallial cells, and of a
sterile sister cell of the antheridium, as well as the absence of a cell
wall from the mother cell of the antheridium, and lastly the presence
of naked generative nuclei instead of generative cells in the pollen-
tube, are points in which the Angiosperms differ from Gymnosperms.

FIG. 550. — Development of the embryo-sac in Polygonum diraricatum. m, Mother cell of the
embryo-sac ; emb, embryo-sac ; st, sterile sister cells ; e, egg-cell ; s, synergidae ; p, polar
nuclei ; a, antipodal cells ; fc, secondary nucleus of the embryo-sac ; cTia, chalaza ; mi, micro-
pyle ; ai, ii, outer and inner integuments ; fun, funiculus. (1-7 x 320, 8 x 135. After
STRASBURQER.)

The reduction of the male prothallium has thus gone so far that only
the indispensably necessary parts remain.

(b) MACROSPORES. -- The characteristic differences which the
Angiosperms show from the general course of development of the
MACROSPORANGIUM in the Gymnosperms commence with the cell
divisions in the single, functional, macrospore-mother-cell resulting
from the tetrad division (Fig. 550, 1-5). The "PRIMARY NUCLEUS of
the embryo-sac" divides and the daughter nuclei separate from one
another. They divide twice in succession so that eight nuclei are
present. After this, cell formation commences around these nuclei
(Fig. 550, 6-8). Both at the upper or micropylar end of the embryo-

572

BOTANY

PART II

sac and at the lower end three naked cells are thus formed. The two
remaining " POLAR NUCLEI " move towards one another in the middle
of the embryo-sac, and fuse to form the "SECONDARY NUCLEUS of
the embryo-sac." The three cells at the lower end are called the
ANTIPODAL CELLS ; they correspond to the vegetative prothallial cells,
which in Gymnosperms and in Gnetum fill the cavity of the embryo-
sac. The three cells at the micro-
pylar end constitute the "EGG
APPARATUS." Two of them are
similar and are termed the SYNER-
GIDAE, while the third, which pro-
jects farther into the cavity, is the
EGG -CELL or OVUM itself. The
synergidae assist in the passage
of the contents of the pollen-tube
into the embryo-sac. Here also
the process of reduction has gone
as far as possible ; in place of the
more or less numerous archegonia
of the gymnospermous macrospore
only a single egg-cell is present.

FIG. 551.— Ovary of Polygonum Convol-
vulus during fertilisation, fs, Stalk-
like base of ovary ; fu, funiculus ; cha
chalaza ; nu, nucellus ; mi, micro pyle
ii, inner, ie, outer integument ; e
embryo-sac ; ek, nucleus of embryo
sac ; ei, egg apparatus ; an, antipodal
cells ; g, style ; n, stigma ; p, pollen
grains ; ps, pollen - tubes. ( x 48.
After SCHENCK.)

FIG. 552.— Funkia ovata. Apex of nucellus,
showing part of embryo-sac and egg
apparatus before fertilisation ; o, egg-cell ;
s, synergidae. (x 390. After STRAS-

BURUER.)

The significance of the synergidae is difficult to determine unless they
are regarded as archegonia which have become sterile or, with TREUB
and PORSCH, as neck cells of an archegonium transformed to the
egg apparatus (Fig. 552).

In some cases the mother cell of the embryo-sac does not undergo a tetrad
division, but forms only three or two daughter cells or is directly transformed into
the embryo-sac without dividing. The last is the case in Lilium, where the mature
embryo-sac contains the usual eight nuclei. In Cypripedium and Plumbagella, on
the other hand, the number of nuclei is reduced to four by the omission of the last

DIV U

SPERMATOPHYTA

573

division. There may then be an egg-cell, an antipodal cell, and two polar nuclei,
or alternatively in Cypripedium an egg-cell, two synergidae, and one polar nucleus.
In all these cases the reduction division takes place in the embryo-sac, being trans-
ferred from the end of the sporophyte generation to the commencement of the
gametophyte generation.

The microspores, which cannot reach the macrospore directly,
germinate on the stigma (Fig. 551). The pollen-tube penetrates for
the length of the style, and as a rule the tip enters the micropyle
of an ovule and so reaches the apex of the nucellus. This most usual
course of the pollen-tube is termed POROGAMY, but many cases of
departure from it have become known of recent years.

FIG. 553. — Ovule of Ulmus ])eduncuh/tu.
es, Embryo-sac; m, micropyle; ch,
chalaza ; t, pocket-like space between
the integuments. The pollen-tube,
ps, penetrates directly through the
two integuments and reaches the apex
of the nucellus. (After NAVVASCHIN.)

FIG. 554.— Longitudinal section of an ovary of
Juglans regia to show the chalazogamy. ps,
Pollen-tube ; e, embryo-sac ; cha, chalaza.
(Somewhat diagrammatic, x 6.)

TREUB first showed in Oasuarina that the pollen-tube entered the
ovule by way of the chalaza, and thus reached the peculiar sporo-
genous tissue, which in this case develops a number of macrospores
or embryo-sacs. CHALAZOGAMY, as this mode of fertilisation is
termed in contrast to POROGAMY, has been since shown, especially by
NAWASCHIN, to occur in a large number of forms. These belong to
the Casuarinaceae, Juglandaceae, Betulaceae, Ulmaceae, Celtoideae,
Urtioaceae, Cannabinaceae, and Euphorbiaceae, which all have the
common character of the pollen-tube growing within the tissues, and
avoiding entrance by the micropyle. This in some cases (Urticaceae)
becomes closed or, as in the Euphorbiaceae, is covered by the obturator.
The pollen-tube makes its way to the embryo-sac sometimes from the
chalazal end and sometimes from the side of the ovule (Fig. 553),

574 BOTANY TART n

penetrating the tissues that lie between it and the egg apparatus.
Since, according to the opinion of many authors, the families
mentioned above stand at the lower end of the series of Dicotyledons
where a connection with the Gymnosperms might be looked for, this
type of fertilisation may be regarded as departing from the behaviour
of the more numerous porogamic Angiosperms and approximating to
the original relations in Gymnosperms. In the latter the whole over-
lying tissue of the nucellus has to be penetrated by the pollen-tube
to reach the embryo-sac (Figs. 545, 553, 554).

In a more recent work NAWASCHIN shows that there are also
indications in the development of the contents of the pollen- tube that
these forms are at a lower stage than the majority of Angiosperms.

In Juglans the two generative nuclei remain
enclosed by a common protoplasmic mass
K (^g- 555) which even enters the embryo-

sac > ^ then gradually disappears and the
naked nuclei emerge and fulfil their re-
spective functions. NAWASCHIN points
out that these relations agree with what
is found in many Gymnosperms. Thus
WM cL they afford a further clear indication that
the transition from the latter group is
to be looked for in these lower families
of the Angiosperms.

When the pollen-tube, containing the
two generative cells, has reached the

Fir, ^.-Juglans nigra. a, Part of ernbryO-saC, its Contents CSCape and pass
the embryo -sac in longitudinal . J r. 1

section before fertilisation, sho*- by way of one of the synergidae to the
ing the relation of the bimicieate ovum ; the corresponding synergida then

rCS±££:±S£ dies- One of the two senerative

magnified. (After NAWASCHIN.) f US6S With the IlUCleUS of the OVlim, w

then becomes surrounded by a cellulose

wall. The second generative nucleus passes the ovum and unites with
the large secondary nucleus of the embryo-sac to form the ENDOSPERM
NUCLEUS (Figs. 556, 557). Both the male nuclei are often spirally
curved like a corkscrew, and NAWASCHIN, who first demonstrated the
behaviour of the second generative nucleus, compares them to the
spermatozoids of the Pteridophyta. The further development usually
commences by the division of the endosperm nucleus, from which a
large number of nuclei lying in the protoplasm lining the wall of the
embryo-sac are derived. The endosperm arises by the formation of
cell walls around these nuclei and their proper surrounding proto-
plasm, and by the increase in number of the cells thus formed (Fig.
565 A) to produce a massive tissue.

The distinctive feature of the development of the endosperm in
Angiosperms from the prothallus of Gymnosperms -lies in the

DIV. n

SPERMATOPHYTA

575

interruption which occurs in the process in the case of the endosperm.
In the embryo-sac, when ready for fertilisation, only an indication of
the prothallus exists in the vegetative, antipodal cells. The true
formation of the endosperm is dependent on the further development
of the embryo -sac, and waste of material is thus guarded against.
The starting-point of this endosperm formation is given by the
secondary nucleus of the embryo-sac, which needs to be stimulated

FIG. 556.— Fertilisation of Lilium Martagon. One
of the male nuclei is close to the nucleus of
the ovum, the other is in contact with the
nuclei of the embryo-sac. Lettering as in Fig.
557. (Diagrammatic.)

FIG. 557. — A, Embryo-sac of HtHanthiis
annuus (after NAWASCHIN). B, The male
nuclei more highly magnified, ps, Pollen-
tube ; sj, .«2, synergidae ; spi, sp%, male
nuclei ; ov, egg-cell ; efc, nucleus of em-
bryo-sac ; a, antipodal cells.

by fusion with the second generative nucleus to form the endosperm
nucleus, before it enters on active division.

From the fertilised ovum enclosed within its cell wall a PRO-
EMBRYO consisting of a row of cells is first developed ; the end cell
of this row gives rise to the greater part of the EMBRYO (9). The
rest of the pro-embryo forms the SUSPENSOR. Between the embryo
and suspensor is a cell known as the HYPOPHYSIS, which takes a
small part in the formation of the lower end of the embryo. The
segmentation of the embryo presents differences according to whether
the plant belongs to the Monocotyledons or Dicotyledons. IN THE

LATTER, TWO COTYLEDONS ARE FORMED AT THE END OF THE GROWING

576

BOTANY

PAKT IT

EMBRYO (Fig. 558), AND THE GROWING POINT OF THE SHOOT
ORIGINATES AT THE BASE OF THE DEPRESSION BETWEEN THEM.
MONOCOTYLEDONS, ON THE OTHER HAND, HAVE A SINGLE LARGE
TERMINAL COTYLEDON, THE GROWING POINT BEING SITUATED
LATERALLY (Fig. 559). In both cases the root is formed from the
end of the embryo which is directed towards the micropyle ; its
limits can be readily traced in older embryos.

After fertilisation a considerable accumulation of reserve materials is necessary
in the embryo-sac both for the development of the embryo and for its future
use. It is thus of importance that a means of transfer of these materials
should exist. In the simplest cases the endosperm simply enlarges, crushing the
surrounding tissues of the nucellus ; often the antipodal cells, which are the
structures which lie nearest to the chalaza, are entrusted with the function of

FIG. 558. — Stages in the development of the embryo of Capsella bursa
pastoris (A-D). h, Hypophysis ; et, suspensor ; c, cotyledons ; p,
plumule. (After HANSTEIN, magnified.)

FIG. 559. — Young embryo
of Alisma Plantago. c,
Cotyledon ; v, growing
point. (After HANSTEIN,
magnified.)

nourishing the embryo-sac. They then increase in number and sometimes undergo
considerable further development. Other portions of the embryo-sac may grow
out as long haustoria which sometimes emerge from the micropyle and some-
times penetrate the tissue beneath the chalaza. In some cases, especially in
insectivorous and semi-parasitic plants, a special store of reserve material is laid up
in this position for transference to the macrospore (Fig. 560).

A further departure in the mode of development of the embryo-sac and embryo
is met with in some plants which live under quite peculiar conditions of life, such
as the Podostemaceae which occur in rushing mountain streams in tropical and
sub-tropical regions. In this case during the short dry period the immature
flowers rapidly develop at the cost of material which has been previously stored
up. Pollination, fertilisation, and the development of the seed are rapidly
effected in a shortened form, so that on the return of the aquatic conditions the
ripe seeds find the conditions for germination and serve to multiply and spread
the plants.

In some cases plants have more or less completely lost the
capacity for sexual reproduction, which has been replaced by other

DIV. n SPERMATOPHYTA 577

modes of reproduction that can often be distinguished only by
careful investigation. In place of the various expressions used by
STRASBURGER and WINKLER which involve obscurity, the definitions

Fin. 5'iO.— Haustoria of the embryo-sac of Melampyrum nemorosum (after BALICKA-IWAXOWSKA).
b, Haustoria of the chalazal end ; c, nutritive tissue ; d, branch of the vascular bundle ; e,
funicle ; /, embryo; (/, the suspensor; a, alt ay/, haustorial tubes arising early from the micro-
pylar end, spreading widely in the funicle and sometimes penetrating the epidermis ; h, the
base of attachment of these ; i, cross-walls in the tubes.

of A. ERNST (10) may be employed. According to him PARTHENO-
GENESIS is the apomictic (i.e. resulting without fertilisation) develop-
ment of gametes (especially egg-cells) of a sexually differentiated and
sexually functional plant or animal, whether the process is autonomous

578 BOTANY PART n

or induced by external conditions. It occasionally alternates with
sexual reproduction, especially in lower plants in which the reduction
division follows on the union of the gametes, and results from the
influence of external conditions on the gametes.

APOGAMY, on the other hand, is the obligate apomictic formation
of an embryo from cells of a diploid or heteroploid gametophyte.
Ovogenic apogamy is when the young plant arises without a sexual
process from the egg-cell. Somatic apogamy is when it arises from
other cells of the gametophyte. APOSPORY is the complete omission
of spore formation.

Thus in Fig. 561 a case of the apomictic development of adventitious
embryos is represented. Vegetative growths from synergidae or
from adjoining cells of the nucellus form in the embryo-sac and affect
or completely prevent the development of the fertilised egg. Nucellar

FIG. 5(51. — Vegetative formation of embryos in Funkia ovata. n, Nucellus with cells in process
of forming the rudiments (ae) of the adventitious embryos ; S, synergidae ; E, egg-cells, in
the figure on the right developing into an embryo ; n, inner integument. (After STRASBURGER.)

embryos of this kind are formed only after the stimulus of pollination
in Funkia and Citrus aurantium. In the well-known Euphorbiaceous
plant Caelebogyne ilicifolia, which occurs in cultivation in female
specimens only, and in species of Calycanthus, it takes place without
this stimulus. In these two latter cases we have complete loss of
sexuality and somatic apogamy. Numerous cases of ovogenic
apogamy have been discovered of recent years. In Alchemilla,
Thalidrum, Taraxacum, etc., the pollen grains are usually functionless
and the reduction of chromosomes in the development of the embryo
sac is suppressed, so that the nuclei retain the diploid number of
chromosomes ; the plants have become apogamous. According to the
investigations of OSTENFELD and ROSENBERG, the genus Hieracium
is of special interest, since the formation of the embryo within the ovule
may commence in very various ways. In most cases a tetrad formation
accompanied by a reduction division takes place, but only some of
these ovules are found to have a normal embryo -sac capable of
fertilisation; as a rule this is displaced by a vegetative cell which
develops into an embryo-sac aposporously (Fig. 562). In exceptional
cases apogamous embryo-sacs are formed.

DTV. H

SPERMATOPHYTA

579

The Seed

The entire structure developed from the ovule after fertilisation
is termed the SEED. Every seed consists of the more or less advanced
EMBRYO developed from the fertilised ovum, the ENDOSPERM surround-
ing the embryo, and the pro-
tective SEED-COAT. The seed-
coat always is derived from
the integument or integu-
ments ; their cells, by the
thickening, suberisation, and
lignifi cation of the walls, give
rise to an effective organ of
protection against drying and
injury for the dormant young
plant within. A special de-
velopment of the epidermis of
the seed into mucilage cells
is of frequent occurrence
(Quince, Linum, many Cruci-
ferae, etc.). The mucilage
serves as a first means of
fixation in the soil and also
retains wTater which is neces-
sary for germination. Such
other features of the surface
as hairs, prickles, etc., have
usually the former function,
if they do not stand in relation
to the distribution of the seed.

Points of morphological
importance in the seed -coat
are (1) the MICROPYLE, (2)
the HILUM ( = place of attach-
ment to the funicle), and (3)
the RAPHE. From what was

Said above (p. 540) it follows FlG> 5(32-~ Aposporous origin of the embryo -sac of

that the micropyle and hilum

will lie at opposite poles of

the seed when the ovule is

atropous (Fig. 508). In seeds

derived from anatropous ovules (i.e. those in which the funicle lies

along one side of the ovule, which is bent round at the chalaza) the

hilum and micropyle are close together. Only seeds of this kind

possess a raphe connecting the hilum and chalazal region. Campylo-

Hieracium flagellare. o, Normal tetrad of macro-
spores ; 6, c, the disorganisation of this. The
diploid embryo-sac arises from a cell of the integu-
ment that is recognisable in a. (After ROSENBERG
and A. ERNST, 1918.)

580

BOTANY

PART II

tropous ovules develop into seeds resembling those derived from
anatropous ovules, but the embryo is curved.

In some cases the function of the seed-coat is modified owing to the protection of
the seed or seeds being undertaken by the pericarp ; this or its innermost layers
are developed as sclerotic cells and form the stone of the drupe or shell of the
nut. In such cases (e.g. Almond, Cherry-Laurel, Cherry, Pepper, etc.), since any
special development of the seed-coat is unnecessary, it tends to become reduced ;
its cells do not thicken or modify their walls and the various layers become
simply compressed.

The nutritive tissue in the seeds is developed, in the case of
Gymnosperms (except in Gnetum\ by the time of fertilisation and

FIG. 563. — Part of section throligh one of the
cotyledons of the Pea, showing cells with
reserve material, am, Starch grains ; al,
aleurone grains ; p, protoplasm ; n, nucleus,
(x 160. After STRASBURGER.)

FIG. 564. — Transverse section of the seed of CoZ-
chicum, showing the reserve-cellulose of the
endosperm within the seed-coat.

constitutes the prothallium (cf. p. 565). This fills the embryo-sac and
nourishes the embryo, which grows down into it. The surrounding
tissue of the nucellus becomes crushed so that the embryo-sac extends
to the seed-coat. The cells of the endosperm are packed with reserve
materials (starch, fat, proteid), and these are utilised in the further
development of the embryo ; this takes place on germination,
usually after a period of rest.

The nutritive tissue in the Angiosperms (and of Gnetum) arises, on
the other hand, after the egg-cell has been fertilised. It originates
from the secondary nucleus of the embryo-sac derived by the fusion
of the two polar nuclei. This is stimulated to division after fusion
with the second generative nucleus. The nuclei produced by this
process of division are distributed in the protoplasm which lines the wall
of the embryo-sac, and when a large number has been formed the

DTV. n

SPERMATOPHYTA

581

protoplasm divides to form numerous cells. These by further division
fill the whole embryo-sac with the tissue of the endosperm.

In Angiosperms also the endosperm as a rule compresses the
remains of the nucellus. Reserve

materials such as starch, fatty oil, " ES^r- B

and aleurone grains are accumulated
in the cells (Fig. 563) ; in other
cases the greatly thickened walls
form a store of reserve cellulose

FIG. 565. — A, Seed of Hyoscyamus niger, showing
the dicotyledonous embryo embedded in the
endosperm ; B, seed of Elettaria Cardamomum,
enveloped by a thin aril ; the white, mealy
perispenn next to the seed-coat encloses an
oleaginous endosperm (shaded), in which the
monocotyledonons embryo lies embedded.
(After BERG and SCHMIDT.)

FIG. 566. — Capsella bursa pastoris. A, Longi-
tudinal section of a ripe seed; h, hypocotyl;
c, cotyledons ; v, vascular bundle of the
funicle ( x 26). B, Longitudinal section of
the seed -coat after treatment with water ;
e, the swollen epidermis ; c, brown, strongly
thickened layer ; *, compressed layer of
cells; a, the single persisting layer of
endosperm cells containing aleurone grains.
(x 250. After STBASBURGER.)

(Fig. 564). In a few cases, as in Piperaceae, Scitamineae, etc., the
nucellus persists and also serves as a nutritive tissue; it is then

nucellus persists and also serves as a

FIG. 567. — A, Seed of Papaver Rhoeas; fe,
the hilum. B, Seed of Corydalis ochro-
leuca ; m, micropyle ; c, caruncula.
C, Seed of Chel idonium majus. D, Seed
of Xymphaea alba with its arillus.
(After DUCHARTRE.)

FIG. 568. — A. Myristica fragrans, seed from which the
arillus (ar) is partly detached. B, Myristica argentea,
seed after removal of the arillus ; Ch, chalaza ; r,
raphe ; h, hilum. (After WARBURG, f nat. size.)

termed PERISPERM (Fig. 565 B}. When lamellae of the perisperm
or of this and the seed-coat grow into the endosperm, they usually
differ from the latter in colour and contents ; the endosperm is then
said to be ruminated (Myristica, Areca).

582

BOTANY

PART I

In very many cases, e.g. Leguminosae Cruciferae, etc., not only
is the nucellus absorbed by the endosperm, but the latter is com-
pletely displaced b}r the embryo. The reserve materials are then
stored up in the cotyledons or in the whole body of the embryo
(Fig. 566).

Lastly, a structure known as the ARILLUS must be mentioned,
which usually stands in relation to the distribution of the seeds. It
arises as a succulent and usually brightly coloured outgrowth from
the funicle. It grows up around the ovule and ultimately comes to
invest the seed more or less completely (Figs. 567 D, 568, 586).
An outgrowth in the neighbourhood of the micropyle, which is found
in the Euphorbiaceae, is termed a CARUNCULA (Fig. 567 C, #).

The Fruit (n)

The effect of fertilisation is not only seen in the macrosporangia
but extends to the macrosporophylls or carpels. The structures of

very various form which are
formed from the carpels (often
together with the persistent
calyx and the floral axis) are
called FRUITS, and serve
primarily to protect the de-
veloping seeds. In Gymno-
sperms, where the ovules are
borne freely exposed on the
carpels, no fruits in the strict
sense can exist, since no ovary
is present. Thus in Cycas,
Ginkgo, Taxus, Podocarpus,

FIG. 569.-Collective fruit of Rosa alba, consisting of Gnetum, and Ephedra W6 Can
the fleshy hollowed axis s', the persistent sepals s, Only Speak of Seeds and not of

<aifl£eD?r^ fruits- When> however, the

carpels after fertilisation close

together as in the cones of some Gymnosperms and the berry-like
cones of Juniperus, a structure analogous to the angiospermic fruit is
formed, and the term fruit may be used.

A great variety in the development of the fruit in Angiosperms
might be anticipated from the range in structure of the gynaeceum
described above. The simplest definition of a fruit is the ripened ovary,
but difficulties arise in the case of apocarpous gynaecea.

The product of the individual carpels associated in such apocarpous gynaecea
as those of the Rosaceae will here be termed PARTIAL FRUITS or FRUITLETS, while
the product of the whole gynaeceum will be spoken of as the FRUIT or the
COLLECTIVE FRUIT. The hollowed-out or projecting floral axis bearing the carpels
may be included in the fruit. Thus the Strawberry is a collective fruit composed

DIV. n

SPERM ATOPHYTA

583

of the succulent receptacle bearing the small yellow nut-like fruitlets. In the
Apple the core only is the fruit, the succulent tissue being derived from the
hollowed floral axis surrounding and fused with the carpels. In the Rose there is
similarly a collective fruit, the fruitlets being the hard nutlets enclosed by the
succulent receptacle (Fig. 569). In the case of fruits resulting from syncarpous
gynaecea the further development of the wall of the ovary as the PERICARP has to
be especially considered. The outermost, middle, and innermost layers of this are

Fir;. 570. —Modes of dehiscence of capsular fruits. A, B, Capsule of Viola tricolor before and after
the dehiscence; C, poricidal capsule of Antirrhinum majus (magnified); D, E, pyxidium of
Ancujdllis arvensis before and alter dehiscence.

distinguished as EXOCARP, MESOCABP, and EXDOCARP respectively. According to
the nature of the pericarp the forms of fruit may be classified as follows :

1. A fruit, with a dry pericarp, which opens when ripe, is termed
a" CAPSULE (Fig. 570).

When dehiscence takes places by a separation of the carpels along their lines of
union the capsule is SEPTICIDAL ; when the separate loculi open by means of a
longitudinal split, it is termed LOCULICIDAL, and when definite circumscribed open-

Fio. 571.— Dry indehiscent fruits. A, Xut of Fumaria
officinalis (x C). B, Achene of Fagopyntm esculent urn
(x 2). (After DUCHA.RTRE.)

FIG. 572.— Schizocarp of Galium,
mottugo. (x 6. After Du-

CHARTRE.)

ings are formed, it is termed PORICIUAL. As special types of frequent occurrence
may be mentioned : the FOLLICLE, which is a capsule developed from a single
carpel and opening by separation of the ventral suture, e.g. Aconitum (Fig. 644) ;
the LEGUME or pod, which differs from the follicle in dehiscing by both ventral
and dorsal sutures, e.g. Laburnum (Fig. 711).

2. DRY INDEHISCENT FRUITS have a dry pericarp which does
not open at maturity. Those with a hard pericarp are termed NUTS,
e.g. Hazel-nut, Lime (Fig. 669), Helianthiis (Fig. 784 A).

584

BOTANY

3. When a dry fruit, consisting of several carpels, separates at
maturity into its partial fruits without the latter opening, it is
termed a SCHIZOCARP (e.g. Umbelliferae, Malm, Galium, Fig. 572).

4. A BERRY (Fig. 573) is a fruit in which all the layers of the
pericarp become succulent, as in Vaccinium, Fitis, etc.

5. In the DRUPE the pericarp is differentiated into a succulent
exocarp and a hard endocarp. Prunus Cerasus (Fig. 697) and Juglans
regia (Fig. 602) are familiar examples.

When, on the other hand, the group of fruits borne on an
inflofescence has the appearance of a single fruit, the structure may be
termed a SPURIOUS FRUIT. The Fig (Ficus) is the best-known example
of this, but similar spurious fruits are especially frequent in the
v^ Urticaceae and Moraceae. The com-

& «i parison of a Blackberry which is

the product of a single flower with
the spurious fruit of the Mulberry

Fia. 573.— Fruit of Physalis alkekengi,
consisting of the persistent calyx
s, surrounding the berry fr, derived
from the ovary. (After DUCHARTRE.)

FIG. 574.—^, Collective fruit of Rubus fruti-
cosus, consisting of a number of drupes.
B, Inflorescence of Mulberry (Morus nigra)
bearing a number of small drupes. (After
DUCHARTRE.)

will show how closely the two structures may resemble one another
(Fig. 574).

Distribution of Seeds (12)

The most important means by which Spermatophytes compete with
others living under the same conditions is to produce as many seeds
as possible. With the number of descendants the probability that some
at least will succeed is increased. The number of seeds by itself
would, however, be of little avail if all the seeds remained in the place
of their origin. Thus good arrangements for the distribution of the
seeds are of the greatest importance, and the form and construction of
fruits and seeds exhibit the great influence of this factor.

The same agents are available in the distribution of seeds as in
the conveyance of pollen — -currents of air and water, animals, and in
addition human traffic. A distinction must be made, however, between
the conveyance of pollen and of seeds, in that while a pollen grain is

DIV. n

SPERMATOPHYTA

585

extremely small and weighs very little, seeds contain a certain
amount of reserve materials and are thus larger and heavier. In
spite of this the transport of seeds by the wind is the main means of
their dispersal.

Often the suitability of seeds for wind-dispersal is due simply to their minute
size and their lightness ; thus millions of seeds are produced in a capsule of
Stanhopea, and the weight of a seed of Dendrobium attenuatum has been determined
to be about -5$^ milligramme. Thus these Orchids play a part as epiphytes in damp
tropical forests only equalled by Ferns, the spores of which are as light. A much
more common arrangement is found in heavier seeds when the volume is increased
and a large surface is offered to the wind. Either the whole surface of the seed
bears longer or shorter hairs as in the Willow (Fig. 611), Poplar (Fig. 612), and
Cotton (Fig. 667,}, or a longer tuft of hairs is borne at one end as in the
Asclepiadaceae and Apocynaceae (Strophanthus, Fig. 745), and many Gesneriaceae
and Bromeliaceae. An equally frequent arrangement in other families of plants is

Fro. 575.— Winged seed of Pithecoctenium echinatum. (After NOLL. Nat. size.)

the development of a flat wing formed of a thin and light membrane. This in our
Firs (Fig. 591) and Pines (Fig. 593) is split off from the ovuliferous scale, while in
Rhododendron, Bignoniaceae, some Cucurbitaceae (Zanonici), and in the Rubiaceae
(Cinchona, Fig. 766) it develops on each seed within the ovary. In no case is it
more perfect than in Pithecoctenium echinatum (Fig. 575), where the delicate silky
wing leads to the falling seed assuming an almost horizontal position and being
carried far even by a slight breeze.

Other parts of the flower or fruit may be developed as wings, especially when
one-seeded fruits (or schizocarps) are concerned. Examples of this are afforded by
the sepals of the Dipterocarpaceae, the large bract of the inflorescence of the
Lime (Fig. 669), the bract and bracteoles of Oarpinus (Fig. 605), and more
commonly the wall of the ovary as in Betula (Fig. 604), Alnus, Ulmus (Fig. 613),
Polygonaceae (Fig. 618 D), Acer (Fig. 684), Fraxinus (Fig. 739), or the fruits of
the Typhaceae, Eriophorum (Fig. 809) and Anemone (Fig. 641). The same use is
served by the crown of hairs (pappus) which is developed at the upper end of one-
seeded fruits such as those of the Yalerianaceae (Fig. 769) and Compositae
(Figs. 780, 785), especially when it has a parachute-like form due to the later
elongation of the upper end of the fruit as in Taraxacum, Tragopogon, etc.
According to DINGLER the fall in air as compared with that in a vacuum in the
first second is six times slower in the case of the fruits of Cynara Scolymus provided

586

BOTANY

PART II

with scaly hairs ; in Pinus sylvestris the fall is seven times and in Pithecoetenium
thirty times slower.

The distribution of seeds and fruits by ocean currents is important for many
plants. The strand-flora of the Malayan Archipelago, for example, consists, accord-
ing to SCHIMPER'S investigations, exclusively of plants with floating fruits or seeds,
the adaptations of which correspond more or less to those of the Coco-nut (Fig. 821)
which is distributed everywhere on tropical coasts. A thick exocarp consisting of
a coarsely fibrous tissue renders the fruit buoyant and protects the brittle and stony
endocarp from being broken against the rocks and stones of the shore. A very
similar structure is exhibited by species of Barringtonia, Cerbera Odollam (Fig.
576), Terminalia catappa, Nipa fruticans, and many smaller plants belonging to

the shrubby and herbaceous
vegetation of the dunes and
strand. In all cases the
capacity of floating for a long
time is a condition of the dis-
tribution of the seeds and the
success of the species. -•

The distribution of fruits
and seeds by means of animals
depends as a rule upon the
succulent and attractive fruits
serving as food for birds, the
undigested seeds being shed. A
familiar example is afforded by
the Elder (Sambucus nigra),
the black fruits of which are
eaten by various birds in
summer. There are many such
cases, arid for some seeds the
passage through the intestine
of the animal appears to be a
necessary preliminary to ger-
mination. The development of
The an arillus (cf. p. 582) is in many
cases an adaptation to distribute
the seed by means of animals.
The arillus of Taxus with its
bright red colour which surrounds the single seed is greedily eaten by blackbirds ;
the red fruits of Euonymus when they open expose four seeds with bright red arilli,
which are eaten by chaffinches. The Nutmeg is distributed over the islands about
the Moluccas by a large pigeon which is attracted by the bright red arillus around
the black seed which is exposed on the dehiscence of the fruit. In a similar way our
Mistletoe in winter, when little other food can be obtained, is eaten by blackbirds
and other birds ; when the birds clean their beaks the seeds remain attached to the
branches by reason of the viscid substance around them and are able to germinate
in this position. The spread of plants with hooked fruits, etc., such as Galium
aparine, species of Lappa (cf. Fig. 781), Bidens, Xanthium, etc., by means of the
fur of quadrupeds, the general distribution of water-plants from one pond to
another by aquatic birds, and the distribution of the Hazel-nut, etc., by means
of squirrels, do not require detailed description. Lastly, the distribution of certain

FIG. 576.— Fruit of Cerbera Odollam, from the drift.

succulent endocarp is wanting, so that the buoyant tissue
traversed by coarse fibrous strands is exposed. (After

SCHIMPER.)

DIV. n

SPERMATOPHYTA

seeds by means of ants must be mentioned ; these animals are attracted to remove
and accumulate the seeds by the abundance of oil in the elaiosome-containing
tissue of appendages such as the caruncula.

It is a matter of general knowledge that man by his commerce and industry
has exerted great influence on the distribution of food-plants and other plants of
economic value. In this way the seeds of many weeds have been unintentionally
distributed over the inhabited earth, a fact that could be illustrated by numerous
examples.

Germination (1S)

Seeds which have escaped the various risks of distribution require to be soon
covered with soil. Small seeds readily find shelter in cracks or depressions of the
soil and become fixed there owing to special
properties of their surface. Larger seeds
are sufficiently covered by fallen leaves.
The fruitlets of Erodium and other Gerani-
aceae, of Avena sterilis, species of Stipa and
other Gramineae penetrate the soil by the
aid of their hygroscopic curvatures (cf. p.
334, Fig. 275) ; the presence on their sur-
face of backwardly-directed hairs prevents
their losing the position reached. The
burial of the fruits of Arachis hypoguea, Tri-
foliiim suUcrraneum, and OJcenia hypogaea

)

FIG. 577.— Thuja occidental is. A, Median longi-
tudinal section of the ripe seed. B-E, Stages
in germination ; h, hypocotyl ; c, cotyledons ;
r, radicle ; v, growing point of stein. (A x 5 ;
B, C x 2 ; D, E nat. size. After SCHENCK.)

FIG. 578.— Pinus pinea. Germination.
(After SACHS.) I, Longitudinal sec-
tion of the seed ; y, micropylar end.
II, Early stage of germination ; s,
seed-coat ; e, endosperm ; to, primary
root; x, broken -through embryo-sac ;
r, red layer of the seed-coat. Ill,
The cotyledons (c) have escaped from
the exhausted seed ; he, hypocotyl ;
«/, lateral roots.

is brought about by the growth of their positively geotropic stalks, while negative
heliotropism determines the insertion of the fruits of Lin aria cymbalaria into
the crevices of the walls on which the plant lives (cf. p. 351).

When the seeds find sufficient moisture they swell considerably. With this

588

BOTANY

PART II

they lose some of their resistance to such dangers as extremes of temperature and
desiccation ; their former resistance was due to the small proportion of water they
contained. The next step is the rupture of the seed-coat, which, as a rule, is
effected by the emerging root. The root at once bends downwards geotropically
and, by means of its root-hairs, which are especially long and numerous at the

FIG. 579. — Seedlings, a, of Scorzonera
humilis ; b, of Iris pseudamrus. (After
KLEBS.)

FIG. 580. — Section through the upper part
of the fruit of Acrocomia sclerocarpa. S,
The hard shell ; P, the plug which is
pushed out of the shell by the ger-
minating embryo, K ; E, endosperm.
(After PFITZER.)

FIG. 581.— Kandelia Rheedii. The massive root of the
seedling (1) has broken out of the fruit. When
the plant separates from the fruit the root will
become inserted into the muddy soil. (From
SCHIMPER'S Plant-Geography.)

junction of the root and hypocotyl, fastens the seedling in the soil. Meanwhile
the hypocotyl grows and gradually emerges from the seed -coat, while the
cotyledons as a rule remain for a time enclosed in the latter and absorb the
remainder of the reserve material (Figs. 577, 579). This process leads to the
hypocotyl becoming more and more strongly curved, and the tension resulting
from its further growth withdraws the cotyledons from the seed -coat. The
seedling then becomes erect, the leaves are expanded and can assimilate, and thus
its independent life commences. The number of cotyledons is usually 2, but
in some genera of Coniferae varies from 3-oo (Fig. 578).

DIV. n SPERMATOPHYTA 589

This most frequent type of germination is characterised by the cotyledons
being expanded above ground and is termed EPIGEAL. It is nearly always found
in the case of small seeds.

HYPOGEAL germination is for the most part found in large-seeded Dicotyledons,
the cotyledons of which contain the stored reserve materials (e.g. Vicia, faba,
Pisum, Aesculus, Juglans, etc.). It is characterised by the cotyledons remaining
enclosed in the seed-coat after the root has penetrated into the soil ; the epicoty-
ledonary stem emerges from between the cotyledons, becomes erect, and bears the
later leaves in the usual way. While there is a sharp morphological distinction
between the two types of germination, the difference is of little systematic value ;
within the Papilionaceae many intermediate conditions are found, and in the
genus Phaseolus, Ph. vulgaris is epigeal and Ph. multiflonis hypogeal.

The germination of monocotyledonous seeds differs from the cases described
above in that after the main root has emerged the sheathing base of the larger
or smaller cotyled*on emerges from the seed. Its tip remains either for a time
or permanently in the seed, and serves as an absorbent organ to convey the reserve
materials stored in the endosperm to the seedling. The first leaf of the latter
soon emerges from the sheathing base of the cotyledon (Fig. 579 b}. Very hard
seed-coats are often provided with special arrangements to enable the root to
escape. Thus in the coco-nut three openings are present, one corresponding to
each carpel. The opening behind which the tip of the root of the single embryo
is situated is covered by a very thin layer, while the two other openings are
firmly closed. The hard stony seed -coat of another Palm (Acrocomia sderocarpa)
(Fig. 580) has a loosely fastened plug opposite the tip of the root. In the whole
family of the Scitamineae there is a limited thinner region of the hard seed-coat
above the root-tip of the embryo, which is lifted up as a sort of lid on germination.

The so-called " viviparous " plants show peculiar arrangements which can only
be briefly mentioned here (Fig. 581). Vivipary is found in the inhabitants of
tropical mangrove-swamps and is to be regarded as an ecological adaptation to
the conditions of life. The one-seeded fruits germinate while still attached to the
parent plant, i.e. the pericarp is ruptured by the radicle of the embryo which first
grows from the micropylar end of the seed. The hypocotyl which thus becomes
free may attain .the length of over 1 metre in Rhizophora (cf. Fig. 716). This
swells somewhat in the lower part, and the embryo thus hangs by its absorbent
cotyledons which remain in the seed, until it separates from the plant owing to
its own weight, and, falling vertically, sticks into the soft mud.

Arrangement of the Classes, Orders, and Families
CLASS I

Gymnospermae (14)
Order 1. Cycadinae

This includes the single Family Cycadaceae. These are woody plants
restricted to tropical and sub-tropical regions. Cycas is a native of Asia ;
Macrozamia and Bowenia of Australia. Encephalartos and Stangeria are African,
while America has the genera Dioon, Ceratozamia, Zamia, and Microcycas. The
stem, Avhich undergoes secondary growth in thickness, is as a rule unbranched or
forms a sympodium, and bears large, pinnate foliage leaves. These, which are

590

BOTANY

PART II

of firm leathery texture and persist for a number of years, alternate with smaller
scale leaves and form a large terminal crown. The surface of the cylindrical or
tuberous stem is clothed with the scale leaves and the bases of the old foliage

Fio. 582. — Gycas revoluta, female plant in flower. (From a photograph.)

leaves. Mucilage ducts are present in all parts of the plant. The vascular bundles
are collateral, but their xylem consists of tracheides only.

The Cycadaceae are dioecious. Fig. 582 represents a female plant of Cycas
revoluta, in which the growing point forms alternate zones of foliage leaves and
macrosporophylls. When young the foliage leaves are rolled up circinately as
in the Ferns. One of the sporophylls is represented in detail in Fig. 582a. It
shows the pinnate form of the foliage leaf, but is densely covered with brown hairs,

DJV. n

GYMNOSPERMAE

591

and chlorophyll is wanting. Towards the base two to eight macrosporangia are
borne on the margins, in the place of pinnae. It is evident that each female plant
of Cycas which has reached the flowering condition
exhibits a regular succession of flowering and vegeta-
tive periods. The flower represented by the group
of sporophylls is always grown through by the further
development of the apex which does not branch.
The male plant of Cycas and the other Cycadaceae
bear their sporophylls in terminal cones often of

FIG. 582o. — Macros porophyll
(Carpel) of Cycas revoluta.

FIG. 5826.— Microsporophyll (stamen) of Cycas circinalis.

great size, while the further growth of the plant is effected by a lateral bud
which continues the direction of growth of the sympodial axis, displacing the
cone to one side.

The cones consist of numerous sporophylls arranged spirally on the axis. The
microsporophylls bear large numbers of micro-
sporangia on the lower surface (Fig. 5826).

The macrosporophylls of the cone-bearing Cyca- /a /I

daceae are considerably modified as compared
with Cycas, and each bears two marginal macro-
sporangia (Fig. 583). For the developmental
history cf. p. 562.

Order 2. Ginkgoinae

The single representative of the Family of
the Ginkgoaceae which forms this order is
Ginkgo biloba. This tree comes from Japan, but
is often seen in cultivation in Europe. The
long -stalked leaves are divided dichotoniously
into two or more lobes and are shed annually.
The flowers are dioecious. The numerous stamens FIG 5S3._Cernto:amia robusta. Macro.
are situated on an elongated axis which bears sporophy 11 with two macrosporangia.
no enveloping leaves. Microsporaugia with an (After GOEBEL.)
" endothecium " (cf. p. 546). Macrosporangia in

pairs at the summit of short shoots ; sporophylls reduced to a collar-like out-
growth around the base of the sporangium (Fig. 584). Developmental history,
cf. p. 562.

592

BOTANY

PART II

Order 3. Coniferae

The Coniferae include conspicuous trees or shrubs with woody
stems. The possession of small, undivided, firm leaves, flat or
needle-shaped, of xerophilous structure, and usually lasting for several
seasons, is a common character of the plants of the order ; they thus
with a few exceptions, such as the Larch, belong to the evergreen
vegetation. All Conifers are profusely branched, and a distinction
into long and short shoots is evident in the genera Pinus, Larix, and

d It

FIG. 584. — Girikgo biloba. Male branch with flower; the leaves are not yet full-grown, a, b,
Stamens ; c, female flower ; c?., fruit ; e, stone of same ; /, stone in cross section ; g, in longi-
tudinal section showing the embryo ; h, female flower with an exceptionally large number
of ovules borne on separate stalks. (Male flower and c, nat. size ; d, slightly reduced ; the
other figures magnified. After RICHARD ; a-d after EICHLEK.)

Cedrus. In all cases the direction and rapidity of growth of the main
axis differs from that of the lateral branches. This is especially seen
in young individuals ; old trees are often more irregular in outline.

The absence of vessels from the xylem of young plants and from
the secondary wood is an anatomical characteristic (cf . p. 151). Their
place is taken by large tracheides with peculiar bordered pits on the
radial walls ; these form a very uniform wood. The majority of the
Coniferae have resin abundantly present in all the parts of the plant.

The Coniferae in contrast to the Cycadinae are mostly inhabitants
of temperate regions, and are among the trees which approach nearest
to the polar regions. Within the tropics they are mostly confined to
mountains.

DIV. II

GYMNOSPERMAE

593

The Coniferae are divided into two families on account of differ-
ences in the floral structure.

The Taxaceae have female flowers with one or few macrosporangia ;
the latter are usually provided with an arillus. The flowers are usually
not definite cones. Mostly dioecious.

FIG. 585.— Taxus toccata. A. branch with female flowers; . two ovules on the same shoot (nat.
size). B, Leaf with axillary, fertile shoot (x 2). C, Median longitudinal section of a primary
and secondary shoot ; r, vegetative cone of the primary shoot ; a, rudiment of the aril ; c,
rudiment of the embryo-sac : n. nucellus ; i, integument ; w, micropyle (x 4S). (After STRAS-
BIRGER.) l'oiso.\ors.

The Pinaceae, on the other hand, have a number of ovules in each
female flower, the latter being a cone with numerous sporophylls borne
on an axis. Arillus not present. Usually monoecious.

Family Taxaceae. —The plants belonging to this family are grouped in a
number of small genera distributed in the southern hemisphere. The most
important genus is Podocarpus, the numerous species of which are Avidely distributed
in temperate East Asia and in Australia and New Zealand, and also occur as stately
trees on the mountains of the Asiatic tropics. The female flowers are small shoots",

594

BOTANY

PART II

the sporophylls of which are swollen and succulent ; one or two sporophylls bear at
the summit a single anatropous ovule surrounded by a fleshy arillus. The male
flowers, which are borne on the same or on distinct individuals, are small cones
consisting of numerous sporophylls attached to a short erect axis. Each sporophyll
bears two microsporangia on the lower surface ; the microspores are provided with
distended wings.

Taxus baccata is the only European representative of the family. The Yew,
which is now for the most part artificially introduced, had formerly a wide distribu-
tion as an evergreen undergrowth in our native woods (Figs. 585, 586). The
Yew tree attains a height of 10 m. Isolated examples of large size occur. All

FIG. 586. — Taxus baccata, bearing fruits. (£jnat. size.)

the branches are shoots of unlimited growth. The leaves stand on all sides of
the ascending main shoots, but in two rows on the horizontally-expanded lateral
branches. They are narrow, flat leaves and persist for several years. The tree is
dioecious ; the flowers are situated on the lower surface of the twigs and arise in the
axils of the leaves of the preceding year. The male flowers are invested at the base
by a number of scale leaves and contain some 10 peltate stamens, each of which
bears 5-9 pollen sacs. The mode of opening of the sporangia is peculiar. The outer
wall splits at the base and along the side of each pollen-sac, so that the whole stamen
resembles an umbrella turned inside out ; the pollen remains for a time in the
pocket -like depressions, from which it is removed by the wind. The female
flower usually develops singly as a secondary, axillary shoot of the uppermost

DIV. IT

GYMXOSPERMAE

595

scale leaf of a primary shoot ; the apex of the latter is displaced to the side and
does not develop further. Each flower consists of a single, atropous ovule with

Fi«;. 587.— Jfettipmu communis. Twigs bearing fruits and male flowers. § nat. size.) OFFICIAL.
A, Male flower : B, fertile shoot with female flower ; C, female flower with one scale bent out
of place ; D, fruit. (All magnified. After BERG and SCHMIDT.)

one integument. The drop of fluid excreted from the rnicropyle of many Gyrnno-
s perms is especially well shown by the Yew. As the seed develops, a fleshy arillus
springs from its base and surrounds the mature seed like a bright red cup. The

596

BOTANY

PART II

foliage and seed are poisonous, but the aril, which induces birds to distribute the
seed, is harmless.

Family Pinaceae.— This family includes the most important Coniferae, and on
grounds of differences in leaf arrangement and in the position of the ovules is
divided into two sub-families. The forms with the leaves opposite or in whorls
are included in the Cupressineae ; they also have the ovules erect. All the forms
with alternate leaves are included in the Abietineae, and, almost without exception,
they also possess inverted ovules.

FIG. 588. — Juniperus Sabina: branch with fruit. Poisoxous. (After H. SCHENCK.)

Sub-family Cupressineae. — Some of the Cupressineae have needle-shaped leaves
in whorls (Juniper, Fig. 587) ; others have decussately-arranged, scale-like leaves
(Thuja, Juniperus sabina, Fig. 588). The former type is to be regarded as the
more primitive, for the seedlings of Thuja have needle-shaped leaves, and individual
branches of scale-leaved forms of Juniperus revert to the needle-shaped leaves in
whorls of three. The short shoots of Taxodium distichum have two ranks of leaves
and are shed as a whole.

The Cupressineae, with the exception of Juniperus, are monoecious. The male
flowers of Juniperus communis stand in the leaf axils. At their base are a number
of small scale leaves (Fig. 587 A, a}, above which come several whorls of peltate
sporophylls (c) bearing 2-4 microsporangia (d) on the lower surface. The sporangia
open by a vertical slit parallel to the long axis of the sporophyll. The female
flowers occupy a corresponding position. The scale leaves at the base (Fig. 587 B]
are succeeded by a whorl of carpels (C, 6), each of which bears a single upright ovule

DIV. n

GYMNOSPERMAE

597

in a median position (c). After fertilisation a succulent parenchymatous growth
mainly of the basal portions of the sporophylls raises the seeds and presses them
together, without, however, obliterating the central space altogether. The three
carpels become completely coherent above the seeds, but the place of union is still
indicated by the scar at the apex of the ripe fruit. The succulence of the carpels
gives the fruit the appearance of a berry. Juniperus is the only genus of the
Cupressineae with such fruits ; the others, such as Cupressus, Thuja, Taxodium,
have cones, and bear the ovules on a slight outgrowth of the scale.

Juniperus communis, Juniper, is a shrub or small tree distributed over the
northern hemisphere. J. Sabina, a prostrate shrub of the Alps and other moun-

FIG. 589.— Taxodium mexicanum in the churchyard of S. Maria de Tule at Oaxaka.
This giant tree is one of the oldest living. (From a photograph.)

tains of central and southern Europe. The Cypress (Cupressus sempervirens) in
the Mediterranean region. Species of Thuja are commonly grown as ornamental
trees. Taxodium distichum is a deciduous tree, forming extended swampy woods
on the north coast of the Gulf of Mexico from Florida to Galveston. T. mexicanum
is evergreen and is widely distributed on the highlands of Mexico ; very large
specimens occur such as the giant tree of Tule, which at a height of 40 m. was
30 m. in circumference, and was estimated by VON HUMBOLDT to be 4000 years old
(Fig. 589).

Sub-family Abietineae. — The floral structure of the Abietineae may be described
in the first place. The male flowers (cf. p. 544) consist of an axis bearing
scale leaves at the base, and, above this, numerous stamens; the pollen -sacs
(microsporangia) are situated on the lower surface of the stamen. In the Abietineae
in the narrower sense there are two pollen-sacs, but in Agathis and Araucaria

2Q1

598

BOTANY

PAET II

there are 5-15. The microspores are usually winged. The female flowers are
always cones, consisting of an axis bearing the closely approximated scales, which
protect the ovules ; the scales later become lignified. In Agathis and Araucaria
each scale bears a single anatropous ovule at its base. The condition of affairs in
Sequoia and Sciadopitys is similar, but the outgrowth is more clearly denned;
each scale bears 4-9 anatropous ovules. In the Abietineae proper the limits of the
two scales are still more marked. The two anatropous ovules are borne on an

FIG. 590. — Abies pectinata. A, Male flower ; /, scale leaves ; h, sporophylls. B, Bract-scale (d) and
ovuliferous scale (fr), seen from below. C, The same from above, sa, the winged seeds.
(After BERG and SCHMIDT.) D, Abies Nordmanniana with ripe cones, the scales in part
shed. (Reduced from ENGLER and PRANTL.)

inner scale, which, at its base, is continuous with the scale of the cone. THE

OUTER SCALE IS CALLED THE BRACT SCALE, THE INNER THE OVULIFEROUS SCALE

(Figs. 590, 593). The ovuliferous scale is the more strongly developed, and it is
the part that becomes lignified and affords protection to the ovules. Even at the
period of flowering the bract scale is usually concealed by the ovuliferous scale
and only to be detected on close inspection. In other forms, however (e.g. Abies,
Fig. 590, Pseudotsuga Douglasii, etc.), the bract scales even in the older cone
project prominently between the ovuliferous scales.

Most important Genera and Species.— Agathis (Dammara) is distributed in
the Malayan Archipelago and extends to New Zealand ; A. australis and A.

THV. n

GYMNOSPERMAE

599

Dammara yield Kauri Copal but no Dammar Resin ; Araucaria brasiliana and A.
imbricata are stately S. American forest trees. The genus Sequoia includes the
most gigantic trees known ; specimens of S. gigantea from the Californian Sierra
Nevada attain a height of 100 m. and a diameter of 12 m. The beautiful
S. sempervirens from the coastal mountains is hardly inferior in size.

The Silver Fir (Abies pectinata, Fig. 590 A -C] is a native of the mountains of
the middle and south of Europe. It bears only long shoots. The flat, needle-like
leaves, marked below by two white lines and emarginate at the tip, are borne on all

FIG. o'.'l. — Ficea excelsa (\ nat. size). 1, Twig with male flowers. J. Terminal female flower. 3,
Pendulous cone. k. Microsporophyll. 5, Macros porophyll ; the bract-scale is covered by the
large, bent-back, ovuliferous scale ; an ovule is visible at the base of the ovuliferous scale.
6, Ripe seed with the wing funned by a detached portion of the ovuliferous scale, (x 4-6.)

sides of the axis, but are twisted into a horizontal position on the branches
illuminated from above. They live for 6-8 or even for 15 years. The male
flowers stand in the leaf-axils on the under side or on the flanks of the shoot,
and grow downwards so that the pollen-sacs are directed upwards. The wall of
the sporangium opens by an obliquely longitudinal split, which gapes widely and
allows the winged microstores to escape. The female flowers arise from the
upper side of a b*ranch and are directed vertically upwards. The bract-scales
are longer than the broad, ovuliferous scales. The fertilised cones retain the
upright position, and when ripe the scales separate from the axis and so set the
seeds free from the plant. The development of the seeds takes a year. Abies

2 Q 2

600

BOTANY

TART II

Nordmanniana from the Caucasus (Fig. 590 Z>), A. concolor, A. balsamea, and
A. nobilis from N. America are in cultivation.

Picea excelsa, the Spruce (Fig. 591), is a fine tree of pyramidal shape ; it has
no short shoots, and the long shoots bear on all sides pointed, quadrangular,
needle-shaped leaves, which on horizontal or pendulous branches stand more
or less erect. They live for 5-7 years, and on main shoots for 12 years. Male
flowers as a rule on shoots of the previous year ; on flowering they become twisted
into an erect position. The two pollen-sacs open by a longitudinal slit. Female
flowers terminal on the shoots of the previous year, usually near the summit of

the tree. They stand erect at

? the time of flowering. The

ripe cones are pendulous and,
after setting free the seeds from
between the scales, fall in pieces.
The development of the seeds
is completed in one year. Picea
orientalis from Asia Minor,
Picea omorica from Serbia, and
Picea alba from N. America
are frequently cultivated.

Larix europaea, the Larch
(Fig. 592), is one of the few
deciduous Conifers and replaces
its foliage annually. There is
a differentiation into long and
short shoots. The former bear
the narrow linear leaves on all
sides and continue the branch-
ing of the pyramidal tree, the
lower branches of which often
droop downwards. The short
shoots arise in the axils of the
leaves of the long shoots of the
preceding year, and bear a
rosette of 30-40 leaves which are

somewhat shorter but resemble

FIG. W2. -Larix europaea. Long shoots of the preceding thoge of the j shoots The
year, that on the right bearing vegetative short shoots . . .

and that on the left male and female flowers in place of flowers occur in a position corre-
them. (From ENOLER and PRANTL.) spending to that of the short

shoots. The male flowers are

bent downwards when fully developed, and the opening of the upwardly directed
pollen-sacs occurs as in Abies. The erect female cones produce seed in the same
year. Species of Cedrus are evergreen forest trees from the Atlas Mountains,
Lebanon, and the Himalayas, and are grown in pleasure grounds.

The most advanced differentiation of the vegetative organs is found in the
genus Pinus ; P. sylvestris, the Scotch Fir, will serve as an example (Fig. 593).
Young seedlings in the first or second year have long shoots bearing needle-shaped
leaves. On older plants this type of foliage is lost ; the needles are replaced by
colourless, membranous scale leaves in the axils of which stand the short shoots
(cf. the explanation of Fig. 593). The needles are shed in three years. The seeds
ripen in the second year, and are set free by the separation of the scales of the

-1'inus syh-estris (3 nat. size). 1, Shoot of unlimited growth bearing short shoots : at the
top the shoot of the current year. At the base of the latter are numerous male flowers each in
the place of a short shoot, and nearer the tip brown scale leaves, in the axil of each of which
is a short shoot. 2, Similar branch bearing a young female flower at the summit of the shoot
of the current year, in place of a branch of unlimited growth. Two dependent green cones
are borne on the shoot of the preceding year. 3, Cone of the year before last, opened to allow
of th«> escape of the seeds. 4, A microsporophyll. •>, Macrosporophyll from the adaxial side
showing the ovuliferous scale with the two ovules at the base. 6, Macrosporophyll from the
abaxial side showing the small bract-scale below the large ovuliferous scale. 7, Ripe seed with
its wing derived from the superficial layers of the ovuliferous scale, (x 4-7.) OFFICIAL.

601

602

BOTANY

PART II

cone, which till then have been closely pressed together. The cones subsequently
are shed. Pinus montana, a dwarf Pine occurring on mountains ; P. pinea, P.

cembra, Avith edible seeds ; P. laricio, Corsican
Pine from Austria ; P. Pinaster, Maritime Pine
from the Mediterranean region ; P. taecla, P.
Strobus, Weymouth Pine, P. Lambertiana from
N". America.

POISONOUS. — Jtmipents Sabina, Taxus baccata.
OFFICIAL. — Juniperus oxycedrus and other
species yield OLEUM CADINUM ; Juniperus com-
munis, OLEUM JUNIPERI ; Abies balsamea sup-
plies TEREBINTH i NA CANADENSis ; Abies siUrica
supplies OLEUM PINI SIBIRICAE ; Pinus sylvestris
and other species produce OLEUM TEIIEBINTHINAE
and RESINA ; P. sylvcslris, etc., PIX LIQUIDA ;
unofficial products are obtained from other species
of Pinus.

Order 4. Gnetinae

The only Family in this order is that of the
Gnetaceae, to which only three genera belong :
FIG. 594.— Ephedra altissima. 1, Habit Ephedra (Fig. 594), leafless shrubs of warm dry

of a male inflorescence. .?, An
inflorescence with unripe fruits.
(§ nat.

regions of the northern hemisphere ; IVelwitschia
mirabilis (Fig. 595), a monotypic plant from
the deserts of South-West Africa ; the widely
expanded summit of the stem bears after the cotyledons only a single pair of
leaves, which are 1 m. in length and continue to grow at their bases ; Gnctum
(Fig. 597), tropical trees or climbers with broad, reticulately-veined leaves. These

Fig. 595. — Welwitscliia mirabilis. Young plant (from EXCJLER and PRANTL).

genera, while differing widely in appearance, agree in possessing opposite leaves
(in Ephedra reduced to scales), in the development of vessels in the secondary
wood, the absence of resin canals, and in the presence of a perianth to the flowers,
which are usually dioecious (Fig. 596).

These points of agreement with both Gymnosperms and Angiosperms make
the group in many ways an intermediate one between the two classes. Insects
visit the flowers of all three genera, though they are as yet only known to effect

DIV. n

GYMXOSPERMAE

603

pollination in the case of Ephedra campylopoda. On the development of the
sexual generation cf. p. 569.

FIG. 596.— A, Ephedra altissima. Male flower (x 16, after STRASBCRGEB) ; pg, perigone; 6, leaf.
B, Gnctum Gnemon, longitudinal section of a female flower (x 32, after LOTSY); n, nucellus ;
ii, inner, and ai, outer integuments ; pg, integument-like investment or perianth

FIG. 597.— Outturn Gnemon. Branch with male inflorescences, (k nat, size.)

604

BOTANY

PART II

Fossil Gymnosperms (15)

In contrast to what was seen to be the case for the Pteridophyta, Gymnosperms
have not yet been detected in Cambrian and Silurian strata. They appear first in

Mil

^-"

FIG. 598. — 1, Cordaites subglomeratus, longitudinal section of a male flower -bud; bt investing
bracts ; a, stamens with several anthers. 2, A pollen grain ; the prothallial cell is separated
by a curved wall while the rest of the grain is divided into a number of cells. 3, C. Williamsoni,
longitudinal section of a female inflorescence; b, leaves; s, seed in longitudinal section.
4, C. Grand' Euryi, longitudinal section of an ovule, showing the deep pollen chamber in the
nucellus containing a number of pollen grains. (After RENAULT.)

the Devonian, but are sparingly represented and first form an important constituent
of the flora in the Carboniferous. From the Cycadofilices, which possessed steins
with secondary thickening and fern-like foliage and had been regarded as Pteri-
dophyta, OLIVER and SCOTT have recently separated the Pteridospermeae ; which
may be shortly characterised as fern - like seed - plants. These have been con-
sidered in connection with the Pteridophyta (p. 534).

Cordaitaceae. — Cordaites is a peculiar type confined to the Palaeozoic rocks.
Owing to the excellence of the preservation of the remains, its morphology is as

DIV. II

GYMNOSPERMAE

605

well known as that of the existing Gymnosperms. The Cordaitaceae were loft}-,
branched trees with linear or broad and lobed leaves with parallel venation.
Their flowers differ considerably from those of recent Gymnosperms. The
male and female flowers are borne on spike -like axillary inflorescences. The
female flower consists of a single atropous ovule with some bracteoles at its
base ; these resemble the vegetative foliage leaves (Fig. 598, 3, 4). At the
summit of the nucellus is a deeply sunken pollen chamber in which pollen grains
are often met with. The male flowers terminate small shoots that are surrounded
by a number of sterile bracts and at the summit produce a number of stamens
each of which has 2-4 anthers (Fig. 598, 1). An important fact as bearing
on the phylogenv of the group is the presence of a male prothallus as a small

FIG. 599.— Reconstruction of the longitudinal section of the flower of C><"/«"'''"t (Bennettites)
ingens. (From SCOTT after WIELAXD.)

multicellular body (Fig. 598, 2). The ovules and seeds show great structural
agreement with those of Cycas and Ginkgo. With the exception of some less
common fossils (Cycadites, Dicranophyllum), which may be placed with the Gink-
goineae, Cordaitcs is the most richly represented type of Gymnosperm found in the
Carboniferous rocks. Undoubted Cycadophyta make their appearance in the
lower Rothliegende.

The Cordaiteae disappear in the lower Mesozoic strata. The Gymnosperms
flora can be followed through the Trias, in which it consisted of extinct types
of Cycadophyta, Giukgoineae, and Coniferae, to the Jurassic period. In the
latter it attained a great development in that both the Ginkgoineae and the
Cycadophyta attained their maximum development.

Bennettitaccac. — SCOTT has recently given an account of the appearance and
the high degree of organisation attained by the Mesozoic Cycadophyta, from the
knowledge obtained by WIELAND'S study of the abundant material found in North
America. The name Cycadeoidea proposed by the American author is synony-

606

BOTANY

PART II

mous with Bennettites ; fruits derived from the hermaphrodite flowers were
already imperfectly known from European strata under the latter name. The
short and sometimes branched stems resembled recent Cycads in their appearance
and foliage and bore flowers which were hermaphrodite and 12 cm. in length.
A hundred or more spirally arranged perianth leaves surrounded a whorl of 18-20
microsporophylls, which were united at the base to form a deep cup, in the centre
of which the gynaeceum arose (Fig. 599). The pinnate microsporophylls, 10 cm.
in length, resemble the leaves of Ferns, and the microsporangia resemble the

sporangia of the Marattiaceae. The gynaeceum
consists of numerous, long-stalked, atropous ovules
which are surrounded and separated by scale leaves :
the microsporophylls, however, open freely on the
exterior. The ripe seeds contained a highly de-
veloped dicotyledonous embryo and had no endo-
sperm. They were protected and enclosed by the
closely crowded outer ends of the scale leaves (Fig.
600). Just as the Palaeozoic Pteridosperms com-
bine the characters of Ferns and Gymnosperms,
the flowers of the Mesozoic Bennettites or Cycade-
oidea show a combination of characters of Angio-
sperms, Gymnosperms, and Ferns.

True Araucarieae appear in the Jurassic ;
on this account, as well as on account of their
organisation, this group may be regarded as the
oldest of the existing Coniferae. In the Wealden,
Cycadineae and Ginkgoineae along with some Coni-
ferae were dominant among the Gymnosperms.

FIG. 600. — Longitudinal section J ,

of a fruit of Bennettites Gibson- ^ passing to the Cretaceous strata the ancient
ianus. (After SCOTT.) types are found to be reduced, while the Coniferae

become more numerous. Among the latter appeal-
existing genera (Dammara, Sequoia, Pinus, Cedrus, Abies, Callitris, etc.). The
Taxaceae also appear to be represented, but the remains are of uncertain affinity.

The Tertiary Gymnosperms belong entirely to existing types and for the
most part to existing species. The Coniferae are dominant ; the Ginkgoineae
are represented only by Ginkgo biloba, but this occurred in Europe along with
other species now limited to Eastern Asia or North America (Cryplomeria
japonica, Taxodium distichum, Sequoia gigantea, S. sempervirens, Pinus Strobus,
etc.). One Cycadaceous plant (Enccphalartos] is also known.

CLASS II
Angiospermae (16)

The long-disputed question as to whether the Monocotyledons or
Dicotyledons are the more primitive is perhaps settled by the
derivation of the Monocotyledons from the Polycarpicae among the
Dicotyledons ; these exhibit features of agreement with Monocoty-
ledons in floral construction, anatomical structure, and in morphological
characters. On this account the Monocotyledons will be placed after
the Dicotyledons in the following systematic arrangement.

DIV. n ANGIOSPERMAE 607

Any direct transition from Gymnosperms to Monocotyledons is
thus out of the question while a relation of dicotyledonous plants to
Gymnosperms is not excluded. The parallels and progressive develop-
ments that can be recognised in the male and female organs have been
referred to above (p. 544 f .) ; there are also indications of the deriva-
tion of the one group from the other in the construction of the
flower as a whole. In attacking this problem WETTSTEIN attempts
to derive the simplest flowers of the Angiosperms from Gymnosperm
inflorescences.

A male flower with a single perianth and superposed stamens could be derived
from a whorl of scale leaves with simple axillary male flowers. Since in male
inflorescences of Ephedra single female flowers occasionally appear, it is possible
that the female organs might become associated with the stamens. The proba-
bility of such a transition is increased by the fact that insect -pollination has
been observed in inflorescences of this kind.

If the systematic arrangement of the Dicotyledons is based on this
idea, the most simply constructed flowers would be those with one
whorl of perianth segments and borne in catkins. Thus the
Casuarinaceae, Juglandaceae, Betulaceae, Ulmaceae, etc., will be placed
at the beginning of the system, and to them will be connected the
other families with a simple perianth which are grouped together as
Monochlamydeae. To these in turn may be connected the Dialypetalae,
the flowers of which have both calyx and corolla. The forms with a
gamopetalous corolla are separated as the Sympetalae, and the other
Monochlamydeae and Dialypetalae contrasted with them as Chori-
petalae ; the forms without perianth are grouped with the Choripetalae.
Jiince within the Monochlamydeae various lines lead from forms with a
simple perianth to those with a pentacyclic structure, any arrange-
ment in a simple ascending series is impossible. Various parallel series
lead from simple to highly organised floral structure, and similarly
numerous parallel series are found in the Dialypetalae. Thus the
natural or phylogenetic relationships can only be exhibited in an
incomplete fashion in the following arrangement.

In addition to this line of transition from Gymnosperms to
Angiosperms another possibility has to be seriously considered ; this
was pointed out a considerable time ago by H. HALLIER. He treated
the Polycarpicae, from which the Monocotyledons have been derived
above, as the starting-point for the Dicotyledons generally. This view
finds support in a biological observation of DIELS (17), who showed that
both some South African species of Encephaknios and some of the
Polycarpicae are pollinated by beetles. Since the Coleoptera are the
phylogenetically oldest flower-visiting insects and appear as the
pollinating agents in the oldest family of Gymnosperms, a similar age
may be inferred for the Polycarpicae that are pollinated by beetles.

The morphological construction of the flower of the Polycarpicae, with its
spiral arrangement of all the floral leaves, presents resemblances to the greatly

608 BOTANY PART n

elongated axis of the flowers of Gymnosperms. The Gnetaceae, which are also
treated by WETTSTEIN as a connecting link between Gymnosperms and Angio-
sperms, foreshadow in the androgynous inflorescence of Gnetum a flower like those
of the Polycarpicae. Further, the Calycanthaceae, which are placed in the latter
group, have an extensive sporogenous tissue in the nucellus such as is only known
in some Gymnosperms, in Casuarina, and in Rosaceae, a family that is to be
connected with the Calycanthaceae.

The evidence for this second possible line of progression renders it
as probable as the one first mentioned. Both regard the Gnetaceae
as a transition family, and it is thus conceivable that both lines of
development have been followed in plant-evolution. The less highly

organised Monochlamydeae would
come in the manner indicated by
WETTSTEIN from Ephedra to Dico-
tyledons ; the Dialypetalae in the

^y . \ second way from Gnetum to the

£ Polycarpicae. So long as develop-
mental and morphological evidence
is insufficient to establish a common
origin of the two sets of Dicotyle-
; <lons and their connection as sug-

gested by HALLTER in the Hama-
melideae, this double origin appears
most probable.

SUB-CLASS I
Dicotylae

^ The Dicotyledons with few ex-

ceptions possess a pair of seed-
leaves. The distinction of hypogeal
and epigeal germination has been

FIG. 601,-Leaf of Crataegus with reticulate ^Scribed On p. 589. _

venation, (f nat. size. After NOLL.) The stem has a circle of open

vascular bundles, while the root

on transverse section shows a regularly alternating arrangement of
the xylem- and phloem-groups (cf. p. 136, Fig. 163). The meristem
situated in the vascular bundles of the stem, or to the inner side of
the phloem in the root, soon becomes completed across the medullary
rays and forms a complete, meristematic ring. By means of this
cambium a regular growth in thickness of the stem and root takes
place.

The typical form of leaf found among Dicotyledons is provided
with a longer or shorter petiole, and often has a pair of stipules
developed from the leaf-base ; a leaf-sheath is usually absent. The
lamina may be simple or compound ; the latter condition is always

DIV. n ANGIOSPERMAE 609

the result of lateral branching during the development of the leaf.
The margin of the leaf presents considerable variety. The venation
is as a rule reticulate (Fig. 601).

The flowers in Dicotyledons are typically pentamerous and penta-
cyclic, but there are numerous exceptions to this. The floral formula
in the most regularly constructed representatives is K5, C5, A5 + 5,
G5.

Series I. Choripetalae

A. MONOCHLAMYDEAE

The following orders 1-4 agree in the unisexuality and anemo-
phily of their flowers with simple uncoloured perianth. They include
various transitional forms from chalazogamy to porogamy.

Order l. Juglandiflorae

Family Juglandaceae. — Conspicuous, monoecious trees of the northern hemi-
sphere with impari pinnate, aromatic leaves arranged alternately. Stipules wanting.

The Walnut, Juglans regia (Fig. 602), is the best-known representative of the
family. It is endemic in Western Asia and the eastern portion of the Mediter-
ranean region, but the tree is in cultivation throughout Europe. In spring the
axillary buds of the previous season produce long, thick, pendulous catkins bearing
numerous flowers. Each of the latter has 3-5 perianth segments, and these together
with the two bracteoles are adherent to the bract and surround the numerous
stamens, which face towards the tip of the inflorescence. The female flowers in
smaller numbers are borne at the summit of the young shoots. The two carpels
terminate in large, feathery, diverging stigmas. The perigone is adherent to the
bract and bracteoles and reaches to the summit of the inferior ovary. The single
loculus encloses an atropous, basal ovule. Fruit, a drupe. The exocarp contains
abundant tannin. The hard endocarp is divided into two valves in the plane
of the dorsal sutures of the coherent carpels, the limits of which are indicated
by the partial septum at the lower part of the fruit. Within the stone is the
embryo, enclosed in a thin seed-coat. The large cotyledons, which contain oil,
are lobed in correspondence with the false septa that project from the inner surface
of the ovary. Endosperm wanting. Other species of Juglans and Carya yield
edible seeds and valuable timbers.

Order 2. Quereiflorae (18)

Trees or shrubs usually with entire leaves and deciduous stipules.
Monoecious. Flowers in catkins. Ovary inferior ; ovules pendulous.
Fruit, a one-seeded nut. Endosperm wanting. Anemophilous. This
order includes most of our important forest-trees.

Family 1. Betulaceae. — Male flowers adherent to the bracts. Ovary bilocular,
with two long stigmas ; a single, pendulous ovule in each loculus. Mainly
distributed in the northern hemisphere.

610

BOTANY

PART II

MOST IMPORTANT GENERA. — Alnus glutinosa, the Alder, is a prominent tree
of damp woods, and is also distributed in swamps and by the banks of streams.
The inflorescences are already evident in the autumn as stalked catkins, the male
long and pendulous, the female erect and short. Male flowers P4, A4 ; a dichasium
of three flowers adherent to each bract (Fig. 603). The female flowers are in

Fio. 602.— Juglans regia. 1, Branch with young leaves, male catkins and at the tip female flowers.
2, Male flower. 3, Female flower. 4, Fruit with the outer layer of the pericarp in part
removed. (£ nat. size.)

pairs, their bracteoles adhering to the bract to form the five-lobed, persistent,
woody scale of the cone. Alnus incana is distinguished by its leaves being grey
and hairy below. Betula verrucosa (Fig. 604), the Birch, has a white bark and long
stalked, triangular leaves. When young, all the parts are covered with numerous
glandular hairs which give the plant an aromatic, resinous odour. The male
inflorescences are formed in the autumn of the previous year, singly or a few
together, at the tip of shoots of unlimited growth. Flowers P2, A2,; in dichasia

DIV. II

ANGIOSPERMAE

611

of three, adherent to the bract. Anthers deeply bifid (Fig. 604, 3, 4). Female

inflorescences solitary, at the apex of small, short shoots of the current year.

Flowers in dichasia of three in relation to each three-lobed scale ; the latter is

composed of the bract and the two adherent bracteoles. Fruits borne on

pendulous catkins ; winged. After the fruits are shed the scales of the catkin

separate. Carpinus Hetulus, the Hornbeam (Fig. 605), is an important forest-tree.

The inflorescences appear in spring, the male, from axillary buds of the previous

year, either want leaves or are accompanied by one or two, the female are usually

terminal. The bract of the

male catkin bears 4-10

stamens, bifid to the base,

but without bracteoles or

perigone. Two female

flowers in relation to each

bract ; each flower with its

special bract and pair of

bracteoles. The three latter

unite to form a three-lobed

involucre which serves as

an aid to distribution of the

fruit by the wind. Corylus

FiG.6Q3.—Alnusglutinoso.. Dia-
grams of the male and female
flowers. Bract b; bracteoles
a |3, a' /3', a, /3,. (After
ElCHLER.)

FIG. 604.— Betula verrucosa. 1, Branch with terminal male catkins
and female catkins on small lateral branches. 2, Female
flower. 5, Male flower. £, Stamen. 5, A catkin in fruit.
6, Fruit. (1 and 5, 5} nat. size ; %-U and 6, enlarged.)

avellana, the Hazel, develops its inflorescences in the preceding year. The male
catkins are freely exposed during the winter, while the female remain enclosed
by the bud-scales, and only protrude their long red stigmas between the scales
at the actual time of flowering. The male flower has no perianth but has a
pair of bracteoles which are adherent to the bract, as are the four deeply bifid
stamens. In the short female catkins a two-flowered dichasium is present in the
axil of each bract as in Carpinus ; the fringed involucre also is derived from
the coherent bracteoles and special bract of each flower. Corylus tubulosa from
southern Europe.

Family 2. Cupuliferae. — Inflorescences in the leaf axils, bearing
male flowers provided with a perianth, and female flowers one or

612

BOTANY

TART II

more of which are enclosed in a cupule (Fig. 606 cp) derived from
united bracteoles. The trilocular ovary has two pendulous anatropous
ovules in each chamber and ends in three stigmas.

Distributed chiefly in the temperate zones of the northern hemisphere, also in
tropical Asia.

FIG. 605. — Carpinus betulus. 1, Branch with male catkins projecting from the buds of the preced-
ing year and female catkins on the growth of the current year. 2, Female catkin in fruit.
3, Male flower. 4, Stamen. 5, Bract \vith two female flowers. 6, Female flower. 7, Fruit.
(1, 2, 7, § nat. size ; 3-6 enlarged.)

MORE IMPORTANT SPECIES. — Fagus sylvatica, the Beech (Fig. 607), is one of our
most important deciduous trees. The leaf is entire, elliptical, shortly stalked,
and, especially when young, covered with fine hairs. Leaves two -ranked.
Inflorescences on shoots of the current season. Male inflorescences capitate and
pendulous, flowers Avith an oblique, bell-shaped perianth and usually 8-12 stamens.
Female inflorescences terminal, capitate and erect ; flowers in two-flowered dichasia.
The cupule surrounds both flowers (Fig. 608 J5), and completely envelops the
triangular, nut-like fruits ; at maturity it opens by splitting into four valves.
Its surface is covered with numerous, blunt prickles.

Castanea vulgaris, the edible Chestnut, is a native of the Mediterranean region.

FIG. 606. — Cupule of Quercus Aegilops. cp, cupula ; gl, fruit.
(After DUCHARTRE.)

FIG. 607.— Fagus syh-aiica. (§ nat. size.) 1, Branch with male and female inflorescences. 2, Male
flower. 3, Female flower. 4, Open cupule with two fruits. 5, Fruit. 6, Transverse section of
a fruit showing the folded cotyledons of the embryo, (c', 3. 6, enlarged.)

613 2 R 1

614

BOTANY

PAKT II

The inflorescences on shoots of the current year bear in some cases only male
flowers, in others female flowers at the base and male flowers above. Flowers

FIG. 608. — Diagrams of the female dichasia of : A, Castanea vuljaris ; B, Fagus sylvatica ; C, diagram
of the single flower of Qiwrcus pedunculata. b, Bract ; a ft, bracteoles ; a, ft,, a' ft', bracteoles
of the secondary flowers adherent to the cupule. (After EICHLF.R.)

grouped in dichasia. Female dichasia three-flowered (Fig. 608 A\ so that three

nuts come to be enclosed within the spiny cupule, which splits into four valves.

The Oaks, Quercus pedunculata (Figs. 609, 610) and Quercus sessiliflora, are the

largest deciduous trees of European woods.
Leaves oval, margins sinuately lobed. The
pendulous male inflorescences spring, at
the time that the new foliage is expanding,
from axillary buds of the shoot of the pre-
ceding year or from the lowest buds of the
shoot of the current year ; flowers solitary,
consisting of a perianth of 5-7 segments
and 6-12 short stamens. Female inflores-
cences erect, few-flowered, in the axils of
the upper leaves of the shoot of the current
year. Flowers solitary ; in Q. peduncu-
lata with long stalks, in Q. sessiliflora
sessile. Each flower is invested by a cupule
longitudinal (Fig. 608 C}, which is at first inconspicuous,
but is fully developed on the ripe fruit.

The Beech yields firewood, tar, and
pyroligneous acid ; the Oak provides a
valuable timber, a bark containing tannin

used in tanning, and cork from the Cork-oak.

OFFICIAL. — The GALLS produced on the young twigs of Quercus infectoria as a

result of puncture by the Gall-wasp, Gynips tinctoria ; Tannic Acid is obtained

from these.

FIG. 609.— Quercus pedunculata,

section of the female flower. 6, The young
cupule; e. ovule; a, ovary; c, perigone ;
/.style; g, stigma. (After BERG and
SCHMIDT, magnified.)

Order 3. Saliciflorae

Family Salicaceae. — Trees and shrubs with simple, alternate, stipulate leaves.
Flowers in dioecious catkins, usually developed before the leaves. Both male
and female flowers are naked arid stand in the axils of bracts. More or less
developed scale-like development of the disc or floral receptacle. Ovary of two
carpels, unilocular. Fruit, a capsule containing numerous, parietal seeds. Seeds
without endosperm ; seed -coat with a tuft of hairs.

DIV. n

ANGIOSPERMAE

615

This family is mainly represented in the north temperate zone. Salix, Willow,
and Populus, Poplar, are the only genera. Salix has erect catkins and is adapted
for pollination by insects ; in relation to this, nectar is secreted by small scales
at the base of the flower. Male flowers scented ; pollen sticky. The number of
stamens varies from 2 to 5 in the different species. Bracts entire (Fig. 611).
Willows occur commonly by the banks of streams. Some species are among the

FIG. 610.— Quercti.? poluni.-utata. A, Flowering branch; B, a male flower (magnified); C, stamens
(magnified) ; D, a female flower (magnified) ; E, infructescence ; F, cupule ; G-H, seed. (After
SCHIMPER.)

more abundant plants of high northern latitudes ; they have subterranean, creeping
stems, only the young shoots projecting from the soil. Populus has anemophilous
flowers ; disc cup-shaped ; no secretion of nectar. The long-stalked roundish leaves
of the Poplars give them a different habit from the Willows. Flowers similar to
those of Salix but with divided bracts. Catkins pendulous (Fig. 612).
SALICIN is obtained from the bark of species of Salix and Populus.

2K2

616

BOTANY

PART II

Order 4. Urtieinae

Herbaceous or woody plants with small, inconspicuous flowers
closely aggregated in the inflorescence. Stamens equal in number
to the leaves of the perigone and superposed on the latter. Ovary
superior, composed of one or two carpels,
usually unilocular, and containing a single,
pendulous ovule. Fruit, a nut or drupe. Seeds
usually containing endosperm.

Family 1. Ulmaceae. — Ulmus campestris (Fig.
613), the Elm, is a common European tree. The
arrangement of the leaves on the sides of the twigs
in two rows and the corresponding branching leads to
the leaf surface exposed on each lateral branch making
a definite angle with the main branch and composing
the regular convex crown of foliage exhibited by older

FIG. 611.— Salix viminalis. A,
Flowering male twig (nat. size).
B, Male flower with subtending
bract (magnified). C, Female
inflorescence. D - E, Female
flowers (magnified). F, Fruit
(nat. size). G, The same mag-
nified. H, Seed (magnified).
(After SCHTMPER.)

Fiu. 612. — Populns iiigra. 1, Male infloi'escence. #, Female
inflorescence. 3, Male flower, k, Female flower. 5, Fruit.
«, Seed. (1, 2, | nat. size ; 3-6, enlarged.)

examples. The leaves are always asymmetrical The flowers stand in groups in
the axils of the leaves of the previous year ; they are hermaphrodite or, by
abortion, unisexual. The stamens are straight in the bud. The tree flowers
in February or March and the fruits ripen before the leaves expand. The fruits

mv. n

ANGIOSPERMAE

617

are broadly winged and adapted to be carried by the wind. U. montana, U. effusa
are closely related forms. Several species of Celtis, in which the fruit is a drupe,
are in cultivation.

Family 2. Moraeeae. — The majority are trees or shrubs with

Fit;. »513. — L'liinix mmpxtrls (§ nat. size). 1, Branch with flowers. .?. Branch with fruits.
3, Single flower, enlarged.

abundant latex. Leaves alternate, stipules caducous. Flowers uni-
sexual in globular or disc-shaped inflorescences ; mostly tetramerous.

IMPORTANT REPRESENTATIVES. — In addition to the Mulberry trees, of which
Morus alba is cultivated for the rearing of Silk-worms and M. nigra (Fig. 574 B)
as a fruit-tree, the genus Ficus deserves special mention. The species occurring
farthest north is the Common Fig(19) (Ficus car -ica, Fig. 614), which is endemic to
the Mediterranean region, and has been long cultivated. It is a low tree with
palmately incised leaves and stipules, which form a cap-like protection to the bud.

618

BOTANY

PART II

The inflorescences are hollow, pitcher-shaped structures with a narrow opening.
The flowers are borne closely crowded together on the inner surface. The flat,
disc-shaped inflorescences of Dorstenia which bear the flowers on the upper surface
are in many respects corresponding structures. On the distribution of the
fruitlets cf. GOEBEL (19). On the pollination of the Fig cf. p. 556. The sweet,
fleshy portion of the edible Fig is developed from the hollowed axis of the
inflorescence together with the perigones of the individual flowers. The small,
hard, seed-like bodies are the fruits developed from the ovaries of the small
flowers. Some species of Ficus are among the largest trees of tropical forests.
The most remarkable is the Banyan (Ficus bengalensis), which occurs in the East
Indies. The seeds, carried by fruit-eating birds, germinate on the branches of

trees, where the plant develops as
an epiphyte. The proper form of
the tree is only seen, however,
after the roots have reached the
soil, and it is no longer dependent
on the scanty food supply obtain-
able in the epiphytic position. The
host- plant is gradually strangled,
additional roots are sent down to
the soil and thicken into pillar-
like supports, and ultimately a
small wood capable of sheltering
an entire village is developed
from the single small seedling.
The latex of Ficus elastica is ob-
tained from the tree by making
incisions in the bark, and serves
as one source of india-rubber.
PIG. 614.— Ficus carica. A, Longitudinal section of Castilloa elastica is another im-
an inflorescence. B, Fertile flower. C. Gall-flower. *• n i

Z), Male flower. (B-D, enlarged ; D, after KERNER ; P°rtant ™bber ' tree ot Centl'al
£, C, after SOLMB-LAUBACH.) OFFICIAL. America. The gigantic inflores-

cences of species of Artocarpus

when in fruit are eaten raw or cooked and form the Bread-fruit of the tropics.
OFFICIAL.— The fruits of Ficus carica.

Family 3. Cannabinaceae. — Humulus lupulus, the Hop, is a native of central
Europe ; it has a perennial rhizome, which annually produces a crop of twining
shoots (Fig. 615). The stem and opposite leaves bear coarse hairs, and the former
bears hooked prickles which prevent it slipping down the support. The male
flowers of this dioecious plant are pentamerous, with straight stamens and grouped
in dichasia the central branches of which are capable of further growth. The
branches of the female inflorescence are catkin-like, the scales being formed of
the pairs of stipules belonging to bracts, the laminae of which are suppressed.
The axillary shoot of the bract is also suppressed, but each stipule has two flowers
in its axil ; each flower is enclosed by its own bract. These bracts project beyond
the stipules when the inflorescence is mature, and give the latter its cone-like
appearance. Upon them are developed the glandular hairs on account of which
the Hop is cultivated.

Oannabis sativa, Indian Hemp, is an annual herb with palmately divided, hairy
leaves, which are opposite below and alternate in the upper portion of the shoot.
The female inflorescence resembles that of the Hop, but the central shoot, which

DIV. II

ANGIOSPERMAE

619

iu that plant is suppressed, grows out in the Hemp to a leafy shoot. Only a single
flower is present in the axil of each bract. The same process is repeated in the
axil of each leaf of the leafy middle shoot, so that the whole female inflorescence
is a repeatedly branched structure. The plant is utilised in Europe for its bast
fibres, which are from one to several centimetres long. The glandular hairs
which cover all parts of the female inflorescence secrete a sticky resinous substance

FIG. 615.— Humulus lupulus. 1, Male inflorescence. 2, Female inflorescence. 3, Two female
flowers in the axil of a bract. 4, Cone-like inflorescences in fruit, (i nat. size.)

which is used medicinally. In the East it is used in the preparation of a narcotic
called Haschisch.

OFFICIAL. — CannaUs saliva provides CANXABIS IXDICA.

Family 4. Urticaceae. — Perennial herbs or less commonly shrubs. Leaves
simple, stipulate. Flowers unisexual by suppression of parts, as a rule bimerous.
P 2 + 2, A 2 -f 2. Stamens inflexed in the bud, and scattering the pollen when they
suddenly straighten. Ovary consisting of a single carpel, uuilocular, with a basal,
atropous ovule. Perianth of the female flower adherent. Flowers in dichasia,
or crowded in dorsiventral inflorescences. Anemophilous. Widely spread in the
tropics.

A number of the Urticaceae are characterised by the possession of stinging
hairs (cf. Fig. 55), e.g. the common Stinging Nettles, Urtica dioica and U. urens,
and the dangerous tropical species of Laportea. Some provide important fibres,
especially Boehmeria nivea from which Ramie fibre is obtained, and of less value,
Urtica cannabina, and our native species of Urtica.

620

BOTANY

PART II

Orders 5-7 are isolated, and also have no evident connection with
one another.

Order 5. Loranthiflorae

Family 1. Santalaceae. — Green plants growing in the soil and partially
parasitic on the roots of other plants from which their haustoria obtain nutrient
materials. In Britain, Thesium.

FIG. 616. — Vlxcum album. With flowers and fruits. (£ nat. size.)

OFFICIAL. — Santalum album, the wood of which when distilled yields OLEUM
SANTALI. The wood is also of economic value.

Family 2. Loranthaceae. — Leafy semi-parasitic shrubs, living on the branches
of trees. They are most abundant in the tropics, and, for instance in South
America, add to the beauty of the forest by their brightly coloured flowers.

Loranthus europaeus, on Oaks in Europe. In Britain Viscum album (Fig. 636),
the Mistletoe, occurs as an evergreen parasite on a number of trees. It has opposite,
obovate leaves. Stem swollen at the nodes. The white berries are distributed by
birds. The sucker, without a root-cap, emerging from the seed penetrates the
cortex of the host to the wood, into which it cannot grow. Its tip is embedded in
the new wood formed by the cambium of the host. Further growth in length
of the sucker is eifected by a zone corresponding in position to the cambium
of the host.

DIV. n

ANGIOSPERMAE

621

Order 6. Polygoninae

Family 1. Polygonaceae. — For the most part perennial herbs, with hollow
stems swollen at the nodes, and alternate, simple leaves. The membranous
stipules of the latter are coherent to form a
sheath or OCHREA protecting the terminal bud ;
when broken through by the growth of the stem,
this remains as a tubular sheath around the lower
part of the internode (Fig. 617).

Mainly natives of the N. Temperate zone.

GENERA. — Rheum, Rhubarb. This is an East
Asiatic genus, with large, radical leaves and a large,
spreading, paniculate inflorescence. Leaves simple,
cordate-reniform, with palmate venation, sometimes
more or less lobed. *The flower has a perigone of
two similar whorls, and two whorls of stamens, the
outer whorl being double by chorisis ; P3 + 3,
A 6 + 3, G (3). Nectar for visiting insects is
secreted by The large scales of the disc. The tri-
angular ovary becomes winged as it develops into
the fruit (Fig. 618). Species of Rheum are culti-
vated as ornamental plants and as vegetables.
Rumex acetosa, Sorrel, with sagittate leaves. The
structure of the flowers of the hermaphrodite
species of Rumex is similar to that of Rheum, but
the inner whorl of stamens is wanting. The
species of Polygonum have a perigone consisting
of five coloured leaves and a varying number of
stamens. The triangular fruits of Fagopyrum
esculentum form Buckwheat (Fig. 571 B}.

OFFICIAL. — The Rhizome of Rheum officinale, Rh. palmatum, and probably
other species yields EADIX RHEI.

FIG. 617. — Leaf of Polygonumamplexi-
caule showing the ochrea, st.
(J nat. size.)

FIG. 618.— Rheum officiwlc. A, Flower: ti, the same cut through longitudinally; C, gynaeceuin

with disc.

nn: D, fruit. (After LURSSEN, magnified.)

Order 7. Piperinae
Single family. Piperaceae.— The genus Piper is important. Flowers as a rule

622

BOTANY

PART II

FIG. 619. — Piper nigrum. (? nat. size.) OFFICIAL.

unisexual and without perianth, as-
sociated in spikes ; typically trimerous
but usually reduced. Ovary unilocular,
ovule solitary, basal and atropous.
Fruit drupe-like. The embryo is em-
bedded in a small endosperm sur-
rounded by a well -developed peri-
sperm. The vascular bundles are
scattered in the cross-section of the
stem resembling the arrangement in
Monocotyledons, but with secondary
thickening.

Piper nigrum, from which the
Peppers are derived, is the most
important representative. This is a

620 -Piper cMa. a Ir b a root.climb natiye to the Malayan

male flower ; c, a female flower in longitudinal J

section ; d, fruit in longitudinal section. OFFI- reglon> but now cultivated through-
CIAL. (After BERG and SCHMIDT.)

out the tropics (Fig. 619). The unripe

DIV. n

ANGIOSPERMAE

623

fruits provide black pepper, while white pepper is obtained from the ripe fruits
after removal of the outer layers of the pericarp.

OFFICIAL. — Piper Betle, Piper nigrum and Piper cubeba (Fig. 620). The latter
is a native of Java and is distinguished by the stilk-like base of the fruit from
that of the Black Pepper. It provides CUBEBAE FRUCTUS.

The orders 8-10 constitute parallel series leading from the simplest
flowers to the Dialypetalae, but are not directly connected with one
another.

Order 8. Hamamelidinae

This includes the two Families Hamamelidaceae and Platanaceae. — Woody
plants, with stipulate leaves. Flowers as a rule inconspicuous, without perianth
and anemophilous. £!onspicuous, entomophilous, flowers with a simple, or more
rarely double, perianth also occur. Two carpels.

OFFICIAL. — STYRAX PRAEPARATUS from Liquidambar orientalis. HAMAMELIDIS
CORTEX and FOLIA from Hamamelis virginiana.

Platanns orientalis and P. occidentalis are commonly planted as shade trees by
the sides of streets.

Order 9. Trieoeeae (20)

Family Euphorbiaeeae. — The plants belonging to the Euphor-
biaceae are of very diverse habit. The order includes herbs, shrubs,
leafless succulent
plants, trees with nor-
mal foliage, and others » m v^
with scale leaves and ifc-II
assimilating phyllo-
clades. The plants
agree, however, in pos-
sessing unisexual, acti-

Fio. 621.— Ovule of Euphorbia
dioica showing the obtur-
ator o. (After PAX in
ENGLER-PRAXTL.)

FIG. 622. — Mercurialls annua (£ nat. size). Mile plant in
flower and single male flower. Portion of a female plant,
single female flower and fruit. Poiso.voi'S.

nomorphic flowers, with a simple perianth or with no trace of the
latter. Androecium diplostemonous or stamens numerous. The
female flowers are especially characterised by the superior, trilocular

624

BOTANY

TART II

FIG. 623.— Euphorbia Lathyris. A, Cyathium (x 5). B, Cyathium cut through longitudinally
'( x 7). C, Fruit after dehiscence showing the central column (c). D, Seed in longitudinal
section showing the embryo embedded in the endosperm ; ca, caruncula ( x 4). (A-D after
BAILLON.)

ovary formed of three carpels; in each loculus are one or two
pendulous ovules with a ventral raphe,
and the micropyle directed upwards
and outwards.

The micropyle is covered by a placental
outgrowth called the obturator (Fig. 621) ;
this assists in conducting and nourishing the
pollen-tube, and disappears after fertilisation
(of. p. 573). The CARUNCULA, which is formed
from the outer integument (Fig. 567 £),

FIG. 624. — Diagram of a dichasial branch of Euphor-
bia, with three cyathia, only the middle one of
which has a fertile female flower. (After EICHLER.)

FIG. 625.— Euphorbia resinifera. (Nat. size.
After BKBG and SCHMIDT.)

DIV. n

ANGIOSPERMAE

625

persists on the other hand in the seed ; the separation of the latter from the
placenta is assisted by it. The fruit is a capsule, the outer walls of which contract
elastically away from* a central column, and thus open the loculi.

The plants of this family are distributed over the whole earth, IMPORTANT
GENERA. — Many Euphorbiaceae are dioecious or monoecious, and have flowers of
relatively simple construction. Thus Mecwialis (Fig. 622), two species of which

Fi<;. 020.— Ricinus communis, greatly reduced. (After BAILLOX.) Porsoxocs and OFFICIAL.

occur in Britain, is characterised by its bicarpellary ovary. Croton is a tropical
genus including valuable official plants, C. Eleuteria and C. Tiylium ; the male
flowers have a double, the female flowers a single perianth. In the Spurges
(Euphorbia"), of which there are several British species, a number of the extremely
simply constructed flowers are grouped in a complicated inflorescence termed a
CTATHIUM (Figs. 623-625). This consists of a naked, terminal, female flower,
borne on a long bent stalk surrounded by a number of groups of male flowers.
Each of the latter is stalked and consists of a single stamen, the limit between
which and the flower-stalk is distinguishable. In some cases the female flower

626

BOTANY

PART II

and each male flower are provided with a small perianth. The whole cyathium,
which is an inflorescence, is always enclosed by five involucral bracts ; alternating

with these are four nectar-secreting glands,
the presence of which increases the likeness
between the cyathium and a flower. The fifth
gland is wanting, and the inverted female flower
hangs down in the gap thus left. Between the
groups of male flowers which stand opposite
to the bracts (Fig. 624) are branched hairs
which are visible when the cyathium is cut
through longitudinally (Fig. 623 B). The
cyathia are usually grouped in dichasia, and
these in turn form an umbellate inflorescence,
with three to many branches. It often
happens that the female flower is only de-
veloped in some of the cyathia, remaining
rudimentary in the others. Many species of
Euphorbia, especially the African species, are
succulent-stemmed plants resembling Cacti in
general appearance (Fig. 625).

Euphorbia, like many but not all the other
plants of the family, contains a milky juice,
which is secreted in non-septate latex-tubes.
This juice, which in many cases is poisonous,
exudes wherever the plant is wounded.

An important constituent of the latex of
species of Hevea (H. Sieberi, discolor, rigidi-
folia, paucifolia, lutea, guyanensis, Spruceana}
is CAOUTCHOUC (of. 19). As Para Rubber
obtained in the tropics of South America,
especially in the Amazon Region, this affords
about one-half of the total rubber supply. In
addition Manihot Glaziovii, another South
American plant of this order, which yields
Ceara Rubber, must be mentioned. A nearly
related plant, Manihot utilissima, provides in
its tuberous roots a very important food in
the tropics. The starch obtained from these
roots forms mandioc or cassava meal, the finest
varieties of which, as tapioca or Brazilian
arrowroot, are of commercial importance.
The shrub, which is a native of Brazil, is now
cultivated throughout the tropics.

Ricinus communis (Fig. 626) is a tall shrub
of tropical Africa. In our climate it is annually
killed by the frost. The hollow stem bears
large palniately-divided leaves. The terminal inflorescences (Fig. 627) are over-
topped by vegetative lateral branches. The male flowers, situated towards the
base, have a membranous calyx of 4-5 sepals, enclosing the branched stamens ;
the end of each branch bears a theca. The female flowers, nearer the summit of
the inflorescence, have 3-5 sepals and a large tripartite ovary. The latter is

FIG. 627. — Ricinus communis. Inflor-
escence (i nat. size) ; young fruit cut
through longitudinally. OFFICIAL.

DIV. n ANGIOSPERMAE 627

covered with warty prickles, and bears three large, bifid, red stigmas. In each
loculus of the fruit is a mottled seed with a whitish caruncula.

OFFICIAL. — Croton Eleuteria (Bahamas) yields CASCARILLA. C. tigliurn (East
Indies), OLEUM CKOTONIS. OLEUM RICINI, Castor Oil, is obtained from Ricinus
communis.

Order 10. Centrospermae

Plants with as a rule hermaphrodite flowers which approximate to
the typical dicotyledonous flower.

Family 1. Chenopodiaeeae. — Perennial or annual herbs, rarely
small woody plants, with alternate leaves. Flowers typically
pentamerous, with a single whorl in both perigone and androecium ;
P 5, A 5, G (2-5).% Stamens opposite the perianth leaves. Eeduced,
unisexual flowers*are not infrequent. The unilocular ovary contains
a basal, campylotropous ovule. Fruit, a nut. Seed with a curved
embryo bent around the floury perisperm.

Many of the Chenopodiaeeae are strand plants or occur on soils containing a
large amount of salt, such as the great Asiatic salt steppes and deserts. The
Spinach (Spinacia oleracea) and the Summer Spinach (S. glabra) are used as vege-
tables. The Sugar Beet (Seta vulgaris, var. rapa) is a plant of great economic
importance. It is a biennial plant, and in the first season forms a thick, swollen
root bearing a bud consisting of a number of thick-stalked, entire, succulent, and
often crisped leaves. From this rosette of leaves there springs in the second season
a highly branched panicle, bearing the inconspicuous greenish flowers. Ovary
formed of three carpels. At the end of the first season the root contains cane-sugar
as a reserve material, which at this stage is extracted from the plant. By constant
selection the percentage of sugar is raised from 7-8 % to an average of 14 % ; it may,
however, reach 21-26 %. The original form of the Sugar Beet is Beta patula.
Chenopodium and Atriplex are common weeds near human dwellings.

Family 2. Caryophyllaeeae. — Annual or perennial herbs, with
simple, linear, usually opposite leaves ; flowers typically pentamerous,
with calyx a-nd corolla. Two whorls of stamens, obdiplostemonous.
Unilocular or incompletely septate ovary. K 5, C 5, A 5 + 5, G (5)
(Fig. 630). Fruit, a capsule. Seeds numerous, embryo curved around
the floury perisperm.

Ccrastium and Stellaria have white flowers and bifid petals, and are conspicuous,
early-flowering forms. Species of Dianthus, Pinks, have frequently attractive
colours and scent, and occur in dry sunny situations. Agrostemma Githago
(Fig. 628), Corn-cockle, is a hairy plant with pink flowers ; it is a common weed
in corn-fields. Since its seeds are poisonous, their mixture with the grain may have
serious results. Saponaria qfficinalis is a herb attaining the height of a metre,
with opposite, broad leaves and rose-coloured flowers. The saponin contained
in all parts of the plant renders it poisonous (Fig. 629).

Family 3. Aizoaceae. Perennial herbs or small shrubs, usually with suc-
culent leaves. Flowers hermaphrodite ; with simple perianth or with a calyx and
a polypetalous corolla derived from modified stamens. Stamens numerous. Carpels
2-oo ; united to form the hygroscopic capsule.

2S 1

628

BOTANY

PART II

Xerophytic plants of hot countries. Mesembryanlhemum ; a large genus,
especially in Africa.

Family 4. Cactaceae. — For the most part leafless plants with succulent stems,
natives of America. In size they range from very small to gigantic forms. Flowers

FIG. 62S.—Agrostemma Gitltago. Flowering shoot and fruit (£ nat. size). Pomoxoi'S.

hermaphrodite, actinomorphic, less commonly dorsiventral. Perianth of many
members, spirally arranged and showing a gradual transition from the calyx to the
corolla. Stamens and carpels numerous. Ovary inferior, unilocular, with numerous
parietal placentas. Ovules with long stalks. Fruit, a berry, the succulent tissue
being largely derived from the stalks of the seeds.

Peireskia and some species of Opuntia possess leaves. Other species of Opuntia

ANGIOSPERMAE

629

have flattened branches (Fig. 197). Cereus (Fig. 631), Echinocactiis, with longitudinal
ridges on the stem ; Mammil-
laria has free projections (ma-
millae). The numerous groups
of spines on the shoots, ribs, or
separate mamillae correspond
to axillary shoots, the subtend-
ing leaves of which are re-
duced, while the leaves of the
expanded axis of the axillary
shoot are metamorphosed into
spines (Fig. 631).

Cactaceae form a dominant
constituent of the vegetation
in the dry south-western re-
gions of the United States and
in Mexico. They are also widely
distributed in the West Indies
and South America. A similar
habit is found in some Euphor-
biaceae and Asclepiadaceae
living under corresponding
climatic conditions (cf. p. 174).
There are numerous epiphytic
Cactaceae, especially species of
Rhipsalis, Epiphyllum. and
Phyllocactus, which clothe the
branches of trees and atfect
the general aspect of the vege-
tation. Opuntia ficus indica
has become naturalised in the
Mediterranean region. The
fruits of this species and of
others of the genus are edible,
and the plants are cultivated
as fruit-trees. Some Cactaceae.
such as Anhalonium, contain
highly poisonous alkaloids and FIG. tV29.— Saponaria officinalis (£ nat. size). Porsoxocs.
saponin. The Cochineal in-
sect is grown upon species of Opuntia and Nopalea (N. coccinellifera).

B. DlALYPETALAE

Flowers with calyx and corolla.

Order 1 1 . Polyearpieae

Hermaphrodite, usually brightly coloured flowers, with an elongated
receptacle on which the free perianth segments, the stamens and the
apocarpous carpels are spirally arranged ; the carpels are indefinite in

630

BOTANY

PART II

number and may be very numerous. The separation of calyx and
corolla is frequently indistinct, and in some cases (e.g. Calycanthvs)
even the foliage leaves pass with their spiral arrangement into the
bracts of the flower. The stamens have frequently a leaf-like form
with the connective continued beyond the anthers, or forming a leafy
expansion. The stigma terminates the carpel without a definite style.
The pollination is by means of insects ; in some primitive forms by

PIG. 630.- Diagrams of the Caryo-
phyllaceae. A, Viscaria, septa
present in the lower part of the
ovary. B, Silene, septa absent.
(After EICHLER.)

Fio. 631. — Cereus gvometrizans. Two of the ribs or
ridges of a five-ribbed stem bearing flowers and fruits
(| nat. size).

beetles. The structure of the wood in some cases approaches that of
the Coniferae.

The simplest Monocotyledons (Hdobiae) exhibit an unmistakable
relationship to this order; they agree in the numerous stamens and
the apocarpous pistil. It is, however, to be noted that by no means
all the plants of the families united in this order exhibit the above
characters in the same degree. The characteristic features may
indeed be completely wanting, though the existence of intermediate
forms leaves no doubt that the genera in question must be classed here.

Family 1. Nymphaeaceae. — Aquatic plants with submerged or floating leaves,
the latter often of very large size ; the vegetative organs contain latex and thus
indicate a relationship with the Papaveraceae (Figs. 632-634).

ANGIOSPERMAE

631

Nymphaea alba, the White Water Lily (Figs. 632, 633), has large floating leaves
and white flowers, protected by firm green sepals. Within the corolla comes the

FIG. QB-2.—Nt/i,iph<iea alb-.i (i uat. si/e.) The spiral arrangement of the stamens and petals
is shown by their insertions on the ovary to the left.

zone of numerous stamens and the inferior ovary composed of numerous, coherent
carpels. The spiral arrangement of the members of the perianth and androecium

FIG. (333. — Xyiitph'iea.
Floral diagram. (After
NOLL.)

FIG. 634.— .4, Floral diagram. B, Fruit of Cabomla aquatic
showing two carpels developed as partial fruits, (x 4
After BAILLOX.)

is seen by the scars of their insertion when they are removed from the inferior
ovary (Fig. 632), and in the floral diagram (Fig. 633). In Nuphar the ovary is

632

BOTANY

PART II

FIG. 635. — Myristicu. Transverse
section of seed, fa, sch., Seed-
coat ; end, endosperm ; pe, peri-
sperm. OFFICIAL.

superior and the small petals bear nectaries ; the conspicuous calyx renders the flower
attractive. In the American genus Cabomba (Fig. 634) the flowers are trimerous and

the pistil is apocarpous. The finely divided, sub-
merged leaves differ in appearance from the entire,
floating leaves. The carpels are also free in Nelum-
bium, both the leaves and flowers of which are
raised above the surface of the water. Victoria
regia from the Amazon, and Euryale ferox from
tropical Asia, have gigantic floating leaves ; they
are often cultivated in Botanic Gardens. The
flowers of the former are beetle-pollinated, while
the latter is autogamous.

Family 2. Magnoliaceae. — The plants of this
family are all woody with large terminal flowers.
The perianth leaves without distinction into sepals
and petals, the numerous stamens and the apocarpous carpels are all spirally-
arranged in ascending order on the elongated floral axis. The stigma terminates
the carpel without inter,
vening style. Oil-cells in
the stem and leaves.
Pollen - grains with one
germ - pore are character-
istic of the family. Drimys
and Zygogynum have wood
without vessels, like the
Coniferae. Magnolia and
Liriodendron (Tulip tree)
are frequently cultivated.
OFFICIAL. — ANISI

STELLATI FRUCTUS, Star-

anise, is obtained from
Illicium verum (China).
The fruits of Illicium re-
ligiosum (Japan) are poison-
ous.

Family 3. Anonaceae.
— Woody platits of the
tropics, with spirally ar-
ranged stamens and apo-
carpous gynaeceum ; seeds
with ruminated endosperm.

Family 4. Myristica-
ceae.— Resembles the pre-
ceding family, but the
dioecious flowers are more
simply constructed (Figs.
635, 636).

OFFICIAL. — MYRIS-
TICA, Nutmeg. The seed
of Myristica fragrans divested of its testa.

Family 5. Calycanthaceae. —These plants show a continuous sequence from

Fio. 636.— Myristwa fragran*. 1, Twig with male flowers (i nat.
size). 2, Ripe pendulous fruit opening. ^, Fruit after re-
moval of one-half of the pericarp, showing the dark brown
seed surrounded by the ruptured arillus. It, Kernel freed
from the seed-coat. OFFICIAL.

ANGIOSPEBMAE

633

the foliage leaves to the numerous free perianth leaves, stamens, and carpels borne
on the depressed floral axis. The connection of the Rosaceae may perhaps be here.

Family 6. Ranunculaeeae. — The plants belonging to this family
are annual herbs (Myojsurus), more commonly perennial herbs (Calthd)
or rarely woody plants (species of Paeonia) with alternate, exstipulate
leaves. Flowers hermaphrodite, the members in many cases arranged

FIG. ii37.— Floral diagrams of Raimnculaceae. A, Adonis autumnalis. B, Aconitinn nupdlus.
C, Aquilegia vulgari*. D, Cimiclfugn racemosa. (After EICHLER.)

spirally; this is very evident in Myosurus. Perianth either forming
a simple or double perigone (Aconitiim) or differentiated into calyx
and corolla (Ranunculus). Stamens indefinite. Pollen-grains with at
least three places of exit for the pollen- tubes. Carpels three to
indefinite, borne on the convex receptacle (Fig. 638), and forming an
apocarpous, superior ovary. Ovules, borne on the ventral suture,

FIG. 638.— a. Flower of li'inunculus sceleratun ; b, the same, cut through longitudinally ;
magnified. (After BAILLON.)

singly or in numbers. The partial fruits are follicles (Paeonia),
achenes (Anemone), or berries (Hydrastis). Seed with a small embryo
enclosed within the large, oily endosperm.

IMPORTANT GENERA. — Many of our commonest meadow and woodland plants
belong to this order. They are all in greater or less degree poisonous. A number
of species of Ranunculus, characterised by the usually yellow flowers, convex
receptacle, and fruit composed of numerous free achenes, occur in Britain. The
petals have a nectary at the base. Leaves palmately divided more or less deeply.
R. sceleratus is very poisonous (Figs. 638, 639). R. arvensis with large, spiny

634

BOTANY

PART II

FIG. 639. — Ranunculus scekrat'Us (| nat. size). POISONOUS.

DIV n

AXGIOSPERMAE

635

FIG. 640. — Hi i a. u ncuhis
Carpel in

longitudinal section.
(Enlarged. After
BAILLON.)

FIG. 641. — Anemone PulsutiUa (£ nat. size). Poisosous.

636

BOTANY

PART II

achenes or nutlets (Fig. 640). The aquatic species of Ranunculus, belonging to
the section Batrachium, are often heterophyllous (Fig. 35), the floating leaves
serving to support the flowers above the surface of the water.

Species of Anemone are also widely distributed in Europe. A. nemorosa occurs
commonly in woods and is one of our early spring flowers. It has a horizontal,

subterranean rhizome, which
terminates in a flower, the
further growth of the plant
being carried on by a lateral
shoot. Perianth simple,
petaloid. All species of
Anemone have, at a greater
or less distance from the
perianth, a whorl of, usually,
three leaves forming an in-
volucre (Fig. 641). In A.
hepatica this stands just
below the perianth and thus
resembles a calyx. All the
species are to some extent
poisonous, especially A.
Pulsatilla (Fig. 641). The
plants of the genus Clematis
are mostly woody and differ
from other Ranunculaceae
in having opposite leaves.
Many species are cultivated.
C. vitalba is one of our few
native lianes. The achenes
of the species of Clematis
and of many kinds of
Anemone are provided with
hairy or feathery append-
ages, which facilitate their
distribution by the wind.
Caltha palustris, the Marsh
Marigold (Fig. 642), is one
of the most conspicuous
spring flowers in damp
meadows. Perianth simple,
bright yellow. Leaves cor-
date or reniform, short-
stalked, with erect sheath-
ing base. Fruit, as in the species of Helleborus that flower in the winter, composed
of follicles. The Monkshood (Aconitum napellus) (Figs. 643, 644) is a stately
perennial herb with underground tubers and occurs most commonly in alpine
meadows. The leaves are palmately divided, the segments being in turn pinnately
lobed. Inflorescence a dense raceme, reinforced by lateral inflorescences standing
in the axils of the upper leaves. Flowers zygomorphic. One of the five dark-
blue sepals is helmet-shaped, and protects two long-stalked, tubular, two-lipped
nectaries, which correspond to petals. The remaining petals are wanting or are

FIG. 642.— Caltha palustris (§ uat. size). Poisoxocs.

DIV. II

ANGIOSPERMAE

reduced to inconspicuous, narrow structures. Aconitum Lycoctonum lias smaller

feSI *

FIG. t544.— A'-onitum napellus (nat. size). 1, Flower seeii obliquely from in
front 2, Flower in longitudinal section. 3, The nectaries, formed from
petals, and the androecium after the perigone has been removed. 4, Fruit
composed of three apocarpous carpels. .5, Follicles opened.

FIG. QM.—Awnitum n:tpellu* (i nat. size). OFFICIAL and Poisosous.
yellow flowers of similar construction. All the species are poisonous. Aquilegia,

638

BOTANY

PART II

Delphinium, and Paeonia are favourite ornamental plants with showy flowers.
In Actaea and Hydrastis the fruit is a berry.

OFFICIAL. — ACONITI RADIX is obtained from Aconitum napellus. STAPHIS-
AGRIAE HEM INA from Delphinium staphisagria. HYD RASTIS RHIZOM A from the North

American Hydrastis Canaden-
sis (Fig. 645), a perennial herb
which sends its subaerial
shoots up from the subter-
ranean rhizome ; the base of
the shoot has keeled scale-
leaves in two ranks. The
flowers are solitary and ter-
minate the shoots, each of
which bears two foliage leaves.
The simple white perianth
falls when the flower opens.
The androecium and the apo-
carpous gynaeceum consist of
numerous members. The fruit
consists of numerous, small
berries, each of which in-
cludes 1-2 seeds. The alka-
loid HYDKASTINE is obtained
from the rhizome.

The further families of the
Polycarpicae show a limita-
tion to three in the whorls of
the simple, or more usually
double, perianth and of the
stamens.

Family 7. Berberidaceae
has only one carpel, while there
are three carpels in Family 8,
Menispermaceae. In Berberis
vulgaris the leaves on the
shoots of unlimited growth
are transformed into spines.

OFFICIAL. — TODOPHYLLI
RHIZOMA obtained from the
N. American Berberidaceous
plant, Podophyllum pelta-
tum (Fig. 646), P. emodi,
Berberis Aristata, CALUMBAE
RADIX from the twining
Menispermaceous plant Jateorhiza columba.

Family 9. Lauraceae.— Flower also composed of trimerous whorls ; perianth
3 + 3; stamens 3 + 3. The three stigmas of the single, one-seeded pistil indicate
its origin from three coherent carpels. Fruit, a berry or drupe. Anthers valvate.
Aromatic trees or shrubs with entire leathery leaves, which usually persist for
several seasons. Only Sassafras (Fig. 647), which has three-lobed leaves as well
as simple ones, sheds its foliage annually. Laurus nobilis, the Laurel, is a

FIG. 045. — Hydraslis canadensis (^ nat. size). The apocarpous
fruit to the left. OFFICIAL.

DIV. n

ANOIOSPERMAE

639

dioecious, evergreen tree of the Mediterranean region, which was well known iu
the early period of the Grecian civilisation ; it is frequently grown in cool green-
houses (Figs. 649, 650). Large plantations are grown at the Lake of Garda, where
the oil is extracted, and here the trees ripen their oval, blackish-blue drupes in
October. The genus Cinnamomum includes a number of economically important
trees such as the Camphor tree from Japan and China and the Cinnamon tree from
China and Ceylon. The latter is a stately evergreen with smooth, leathery leaves
and inconspicuous, greenish flowers in axillary inflorescences. Persea gratissima
(Fig. 648) is a native of tropical Mexico, and is frequently cultivated as a fruit
tree in the tropics. Its fruit is known as the Avocado Pear. Species of Cassytha,

FIG. 646.— Podophyllum peltatum (£ nat. size). OFFICIAL. (From Nat. Pflanzenfamilien.)

the only genus of the family including herbaceous species, occur throughout the
tropics as parasites resembling Cuscuta.

OFFICIAL. — CAMPHORA, Camphor, is obtained from Cinnamomum Camphora.
GINNAMOMI CORTEX and OLEUM ciNNAMOMi from Cinnamomum zeylanicum.
Cinnamomum Oliver i.

Family 10. Aristolochiaceae. — The zygomorphic flowers (Fig. 534) have a
simple coherent perianth and the androecium and gynaeceum united to form a
gynostemium. OFFICIAL. — Aristolochia serpentaria, A. reticulata.

The parasitic Rafflesiaceae and the insectivorous families of the Cephalotaceae,
Sarraceniaceae, Nepenthaceae and Droseraceae may best be placed with the
Polycarpicae.

Order 12. Rhoeadinae

Herbs, or more rarely shrubs, with alternate, exstipulate leaves.
Flowers hermaphrodite, cyclic ; whorls usually bimerous. Ovary

640

BOTANY

PART II

FIG. 647. — Sassafras officinale. (£ nat. size. After BERG and SCHMIDT.) 1, Male inflorescences on
a still leafless branch. 2, Fruits on a leafy shoot. 3, Male flower, k, Female flower. 5, 6,
Closed stamens of the two outer whorls. 7, Opened stamen of the innermost whorl. 8, Ovary
showing the style and the ovule.

superior, unilocular. Placentas on the
united margins of the carpels, project-
ing more or less into the cavity (Fig.
651). Stigmas commisural, i.e. situated
immediately over the sutures. Dehis-
cence of the fruit by separation of the
middle portions of the carpels from the
persistent placentas.

Family 1. Papaveraceae. — This family con-
nects the order to the Polycarpicae by such
characters as the presence of laticiferous tubes

FIG. 648.— Floral diagram of Persea.
(After EICHLER.)

FIG. 649. — Laurus nobilis with male
flowers. (£ nat. size.)

Fio. 650.— Laurus nobilis with fruits
(i nat. size.)

641

642

BOTANY

(Nymphaeaceae), occurrence of trimerous flowers in Bocconea (Berberidaceae), the
stigmas situated directly above the carpels and the occasional occurrence of an apo-
carpous gynaeceum (e.g. Platy-
stemori). The increase in number
of stamens is brought about by
chorisis ; they are cyclic. The
seeds have abundant endosperm.
Chelidonium majus, Celandine,
has yellow latex and a bicar-
pellary ovary. A number of
species of Escholtzia, Argemone,
and Papaver are cultivated as
ornamental plants. Papaver
Rhoeas, the Poppy (Fig. 652),
is a common weed in corn-fields
or dry meadows. The bent posi-
tion of the flower-bud is char-
acteristic of many Papaveraceae.
Papaver somniferum, which is of
oriental origin, has abundant
white latex. The plant has a

FIG. 651. — Floral diagram of Glaucium
(Papaveraceae). (After EICHLER.)

FIG. 653. — Floral diagram of Corydalis
cava. (After EICHLER.) At the
base of the stamen standing above
the spnr is a nectary.

FIG. 652.— Papaver Rhoeas. (£ nat. size.) OFFICIAL.

glaucous bloom and, except on the flower-stalks, which bear a few bristly hairs,
is glabrous. Leaves sessile, margin irregularly serrate or lobed. Petals violet or
white with a dark patch at the base. Ovary unilocular, incompletely septate by
the projection inwards of the numerous placentas. Fruit ripens erect on the

DIV. II

AXGIOSPERMAE

643

peduncle. In Papaver the separation of the central portion of each carpel from
the placentas at dehiscence is limited to the tips of the carpels. These portions bend
outwards just below the flat stigmatic expansion, and the kidney-shaped seeds are

Fio. 654. — Cruciferae.
Floral diagram (Brassica).

FIG. 655. — Cardamine prattnsis. Flower with
perianth removed, (x 4. After BAILLOX.)

thrown out of the small openings when the capsule, borne on its long stalk, is
moved by the wind.

OFFICIAL. — Papaver somniferum, the Opium Poppy, yields PAPAVERIS CAPSULAE
and OPIUM. Papaver Rhoeas yields RHOEADOS PETALA.

Family 2. Fumariaceae. — This small family is of interest on account of the

FIG. (55(3.— Cruciferous fruits. A, CTieiranthus cheiri ; B, Lepidium sativum ; C, Capsella bursa
pastoris; D, Lunaria Mennis, showing the septum after the carpels have fallen away.
E, Cra-nbe maritima. (After BAILLON.)

occurrence of transversely zygomorphic flowers in Corydalis (Fig. 653) and a
bi-symmetrical corolla with two spurs in Dicentra spectabilis. The fruits are
nutlets in Fumaria and capsules in Corydalis and Dicentra. Seeds with endosperm.

Family 3. Crueiferae (21). — This family is mainly distributed in

644

BOTANY

PAUT II

the northern hemisphere. Annual, biennial, or perennial herbs

without milky juice. Inflorescence racemose, usually without bracts

or bracteoles. Flowers actinomorphic, always lateral, composed of

bimerous whorls. Floral

formula, K 2 + 2, C 4, A 2 + 4,

G (2) (Fig. 654). The outer

whorl of sepals stands in the

median plane ; the four petals

alternate with the sepals. The

two outer stamens are shorter

than the four inner ones

which stand in the median

plane. The latter correspond

yroo

FIG. 657. — Transverse section of the seed
of Brassica nigra. rail, radicle ; cot,
cotyledons ; proc, vascular bundles.
(After MOLLER.)

FIG. 658.— Seeds of Cruciferae cut across
to show the radicle and cotyledons.
A, Cheiranthus cheiri(x. S);B,Sisym-
brium alliaria ( x 7). (After BAILLON.)

FIG. 659.— Brassica nigra.
OFFICIAL.

nat. size.)

to two stamens branched to the base. The carpels form a superior,
usually pod-like, ovary, which is divided into two chambers by a
false septum stretching between the parietal placentas (Fig. 656 D).
The fruit opens by the separation from below upwards of the main
portion of each carpel, leaving the seeds attached by their stalks to
the central portion formed by the placentas together with the false
septum. Rarely the fruit is indehiscent (e.g. Isatis). Embryo

DIV. II

ANGIOSPERMAE

645

curved. Endosperm wanting or reduced to a single layer of cells
coherent with the seed-coat (Figs. 657, 658).

The number of species and their abundance make the Cruciferae one of our
most important native families of flowering plants. Their brightly coloured,
mostly yellow flowers render them conspicuous in various situations and at all
periods of the year. The nectaries, which are borne on the receptacle at the base
of the stamens, also show that the flowers are entomophilous. The family includes
a number of economic plants
and others cultivated for
their flowers.

Chciranthus Cheiri, the
Wallflower (Figs. 656 A,
658 A). Matthiola, «the
Stock. Numerous species
of Brassica have been long
in cultivation ; B. oleracea,
the Wild Cabbage, in its
various forms — (a) sylvestris,
which occurs on the coasts
of Northern Europe and is
to be regarded as the wild
form ; (b) acephala, Borecole
or Kale ; (c) gonglyodes,
Turnip - rooted Cabbage ;
(d) gemmifera, Brussels
Sprouts ; (e) sabauda,
Savoys ; (/) capitata, the
Cabbage ; (g) botrytis, Cauli-
flower and Broccoli. Bras-
sica ca/itpestris, with the
cultivated forms— (a)
annua, (b} oleifera, (c) rapi-
fera. Brassica napus, the
Turnip — (a) annua, (b) olei-
lubrassica. Bras-
sica nigra, Black Mustard
(Figs. 657. 659), an annual
plant derived from the
eastern Mediterranean
region, was cultivated even
in ancient times. The radical leaves are long-stalked and lyrate with rounded
terminal lobes ; on ascending the copiously-branched stem they become lanceolate
and gradually smaller. The plant is glabrous except for some bristly hairs on the
upper surface of the leaf. Inflorescence a raceme ; the bright yellow flowers stand
out from the main axis, while the developing fruits are erect and applied to the
axis. Sinapis alba, White Mustard, is a hairy plant, distinguishable from the Black
Mustard by the long broadly-beaked fruits, the valves of which bear coarse bristly
hairs. The fruits project from the axis of the inflorescence. The seeds are
yellowish - white and twice as large as those of Brassica nigra. Anastatica
hierochuntica, Hose of Jericho, is an annual desert plant of X. Africa characterised

FIG. 660.— Capparis spinosa. Flowering branch and a young
fruit borne on the gynophore. (£ nat. size.)

646

BOTANY

PART II

by the hygroscopic movements of its branches (cf. p. 333). Cranibe (Fig. 656 E],
with the lower portion of the siliqua sterile, and Cakile are thick-leaved, strand
plants. Raphanus sativus, the Radish. Vcsicaria, Aubrictia, Draba, Lunaria
(Fig. 656 D}. Cochlearia ojficinalis, Scurvy Grass. Erophila, Ibcris with somewhat
zygomorphic flowers. Capsella bursa pastoris, Shepherd's purse (Fig. 656 C}.
Isatis tinctoria, Woad.

OFFICIAL. — SINAPIS NIGUAE SEMINA, from Brassica nigra. ARMORACIAE
RADIX, from Cochlearia Armoracia.

Family 4. Capparidaceae. — Capparis spinosa is a small shrub occurring on
rocky ground in the Mediterranean region. The leaves are simple with short,
recurved, spiny stipules. The actinomorphic flowers are axillary and solitary ; the
androecium by chorisis consists of numerous members. In this respect and in the
presence of a gynophore which raises the pistil above the rest of the flower (Fig.
660), there are differences from the Cruciferae. The fruit is a berry which reaches
the size of a plum and contains numerous seeds. Capers are prepared from the
young flower buds.

Order 13. Cistiflorae

The plants belonging to this order are characterised by their usually regular,
pentamerous flowers ; the stamens are increased in number by chorisis, or when

FIG. 661. — Floral diagram of
Helianthemum vulgare (Cis-
taceae). (EICHLER.)

FIG. 662. — Floral diagram
of Viola. (After NOLI,)

FIG. 663. — Thea chinensis. Flowering shoot
(§ nat. size) ; fruit and seed.

the separation of the branches is incomplete they form distinct bundles ; the
superior ovary is usually trimerous.

DIV. II

ANGIOSPERMAE

647

Family 1. Cistaceae. — Pentamerous, regular flowers, with numerous stamens
and three to five carpels united to form a unilocular or multilocular ovary with a
single style and parietal placentas. In Britain the Rock Rose (Helianthemum
vulgare) (Fig. 661). Many species of Cistus are characteristic shrubs of the vegeta-
tion of the Mediterranean region.

Family 2. Violaceae. — Distinguished by dorsiventral flowers with only five
stamens. Ovary unilocular with a simple style. The flowers have the anterior petal
prolonged backAvards as a spur, into which two nectar- secreting processes of the two
anterior stamens project (Fig. 662).

Family 3. Ternstroexniaceae have a gradual transition from sepals to petals,
like that found in the Magnoliaceae, numerous stamens, and a trilocular ovary
with axile placentation. The Tea-plant (Fig. 663) and the Camellia belong to
this family.

Family 4. Guttiferae. — Distinguished by the schizogenous glands and the
union in bundles of th5 stamens. Hypericum is a British representative. The red
contents of the secretory organs of Garcinia Hanburyi when dried form Gamboge.

Family 5. Dipterocarpaceae. —Characterised by the great enlargement of some
or all the sepals after fertilisation. Dryobalanops Camphora yields Borneo Camphor.
Dammar is obtained from Shorea Wiesneri.

Order 14. Columniferae

The essential character of this order is afforded by the androecium
of the regularly pentamerous, actinomorphic, hermaphrodite flowers.

One of the two whorls of stamens,
usually the outer one, is suppressed
or only represented by staminodes,
while the other whorl has undergone
a greater or less increase in the

FIG. 664.— Flower of Althaea officinalis, cut
through longitudinally. o, Outer; 5,
inner calyx ; c, petals ; d, androecium ;
/, pistil ; e, ovule. (After BERG and

SrHMIDT.)

FIG. 665. — Malvaceae.
Floral diagram (Malva).

FIG. 666. — Malva sylrestris. a, Flower :
b, flower-bud ; c, fruit. (Nat. size.)

648

BOTANY

PART II

number of its members by chorisis. The branching is frequently
accompanied by cohesion of the filaments. The carpels also some-
times exhibit an increase in number as a result of branching. The
superior ovary is then divided into a corresponding number of loculi.
Family 1. Malvaceae. — Characterised by the flowers with the

FIG. 667.— Flowering branch and open fruit of Gossypium herbaceum. (£ nat. size.) OFFICIAL.

corolla contorted in the bud. Protandrous. Stamens united into a tube
around the ovary ; the free ends of the stamens, each of which bears
a single reniform theca, project from the margin of the staminal
tube. K 5, C 5, Aoo, G (3) or oo. Pollen grains with spiny exine, so
that they readily adhere to the hairy bodies of insects (Fig. 514).

The genus Malva which occurs in Britain includes perennial herbs, with long-
stalked, palmately-veined leaves. Flowers solitary or in small cymose inflorescences,

DIV. n

ANGIOSPERMAE

649

in the axils of leaves. Three free segments of the epicalyx. Petals usually rose-
coloured, deeply notched (Fig. 666). In Althaea the whole plant is clothed with
stellate hairs, giving it a soft velvety appearance. Epicalyx of 6-9 segments
united at the base. The fruit is a schizocarp consisting of numerous carpels
arranged in a whorl.

Hibiscus and Gossypium are shrubs with three- to five-lobed leaves with long
stalks. Flowers with a large epicalyx of three segments, which completely covers
the calyx. Fruit of three to five carpels, loculicidal. Seed of Gossypium covered
with long hairs which aid in its dispersion by the wind. When stripped from
the seeds and cleaned these hairs
form cotton wool. The most
important species of Cotton are
G. barbadcnse, G. arbor eum, G.
herbaceum (Fig. 667).

FIG. 608.— Tiliaceae. Floral diagram
(Tilia). (After EICHLER.)

FIG. 669.— Tilia ulmifolia. A, Inflorescence (a), with
bract (ft), (nat. size). B, Longitudinal section of
fruit (magnified) ; o, pericarp ; p, atrophied dissepi-
ment and ovules ; q, seed ; r, endosperm ; s, embryo ;
t, its radicle. (After BERG and SCHMIDT.)

FIG. 670.— Sterculiaceae.
Floral diagram (Theo-
broma). (After EICHLER.)

OFFICIAL.— Gossypium bdrbadense and other species yield

Family 2. Tiliaceae. — Plants with simple stalked leaves provided with
deciduous stipules. Calyx polysepalous. Aestivation of calyx and corolla valvate.
Stamens completely free from one another with introrse anthers ; usually only
the inuer whorl is present and has undergone branching (Fig. 668). Style simple.

Most of the genera are tropical. The herbaceous species of Corchorus yield
Jute. In Britain two species of Tilia, Lime, occur. These are stately trees with
two-ranked petiolate leaves, the stipules of which are soon shed. The leaves,
which have a serrate margin, are asymmetrical. The inflorescence (Fig. 669 A]
is coherent with a bract tor half its length ; this serves as a wing in the distribu-
tion of the fruit. The umbel - like inflorescence of the Lime is composed of
dichasia ; Tilia platyphyllos has 3-7, T. parvifolia 11 or more flowers in the

650

BOTANY

PART II

inflorescence. The hairy ovary lias two ovules in each of its five loculi. The fruit
only contains one seed (Fig. 669 B).

Family 3. Sterculiaceae. — This family which is distributed in the tropics
resembles the Tiliaceae. Flowers with a gamosepalous calyx ; corolla twisted in

FIG. 671.— Theobroma Cacao. 1, Stem bearing fruits. 2, Flowering branch. 3, Flower, k, Circle of
stamen. 5, Stamen from anterior side. (3, It, about nat. size ; 5, enlarged ; 1, 2, greatly
reduced.) OFFICIAL.

the bud ; stamens coherent to form a tube. The antisepalous stamens are stami-
nodial ; the antipetalous stamens are often increased in number. Anthers extrorse.
The most important plant is the Cocoa tree (Theobroma Cacao, Figs. 670, 671).
It is a native of tropical Central and South America, but has long been cultivated.
It is a low tree with short-stalked, firm, brittle, simple leaves of large size, oval
shape, and dark green colour. The young leaves are of a bright red colour, and,

ANGIOSPERMAE

651

as in many tropical trees, hang limply downwards. The flowers are borne on
the main stem or the older branches, and arise from dormant axillary buds
(CAULIFLOUY). Each petal is bulged out at the base, narrows considerably above
this, and ends in an expanded tip. The form of the reddish flowers is thus some-
what urn-shaped with five radiating points. The pentalocular ovary has numerous
ovules in each loculus. As the fruit develops, the soft tissue of the septa extends
between the single seeds ; the ripe fruit is thus unilocular and many-seeded. The
seed-coat is tilled by the embryo, which has two large, folded, brittle cotyledons.
Cola acuminata and C. vcra, natives of tropical Africa, yield the Kola nuts which
are used in medicine.

OFFICIAL. — Theobroma Cacao, from which OLEUM THEOBEOMATIS is obtained.

Orders 15-17 are connected by a number of characters such as
reduction in number of stamens, presence of a disc, one-seeded loculi
in the fruit ; these may indicate a common relationship to the
Tricoccae or to the forms from which the latter order came.

Order 15. Gruinales

The flowers of the majority of the plants belonging to this order
are hermaphrodite, pentamerous, and radially symmetrical, with a
superior, septate ovary. K 5, C 5,
A 5 + 5, G (5). When the flowers
are zygomorphic they frequently ex-
hibit reduction (Polygalaceae). Stamens
coherent at the base, obdiplostemonous

FIG. 672. — Floral diagrams of Geraniaceae. A, Geranium
pratense. B, Pelargonium zonale. (After EICHLER.)

FIG. 673. — Fiuit of Pelargonium in-
quinans. (x 3. After BAILLON.)

or haplostemonous. Nectaries to the outer side of the stamens or
as an annular disc within the stamens (Rutaceae). Ovules usually
pendulous, with the micropyle directed upwards and the raphe ventral ;
or the micropyle is downwardly directed and the raphe dorsal.

Family 1. Geraniaceae. — The genera Geranium with actinomorphic and Pelar-
gonium with dorsiventral flowers both have stalked, palmately- veined leaves.
Two ovules in each loculus. When ripe the five beaked carpels separate from a
central column, and either open to liberate the seeds, or remain closed and by the
hygroscopic movements of the awn-like portion bury the seed in the soil (Fig.
673 ; cf. Fig. 275, p. 334).

652

BOTANY

PART II

Family 2. Linaceae. — Linum usitatissimum, Flax (Fig. 674), has long been
in cultivation. It is an annual, and bears numerous blue flowers, which last
only a short time, in racemose cincinni. The flower has its stamens united
at the base and five free styles. The stem bears numerous small narrow leaves.
The bast-fibres after proper
preparation are woven into
linen. The seeds from the
5-locular capsule yield oil.

OFFICIAL. — LINUM,
seeds of Linum usitatissimum.

Family 3. Erythroxylaceae.
— Erlhroxylon Coca is a small
Peruvian shrub, with entire,
simple leaves and axillary
gioups of small white flowers
(Fig. 675). Cocaine is obtained
from the leaves of this plant.

the

FIG. 674. — Linum usitatissimum.
A, Flower. B, Androecinm and
gynaeceum. C, Capsule afUr
dehiscence. (A, nat. size ; B, C
x3.) OFFICIAL.

FIG. 675. — Erythroxylon Coca. (§ nat. size.)

Family 4. Zygophyllaceae.

OFFICIAL. — Guiacum sanctum and Guiacum ojficinale, West Indian trees with
opposite, paripinnate leaves. Ovary bicarpellary, bilocular. Fruit winged.
They yield GUIACI LIGNUM and GUIACI IIESINA.

Family 5. Rutaceae.— IMPORTANT GENEKA. — Ruta graveolcns ( Fig. 676), the
Rue, is a somewhat shrubby plant with pinnately-divided leaves. The terminal
flowers of the dichasial inflorescences are pentamerous in robust examples ; all
the other flowers are tetramerous with a large intrastaminal disc. Dictamnus
Fraxinella has panicles of conspicuous, dorsiventral flowers ; the carpels are free
in their upper portions. The important genus Citrus (22) has peculiarly con-
structed flowers (Figs. 677, 678). The numerous stamens are united in bundles

DIV. n

ANGIOSPERMAE

653

and arranged in a single whorl. The number of carpels is also increased.

fruit is a berry ; the succulent

portion is formed of large cells

with abundant cell -sap which

project into and fill up the loculi

of the ovary. The seeds have

usually several embryos (cf. p.

578). The leaves of many species

are simple and provided with more

or less winged petioles. Other

species have trifoliate leaves, and

the articulation at the base of the

lamina shows that the apparently

simple leaves correspond to im-

paripinnate leaves, 5f which only

the terminal leaflet is developed.

The thorns at the base of the leaf

are derived by modification of the

first leaves of the axillary bud.

The

FIG. 677.— Floral diagram of Citrus
vulgaris. (After EICHLER.)

Citrus is originally an East
Asiatic genus ; a number of
species inhabit the warmer
valleys of the Himalayas.
All the important cultivated
forms have been obtained
from the Chinese. Citrus
decumana, the Shaddock, is
tropical ; C. medico, is the
form which was known to the
Greeks in the expeditions
of Alexander as the Median
apple. It is now widely
spread and has a number of
varieties of which Citrus
(medico) Limonum is the
Lemon. This tree was intro-
duced into the Mediterranean
region in the third or fourth
century. Citrus (medico)

FIG. 678. — Citrus vulgaris. (£ nat. size.) OFFICIAL.

654

BOTANY

TART II

Bajoura has thick-skinned fruits from which citron is obtained. Citrus Aurantium
occurs in two distinct forms, C. (Aurantium) vulgaris (Fig. 678) and C. (Auran-
tium} sinensis. Citrus nobilis, the Mandarin, is also of Chinese origin. Chimaeras,
called Bizzaria, have been obtained by grafting between Citrus Aurantium and
C. Limonum. Pilocarpus jaborandi, a tree-like shrub with large, imparipinnate
leaves, native of Eastern Brazil.

FIG. 679. — Quassia amara. (Nat. size. After BERG and SCHMIDT.)

OFFICIAL. — Citrus Aurantium, var. Bigaradia, yields AURANTII CORTEX
SICCATUS, AURANTII CORTEX RECENS, and AQUA AURANTii FLORis. Citrus medica,
var. limonum, gives LIMONIS CORTEX, and LIMONIS succus. Aegle marmelos
yields BELAE FRUCTUS. BUCHU FOLIA are obtained from Barosma betulina.

Family 6. Simarubaceae. — Contain bitter principles. Quassia amara
(Surinam) (Fig. 679), a small tree with beautiful leaves and showy flowers.

OFFICIAL. — QUASSIAE LIGNUM from Picrasma excelsa (West Indies).

DIV. n

ANGIOSPERMAE

655

Family 7. Burseraceae. — Woody plants with resin passages. Commiphora
abyssinica and C. Sehimperi are trees found in Arabian East Africa. Boswellia
Carteri and B. Bhau Dajianae are 'small trees from the
same region which yield OLIBANUM. Canarium.

OFFICIAL. — MYRRHA, Myrrh, from Balsamodendron
Myrrha and other species.

Family 8. Polygalaceae. — K5, C3, A (8), G(2). The
two lateral sepals are petaloid. Three petals, the lowest
of which forms a keel. Stamens 8, coherent into a tube
(Figs. 680-682). Polyyala chamaebuxus is a small shrubby
plant occurring in the Alps. P. vulyaris and P. amara
occur in Britain.

OFFICIAL. — Polygala Senega (North America) yields

SENEGAE RADIX.

Order 16. Sapindinae

This includes the following families : —
Family 1. Sapindaceae. — Tropical. The crushed seeds
of Paullinia cupana, a liane of Brazil, yield GUARANA.

Fio. 680.— Floral diagram of Polygala myrtifolia. (After EICHLER. )

FIG. 681.— Polygala Senega. A, Flower ; a, small ; 6, large sepals ;
c, keel ; e, lateral petals ; d, androecium. B, Androecium ; h, anthers
(magnified). (After BERG and SCHMIDT.) OFFICIAL.

FIG. 682.— Polygala Senega.
(£nat. size.) OFFICIAL.

Family 2. Anacardiaceae.— Mostly tropical. Mangifera indica ; Rhus toxico-
dendron • Pistacia.

Family 3. Aquifoliaceae. — Ilex aquifolium. The Holly, an evergreen shrub or
tree of Western Europe (Fig. 683). 7. paraguariensis yields Paraguay Tea or Mate.

656

BOTANY

I'ART II

FIG. 683.— Floral diagram of Ilex aquifolium.
(After EICHLER.)

FIG. 684.— Acer pseudoplatanus (% nat. size). 1, Branch with pendulous terminal inflorescence.
S, Male flower. 3, Female flower. 4, Fruit. 5, Floral diagram. (2 and 3 enlarged.) (After
EICHLER.)

DIV. II

ANGIOSPERMAE

657

Family.,,4. Aceraceae. — Include Maples and Sycamores with their character-
istically winged fruits (Fig. 684).

Family 5. Hippocastanaceae. — The Horse-chestnut. Aesculus hippocastanum.

Order 17. Frang-ulinae

This order is characterised
stamens and the intrastaminal
disc.

Family 1. Rhamnaeeae. —
The only native genus of this
family, which is distributed in
the tropics, is Rhamnus.

by the single whorl of antipetalous
B O

Rh. Frangula (Figs. 685 B, 686,
687), the Berry-bearing Alder, is a
shrub with alternate, entire leaves
provided with small stipules. The
flowers are solitary or in groups in
the axils of the leaves ; pentamerous,
with two carpels. The floral receptacle forms

FIG. 635. — Floral diagrams of A, Rhamnus cathartica
(represented as hermaphrodite), and B, Rh.
Frangula. (After EICHLER.)

a cup-shaped disc. Two (less
commonly three) carpels ; stigma
undivided. Fruit, a drupe with
two or three seeds. Rh. cathar-
ticus has usually spiny branches
bearing opposite leaves with
serrate margins. Flowers tetra-
rnerous throughout (Fig. 685 A),
dioecious by suppression - of
stamens or carpels ; female flower
with four free styles and a four-
seeded drupe. Seeds with a
dorsal raphe. Colletia spinosa

FIG. 686.— Rhamnus Frangula (£nat. size). Flowering
branch and portion of a branch bearing fruits.

FIG. 687.— Rhamn us Frangula. Flower
cut through longitudinally, a, Re-
ceptacle ; b, calyx ; c, petal ; d, a
stamen; e, pistil (magnified). (After
BERO and SCHMIDT.)

and C. cru-ciata are leafless South American shrubs ; the thorns of the former
are cylindrical, those of the latter flattened laterally.

658

BOTANY

PART II

OFFICIAL. — Rhamnus purshianus yields CASCARA SAGRADA or RHAMNI

PURSHIANI CORTEX.

Family 2. Vitaceae (Figs. 688, 689).— The genera Vitis, Ampelopsis, and
Parthenocissus in the northern hemisphere and the tropical genus Cissus belong
here. Vitis vinifera, the Grape Vine, is a cultivated plant with numerous races
and varieties. The tendrils correspond to shoots and stand opposite to the
leaves ; they are at first terminal, but become displaced to one side by the develop-
ment of the axillary shoot. The inflorescence is a panicle taking the place of a
tendril ; intermediate forms between inflorescences and tendrils are of frequent
occurrence. Calyx only represented by a small rim ; the pentamerous corolla,
with the petals united by their tips, is thrown off when the flower opens. Raisins
are obtained from Vitis vinifera. Currants are the seedless fruits of Vitis vinifera,

FIG. 088.— Vitis vinifera. Opening
flower, a, Calyx ; b, corolla ; c,
disc ; d, stamens ; e, ovary (mag-
nified). (After BERG and SCHMIDT.)

FIG. 689. — Floral diagram of Ampelopsis
hederacea. (After EICHLER.)

var. apyrena. Species of Parthenocissus distributed in North America and Asia
go by the name of Wild Vines ; some of them have tendrils with adhesive discs
(Fig. 210).

Order 18. Rosiflorae

The cyclic flowers are in other respects similar to those of the
Polycarpicae ; the connection of the Rosaceae with the Calycanthaceae
is particularly close. The single carpel in the Pruneae and the
dorsiventral flowers of the Chrysobalaneae lead on to the Leguminosae.

The order includes plants of very diverse form and construction
with alternate leaves. The flowers are almost always actinomorphic
with the members arranged in whorls ; they have five, ten or
numerous stamens and carpels, the pistil is as a rule apocarpous. The
large part played by the floral axis in the construction of the flower
and fruit is characteristic. K5, C5, A5-oo , Gl-oo .

Family 1. Crassulaceae. — Succulent herbs (cf. p. 174) or under-shrubs with
cymose inflorescences. Sedum (Fig. 690) with pentamerous flowers ; there are a
number of British species. Sempenrivum, flowers with from six to an indefinite
number of members in the whorls ; S. tectorum. Bryophyllum with tetramerous
flowers, noteworthy on account of the abundant formation of buds in the indenta-
tions of the margin of the leaf. Crassula ; South African forms mimic stones by
their globular form (23).

DIV. n

ANGIOSPERMAE

659

Family 2. Saxifragaceae. — Herbs or woody plants with hermaphrodite,
obdiplostemouous flowers. Fruit a capsule or a berry formed of two carpels and
containing an indefinite number of albuminous seeds. Saxifraga, Saxifrage, small
herbaceous plants which are especially numerous on crags and rocky ground in

•lite.

FIG.

.—.<«! urn Tdephium.
(x 4,

a, Flower ; 6, flower in longitudinal section.
After H. SCHESCK.)

mountainous districts. They have a rosette of radical leaves and bear numerous
pentamerous flowers grouped in various types of inflorescence. The two partially
inferior carpels are distinct from one another above. Parnassia palustris is common
on wet moors, pentamerous flower with 4 carpels. One whorl of stamens modified

FIG. 691.— Ribes rubrum. (§ nat. size.)

into palmately-divided staminodes, which serve as nectaries. The species of Ribes
have an inferior ovary which develops into a berry, and on this account are
commonly cultivated. R. rubrum (Fig. 691), Red Currant, R. nigrum, Black
Currant, R. grossularia, Gooseberry. Other Saxifragaceae are favourite ornamental
plants, e.g. Ribes aureum and R. sanguineum, Hydrangea, Philadelphus, and
Deutzia.

660

BOTANY

PART II

Family 3. Rosaceae (24). — Characteristic features of this family
are the constant presence of stipules, the absence of endosperm from
most of the seeds, the apocarpous fruits, and, as a rule, the numerous
stamens (Fig. 692). The two latter features are also found in the
Ranunculaceae, or generally in the Polycarpicae, but the floral members
are there spirally arranged while in the Rosaceae they are in whorls,
and the flowers are perigynous.

In many cases the increase in number of members of the androecium and
gynaeceum proceeds from an intercalary zone of the hollowed floral axis, and
continues for a considerable period. The introduction of new members is deter-
mined by the spatial relations, so that differences in the numbers of members are
found in individuals of the same species.

The genus Spiraea has typically pentamerous flowers with superior ovaries ;
many species are cultivated as ornamental shrubs (Fig. 692 E). Quillaja Saponaria
(Fig. 693), from Chili, is an evergreen tree with shortly -stalked, alternate,

Fio. 692. — Floral diagrams of Rosaceae. A, Sorbus domestica. B, Prunus Padus. C, Rosa
tomenlosa. D, Sanguisorba officinalis. E, Spiraea hypericifolia. (After EICHLER.)

leathery leaves and terminal dichasia usually consisting of three flowers. The
flower has a five-toothed, nectar- secreting disc projecting above the large sepals.
Five of the stamens stand at the projecting angles of the disc opposite the sepals ;
the other five are inserted opposite the petals at the inner margin of the disc.
Petals narrow, white. Ovary superior. Only the middle flower of the dichasium
is hermaphrodite and fertile, the lateral flowers are male and have a reduced
gynaeceum. Fruit star-shaped, composed of partial fruits. Each carpel dehisces
by splitting into two valves. Seeds winged.

The genera Pyrns, Cydonia, etc., are distinguished from the other Rosaceae by
their inferior ovary, which usually consists of five carpels bound together by the

DIV. II

ANGIOSPERMAE

661

hollow floral receptacle so that only the styles are free. The fruit resembles a
berry, the floral receptacle becoming succulent. The boundaries of the separate
loculi are formed of parchment-like or stony tissue. Pyrus mains, Apple (Fig.
521, 3 ; Fig. 694), and P. communis, the Pear, are important and long-cultivated
fruit trees, of which numerous varieties are grown. Cydonia vulgaris, the Quince,
has large, solitary, rose-coloured flowers. The fruits are in shape like an apple
or pear, covered with fine woolly hairs and with a pleasant scent, though not
edible when uncooked. In Mespilus germanica, the Medlar, the fruit has an
apical depression surrounded by the remains of the calyx. The evergreen
Eriobotrya japonica, is commonly planted in the Mediterranean region; Sorbiis

FIG. 693.— Quillaja Saponaria. (£ nat. size.
After A. MEYER and SCHUMANN-.)

FIG. 694.— Pyrus malus. Flowering shoob
single flower, and fruit in longitudinal
section. (£ nat. size.)

(Pyrus} aucuparia, the Rowan. Crataegus (Mespilus} oxycantha, the Hawthorn,
in hedges or planted as an ornamental tree (cf. p. 318).

A concave, pitcher -shaped floral axis with one to many free carpels, each of
which encloses 1-2 ovules, characterises the genus Rosa. The partial fruits are
nut-like, and are enclosed by the hollowed floral axis (Figs. 569, 692 (7). The
leafy development of the numerous stamens has given rise to the cultivated
double forms. Agrimonia and Hagenia abyssinica have a dry cup-shaped receptacle.
Hayenia is a dioecious tree with unequally pinnate leaves, the adherent stipules of
which render the petiole winged and channelled. Inflorescence a copiously
branched panicle. Each flower has two bracteoles and an epicalyx. The flowers
are unisexual by suppression of the male and female organs- respectively. The
corolla later falls off and the sepals become inrolled, while the epicalyx enlarges.
The two free carpels have each a single ovule. Fruit one-seeded (Figs. 695, 696).
AlchemiUa has no petals (Fig. 521, 2). Sanguisorba officinalis has polygamous

662

BOTANY

PART II

flowers, without epicalyx or corolla, aggregated in heads. Flowers tetramerous
with 1-2 carpels (Fig. 692 D). These are greatly reduced forms.

FIG. 695. — Hagenia abyssinica. 1, Female flower ; e, epicalyx ; /, calyx ; g, corolla (x 4).
2, Fruit (nat. size), with enlarged epicalyx. (After BERG and SCHMIDT.) OFFICIAL.

FtG. 696. — Hagenia abyssinica. Inflorescence (J nat. size). (After BERG and SCHMIDT.) OFFICIAL.

DIV. n

AtfGIOSPERMAE

663

Potentilla with a number of British species has a flattened receptacle, epicalyx,
and an apocarpous pistil. Geum and Dryas have hairy carpels which elongate in
fruit and are distributed by the wind. Fragraria, Strawberry, with small achenes
situated on the succulent, enlarged, floral receptacle. Rubus, Blackberry, has
numerous species, mostly scrambling shrubs with recurved prickles. Leaves

FIG.

)7. — Primus remfus (§ rial. size). 1, Flowering shoot ; 2, flower cut in two
(slightly enlarged) ; 3, fruits ; It, fruit cut through longitudinally.

trifoliate. E. iclaeus, the Raspberry, is one of the few species which are not
straggling climbers. The small drupes are closely crowded on the convex receptacle,
forming the collective fruit.

The group of the Pruneae which includes a number of important trees bearing
stone-fruits has a single carpel situated in the middle of the flat expanded floral
receptacle (Fig. 692 B}. Prunus cerasus, the Wild Cherry (Fig. 697) ; P. avium,
Gean ; P. domestica, the Plum; P. arrncniaca, the Apricot, and P. persica, the
Peach, are of Chinese origin ; P. Amygdalus, the Almond, from the eastern Mediter-
ranean region. The succulent mesocarp of the Almond dries up as the fruit ripens
and ruptures, setting the stony endocarp free.

664

BOTANY

POISONOUS. — The seeds of many Rosaceae contain amygdalin, but usually not
in such amount as to be poisonous, owing to the resulting hydrocyanic acid, when
eaten fresh in small quantity ; this is, however, often the case with the residuum
left after the seeds, e.g. of bitter almonds, have been crushed. The leaves of the
Cherry Laurel (Prunus laurocerasus] may also give rise to toxic effects.

OFFICIAL. — ROSAE GALLICAE PETALA from cultivated plants of Rosa gallica ;
OLEUM ROSAE and AQUA ROSAE from Rosa damascena. AMYGDALA DULCIS and
AMYGDALA AMARA from Prunus amygdalus. PRUNUM from Prunus domestieus.

PRUNI VIRGINIANAE CORTEX from Prunus sero-

A J?

tina. LAUROCERASI FOLIA from Prunus lauro-
cerasus. Cusso from Hagenia abyssinica.
QUILLAIAE CORTEX from Quillaja Saponaria.

Order 19. Leguminosae

The common characteristic of all
Leguminosae is afforded by the pistil.
This is always formed of a single carpel,

FIG. 698.— Floral diagrams of Mimo- *

saceae. A , Mimosa pudica. B, Acacia the ventral suture of which is directed
iophantha. (After BICHLER.) to the dorsal side of the flower (Figs.

698, 701, 706). It is unilocular, and

bears the ovules in one or two rows on the ventral suture. The fruit
is usually a pod (legume), which dehisces by splitting along both the
ventral and dorsal sutures (Fig. 711). Nearly all Leguminosae have

FIG. 699.— Acacia nicoyensis. From Costa Rica. /, Leaf and part of stem ; S, hollow thorns in
which the ants live ; F, food bodies at the apices of the lower pinnules ; N, nectary on the
petiole. (Reduced.) II, Single pinnule with food-body, F. (After F. NOLL. Somewhat
enlarged.)

alternate, compound, stipulate leaves. Many are provided with
pulvini (Figs. 132, 290, 291), which effect variation movements of the
leaves and leaflets.

Family 1. Mimosaeeae. — Trees, and erect, or climbing, shrubby
plants with bipinnate leaves. Flowers actinomorphic, pentamerous or

DIV, n

ANGIOSPERMAE

665

tetramerous (Fig. 698). Aestivation of sepals and petals valvate.
Stamens free, numerous, or equal or double in number to the petals.

FIG. 700.— Acacia catechu. (§ uat. size. After MEYER and SCHUMANN.) OFFICIAL.

The colour of the flower is due to the length and number of the
stamens, the corolla being as a rule inconspicuous. The pollen grains
are often united in tetrads or in larger numbers. The flowers are
grouped in spikes or heads. Embryo straight in the seed.

666

BOTANY

PART II

FIG. 701. — Floral diagrams of Caesalpiniaceae. A, Cercis siliquastrum. B- Tamarindus indica.

(After EICHLER.)

FIG. 702. Cassia angustifolia. (§ nat. size. After A. MEYER and SCHUMANN.) OFFICIAL.

DIV. II

ANGIOSPERMAE

667

There are no representatives native to Europe of this family, which is
abundant in the tropics. The Sensitive Plant (Mimosa pudica) (Fig. 291) occurs
as a weed throughout the tropics and exhibits great irritability to contact.
Numerous species of the genus Acacia are distributed through the tropics
and sub-tropics of the Old and New Worlds ; some are in cultivation in the
Mediterranean region. The Australian forms of the genus are frequently

FIG. 703. — Tamarindus indica. (| nat. size. After A. MEYER and SCHUMANN.) OFFICIAL.

characterised by possessing phyllodes (Figs. 136, 192), the vertical position of
which contributes to the peculiar habit of the Australian forests. Some American
species of Acacia are inhabited by ants (Fig. 699) which live in the large stipular
thorns and obtain food from Belt's food-bodies (25) at the tips of the pinnules. A
mutual symbiosis has not been demonstrated in this case. Many species of Acacia
are of considerable economic value owing to the presence of gums and tannins in
the cortex or in the heart-wood. A. catechu (Fig. 700) and A. sum a are East
Indian trees from Avhich Catechu is obtained.

OFFICIAL. — By the disorganisation of the parenchyma of the stem of Acacia

668

BOTANY

PART II

Senegal (Soudan and Senegambia) and of other species, ACACIAE GUMMI is obtained.
This exudes from wounds as a thick fluid and hardens in the air. A. arabica,
A. catechu and A. decurrens are also official.

Family 2. Caesalpiniaeeae. — Trees or shrubs with pinnate or
bipinnate leaves. Flowers usually somewhat dorsiventral. Corolla

FIG. 705. — Krameria triandra. (f nat.
size. After A. MEYER and SCHU-
MANN.) OFFICIAL.

FIG. 704. — Tamarindus in-
dica. Fruit in longitu-
dinal section. M , the fleshy
mesocarp. (After BERG
and SCHMIDT.) OFFICIAL.

FIG. 706. — Floral diagrams of Papilionaceae.
A, Vicia Faba. B, Laburnum vulgare. (After EICHLER.)

with ascending imbricate aestivation (Fig. 701) or wanting. Typical
floral formula :K5, C 5, A5 + 5, G- 1. The number of petals and
stamens is often incomplete. Embryo straight.

Abundantly represented in the tropics and sub-tropics.

In Cassia angustifolia the sepals and petals are both five in number and free

DIV. II

ANGIOSPERMAE

669

(Fig. 702). The lower overlapping petals are somewhat larger than the upper ones.

Of the ten stamens the three upper ones are short and sterile, while the other

seven, the filaments of which are curved and convex below, diminish in length

from above downwards. The anthers open by means of terminal pores. The pod

is compressed and broad and flat. The flowers are borne in racemes in the axils

of the leaves of the shrub, which is about a metre high. The bright green,

equally pinnate leaves have

small stipules at the base.

Tamarindus indica (Fig. 703)

is a handsome tree, native to »

tropical Africa, but now planted

throughout the tropics. Its

broadly - spreading crown of

light foliage makes it a favourite

FIG. 707.— Lotus corniculatus (% nat.
size). Flowering shoot ; flower, keel,
stamens. Carpel (nat. size) and fruit
(4 nat. size).

FIG. 70S.—Myroxylon Pereirae. (g nat. size. After BERG
and SCHMIDT.) OFFICIAL.

shade-tree. The racemes of flowers are terminal on lateral twigs bearing equally
pinnate leaves. The individual flowers are markedly zygomorphic. The fruit is
peculiar. The pericarp is differentiated into an outer brittle exocarp, a succulent
mesocarp, and a firm endocarp consisting of stone-cells investing the more or less
numerous seeds individually (Fig. 704). The almost imperceptibly dorsiventral
flowers of Copaifera have no corolla ; the four sepals are succeeded by 8-10 free
stamens. The fruit is one-seeded but opens when ripe. The seed is invested on

670

BOTANY

PART II

one side by a succulent, irregularly-limited arillus. None of the Caesalpiniaceae
are British. Ceratonia siliqua and the cauliflorous (cf. p. 651) Cercis siliquastrum
from the Mediterranean region (Fig. 701 A) and Glcditschia triacanthos (N. Am.)
(Fig. 199), are sometimes cultivated as ornamental plants.

OFFICIAL. SENNA INDICA, the pinnae of Cassia angustifolia (Trop. East Africa

and Arabia, cultivated at Tinnevelly in Southern India) ; SENNA ALEXANDRINA
from C.acutifolia ; Cassia fistula (Trop. Am.) yields CASSIAE PULPA ; COPAIBA is
obtained from Copaifera Langsdorfii and other species ; TAMARINDUS from the
succulent mesocarp of Tamarindus indica ; HAEMATOXYLI LIGNUM, the heart-wood
of Ifaematoxylon campechianum (Trop.
Am.) ; KRAMERIAE RADIX from Krameria
triandra, a shrub growing in the Cor-
dilleras. Flowers atypical ; the sepals
brightly coloured within ; the corolla
small. Three stamens opening by pores
at the summit. Fruit spherical, prickly.
Leaves simple, silvery white (Fig. 705).

Family 3. Papilionaeeae.—
Herbs, shrubs, or trees with, as a
rule, imparipinnate leaves. Flowers
always markedly zygomorphic.

FIG. IQd.—Myroxylon Pereirae. See Text. (En-
larged. After BERG and SCHMIDT.) OFFICIAL.

FIG. 710. — Fruit of Myroxylon Pereirae.
(§ nat. size.) OFFICIAL.

Calyx of five sepals. Corolla of five petals, papilionaceous, with
descending imbricate aestivation (Fig. 706). Stamens 10; filaments
either all coherent into a tube surrounding the pistil (Lupinus) or the
posterior stamen is free (Lotus), or all are free (Myroxylon, Fig. 709).
Seeds with a curved embryo.

Abundantly represented in the temperate zones ; fewer in the tropics.

The component parts of a papilionaceous flower are seen separately in Fig. 707.
The posterior petal, which overlaps the others in the bud (Fig. 706), is termed the
standard (vexillum). The two adjoining lateral petals are the wings (alae), and the
two lowest petals, usually coherent by their lower margins, together form the keel

DIV. II

ANGIOSPERMAE

671

(carina). The upper ends of the stamens are usually free and curve upwards, as
does also the style bearing the stigma.

The genus Myroxylon is of importance on account of the balsam obtained from
species belonging to it. Myroxylon Pereirae is a tree of moderate height with
alternate, imparipinnate leaves (Fig. 708). The flowers are borne in the terminal
racemes and have a large vexillum, the other petals remaining narrow and incon-

FIG. 711.— Laburnum vulgare. (^ nat. size.) Poisosocs.

spicuous. The stamens are only coherent at the base, and bear conspicuous,
reddish-yellow anthers (Fig. 709). The fruit is very peculiar. The ovary has a
long stalk and bears two ovules near the tip. One of these develops into the seed
of the indehiscent, compressed pod, which has a broad wing along the ventral
suture and a narrower wing along the dorsal suture (Fig. 710). The bell-
shaped calyx persists on the stalk. Genista, Sarothamnus, Lupinus, Cytisus
have all ten stamens united (Fig. 706 B) ; their leaves are pinnate or simple, with
entire margins. The Laburnum (Laburnum vulgare, Fig. 711) is one of the
commonest ornamental trees of our gardens and grows wild in the Alps. It has

672

BOTANY

PART II

tripinnate leaves and long pendulous racemes of yellow flowers. Ulex, Furze, a
characteristic British plant. Spartium, distributed in the Mediterranean region.
Trifolium, Clover, with persistent calyx and corolla. Leaves trifoliate. Flowers
aggregated in heads. Stamens (9) + 1. Fruits indehiscent. Medicago, Mediek, with
deciduous corolla ; fruit sickle-shaped or spirally twisted. Melilotus, Melilot, with
racemose inflorescences. Trigonella with long pods. Ononis, Rest-Harrow with

ten coherent stamens. The
increase in the amount of
nitrogen in the soil effected by
the root-tubercles (of. p. 260,
Figs. 251, 252) of Legu-
minosae finds its practical
application in European agri-
culture in the cultivation of
species of Trifolium, Medi-
cago, and Lupinus, Lotus,
Bird's-foot Trefoil (Fig. 707) ;
leaves imparipinnate, lowest
pair of leaflets owing to the
absence of the petiole resem-
bling stipules. Anthyllis,
Kidney- Vetch. In species of
Astragalus, which are low
shrubs of the eastern Medi-
terranean region and of
western Asia, the rachis of
the leaf persists as a sharply
pointed thorn for years after
the leaflets have fallen. These
spines serve to protect the
young shoots, leaves, and
flowers (Fig. 712). Our native
species are herbaceous. Ho-
binia (Fig. 198) is an Ameri-
can tree of rapid growth with
very brittle wood, which is
often planted and known as
False Acacia. Glycyrrhiza,
Liquorice, is a native of S.
Europe. Wistaria sinensis
is a climber with beautiful
blue flowers, often grown
against the walls of houses.
Distinguished by the jointed
pods in which the seeds are isolated by transverse septa are Coronilla
(Fig. 713), Ornithopus sativus, Bird's-Foot, and Arachis hypogaea, Ground-nut, an
important, oil-yielding fruit of the tropics and sub-tropics. After flowering the
flower -stalks penetrate the soil in which the fruits ripen. Vicia, Vetch;
Pisum, Pea (Fig. 208) ; Lens, Lentil ; Lathyrus, Everlasting Pea (Fig. 209).
Leaves with terminal tendrils, corresponding to the terminal leaflet ; the leaves
may thus appear to be paripinnate. The cotyledons remain within the seed-coat

FIG. 712. — Astragalus gummifer. (| nat. size. After
A. MEYER and SCHUMANN.) OFFICIAL.

DIV. II

ANGIOSPERMAE

673

and do not become green. Ficia Faba, the Broad Bean, is an erect plant, without

tendrils ; the terminal leaflet is reduced to a bristle-shaped stump. Phaseolus,

Kidney Bean, and Physostigma

are twining plants with tripin-

nate leaves. Physostigma veno-

sum, a West African climber,

yields Calabar Bean.

POISONOUS. — Among our
common Leguminosae only
Laburnum vulgare and the
related genus Cytisus are
extremely poisonous. Coronilla
varia (Fig. 713), with umbels of
rose-coloured flowers, a^nd Wis-
taria sinensis are also poisonous.

OFFICIAL. — Astragal us gum-
mifer and other species yield

TRAGACANTHA. GLYCYRUHIZAE

RADIX is obtained from Gly-
cyrrhiza glabra. tipartium sco-
parium yields SCOPARII CACU-
MIXA. Andira araroba, .a
Brazilian tree, contains a
powdery excretion in cavities
of the stem called ARAIIOBA ;
CHRYSAROBINUM is obtained
from this. The heart-wood of
Pterocarpus santalinus, an East
Indian tree, is PTEROCARPI LIG-
NUM. KINO is obtained from
the juice flowing from incisions
in the trunk of Pterocarpus
marsupium. Myroxylon toluifera (S. America) yields BALSAMUM TOLUTANUM, and
M. Pcreirae (San Salvador) BALSAMUM PERUVIANUM. Arachis hypogaea yields
OLKUM ARACHIS. Butea frondosa yields BUTEAE GUMMI.

FIG. 713. — Coronilla varia (nat. size). PofSOXOUS.

Order 20. Myrtiflorae

This order differs from the Rosiflorae by the inferior ovary and
the absence of stipules.

Family 1. Thymelaeaceae.— Ovule pendulous. Daphne Mezereum (Fig. 714)
is a poisonous shrub, possibly native to Britain, which flowers in February and
March before the leaves appear. The flowers are rose-coloured, scented, tetramerous,
and have no corolla. The leaves form a close tuft until the axis elongates. The
fruit is a- bright red berry. In the Alps and in the Mediterranean region there
are several species of Daphne, all of which are poisonous.

OFFICIAL.— Daphne Mezereum, D. Laureo/a, and D. Gnidium yield MEZEREI
CORTEX.

Family 2. Elaeagnaceae.— Ovule erect, ffippophae. Elaeacjnus. The leaves
and young twigs are covered with shining peltate hairs.

Family 3. Lythraceae. — Ly thrum salicaria. Purple Loosestrife. Flowers

2 x

674

BOTANY

PART II

typically hexamerous with two inferior carpels. Heterostyled with three forms of

flower (cf. p. 560).

Family 4. Onagraceae. — Flower tetramerous throughout. Androecium obdiplo-

stemonous. Epilobium, Willow-herb, with numerous species ; the fruit is a

capsule, and the seeds have hairs serving for wind-dispersal. Oenothera (Fig. 715).

The power of mutating possessed by plants of this genus was recognised by DE VRIES

and forms the experimental
basis of his hypothesis of muta-
tion. Circaea, Enchanter's
Nightshade. Trapa, Water
Nut. Many forms are in culti-
vation, for instance the species
of Fuchsia, in which the calyx
is petaloid. These plants are
natives of America. Fruit a
berry.

Family 5. Rhizophoraceae.
— Plants occurring in the Man-
grove formation along tropical
coasts, characterised by vivipary
and the possession of stilt-
roots, or respiratory roots (Fig.
189). These adaptations are re-
lated to the peculiarities of the
situations in which the trees
grow. Rhizophora (Fig. 716) ;
JBruguiera ; Ceriops. Kandelia,
(Fig. 581). All occur on the

FIG. 714. — Daphne Mezereum (£ nat. size).
OFFICIAL and POISONOUS.

FIG. 715. —Floral diagram of OenotJiera
(Onagraceae). After NOLL.

coasts of the Indian Ocean. Species of Rhizophora are more widely distributed
on tropical coasts.

Family 6. Myrtaceae. — Evergreen shrubs or trees ; leaves opposite,
leathery, often aromatic. Flowers actinomorphic, tetramerous or
pentamerous. Androecium of many stamens, which are often arranged
in bundles which have originated by branching. Carpels two or
many (Fig. 717) united with the floral axis to form the inferior ovary.
Fruit, usually a berry or a capsule.

Mainly distributed in tropical America and in Australia.

The Myrtle (Myrtus communis), which occurs in the Mediterranean region, is

DIV. n

ANGIOSPERMAE

675

the only European species. Species of Eucalyptus (x) from Australia, especially E.
globulus, are commonly planted in Italy, on account of their rapid growth and useful
timber. Young plants have opposite, sessile leaves, but older trees bear stalked,
sickle-shaped leaves which hang vertically. The shadeless condition of the
Australian forests formed by these trees depends in part on this character, but

FIG. 716. — Rhizophora conjugata (J nat. size).

is partly due to the distance apart of the individual trees. E. amygdalina, which
reaches a height of 150 m. and a circumference of 30 m. at the base of the trunk,
is one of the largest forest trees known. Psidium guayaxa and some species of
Eugenia bear edible fruits ; the former is especially valued. Eugenia caryophyllata
(Moluccas) is of economic importance, its unopened flower-buds forming Cloves
(Fig. 718). This tree is commonly cultivated in the tropics. In Fig. 718 the
inferior ovary, formed of two carpels, is also seen in longitudinal section.

676

BOTANY

PART II

Species of Sonneratia are frequently the constituents of the mangrove vegetation

that advance farthest into the sea ;
their pneumatophores therefore attain a
considerable height (Fig. 188).

OFFICIAL. — Eugenia caryophyllata
yields CARYOPHYLLUM, Cloves. PIMENTA,
Allspice, from Pimenta officinalis. OLEUM
CAJUPUTI from Melaleuca leucadendron,
a tree of less height but resembling the
Eucalyptus trees; it is cultivated in

FIG. 717.— Floral diagrams of Myrtaceae. A,
Myrtus communis. B, Eugenia aromatica.
(After EICHLER.)

the Moluccas (Burn) for the sake of the
OQ ^ yields j its specific name refers

to the white colour of the bark. OLEUM EUCALYPTI and EUCALYPTI GUMMI

from Eucalyptus globulus and other species.

FIG. 718.— Eugenia caryophyllata (§ nat. size). Flowering branch. A bud cut in half and an opened
flower (about nat. size). OFFICIAL.

Family 7. Punicaceae. — Single genus Punica. Panica granatum is a tree

ANGIOSPERMAE

677

originally introduced from the East and now largely cultivated in the Mediterranean

FIG. 7lv.—Punii:a granatum (i nat. size). 1, Branch bearing a flower and a bud.
2, Flower in longitudinal section. 3, Fruit. (See text.)

region on account of its acid refreshing fruits known as Pomegranates (Fig. 719)

Leaves small, entire. Flower with a stiff, red

calyx, an indefinite number of petals, and

numerous stamens ; the 7-14 carpels are arranged

in two tiers, the upper of which corresponds in

number to Che sepals, the lower to the half of

this (Fig. 720). Fruit enclosed by a leathery

pericarp with numerous seeds in the loculi of

both tiers. The external layers of the seed-coat

become succulent and form the edible portion of FlG 72o. -Floral diagram of Punica

the fruit. granatum. (After EICHLER.)

Order 21. Umbelliflorae

Inflorescence as a rule an umbel. Flowers hermaphrodite,
actinomorphic ; a single whorl of stamens and an inferior bilocular
ovary, the upper surface of which forms the nectary. Carpels
two. A single pendulous ovule in each loculus.

The affinities of the Umbelliflorae are to be sought in the Gruinales to the

678

BOTANY

PART II

Frangulinae. The increasingly tetracyclic floral construction, the formation of a

disc in the flower, the forma-
tion of secretory reservoirs.'and
the

canals, and the one -seeded
loculi of the fruit are all points
of resemblance to the Umbelli-
florae.

Family 1. Cornaceae. —
Cornus mas, the Cornelian
Cherry (Fig. 721), expands its
umbels of tetramerous yellow
flowers before the leaves appear.
Each umbel is subtended by
four bracts. The inflorescences
for the succeeding year are
already present in the axils
of the leaves by the time the
fruit is ripe. In Britain two
species occur : 0. sanguinea,
the Dogwood, and C. suecica,
an arctic and alpine plant
which reaches its southern
limit in Germany.

Family 2. Araliaceae. — In
Britain the only representa-
tive of the family is the Ivy
(Hedera Helix) (27), a root-
climber. The elliptical pointed

FIG. 721.— Cornui mas (£ nat. size). 1, Flowering twig.
Twig with fruits. 3, Flower seen from above. A, Flower
in longitudinal section. (3, k, enlarged.)

FIG. 722.— Umbelliferae. Floral
diagram (Stter). (After NOLL.)

FIG. 723.— Fruits of Umbelliferae in cross section. 1, Foenv-nlinn
capillaceum. 2, Pimpinella anisum. 3, Conlum maculatum.
It, Coriandrum sativum (It modified after a figure by CRUDE).

leaf form appears on the orthotropous shoots of older plants, which in late

DIV. n

ANGIOSPERMAE

679

summer or autumn bear the flowers. The leaves of the creeping or climbing plagio-
tropous shoots are lobed and usually have shorter stalks. Calyx with five pointed
sepals corresponding to the five ribs on the inferior ovary. The corolla is
greenish in tint ; the large disc on the upper surface of the ovary attracts the
visits of flies and bees. The fruits ripen during the winter and become blackish-
blue berries ; these are eaten by birds and
in this way the seeds are distributed.

Family 3. Umbelliferae.—
Herbaceous plants sometimes of
large size. The stem, which has
hollow internodes and enlarged
nodes, bears alternate leaves ; these
completely encircle the stem with
their sheathing base, which is often
of large size. The leaves are only
rarely simple ; usually they are
highly compound. Inflorescence
terminal, frequently overtopped by
the next younger lateral shoot. It
is an umbel, or more frequently a
compound umbel, the bracts forming
the involucre and partial in-
volucres, or an involucre may be
wanting. Flowers white, greenish,
or yellow ; other colours are rare.
K 5, C 5, A 5, G (2). The sepals
are usually represented by short
teeth. The flowers at the circum-
ference of the compound umbel
sometimes become zygomorphic by
the enlargement of the outwardly FlG m._CftrHW OTrri (, nat. size). In.

directed petals. Ovary always bi- florescence bearing fruits. Single flower,

carpellary and bilocular; in each
loculus a single ovule which hangs
from the median septum with its micropyle directed upwards and
outwards. The upper surface of the carpels is occupied by a swollen,
nectar -secreting disc continuing into the longer or shorter styles,
which terminate in spherical stigmas. Fruit a schizocarp, splitting
in the plane of the septum into two partial fruits or mericarps. In
many cases the latter remain for a time attached to the carpophore,
which originates from the central portion of the septum ; this separates
from the rest of the septum and bears the mericarps hanging from its
upper forked end (Figs. 722-728).

The main areas of distribution of the Umbelliferae are the
steppe region of Western Asia, Central North America, Chile, and
Australia.

2X1

and carpophore bearing the mericarps
(enlarged). OFFICIAL.

680

BOTANY

PART II

For systematic purposes the fruits are of great importance. Each half of the
fruit has five ribs, beneath which the vascular bundles lie. The marginal ribs of
each partial fruit frequently lie close together at the septum or they may be
distinct ; they may resemble the three dorsal ribs or differ more or less from them.
Between the five primary ribs four secondary ribs are sometimes present. Usually

FIG. 725.— Cicuta virosa. Rhizome cut through longitudinally (£ nat. size). Fruit (enlarged).

POISOXOFS.

furrows (valleculae) occur between the ridges, and beneath each furrow a large oil
duct (vitta) is found, extending the whole length of the fruit. On either side of
the carpophore a similar oil duct is present in the septum, so that each mericarp
has six of these vittae (Fig. 723, 1). In some species additional small ducts are
present (Fig. 723, 2, 3). The form of the fruit as seen in a cross section differs
according to whether the diameter is greater in the plane of the septum or at
right angles to this. The character of the marginal and dorsal ridges and the

DIV. II

ANGIOSPERMAE

681

presence or absence of secondary ridges or vittae serve to distinguish the fruits,
and are indispensable aids in determining the species. Since many of the
fruits are employed in medicine or as spices, while others are poisonous, their
distinction becomes a matter of importance. The endosperm of the seeds contains
a fatty oil as reserve material.

FIG. 726.— 1, Ocnanthefistulisa (A nat. size). 2, Group of fruits. 3, Single fruit (enlarged).

Poisosocs.

In the following genera the endosperm is flat or slightly convex on the ventral
side (Fig. 723, 1, 2). Pimpinella, Burnet-Saxifrage. P. anisum, Anise, is an
annual plant, the seedlings of which exhibit increasing subdivision of the lamina
in successive leaves. Carum carvi, Carraway, has long been cultivated (Fig.
724); leaves bipinnate, the lowest pinnae resembling stipules. The large lower
pinnules are usually placed horizontally on the vertical rachis of the leaf; the
terminal pinnules are simple and linear. The terminal umbel, the flowers of

682

BOTANY

PART II

which open first, is overtopped by the lateral umbels arising from the leaf-axils.
Biennial. Foeniculum (Fennel) and Levisticum (Lovage) have yellow flowers.
Petroselinum (Parsley), Pastinaca (Parsnip), Daucus (Carrot), Apium (Celery),
and Anethum (Dill), are used as vegetables. Cicuta (Water-Hemlock, Fig. 725),
Sium (Water-Parsnip), Oenanthe (Fig. 726) and Berula, are marsh- or water-plants.
Aethusa cynapium (Fool's Parsley, Fig. 727) has the ribs of the fruit keeled ;
umbels with three elongated, linear, involucral leaves directed outwards. All the
last-named plants are poisonous. Archangelica officinalis is a conspicuous plant

FIG. 727.—Aet,Jwisa cynapium (§ nat. size). B, Single umbel. C, Fruit (enlarged). POISONOUS.

reaching a height of 2 metres, with large bipinnate leaves provided with saccate,,
sheathing bases ; the greenish flowers are markedly protandrous.

In the following genera the ventral side of the endosperm is traversed by
a longitudinal groove. Scandix, Anthriscus (Beaked Parsley), Chaerophyllum
(Chervil). Conium maculatum, the Hemlock, is a biennial plant often of con-
siderable height ; it is completely glabrous, the stem and leaf-stalks often with
purple spots ; leaves dull green, bi- to tri-pinnate. The ultimate segments end in
a small, colourless, bristle-like tip. Fruit with wavy, crenate ridges and without
oil-ducts in the valleculae. The whole plant has a peculiar, unpleasant odour
(Fig. 728).

DIV. II

ANGIOSPERMAE

The ventral side of the endosperm is concave (Fig. 661, 4). Coriandrum
sativum is an annual plant ; flowers zygomorphic owing to the enlargement of the
sepals and petals at the periphery of the umbel. Fruit spherical ; mericarps

FIG. 728. — Conium maculatiirn (£ nat. size). Poisoxoi'S.

closely united, with ill-marked primary ridges and somewhat more distinct
secondary ridges.

OFFICIAL. — Ferula foetida (Persia), ASAFETIDA. Dorema Ammoniacum

(Persia), AMMOXIACUM. Pimpinella anisum, ANISI FRUCTUS. Coriandrum sativum,

CORIAXDRI FRUCTUS. Foeniculum capillaceum, FOENICULI FRUCTUS. Carum

I:ARUI FRUCTUS. Carum coplicum, Anethum (Peucedanum) gravfolens,

AXETHI FRUCTU.S.

684

BOTANY

PART II

Series II. Sympetalae

The common character of all Sympetalae is afforded by the
perianth which consists of a calyx and a gamopetalous corolla. The
flowers are, without exception, cyclic. The number of whorls -is
either five or four, and on this distinction the two groups Pentacyclicae
and Tetracydicae are based. The Sympetalae does not correspond to
a single closely related group but is composed of derivations of a
number of natural series which have attained a similar high condition
by progressive reduction in the number of members in the individual
whorls and in the number of the whorls. Thus the common character
of a gamopetalous corolla is purely superficial. Though the distribu-
tion of the various groups of Sympetalae in relation to those of the
Choripetalae is not adopted here, this is for reasons of space and
because the affinities of all the groups are not as yet certain.

From what has been said it follows that the most natural arrange-
ment is according to the height of organisation, i.e. to the degree of
reduction that has been reached. The Pentacyclicae are therefore
placed first and followed by the Tetracydicae.

A. PENTACYCLICAE

Order 1. Erieinae

Family 1. Ericaceae. — Evergreen, shrubby plants with small,
often needle-shaped leaves. Anthers characterised by the possession

FIG. 729. — Arctostaphylos Uva ursi. 1, Flowering branch. 2, Flower in longitudinal section.
3, Pollen tetrad. £, Fruit. 5, Fruit in transverse section. (After BERG and SCHMIDT.) OFFICIAL.

of an " exothecium " (p. 545), opening by pores or splits, frequently
provided with horn-like appendages, on which account the group is
also termed Bicornes.

mv. IT

ANGIOSPERMAE

685

Flowers which are pentamerous in all five whorls
are found in the species of Rhododendron or Alpine
Rose, in Ledum palustre, and Andromeda ; all these
have a capsular fruit derived from the superior ovary.
Arctostaphylos Ura ursi is similar, but the fruit is a
drupe (Fig, 729). Pentamerous flowers with an inferior
ovary which becomes a berry are found in the genus
Vacoiwium (Fig. 730), V. vitis idea, Cowberry, V.
iiiyrtillus, Blaeberry. The remains of the calyx persist
on the summit of the fruit. A reduction of the number
of members of the whorls to four is met with in the
genus Erica with a superior ovary, many species being

FIG. 730.— Floral diagnun of
Vaccinium (Ericaceae).

FIG. 73l.—Palaquium.Gutta. (i nat. size. After A. MEYER and SCHUMANN.)

686

BOTANY

PART II

native to the Mediterranean region and the Cape. Erica tetralix is distinguished from
the closely related Heather, Calluna vulgaris (w) by its corolla being longer than
the calyx ; both are abundant in Britain.

OFFICIAL. — Arctoslaphylos Uva ursi yields UVAE URSI FOLIA. Gaultheria pro-
cumbens yields OLEUM GAULTHERIAE.

Order 2. Diospyrinae

The Sapotaceae is a tropical family; the plants contain latex. Species of
Palaquium (Fig. 731) and Payena from the Malayan Archipelago are the trees
from which gutta-percha is obtained. Balata is obtained from Mimusops ; trees
found throughout the tropics.

Ebenaceae. — Diospyros Kaki is a Japanese fruit tree ; D. Ebenum, ebony.

Styracaceae. — The origin of Benzoin (BENZOINUM), an official resin, from
Styrax Benzoin, though generally assumed, is open to doubt.

FIG. 733. — Anagallis arvensis
(i nat. size). Longitudinal
section of flower, and cap-
sule at dehiscence (en-
larged).

FIG. 734. — Cyclamen europaeum. A, Entire plant. B, Fruit.
(After REICHKNBACH.) POISONOUS.

DIV. n ANGIOSPERMAE 687

Order 3. Primulinae

Family 1. Primulaceae. — The floral diagram (Fig. 732) shows only one whorl
of stamens, since these stand opposite the petals ; the outer whorl of stamens is
absent ; in normal Tetracyclicae it is the inner whorl that is missing. The free-
central placentation is characteristic. The genus Primula is widely distributed ;
the British species show the superior unilocular ovary with a single style, charac-
teristic of the family ; heterostylic. Anagallis (Fig. 733), capsule opens by a lid.
Cyclamen (Fig. 734). The uncooked tubers of Cyclamen and Anagallis, and the
glandular hairs of a number of species of Primula (P. obconica, Corthusa
matthioli (w)} are poisonous.

B. TETRACYCLICAE

1. Ovary Superior

The Tetracyclicae have only four regularly alternating whorls in
the flower. They can be divided into two groups of orders according
to the position of the ovary. This is superior in the orders Contortae,
Tubiflorae, and Personatae ; in all these the ovary is composed of two
carpels. The orders with an inferior ovary are the Rubiinae and
Synandrae. In the Rubiinae the carpels are as a rule two, but
sometimes three or one ; in the Synandrae which are characterised by
the united anthers, the carpels vary from five to three, two, or
only one.

These common characters having been recognised, the families
within the various orders may be dealt with.

Order 4. Contortae

Plants with decussate, usually simple leaves and actinomorphic
flowers, the corolla of which is often contorted in the bud. Stamens
epipetalous.

Family 1. Oleaceae. — This is readily recognised by the two stamens. The
corolla is usually tetramerous as is shown in the floral diagram of Syringa (Fig.
735). Besides Ligu strum, Jasminum, and Syringa,
Olea europaea, the Olive Tree or Olive, is the most im-
portant plant of the family (Fig. 736). It is a native
of the Mediterranean region, where it is also cultivated.
The flower and fruit correspond to the type for the
family (Fig. 737). The drupe contains a fatty oil both
in the succulent exocarp and in the endosperm (Fig.
738). Fraxinus, the Ash, differs from the type of the
order in having pinnate leaves ; F. excelsior has
apetalous, anemophilous flowers, which appear before FlG- 735.— Oleaceae.

the leaves. F. ornus, the Flowering Ash, has a Floral diagram (%nn!7a).
double perianth and is entomoplulous ; it is polygamous, having hermaphrodite
flowers as well as female flowers with black sterile anthers ; the corolla is divided
to the base. It is cultivated in Sicily for the sake of the mannite it yields.

OFFICIAL. — Olea europaea yields OLEUM OLIVAE.

688

BOTANY

PAKT II

Family 2. Loganiaceae. — Species of Strychnos, which are trees or lianes climbing

by means of hook -tendrils,
yield the well-known curare
of South America, and the
arrow poison used by the
Malays.

OFFICIAL. — Strychnos nux
vomica is a small tree or shrub
of Southern Asia, the fruits
of which are berries with a
firm rind ; in the succulent
pulp a small number of erect,
circular, disc - shaped seeds
are embedded (Fig. 740). It
yields NUX VOMICA and

STRYCHNINA. GELSEMII

RADIX is obtained from Gel-
semium nitidum, which is a
native of North America.

Family 3. Gentianaceae.
— This is recognisable by the
unilocular ovary and the
clearly contorted corolla when
in bud (Fig. 741). Gentiana,
is a genus with numerous
species. Plants of larger or
smaller size, especially abun-
dant in the Alps. Flowers
brightly coloured. This genus
affords one of the best ex-
amples of seasonal dimor-
phism, i.e. the splitting of a
species into two closely related
forms which develop at
FiG.736.-OZeamro^ainfruitanat. size). OFFICIAL. different seasons. Since the

FIG. 737. — Olea europaea. A, Corolla spread out.
B, Calyx and ovary in longitudinal section. (En-
larged. After ENGLER-PRANTL.)

FIG. 738.— Olea europaea. Drupe, h, Stone.

height of the vegetative period of the alpine meadows coincides with their
annual mowing, this expresses itself in the distinction of an early form, fruiting
before the meadows are cut, and a late form developing after this has taken

ANGIOSPEBMAE

place (30). Erythraea, Centaury. Menyanthes, Bog-Bean. L'imnanthemum, aquatic
plants with floating leaves.

OFFICIAL. — Gentiana lutea and other species yield GEXTIAXAE IIADIX. CHIRATA
is obtained from Swertia chirata (N. India).

Family 4. Apoeynaeeae. — Evergreen plants with latex. Especially
numerous in the tropics.
Stigma ring-shaped.
Carpels only united in
the region of the style,
free below and separat-
ing after fertilisation.
Usually two follicles
with numerous seeds
provided with a tuft of
hairs (Figs. 744, 745).

The only British species
is Vinca minor, the ever-
green Periwinkle, occurring

FIG. 730. — Fraxinus ornu&
Flower and fruit.

FIG. 740. — Strychnos mix vomica (i nat. size). Fruit and seed
whole and in cross-section. OFFICIAL and Poisonous.

in woods (Fig. 742). Xerium oleander (Fig. 743), a native of the Mediterranean
region. The floating fruit of Cerbera Odollam, from the mangrove vegetation, is
shown in Fig. 576.

OFFICIAL. — Strophanthus kombe and" S. hispidus (31) (Fig. 745), lianes of tropical
Africa, yield STUOPHAXTHI SEMIXA. A bark is obtained from Alstonia constricta
and A. scholar is.

Caoutchouc (3i) is obtained fromjftefcgia elastica and other species, trees of tropical
W. Africa. It is also obtained from numerous species of Latidolphia (L. KirTcii,
Heudelotii, comorensis, etc.), Carpodinus from tropical Africa. Hancornia speciosa,
a tree of the dry Brazilian Campos, and Jniloughbeia firma, W.flavescens, and other
species of this Malayan genus of lianes, are also rubber-yielding plants. Gutta-
percha is present in the latex of Tabernaemontana Donnell Smithii, Central America.

Family 5. Aselepiadaeeae. — Similar and closely related to the
Apoeynaeeae but differing in the carpels being free, only united by the
prismatic stigma. Stamens united at the base, with dorsal, nectar-
secreting appendages forming a corona. The pollen of each pollen sac

2 Y

690

BOTANY

PART II

is united into a pollinium, the stalk of which is attached to a glandular
swelling (adhesive disc) of
the angular stigma. These
adhesive discs alternate with
the stamens so that the two
pollinia attached to each
disc belong to the halves
of two adjoining stamens.
Visiting insects remove, as
in the Orchidaceae, the pol-
linia and carry them to
another flower (Fig. 746).

FIG. 741. — Gentiana lutea. a and b,
Flower - buds (nat. size), showing
calyx (a) and twisted corolla (ft) ;
c, transverse section of ovary.
OFFICIAL. (After BERG and
SCHMIDT.)

FIG. 742. — Vinca minor (§ nat. size).

Vincetoxicum officinale (Fig. 747) is a European herb with inconspicuous white
flowers and hairy seeds which are borne in follicles ; poisonous. Other forms are
mostly tropical or sub - tropical. The succulent species of Stapelia, JToodia,
Trichocaulon, etc., which resemble Cactaceae in habit, and inhabit S. African
deserts, and Dischidia rafflesiana (33), the peculiar pitcher plant of the Malayan
region, the pitchers of which serve to condense water, deserve special mention.
Hoya carnosa is frequently cultivated.

OFFICIAL. — Hemidesmus indicus yields HEMIDESMI RADIX.

Order 5. Tubiflorae

Flowers pentamerous, actinomorphic, or zygomorphic. Carpels 2.
Ovary superior, bilocular, with two ovules, which are frequently

DIV. II

ANGIOSPERMAE

691

separated by a false septum, in each loculus. The normal number of
stamens is reduced in the zygomorphic flowers to four or two. This
order may be connected with the Gruinales and Rosiflorae.

FIG. 743.— Xerium oleander (£ nat. size). Poisoxocs.

Family 1. Convolvulaceae. — Many of the plants of this family are twining
plants with alternate sagittate leaves and wide, actinomorphic, funnel-shaped
corolla, which is longitudinally folded in the bud. Ovules erect ; fruit a capsule.

Convolvulus arvensis, a perennial, twining, herbaceous plant occurring every-
where by waysides, and as a weed in corn-fields. Flowers solitary, long-stalked,

Fio. 744.— Strophanihus hispidus. Ovary in longitudinal section. (J,° ; after ENGLER-PRANTI..)

Fio. 'US.—Strophanthns hispidus (i nat. size. After MEYER and SCHUMANN). Fruit (1 nat. size).
Seed (£ nat. size). (After SCHUMANN in ENOLER-PRANTL.) OFFICIAL.

692

DIV. II

ANGIOSPERMAE

693

situated in the axils of the leaves and sometimes in the axils of the bracteoles of
another flowei'. Calystegia has two large bracteoles placed immediately beneath
the calyx. C. sepium. The Dodder (Cuscuta) is a slender parasitic plant con-
taining very little chlorophyll, which attaches itself by means of haustoria to a

FIG. 746. — Asclepiasciirassavica. A, Flower ; an,, androeceum (x 4). B, Calyx and gynaeceum
fn, ovary ; fc, adhesive discs (x 6). C, Pollinia (more highly magnified). (After BAILLON.)

Fin. m.—Vincetoriciun officin
(i nat. size). Poisoxocs.

Fir;. 74S.— Exogonium purga (% nat. size. After BERG and
SCHMIDT). OFFICIAL.

number of different host plants (Fig. 221). Ipomaea : several species are cultivated
as ornamental plants. /. pcscaprae is one of the strand plants of tropical countries.
OFFICIAL.— JALAPA is obtained from Exocjonium purga (Fig. 748), a twining
plant, with tiiberous lateral roots, occurring on the wooded eastern slopes of the
Mexican tableland. Ipomaea hcderacca, I. orizabcnsis, I. turpethum. SCAM-
MOXIAE RADIX is the dried root of Conv>:>l-cV'HS Sca/nmonm (Asia Minor).

694

BOTANY

PART II

Family 2. Boraginaeeae. — Contains herbs usually covered with
coarse hairs. Sympliytum (Comfrey), Borago (Borage), Anchusa ( Alkanet),
Echium (Bugloss) (Fig. 750), Myosotis (Forget-me-not), are among the
commonest and .most conspicuous herbaceous plants of our flora ; all
have entire, alternate leaves, covered with harsh hairs and relatively
large flowers of a lighter or darker blue, grouped in complicated
inflorescences. Flowers actinomorphic or zygomorphic. Petals fre-

FIG. 750.— Echium vulgare. Inflorescence (£ nat. size).
Single flower and fruit, composed of four nutlets (enlarged).

FIG. 749.— Borago officinalis. a,
Flower ; b and c, fruit (nat. size).

FIG. 751. — Floral diagrams of (A) Verbena officinalis (after
EICHLER), and (B) Lamium (Labiatae) (after NOLL).

quently provided with scales standing in the throat of the corolla.
Ovary always bilocular but divided by false septa into four one-seeded
nutlets. The style springs from the midst of the four-lobed ovary.

Family 3. Verbenaeeae. — Clearly dorsiventral flowers, with only
four stamens; the ovary contains only four ovules (Fig. 751), but the
style is terminal. Tectona grandis, Teak-tree ; Avicennia (33) a vivipar-
ous mangrove plant.

Family 4. Labiatae. — Distributed over the earth. Herbs or
shrubs with quadrangular stems and decussate leaves without stipules.
Leaves simple ; plants often aromatic owing to the presence of glandular

DIV. n

AXGIOSPERMAE

695

hairs. Flowers solitary in the axils
of the leaves, or forming apparent
whorls. The small inflorescences
are dichasia or double cincinni,
and are often united in larger
spike- or capitulum-like inflores-
cences. Flower zygomorphic (Fig.
751). Calyx gamosepalous, with
five teeth ; corolla two-lipped, the
upper lip consisting of two, the
lower of three petals ; stamens in
two pairs, two long and two short,
rarely only two (Salvia, Ros-
marinus). ThS ovary (Fig. 751)
corresponds to that of the Bora-
ginaceae ; it has a ring-shaped
nectary at the base.

The Labiatae include a considerable
proportion of our commonest native
spring and summer flowers ; Lamium,
Galeopsis (Fig. 752), and Stachys have
the upper lip helmet-shaped, Ajuga has
it very short, while in Teucriwn the

FIG. 752. — Galeopsis ocliroleuca. a, Flower ; b, the
same with calyx removed ; c, corolla cut open.
showing stamens and style ; d, cnlyx and
gynaeceum ; e, fruit. (a, b, nat. size ; c, d,
e x 2.)

FIG. 753. — Lavandula vera (i nat. size).
OFFICIAL.

696

BOTANY

PART II

upper lip is deeply divided.

Nepeta and Glechoma differ from the majority of
the order, in having the posterior stamens longer
than those of the anterior pair. Salvia, Sage,
has the two stamens that remain peculiarly con-
structed in relation to pollination (Fig. 754, cf. Fig.
528). Many Labiatae are of value on account of
their aromatic properties. They are especially
abundant in the xerophytic formation of shrubby
plants in the Mediterranean region to which the
name Maquis is given.

OFFICIAL. — -Rosmarinus officinalis yields OLEUM
ROSMARINI. Lavandula vera (Fig. 753) (Mediter-
ranean region), OLEUM LAVANDULAE. Mentha
piperita, OLEUM MENTHAE PIPEUITAE. M. viridis,
OLEUM MENTHAE VIRIDIS. M. arvensis and M.
piperita yield MENTHOL. Thymus vulgaris and
Monarda punctata yield THYMOL.

Order 6. Personatae

The Personatae are of common origin
with the Tubiflorae. The flowers are actino-
morphic or zygomorphic. There are, how-
ever, no false septa in the ovary, and the
number of ovules is usually a larger one.

Family 1. Solanaeeae. — Herbs or small
woody plants, with nearly always actino-
morphic flowers. Petals plaited. Ovary
bilocular, septum inclined obliquely to the
median plane. Ovules numerous, on a thick
placenta (Fig. 755). Fruit, a capsule or a
berry. Seeds with
endosperm; embryo
usually curved.
Anatomically the
order is character-
ised by possessing
bicollateral vascular
bundles.

Many species of
Solatium occur as
weeds. Flowers actino-
morphic ; fruit a berry.
S. nigrum, Night-
shade. S. dulcamara,
Bitter-sweet (Fig. 756),
is a shrubby plant,
climbing by means of
its stems and petioles, and especially common in thickets by the banks of

Fio. 754. — Salvia officinal is. Flowering shoot (£ nat. size). Tubular
corolla slit open to display the stamens (enlarged).

DIV. II

AXGIOSPERMAE

697

streams and similar situations. S. tuberosum, the potato. Lycopersicum, the
tomato. On graft-hybrids, periclinal chimaeras and gigas-forms of Solanum, cf.
p. 299 and H. WIXCKLER (34). The Deadly Night-
shade, Atropa belladonna (Fig. 757). a very poisonous
shrubby plant occurring in Europe, is recognisable
by the actinomorphic flowers, with a short, wide,
tubular corolla of a dirty purple colour. The main
shoot is, to begin with, radial, but branches below the
terminal flower into, as a rule, three equally vigorous
lateral shoots, which exhibit further cicinnal branching.
By the carrying up of the subtending bract upon the
lateral shoot an appearance of paired leaves is brought Fl°- 755.— Solanaceae. Floral
about. Capsicum annuum, Spanish Pepper, has a dry, ^^m <peiimia>' <After
berry-like fruit. It resembles Atropa in its branching

and the position _of its leaves. Datura Stramonium, Thorn-apple (Fig. 758), is
an annual plant, widely spread in Europe, Asia, and IS". America. It has

FIG. 756. — Solanum dulcamara (% nat. size). Porsoyocs.

incised, palmately- veined leaves, large, white, terminal flowers, and spiny
fruits. Nicotiana tabacum (Fig. 759) is a South American plant with numerous
cultivated varieties. Its large alternate leaves, which bear numerous glandular
hairs, form TOBACCO, after being dried and prepared. Hyoscyamus niger, the

698

BOTANY

PART 11

Henbane (Fig. 760), is an annual plant occurring in Central Europe, North Africa,
and Western Asia. The leaves are clothed with glandular hairs. Flowers slightly

FIG. 757.—Atropa belladonna (J nat. size). OFFICIAL and Poisonous.

zygomorphic, of dull yellowish-violet colour with darker markings ; inflorescence,
a cincinntis. Fruit a pyxidium.

All Solanaceae are more or less poisonous partly on account of the presence of

DIV. II

ANGIOSPEBMAE

699

considerable amounts of alkaloids or poisonous glucosides. Species of Solanum,

FIG. 758. — Datura Stramonium (i nat. size). Mature fruit after dehiscence.
OFFICIAL and Poisosous.

Atropa, Datura, Hyoscyamus, and Nicoti-ana are among the most poisonous plants
met with in this country.

'^faf

FIG. 759.— Nicotiana tabacum (£ nat. size). Poiaoxous. a, Flower ; b. corolla cut open and spread

out flat ; c, ovary; d and e, young fruit, (a, I, c, nat. size ; d, e x 2.)

700

AXGIOSPERMAE

701

FIG. 1 7*50. — Hyoscyamus niger. Flowering shoot and fruit (i nat. size). OFFICIAL and Poisoxovs.

1. — Verbascum thapsiforme. a, Flower
?>, calyx and style (nat. size).

-Scrophulariaceae. Floral diagrams.
•cum. B, Gratiola. (After EICHLER.)

702

BOTANY

PART II

FIG. 763.— Digitalis purpurea (£ nat. size), a, Corolla cut open and spread out ; b, calyx and
pistil; c, fruit after dehiscence; d, transverse section of fruit (nat. size). OFFICIAL and
POISONOUS.

DIV. II

AXGIOSPERMAE

703

OFFICIAL. — Capsicum
minimum yields CAPSICI
FRUCTUS. Atropa bella-
donna yields BELLA-

DONXAE FOLIA, BELLA-
DONNAS KADIX, and

ATROPINA. Datura Stra-
monium, STRAMONII
SEMINA and STRAMONII

FOLIA. D. fastuosa, D.
metel. Hyoscyamus niger,

HYOSCYAMI FOLIA.

Family 2. Serophu-
lariaeeae. — Flowers
zygomorphic. "Corolla
not plaited in the bud.
Number of stamens
nearly always incom-
plete. Carpels median.
Fruit, a bilocular cap-
sule.

Verbascum (Fig. 761),
the Mullein ; biennial
herbs, which in the first
season form a large rosette
of woolly leaves from
which the erect inflores-
cence arises in the second
year. The single flowers
have five stamens, and
are only slightly zygo-
morphic ; the three pos-
terior stamens have hairy
filaments, and are further
distinguished from the
two anterior stamens by
the transverse position of
their anthers. Linaria
and Antirrhinum have a
two -lipped corolla with
four stamens. Digitalis,
Foxglove (Fig. 763), has
an obliquely campanulate
corolla and four stamens.
The flowers hang from
one side of the ascending
raceme, which is produced
in the second year. Grati-
ola and Veronica with
onlv two fertile stamens.

FIG. 7G4. — Orobnnche minor, parasitic on Trifolium repens
(i nat. size). Single flower (enlarged).

704 BOTANY PART n

A special group includes a number of closely related genera which have
adopted a more or less completely parasitic mode of life. The most completely
parasitic form is Lathraea (35), the species of which have no trace of chlorophyll ;
L. squamaria, the Tooth wort, is parasitic on the roots of the Hazel. Many (e.g.
Toszia, Bartsia, Euphrasia, Odontites, Pedicularis, Melampyrum, Alectorolophus)
are semiparasitic. Although they possess green leaves they attach themselves
by means of haustoria to the roots of other plants, from which they obtain
nutrient materials.

OFFICIAL. — Digitalis purpurea yields DIGITALIS FOLIA. Picorhiza kurroa.

Family 3. Orobanchaceae. — Root -parasites, without chlorophyll. Flower as
in the Scrophulariaceae, but with a unilocular ovary. Several British species of
Orobanche, parasitic on various host plants (Fig. 764).

Family 4. Lentibulariaceae. — Marsh- or water-plants. They capture and digest
insects. Utricularia (3G), Pinguicula.

Family 5. Plantaginaceae. — Reduced forms. Litorella lacustris. Plantago.
Plantain ; anemophilous, and protogynous.

OFFICIAL. — Plantago ovata.

2. Ovary Inferior
Order 7. Rubiinae

This order is related to the Umbelliflorae, where also the ovary is
inferior. The flowers are tetramerous or pentamerous ; the numbers
of stamens and carpels vary in the zygomorphic and asymmetric
flowers.

Family 1. Rubiaeeae (37). — Herbs, shrubs, or trees, with simple
decussate leaves and stipules. Flowers actinomorphic. Ovary
bilocular.

The few native Rubiaeeae all belong to the group represented by
Asperula (Woodruff), Galium, EuUa. These genera are characterised
by the resemblance of the stipules to the leaves ; usually a whorl of
six members is borne at each node, but sometimes it is reduced
to four by the union of the stipules in pairs ; the numbers may,
however, vary.

In the tropics the Rubiaeeae are abundantly represented by trees, shrubs,
climbers, and epiphytes. One of the most important Rubiaeeae is Cinchona, a
genus from the S. American Andes, now cultivated in the mountains of nearly all
tropical colonies (Fig. 765). Stipules deciduous. Flowers in terminal panicles ;
corolla tubular, with an expanded terminal portion fringed at the margin.
Fruit, a capsule, with winged seeds (Fig. 766). Coffea, the Coffee plant, is a
shrub ; C. arabica (Fig. 767) and C. liberica are important economic plants,
originally derived from Africa, and now cultivated throughout the tropics. The
fruits are two-seeded drupes. The pericarp becomes differentiated into a succulent
exocarp and a thin stony endocarp, which encloses the two seeds with their thin
silvery seed-coats. These are the coffee-beans. The noteworthy tuberous epiphytic
plants Hydnophytum and Myrmecodia (37) have also succulent fruits ; according
to the most recent investigations they utilise the excreta of the ants which inhabit
the cavities in the stems. Species of Psychotria and Pavetta are also of physio-

DIV. n

ANGIOSPERMAE

705

logical interest on account of the nitrogen-fixing bacteria harboured in their
leaves. The association is higher than that of the Leguminosae with the bacteria
in their root-nodules in that the bacteria here are present in the seeds and are thus
handed on to a new generation.

OFFICIAL. — Cinchona succirubra yields CINCHONAE RUBRAE CORTEX. QUININE

FIG. 765. — Cinchona succirubra (nat. size). OFFICIAL. (After SCHUMANN and ARTHUR MEYER.)

is obtained from this and other species of Cinchona. Uragoga (Psychotria]
Ipecacuanha yields IPECACUANHA. CATECHU is obtained from Ourouparia
(Uncaria) gambir.

Family 2. Caprifoliaceae. — -Woody plants, usually without stipules. Viburnum
has actinomorphic flowers with a trilocular ovary. The fruit contains only one
seed. The sterile marginal flowers, which are alone represented in cultivated forms,

706

BOTANY

serve as the attractive apparatus. Sambucus, Elder, has irnparipinnate leaves,
glandular stipules, and actinomorphic flowers. Zygomorphic flowers are found in
the Honeysuckle (Lonicera periclymenuni), one of our native lianes ; the long- tubed,
sweet-scented flowers are attractive to long - tongued Sphingidae. DierviUa
( Weigelia] a favourite ornamental shrub.

OFFICIAL. — Viburnum prunifolium.

Family 3. Valerianaceae. — Herbs or small shrubs, with decussately-arranged
leaves and asymmetrical flowers. Calyx only developed on the fruit as a "pappus, '

FIG. 766. — Cinchona suceirubra. A, Flower. B, Corolla split open. 0, Ovary in longitudinal
section. D, Fruit. E, Seed. (D nat. size, the others enlarged.) (After A. MEYER and
SCHUMANN.) OFFICIAL.

i.e. a feathery crown assisting in wind-dispersal. Valeriana, the Valerian (Figs.
769, 770), has a spurred pentamerous corolla, three stamens, and three carpels, only
one of which is fertile.

OFFICIAL. — Valeriana officinalis yields VALERIANAE RHIZOMA. V. Wallichii.

Family 4. Dipsaceae. — Herbaceous plants with opposite leaves and tetramerous
or pentamerous actinomorphic or zygomorphic flowers. The individual flowers
have an epicalyx which persists on the fruit and serves as a means of dispersal ;
they are associated in heads surrounded by sterile bracts.

Dipsacus, the Teazel, has recurved hooks on the involucral and floral bracts.
Corolla with four lobes, four stamens, and one carpel containing a pendulous, ana-

DIV. II

AXGIOSPERMAE

707

tropous ovule ; endosperm present in the seed (Fig. 771). Succisa (Fig. 772)
has a four-lobed corolla ; bracts are present on the common receptacle. Scabiosa

FIG. 767.— Co/ea arabica (£ nat. size). Single flower, fruit, seed enclosed in endocarp, and freed
from it (about nat. size).

has the marginal flowers of the head larger and dorsiventral. Knautia has
tetramerous flowers ; no floral bracts.

Order 8. Synandrae

The common character of this eighth* and last order is found in
the fact that the stamens in one way or another are fused or united
together. The flowers may be actinomorphic or zygomorphic.

Family 1. Cucurbitaceae. — This family, in the frequently incomplete sympetaly
it exhibits, shows a relationship to the Choripetalae, although to groups which
have not been mentioned in this short survey. The Cucurbitaceae include
herbaceous, coarsely hairy, large-leaved plants. Flowers diclinous ; monoecious
or less commonly dioecious. Calyx and corolla adherent below. Anthers united
in pairs or all coherent ; cO-shaped. Ovary trilocular (Fig. 773). Fruit, a berry,

FIG. 768.— Uragoga Ipecacuanha (£ nat. size). Infrutescence by the side. OFFICIAL.

Fio. 7C9.— Valeriana officinalis. a, Flower (x 8) ; b, fruit
(enlarged). OFFICIAL.

708

FIG. WO.— Valeriana. • Floral
diagram. (After NOLL.)

DIV. II

ANGIOSPERMAE

709

with a firm rind. The branched or unbrauched tendrils correspond in their lateral
position to a bract. Oucumis sativus, the Cucumber, and Cucumis Melo, the Melon,
are commonly cultivated. The Cucumber is parthenocarpic (38), i.e. pollination of
the stigma is not necessary for the setting of the fruit. Cucurbita Pepo, the
Pumpkin. Bryonia, Bryony. Citrullus Colocynthis is a perennial plant inhabiting

Fn;. 771. — Fruit of Dipsacvs
fiUlonum in longitudinal
section. hk, Calyx tube;
end, endosperm ; em, em-
bryo. (After BAILLON.)

a c f>

FIG. 772.— Succisa pratensis. a, Flower with epicalyx ;
6, the same after removal of epicalyx ; c, fruit in
longitudinal section ; /, ovary ; hk, epicalyx. (After

H. SCHEXCK.)

the Asiatic and African deserts north of the equator. Leaves deeply three-lobed and
pinnately divided. Tendrils simple or forked ; male and female flowers solitary in
the axils of the leaves. The fruit is a dry berry (Fig. 774). Ecballium elaterium.

OFFICIAL. — Citrullus colocynthis yields COLOCYNTHIDIS PULPA. Cucurbita
maxima, seeds.

The association of the following families with the Cucurbitaceae is only
possible on the morphological character
afforded by the united anthers. A
real relationship must not therefore
be assumed, especially since the in-
vestigations of KRATZER have shown
how various is the course of develop-
ment of the seeds. There was, how-
ever, no better place in this short
systematic account to treat of the very
isolated Cucurbitaceae.

Family 2. Campanulaceae.— Herbs
with -milky juice ; flowers actino-
morphic ; ovary as a rule trilocular

or pentalocular. The stamens are inserted on the floral axis and have their
anthers joined together. The genus Campanula (Figs. 775, 776) has a number of
British species with blue bell-shaped flowers. Phyteuma has spike-like inflores-
cences, the petals only separate near the base. Only after the pollen which has
been shed in the bud has been swept out by the hairs on the style (w) do the
petals open and the arms of the stigma spread apart. Jasione has capitulate
inflorescences resembling those of Compositae.

Family 3. Lobeliaceae differ from the Campanulaceae in the zygomorphic
flowers and two carpels. The median sepal is anterior and conies below a deep

FIG. 773. — Ecballium (Cucurbitaceae). Diagrams of
(.4) a male and of (B) a female flower. (After
EICHLER.)

710

BOTANY

PART II

ision in the

incision

corolla. The normal position is assumed by torsion of the whole

FIG. Ttl.—Citrullus colocynthis (I nat. size). 1, Shoot with male and female flowers. 2, Apex of a
shoot with a male flower-bud and tendrils. 3, Male flower with corolla spread out. k, Female
flower cut through longitudinally. 5, Young fruit cut transversely. OFFICIAL.

flower through 180° or inversion of the flower (Fig. 777). In Britain Lobelia
Dortmanna, an aquatic plant of northern regions, has a similar habit to Litorella.
OFFICIAL. — Lobelia inftata from N. America (Fig. 778) yields LOBELIA.

DIV. II

ANGIOSPERMAE

711

Family 4. Compositae. — Distributed over the whole earth. For
the most part herbs of very various habit ; some tropical forms are
shrubs or trees, e.g. Senecio Johnstoni. The flowers are associated in

FIG. 775. — Floral diagram of Campanula
medium. (After EICHLER.)

FIG. 776. — Campanula rotundifolia. a, Flower;
6, the same cut through longitudinally.
(Xat. size.) (After H. SCHEXCK.)

FIG. 777. — Floral diagram of Lobelia
fulgens. (After EICHLER.)

FIG. 778. — Lobelia inflata. Upper por-
tion of plant with flowers and fruits.

heads. The single flowers are actinomorphic or zygomorphic. Stamens
five ; anthers introrse, cohering by their cuticles to form a tube
(Fig. 779) which is closed below by the unexpanded stigma. The
pollen is shed into the tube formed by the anthers and is swept out
by the brush-like hairs of the style as the latter elongates. The

2 zi

712

BOTANY

PART II

style is bifid above. Ovule erect, anatropous (Fig. 780).

exalbuminous. The fruits are achenes, often bearing at the upper

end a crown of hairs, the

pappus. This corresponds

to the calyx and aids in "^\v '^x

the dispersion of the fruit

by the wind (Figs. 780,

FIG. 779.— Compositae. Floral
diagram (Carduits).

FIG. 780. — Arnica montana. a, Ray-flower ; b, disc-
flower ; c, the latter cut through longitudinally.
(After BERG and SCHMIDT, magnified.)

785). As a reserve material in roots and tubers (Fig. 205) inulin
as a rule is found ; in the seeds aleurone grains and fatty oil.

The individual flowers are either radially symmetrical with a five-lobed corolla
(Fig. 780, b, c) or they are two-lipped as in the South American Mutisieae, the
upper lip having two teeth, the lower three. By suppression of the upper lip

FIG. 781.— Longitudinal section of capitulum— a, of Lappa major with floral bracts ; b, of Matricaria
Chamomilla without floral bracts. (After BERG and SCHMIDT, magnified.)

flowers with a single lip are derived ; such flowers exhibit three teeth at the tip (Fig.
780 a). The ligulate flowers (e.g. of Taraxacum} are similar in general appear-
ance to the latter ; the corolla is here deeply split on one side and its margin
bears five teeth. In addition to those Compositae which have only ligulate
or only tubular florets in the head, there are many which have tubular florest
(disc-florets) in the centre, surrounded by one-lipped florets (ray-florets). These

DIV. II

ANGIOSPERMAE

713

usually differ from one another in sex as well as in colour ; the disc-florets are
hermaphrodite, the ray-florets purely female. The flower-heads are thus hetero-
gamous (Matricaria, Arnica}. Lastly, the marginal
florets maybe completely sterile (Centaurea cyanus)
and serve only to render the capitulum conspicuous
to insects.

One series of genera has only tubular florets in
the head. Carduus (Plumeless Thistle), pappus of
simple, hair-like bristles (Fig. 783). Cirsium, with
feathery pappus. Echinops, with single-flowered
capitula associated in numbers. Lappa (Burdock),

FIG. 782. — Arnica montana. a, Receptacle of capi-
tulum after removal of fruit ; b, fruit in longi-
tudinal section, the pappus only partly shown.
(After BERG and SCHMIDT, magnified.)

Fio. 783. — Androecium of
Carduus crispus (x 10).
(After BAILLON.)

involucral bracts with recurved, hook-like tips (Fig. 781 a). Cynara Scolymus
(Artichoke). Cnicus benedictus (Fig. 786), capitula solitary, terminal, surrounded
by foliage leaves. Involucral bracts with a large, sometimes pinnate, terminal

FIG. 784. — Fruits of — A, Hdianthus annuus; B, Hieracium virosum; C, Cichorium Intybus.
(After BAILLON.)

spine and a felt of hairs. Centaurea with dry, scaly, involucral bracts and large,
sterile, marginal florets.

Other genera have only hermaphrodite ligulate florets in the capitulum,
and have latex in all parts of the plant. Taraxacum officinale (Dandelion) is
a common plant throughout the northern hemisphere. It has a long tap-root,

714

BOTANY

PART II

FIG. 785.— Head of fruits of Taraxacum officinale. The pappus is raised above the fruit on an
elongated stalk. (Nat. size.)

FIG. 786.— Cnicus benedictus. (After BAILLON.)

DIV. II

ANGIOSPERMAE

715

a rosette of coarsely-toothed leaves, and inflorescences, borne singly on hollow

" -vi

Fio. 788. — Artemisia.
Cina. (After Scnr-
MANN and ARTHUR
FIG. tt.—Matricaria ChamomiUa (§ nat, size). MEYER.)

stalks ; • after flowering these exhibit a second period of growth (p. 281) C40).

716

BOTANY

PART II

Fruits with an elongated beak, carrying up the pappus as a stalked, umbrella-
shaped crown of hairs (Fig. 785). Lactuca sativa, Lettuce. L. virosa. L.
Scariola, Compass plant, has leaves which take a vertical position (cf. p. 351).
Cichorium Intybus (Chicory) has blue flowers and a pappus in the form of short,
erect scales (Fig. 784 (7). 0. endivia, Endive. Tragopogon and Scorzonera have a
feathery pappus ; Sc. hispanica. Crepis has a soft, flexible, hairy pappus of

FIG. 789. — Tiissilago Farfara. (After BAILLON.)

brownish colour. Sonchus, pappus of several series of bristles, ffieracium, a large
European genu;» with many forms. Pappus white, rigid, and brittle (Fig. 784 B}.
Usually there are florets of two distinct types in the capitulum. Numerous
species of Aster, Solidago, and Erigeron occur in Europe, America, and Asia.
Species of Aster are cultivated. Species of Haastia and Raoulia are cushion-
shaped plants with woolly hairs in New Zealand (Vegetable Sheep) (Fig. 191).
Inula occurs in Britain ; involucral leaves frequently dry and membranous.
In Gnaphalium, Antennaria, Helichrysum (Everlasting flowers), Leontopodium

DIV. II

ANGIOSPERMAE

717

(Edelweiss), Filago. etc., the dry involucral bracts are coloured. Helianthus
annuus (Sunflower, Fig. 784 A), H. tuberosus (Jerusalem Artichoke). Dahlia,
from America and in cultivation. In Britain Bidens ; herbs with opposite

FIG. 790.— Arnica mor.tana (A nat. size). OFFICIAL.

leaves, sometimes heterophyllous. Achillea, Milfoil ; A. moschata and A. atrata
are corresponding species of the Alps, the one on limestone and the other on schists.
Anthemis nobilis, capitula composed of disc-florets only, or with these more or

BOTANY

less replaced by irregular florets. Anacyclus ojficinarum. Matricaiia Chamomilla
(Chamomile, Figs. 781 b, 787) is an annual copiously-branched herb with a hollow,
conical, common receptacle, yellow disc-florets and white, recurved, female ray-
florets, in the terminal capitula. Chrysanthemum, C. segctum. Tanacetum, flowers
all tubular, marginal florets female. Artemisia has all the florets tubular and
usually the peripheral ones female (A. Absinthium, Wormwood) ; in the few-
flowered capitula of A. Cina (Fig. 788) all the florets are hermaphrodite.

Tussilago Farfara, Coltsfoot, flowers appear before the leaves ; the flowering
stem bears scaly leaves and a single capitulum (Fig, 789) ; the flowers stand
on a smooth receptacle and have a fine white hairy pappus. Female flowers at
periphery in several series. Leaves large, cordate, thick, covered beneath with
white hairs. Petasites ojficinalis, Butter-Bur. Svnecio, plants of diverse habit,
including some trees and succulent plants ; of world-wide distribution. S. vul-
garis has no ray-florets but only tubular hermaphrodite florets. Doronicum,
Cineraria are commonly cultivated. Arnica montana (Figs. 780, 782, 790) has
a rosette of radical leaves in two to four opposite pairs and a terminal inflores-
cence bearing a single capitulum ; from the axillary buds of the two opposite
bracts one (rarely more) lateral inflorescence develops. Calendula and Dimorpho-
theca have the fruits of the capitulum of varied and irregular shapes.

OFFICIAL. — Anacyclus Pyrethrum yields PYRETHRI RADIX. SANTONINUM is
prepared from Artemisia maritima, var. Stechmanniana. Anthemis nobilis yields
ANTHEMEDIS FLORES. Taraxacum officinale, TARAXACI RADIX. Arnica montana,
ARNICAE RHIZOMA. Grindelia camporum.

SUB-CLASS II
Monoeotylae

The Monocotyledons, or Angiosperms which possess a single
cotyledon, are in general habit mostly herbaceous, less frequently
shrubs or trees.

In germination the radicle and hypocotyl of the small embryo
emerge from the seed coat, while the sheath-like cotyledon usually
remains with its upper end within the seed and absorbs the materials
stored in the endosperm, which is usually well developed. The
growth of the main root is sooner or later arrested and its place
taken by numerous adventitious roots springing from the stem. In
the Grasses these are already present in the embryo within the
seed. Thus a single root system derived by the branching of a
main root, such as the Gymnosperms arid Dicotyledons possess, is
wanting throughout the Monocotyledons.

The growing point of the stem remains for a longer or shorter
time enclosed by the sheath of the cotyledon. Later it bears in
two -ranked or alternate arrangement the leaves, which have long
sheaths and continue to grow for a considerable time at their bases.
The growth of the stem is often limited ; branching is in many cases
entirely wanting, and rarely results in the development of a highly
branched shoot-system. The leaves are mostly sessile and parallel-
veined, and of a narrow, elongated, linear, or elliptical shape

DIV. II

ANGIOSPERMAE

719

(Fig. 791). The pinnate or palmate leaves of the Palms and the
perforated leaves of some Araceae are due to the perishing of definite

portions of the lamina during de-
velopment.

Anatomically the Monocotyle-
dons are characterised by their
closed vascular bundles in which
no cambium is developed ; these
are uniformly scattered in the cross-
section of the stem (cf. Fig. 109).

FIG. 791.— Leaf of Polygonal urn multiflomm FIG. 792.— Diagram of a typical Mono-

with parallel venation (f nat. size). cotyledonous flower.

Secondary thickening is consequently wanting in Monocotyledons,
and in the rare cases in which it is found results from the formation
at the periphery of the central cylinder of additional closed bundles
embedded in ground-tissue (cf. p. 142).

The flower in the Monocotyledons is usually pentacyclic and has
two whorls constituting the perianth, an androecium of two whorls,
and a gynaeceum of a single whorl. The typical number of members
in each whorl is three. The two whorls of the perianth are usually
similarly formed and thus constitute a perigone (Fig. 792). The
floral formula of such a flower is P 3 + 3, A 3 + 3, G (3).

(a) Flowers adinomorphic
Order 1. Helobiae

This order includes only aquatic or marsh plants. The radial or
actinomorphic flowers have the gynaeceum frequently apocarpous and
composed of two whorls of carpels, which develop into indehiscent
fruitlets or follicles. Seeds exalbuminous ; embryo large. The order
connects by its floral structure the Monocotyledons with the Poly-
carpicae (cf. p. 630) (14).

Family 1. Alismaceae. — Widely spread in the warm and temperate zones.
Alisma Plantago, Sagittaria sagittifolia, and Butomus umbellatus have long-

720

BOTANY

PART II

stalked panicles or umbels, and occur as marsh plants. The individual flowers

FIG. 793. — Floral diagram of

Echinodorus parmilus, one FIG. 794. — Sagittaria sagittifolia. a, Flower; b, fruit after

of thei Alismaceae. (After removal of some of the carpels. (Magnified ; ft, after

EICHLEK.) ENGLER and PRANTL.)

have a calyx and a white (in Butomus, reddish) corolla. Androecium, with six or

FIG. 795. — Potamogeton natans. Flowering shoot. (3 nat. size.)

more stamens. Gynaeceum apocarpous, with six or many carpels that may be in
whorls or spirally arranged (Fig. 793). Sagittaria is monoecious with flowers that,

DIV. n

ANGIOSPERMAE

721

by suppression of stamens or carpels, are unisexual. Male flowers, with numerous
stamens and sterile carpels ; female flowers, with staminodes and numerous free
carpels inserted. on the convex floral receptacle (Fig. 794). Leaves in Hutomus,
linear, channelled, and triangular in cross-section ; in Alisma and Sagittaria,
long-stalked with spoon-shaped and sagittate leaf-blades respectively. Individuals
of both genera growing in deep flowing water have long ribbon - shaped leaves,
similar to those that appear as a transition type in germination ; such plants do
not flower.

Family 2. Potamogetonaceae. — Many species of Potamogeton are distributed
over the earth in standing or flowing water. Leaves usually submerged, with a
long sheath, slit on one side, formed from the axillary stipules. P. natans,
the common Pond-weed (Fig. 795), at the time of flowering has usually only float-
ing leaves, the cylindrical, submerged water-leaves having disappeared by then/
Ruppia maritime/, and Zanichellia palustris grow in brackish water. Zostera
marina, Grass-wrack, occurs commonly on all north temperate coasts and is used
for stuffing cushions.

Family 3. Hydrocharitaceae. — Hydrocharis morsus ranae and Stratiotes aloides
are floating plants occurring in Britain, which are vegetatively propagated by
runners ; they pass the winter at the bottom of the water, in some cases as special
winter buds, and grow up again in the spring. Flowers dioecious ; entomophilous.
The male flower has several trimerous whorls of stamens ; the female flower
possesses staminodes and two trimerous whorls of carpels. Vallisneria spiralis, a
fresh -water plant of the tropics ex-
tending to the Italian lakes. Elodea
canadensis, the Canadian water -weed
(hydrophilous, cf. p. 553).

Order 2. Liliiflorae

Flowers actinomorphic, com-
posed of five whorls, with superior
or inferior ovary. Both whorls of
the perianth developed alike (Fig.
792). Only in the Iridaceae is
one whorl of the androecium sup-
pressed. The gynaeceum varies
in position, but it is always formed
of three carpels and in most cases
has a trilocular ovary.

Family 1. Juncaceae. — Plants of
grass-like habit. Flower of complete
Liliaceous type ; with scaly perianth.
Wind-pollination. Pollen grains united
in tetrads. Ovary superior, uni- or tri-
locular, bearing three long papillose stigmas. Endosperm floury. Fruit a capsule.
Distributed in the temperate zones of both hemispheres.

Numerous species of Juncus (Rush) occur in our flora, in marshy ground ; the
leaves are cylindrical and have large intercellular spaces. The clusters of small
anemophilous flowers (Fig. 796) are borne on the end of a shoot, but are often dis-
placed to the side by the bract which continues the line of the axis. Fruits with

FIG. 796. — Juncus lamprocarpus. a, Part of an in-
florescence : single flower (&) and gynaeceum
(c) magnified.

722

BOTANY

PART II

FIG. 797. — Colchic/um autumnale (\ nat. size). /, Fruit in transverse section ; </, seed with
embryo (e) (enlarged). Porsoxous and OFFICIAL.

Fir;. 7:n». — Ornithogalum initbcJlatum. a, Entire plant (reduced); b, flower
(nat. size) ; c, flower, part of perigone and androeciiun removed ; d, fruit ;
e, fruit in transverse section, (c-e magnified.)

Fir;. 7$S.—Urginea sciUa
(about TV nat. size).
OFFICIAL. (After BERG
and SCHMIDT.)

723

3 A 1

724 BOTANY PART 11

many seeds. Luzula, with flat leaves and three-seeded fruits, one of the earliest
spring-flowering plants.

Family 2. Liliaeeae. — Typical flower, with coloured, conspicuous
perianth. Entomophilous. Ovary superior. The fruits are septicidal

FIG. 800.— Aloe speciosa and Aloe ferox. With, in the latter, branched inflorescences.
(After MARLOTH.)

or loculicidal capsules, or berries. Seeds numerous. Endosperm
horny or fleshy.

The majority of the Liliaeeae are perennial herbs with bulbs, tubers, or rhizomes.
They mainly inhabit the warm temperate regions. Colchicum autumnale, the
Autumn Crocus (Fig. 797), is a perennial herb growing in meadows. If a plant is
examined in autumn at the time of flowering, the corm (&), to the base of which is
attached the lateral shoot bearing the flowers, will be seen to be enclosed in a
brown envelope. The lateral flowering shoot bears at its base three sheathing

DIV. II

ANGIOSPERMAE

725

leaves not separated by elongated internodes. In the axil of the third of these is a
bud which will form the flowering shoot of the next season. In spring the reserve
materials from the corm are absorbed and the old corm is pushed aside by the
swollen internode which in its turn enlarges to form a new corm. The three
foliage leaves expand their long, channelled, dark green laminae above the soil ;
their sheathing portions closely surround the axis. The latter bears the fruits,
which contain numerous, spherical, black seeds ; these are liberated by the
dehiscence of the capsule at the sutures (Fig. 797 /). Veratrum album is a con-
spicuous herb with a rosette of large, elliptical, longitudinally-folded leaves. The
growth of the main axis is terminated by an inflorescence, which is a panicle more
than a metre in height ; the leaves borne on it have long sheaths and diminish in
size from below upwards. The greenish-white flowers are polygamous. Schoeiw-
caulon (Sabadilla) qjficinale, a bulbous plant
of the Andes with grass-like leaves, has also
septicidal capsules.

Such popular flowers as Tulipa (Fig. 204),
Hijacinthus, Lilium (Fig. 207), Muscari, and
Scilla, and vegetables as Allium, together
with Urginea (Fig. 798), which occurs in the
Mediterranean region, have on the other hand,
without exception, loculicidal capsules. Orni-
thogalum umbellatum (Fig. 799 a-e) will serve
as an example of this group. In autumn the
plant consists of a bulb, each of the fleshy
scales of which has a scar at the upper end. In
the axil of the innermost scale is the stalk of
the spent inflorescence together with a young
bud bearing a number of leaves. Each of these
leaves is provided with an embryonic lamina,
while the contimiation of the shoot is the
embryonic inflorescence. In spring the leaves
grow into long linear structures, and, together
witli the inflorescence, appear above ground.
The inflorescence is sparingly branched ; the FlG
white flowers have a trilocular ovary bearing
a common style. The upper parts of the
leaves wither, while the basal portions become

swollen and fleshy and stored with reserve materials ; the scar at the upper part
of each scale marks the place of separation of the leaf-blade. The annual course
of development is essentially similar in other bulbous plants. The vegetative
period is restricted to a few months, while during the cold or, in the numerous
bulbous plants of warm-temperate climates, the dry seasons, the bulb is protected
by its subterranean situation. Aloe, a genus of African plants containing many
species (Figs. 800, 801), has succulent leaves with spiny margins.

Dracaena (Fig. 802), an arborescent form which attains a great age and a
characteristic appearance, together with the similar genera, Cordyline and Yucca,
and Smilax (Sarsaparilla), a shrubby plant of warmer countries, climbing by
the help of tendril -like emergences at the base of the petioles, have berries.
Other examples are Asparagus with bunches of phylloclades in place of leaves,
Convallaria (Fig. 123), Maianthemum, Polygonatum (Fig. 138), and Paris quadri-
folia (Fig. 803) ; the latter bears whorls of four leaves, sometimes 3-6 leaves (41)

801.— Aloe socotrino. A, Inflores
cence. B, Flower. C, Ovary in cross-
section.

726

BOTANY

PART II

All these plants have creeping rhizomes bearing scale-leaves ; either the apex of
this rhizome grows annually into the erect shoot bearing the foliage leaves and
inflorescences, while the growth of the rhizome is continued by a lateral branch
(Polygonatum), or the rhizome continues its subterranean growth, the leafy shoots
being developed from axillary buds (Paris}.

POISONOUS. — Numerous Liliaceae are more or less poisonous, e.g. Lily of the
Valley, Tulip, Fritillaria, Colchicum, Veratrum, Paris.

OFFICIAL. — Colchicum autumnale, seeds and corm. Aloe vera, A. chinensis.
A. perryi, and other species yield ALOES BARBADENSIS and ALOES SOCOTRINA.
Urginea scilla yields SQUILL. Urginea indica.

FIG. 802. — Dracaena draco. The Dragon Tree of Laguna in the Canary Islands.
(After CHUN.)

Family 3. Amaryllidaceae. —Distinguished from Liliaceae by the inferior
ovary. Mostly tropical and sub-tropical. Leucojum (Fig. 804), the Snowdrop
(Galanthus], and Narcissus resemble the bulbous Liliaceae in habit. The majority
of the genera belong to the tropics or sub-tropics, e.g. Haemanthus, Olivia, Crinum,
species of which are often grown in greenhouses. Agave, large plants with suc-
culent leaves from the warmer regions of America, provide fibres. Agave Sisalana
from Yucatan, one of the most important fibre-yielding plants, is extensively
cultivated in East Africa and other colonies with dry and warm climates. A.
salmiana provides the national drink of Mexico (pulque), obtained by fermenting
the sap that flows on cutting off the inflorescence. Species of Agave are acclimatised
in the Mediterranean region.

Family 4. Iridaeeae. — Distinguished from Liliaceae by their
inferior ovary and by the suppression of the inner whorl of the

DIV. II

ANGIOSPERMAE

727

androecium (Fig. 805). The two whorls of the perianth are not

VI)

Fio. 803. — Parts quadrifolia ($ nat. size). Poisonous.

always similar. Anthers extrorse. The leaves of the Iridaceae are

3A2

728

BOTANY

PART II

always sessile ; the underground portion is a tuberous or elongated
rhizome, less commonly a bulb. Capsule loculicidal. This family is
mainly represented in the Cape and the warmer parts of America.

Fio. 804. — Leucojum aestivum.
a, Inflorescence (reduced) ; b,
gynaeceum and androecium
(nat. size). (After SCHIMPER.)

Fio. 805.— Floral diagram of the
Iridaceae(Jm). ( After SCHENCK.)

Fio. 806.— Crocus sativus. Style with tripartite stigma.
(After BAILLON.)

Crocus sativus, Saffron (Fig. 806), is a plant which has -long been cultivated in
the East ; it has a tuberous rhizome and narrow, grass-like leaves. The flowers
are sterile unless pollinated with pollen of the wild form. The large stigmas

FIG. 807.— Iris gennanica, (£ nat. size).
729

730 BOTANY PART n

furnish Saffron. Other species are cultivated as ornamental plants. Iris, leaves
overlapping in two ranks. The leaf-sheath surrounds the thick fleshy rhizome,
while the sword-shaped blade stands erect and has its two lateral surfaces alike
(Fig. 807). Outer perianth segments bent downwards, inner erect. The three
anthers are roofed over by the three leaf-like styles. In Gladiolus the flowers are
dorsiventral, and the dissimilarity of the perianth leaves is more marked.

Family 5. Bromeliaceae. — Mostly epiphytes ; flowers hermaphrodite. Limited
to tropical and sub-tropical parts of America. The leaves are in rosettes and
are typically xerophytic ; in the forms which grow in the soil they are spiny.
Ananassa sativa is cultivated ; its inflorescence forms the Pineapple.

Order 3. Enantioblastae

Characterised by the atropous ovules ; the embryo is at the summit of the
endosperm at the opposite end from the hilum.

Family. Commelinaceae. Tropical and sub-tropical. Perianth developed as
calyx and corolla. Commelina, Tradescantia. The hairs of the stamens afford
well-known objects for the study of movements of protoplasm and nuclear
divisions.

(b) Flowers more or less reduced
Order 4. Glumiflorae

This order consists entirely of annual or perennial plants of grass-
like habit. It is distributed over the whole surface of the earth.
A woody stem only appears in the genus Bambusa. The association
in more or less complex inflorescences of numerous flowers, which lack
a proper perianth but are enclosed by scaly bracts (glumes), is a
common character of the order. The perianth is either completely
wanting or reduced to a series of scales or bristles. The inner whorl
of stamens is also usually wanting, The superior ovary is always
unilocular and contains only one ovule ; it is formed of three
(Cyperaceae), two (some Carices), or of a single carpel (Gramineae).
The large size and feathery and papillose form of the stigmas stand
in relation to the wind, pollination. Fruits indehiscent.

Family 1. Cyperaceae. — The Sedges are characterised by their
triangular stems, which are usually neither swollen at the nodes nor
hollow, and by their closed leaf-sheaths. The flowers are unisexual and
then usually monoecious (Carex) or are hermaphrodite as in the majority
of the genera ; ovary formed of two or three carpels with an erect,
basal, anatropous ovule. Pericarp not coherent with the seed-coat ;
embryo small, surrounded by the endosperm.

The genera Cyperus, Scirpus, and Eriophorum have hermaphrodite flowers.
Fig. 808 represents a plant of Scirpus setaceus, which is an annual, in flower.
Leaves rigid, channelled above. Fertile shoots with the uppermost internode
elongated. Spikes 1-3, terminal ; enclosed by imbricating bracts and displaced
to one side by the subtending bract, the line of which continues that of

DIV. n

ANGIOSPERMAE

731

the stem. Only the large lowermost bracts are sterile, the others have each
a naked hermaphrodite flower in their axils. The Cotton-grass (Eriophorum
angustifolium), which when flowering is inconspicuous, bears at the summit of its
fertile shoots 3-7 long-stalked erect spikelets with numerous imbricate bracts.
Around the base of each flower are numerous hairs, which are concealed by the
projecting stamens and style. When the plant is in fruit the hairs, which have
become about 3 mm. long, project freely from between the bracts and constitute a
valuable means of dispersal for the fruits. The white colour of the hairs makes

Fto. SOS. — SV!>y.i!/s xetaceus. 1, plant in
flown- ; .?, upper portion of a flowering
shoot ; 3, single flower ; It, the same from
behind ; 5, the same without the bract ;
6, fruit. (1, nat. size, the others x 2-6.
After HOFFMAXX.)

FIG. 800.— Erinpho, «-,„ angugttfjltoim, 1, Inflores-
cence ; 2, a single spikelet ; 3, single flower ;
4, flower with bract removed ; 5, fruit. (1,
about nat. size, the others x 3-5. After
HOFFMANN.)

the now pendulous spikelets of the Cotton-grass a conspicuous feature of peat-moor
vegetation (Fig. 809). Oyperus papyrus, in Egypt and Sicily, provided from its
stems, which are as thick as the thigh, the " paper" of the ancient Papyri.

The genus Carex is for the most part monoecious, and its flowers are naked
and unisexual. Male spikes simple ; in the axil of each bract is a male flower formed
of three stamens (Fig. 810 A). The female spikes bear in the axil of each bract a
secondary shoot; the axis of this is included in the tubular subtending bract
(utriculus) together with the pistil (formed of 2 or 3 carpels), which is borne in the
axil of the bract (Fig. 810 B-E}.

732

BOTANY

PART II

Family 2. Gramineae (42). — The stems of the true Grasses are
cylindrical, and have hollow internodes (exceptions Maize and Sugar-
cane) ; the nodes are swollen ; the leaves are two- ranked and their
sheath is usually split and thickened at the node. At the junction of
the sheath and leaf-blade a membranous structure (the ligule) projects
(cf. Fig. 133). The flowers of the Gramineae are grouped in spicate,
racemose, or paniculate inflorescences, which are always composed
of partial inflorescences, the spikelets. Usually each SPIKKLET bears
several flowers. At the base of the spikelet there are usually (Fig.
811) a pair of sterile bracts (GLUMAE) ; sometimes there is only one
or 3-4 glumes. Continuing the two -ranked arrangement of the

tr. O

FIG. 810.— A, Floral diagram of a male flower
of Carex ; B, of a female flower with three
stigmas ; C, of a female flower with two
stigmas. D, Diagram of female flower of
Carex. E, Diagram of the hermaphrodite
spikelet of Elyna ; a. secondary axis; utr,
utriculus or bract of the secondary axis.
(After BICHLER.)

FJG. 811. — Diagrammatic
representation of a Grass
spikelet. g, The glumes ;
Pi and p->, the inferior
and superior palea ; e,
lodicules ; B, flower. The
axial parts are repre-
sented as elongated.

glumes come the fertile subtending bracts (PALEA INFERIOR), in the
axil of each of which stands a flower. The subtending bracts are
often awned, i.e. they bear terminally or springing from the dorsal
surface a stiff bristle with backwardly directed hairs (the AWN). The
bracteole of each flower is represented by another scale-like bract, the
PALEA SUPERIOR. Above this come two small scales, the LODICULAE,
the distension of which assists in opening the flower (Fig. 812 .B, C).
Lastly, the axis bears the androecium consisting of a whorl of three
stamens, and the ovary composed of one carpel and bearing two
feathery papillose stigmas. The ovary contains an anatropous, or
slightly campylotropous ovule.

The flowers do not always show such extreme reduction ; thus the flower of
Rice (Fig. 817) has a complete androecium ; that of the Bambuseae is similar and
also has three lodicules, and in Streptochaeta there is a normal monocotyledonous
type of flxnver with all five whorls of members present and three carpels indicated

DIV. II

ANGIOSPERMAE

733

in the development of the ovary. The lodicules can on this evidence be regarded
as corresponding to the inner whorl of the perianth. Possibly the superior palea
represents two coherent leaves of the outer whorl. In the gynaeceum there

remains as a rule only a double
leaf formed of the two lateral
carpels of the three originally
present. According to this view,
which we owe to GOEBEL, the
diagram in Fig. 813 is arrived at.
On the wind-pollination of
Grasses cf. p. 552. The fruit
of the Grasses is termed a
caryopsis ; in it the pericarp
and seed -coat are intimately
united. The embryo lies in
contact with the endosperm by
means of its cotyledon ; this
forms the SCUTELLUM, and in
germination serves as an ab-
sorbent organ by means of

FIG. 812.—Festuca elatior. A, Spikelet (compare Fig. 811),
with two open flowers below which the two sterile
glumes are seen (x 3). B, Flower ; the two lodicules
are in front, the superior palea behind ; the ovary
bears two feathery stigmas ( x 12) . C, A single lodicule
(x 12). D, Ovary seen from the side with the stalk of
one of the removed stigmas (x 12). (After H.SCHEXCK.)

FIG. 813.— Diagram of the Grass flower.
The missing parts are dotted; ax,
end of the axis of the spikelet ; pi,
palea inferior ; ps, palea superior
(outer perigone) ; I, lodiculae (inner
perigone) ; .<tf, outer, st', inner whorl
of stamens ; c, lateral carpels ; c',
dorsal carpel. (After SCHUSTER.)

which the reserve, materials in the endosperm are taken up by the seedling
(Fig. 814).

The most important economic plants belonging to this order are the Cereals
(Fig. 815). Wheat, Triticum. Spikelets single, with two or more flowers ; glumes
broadly ovate. KOERNICKE distinguishes as species of Wheat— (1) Tr. vulgare, with
a number of sub-species ; (2) Tr. polonicum ; (3) Tr. monococcum. Rye, Secale
cereale ; spikelets single, 2- flowered ; glumes acute. Barley, Hordeum vulgare ;

734

BOTANY

PART II

spikelets one-flowered, in groups of three ; in the sub-species H. hexastichum
and H. tetrastichum all the rows of spikelets are fertile, in H. distichum only the
middle row. Oat, Avena sativa. Maize, Zea mais. The above are all cultivated
in temperate climates, the Maize largely in America, the others also in Western
Asia and the south-east of Europe. In the wild state only Triticum monococcum,
var. aegilopodioides (from which Tr. monococcum is derived), Triticum dicoccoides
as the original form of Wheat, Secale montanum, and Hordeum spontaneum (allied
to H. distichum) are known. In these wild forms the spikelets fall from the
rachis at maturity, a character that would be unsuitable in cultivated forms.

The most important tropical food-plant of the order is Rice, Oryza sativa (Fig.
817), which is largely cultivated to the limits of the warmer temperate regions,
and, when sufficient moisture is available, yields an enormous harvest (Fig. 818).
In Africa several varieties of Millet, Andropogon Sorghum, are cultivated, and it

IG. 814.— Part of median longitudinal section of a grain of Wheat, showing embryo and scutellum
(sc) ; vs, vascular bundle of scutellum ; ce, its columnar epithelium ; I', its ligule ; c, sheathing
part of the cotyledon ; pv, vegetative cone of stem ; hp, hypocotyl ; I, epiblast ; r, radicle ;
d, root-sheath ; m, micropyle ; p, funiculus ; vp, its vascular bundle ; /, lateral wall of groove
cp, pericarp, (x 14.) (After STRASBURGER.)

forms the most important cereal for that continent. Panicum miliaceum and
P. italicum, of Asiatic origin, are still cultivated, though to a diminished extent,
in the Mediterranean region. The Sugar-cane, Saccharum officinarum, is another
important food-plant ; it is a perennial, growing more than six feet high, and
occurs in tropical Asia. The sugar-cane is cultivated in all tropical countries,
and cane-sugar is obtained from the sap expressed from the solid stem.

Among the most important of our meadow-grasses may be mentioned
Agrostis alba, Alopecurus pratensis, Anthoxanthum odoratum, Arrhenatherum
elatius, Avena flavescens, A. pubescens, jBriza media, Dactylis glomerata, Holcus
lanatus, Lolium perenne, Phleum pratense, Poa pratensis, and species of Aira,
Bromus, Calamagrostis, Festuca, Melica, etc. The tropical species of Bambusa,
which grow to the height of trees, are utilised in many ways ; from the stems
are constructed houses, walls, flooring, ladders, bridges, cordage, water- vessels,
cooking utensils, water-pipes, etc., and the plant is indispensable in the countries
in which it occurs.

DIV. n

ANGIOSPERMAE

735

POISONOUS. — Lolium temulentum (Fig. 819) has its fruits sometimes infested
with fungal hyphae. These fruits owing to the alkaloids they contain are poisonous,
but fruits free from fungus are harmless (43) ; the plant is an annual, and can be

FIG. 815.— Cereals. A, Rye, Secale cereals. B, Spelt, Triticum Spelta. C, Two-ranked barley,

Hordeum vulgare, distichum. D, Wheat, Triticum rulgare.

distinguished by the absence of sterile shoots from the common Lolium perenne
and L. multifiorum.

OFFICIAL. — AMYLUM (starch) is obtained from Triticum sativum, Oryza saliva,
Zca, mais, etc. ; Agropyrum repens.

736

BOTANY

PART II

FIG. 816.— A, Spikelet of Rye ; two-flowered. B, Spikelet of Wheat with a number of flowers.

FIG. 81V.— Oryza sativa. Panicle (J nat. size), and a single spikelet (enlarged).
OFFICIAL.

DIV. II

ANGIOSPERMAE

737

Order 5. Spadieiflorae

The common character of this order is afforded by the peculiar
inflorescence ; this is a spike with a thick, swollen, often fleshy axis
and is termed a spadix. The flowers are mostly diclinous,
monoecious, or more rarely dioecious.

Family 1. Typhaceae. — Marsh plants, with long, linear leaves and long-
stalked spikes, which bear a large number of flowers, the male above, the female
lower down. Perianth wanting.

FIG. 818.— Terraced land in Ceylon for the cultivation of Rice. The water required for the young
plants flows from terrace to terrace through gaps in the boundary walls. In the foreground
Bananas, and to the right a Coffee plantation. In the centre Areca palms. (From a photograph.)

Family 2. Sparganiaceae. — Connected with the preceding family. Spikes
spherical. Flowers with a perigone, but otherwise like the Typhaceae.

Family 3. Pandanaceae. — Screw -pines. Trees of peculiar appearance, sup-
ported by prop-roots, or climbing shrubby plants ; all belong to the tropical
countries around the Indian Ocean and to the Pacific islands. Leaves elongated,
spiny, channelled above, arranged without bare internodes in three ranks on the
axis. Inflorescences, $ or ? , are terminal spikes in the axils of sheathing bracts.
Flowers without perianth, Pandanus (cf. Fig. 822 in front of the Palms), Freycinetia
(cf. p. 558).

738

BOTANY

PART II

Family 4. Palmae (44). — The Palms are an exclusively tropical
and subtropical family, the members of which mostly attain the size of
trees. Their slender stem is simple and usually of uniform diameter
throughout ; only the African species of Hyphaene have branched
stems. Other forms show evident growth in thickness towards the

base and sometimes for
half the height of the
stem ; this either depends
on enlargement of the
elements already present,
or to a limited extent on
new formation of tissues
when required. The leaves,
which are often of gigantic
size, form a terminal crown.
They are either pinnately
or palmately divided, the
division coming about by
the death of definite por-
tions of tissue in the young
leaf in the bud, and subse-
quent tearing along these
lines. The inflorescence
is in some cases terminal
(Mctroxylon), and the in-
dividual perishes with the
development of the fruits.
More often the inflores-
cences are axillary. When
young, they are enclosed
by a massive resistant
sheath, the spathe ; this
bursts open and permits
of the unfolding of the
simple, or more usually

branched, inflorescence.
B

The individual flowers are
as a rule unisexual and con-
structed on the ordinary mono-
cotyledonous type; P3+3, A 3 + 3, in the male flowers, and P3 + 3, G (3),
in the female flowers. In Oocos their distribution is monoecious. Fig. 820 repre-
sents the inflorescence of Cocos nucifera, still partly enclosed by the spathe. The
male flowers are crowded on the terminal branches of the inflorescence, while the
female flowers are considerably larger and stand singly lower down. The ovary,
which is here composed of three united carpels, becomes, as a rule, unilocular in
the fruit, since only one carpel develops further. The ripe fruits are borne

FIG. 819. — Lolium temulentum. POISONOUS.
(After H. SCHENCK.)

DIV. II

ANGIOSPERMAE

739

YT.V \

.'• '•-" •'•- \

- I

'V- "-fY

« V /t •' v 'v, SF

'. V; : ;\ .'i ,,-X \ -.

,^ /^v' '

^s <i.; ^ '

FIG. 820. — Cocos nucifenu Inflorescence of the Coco-nut Palm. (Greatly reduced.)

740 BOTANY PART n

in small numbers on each inflorescence. Each consists of a coarse, fibrous
exocarp, which contributes to the buoyancy of the fruit in water, and thus leads to
the wide distribution of this palm on tropical coasts, and a hard endocarp. At the
base of each carpel a germinal pore is present in the endocarp (Fig. 821), but only the
one in relation to which the embryo lies remains permeable. The endosperm forms
a thick layer within the endocarp ; it is rich in fatty substances and produces the
COPEA of commerce. The space within the endosperm is partially filled with fluid,
the "milk" of the coco-nut, which is possibly of service in germination. The
embryo on germination develops a massive absorbent organ which' grows into the
cavity of the fruit and serves to absorb the reserve materials. Fig. 822 shows the
general habit of Coco-nut palms.

Differences are, however, found within the order. In Areca catechu (Fig. 818)
the fruit developed from a similar ovary to that of Oocos is a berry, the exocarp

becoming partly fibrous and partly succulent.
The white endosperm is here of stony consist-
ence, cellulose being stored as a reserve material ;
the endosperm is ruminated, i.e. the dark seed-
coat grows into it at many points and gives it a
veined appearance. The fruit of the Date Palm
(Phoenix dactylifera) is also a berry, but this
arises from one of the carpels of the apocarpous
gynaeceum, the other two not developing. In
contrast to the other genera mentioned, Phoenix
is dioecious. Other important economic plants
among the Palms are Elae'is guineensis, the African
Oil Palm, species of Calamus which yield Malacca
FIG. 821. — Coco -nut after partial Cane, and species of Metroxylon, from which Sago
removal of the fibrous exocarp. is obtained ; the two latter are found in the
(Reduced. After WARMINO.) Asiatic -Australian region of the tropics. Phyt-

elephas macrocarpa, an American Palm which

does not form a trunk, yields vegetable ivory (the hard endosperm). Several
species yield a flow of sugary sap on cutting off the inflorescence, and this
is sometimes fermented to make Palm- wine and sometimes used as a • source of
cane-sugar (Arenga saccharifera).

Family 5. Araeeae. — The Araceae are mostly herbs or shrubs ;
they take a conspicuous place as root-climbers in the damp tropical
forests. The leaves of some species (e.g. Monstera) have the large
lamina incised or perforated ; this comes about by the death of
definitely limited areas and is comparable to the method by which the
leaves of Palms become compound. The flowers are greatly reduced,
usually diclinous, borne on a swollen, fleshy axis ; a spathe, often of
bright colour and serving to render the inflorescence conspicuous,
is present at the base of the spike (e.g. Anthurium scherzerianum,
Richardia aethiopica, both of which are commonly cultivated). Fruit
usually a red, bluish, or white berry.

Acorus calamus has, in the course of the last two or three centuries, spread to
this country from the East. It has complete, hermaphrodite flowers ; ovary tri-
locular. The short spadix is terminal, but is displaced to one side by the spathe
which resembles the foliage leaves (Fig. 823).

DIV. II

ANGIOSPERMAE

741

POISONOUS. — Many Araceae are poisonous. Ga.Ua, palustris in peaty swamps.
Arum maculatum (Fig. 824), a perennial herb with tuberous rhizome, common in
woods. It develops a number of stalked, hastate leaves, the brown spots on which
give the plant its specific name. The flowers are monoecious, without perianth ;
the female flowers stand at the base of the spadix and the male a short distance
above them. Above the latter come a number of sterile flowers with downwardly

FIG. 822.— Coco-nut Palms at Hilo, Hawaii. Pandanus odoratissimus in front of the Palms.

directed, hair-like points, which stand at the level of the constricted portion of the
spathe ; this is widely open above. These hairs allow insects, attracted by the
peculiar scent or seeking warmth, to creep into the lower expanded portion
of the spathe, but prevent their return until the female flowers have been
pollinated from another individual. When this is accomplished the hairs wither
and the anthers open. The escaping insects, now dusted with pollen, may enter
other inflorescences and pollinate the flowers.

3BI

742

BOTANY

PART II

Tropical plants, sometimes of large size, in a few cases arborescent.
Flowers dorsiventral or asymmetrical. Perianth differentiated into

FIG. 823. — Acorus calamus. Flowering plant. Single flowers seen from above and from the side.

(i nat. size.)

calyx and corolla. Androecium greatly reduced ; some of the
stamens represented by staminodes, and resembling the segments
of the corolla. Ovary inferior, trilocular. Seeds with perisperm.

Drv. ii ANGIOSPERMAE 743

Family 1. Musaceae. — The Banana (Musa] is one of the most important plants

FIG. 824.— Arum maculatum (\ nat. size). Inflorescence and fruits (§ nat, size). Poisoyovs.

of all tropical countries. The apparent, erect stem is formed of the closely over-
lapping, sheathing bases of the large leaves. Inflorescence, terminal, pendulous,

FIG. 825.— Floral diagram of Zingiberaceae (after EICHLER). b, Bract ; r, bracteole ; k, calyx ;
pi-3, segments of corolla ; ssti, sst^, staminodes of the outer whorl of the androecium ; * the
suppressed stamen of this whorl ; st, the single fertile stamen; I, petaloid staminodes of the
inner whorl of the androecium forming what is known as the labellum.

FiG.826.—Zingiberofficinale.

nat. size. After BERO and SCHMIDT.) OFFICIAL.

744

ANGIOSPERMAE 745

bearing the crowded and mainly parthenocarpic C45) berry-like fruits. M. textilis
yields Manila Hemp. llavenala has a woody stem. Strelitzia reginae (Fig. 529)
from the Cape is cultivated on account of the beauty of its flowers.

Family 2. Zingiberaceae. — Flowers in spikes, which in some cases resemble
capitula. Flower dorsi ventral. Calyx inconspicuous, tubular. Corolla with
three lobes. The outer whorl of the androecium is wanting or represented by two
lateral staminodes (Fig. 825, sstlt $st2). Only the posterior stamen of the inner
whorl (st) is fertile; the two others are joined to form the brightly - coloured
petaloid labellum (I). The style lies in the tubular groove between the thecae of
the stamen. Fruit a capsule. Most plants of the family belong to tropical Asia.

Zingiber ojficinale, the Ginger, is an ancient cultivated plant of Southern Asia,
now cultivated throughout the tropics (Fig. 826). The flattened branched
rhizome is in contact with the soil by its narrow side. Leaves, two -ranked ;
main shoot continued by the growth of axillary buds of the lower surface. The
leafy shoots, in spite of their length, are composed of the sheaths of the large,
simple, entire leaves, the axis remaining extremely short. Only the flowering
shoots are solid ; they remain shorter and bear scale leaves with large sheaths
but no lamina. Bracts large and, especially at their margins, brightly coloured.
Flowers, bright yellow, with a conspicuous, violet, and spotted labellum. Elettaria
Cardamomum and Curcuma have the stalks bearing their inflorescences similarly
provided with scale leaves. Alpinia and Hedychium, the latter of which is often
cultivated, have on the other hand normal leafy shoots bearing the terminal
inflorescence.

OFFICIAL. — Zingiber qfficinale, rhizome yields GINGER. Elettaria Cardamomum
yields CARDAMOM SEEDS.

Family 3. Cannaceae. — Large-leaved herbs ; often in cultivation. Flowers
asymmetrical (Fig. 827). Only one half stamen fertile (i.e. anther with only one
theca), the other half being petaloid.

Family 4. Marantaceae. — Large -leaved herbs. Leaves with pulvinus at
junction of stalk and lamina. Stamen as in preceding order. Arrowroot is
obtained from Maranta arundinacea.

Order 7. Gynandrae

Family Orehidaeeae. — Perennial, herbaceous plants growing as
epiphytes or in the ground, with hermaphrodite, zygomorphic flowers.
Perianth petaloid, the posterior segment of the inner whorl developed
as a lip or labellum, which frequently bears a spur. (The " labellum "
of the Scitamineae being formed of two staminodes is entirely
different morphologically.) Androecium formed of the three
anterior stamens only ; the middle stamen, belonging to the outer
whorl, is fertile ; the other two are represented by staminodes. Cypri-
pedium has these two lateral stamens of the inner whorl fertile.
Gynaeceum formed of three carpels, syncarpous ; ovary inferior, uni-
locular. Fruit, a capsule. Seeds extremely numerous, borne on
parietal placentas (Figs. 828, 831). The fertile stamen is adherent to
the style and forms with it the COLUMN or GYNOSTEMIUM ; this projects
more or less in the centre of the flower. The labellum, which serves

746

BOTANY

PART II

as an alighting place for visiting insects, becomes anterior either by
the torsion of the whole flower through 180° (cf Figs. 828, 831) or

by the flower being bent back-
wards.

The Orchidaceae attain their
highest development in the tropics
where they form an important part
of the epiphytic vegetation. Orchis,
Ophrys, Gymnadetiia, Platanthera
with tubers ; Epipactis, Cephalan-
thera, Listera with branched
rhizomes ; Neottia, the Bird's-nest
Orchid, Epipogon, Coralliorrhiza,
Limodorum almost destitute of
chlorophyll. They live saprophyti-
cally or more correctly as parasites

FIG. 827. — Flower of Canna iridiflora. f, Ovary ;
k, calyx ; c, corolla ; I, labellum ; st^-s> the
other staminodia ; a, fertile stamen ; g, style.
(£ nat. size.)

FIG. 828. —Orchidaceae. Floral
diagram (Orchis). (Modified after NOLL.)

at the expense of their mycorrhiza (46). Cypripedium, Ladies' Slipper, with two
lateral fertile stamens of the inner whorl.

Orchis militaris, which is represented in Fig. 833, will serve as an example for

FIG. 829.— Orchis militaris. Longitudinal
section passing through the old and new
tubers. (After LUERSSEN.)

FIG. 830.— Root-system of Orchis latifolia. b,
Base of stem ; s, scale leaf ; t', old, t", young
tubers ; fc, bud ; r, roots. (After H.
SCHENCK.)

more detailed consideration. At the period of flowering a pair of fleshy tubers will
be found at the base of the plant, both of which are covered with root hairs. The
large or brown tuber of more spongy texture continues above into the stem which

DIV. II

ANGIOSPERMAE

747

terminates in the pyramidal inflorescence ; this stem is surrounded at the base
by a pair of scale leaves and the sheaths of the 2-4 elongated, elliptical foliage
leaves. The smaller tuber is of firmer consistence and of a white colour ; it bears,
as is shown in the longitudinal section (Fig. 829), a bud on its summit which
already shows a pair of scale leaves. This tuber has arisen as an axillary bud in
relation to one of the first scale leaves of the plant, and with its tuberous, swollen,
first root has broken through the subtending scale leaf (Fig. 829). It is destined
to replace the parent plant in the succeeding season.

FIG. 831.— Orchis militaris. A, Flower: a,
bract ; b, ovary ; c, the outer, and d, the two
anterior inner perigone leaves ; e, label-
lum with the spur/; g, gynostemium. B,
Flower after removal of all of the perigone
leaves with exception of the upper part of
thelabellum: h, stigma ; I, rostellnm ; /,-,
tooth-like prolongation of the rostellum ;
m, anther ; n, connective ; o, pollinium ; q,
viscid disc ; p, staminodium. C, A pollin-
ium : r, caudicle ; s, pollen. D, Fruit in
transverse section. (After BERG and
SCHMIDT.)

Fio. 832.— Vanilla planifolia, (reduced. After BERG
and SCHMIDT ; from ENGLER and PRANTL). A,
Labellum and gynostemium. B, Gynostemium
from the side. C, Summit of the gynostemium from
in front. D, Anther. E, Seed. (Magnified.)

In considering the flower, the spiral torsion of the ovary, which brings the
labellum into the anterior position, must first be recognised. The labellum is
tripartite and the larger middle segment is bifid at its free end. At the base of
the labellum a spur is formed by the bulging out of this segment of the perianth ;
this serves as the nectary, and the opening leading into it is situated just below the
gynostemium (Fig. 831 A, E}. The latter bears on the side that is turned towards
the lower lip, and to an insect alighting on this, the large stigmatic surface (h)
corresponding to two confluent stigmatic lobes. The third stigmatic lobe is trans-
formed into a structure termed the rostellum (I, k) and stands in relation to the
male organ. The single fertile anther consists of two thecae joined together by the
connective which appears as the end of the gynostemium. The whole mass of

748

BOTANY

PART II

FIG. 833.— Orchis militaris (£ nat. size).

pollen of each of the two pollen
sacs is joined together by an
interstitial substance which
continues below to form a
stalk ; the whole structure,
which has a waxy consistence,
is called a pollinium, and the
stalk goes by the name of the
caudicle. The caudicles ter-
minate below in contact with
the rostellum which forms tough
adhesive discs. This relation
to the rostellum serves to keep
the pollinia, which lie free in
the pollen sacs, in position, and
the adhesive discs attach the
pollinia to any body that comes
in contact with them. If an
insect alights on the lower lip
and attempts to reach the nectar
secreted in the spur, its head or
tongue must touch the rostel-
lum and the pollinia will become
attached to it. As the adhesive
discs dry they cause the pollinia
to bend forward, so that Avhen
the insect visits a second flower
they will be brought in contact
with the stigmatic surfaces.

All Orchids are similarly
adapted to insect visitors,
though in many the contri vances
are far more complicated ; pol-
lination does not take place in
the absence of the insects (47).
In many cases the adaptations
are so specialised to particular
insects that no other insect will
do instead. Thus Vanilla (Fig.
832) brought from its American
habitats to other tropical coun-
tries remains sterile on account
of the absence of the pollinating
insect. On this fact being dis-
covered artificial pollination
was resorted to and the plants
can thus be induced to bear
fruits regularly. It should be
mentioned that in some forms,
e.g. Vanilla, the pollen remains
powdery. Many tropical

DIV. ii ANGIOSPERMAE 749

Orchids are cultivated in greenhouses on account of the beauty of their flowers,
e.g. Cattleya, Laelia, Vanda, Dendrobium, etc.

Fossil Angiosperms (13)

The first undoubted Angiosperms appear in the Upper Cretaceous. They are
represented by numerous species which, like the recent forms, can be divided
into Monocotyledons and Dicotyledons. The most ancient forms are known only
as leaves, so that their determination is a matter of difficulty. They agree essen-
tially with living Angiosperms, and since they show no similarities to Gymnosperms
or Pteridophytes, do not aid in bridging over the gap between the Angiosperms
and these groups.

The Angiosperms of the Eocene and the Oligocene can be determined with greater
certainty ; even in Northern Europe representatives of existing tropical and sub-
tropical families occurred, e.g. Palmae, Dracaena, Smilax among Monocotyledons,
numerous Querciflorae (esp. Quercus), Lauraceae (Cimiamomum, etc.), Leguminosae,
etc., among Dicotyledons. From the Miocene onwards the specific forms are in
part identical with those now living, and in the Quaternary strata all the remains
are of existing species. The general character of the Tertiary flora in Europe was,
however, very different from that of the present day. It had the aspect of the
flora of a much warmer region and (as in the case of the Gymnosperms) contained
forms which now exist only in distant regions.

INDEX OF LITEKATUKE

INTRODUCTION AND, MORPHOLOGY BY H. FITTING
Introduction

(a) CHARLES DARWIN, On the Origin of Species by Means- of Natural Selection,
1859. (2) E. HAECKEL, Generelle Morphologic der Organismen, 1866, p. 52.
(3) C. v. NAGELI, Theorie der Abstammungslehre, 1884, p. 326 ; F. A. WENT,
Biologisches Zentralblatt, vol. xxvii. 1907, p. 257 ; K. GOEBEL, Organographie,
2. Aufl. vol. i. 1913, pp. 39 ff.

Section I. Cytology

The Living Cell Contents. — (4) E. STRASBURGER, Progressus rei botanicae,
vol. i. 1906, p. 1 ; E. KUSTER, Zelle in Handwbrterb. der Naturwiss. Jena, vol. x.
1914, p. 748. (5) Literature collected by A. GUILLIERMOND, Revue gen. de Bot.
vol. xviii. 1906, p. 392 ; E. ZACHARIAS, Bot. Ztg. 1907, p. 265 ; A. MEYER, Die
Zelle der Bakterien, Jena, 1912 ; E. PARAVICINI, Bakt. Zentralbl. II. vol. xlviii.
1918, p. 337. (6) A. J. EWART, Physics and Physiology of Protoplasmic streaming
in Plants, Oxford, 1903 ; PAUL KRETZSCHMAR, Jahrb. f. wiss. Bot. vol. xxxix.

1904, p. 273. (7) J. W. MOLL, Progress, rei botan. vol. ii. 1908, p. 227 ; E. STRAS-
BURGER, Das kleine bot. Praktikum, 8. Aufl. 1919, and Das botanische Praktikum,
5. Aufl. 1913 ; H. SIEBEN, Einfuhrung in die bot. Mikrotechnik, Jena, 1913.
(8) E. ZACHARIAS, Progress, rei botan. vol. iii. 1910, p. 67. (9) A. FISCHER,
Fixierung, Farbung und Bau des Protoplasma, 1899, and A. DEGEN, Bot. Ztg.

1905, 1. Abt. p. 202. (10) N. GAIDUKOV, Dunkelfeldbeleuchtung und Ultra-
mikroskopie in der Biologic und der Medizin, 1910. (n) E. W. SCHMIDT, Progress,
rei botan. vol. iv. 1912, p. 163, and Ztschr. f. Botan. vol. iv. 1912, p. 707 ;
J. DUESBERG, References in Ergebn. d. Anatom. u. Entwicklungsgeschichte, vol.
xx. 1912, p. 567 ; K. RUDOLPH, Ber. deutsch. bot. Ges. vol. xxx. 1912, p. 605 ;
G. LEWITZKY, Ber. deutsch. bot. Gesellsch. vol. xxxi. 1913, p. 517 ; A. SCHERRER,
Festschr. z. Einweihung d. Inst. fur allg. Bot. Zurich. Jena, 1914 ; A. GUILLIER-
MOND, Rev. gen. de bot. vol. xxv. bis, 1914, p. 295 ; vol. xxvi. 1914, p. 295 ; FR.
MEVES, Arch. f. mikr. Anatomic, vol. Ixxxix. 1. Abt. 1917, p. 249 ; D. M. MOTTIER,
Ann. of Bot. vol. xxxii. 1918, p. 91. P) Cf. the most recent works of GREGOIRE
and his pupils, and of E. STRASBURGER ; also H. LUNDEGARDH, Beitr. z. Biol. d.
Pflanzen, vol. xi. 1912, p. 373 ; includes literature. (13) A. GUILLIERMOND,
Progr. rei bot. vol. iv. 1913, p. 389 ; H. v. NEUENSTEIN, Arch. f. Zellforsch. vol.
xiii. 1914, p. 1. (14) A. F. W. SCHIMPER, Bot. Ztg. 1880, p. 886, and Jahrb. f.
wiss. Bot. vol. xvi. 1885, p. 1 ; ARTHUR MEYER, Das Chlorophyllkorn, 1883, and
Bot. Ztg. 1888, p. 489 ; J. H. PRIESTLEY and A. A. IRVING, Ann. of Bot. vol.
xxi. 1907, p. 407 ; A. SAP£HIN, Untersuchungen iiber die Individuality d.

751

752 BOTANY

Plastide, Odessa, 1913 ; Archiv f. Zellforschung, vol. xiii. 1915, p. 319. (15)
Especially L. MARCHLEWSKI, E. So HUNK, N. A. MONTEVERDE, M. TSWETT,
R. WILLSTATTER ; cf. especially R. WILLSTATTER and A. STOLL, Untersuchungen
iiber Chlorophyll, Berlin, 1913 ; C. v. WISSELINGH, Flora, vol. cvii. 1915, p. 371.
(16) TH. W. ENGELMANN, Bot. Ztg. vol. xl. 1882, p. 663 ; vol. xli. 1883, p. 1 ;
H. MOLISCH, Bot. Ztg. vol. Ixiii. 1905, 1. Abt. p. 131 ; H. KYLIN, Svensk. bot.
tidskr. vol. vi. 1912, p. 531. (17) H. KYLIN, Ztschr. f. physiol. Chemie, vol.
Ixxxii. 1912, p. 221 ; R. WILLSTATTER and H. J. PAGE, Ann. d. Chemie, vol.
cccciv. p. 237. (18) E. GOERRIG, Beih. Bot. Zentralbl. I. vol. xxxv. 1918, p. 1.
(19) W. ROTHERT, Bull, intern, ac. sc. de Cracovie ser. B, 1914, p. 1. (20) As regards
the botanical side the numerous works of E. STRASBURGER, M. TREUB, L. Gui-
GNARD, W. BELAJEFF, J. B. FARMER, B. NEMEC, V. GREGOIRE, A. WYGAERTS,
E. ESCOYEZ, J. BERGHS, 0. ROSENBERG, CH. ALLEN, K. MIYAKE, J. B. OVERTON
and others ; cf. also TH. BOVERI, Ergebnisse iiber die Konstitution der chroma-
tischen Substanz des Zellkerns, 1904 ; M. PICARD, Bull. Torrey Bot. Club, vol. xl.
1913, p. 575. (21) G. TISCHLER, Progr. rei bot. vol. v. 1915, p. 164 ; H. WINKLER,
Ztschr. f. Hot. vol. viii. p. 417. f22) E. STRASBURGER in Wiesner-Festschiift,
1908, p. 24. (23) R. A. HARPER, Jahrb. f. wiss. Bot. vol. xxx. 1897, p. 249 :
P. N". SCHURHOFF, Jahrb. f. wiss. Bot. vol. Ivii. 1917, p. 363.

The Larger Non-living Inclusions of the Protoplasts. (24) H. MOLISCH, Mikro-
chemie der Pflanze, Jena, 1913 ; 0. TUNMANN, Pflanzenmikrochemie, Berlin, 1913.
(25) J. DEKKER, Die Gerbstoffe, Berlin, 1913. (26) R. WILLSTATTER, Sitzungsber.
preuss. Akad. d. Wiss. 1914, pp. 402, 769 ; H. SCHROEDER, Ztschr. f. Bot. vol. ix.
1917, p. 546 ; cf. also H. MOLISCH, Bot. Ztg. 1905, 1. Abt. p. 161 ; also B. L.
BUSCALIONI and G. POLLACCI, Atti istit. bot. Univ. Pavia, N.S. vol. viii. 1903,
pp. 135 ff. ; 0. GERTZ, Studier ofver Anthocyan, Lund, 1906. (27) A. TSCHIRCH,
Die Harze und die Harzbehalter, 1900. (>28) Literature in A. GUILLIERMOND and
J. BEAUVERIE, Ann. des sc. nat. Bot. IX. Ser. vol. viii. 1908, p. 173. C29)
C. NAGELI, Die Starkekorner, 1858 ; A. F. W. SCHIMPER, Bot. Ztg. 1881, p. 223 ;
A. MEYER, Unters. iiber die Starkekorner, 1895 ; H. PRINGSHEIM, Landwirtsch.
Yersuchsstationen, vol. Ixxxiv. 1914, p. 267.

The Cell- Wall.— (30) Literature to 1904 in L. GAUCHEK, Etude generale stir la
membrane cellulaire chez les vegetaux, 1904, and since in FR. CZAPEK, Biochemie
der Pflanze, 2. Aufl. vol. i. 1913, p. 629 ; 0. RICHTER, Ztschr. f. wiss. Mikr. vol.
xxii. 1905, p. 194 ; Zur Membranstreifung W. KRIEG, Beih. z. bot. Zentralbl. vol.
xxi. 1907, p. 245. (31) E. HANNIG, Flora, vol. cii. 1911, p. 209. (32) F. CZAPEK,
Biochemie der Pflanzen, 2. Aufl. vol. i. 1913, p. 629 ; PETER KLASON, Schriften
des Yereins der Zellstotf- und Papier-Chemiker, vol. ii. 1911 ; FR. CZAPEK, Ztschr.
f. Bot. vol. iii. 1911, p. 500 ; J. KONIG and E. RUMP, Chemie und Struktur der
Pflanzen-Zellmembran, Berlin, 1914 ; C. G. SCHWALBE, Die Chemie der Zellulose,
2. Aufl. Berlin, 1918. (33) Cf. F. CZAPEK in (30), vol. i. p. 634 ff. ; A. YIEHOEVER,
Ber. deutsch. bot. Gesellsch. vol. xxx. 1912, p. 443. (34) F. EHRLICH, Chemiker-
Zeitg. vol. xli. 1917, p. 197. (35) VAN WISSELINGH, 'Archives neerland.
vol. xxvi. 1892, p. 305, and vol. xxviii. 1898, p. 373. (36) ORMOND BUTLER, Ann.
of Bot. vol. xxv. 1911, p. 107 ; gives the literature on p. 150 ; J. GRUSS, Jahrb. f.
wiss. Bot. vol. xlvii. 1910, p. 391.

Section II. Histology

(37) A. DE BARY, Vergl. Anat. d. Vegetationsorgane, 1877 ; G. HABERLANDT,
Physiologische Pflanzenanat. 5. Aufl. 1918 ; H. SOLEREDEK, Syst. Anat. d.

INDEX OF LITERATURE 753

Dikotyledonen, 1899 ; English translations of the three preceding works ; W.
ROTHERT, Gewebe. Handwbrterb. d. Naturwiss. iv. Jena, 1913, p. 1144 ;

E. STRASBURGER, cited in (7) ; A. MEYER, Erstes mikroskop. Praktikum, 3. Aufl.
Jena, 1915. (») For the literature cf. in (4) (») G. KRABBE, Das gleitende
Wachstum b. d. Gewebebildung der Gefasspflanzen, Berlin, 1886 ; F. NEEF,
Ztschr. f. Bot. vol. vi. 1914, p. 465. (*>) L. DIELS, Flora, vols. cxi.-cxii. 1918,
p. 490. (41) On Stomata E. STRASBURGER, Jahrb. f. wiss. Bot. vol. v. 1866,
p. 297 ; S. SCHWEXDENKB, Monatsber. d. Berl. Akad. d. Wiss. 1881, p. 883,
etc. ; S. H. ECKERSON, Bot. Gaz. vol. xlvi. 1908, p. 221. f42) G. HABERLANDT,
Die Sinnesorgane im Pflanzenreich, 2. Aufl. 1906. (43) G. MYLIUS, Biblioth.
botan., Heft 79, 1912. (**) S. SCHWENDENER, Das mechanische Prinzip im Bau
der Monokotylen, 1874; H. AMBRONN, Jahrb. f. wiss. Bot. vol. xii. 1879. (**)
A. W. HILL, Ann. of Bot. vol. xv. 1901, p. 575, and vol. xxii. 1908, p. 245 ;
A. F. HEMENWAY, Botan. Gazette, vol. Iv. 1913, p. 236 ; E. W. SCHMIDT, Bau u.
Funktion der Sieblohre, etc. Jena, 1917. C46) W. ROTHERT, Abhandlungen d.
Akad. d. Wiss. Krakau, 1899, p. 433. (47) H. MOLISCH. Studien iiber Milchsaft und
Sehleimsaft der Pflanzen, 1901. C48) M. NIEUWENHUIS-V. UEXKtfLL-Gt'LDENBAND,
Rec. trav. bot. neerland. vol. xi. 1914, p. 291.

Section III. Organography

Structure of the Thallus and of the Typical Cormus.— (49) K. GOEBEL, Ver-
gleichende Entwicklungsgeschichte der Pflanzenorgane, 1883, and Organographie
der Pflanzen, 1898-1901, 2. Aufl. vol. i. 1913, vol. ii. 1915-18 ; J. VELENOVSKY,
Yergleichende Morphologic der Pflanzen, 4 vols. Prag, 1905-14 ; KERNER VON
MARILAUN-HANSEN, Pflanzenleben, 3. Aufl. vol. ii. 1913 (English translation) ;

F. PAX, Allgemeine Morphologic der Pflanzen, 1890. C50) F. OLTMANNS, Mor-
phologic und Biologic der Algen, 1904 ; A. DE BARY, Vergl. Morphol. u. Biologic
der Pilze, 1884 (English translation). (51) F. SCHUTT, Das Pflanzenleben d.
Hochsee, 1893. (5J) E. DE WILDEMAN, Mem. couronn&s et publics par 1'Acad.
des sciences de Belgique, vol. liii. 1893. (53) H. LEITGEB, Untersuchungen
iiber die Lebermoose, vols. i.-vi. 1874-79; K. GOEBEL, Organographie, 2. Aufl.
vol. ii. Jena, 1915 ; D. H. CAMPBELL, The Structure and Development of Mosses
and Ferns, 2nd ed. 1905. (w) Cf. GOEBEL, cited in C53). C55) F. HERRIG, Flora,
vol. cvii. 1914, p. 327. C56) W. HOFMEISTER, Allgemeine Morphologic der
Gewachse, Leipzig, 1868. (57) S. SCHWENDENER, Mechanische Theorie der
Blattstellungen, 1878, and many papers in the Sitzungsber. d. Akad. d. Wiss.
Berlin ; HANS WINKLER, Jahrb. f. wiss. Bot. vol. xxxvi. 1901, p. 1, and vol.
xxxviii. 1903, p. 501 ; other literature in these. (M) See the works quoted
under (37). (59) E. STRASBURGER, Uber den Bau und die Verrichtung der Lei-
tungsbahnen in den Pflanzen, 1891, pp. 98, 297 ; G. CHAUVEAUD, Ann. d.
scienc. nat. bot. IX. Ser. vol. xiii. 1911, p. 113 ; F. J. MEYER, Progress, rei bot.
vol. v. 1917, p. 521. («) J. C. SCHOUTE, Die Stelartheorie, 1902 ; H. SOLMS-
LAUBACH, Bot. Ztg. 1903, 2. Abt. Sp. 37, 147 ; A. G. TANSLEY, New Phyto-
logist, No. 2, 1908 ; F. J. MEYER, Beihefte z. bot. Zentralbl. vol. xxxiii. 1. Abt.
1917, p. 129. (61) v. DEINEGA, Flora, vol. Ixxxv. 1898, p. 439. C62) M. KORD-
HAUSEN, Ber. deutsch. bot. Gesellsch. vol. xxx. 1912, p. 483. (**) E. KEUMANN-
REICHARDT, Beitr. z. allg. Bot. vol. i. 1917, Heft 3. (64) K. DOMIN, Ann. d.
jard. bot. Buitenzorg, vol. xxiv. 1911, p. 117. (K) E. BRICK, Beih. z. bot. Zentralbl.
vol. xxxi. I. 1913, p. 209; P. NEESE, Flora, vol. cix. 1917, p. 144. («) M.
RACIBORSKI, Handworterb. d. Xaturwiss. vol. ix. 1913, Jena, p. 352. (OT) K.

3 c

754 BOTANY

GOEBEL, Einleitung in die experimentelle Morphologic d. Pflanzen, 1908, p. 165.
(<*) E. RtfTER, Flora, vol. ex. 1918, p. 195. (69) F. SCHWARZ, Unters. a. d. bot.
Inst. in Tiibingen, vol. i. 1883, p. 135. (70) K. KROEMER, Biblioth. botan., Heft
59, 103 ; H. MULLER, Bot. Ztg. vol. Ixiv. 1906, p. 53 ; M. PLAUT, Die physiol.
Scheiden d.' Gymnospermen, Equisetaceen u. Bryophyten, Diss. Marburg, 1909;
Mitteil. d. Kais.-Wilh. Inst. f. Landw. Bromberg, 1910, vol. iii. p. 63 ; Jabrb. f.
wiss. Bot. vol. xxviii. 1910, p. 143. (71) G. RUMFF, Bibl. botan. Heft 42, 1904.
(72) PH. VAN TIEGHEM, Traite de botan. 2nd ed. 1891, p. 700 ; includes the
literature. (73) FR. WETTSTEIN, Beihefte z. bot. Zentralbl. II. vol. xx. 1906, p. 1.
(74) GOEBEL, quoted in (67). (75) M. BUSGEN, Bau u. Leben unserer Waldbaume,
2. Aufl. Jena, 1917 ; H. LUNDEGARDH, Kungl. Svensk. Yet. Akad. Handl. vol.
Ivi. 1916, No. 3. (76) J. C. SCHOUTE, Ann. jard. bot. Buitenzorg, 2e ser. vol. xi.
1912, p. 1 ; A. BORZI and G. CATALANO, Keale acad. d. Lincei. vol. cccix. 1912,
p. 167. (77) Of. the works under (49) and STRASBURGER under (59). (78) J. KLINKEN,
Bibl. botanica, Heft 84, 1914. (79) E. ANTEVS, Progr. rei bot. vol. v. 1917,
p. 285. (80) 0. GERTZ, Lund's univers. arsskrift N.F. II. vol. xii. 1916. (81)
H. JANSSONITJS, De tangentiale groei van eenige pi \ arm. Basten. Diss. Groningen,
1918. (82) P. BASICKE, Bot. Ztg. 1908, p. 55. (83) E. KIJSTER, Pathologische
Pflanzenanatomie, 2. Aufl. 1916.

Adaptations of the Cormus to its Mode of Life and to the Environment.— C84)
K. GOEBEL, Pflanzenbiologische Schilderungen, Marburg, 1889-93 ; F. A. W.
SCHIMPER, Pflanzengeographie auf physiol. Grundlage, Jena, 1898 (English
translation, 1903) ; FR. W. NEGER, Biologie d. Pflanzen, Stuttgart, 1913 ; G.
KARSTEN, Lehrbuch d. Biologie, 2. Aufl. Leipzig, 1914 ; E. WARMING-?.
GRAEBNER, Lehrb. d. okolog. Pflanzengeographie, 3. Aufl. Berlin, 1918 (English
translation), and the works named under (49). (85) H. SCHENCK, Biologie der
Wassergewachse, Bonn, 1886 ; K. GOEBEL, Pflanzenbiolog. Schilderungen, 1891,
vol. ii. p. 215 ; H. GLUCK, Untersuchungen iiber Wassergewachse, 3, Jena, 1905-
1911. C86) J. SHREVE, Journ. of Ecology, vol. ii. 1914, p. 82. (87) K. GOEBEL,
cf. (84) ; 0. RENNER, Flora, vol. c. 1910, p. 451 ; MARLOTH,. Flora des Kaplandes ;
H. FITTING, Ztschr. f. Bot. vol. iii. 1911, p. 109 ; A. ENGLER, Sitzungsber.
d. kgl. preuss. Akad. d. Wiss. 1914, p. 564 ; in addition numerous works on the
Xerophytes of American deserts in the Publicat. of the Carnegie Institution,
Washington. (88) E. WARMING, Mem. acad. royal, d. scienc. de Danemark,
8e ser. vol. ii. 1918, p. 297. (89) H. SCHENCK, Beitr. z. Biologie und Anatomie
d. Lianen, Jena, 1892-93. (90) K. GOEBEL, Pflanzenbiologische Schilderungen,
vol. i. p. 147 ; A. F. W. SCHIMPER, Die epiphytische Vegetation Amerikas, Jena,
1888. (91) CH. DARWIN, Insectivorous Plants, 1876 ; K. GOEBEL, Pflanzen-
biologische Schilderungen, 1893, vol. ii. ; CLAUTRIAU, Mem. publ. par 1'acad. de
Belgique, vol. lix. 1900 ; G. SCHMID, Flora, vol. iv. 1912, p. 335. (92) L. KOCH,
Die Klee- und Flachsseide, Heidelberg, 1880 ; PEIRCE, Annals of Botany, 8,
1894 ; KOCH, Entwicklungsgesch. d. Orobanchen, Heidelberg, 1887 ; H. SOLMS-
LAUBACH, Rafflesiaceen in ENGLER, Das Pflanzenreich, Leipzig, 1901.

Organs of Reproduction.— (93) The works named under (49- 5°. 53). (94) W. N.
STEIL, Bot. Gazette, vol. lix. 1915, p. 254. (95) H. WINKLER, Progr. rei botan.
vol. ii. 1908, p. 293 ; A. ERNST, Zeitschr. f. indukt. Abstammungslehre, vol. xvii.
1917, p. 203 ; A. ERNST, Bastardieruug als Ursache der Apogamie im Pflanzen-
reiche, Jena, 1918. (96) H. KYLIN, Ztschr. f. Bot. vol. viii. 1916, p. 545; 0.
RENNER, Biolog. Zentralbl. vol. xxxvi. 1916, p. 337 ; J. BUDER, Ber. d. deutsch. bot.
Gesellsch. vol. xxxiv. 1916, p. 559. (97) CH. J. CHAMBERLAIN and J. M. COULTER,
Morphology of Gymnospewns, 1910, and Morphology of Angiosperms, 1903.

INDEX OF LITERATURE 755

(*) W. EICHLEK, Bliitendiagramme, 1875-78. (») H. MULLEK, Die BefruchtuDg
der Blumen d. Insekten, Leipzig, 1873, and Alpenblmnen, 1881 ; 0. KIRCHNER,
Blumen und Insekten, 1911. (10°) A. KEENER VON MAUILAUN, Pflanzenleben,

2. Aufl. vol. ii. 1905 (English translation). (101) G. KLEBS, Untersuch. ana dem
botan. Inatitut Tubingen, vol. i. 1885. (102) E. STRASBURGER in papers published
in vols. xlii. xliv. and xlv. of the Jahrb. f. wiss. Bot. 1906-1908 and in Histol.
Beitr. Heft 7, 1909. (103) J. B. FARMER, Quart. Journ. Micr. Soc. vol. xlviii.
1905, p. 489; D. M. MOTTIER, Ann. of Bot. vol. xxi. 1907, p. 309 ; V. GREGOIRE,
La Cellule, vol. xxii. 1905, p. 221 ff. and vol. xxvi. 1910, p. 223 ; includes the
literature to 1910 ; PICARD, cf. (ao).

Section IV. The Theory of Descent and the Origin of New Species

(i04) CH. DARWIN, On the Origin of Species by Means of Natural Selection,
1859 ; ibid. Animals and Plants under Domestication ; ibid. The Descent of
Man ; E. HAECKEL, Generelle Morphologic, Neudruck, Berlin, 1906 ; Natiirliche
Schbpfungsgeschichte ; A. WEISMANN, Vortrage iiber die Deszendeuztheorie,

3. Aufl. Jena, 1913 ; J. P. LOTSY, Vorlesungen iiber Deszendenztheorien, Jena,
1906 ; L. PLATE, Der gegenwartige Stand der Abstammungslehre, Leipzig,
1909; ABEL, BRAVER, etc., Abstammungslehre, 12 Vortrage, Jena, 1911; K. C.
SCHNEIDER, Einfiihriing in die Deszendenztheorie, 2. Aufl. Jena, 1911 ; R. HESSE,
Abstammungslehre und Darwinismus (Aus Natur und Geisteswelt, vol. xxxix.),
5. Aufl. 1918 ; L.- PLATE, Deszendenztheorie, Handworterb. d. Naturwiss. vol. ii.
Jena, 1912, p. 897 ff. (105) J. LAMARCK, Philosophic zoologique, 1809 ; H. SPENCER,
The Principles of Biology, 1876 ; C. v. NAGELI, Mechanisch-physiologische Theorie
der Abstammungslehre, Miinchen, 1884 ; R. SEMON, Die Mneme, 3. Aufl. 1911 ;
A. PAULY, Da-rwinismus und Lamarckismus, Miinchen, 1905 ; R. v. WETTSTEIN,
Der Neo-Lamarckismus, Jena, 1903 ; Handb. d. system. Botanik, Leipzig and
Wien, 2. Aufl. 1911, p. 32 ; 0. HERTWIG, Das Werden der Organismen, 2. Aufl.
Jena, 1918 ; C. DETTO, Die Theorie der direkten Anpassung, Jena, 1904. (106)
G. ROMANES, Darwin and after Darwin ; L. PLATE, Selektionsprinzip uud
Probleme der Artbildung, 3. Aufl. Leipzig, 1908 ; A. WEISMANN, Die Selektions-
theorie, Jena, 1909 ; C. DETTO, Die Theorie der direkten Anpassung, Jena, 1904.

PHYSIOLOGY BY L. JOST
Introduction

(]) The fullest exposition of plant -physiology is to be found in PFEFFER,
Physiology of Plants (Eng. trans. 1900-1906). This deals with the literature from
1897 to 1904, and only the fundamental work and the most important recent litera-
ture is given below. As an introductory work on the subject may be mentioned
JOST, Vorlesungen iiber Pflanzenphysiologie, 3. Aufl. Jena, 1913 (English trans-
lation). As introductory to experimental work DETMER (1912), Das kleine pflanzen-
physiologische Praktikum, 4. Aufl. Jena ; CLAUSSEN (1910), Pflanzenphys. Versuche
und Demonstrationen fur die Schule, 2. Aufl. Leipzig and Berlin. (2) BERNARD
(1878), Lecons sur les phenomenes de la vie, Paris ; SACHS (1882), Vorlesungen
liber ^Pflanzenphysiologie, Leipzig, Vorlesung 12 ; KLEBS (1904), Biol. Cbl. 24,
distinguishes three sorts of causes: (1) external; (2) internal; (3) the specific
structure. Under the last he includes the determinants (p. 296) which are the
causes of specific structure. As internal causes he recognises all within the plant
that acts on these determinants. (3) MOLISCH (1897), Das Erfrieren der Pflanzen,
Jena ; MEZ (1905), Flora, 94 ; WINKLER (1913), Jahrb. f. wiss. Bot. 52 ; MAXIMOW

756 BOTANY

(1914), ibid. 53; KYLIN (1917), Ber. hot. Ges. 35. The significance of temperature
for the geographical distribution of plants is more fully treated in SCHIMPER
(1898), Pflanzengeographie, Jena (English translation) ; SOLMS-LAUBACH (1905),
Gesichtspunkte der Pflanzengeographie, Leipzig ; IHNES'S Phaenological Chart of
the Coming of Spring in Europe should be mentioned (Petermanns Mitt. 1905,
Heft 5). (4) SCHIMPER, see (3). (5) BECQUEREL (1909 and 1910), Compt. rend.
Paris, 148 and 150; NEUBERGER (1914), Botan. Centralblatt, 126, p. 665 (Kef.) ;
EsTREiCHER-KiERSNowsKA, ibid. 134, p. 244 (Ref.).

Metabolism

(6) CZAPEK (1905), Biochemie der Pflanzen, Jena, vol. i. [2. Aufl. 1913] ; EULER
(1908), Grundlagen und Ergebnisse der Pflanzenchemie, Braunschweig ; NATHANSON
(1910), Stoffwechsel der Pflanzen, Leipzig.

Chemical Composition; Absorption. — (7) E. WOLF (1871, 1880), Aschen-
analysen von land- und forstwirtschaftlichen Produkten, Berlin ; KONIG (1882),
Zusammensetzung der menschlichen Nahrungs- und Genussmittel, Berlin. (8)
NAGELI (1858), Pflanzenphys. Unters. 3 ; OSTWALD (1909), Grundriss der Kolloid-
chemie, Lpzg. (9) PFEFFER (1877), Osmotische Untersuchungen, Leipzig ; ibid.
(1886), Unters. a.d. hot. Institut Tubingen, 2 ; ibid. (1890), Abh. d. math.-phys. Kl.
d. sachs. Gesellsch. Leipzig ; DE VRIES (1884), Jahrb. wiss. Botanik, 14. (9a) RIPPEL
(1918), Ber. bot. Ges. 36 ; HANSTEEN-CRANER (1914), Jahrb. wiss. Bot. 53.
(10) URSPRUNG and BLUM (1916), Ber. bot. Gesellsch. 34 ; BLUM (1916), Beihefte
bot. Centralbl. (I.) 33. (u) ESCHENHAGEN (1889), Diss. Leipzig; LEPESCHKIX
(1910), Berichte d. bot. Ges. 28 ; TRONDLE (1910), Jahrb. wiss. Botanik, 48 ;
FITTING (1915), Jahrb. wiss. Bot. 56. (12) FITTING (191.1), Ztschr. f. Bot. 3 ;
BRIGGS and SHANTZ (1913), Flora, 105; SHIVE and LIVINGSTON (1914), Plant
World, 17. (13) BURGERSTEIN (1904), Transpiration der Pflanzen, Jena ; RENNER
(1910), Flora, 100 ; ibid. (1912), Ber. bot. Ges. 30. (14) HOHNEL (1879, 1880),
Mitt. a. d. forstl. Versuchswesen Osterreichs, 2 ; BRIGGS and SHANTZ (1914 and
1916), Jouru. of Agric. Research, 3 and 5. (15) STAHL (1894), Bot. Ztg. 52 ; STEIN
(1912), Ber. bot. Ges. 30; MOLISOH (1912), Ztschr. f. Bot. 4 ; NEGER (1912), Ber.
bot. Ges. 30; WEBER, Fr. (1916), Ber. bot. Ges. 34; WEBER (1916), Ber. bot.
Ges. 34. (16) BURGERSTEIN, see (13) ; LEPESCHKIN (1906), Beihefte bot. Centralbl.
19 ; BRUCKE (1844), Annalen d. Physik, 63 ; (OSTWALDS Klassiker, No. 95);
PFEFFER (1877), Osmotische Untersuchungen, Leipzig ; ibid. (1890), Abh. d. Kgl.
Gesellsch. d. Wiss. Leipzig ; WIELER (1893), Cohns Beitr. z. Biologie, 6 ; RUHLAND
(1915), Jahrb. wiss. Bot. 53 ; FABER, v. (1915), Jahrb. wiss. Bot. 56. (17)
LEPESCHKIN and PFEFFER, see (16). (18) STRASBURGER (1891), Ban u. Verrich-
tungen d. Leitungsbahnen, Jena; URSPRUNG (1907), Biolog. Centralbl. 27;
Jahrb. wiss. Bot. 44 ; RENNER (1913), Handw. d. Naturw. 10 ; EWART (1908),
Philos. Transact. Roy. Soc. (B) 199 ; ibid. (1910), Annals of Botany, 24. (19)
DIXON (1909), Prog, rei bot. 3 ; DIXON and JOLY (1894), Annals of Bot. 8 ;
ASKENASY (1895, 1896), Verh. naturw. Verein Heidelberg, N.F. 5 ; STEINBRINCK
(1906), Jahrb. wiss. Bot. 42 ; RENNER (1911), Flora, 103 ; (1915) Jahrb. wiss. Bot.
56 ; (1918) Ber. bot. Ges. 36 ; HOLLE (1915), Flora, 108 ; JOST (1916), Z. f. Bot. 8 ;
URSPRUNG (1915, 1916), Ber. bot. Ges. 33 and 34 ; LINDNER (1916), Beitr. z.
Biologie, 13 ; NORDHAUSEN (1917), Jahrb. wiss. Bot. 58. (19a) KNOP (1861),
Landvv. Versuchsstationen, 3 ; APPEL (1918), Zeitschr. f. Bot. 10. ('•») RICHTER
(1919), Sitzungsber. Wien. Akad. 118, 2. Abt. ; ibid. (1911) Die Ernahrung der
Algen, Leipzig ; OSTERHOUT (1912), Bot. Gaz. 54.— The behaviour of halophytes in
relation to sodium chloride is not made perfectly clear by the work of PEKLO (Ost.

INDEX OF LITERATURE 757

botan. Zeitschr. 1912). (a) KRATZMANN (1913), Sitzungsber. Wien. Akad. 1. Abt.
C22) HOBER (1911), Physikal. Chemie der Zelle, 3. Aufl. Leipzig ; RUHLAND (1908),
Jahrb. wiss. Botanik, 46 ; (1915) ibid. 55 ; MEURER (1909), ibid. ; CZAPEK (1911),
Methode zur direkten Bestimmung der Oberflachenspannung der Plasmahaut,
Jena ; (1915) Jahrb. wisa Bot. 56 ; PANTANELLI (1915), ibid. 56 ; OSTERHOUT
(1915, 1916), Botan. Gazette, 59, 61 ; FITTING (1915, 1917), Jahrb. wiss. Bot. 56,
57 ; HOFFLER (1918), Ber. bot. Ges. 36. (23) PFEFFER (1886), Unters. botan.
Institut Tubingen, 2 ; RUHLAND (1914), Jahrb. wiss. Bot. 54 ; KUSTER (1911),
Jahrb. wiss. Bot. 50 ; WISSELINGH (1913), Proc. Ak. v. Wetensch. 15. (**) KUNZE
(1906), Jahrb. wiss. Bot. 42 ; BACHMANN, Ber. bot. Ges. 22 and 29 ; SCHULOW
(1913), Ber. bot. Ges. 31. (25) BROWN and ESCOMBE (1900), Philos. Transact. (B)
193. (26) MAYER, ADOLF (1901), Agrikulturchemie, 5. Aufl. Heidelberg. (w)
SCHIMPER (1889), Pflanzen geographic auf biolog. Grundlage, Jena (English
Translation) ; ENGLER (1879-82), Vers. einer Entwicklungsgeschichte d. Pflanzen-
welt, Lpzg. ; SOLMS-LAUBACH (1905), Die leitenden Gesichtspunkte d. Pflanzen-
geographie, L. (*) CLAUSSEN (1901), Flora, 88; LINDNER (1916), Beitr. z.
Biologie, 13.

Assimilation and Translocation. — (28a) WILLSTATTER and STOLL (1918),
Unters. lib. Assimilation der Kohlensaure ; WISLICENUS (1918), Ber. chem. Ges. 51 ;
SCHRODER, H. (1917), Die Hypothesen iiber die chem. Vorgange b. d. Kohlen-
saureassimilation (1918), Ber. d. bot. Ges. 36. (a) REINKE (1884), Bot. Ztg. 42 ;
EXGELMAXX (1884), Bot. Ztg. 42 ; TIMIRIAZEFF (1903), Proc. R. Soc. (B) 72 ;
KNIEP and MINDER (1909), Zeitschr. fur Botanik, 3 ; RICHTER (1912), Ber. bot.
Ges. 30 ; URSPRUNG (1918), Ber. bot. Ges. 36. I29*) BROWN (1905), Proc. R. Soc.
(B) 76 ; PURIEWITSCH (1914), Jahrb. wiss. Bot. 53. C30) WILLSTATTER and
STOLL (1915), Sitzungsber. Berl. Akad. ; WILLSTATTER in (28a). (30a) SCHRODER
(1919), Die Naturwissenschaften. <31) NATHANSOHN (1910), Stoffwechsel der
Pflanzen, Leipzig ; ANGELSTEIN (1910), Beitr. zur Biologie, 10 ; KNIEP (1915),
Jahrb. wiss. Bot, 56. (32) HANSEN (1912), Nat. Rundschau, 27 ; FISCHER (1912),
Ber. bot. Ges. 30. f32*) A. MEYER (1918), Ber. bot. Ges. 36. C33) KREUSLER,
Landw. Jahrb. 14, 16, 17, 19; GILTAY (1898), Annales jard. bot. de Buitenzorg, 15;
SACHS (1884), Arbeiten Bot. Institut Wiirzburg, 3 ; BROWN and ESCOMBE (1900),
Philos. Transactions R. Soc. (B) 193 ; BLACKMAX (1905), Annals of Botany, 19 ;
ibid. Proceedings Royal Soc. (B) 76 ; THODAY (1910), Proc. Royal Soc. (B) 82.
(3i) WINOGRADSKI (1890-91), Annales Institut Pasteur, 4 and 5 ; HUEPPE (1906),
Ergebnisse d. intern, bot. Congr. Wien ; KRZEMIENIEWSKI (1908), Bull. acad.
Cracovie ; XIKLEWSKI (1910), Jahrb. wiss. Bot. 48; LEBEDEFF (1909), Ber.
deutsch. bot. Ges. 27 ; LIESKE (1911), Jahrb. wiss. Bot. 49 ; KEIL (1912), Beitr.
z. Biologie, 11 ; Muxz (1915), Z. Phys. d. Methanbakterien, Diss. Halle. (»)
DARWIN (1876), Insectivorous Plants; GOEBEL (1893), Pflanzenbiolog. Schilde-
rungen, 2, Marburg ; CLAUTRIAU (1900), Mem. publ. p. 1'acad. de Belgique, 59 ;
SCHMID (1912), Flora, 104 ; LUTZELBURG (1910), Flora, 100 ; RUSCHMANN (1914),
Z. Okologie von Pinguicula . . ., Diss. Jena; STERN (1917), Flora, 109. (M)
HEIXRICHER, Jahrb. wiss. Bot. 31, 32, 36, 37, 46, 47. (3V) WINOGRADSKI (1895),
Archives d. sc. biologiques, 3 ; ibid. (1902), Centralblatt f. Bakteriologie (II.), 9];
KOCH (1904) in LAFAR, Technische Mykologie, 3, Jena; HELLRIEGEL and WILFARTH,
Stickstoffnahrung d. Gramineen u. Leguminosen, Berlin ; HILTNER (1904) in
LAFAR, Technische Mykologie, 3, Jena ; DE BARY (1879), Erscheinung d. Symbiose,
Strassburg; FISCHER, A. (1903), Vorlesungen iiber Bakterien, 2. Aufl. Jena;
BREDEMANN (1909), Centralbl. Bakt. 2. Abt. 23 ; KKZEMIENIEWSKI (1908), Bull,
acad. Cracovie ; STOKLASA (1908), Centralbl. Bakt. (2. Abt.) 21. (M) LAWES,

768 BOTANY

GILBERT and PuGH(1862), Philos. Transact. 151 ; SCHULTZ-LUPITZ (1881), Landw.
Jahrb. 10. (39) KAMIENSKI (1881). Botan. Ztg. 39 ; FRANK (1887, 1888), Berichte
bot. Gesellsch. 5, 6 ; STAHL (1900), Jahrb. wiss. Bot. 34 ; SHIBATA (1902), Jahrb.
wiss. Bot. 37 ; BERNARD (1909), Annales des sciences nat. (9) 9 ; BURGEFF (1909),
Wurzelpilze der Orchideen, Jena ; WEYLAND (1912), Jahrb. wiss. Bot. 51 ; MIEHE
(1918), Flora, 111. (39») NIENBURG (1917), Ztschr. f. Bot. 9. (40) v. FABER
(1912), Jahrb. wiss. Bot. 51 ; (1914) ibid. 54 ; MIEHE (1913 and 1917), ibid. 53
and 58. (40a) The remarkable discoveries of BIEDERMANN, 1916 (Fermentforschung)
on the origin of diastase in boiled "starch solution" are still too isolated to be
treated in the text. (41) GREEN (1901), The Soluble Ferments and Fermentation ;
DUCLAUX (1899), Traite de microbiologie, 2, Paris ; BUEDIG (1891), Anorgan.
Fermente, Leipzig ; HOBER (1911), Physikal. Chemie d. Zelle, 3. Aufl. Leipzig ;
OPPENHEIMER (1910), Die Fermente, 3. Aufl. L. (42) CZAPEK (1897), Sitzungs-
berichte .Wiener Akad. 106 ; DELEANO (1911), Jahrb. wiss. Bot. 49. (43) TEO-
DORESCO and POPESCO, Annal. sc. de 1'univ. de Jassy, 9 ; SWART (1914), Stoff-
wanderung in ablebenden Blattern, Jena. (w) CZAPEK and EULER in (5).

Eespiration and Fermentation. — (*) WORTMANN (1880), Arb. bot. Institut
Wiirzburg, 2 ; PFEFFER (1885), Unters. bot. Inst. Tubingen, 1 ; JOHANNSEN (1885),
[Inters, a. d. bot. Inst. Tubingen, 1 ; STICK (1891), Flora, 74 ; KOSTYTSCHEW
(1913), Ber. bot. Ges. 31. (46) PALLADIN (1909), Biochem. Zeitschr. 18 ; BACH
(1910), Abderhaldens Fortschritte der naturwissenschaftlichen Forschung, 1 ;
KOSTYTSCHEW (1911), Jahrb. wiss. Bot. 50. (47) WINOGRADSKI (1887), Botan.
Ztg. 45 ; (1890-91) Annales Institut Pasteur, 4, 5 ; NIKLEWSKI (1907), Bull,
acad. Cracovie ; SOHNGEN (1906), Cbl. Bakt. (II.) 15 ; cf. also the literature in t23) ;
MEYERHOF, Pfliigers Archiv f. Phys. 164-166. (48) Cf. CZAPEK, EULER and
NATHANSOHN in (6) ; OPPENHEIMER, cited in (41) ; KRUSE (1910), Mikrobiologie ;
BENECKE (1912), Bau und Leben d. Bakterien, L. (49) BUCHNER, E. and H., and
HAHN (1903), Die Zymasegarung, Miinchen ; BUCHNER (1908), Biochem. Zeitschr. ;
FISCHER, A. (1903), Vorles. iib. Bakt. 2. Aufl. Jena ; MAYER, AD. (1906), Lehrb.
d. Agrikulturchemie, vol. iii. 6. Aufl. Heidelberg ; EULER (1911), Zeitschr. fur
physiol. Chemie, 70 ; EULER and LINDNER (1915), Chemie der Hefe und der
alkohol. Garung, Lpzg. (50) MOLISCH (1914), Ztschr. f. Botan. 6 ; LEICK (1916),
BioK Centralbl. 36. (51) MOLISCH (1912), Leuchtende Pflanzen, Jena, 2. Aufl.

Development

(M) PFEFFER (1904); Physiologic, 2 ; WINKLER (1913), Entwicklungsphysiologie
in Handworterb. d. Naturw. vol. iii. Jena.

Introductory Remarks.— (53) SACHS (1873), Arb. bot. Inst. Wiirzburg, 1 ;
BURKOM (1915), Proefschrift Utrecht (1913) K. Ak. Amsterdam. Proc. (54) SACHS
(1882), Vorlesungen iiber Pflanzenphysiologie ; BERTHOLD (1904), Unters. z.
Physiol. der pflanzl. Organisation, Leipzig. (55) VOCHTING (1878), Organbildung,
Bonn ; ibid. (1908), Untersuchung z. exp. Anatomie u. Pathologic, Tiibingen ;
SIMON (1908), Jahrb. wiss. Bot. 45 ; Berichte bot. Ges. 26 ; GOEBEL (1902), Biolog.
Centralbl. 22 ; NEMEC (1905), Studien iiber Regeneration, Berlin ; KORSCHELT
(1907), Regeneration und Transplantation, Jena ; MORGAN (1907), Regeneration ;
WINKLER (1913), Handworterb. d. Naturw. Jena, vol. iii. "Entwicklungs-
physiologie"; LINSBAUER (1915), Denkschr. d. Akad. Wien, 93. (56) KASSNER
(1910), Zeitschr. f. Pflanzenkrankheiten, 20.

Factors of Development.— (57) BLAAUW (1914 and 1915), Ztschr. f. Bot. 6 and 7 ;
VOGT (1915), Ztschr. f. Bot. 7 ; SIERP (1918), Ztschr. f. Bot. 10. (57a) KLEBS
(1917), Sitzb. Heid. Akad. math. -nat. Kl. (58) KORNICKE (1904), Ber. bot. Ges. 22 ;

INDEX OF LITERATURE 759

(1915), Jahrb. wiss. Bot. 56; URSPRUNG (1917), Ber. hot. Ges. 35. (») STAHL
(1883), Jen. Zeitschr. f. Natunviss. 16 ; NORDHAUSEN (1901), Jahrb. wiss. Bot.
37 ; Ber. bot. Ges. 30 (1912). (»»*) VOECHTING (1918), Unters. z. exp. Anatomic u.
Pathologic, Tubingen. (59b) SCHILLING (1915), Jahrb. wiss. Bot. 55. (M) KUSTER
(1911), Die Gallen der Pflanzen ; (1916) Pathol. Pflanzenanatomie, Jena;
MAGNUS (1914), Entstehung d. Gallen, Jena; MOLLIARD (1918), Botanisches
Centralbl. 138. ("») HEINRICHER (1916), Deukschr. Ak. Wiss. Wien, math.-nat.
Kl. 93 ; BURGEFF (1909), Die Wurzelpilze der Orchideen, Jena. (61) GOEBEL
(1880), Bot. Ztg. 38 ; id. (1908) Experimentelle Morphologic, Leipzig ; VOCHTIKG
(1892), Die Transplantation, Tiibingen ; id. (1885) Jahrbiicher f. wiss. Bot. 16.
(61a) WINKLER (1908), Ber. d. bot. Ges. 26a ; id. (1909) Zeitschr. f. Bot. 1 ;
id. (1910), ibid. 2 and Ber. bot. Ges. 28 ; NOLL (1905), Sitzungsber. niederrh.
Gesellschaft f. Xatur- und Heilkunde ; STRASBUUGER (1907). Jahrb. wiss. Bot. 44 ;
id. (1909), Ber. bot. Ges. 27 ; BUDER (1911), Zeitschr. f. Abstammungslehre, 5 ;
MACFARLANE (1895), Transact. R. Soc. Edinb. 37 ; BAUR and WINKLER (1911),
Zeitschr. f. Bot. 3*; BAUR (1911), see (*>) ; WINKLER (1912), Unters. iiber Pfropf-
bastarde, Jeua ; MEYER (1915), Zts. f. Abstammungslehre, 13. (61b) WINKLER
(1916), Zts. f. Botan. 8 ; BURGEFF (1914-15), Flora, 107 and 108.

Course of Development.— (62) SORAUER (1913), Pflanzenkrankheiten, Berlin,
4. Aufl. C53) PENZIG (1890), Pflanzenteratologie. («) KUSTER, E. (1916), Patholog.
Pflanzenanatomie, Jena, 2. Aufl. (65) KLEBS (1912), Biolog. Centralbl. 32; id.
(1914), Abh. Heidelb. Akad. ; id. (1915), Jahrb. wiss. Bot. 56 ; KUSTER (1918),
Flora, 111 ; LAKON (1915), Biol. Cbl. 35 ; MUNK (1914), Biol. Cbl. 34 ; SIMON
(1914), Jahrb. wiss. Bot. 54 ; WEBER (1915), Ber. bot. Ges. 34 ; KNIEP (1915),
Die Naturwissenschaften, 3 ; VOLKENS (1912), Laubfall u. Lauberneuerung in
d. Tropen, Berlin. (M) FISCHER, A. (1907), Ber. bot. Ges. 25 ; CROCKER and
DAVIS (1914), Bot. Gaz. (»). (CT) GASSNER (1915), Jahrb. wiss. Bot. 55 ; LEHMANN
(1915), Zts. f. Bot. 7 ; (1913) ibid. 5 ; (1918) Ber. bot. Ges. 36 ; OTTENWALDER
(1914), Zts. f. Bot. 6. (») JOHANNSEN (1906), A'therverfahren b. Treiben, Jena ;
MOLISCH (1909), Das Warmbad, Jena ; JESENKO (1912), Ber. bot. Ges. 30 ; LAKON
(1912), Zeitschr. f. Bot. 4 ; MtiLLEU-TnuRGAU and SCHNEIDEK-ORELLI, Flora, 101
and 104 ; WEBER (1916), Sitzungsber. Ak. Wien, i. 125. («) Cf. GOEBEL (1908),
Exp. Morphologic, Lpzg. ; (1916) Biolog. Centralbl. 36 ; WINKLER, cited in (52).
(70) WINKLER (1916), Zts. f. Bot. 8 ; GERASSIMOFF (1904), Bot. Cbl. Beih. 18 .and
Bull. Soc. Natur. Moscou ; MARCHAL (1907 and 1909), Bull. acad. Belg. (71)
KRAUS (1868), Jahrb. wiss. Bot. 7 ; SACHS (1903), Flora, 77 ; SIERP (1913), Jahrb.
wiss. Bot. 53 ; KRAUS (1915), Sitzungsber. phys. med. Ges. Wiirzburg. C72)
HABERLANDT (1913, 1914), Sitzungsber. Berliner Akad. ; KARSTEN (1-915 and
1918), Ztschr. f. Bot. 7 and 10 ; LAMPRECHT, Beitr. z. allg. Botanik, 1. 073)
STRASBURGER (1898-99), Deutsche Rundschau ; SCHENCK (1907), Wiss. Ergeb-
nissfc der Tiefsee Expedition, vol. ii. Heft 3, Jena. (74) KLEBS (1903),. Willkiir-
liche Entwicklungsanderungen, Jena ; id. (1896), Fortpflanzungsphysiologie nied.
Organismen, Jena; (1918) Flora, 111. (75) CORRENS (1907), Bestimmung und
Vererbung des Geschlechts, Berlin; STRASBURGER (1909), cited in (79) ; (1910)
Jahrb. wiss. Bot. 48 ; NOLL (1907), Sitzungsber. niederrh. Ges. (76) NOLL (1902),
Sitzungsber. niederrh. naturf. Gesellsch. ; EWERT (1907), Parthenokarpie . . . d.
Obstbaume, Berlin ; MULLER-THURGAU (1908), Landw. Jahrb. d. Schweiz. (")
FITTING (1909-10), Zeitschr. f. Bot. 1, 2 ; (1909) Biolog. Centralbl. 29. (78)
Another view is held by SCHELLENBERG, Report of meeting of 15th Nov. 1907 of
the Gesellschaft schweizerischer Landwirte. (79) WINKLER (1908), Progr. rei
bot. 2 ; STRASBURGER (1909), Zeitpunkt der Bestimmung des Geschlechts,

760 BOTANY

Apogamie, Parthenogenesis, etc., Jena ; ERNST (1918), Bastardierung als Ursache
der Apogamie, Jena. (w) STRASBURGER (1905), Die stofflichen Grundlagen der
Vererbung, Jena ; CORRENS (1912), Die neuen Vererbungsgesetze, Berlin ; HACKER
(1911), Allgemeine Vererbungslehre, Braunschweig ; JOHANNSEN (1909), Elemente
der exakten Erblichkeitslehre, Jena ; BAUR (1911), Einfiihrung in die exp.
Vererbungslehre, Berlin. On the whole subject consult the Zeitschrift fur induktive
Abstammungs- und Vererbungslehre, Berlin. (81) KOLREUTER (1761-66), Vorl.
Nachr. v. einigen d. Geschlecht d. Pflanzen betreffenden Versuchen und Beobach-
tungen (OsxwALDs Klassiker, No. 41) ; FOCKE (1881), Die Pflanzenmischlinge,
Berlin; DE VRIES (1903), Die Mutationstheorie. (82) MENDEL (1901), Flora, 89
(OSTWALDS Klassiker, No. 121) ; CORRENS (1903), MENDELS Briefe an NAGELI (Abh,
Sachs. Ges. d. Wiss. 29) ; DE VRIES (1900), Berichte bot. Ges. 18 ; id. (1903),
Die Mutationstheorie, Leipzig; CORRENS (1900), Berichte bot. Ges. 18; TSCHERMAK
(1900), Zeitschr. f. landw. Versuchswesen in Osterreich. (83) CORRENS (1918),
Sitzungsber. Akad. Berlin. (84) ROSEN (1911), Beitr. z. Biologic, 10; id. (1913),
Beitr. z. Pflanzenzucht, Heft 3 ; LEHMANN (1914), Zeitschr. f. ind. Abst. 13.
(M) DARWIN (1868), Animals and Plants under Domestication ; DE VRIES (1903),
see t82) ; JOHANNSEN (1909), Elemente der exakten Erblichkeitslehre, Jena ; BAUR
(1914), Einf. in die Abstammungslehre, 2. Aufl. Berlin. (86) DE VRIES (1903),
cited in (82) ; ibid. (1912) Die Mutationen in der Erblichkeitslehre, Berlin;
KORSCHINSKY (1906), Flora, 89 ; WOLF (1909), Zeitschr. f. Abstammungslehre, 2 ;
LEHMANN (1914), Naturwissenschaften, 2 ; HAENICKE (1916), Ztschr. f. Bot. 8.
(87) DARWIN (1859), Origin of Species; KLKBS (1916), Zts. f. Abst. u. Vererbg. 17 ;
LAMARCK (1809), Philosophic zoologique ; LOTSY (1908), Vorlesungen lib. Deszen-
denztheorie, Jena ; RENNER (1917), Zts. f. Abst. u. Vererbg. 18 ; LEHMANN (1918),
Ztschr. f. Botanik, 10 (collected references).

Movement

(88) PRINGSHEIM (1912), Reizbewegungen d. Pfl., Berlin; JOST (1913), Reizbe-
wegungen in Handw. d. Naturwissenschaften, Jena, vol. viii. (89) ULEHLA (1911),
Biolog. Centralbl. 31 ; BUDER (1915), Jahrb. wiss. Bot. 56. (90) MULLER (1908),
Ber. bot. Ges. 27. (91) FECHNER (1915), Ztschr. f. Bot. 7 ; SCHMIDT (1918), Flora,
111. (92) ROTHERT (1901), Flgra, 88 ; JENNINGS (1910), Das Verhalten der
niederen Organismen, Lpzg. ; BUDER (1915, 1917), Jahrb. wiss. Bot. 56, 58 ;
NIENBURG (1916), Ztschr. f. Bot. 8 ; OLTMANNS (1917), Ztschr. f. Bot. 9. (93)
SENN (1908), Die Gestalts- und Lageveranderungen der Pflanzenchromatophoren,
Leipzig ; (1919) Ztschr. f. Bot. 11. (94) PFEFFER (1884), Unters. Bot. Institut
Tiibingen, 1 ; ROTHERT (1901), Flora, 88 ; KNIEP (1906), Jahrb. wiss. Bot. 43 ;
BRUCHMANN (1909), Flora, 99; SHIBATA (1911), Jahrb. wiss. Bot. 49; KUSANO
(1909), Journ. Coll. of Agric. Tokyo, 2 ; PRINGSHEIM (1916), Zts. f. physiolog.
Chemie, 97. (95) STEINBKINCK (1906), Biol. Centralbl. 26. (96) RENNER (1915),
Jahrb. wiss. Bot. 56 ; URSPRUNG (1915), Ber. bot. Ges. 33. (9V) PFEFFER (1893),
Die Reizbarkeit d. Pfl. (Verb., d. Ges. d. Naturforscher) ; NOLL (1896), Sinnesleben
d. Pflanze (Ber. Senckenberg. Gesellsch.) ; FITTING (1905-1907), Reizleitung (Ergeb-
nisse d. Physiologic, 4, 5) and Jahrb. wiss. Bot. 44 and 45 ; JOST (1913), Reizbe-
wegungen in Haiidworterb. d. Naturw. Jena, vol. viii. (98) POLOWZOW (1909),
Unters. iiber Reizerscheinungen, Jena ; KNIEP (1916), Fortschr. d. Psychologie, 4.

Tropisms.— (") KNIGHT (1806), OSTWALDS Klassiker, 62 ; DUTROCHET (1824),
Rech. sur la structure intime (OSTWALDS Klassiker, 154); HOFMEISTER (1863),
Jahrb. wiss. Bot. 3 ; FRANK (1868), Beitrage z. Pflanzenphysiologie, Leipzig ;
SACHS (1874), Arb. bot. Inst. Wurzburg, 1 ; (1879) ibid. 2 ; LUXBUKG (1905),

INDEX OF LITERATURE 761

Jahrb. wiss. Bot. 41 ; SCHOBER (1899), Anschauungen iiber Geotropismus seit
Knight, Hamburg, Programm ; FITTING (1905), Jahrb. wiss. Bot. 41 ; id. (1913),
Handworterb. d. naturw. Reizbewegungen, vol. viii. Jena ; GILTAY (1910),
Zeitschr. f. Botan. 2 ; ENGLER, A. (1918), Tropismen u. exzentrisches Dicken-
wachstum, Zurich. (10°) SIMON (1912), Jahrb. wiss. Bot. 51 ; HARDER (1914), Ber.
bot. Ges. 32. (101) JOST (1901), Botan. Ztg. 59 ; Riss (1915), Zeitschr. f. Botanik,
7. (102) SCHWENDENER (1881), Sitzungsber. Berlin. Akad. ; WORTMANN (1886),
Botan. Ztg. 44 ; NOLL (1892), Heterogene Induktion, Leipzig ; id. (1901),
Sitzungsber. niederrhein. Ges. ; NIENBURG (1911), Flora, 102; BREMEKAMP (1912),
Rec. trav. bot. neerland. 9 ; MIEHE (1915), Jahrb. wiss. Bot. 56. (103) NOLL (1892),
Heterogene Induktion, Leipzig ; NEMEC (1900), Berichte bot. Gesellsch. 18 ; further,
Jahrb. wiss. Bot. 36 ; id. Studien iiber Regeneration, Berlin, 1905 ; HABERLANDT
(1900), Berichte d. bot. Gesellschaft, 18 ; also Jahrb. wiss. Bot. 38, 42, 44 ; BUDER
(1908), Ber. bot. Gesellsch. 26; DARWIN (1899), Annals of Botany, 13; (1903)
Proc. R. Soc. 71 ^ (1904) ibid. 73 and British Assoc. Cambridge ; NOLL (1902),
Berichte bot. Ges." 20 ; (1905) Sitzungsber. niederrh. Gesellsch.; CZAPEK (1895
and 1898), Jahrb. wiss. Bot. 27, 32 ; FITTING (1905), cited in (") ; ZIELINSKY
(1911), Zeitschr. f. Bot. 3 ; KNOLL (1909), Sitzungsber. Wien. Akad. (I.) 118 ;
BISCHOFF (1911), Beihefte botan. Cbl. 28 ; HABERLANDT (1914), Sitzungsber. Ak.
Berlin ; DEWERS (1914), Beih. bot. Cbl. 31 ; ZOLLIKOFER (1918), Ber. bot. Ges. 36.
(104) RUTTEN-PEKELHARING (1910), Trav. botan. neerl. 7 ; MAILLEFER (1910), Bull,
soc. vaudoise des sc. nat. 46 ; id. (1912), ibid. 48 ; FROSCHEL (1909), Naturw.
Wochenschr. ; THONDLE (1913), Jahrb. wiss. Bot. 52 ; (1915) N. Denkschr.
schweiz. nat. Ges. 51. ,(105) WIESNER (1878-80), Heliotrop. Erscheinungen
(Deukschriften k. k. Akad. Wien) ; STAHL (1881), Kompasspflanzen, Jena ;
OLTMANNS (1892 and 1897), Flora, 75 and 83 : E. PRINGSHEIM (1907-1909), Beitr.
z. Biologic, 9; ARISZ (1911), Kon. Akad. Amsterdam. Proceed. ; NOACK (1914),
Zeitschr. f. Bot. 6 ; BUDER (1917), Jahrb. wiss. Bot. 58 ; KARSTEN (1918),
Flora, 111; ENGLER, A., see (") ; HEILBRONN (1917), Ber. bot. Ges. 35. (106)
BLAAUW (1918), Med. van Landbouwhooge School Wageningen, 15. (107) OLTMANNS
(1897), Flora, 83 ; PRINGSHEIM (1907-1908), Beitr. z. Biologic, 9 and 10 ; ARISZ
(1915), Rec. des trav. bot. neerland. 12. (J08) DARWIN (1881), Power of Movement
in Plants ; VOCHTING (1888), Bot. Ztg. 46 ; ROTHERT (1894), Cohns Beitr. z.
Biolog. 7 ; HABERLANDT (1905), Lichtsinnesorgane L. ; id. (1916), Sitzb. Berl.
Akad. ; FITTING (1907), Jahrb. wiss. Bot. 44 and 45 ; KNIEP (1907), Biolog.
Centralbl. 27 ; NORDHAUSEN (1907), Ber. bot. Ges. 25 ; Gius (1907), Sitzungsber.
Wien. Akad. 116 ; BOYSEN-JENSEN (1911), Acad. de Danemark, Bulletin ; BLAAUW
(1909), Die Perzeption des Lichtes, Nymwegen ; VAN DER WOLK (1911), Proc.
Akad. Amsterdam. (109) FITTING (1907), Jahrb. wiss. Bot. 44 ; BOYSEN-JENSEN
(1911), Ber. bot. Ges. 31 ; PAAL (1914), Ber. bot. Ges. 32 ; (1918) Jahrb. wiss.
Bot. 58. (109a) HABERLANDT (1916), Sitzungsber. Akad. Berlin ; NORDHAUSEN
(1917), Zts. f. Botan. 9. (110) MOLISCH (1889), Sitzungsanzeiger Wien. Akad. ;
MIYOSHI (1894), Flora, 78 and Botan. Ztg. 52 ; SAMMET (1905), Jahrb. wiss. Bot.
41 ; LILIENFELD (1905), Ber. bot. Ges. 23 ; SACHS (1872), Arb. bot. Inst. Wiirzburg,
1 ; MOLISCH (1883), Sitzungsber. Wien. Akad. 88 ; MOLISCH (1884), Sitzungsber.
Wien. Akad. 90 ; POLOWZOW (1909), Untersuchungen ttber Reizerscheinungen bei
den Pflanzen, Jena ; PORODKO (1912), Ber. bot. Ges. 30. (m) DARWIN (1876),
Climbing Plants ; PFEFFER (1885), Unters. bot. Institut Tubingen, 1 ; FITTING
(1903), Jahrb. wiss. Bot. 38 ; SCHENCK (1892), Beitrage zur Biologic der Lianen,
Jena ; PEIRCE (1894), Annals of Bot. 8. (ll2) STARK (1916), Jahrb. wiss. Bot. 57 ;
(1917) Ber. bot. Ges. 35.

762 BOTANY

Nastic Movements.— (113) KNIEP (1913), Handw. d. Naturw. Jena, vol. viii.,
Reizerscheinungen ; LINSBAUER (1916), Flora, 109; GOEBEL (1916), Biol. Cbl. 36.
(ii4) PFEFFER (1875), Periodische Bewegungen, Leipzig ; ibid. (1907) Unters. liber
Entstehung d. Schlafbewegungen (Abh. K. Ges. d. Wiss. Leipzig) ; FISCHER
(1890), Bot. Ztg. 48 ; OLTMANNS (1895), Bot. Ztg. 53 ; STAHL (1897), Bot. Ztg.
55 ; STOPPEL (1910), Zeitschr. f. Bot. 2 ; STOPPEL and KNIEP (1911), ibid. 3 ;
ERBAN (1916), Ber. bot. Ges. 34. (11B) PFEFFER (1915), Abh. Kgl. Gesellsch.
Leipzig, 34 ; STOPPEL (1916), Ztschr. f. Bot. 8. (m) DARWIN (1876), Insectivorous
Plants ; COKRENS (1896), Bot. Ztg. 54 ; BENECKE (1909), Zts. f. Botanik, 1 ; HOOKER
(1916), Bull. Torrey Club, 43. (m) BRUCKE (1848), Archiv f. Anatomie u.
Physiol. (OSTWALDS Klassiker, 95); BERT (1867-70), Mem. Soc. Bordeaux,
Paris ; PFEFFER (1873), Physiolog. Untersuchuugen ; HABERLANDT (1890), Das
reizleitende Syst. d. Sinnpflanze, Leipzig; id. (1901), Sinnesorgane im Pflanzen-
reich, Leipzig ; PFEFFER (1873), Jahrb. wiss. Bot. 9 ; FITTING (1903), Jahrb. wiss.
Bot. 39 (1905, 1906), Ergebnisse d. Physiol. 4, 5 ; LINSBAUER (1908), "Wiesner-
Festschrift, Wien ; LTJTZ (1911), Zeitschr. f. Botanik, 3 ; BOSE (1913), Res. on
Irritability of Plants, Bombay and Calcutta. (118) LINSBAUER (1914), Ber. bot.
Ges. 32 ; BOSE, cited in (m). (119) STARK, see (112).

THALLOPHYTA, BRYOPHYTA, PTERIDOPHYTA, BY H. SCHENCK

(*) ENGLER-PRANTL, Nattirl. Pflanzenfamilien, vol. i. ; LOTSY, Vortrage iiber
botaniscbe Staramesgeschichte, vol. i. 1907, vol. ii. 1909 ; L. RABENHORSTS
Kryptogamenflora von Deutschland, Osterreich und der Schweiz ; PASCHER, Die
Siisswasserflora Deutschl., Osterreichs u. d. Schweiz. (2) KLEBS, Die Beding. der
Fortpflanzung bei niederen Algen und Pilzen, 1896, and Jahrb. f. wiss. Botanik,
vols. xxxii.-xxxiv., also Willkiirl. Entwicklungsand. bei Pflanzen, 1903.

Lower Thallophyta. — (3) A. FISCHER, Vorlesung. iiber Bakterien, 1897, 2. Aufl.
1903 ; MIEHE, Bakterien, Leipzig, 2. Aufl. 1918 ; LEHMANN and NEUMANN,
Bakteriologie ; GUNTHER, Bakteriologie ; HEIM, Lehrb. d. Bakteriologie ;
LOHNIS, Landwirtsch. bakteriolog. Praktikum, 1911 ; BENECKE, Bau und Leben
der Bakterien, 1912 ; A. MEYER, Die Zelle der Bakterien, 1912 ; VIEHOVER, Ber.
deutsch. bot. Ges. vol. xxx. 1912, p. 443. (3a) BUDER (Thiospirillum), Jahrb.
wiss. Bot. vol. Ivi. 1915, p. 529. (4) MOLISCH, Die Purpurbakterien, Jena, 1907.
(5) MOLISCH, Leuchtende Pflanzen, 2. Aufl. 1912. (6) VON FABER, Jahrb. wiss.
Bot. vol. li. 1912, p. 283. (7) SORAUER, LINDAU, REH, Handbuch der Pflanzen-
kraukheiten, 1906 ; W. MAGNUS, Ber. deutsch. bot. Ges. vol. xxxiii. 1915, p. 96.
(8) MIEHE, Ztschr. f. Hygiene u. Infekt. vol. Ixii. 1908, p. 155. (9) KEIL,
Schwefelbakterien, Diss. Halle a. S. 1912 ; MOLISCH, Die Eisenbakterien, 1910 ;
LIESKE, Jahrb. f. wiss. Bot. vol. xlix. 1911, p. 91. (10) A. FISCHER, Unters. iiber
den Bau der Cyanophyceen u. Bakterien, 1897, also Bot. Zeitg. 1905, p. 51 ;
HEGLER, Jahrb. f. wiss. Bot. vol. xxxvi. 1901, p. 229 ; MASSART, Recueil de 1'inst.
bot. de Bruxelles, vol. v. 1902 ; BRAND, Ber. deutsch. bot. Ges. 1901, p. 152 ;
1905, p. 62, and Beihefte bot. Ztrbl. vol. xv. 1903, p. 31 ; FRITSCH, Beihefte bot.
Zentrbl. vol. xviii. 1905, p. 194 ; OLIVE, Beihefte bot. Ztrbl. 1905, vol. xviii.
p. 9 ; GUILLIERMOND, Revue gener. de bot. vol. xviii. 1906, p. 392 ; PRINGSHEIM,
Die Naturwissenschaften, 1913, p. 495 ; FECHNER, Ztschr. f. Bot. vol. vii. 1915,
p. 289 ; PIEPER, Dissert. Berlin, 1915 ; KLEIN, Anzeig. Akad. Wien, vol. lii. 1915.
(10») G. SCHMIDT, Flora, N.F. vol. xi. 1918, p. 327 ; R. HARDER, Ztschr. f. Bot.
vol. x. 1918, p. 177. (lob) R. HARDER, Ztschr. f. Bot. vol. ix. 1917, p. 145. (")
OLTMANNS, Morphologic und Biologic der Algen, vol. i. 1904, vol. ii. 1905, and

INDEX OF LITERATURE 763

Handwb'rterb. der Naturw. vol. i. (12) SEXN, Ztschr. f. wiss. Zool. vol. xcvii.
1911, p. 605 ; F. DOFLEIN, Lehrbuehder Protozoenkunde, 4. Aufl. 1916 ; PASCHER,
Ber. deutsch. bot. Ges. vol. xxix. 1911, p. 193, vol. xxxii. 1914, p. 136, vol. xxxiv.
1916, p. 440, and Archiv f. Protistenk. vol. xxv. 1912, p. 153, vol. xxxvi. 1915, p. 81 ;
PASCHER, Flagellaten u. Rhizopoden in ihren gegenseitigen Beziehungen, 1917.
(12a) LEMMERMANN, Ber. deutsch. bot. Ges. voLxix. 1901, p. 247. (12b) LOHMAXX,
Archiv f. Protistenk. vol. i. 1902, p. 89 ; SCHILLER, Die Xaturwissenschaften,
vol. iv. 1916, p. 277. (1Sc) G. HAASE, Archiv f. Protistenk. vol. xx. 1910, p. 47 ;
CH. TERXETZ, Jahrb. wiss. Bot. vol. li. 1912, p. 435. (13) LISTER, A Monograph
of the Mycetozoa, 1894 ; HARPER. Bot. Gaz. vol. xxx. 1900, p. 217 ; PAVILLARD,
Progressus rei bot. vol. iii. 1910, p. 496 ; PASCHER, Ber. deutsch. bot. Ges.
vol. xxxvi. 1918, p. 359. (14) JAHX, Ber. deutsch. bot. Ges. 1911, p. 231.
(ls) WOROXIN, Jahrb. f. wiss. Bot. vol. xi. 1878, p. 548 ; NAWASCHIX, Flora,
1899, p. 404 ; PROWAZEK, Arb. kais. Gesundheitsamt, vol. xxii. 1905, p. 396 ;
MARCHAXD, C. r. Acad. Paris, vol. cl. 1910, p. 1348 ; SCHWARTZ, Annals of Bot.
vol. xxv. 1911, p."V91, and vol. xxviii. 1914, p. 227 ; JAHX, Ztschr. f. Bot vol. vi.
1914, p. 875. (16) THAXTER, Bot. Gaz. vol. xiv. 1892, p. 389 ; vol. xxiii. 1897,
p. 395, and vol. xxxvii. 1904, p. 405 ; QUEHL, Ctrbl. f. Bakt. vol. ii. 16, 1906,
p. 9 ; VAHLE, ibid. vol. xxv. 1909, p. 178. (") SCHUTT, Die Peridin. der
Planktonexpedition, 1895; SCHILLING, Flora, 1891, p. 220; Ber. deutsch. bot.
Ges. 1891, p. 199 ; JOERGEXSEX, Die Ceratien, Leipzig, 1911 ; KLEBS, Verh. nat.
med. Verein Heidelberg, vol. ix. 1912, p. 369 ; SCHILLING, Die Dinoflagellaten in
PASCHERS Siisswasserflora Deutschlands, 1913. (18) SCHUTT, Das Pflanzenleben der
Hochsee, 1893 ; GRAX, Das Plankton des norwegischen Nordmeeres, 1902 ;
KARSTEX, Wiss. Ergeb. der deutscheu Tiefsee-Expedition, 1898-99, 1905-1907.
(19) KLEBS, cf. (17). (») DIPPEL, Diatomeen der Rhein-Mainebene, 1905 ; VON
SCHOXFELDT, Diatomaceae Germaniae, 1907 ; 0. MULLER, Ber. deutsch. bot. Ges.
1898-1909 ; HEIXZERLIXG, Bibl. bot. Heft 69, 1908 ; MANGIN, Ann. sc. nat.
9e ser. vol. viii. 1908, p. 177 ; KARSTEX, Handworterb. d. Naturw. vol. ii. p. 960 ;
KARSTEX, Ztschr. f. Bot. vol. iv. 1912, p. 417. (21) GRAX, Die Diat. der arkt.
Meere, Fauna arctica, vol. iii. 1904 ; KARSTEX, Ber. deutsch. bot. Ges. 1904,
p. 544, and Wiss. Ergebn. der d. Tiefsee-Exped. vol. ii. 2. Teil, 1907, p. 496 ;
P. BERGOX, Bull. soc. bot. France, vol. liv. 1907, p. 327 ; PAVILLARD, Bull. soc.
bot. France, vol. Ixi. 1914, p. 164 ; SCHILLER, Ber. deutsch. bot. Ges. vol. xxvii.
1909, p. 351. (22) BEXECKE, Jahrb. f. wiss. Bot. vol. xxxv. 1900, p. 535 ;
KARSTEX, Flora, Ergzb. 1901, p. 404 ; RICHTER, Denkschr. Akad. Wien, vol.
Ixxxiv. 1909. (w) SAUVAGEAU, Station d'Arcachon, Travaux des labor, vol. ix.

1906, p. 49, and vol. x. 1907, p. 1. (24) W. WEST and G. S. WEST, A Monograph
of the Brit. Desmid. vol. i. 1904 ; KAUFFMAXX, Ztschr. f. Bot. 1914, p. 721.
(2s) LUTMAX, Bot. Gaz. vol. xlix. 1910, p. 241, and vol. li. 1911, p. 401 ; VAX
WISSELIXGH, Ztschr. f. Bot. vol. iv. 1912, p. 337. (26)iTROXDLE, Ztschr. f. Bot. vol.
iii. 1911, p. 593, and vol. iv. 1912, p. 721 ; KURSSAXOW, Flora, vol. civ. 1911, p. 65.

Algae.— I27) PASCHER, Hedwigia, vol. liii. p. d. (») KUTZIXG, Tabulae
phycologicae. C29) WOLLE: s WEBER, Ber. deutsch. bot. Ges. vol. xxvi. 1908,
p. 238. (ao) GOROSCHANKIX, Flora, 1905, p. 420. (31) GERXECK, Beihefte bot.
Centralbl. vol. xxi.2 p. 221; TREBOUX, Ber. deutsch. bot. Ges. vol. xxx. 1912,
p. 69. (y2) GRIXTZESCO, Rev. gener. de bot. vol. xv. 1903, p. 5. (™) HARPER,
Bull. Univ. Wisconsin, No. 207, 1908, p. 280. (3*) PASCHER, Hedwigia, vol. xlvi.

1907, p. 265 ; VAN WISSELINGH, Beih. bot. Ctrbl. vol. xxiii. I. 1908. (M) ALLEN,
Ber. d. bot. Gesellsch. 1905, p. 285. (») HABERLANDT, Sitzb. Akad. Wien,
vol. cxv. I. 1906, p. 1 ; SVEDELIUS, Ceylon Marine Biolog. Reports, Xo. 4, 1906.

764 BOTANY

(37) FREUND, Beih. hot. Ctrbl. vol. xxi. I. 1907, p. 55. C38) DAVIS, Bot. Gazette,
vol. xxxviii. 1904, p. 81 ; HEIDINGER, Ber. deutscli. bot. Ges. vol. xxvi. 1908,
p. 312. (39) SKOTTSBERG, Wiss. Erg. der schwed. Siidpolarexpedition, vol. iv.
Lief. 6, 1907, p. 80 ; FRYE, RIGG and CRANDALL, Bot. Gaz. vol. Ix. 1915, p. 473.

(40) SAUVAGEAU, Societe sc. d'Arcachon, Station biol. 11« annee, 1908, p. 65.

(41) SAUVAGEAU, C. rend. Soc. de biolog. Paris, vol. Ixii. 1907, p. 1082 ; SCHILLEU,
Internat. Revue der ges. Hydrobiol. vol. ii. 1909, p. 62 ; F. BORGESEN, The Species
of Sargassum, Kopenhagen, 1914, and The Marine Algae of the Danish West Indies,
Part II. 1914, p. 222. (42) HANSTEEN, Jahrb. f. wiss. Bot. vol. xxxv. 1900, p. 611 ;
HUNGER, ibid. vol. xxxviii. 1903, p. 70 ; KYLIN, Ztschr. f. Bot. vol. iv. 1912,
p. 540 ; KYLIN, Ztschr. f. phys. Chemie, vol. xciv. 1915, p. 337, and Ber. deutsch.
bot. Ges. vol. xxxvi. 1918, p. 10 ; WILLE, Univers. Festschrift Christiania, 1897 ;
SYKES, Annals of Bot. vol. xxii. 1908, p. 292 ; KNIEP, Internat. Revue der
Hydrobiologie, vol. vii. 1914, p. 1. (43) YAMANOUCHI, Bot. Gaz. vol. xlviii. 1909,
p. 380, and Bot. Ztrbl. vol. cxvi. 1911, p. 435 ; YAMANOUCHI, Bot. Gaz. vol. liv.
1912, p. 441. (44) KYLIN, Ber. deutsch. bot. Ges. vol. xxxv. 1917, p. 298.
(45) WILLIAMS, Annals of Bot, vol. xi. 1897, p. 545, and vol. xviii. 1904, pp. 141 and
183, vol. xix. 1905, p. 531 ; LEWIS, Bot. Gaz. vol. 1. 1910, p. 59 ; MOTTIER,
Annals of Bot. vol. xiv. 1900, p. 163. (46) SAUVAGEAU, C. rend. Paris, vol. clxi.
1915, vol. clxii. 1916, vol. clxiii. 1917 ; KYLIN, Svensk. bot. Tidsk. vol. x. 1916,
p. 551, vol. xii. 1918, p. 21 ; PASCHER, Ber. deutsch. bot. Ges. 1918, p. 246 ;
KUCKUCK, ibid. 1917, p. 557. (47) YAMANOUCHI, Bot. Gaz. vol. xlvii. 1909,
p. 173 ; NIENBURG, Flora, vol. ci. 1910, p. 167, and Ztschr. f. Bot. vol. v. 1913,
p. 1 ; SAUVAGEAU (Cystoseira), Bull. stat. biol. d'Arcachon, 14. Jahrg. 1912 ;
KYLIN, Ber. deutsch. bot. Ges. vol. xxxiv. 1916, p. 194 ; MEVES, Archiv f. mik.
An. vol. xci. 1918, p. 272. (48) MOTTIER, Annals of Bot. vol. xviii'. 1904, p. 245 ;
STRASBURGER, Wiesner-Festschrift, 1908, p. 24 ; SCHENCK, Bot. Jahrb. f. System,
vol. xlii. 1908, p. 1 ; OEHLKERS, Ber. deutsch. bot. Ges. vol. xxxiv. 1916, p. 223 ;
GOEBEL, Flora, N.F. vol. x. 1918, p. 344. (48a) ERNST, Bastardierung als Ursache
der Apogaraie im Pflanzenreich, 1918. (49) WOLFE, Annals of Bot. vol. xviii.
1904, p. 607 ; YAMANOUCHI, Bot. Gazette, vol. xli. 1906, p. 425 ; KURSSANOW,
Flora, vol. xcix. 1909, p. 311 ; SVEDELIUS, Ber. deutsch. bot. Ges. vol. xxxii.
1914, p. 48 ; SCHILLER, Osterr. bot. Ztschr. 1913, No. 4 ; v. FABER, Ztschr. f.
Bot. vol. v. 1913, p. 801 ; KYLIN, Ber. deutsch. Bot. Ges. vol. xxxv. 1917, p. 155.
(49a) SVEDELIUS, Kgl. Svensk. Vetenskapsakad. Handl. vol. xliii. 1908, p. 76.
(49b) SVEDELIUS, Ber. deutsch. bot. Ges. vol. xxxv. 1917, p. 225. (49c) LEWIS,
Annals of Bot. vol. xxiii. 1909, p. 639, and Bot. Gazette, vol. liii. 1912, p. 236 ;
KUCKUCK, Ztschr. f. Bot. vol. iii. 1911, p. 180 ; SVEDELIUS, Svensk. Bot.
Tidskrift, vol. v. 1911, p. 260, and vol. vi. 1912, p. 239 ; RIGG and DALGITY, Bot.
Gaz. vol. liv. 1912, p. 164 ; SVEDELIUS, Ber. deutsch. bot. Ges. 1914, p. 106 ;
Svensk. bot. Tidsk. vol. viii. 1914, p. 1 ; Nova acta reg. soc. sc. Upsaliensis, ser. 4,
vol. iv. 1915 ; KYLIN, Ber. deutsch. bot. Ges. 1916, p. 257 ; Ztschr. f. Bot. 1916,
pp. 97 and 545. (50) KUCKUCK, Sitzb. Akad. Berlin, 1894, p. 983 ; STURCH,
Annals of Bot. vol. xiii. 1899, p. 83 ; EDDELBUTTEL, Bot. Ztg. 1910, p. 186.

Fungi.— (51) DE BARY, Vgl. Morphologic und Biolog. der Pilze, 1884 (English
Translation). (52) BREFELD, Bot. Unters. liber Schimnielpilze, Unters. aus dem
Gesamtgebiet d. Mykologie, vols. i.-xv. 1872-1912 ; VON TAVEL, Vgl. Morphol.
d. Pilze, 1892 ; E. FISCHER, Handworterb. d. Naturw. vol. vii. p. 880 ; A.
GUILLIERMOND, Progr. rei bot. vol. iv. 1913, p. 389. (53) BALLY, Jahrb. f. wiss.
Bot. vol. 1. 1911, p. 95, and Mykolog. Ctrbl. II. 1913, p. 289 ; GERTR. TOBLER,
Die Synchytrien, Jena, 1913 ; KUSANO, Journ. College of Agric. Tokyo, 1912,

INDEX OF LITERATURE 765

p. 141 ; G. SCHNEIDER, (Kartoffelkrebs) Deutsche landw. Presse, 1908, No. 79, and
1909, No. 88. (M) WORONIN, Mem. de 1'Acad. imp. des Sciences de Saint- Petersbourg,
1904, 8e s6r. vol. xvi. No. 4, p. 1. C55) TROW, Annals of Bot. vol. ix. 1895, p. 609 ;
vol. xiii. 1899, p. 130 ; vol. xviii. 1904, p. 541 ; KLEBS, Jahrb. f. wiss. Bot. vol.
xxxiii. 1899, p. 513 ; DAVIS, Bot. Gaz. vol. xxxv. 1903, p. 233 ; CLAIJSSEN, Berichte
deutsch. bot. Ges. vol. xxvi. 1908, p. 144 ; MUCKE, Berichte deutsch. hot. Ges.
vol. xxvi.a 1908, p. 367. t56) WAGER, Annals of Bot. vol. iv. 1889-91, p. 127 ;
vol. x. 1896, pp. 89 and 295 ; vol. xiv. 1900, p. 263 ; BERLESE, Jahrb. f. wiss. Bot.
vol. xxxi. 1898, p. 159 ; DAVIS, Bot. Gaz. vol. xxix. 1900, p. 297 ; STEVENS, Bot.
Gaz. 1899, vol. xxviii. p. 149 ; 1901, vol. xxxii. p. 77 ; 1902, vol. xxxiv. p. 420, and
Ber. deutsch. bot. Ges. 1901, p. 171 ; TROW, Annals of Bot. vol. xv. 1901, p. 269 ;
MIYAKE, Annals of Bot. 1901, p. 653 ; ROSENBERG, Bihang till Svensk. Ak. vol.
xxviii. 1903 ; RUHLAND, Jahrb. f. wiss. Bot. vol. xxxix. 1904, p. 135 ; ROSTOWZEW,
Flora, 1903, p. 405 ; KRUGER, Ctrbl. f. Bakteriol. II. vol. xxvii. 1910, p. 186.
(67) HARPER, Annals of Bot. vol. xiii. 1899, p. 467 ; GRUBER, Ber. deutsch. bot.
Ges. 1912, p. 126 ; McCoRMiCK, Bot. Gaz. vol. liii. 1912, p. 67:; Miss KEENE,
Annals of Bot. vol. xxviii. 1914, p. 455. (57a) BLAKESLEE, Bot. Gaz. vol. xiii.
1906, p. 161 ; vol. xliii. 1907, p. 415, and vol. xlvii. 1909, p. 418 ; HAGEM,
Vidensk. Selskab. Skrifter-Christiania, 1907, No. 7 ; BURGEFF, Ber. deutsch. bot.
GPS. vol. xxx. 1912, p. 679, and Flora, vol. cvii. 1914, p. 259 ; vol. cviii. 1915, p. 440.
(M) BLAKESLEE and GORTNER, Biochem. Bull. II. 1913, p. 542. (M) OLIVE, Bot.
Gaz. vol. li. 1906, pp. 192 and 229. t60) RACIBORSKI, Flora, 1906, p. 106 ; FAIR-
CHILD, Jahrb. f. wiss. Bot. vol. xxx. 1897, p. 285. (61) HARPER, Jahrb. f. wiss.
Bot. vol. xxx. 1897, p. 249, also Annals of Bot. vol. xiii. 1899, p. 467 ; vol. xiv.
1900, p. 321 ; GUILLIERMOND, Revue gener. de bot. vol. xvi. 1904, pp. 49 and
130 ; vol. xxxiii. 1911, p. 89 ; CLAUSSEN, Bot. Ztg. 1905, p. 1 ; MAIRE, C. r. soc.
biol. vol. Iviii. 1905, p. 726*; FRASER and WELSFORD, Annals of Bot. vol. xxii.
1908, p. 465 ; OVERTON (Thecotheus), Bot. Gaz. vol. xiii. 1906, p. 450 ; W.
BROWN, Bot. Gaz. vol. Hi. 1911, p. 275. C32) BLACKMAN and WELSFORD,
(Gnomonia) Annals of Bot. vol. xxvi. 1912, p. 761 ; NIENBURG, (Polystigma)
Ztschr. f. Bot. vol. vi. 1914, p. 369 ; KILLIAN, (Venturia) Ztschr. f. Bot. vol. ix.
1917, p. 353 ; RAMLOW, (Ascoboleen) Mykol. Ctrbl. vol. v. 1914, p. 177 ; DODGE,
Bull. Torrey Bot. Club, vol. xli. 1914, p. 157 ; KILLIAN, (Cryptomyces) Ztsch. f.
Bot. vol. x. 1918, p. 49. t63) SCHIKORRA, Ztsch. f. Bot. vol. i. 1909, p. 379.
(w) FRASER, Annals of Bot. vol. xxi. 1907, p. 349. C65) HARPER, Ber. deutsch.
bot. Ges. 1895, p. 475, and Jahrb. f. wiss. Bot. vol. xxix. 1895, p. 655 ; NEGER,
Flora, 1901, p. 333, and 1902, p. 221 ; SALMON, Annals of Bot. vol. xx. 1906, p.
187; HARPER, Carnegie Institution of Washington, publ. No. 37, 1902 (Phyllactinia).
(66) FRASER and CHAMBERS, Annales mycolog. vol. v. 1907, p. 419. C67) MIEHE,
Medic. Klinik, 1906, p. 943. (^J WEESE, Ztsch. f. d. landw. Versuchswesen
Osterreich, 1911 ; VOGES, Ctrbl. Bakter. vol. xxxix. 1914, p. 641. (69) HARPER,
Annals of Bot. vol. xiv. 1900, p. 321 (Pyronema) ; CLAVSSEN, Bot, Ztg. 1905, p. 1
(Boudiera), and Berichte der deutsch. bot. Ges. 1906, p. 11 ; CLAUSSEN, (Pyronema)
Ber. d. bot. Ges. 1907, p. 586, and Ztsch. f. Bot. vol. iv. 1912, p. 1. (70) KROMB-
HOLZ, Abb. u. Beschreib. der Schwamme, 1831-46 ; LEXZ, Niitzl. schadl. u. verdacht.
Schwanime, 1890 ; GRAMBERG, Pilze der Heimat ; MICHAEL, Fiihrer fiir Pilzfreunde ;
RULL, Unsere essb. Pilze ; SYDOW, Taschenbuch der wichtigeren essbaren u. giftigen
Pilze ; DITTRICH, Ber. deutsch. bot. Ges. vol. xxxiv. 1916, pp. 424 and 719 ; A.
RICKEN, Vademecum fiir Pilzfreunde, 1918, and Die Blatterpilze (Agaricaceae)
Deutschlands, 1915. (71) FISCHER, Bot. Ztg. 1908, p. 141 ; BUCHHOLTZ, Ann.
mycol. vol. vi. 1908, p. 539 ; FISCHER, Ztschr. f. Bot. vol. ii. 1910, p. 718.

766 BOTANY

(72) GIESENHAGEN, Flora, Erzgb. 1895, p. 267, and Bot. Ztg. 1901, p. 115 ; IKENO,
Flora, 1901, p. 229, and 1903, p. 1. (73) GUILLIERMOND, Rev. gener. de bot. 1903,
p. 49 ; E. C. HANSEN, Ztrbl. f. Bakt. 2. Abt. vol. xii. 1904 ; GUILLIEIIMOND,
Rev. gener. de bot. 1905, p. 337 ; MAIICHAND, Rev. gen. bot. 1913, p. 207.
(74) THAXTER, Mem. of Americ. Acad. Boston, 1896, and vol. xiii. 1908 ; FATJLL,
Annals of Bot. vol. xxvi. 1912, p. 325. (75) RUHLAND, Bot. Ztg. 1901, p. 187 ;
FRIES, Ztschr. f. Bot. vol. iii. 1911, p. 145, and vol. iv. 1912, p. 792 ; KNIEP,
Ztschr. f. Bot. vol. iii. 1911, p. 531. (76) HECKE, Ber. d. bot. Ges. 1905, p. 248 ;
LANG, Ztrbl. f. Bakt. II. vol. xxv. 1910, p. 86 ; RAWITSCHEH, Ztschr. f. Bot. vol.
iv. 1912, p. 673, and Ber. deutsch, bot. Ges. vol. xxxii. 1914, p. 310 ; WERTH,
Arbeit, kais. biol. Anst. vol. viii. 1911, p. 427 ; PARAVICINI, Ann. mycol. vol.
xv. 1917, p. 57. (") Many papers by P. MAGNUS, KLEBAHN, SYDOW, ERIKSSON,
TISCHLER, E. FISCHER, LAGERHEIM, etc. ; P. et H. SYDOW, Monograph ia
Uredinarum ; MAIRE, Progr. rei bot. vol. iv. 1911, p. 109. (78) BLACKMAN,
Annals of Bot. vol. xviii. 1904, p. 323 ; BLACKMAN and FRASER, ibid. vol. xx.
1906, p. 35 ; CHRISTMAN, Bot. Gaz. vol. xxxix. 1905, p. 267 ; CHKISTMAN, Trans-
act. Wisconsin Acad. vol. xv. 1907, p. 517, and Bot. Gazette, vol. xliv. 1907,
p. 81 ; OLIVE, Annals of Bot. vol. xxii. 1908, p. 331 ; DITTSCHLAG, Ztrbl. f.
Bakt. II. vol. xxviii. 1910; KURSSANOW, Ztschr. f. Bot. II. 1910, p. 81 ; WERTH
and LUDWIGS, Ber. deutsch. bot. Ges. vol. xxx. 1912, p. 523 ; FROMME, Bot. Gaz.
vol. Iviii. 1914, p. 1 ; KURSSANOW, Ber. deutsch. bot. Ges. vol. xxxii. 1914, p.
317. (79) KLEBAHN, Die wirtswechselnden Rostpilze, 1904. (80) ERIKSSON and
TISCHLER, Svenska Vet. Akad. Handl. 1904, vols. xxxvii. xxxviii ; KLEBAHN, Ber.
deutsch. bot. Ges. 1904, p. 255 ; E. FISCHER, Bot. Ztg. 1904, p. 327 ; MARSHALL
WARD, Annals of Bot. vol. xix. 1905, p. 1. (81) HOFFMANN, Ztrbl. f. Bakt. 2.
Abt. vol. xxxii. 1911 ; WERTH, ibid. vol. xxxvi. 1912. (81a) KUNKEL, Araeric.
Journ. of Bot. vol. i. 1914, p. 37. (8-) KNOLL, Jahrb. wiss. Bot. vol. 1. 1912, p.
453, and Ber. deutsch. bot. Ges. vol. xxx. 1912, p. 36. (s'3} H. KNIEP, Ztschr. f.
Bot. vol. v. 1913, p. 593 ; vol. vii. 1915, p. 365 ; vol. viii. 1916, p. 353 ; Flora,
N.F. vols. xi.-xii. 1918, p. 380. (84) R. HARTIG, Der echte Hausschwamm, 1885,
ed. 2 by VON TUBEUF, 1902 ; MOLLER and FALCK, Hausschwammforschungen,
vols. i.-vi. 1907-1912 ; MEZ, Der Hausschwamm, Dresden, 1908 ; FALCK, Mykolog.
Unt. u. Ber. I. 1913. . (85) MOLLER, Pilzgarten sudamerik. Ameisen, 1893 ;
HOLTERMANN, • Schwendener-Festschrift, 1899; FOREL, Biolog. Zentralbl. 1905,
p. 170 ; HUBER, Biol. Zentralbl.1905, p. 606. (86) E. FISCHER, Denkschr. Schweiz.
nat. Ges. vols. xxxii. and xxxvi. ; MOLLER, Brasil. Pilzblumen, 1895 ; ATKINSON,
Bot. Gaz. vol. li. 1911, p. 1.

Lichens.— (87) WINKLER, Pfropfbastarde, 1. Teil, 1912, p. 102 ; TREBOUX,
Ber. deutsch. bot. Ges. vol. xxx. 1912, p. 77 ; NIENBURG, Ztsch. f. Bot. 1917, p.
530. C88) ZOPF, Die Flechtenstoffe, 1907 ; STAHL, Hackel-Festschrift, 1904, p.
357. (89) BAUR, Flora, 1901, p. 319, also Bot. Ztg. 1904, p. 21 ; WOLFF, Flora,
Ergzb. 1905, p. 31 ; NIENBURG, Flora, vol. xcviii. 1908, p. 1 ; F. BACHMANN,
Annals of Bot. vol. xxvi. 1912, p. 747. (90) MOLLER, Kultur fiechtenbild. Ascomy-
ceten, 1887, and Bot. Ztg. 1888, p. 421 ; GLUCK, Flechtenspermogonien, Habilita-
tionsschr. Heidelberg, 1899. (Wa) FREDA BACHMANN, Arch. f. Zellforschung,
vol. x. 1913, p. 369. (91) JOHOW, Jahrb. f. wiss. Bot. vol. xv. 1884, p. 361 ;
MOLLER, Flora, 1893, p. 254 ; POULSEN, Vid. Medd. Kopenhagen, 1899.

Bryophyta.— (92) GOEBEL, Organographie II. Bryophyten, 2. Aufl. 1915 ;
Pteridophyten, 2. Aufl. 1918 ; CAMPBELL, The Structure and Development of Mosses
and Ferns, 2nd ed. 1905 ; RABENHORST, Kryptogamenflora, vol. vi. ; Lebermoose by
K. MULLER, vol. iv. ; Laubmooseby LIMPRICHT ; LOESKE, Die Laubmoose Europas.

INDEX OF LITERATURE 767

(•93) GOEBEL, Flora, vol. xc. 1902, p. 279; DAVIS, Annals of Bot. vol. xvii.
1903, p. 477 ; HOLFERTY, Bot. Gaz. vol. xxxvii. 1904, p. 106 ; MELIN, Svensk.
Bot. Tidskr. vol. x. 1916, p. 289 ; FLORIN, Svensk. Bot. Tidskr. vol. xii. 1918, p.
464. t94) ALLEN, Archiv f. Zellforschung, vol. viii. 1912, p. 179 ; WOODBURN,
Annals of Bot. vol. xxvii. 1913, p. 93 ; WALKER, ibid. p. 116. C95) ZIELINSKI,
Flora, vol. c. 1910, p. 1. (M) PFEFFER, Unters. bot. Inst. Tubingen, I. II. ;
LIDFORS, Jahrb. f. wiss. Bot. vol. xli. 1904, p. 65 ; AKERMAN, Ztschr. f. Bot.
vol. ii. 1910, p. 94. (97) KREH, Nova Acta Acad. Leop. vol. xc. 1909, p. 214 ;
CORRENS, Unt. iiber Vermehrung der Laubmoose durch Brutorgane und Stecklinge,
Jena, 1899; BUCH, Brutorgane der Lebermoose, Dissert. Helsingfors, 1911.
(w) SCHENCK, Bot. Jahrbiicher f. Syst. vol. xlii. 1908, p. 1. (") ANDREAS, Flora,
1899, p. 161 ; DOUIN, Rev. gener. de bot. vol. xxiv. 1912, p. 392 ; CLAPP, (Aneura)
Bot. Gaz. vol. liv. 1912, p. 177 ; K. MEYER, (Corsinia) Bull. soc. imp. des nat.
Moskau, 1911, p. 263, and Ber. deutsch. bot. Ges. vol. xxxii. 1914, p. 262;
SCHIFFNER, Progressus rei bot. vol. v. 1917. (10°) N&MEC, Beihefte Bot. Ztrbl.
vol. xvi. 1904, p. 253 ; GOLENKIN, Flora, vol. xc. 1902, p. 209 ; SCHIFFNER,
Anuales jard. Buiteiizorg Supp. III.2 1910, p. 473 ; GARJEANNE, Flora, vol. cii.
1911, p. 147. (101) LANG, Annals of Bot. vol. xxi. 1907, p. 201 ; CAMPBELL,
Annals of Bot. vol. xxi. 1907, p. 467, and vol. xxii. 1908, p. 91. (lola) PEIRCE,
Bot. Gaz. vol. xlii. 1906, p. 55. (102) GOEBEL, Flora; vol. ci. 1910, p. 43 ;
GEHRMANN, Ber. deutsch. bot. Ges. vol. xxvii. 1909, p. 341. (103) CAREER, Bot.
Gaz. vol. xxxvii. 1904, p. 161 ; LEWIS, Bot. Gaz. vol. xli. 1906, p. 110 ; PIETSCH,
Flora, vol. ciii. 1911, p. 347 ; BLACK, Ann. of Bot. vol. xxvii. 1913, p. 511.
(104) HABERLANDT, Jahrb. f. wiss. Bot. vol. xvii. 1886, p. 359 ; TANSLEY and
CHICK, Annals of Bot. vol. xv. 1901, p. 1 ; CORRENS, Vermehrung der Laubmoose,
1899 ; VATJPEL, Flora, 1903, p. 346 ; STRUNK, Diss. Bonn, 1914 ; GREBE, Studien
zur Biol. u. Geogr. d. Laubmoose, Hedwigia, vol. lix. 1917. (105) K. GIESENHAGEN,
Annals jard. Buitenzorg, Suppl. 32, 1910, p. 711. (10fl) ZEDERBAUER, Ostr. bot.
Ztschr. 1902 ; MERL, Flora, vol. cix. 1917, p. 189. (107) STEINBRINCK, Ber.
deutsch. bot. Ges. vol. xxvi.a 1908, p. 410; vol. xxvii. 1909, p. 169, and vol.
xxviii. 1910, pp. 19 and 549. (108) HABERLANDT, Jahrb. f. wiss. Bot. vol. xvii.
1880, p. 357 ; PORSCH, Der Spaltoffnungsapparat im Lichte der Phylogenie, 1905,
p. 33. (109) BRYAN, Bot. Gaz. vol. lix. 1915, p. 40 ; MELIN, Svensk. bot. Tidskr.
vol. x. 1916, p. 289. (no) DIHM, Flora, Ergzbd. 1894, p. 286 ; GOEBEL, Flora,
1895, p. 459 ; STEINBRINCK, Flora, Ergzbd. 1897, p. 131, and Biolog. Ztrbl. 1906,
p. 727 ; KUNTZEN, Diss. Berlin, 1912. (ni) ZIELINSKI, Flora, vol. c. 1909, p. 6.

Pteridophyta.— (m) BOWER, The Origin of a Land Flora, London, 1908.
(us) PFEFFER, Unters. bot. Inst. Tiibingen, vol. i. p. 363 (Fame, Selaginella);
SHIBATA, Bot. Mag. Tokyo, vol. xix. 1905, p. 39 (Salvinia) ; ibid. pp. 79 and 126
(Equisetum) ; Ber. d. bot. Ges. 1904, p. 478, and Jahrb. f. wiss. Bot. vol. li. 1905,
p. 561 (Isoetes) ; LIDFORS, Ber. d. bot. Ges. 1905, p. 314 (Equisetum) ; BRUCH-
MANN, Flora, vol. xcix. 1909, p. 193 (Lycopodium) ; BULLER, Annals of Bot. vol.
xiv. 1900, p. 543 (Fame) ; SHIBATA, Jahrb. wiss. Bot. vol. xlix. 1911, p. 1
(Equisetum, Fame, Salvinia, Isoetes). (m) HANNIG, Flora, vol. cii. 1911, p. 209
and vol. ciii. 1911, p. 321. (115) HOOKER, Synopsis Filicum, 1883 ; BAKER, Fern
Allies, 1887 ; CHRIST, Farnkrauter der Erde, 1897, and Die Geographic der Fame,
Jena, 1910 ; CHRISTEXSEN, Index Filicum, 1906. (116) CAMPBELL, Annal. Buiten-
zorg, vol. xxii. 1908, p. 99, and Suppl. 31, 1910, p. 69. (m) JEFFREY, Univers.
of Toronto, Biolog. Series, No. 1, 1898 (Botrychiuin) ; BURLINGHAM, Bot. Gaz.
vol. xliv. 1907, p. 34 (Ophiogl.) ; CHRYSLER, Annals of Bot. vol. xxiv. 1910, p. 1 ;
LYON, Bot. Gaz. vol. xl. 1905, p. 455 (Botrychium). (118) STEINBRINCK, Biolog.

768 BOTANY

Ztrbl. 1906, p. 674, and Monatshefte fur d. naturw. Unt. vol. xi. 1918, p. 131.
(119) GOEBEL, Flora, vol. cv, p. 49. (12°) SCHLUMBERGER, Flora, vol. cii. 1911, p.
383. (121) ARNOLDI, Flora, vol. c. 1909, p. 121 ; KUNDT, Beihefte Bot. Ztrbl. vol.
371, 1911, p. 26 ; ZAWIDZKI, Beihefte Bot. Ztrbl. vol. xxviii. 1912, p. 17 ; YASUI,
Annals of Bot. vol. xxv, 1911, p. 469. (121a) PFEIFFER, Bot. Gaz. vol. liv. 1907,
p. 445 ; OES, Ztsrchr. f, Bot. vol. v. 1913, p. 145. (12a) F. SCHNEIDER, Beitr.
z. Entw. der Marsiliaceen, Diss. Berlin, 1912; SHARP, Bot. Gaz. vol. Iviii.
1914, p. 419 ; F. SCHNEIDER, Flora, vol. cv. 1913, p. 347. (123) STRASBURGER,
Flora, vol. xcvii. 1907, p. 123. (124) STEINBRINCK, Biolog. Ztrbl. 1906, p. 724 ;
HANNIG, Flora, vol. cii. 1911, p. 209; LUDWIGS, Flora, vol. ciii. 1911, p. 385;
SHARP, Bot. Gaz. vol. liv. 1912, p. 89 ; VIDAL, Ann. sc. nat. 9e ser. vol. xv. 1912,
p. 1. (125) BRUCHMANN, Flora, vol. ci. 1910, p. 220. (125a) HABERLAND, Beitr.
z. allg. Bot. vol. i. p. 293. (126) BRUCHMANN, Flora, vol. civ. 1912, p. 180 ; vol.
cv. 1913, p. 237, and Zeitschr. f. Bot. vol. xi. 1919, p. 39 ; LYON, Bot. Gaz. vol.
xl.. 1905, p. 285; CAMPBELL, Annals of Bot. vol. xvi. 1902, p. 419; DENKE,
Beiheft z. bot. Ztrbl. vol. xii. 1902, p. 182 ; STEINBRINCK, Ber. deutsch. bot.
Ges. 1902, p. 117, and Biolog. Ztrbl, 1906, p. 737 ; MITCHELL, Annals of Bot. vol.
xxiv. 1910, p. 19 ; SYKES and STYLES, ibid. p. 523 ; WAND, Flora, vol. cvi. 1914,
p. 237. (127) STEINBRINCK, Ber. deutscli. bot. Ges. vol. xxviii. 1910, p. 551, and
vol. xxix. 1911, p. 334. • (128) BRUCHMANN, Flora, 1905, p. 150 ; GOEBEL, Flora,
1905, p. 195. (129) W. SEYD, Zur Biolog. von Selag. Dissert. Jena, 1910 ; NEGER,
Flora, vol. ciii. 1911, p. 74. (13°) HABERLANDT, Ber. d. bot. Ges. 1905, p. 441.
(131) STOCKEY, Bot. Gaz. vol. xlvii. 1909, p. 311.

Fossil Cryptogams.— (132) Of. the palaeophytological textbooks of W. PH.

SCHIMPER, A. SCHENK, B. RENAULT, G. SAPORTA et MARION, SOLMS-LAUBACH,

H. POTONIE, D. H. SCOTT, R. ZEILLER, A. C. SEWARD, W. JONGMANS. R.
ZEILLER, Progressus rei bot. vol. ii. 1907, p. 171. (133) GORDON, Annals of Bot.
vol. xxiv. 1910, p. 821. (134) OLIVER, Biol. Ztrbl. 1905, vol. xxv. p. 401, and Annals
of Bot. vol. xxiii. 1909, p. 73 ; SCOTT, Wiss. Erg. Wiener bot. Kongr. 1905, p.
279 ; further, Progressus rei bot. vol. i. 1907, p. 139, and Smithsonian Report, 1907,
p. 371 ; CHODAT, Archives sc. phys. et nat. 4e per. vol. xxvi. Geneve, 1908 ;
OLIVER and SALISBURY, Annals of Bot. vol. xxv. 1911, p. 1.

SPERMATOPHYTA BY G. KARSTEN
Transition from Pteridophyta to Spermatophyta

(*) W. HOFMEISTER, Vergleich. [Inters, der Keim, Entfalt u. Fruchtbildung
hoherer Kryptogamen und der Samenbild. der Koniferen, Leipzig, 1851 ;
HOFMEISTER, Higher Cryptogamia, London, 1862 ; E. STRASBURGER, Koniferen u.
Gnetaceen, Jena, 1872 ; id. Angiospermen und Gymnospermen, Jena, 1879, and the
comprehensive works : R. VON WETTSTEIN, Handbuch der systematise!] en Botanik,
2. Aufl. Leipzig and Wien, 1911 ; K. GOEBEL, Organographie der Pflanzen, 1. u. 2.
Jena, 1898-1901 (English translation of 1st edition) ; and 2nd ed. 1. u. 2. 1913,
1918 ; J. M. COULTER and CH. J. CHAMBERLAIN, Morphology of Gymnosperms,
Chicago, 1910, and Morphology of Angiosperms, Chicago, 1909. The above
contain lists of literature, and only fundamental and historically important works
or those giving more recent data are referred to here. (2) OVERTON, Reduktion
der Chromosomen, Vierteljahrsschr. d. naturf. Ges. Zurich, 1893 ; E. STRASBURGER,
Reduktionsteilung, Sitzber. K. A. d. W. Berlin, vol. xviii. 1904 ; id. Chromo-
somenzahlen und Reduktionsteilung, Pringsh. Jahrb. vol. xlv. 1908.

INDEX OF LITERATURE 769

Morphology and Ecology of the Flower. — (3) PAYER. Organogenic de la fleur,
1857; BAILLON, Histoire des plantes, vols. i.-xiii. 1867-94; EICHLER, Bliitendia-
grarame, 2 vols. Leipzig, 1875 and 1878 ; A. ENGLER and PRANTL, Natiirl. Pflanzen-
familien, vols. ii.-iv. from 1889; id. Das Pflanzenreich from 1900; BERG and
SCHMIDT, Atlas der offizinellen Pflanzen, 1863, and the second edition by A. MEYER
and SCHUMANN, 1891-1902 ; further, the literature given under (J). (4) CHR. K.
SPRENGEL, Das entdeckte Geheimnis der Natur, 1793 (OSTWALDS Klassiker, Nos.
48-51) ; CH. DARWIN, Ges. Werke, Ubersetzung von CARUS, 1877, vols. ix. and x.;
KNUTH, Handbuch der Bliitenbiologie, 1898 ; 0. KIRCHNEI:, Blumen und Insekten,
Leipzig, 1911 ; G. TISCHLER, Das Heterostylie-Problem, Biol. Zentralbl. 38. 11.
1918 ; id. Festschrift HOHENHEIM. 254, 1918. («) C. HESS, Exper. Unters.
iiber den angeblichen Farbensinn der Bienen, Zoolog. Jahrb. vol. xxxiv. 1913 ;
id. Munch, mediz. Wochenschrift, 1914, No. 27 : id. Arch. f. d. ges. Physiologic,
vol. clxiii. 1916 ; id. ibid. vol. clxx. 1918 ; K. VON FRISCH, Der Farbensinn
und Formensinn d§r Biene, Zoolog. Jahrb. 35, 1914 ; id. Uber den Geruchssinn
der Biene, Zoolog. -bot. Ges. Wien, 68, 1918. The most recent works of the same
author (Biolog. Zentralbl. 39, 3) could unfortunately not be consulted. (6) K.
GOEBEL, Kleistogame Bliiten, Biolog. Zentralbl. vol. xxiv. 1904 ; H. RITZEROW,
Flora, 1907.

Development of the Sexual Generation. — (7) Cf. literature under (l), also
SAKUGORO HIRASE, Ginkgo biloba, Journ. of the College of Science, Univ. imp.
Tokio, vol. viii. 1895, and vol. xii. 1898 ; S. IKENO, Cycas revoluta, Jahrb. f. w.
Bot. vol. xxvii. 1898 ; H. J. WEBBER, Sperm atogenesis and Fecundation of Zamia,
U.S. Dep. of Agricult. Washington, 1901 ; CH. J. CHAMBERLAIN, Fertilization
and Embryogeny in Dioon edule, Bot. Gaz. vol. 1. 1910 ; H. H. W. PEARSON,
Some Observations on Welwitscbia mirabilis, Philos. Transact. Royal Soc. 198,
1906 ; ibid. Further Observ. on Welwitschia, I.e. 200, 1909 ; ibid. On the Micro-
sporangium and Microspores of Gnetum, etc., Ann. of Bot. 1912, vol. xxvi. ; LANCELOT
BURLINGHAM, Araucaria brasiliensis, Bot. Gaz. vol. Iv. 1913; Ivii. 1914; lix. 1915.
(8) Literature under (l), also S. NAWASCHIN, Lilium Martagon., Bull. acad. imp.
Saint-Petersbourg, 1898 ; E. STRASBURGER, Doppelte Befruchtung, Bot. Ztg. 2.
Abt. 1900 ; M. TREUB, Casuarina, Ann. Buitenzorg, vol. x. 1891 ; S. NAWASCHIN,
Birke, Mem. acad. imp. Saint-Petersbourg, 7e ser. vol. xlii. No. 12, 1894 ; id. Ulme,
Bull, de 1'acad. imp. d. sc. de Saint-Petersbourg, 5e ser. vol. viii. No. 5, 1898 ; id.
Corylus, ibid. vol. x. No. 4, 1899 ; id. Entw. d. Chalazogamen, Mem. acad.
etc. 8e ser. vol. xxxi. No. 9, 1913 ; M. BENSON, Amentiferae, Transact. Linn. Soc.
2e ser. Bot. vol. iii. pt. 10, 1894 ; N. ZINGER, Cannabineen, Flora, vol. Ixxxv. 1898 ;
MODILEWSKI, Urticifloren, Flora, vol. xcviii. 1908 ; J. SCHWEIGER, Euphorbiaceen,
Flora, vol. xciv. 1905 ; J. WOLPERT, Alnus u. Betula, Flora, vol. c. 1910 ; 0.
DAHLGREN, Plumbagella, Arkiv f. Bot. vol. xiv. 8, 1915, and Kg. Svensk. Vetensk.
Handl. vol. Ivi. 4, 1916 ; LULA PACE, Fertilization in Cypripedium, Bot. Gaz.
vol. xliv. 1907. (9) J. HANSTEIN, Entwicklung des Keimes, Bot. Abhaudl. vol. L
1, 1870 ; E. STRASBURGER, Chromosomenzahlen, Vererbungstriiger usw., Pringsh.
Jahrb. vol. xlv. 1908 ; id. Apogamie, Parthenogenesis und Reduktionsteilung,
Histolog. Beitr. vol. vii. 1909; HANS WINKLER, Parthenogenese u. Apogamie,
Progr. rei bot. vol. ii. 1908 ; M. TUEUB, Notes sur 1'embryo, etc. (Avicennia),
Ann. Buitenzorg, vol. iii. 1883 ; M. MERZ, Utricularien, Flora, vol. Ixxxiv. 1897 ;
BALICKA - IWANOWSKA, Gamopetales, Flora, vol. Ixxxvi. 1899; F. BILLINGS,
Beitrage zur Samenentwicklung, Flora, vol. Ixxxviii. 1901 ; F. X. LANG, Poly-
pompholyx u. Biblis, Flora, vol. Ixxxviii. 1901; C. H. OSTENFELD and 0. ROSENBERG,
Hieracia, III. ; 0. ROSENBERG, Apogamy in Hieracium, Bot. Tidsskr. vol. xxviii.

770 BOTANY

1907 ; 0. PORSCH, Phylogen. Erkl. d. Embryosackes u. d. dopp. rtefr., Jena, 1907 ;
F. A. F. C. WENT, Podostemaceen, I. and II. Verb. K. Akad. v. Wetensch.
Amsterdam, 1910-12 ; id. Development of Podostemaceae, Extr. du recueil des
travaux hot. n6erlandais, vol. v. 1908 ; W. MAGNUS, Atypische Embryonal-Entw.
der Podostemaceen, Flora, vol. cv. 1913. (I0) A. ERNST, Bastardierung als Ursache
der Apogamie, Jena, G. Fischer, 1918. (n) J.' GAERTNER, De fructibus et
seminibus plantarum, vols. i. and ii. Stuttg. 1789-91. (12) A. P. DE CANDOLLE,
Pflanzenphysiologie ; F. HILDEBRANDT, Verbreitungsmittel der Pflanzen, 1873 ;
A. F. W. SCHIMPRR, Pflanzengeographie, Jena, 1898 ; RUTGER SERNANDER,
Myrmekochoren, Kg. Svensk. Vetensk. Handl. vol. xli. 1906 ; F. MORTON, Ameisen
usw., Mitt. Nat. Ver. Univ. Wien, 1912. (13) G. KLEBS, Keimung, Unters. bot. Inst.
Tubingen, vol. i. 536 ; J. LUBBOCK, Seedlings, vols. i. and ii. 1892 ; E. THEUNE,
Biologic geokarper Pflanzen ; F. COHNS, Beitr. vol. xiii. 1916.

Gymnospermae. — (14) Literature under (1), (3) and (7) ; K. GOEBEL, Pollen-
entleerung, Flora, Ergzbd. 1902, 237. (15) D. H. SCOTT, Palaeozoic Botany, in
Progressus rei bot. vol. i. Jena, 1907 ; this contains the older literature ; NEWELL
ARBER, Origin of Angiosperms, Journ. Linn. Soc. vol. xxxviii. 263, 1907 ; G. R.
WIELAND, American Fossil Cycads, 19Q6, i. Carnegie Inst. Washington; F. W.
OLIVER, Physostoma elegans, Ann. of Bot. vol. xxiii. 1909 ; F. W. OLIVER and
E. J. SALISBURY, Palaeozoic Seeds of the Conostoma Group, Ann. of Bot. vol. xxv.
1911; D. H. SCOTT, The Evolution of Plants, 1911, London; FERNAND
PELOURDE, Les Progres realises dans 1'etude des Cycadophytes de 1'epoque
secondaire, Progressus rei botanicae, vol. v. 2, 1916.

Angiospermae Dicotylae. — (16) Literature under (l) and (a), also H. HALLIER,
Verwandtschaftsverhaltnisse bei ENGLERS Rosalen, Parietalen, Myrtiflora usw.,
Abh. d. Naturw. Vereins Hamburg, 1903 ; this contains earlier views of the same
author ; E. SARGANT, Origin of Monocotyledons, Ann. of Bot. vol. xvii. 1903, and
Bot. Gaz. vol. xxx vii. 1904 ; K. FRITSCH, Stellung der Monokotyledonen, Beibl.
79 in ENGLERS Bot. Jahrb. vol. xxxiv. 1905 ; E. STRASBURGER, Drimys, Flora,
Ergzbd. 1905 ; NAWASCHIN, Chalazogamy, of. (8) ; J. NITZSCHKE, Beitr. z. Phylo-
genie d. Monokotyledonen, 1914 ; CORNS, Beitr. vol. xii. ; 0. LIEHR, 1st die ange-
nommene Verwandtschaft der Helobiae und der Polycarpicae auch in ihrer Zytologie
zu erkennen? COHNS, Beitr. xiii. 1916. (17) L. DIELS, Kaferblumen bei den
Ranales und ihre Bedeutung fiir die Phylogenie der Angiospermen, Ber. deutsch.
bot. Ges. 34, 1916 ; G. KARSTEN, Zur Phylogenie der Angiospermen, Zeitschr. f.
Botanik, x. 1918, 369. (18) BUSGEN, Fagales in KIRCHNER, LOEW, SCHROETER,
Lebensgesch. d. Bliitenpfl. vol. ii. 1, 1913. (19) H. Graf zu SOLMS-LAUBACH,
Herkunft usw. des gew. Feigenbaums, Abh. d. K. Ges. d. W., Gottingen, 1882 ;
FRITZ MULLER, Caprificus u. Feigenbaum, Kosmos, vol. vi. 1882 ; 0. WARBURG,
Kautschukpflanzen, Berlin, 1900 ; E. ULE, Kautschukpflanzen der Amazonasexped. ,
ENGLERS Jahrb. vol. xxxv. 1905 ; K. GOEBEL, Schleuderfruchte bei Urticifloren,
Flora, vol. cviii. 1915. (20) J. SCHWEIGER, Euphorbiaceen, Flora, 94, 1905 ;
A. MARKOWSKI, Gattg. Pedilanthus, Diss. Halle, 1912. (21) H. Graf zu SOLMS-
LAUBACH, Cruciferenstudien, vols. i.-iv. Bot. Ztg. 1900-1906. C22) A. DE
CANDOLLE, Ursprung der Kulturpflanzen, 1884 ; V. HEHN, Kulturpflanzen u.
Haustiere, 7. Aufl. 1902 ; on Bizarrien cf. E. STRASBURGER, Pfropfhy bride n ;
PRINGSHEIMS, Jahrb. vol. liv. 538, 1907. (23) MARLOTT, Kapland, Valvidia-
Exped. vol. ii.3 1908 ; id. Mimicry among Plants, Transact. S. Air. Philos.
Soc. vols. xv. and xvi. 1904-1905. (24) K. GOEBEL, Bot. Ztg. 1882, 353 ;
A. DE CANDOLLE, Origin of Cultivated Plants ; H. Graf zu SOLMS-LAUBACH,
Erdbeeren, Bot. Ztg. vol. i. 45, 1907 ; F. NOLL, Pfropfbastarde von Bronveaux,

INDEX OF LITERATURE 771

Sitzber. niederrh. Ges. Bonn, 1906. C25) TH. BELT, Naturalist in Nicaragua,
1888, 218. C26) L. DIELS, Siidwest-Australien, Veg. d. Erde, vol. vii. 1906.
(27) -pm TOBLER, Die Gattung Hedera, 1912. t28) P. GRAEBNER, Heide, Veget. d.
Erde, vol. v. 1901 ; A. ARTOPOEUS, Ericaceen, Flora, 1903. (29) A. NESTLER, Cor-
tusa Matthioli, Ber. deutsch. hot. Ges. 1912, 330. C30) R. VON WETTSTEIN, Ber. d.
deutsch. hot. Ges. vol. xiii. 303 ; id. Deszendenztheor. Unters. I. Denkschr. k. k. Akad.
d. W. Wien, 1900. (31) E. GILG, Strophanthus, Tropenpfl. 1902 ; id. H. THOMS,
H. SCHEDEL, Ber. deutsch. pharmaz. Ges. 1904. (K) Cf. under (19), and also P. PREUSS,
Exp. nach Zentral- u. Siidamerika, Berlin, 1901 ; WARBURG, Kunene-Sambesi-
Exped. Berlin, 1903. C33) M. TREUB, Ann. de Buitenzorg, vol. iii. 13, 1883. C34)
HANS WINCKLEK, Unters. iiber Pfropfbastarde, vol. i. 1912 ; id. Uber experi-
mentelle Erzeugung von Pflanzen mit abweichenden Chromosomenzahlen, Zeitschr.
f. Botanik, vol. viii. 417, 1916. f35) E. HEINRICHER, Lathraea, Ber. deutsch. bot. Ges.
1893 ; id. Grime Halbschmarotzer, i.-iv. Jahrb. f. w. Bot. 1897, 1898, 1901,
1902, 1909, 1910 ; Ji. VON WETTSTEIN, Monogr. Euphrasia, 1896 ; STERNECK,
Alectorolophus, 1901. (36) K. GOEBEL, Morph. u. biolog. Studien 5, Ann. de
Buitenzorg, vol. ix. ; id. Flora, 1904, 98 ; E. MERL, Utricularien, Flora, vol.
cviii. 1915. I37) M. TREUB, Mynnecodia, Ann. de Buitenzorg, iii. 129, 1883 ;
H. MIEHE, Javanische Studien, Abh. Kg. Sachs. Ak. d. W. vol. xxxii. No. IV.
Leipzig, 1911 ; F. C. vox FABER, Das erbliche Zusammenleben von Bakterien u.
trop. Pflanzen, Jahrb. f. wiss. Bot. Lpzg. 1912, vol. li. 285; id. Die Bakterien-
symbiose der Rubiaceen, ibid. vol. liv. 243, 1914. (») F. NOLL, Cucurbitaceen,
Landw. Jahrb. 30. Ergzbd. P. 1901 ; id. Parthenokarpie, Sitzber. niederrh. Ges.
Bonn, 1902 ; G. BITTER, Bryonia, Abh. Nat. Ver., Bremen, 1904 ; C. CORRENS,
Bestimmung u. Vererbung des Geschlechts, Berlin, 1907 ; J. KRATZER, Verwandt-
schaftliche Beziehungen der Cucurbitaceen, Flora, 110, 275, 1918. C39) L. JOST,
Griffelhaare der Campanulaceen, Flora, Festschrift Stahl, vol. cxi. 1918. C40)
K. MIYAKE, Wachstum des Bliitenschaftes von Taraxacum, Beih. Bot. Zentralbl.
vol. xvi. 3, 1904.

Monocotylae. — (41) PETER STARK, Variabilitat des Laubblattquirls bei Paris
quadrifolia, Zeitschr. f. Botanik, vol. i. 1915 ; id. Bliitenvariationen der Ein-
beere, Zeitschr. f. Abstammungs- u. Vererbungslehre xix. 1918. C42) K. GOEBEL,
Streptochaeta, Flora, 1895, Ergzbd. ; J. SCHUSTER, Grasbliite, Flora, vol. c. 1910 ;
F. KOERNICKE, Handb. d. Getreidebaues, vol. i. Bonn, 1885 ; ALPH. DE CANDOLLE,
Kulturpflanzen, Leipzig, 1884 ; G. SCHNEIDER, Yegetationsvers. mit 88 Hafer-
sorten (bei 2 Sorten fehlt die Ligula), Landwirtsch. Jahrb. vol. xlii. 1913, p.
767 tf'. ; AUG. SCHULZ, Geschichte des Weizens, Zeitschr. f. Naturw. 1911 ; id.
Geschichte des Spelzweizens, Abh. Naturf. Ges. Halle, 1917-18. («) E. HANNIG,
Pilzfreies Lolium, Bot. Ztg. 1907. C44) E. STRASBURGER, Verdickungsweise v.
Palmen, Jahrb. f. w. Bot.- vol. xxxiv. 1906 ; GR. KRAUS, Ann. de Buitenzorg, vol.
xxiv. 1911 ; J. C. SCHOUTE, Dickenwachst. der Palmen, Ann. de Buitenzorg, vol.
xxvi. Leiden, 1912. (45) G. TISCHLER, Parthenokarpe Angiosp.-Friichte, Jahrb.
f. w. Bot. vol. Iii. 1912 ; A. D'ANGREMOND, Parthenokarpie bei Bananen, Ber. deutsch.
bot. Ges. vol. xxx. 1913 ; W. HERRMANN, Blattbewegung der Marantaceen, Flora,
vol. cix. 1916, Diss. Jena ; J. C. COSTERUS, Ban der Blumen von Canna uud der-
jenigen der Marantaceen, Ann. de Buitenzorg, 2e ser. 15, 1916. C46) H. BURGEFF,
Zur Biologie der Orchideen-Mykorrhiza, Diss. Jena, 1909. (4~) H. FITTING, Beein-
flussung der Orchideenbliite durch die Bestaubung usw., Zeitschr. f. Botanik,
vol. i. 1909 ; id. Entwicklungsphysiol. Unters. an Orchideenbliiten, Zeitschr. f.
Botanik, vol. ii. 1910.

SYSTEMATIC INDEX

OF THE

OFFICIAL AND POISONOUS PLANTS

0 Official in Great Britain.

+ Poisonous.

# Official and Poisonous.

before the page indicates figure.

Thallophyta

Claviceps purpurea, *444
Boletus Satanas, *464
Amaiiita muscaria, *465
Amauita phalloide.s, *466
Amauit;i mappa, *466
Amanita verna, *466
Russula emetica, 467
Lactaria tormiuosa, 467

+ Scleroderma vulgar'e, *467, 468

Pteridopbyta
0 Dryopteris (Aspidium) filix mas,

Oil

+ Equisetum, *519, 522

Gymnospermae

+ Taxus baccata, *593, *594, 602

0 Juniperus communis, *587, 602

+ Juniperus sabina, *596, 602

0 Juniperus oxycedrus, 602

0 Abies balsamea, 602

0 Abies sibirica, 602

0 Pinus sylvestris, *601, 602

Querciflorae

0 Quercus iiifectoria, 614

'507,

Urticinae

0 Ficus carica, *618
0 Canuabis sativa, 619

Loranthiflorae
+ Viscum album, *620

Piperinae

0 Piper. Betle, 623

0 Piper nigruiu, *622, 623

0 Piper cubeba, *622, 623

Polygoninae
0 Rheum, species of, 621

Hamamelidinae

0 Liquidambar orientalis, 623
0 Hamamelis virginiana, 623

Tricoccae

+ Mercurialis annua, *623

+ Euphorbia, species of, *624, 626

0 Croton Eleuteria, 627

0 Croton tiglium, 627

0 Ricinus communis, *625, *626 627

773

774

BOTANY

Centrospermae

Agrostemma Githago, 627,

*628

+ Saponaria officinalis, 627, *629
+ Anhalonium, species of, 629

Polycarpicae

+ Ranunculus sceleratus, *633, *634

+ Ranunculus arvensis, 633, *635

+ Caltha palustris, *636

+ Anemone pulsatilla, *635, 636

+ Anemone nemorosa, 636

+ Clematis, species of, 636

+ Helleborus, species of, 636

# Aconitum Napellus, *636, 637, 638

+ Aconitum lycoctonum, and other species,

637

0 Hydrastis canadensis, *638
& Delphinium staphisagria, 638
0 Illicium verum, 632
+ Illicium religiosum, 632
0 Myristica fragraus, *632
© Podophyllum peltatum, 638, *639
0 Jateorhiza columba, 638
0 Cinnamomum Camphora, 639
0 Cinnamomum zeylanicum, 639
0 Cinnamomum Oliveri, 639
0 Aristolochia serpentaria, 639
0 Aristolochia reticulata, 639

Rhoeadinae

0 Papaver somniferum, 643

0 Papaver Rhoeas, *642, 643

0 Cochlearia armor acia, 646

Columniferae

Gruinales

Q Pilocarpus jaborandi, 654

Q Picrasma excelsa, 654

Sapindinae

+ Rims toxicodendron, 655

Frangulinae

Rosiflorae

5 Prunus amygdalus, 664

j$c Prunus laurocerasus, 664

# Quillaja saponaria, *661, 664

Leguminosae

Acacia Senegal, 668

Acacia arabica, 668

Acacia catechu, *666, 668

Acacia decurrens, 668

Cassia augustifolia, *666, 670

Cassia acutifolia, 670

Cassia fistula, 670

Copaifera Langsdorfii, 670

Tamarindus indica, *667, *668, 670

Haematoxylon campechianum, 670

Krameria triandra, *668, 670

Laburnum vulgare, *671

Coronilla varia, *673

Wistaria sinensis, 673

Astragalus gummifer, *672, 673

Glycyrrhiza glabra, 673

Spartium scoparium, 673

Andira araroba, 673

Pterocarpus santalinus, 673

Pterocarpus marsupium, 673

Myroxylon toluifera, 673

Myroxylon Pereirae, *669, *670, 673

Myrtiflorae

* Daphne Mezereum, 673, *674
3^ Daphne Laureola, 673

# Daphne Gnidium, 673

Umbelliflorae

+ Hedera helix, 678

+ Conium maculatum, *683

SYSTEMATIC INDEX OF OFFICIAL AND POISONOUS PLANTS 775

683

+ Cicuta virosa, *680
+ Slum latifolium, 682
+ Oenanthe fistulosa, *681
+ Aethusa cynapium, *682
+ Berula augustifolia, 682

Ericinae

0 Gaultheria procumbens, 686

0 Arctostaphylos Uva ursi, *684, 686

+ Rhododendron, 685

+ Ledum, 685

Primulinae

+ Cyclamen europaeum, *686, 687

+ Auagallis arvensis, *686, 687

+ Primula obconica, 687

+ Corthusa matthioli,' 687

Contortae

0 Olea europaea, *688J'

& Strychnos nux-vomica, 688, *689

0 Gelsemium nitidum, 688

-f Meuyanthes trifoliata, 689

+ Xeriuni Oleander, 689, *691

+ Vincetoxicum officinale, 690, *693

® Hemidesmus indicus, 690

Tubiflorae

0 Exogouium purga, *693
© Ipomoea hederacea, 693
0 Ipomoea orizabensis, 693
© Ipomoea turpethum, 693
© Convolvulus Scammonia, 693
0 Rosin arinus officinalis, 696
© Lavandula vera, *695, 696
© Mentha piperita, 696
© Mentha viridis, 696
0 Mentha arvensis, 696
© Thymus vulgaris, 696
© Mouarda punctata, 696

Personatae

+ Nicotiana tabacum, 699, *700

+ Lycopersicum esculentum, 697

+ Solanum dulcamara, *697

+ Solanum tuberosum, 697

+ Solanum nigrum, 696

+ Atropa Belladonna, *698, 703

+ Datura stramonium, 697, *699, 703

+ Hyoscyamus niger, *701, 703

Q Picorhiza kurroa, 704

Rubiinae

Synandrae

0 Grindelia camportim, 718

Liliiflorae

& Colchicum autumnale, *722, 726

+ Schoenocaulon officinalis, 725

+ Paris quadrifolia, *727

+ Veratrum album, 725, 726

+ Convallaria majalis, 726

Glumiflorae

+ Lolium temulentum, 735, *738

Spadiciflorae

+ Arum maculatum, 741, *743
+ Calla palustris, 741

Scitamineae

INDEX

(Asterisks denote Illustrations)

Abies, *598, 599, 602, 606

Abietineae, 597 ; generative nuclei, 566

Absciss layer, 119, 163

Absorbent roots, 184

Acacia, *171, *664, *665, 667 ; seedling

of, *118

Accessory shoots, 121
Acer, *656 ; bud, *106
Aceraceae, 657
Acetabularia, 404, *406
Achillea, 717'; gynaeceum of, *548
AMya, *432
Achnanthes, 391
Aconitum, *633, 636, *637, 638 ; gynae-

ceum of, *548
Acontae, 393
Acorus, 740, *742 ; flower of, *545 ; root

of, *135
Acrasieae, 385
Acrocarpi, 496
Acrocomia, fruit of, *588
Adam, 638
Actinomorphic, 72
Adaptations, 295 ; origin of, 210
Adonis, *633
Aecidia, 455

Aecidium Euphorbiae, 294
Aegle, 654

Aerenchyma, 49, 167
Aerobes, 275
Aerotaxis, 331
Aerotropism, 352
Aesculus, 657
Aestivation, 87
Aethalium, 384
Aethusa, *682
Agar-Agar, 427
Agaricineae, 465
Agaricus, *464, 467
Agathis, 597, 598
Agave, 726
Aglaozoniu, 414
A'jrirnonia, 661
Agropyrnm, 735

Agrostemma, 627, *628

Agrostis, 734

Aira, 734

Aizoaceae, 627

Ajuga, 695

Akrogynae, 489

Albugo, 432, *433, 434

Albumen crystals, 32

Albuminous substances, 266

Alchemilla, 661 ; flower, *550

Alcoholic fermentation, 275

Alder, Alnus glutinosa

Alectorolophus, 704

Aleurone grains, 30, *31

Alisma, 719, 721 ; embryo of, *576

Alismaceae, 719

Alkaloids, 29, 268

Alkanet, Anchusa

Allium, 725 ; root of, *135, 137

Allogamy, 201, 558

Almond, Primus Amygdalas

Alnus, 610, *611 ; nodules, 261

Aloe, *724, *725 ; epidermis of, *169

Alopecurus, 734

Alpinia, 745

Alsophila, 506, *506, *509

Alstonia, 689

Alternation of generations, 193, 475 ;

scheme of, 543
Althaea, *647, 649
Aluminium, 240
Atnanita, *465, *466, 467
Amarantus, 95
Amaryllidaceae, 726
Amicia, day-position, *358 ; night-position,

*358

Amides, 29
Ammo-acids, 266
Amitotic division, 24
Ammonia, assimilation of, 257
Amoeboid movements, 328
Ampelopsis, *658
Amphibious plants, 293
Amphitheciurn, 481

777

778

BOTANY

Anabaena, 378

Anacardiaceae, 655

Anacyclus, 718

Anaerobes, 275

Anagallis, *686, 687 ; pyxidium, *583

Anakrogynae, 489

Ananassa, 730

Anaphase, 23

Anaptychia, spermogonium, *473

Anastatica, 333, 645

Anatropous ovule, 539, *540

Anchusa, 694

Andira, 673

Andreaea, *491, 494

Andreaeales, 494

Androecium, 546

Andromeda, 685

Andropogon, 734

Aneimia, *509

Anemone, *635, 636

Anemophilous plants, 552

Anethum, 682, 683

Aneura, 81, 488

Angiopteris, 503

Angiospermae, systematic arrangement,

606
Angiosperms, 542 ; flower, 545 ; fossil, 749 ;

macrospores, 571 ; micros pores of, 570
Anhalonium, 629

Animals, distribution of fruits by, 586
Anise, Pimpinella Anisum
Anisophylly, 116, *117
Annual rings, 153
Annularia, *521, 522
Annulus, 334, 508
Anonaceae, 632
Antennaria, 716
Anthemis, 717
Anther, 540, 546
Antheridial mother cell, 542
Antheridium, *199, *201, 369
Anthoceros, 477, *484
Anthocerotales, 483
Anthoclore, 29
Anthocyanins, 29
Anthophaeine, 29
Anthoxanthine, 29
Anthoxanthum, 734
Anthriscus, 682 ; flower of, *559
Anthurium, 740
Anthyllis, 672
Anticlinal cell walls, 307
Antirrhinum, 703 ; capsule, *583
Ants, distribution of seeds by, 587
Apical cell, 46, 78, 79, 85, 131
Apium, 682

Apocarpous gynaeceum, 547
Apocynaceae, 689
Apogamy, 202, 316, 511, 578 ; in Mar-

silia, 517
Apospory, 511, 578

Apothecium, 439

Apple, Pyrus mains

Apposition, growth by, 35

Apricot, Prunus armeniaca

Aquifoliaceae, 655

Aquilegia, *633, 637

Araceae, 740

Arachis, 672, 673

Araliaceae, 678

Araucaria, 597, 598, 599 ; prothallial cells,

566

Archaeocalamites, *521, 522
Archangelica, 682
Archegoniatae, 367
Archegonium, *201, *511
Archidium, 496
Archimycetes, 429
Arctostaphylos, *684, 685, 686
Arcyria, *382
Areca, 740
Arenga, 740
Argemone, 642
Arillus, 582

Aristolochia, *95 ; flowers of, *561 ; polli-
nation of, 556, 560 ; vascular bundle,

*145

Aristolochiaceae, 639
Armeria, *549
Armillaria, 466 ; basidium, *452 ; clamp

formation, *462
Arnica, *712, *713, *717, 718
Arrhenatherum, 734
Artemisia, *715, 718
Artichoke, Cynara Scolymus
Artificial system, 365
Artocarpus, 618
Arum, 741, *743
Ascent of water, 236
Asclepiadaceae, 689
Asdepias, *693
Ascodesmis, 438
Ascolichenes, 471
Ascomycetes, 437 ; asexual reproduction,

439 ; sexual organs, 438
Ascus, 437, 439
Asexual reproductive cells, 195
Ash, Fraxinus

Ash of plants, constituents of, 221, 238
Asparagin, 258
'Asparagus, 72.5
Aspergillaceae, 441
Aspergilli/s, 438, 441, *442 ; couidiophore,

*196

Asperula, 704

Aspidistra, pollination of, 558
Aspidium, *497, 506, *507, 511
Asplenium, development of the sporangium

of,- *500
Assimilated material, quantity of, 253 ;

transformation of. 263 ; translocation

of, 263

INDEX

779

Assimilation, 247 ; amount of, 254 ; of

carbon dioxide, products of, 252
Assimilation experiment, *253
Aster, 716
Asteroxylon, 501
Astragalus, *672, 673
Atriplex, 627

Atropa, 697, *698, 699, 703
Atropous ovule, 539, *540
Attaching roots, 184
Auricularia, 460
Auricularieae, 460
Autogamy, 201
Autonomy of characters, 322
Autotrophic connophytes, 165
Autumn Crocus, Golchicum autumnale
Autumn wood, 153, 154
Auxanometers, 27S, *279
Auxiliary cells, 425
Auxospores, 389, *391
A vena, 734
Avicennia, 694
Axillary buds, 121
Azolla, 513, 515
Azotobacter, 259
Azygospores, 435

Bacillariaceae, 387

Bacillus, 370, *371, *372, 373, 374

Bacillus radidcola, 260

Bacteria, *74, 370 ; pathogenic, 374

Bacterioids, *260

Bacterium, 370

Balsamodendron, 655

Bambusa, 730, 734

Banana, Musa

Banyan, Ficus bengalensis

Bark, 59 ; formation of, 163

Barley, Hordeum vulgare

Barosma, 654

Bartsia, 191, 259, 704

Basidiobolaceae, 436

Basidiobolus, 428, 436

Basidiolichenes, 474

Basidiomycetes, 451

Basidiospores, 451, 455

Basidium, 437, 451, 455

Bast, 68, 158

Bast fibres, 158

Batrachium, 636

Batrachospermum, 423, *424, *425

Beaked Parsley, Anthriscus

Beech, Fagus sylvatica

Beet, Beta vulgaris

Beetles, pollination of flowers by, 607

Beggiatoa, 371, 376

Begonia, 195 ; regeneration, *283, *285

Ben nett itaceae, 605

Bennettites, *605, *606

Benthos, 74

Berberidaceae, 638

Berberis, 638

Berry, 584

Berula, 682

Beta, 627

Betula, 610, *6ll

Betulaceae, 609

Biddulphia, *390

Bignoniaceae, anomalous secondary growth,

*183

Biogenetic law, 209
Bird's-Foot, Ornithopus sativus
Bird's-foot Trefoil, Lotus
Bird's-nest Orchid, Neottia
Bitter principles, 29
Bitter-sweet, Solanum dulcamara
Blackberry, Rubus
Black Currant, Ribes nigrum
Black Mustard, Brassica nigra
Blaeberry, Vaccinium myrtillus
Blasia, 80, *81, *488, 489
Bleeding, 234

Blue-green Algae, Cyanophyceae
Bocconea, 642
Boehmeria, 619
Bog-Bean, 3fenyanthes
Bog Mosses, Sphagnaceae
Boletus, *464
Borage, Borago
Boraginaceae, 694
Borago, *694
Bordered pit, *67
Bostryx, *130
Boswellia, 655
Botrychium, *504, 505
Botrydium, *408
Bouditra, 438, *447
Bovista, 468
Bowenia, 589
Bracteal leaves, 118
Bracteole, 123
Branching, 75 ; cymose, 76, 127 ; dicho-

tomous, 75, *76; false, 76, *78 ;

lateral, 75, *76 ; monopodial, 126 ;

racemose, 125 ; of the root, 138
Branch system, construction of, 123
Brassica, *643, *644, 645
Brim, 734

Broad Bean, Vicia Faba
Bromeliaceae, 730
Bromus, 734

Brown Algae, Phaeophyceae
Bruguiera, 674
Bryales, 494

Bryonia, 709 ; pollen, *541
Bryony, Bryonia
Bryophyllum, 195, 658
Bryophyta, 80, 475 ; antheridia, 477 ;

archegonia, 478 ; fossil, 482 ; phylo-

geny, 481 ; sexual reproduction, 200 ;

sporogonium, 480
Bryopsis, 406, 407

780

BOTANT

Buckwheat, Fagopyrum esculentum

Bud, 86, *88, *89, 176

Bud-scales, 176, 308

Bugloss, Echium

Bulbils, 194

Bulbochaete, 403, *405

Bulbs, 179, 194

Bundle sheath, 102

Burdock, Lappa

Burnet-Saxifrage, Pimpinella

Burseraceae, 655

Butea, 673

Butomus, 719, 721

Butter-Bur, Petasites officinalis

Buttress-roots, 140

Cabomba, *631, 632

Cactaceae, 628

Caeoma, 460

Caesalpiniaceae, 668

Cakile, 646

Calamagrostis, 734

Calamariaceae, 502, 522

Calamostachys, *521, 522

Calamus, 740

Calcium oxalate, 30

Calendula, 718

Calla, 741 ; pollination of, 558

Callithamnion, 422, *424

Callitris, 606

Callose, 64

Calluna, 686

Callus, 64, 159, 164, 298 ; wood, 164

Calobryum, 489

Caltha, *636

Calycanthus, 630

Calyptra, 131

Calyptrosphaera, *379

Calystegia, 693

Calyx, 546

Carabial cells, shape of, *146

Cambium, 47, 100, 142, *145, 147 ;

fascicular, 144 ; interfascicular, 144 ;

repeated formation of, 148 ; in root,

147

Campanula, 709, *711
Campanulaceae, 709
Campylotropous ovule, *540
Canadian Water-weed, Elodea canadensis
Canarium, 655
Cane-sugar, 252, 265
Canna, *746 ; flower of, *552
Cannabinaceae, 618
Cannabis, 618, 619
Cannaceae, 745
Cantharellus, 466
Caoutchouc, 268, 626, 689
Capillitium, 382
Capitulum, 127
Capparidaceae, 646
Capparis, *171, 646

Capriflcus, 556

Caprifoliaceae, 705

Capsdla, *643, 646 ; embryo of, *576 ;

seed, *581
Capsicum, 697, 703
Capsule, loculicidal, 583 ; poricidal, 583 \

.septicidal, 583

Carbohydrates, hydrolysis of, 264 ; fer-
mentations of, 275
Carbon, 221
Carbon dioxide, 245, 247 ; assimilation of,

247

Cardamine, 195, *643
Cardinal points, 219
Carduus, *712, *713
Carez, 731, *732
Carnivorous plants, 185, 258
Carotin, 18

Carpels, 198, 539, 547
Carpinus, 611, *612
Carpodinus, 689
Carpogonium, 424
Carpospores, 424
Carragheen, 427
Carrot, Daucus
Carroway, Garum Carvi
Carum, *679, 681, 683
Caruncula, 582, 624
Carya, 609
Caryophyllaceae, 627
Caspary's band, 57, *58
Caspary's dots, 135
Cassia, *666, 668, 670
Gassy tha, 639
Castanea, 612, *614
Castilloa, 618

Casuarina, chalazogamy, 573
Catkin, *126
Cattleya, 749
Caiderpa, 195, *406
Cauliflory, 651
Cecidia, 295
Gedrus, 606

Celandine, Chelidonium majus
Celery, Apium
Cell-budding, 26
Cell division, 21, *22 ; causes of, 307 ;

a process of reproduction, 310
Cell fusions, 44, 69
Cell plate, 24
Cell sap, 12, 28
Cell wall, 34 ; anticlinal, 47 ; chemical

nature of, 37 ; periclinal, 47
Cells, constituent parts of, 1 1 ; embryonic,

*11 ; form and size of, 10
Cellular plants, 366
Cellulose, 37 ; as a reserve substance,

265

Celtis, 617
Centaurea, 713 ; seismonastic movements,

*362

INDEX

781

Centaury, Eryihraea

Central cylinder, 92, 94

Centriole, 12

Centrosper-mae, 627

Cephalanthera, 746

Cephalotaceae, 639

Cerastium, 627

Ceratiomyxa, 384

Ceratium, *387

Ceratocorys, *387

Ceratonia, 670

Cemtozamia, 589, *591

Cerbera, 689 ,' fruit of, *586

Cercis, *666, 670

Cereus, *174, 629, *630

Ceriops, 674

Oetraria, *469, 471, *472, 474

Chaerophyllum, 682

Chaetocladium, 435

Chalaza, 539

Chalazogamy, 573

Chamomile, Matricaria Chamomitta

Cham, *419, *420, 421

Characeae, 14, 24, 418

Chasmogamous flowers, 561

Cheiranthus, *643, *644, 645

Ckeirostrobus, 522

Chelidoiiiiim, 642 ; mutation, *325 ; seed
of, *581

Chemical influences, effect on development,
293

Chemonasty, 358

Chemosynthesis, 254

Chemotaxis, 331

Chemotropism, 352

Chenopodiaceae, 627

Chenapodiuwij 627

Cherry Laurel, Pr units laurocerasiw

Chervil, Chaerophyllum

Chestnut, Castanea vulgaris

Chicory, Oichorium Intybus

Chimaeras, 299, *302 ; periclinal, 301

Chiropterophilous plants, 558

Chitin, 38

Chlamydomonas, 398, *399

Chlamydothrix, 376

Chlaramoeba, *397

Chlorella, 400, *401

Chlorococcum, 400, *401

Chlorophyceae, 398

Chlorophyll, 18, 250 ; absorption spec-
trum of, *249

Chloroplasts, 17, 250 ; movements of, 330
*331

Choiromyces, 448

Chondriodernia, *13, 382, *383

Chondriosornes, 16

Chondromyces, *385

Cfwndrus, *422, 427

Choripetalae, 609

Chromatin, 17

Chromatophores, 11, 17 ; inclusions of, 32 ;

multiplication of, 24
Chromoplasts, *20
Chromosomes, 21
Chroococcus, 377
Chroolepideae, 402
Chroolepus, 402
Chrysamoeba, *378, 379
Chrysanthemum, 718
Chrysidella, 380
Chrysomonadinae, 379
Chrysojphlyctis, 429
Chrysosplenium, pollination of, 558
Chytridiaceae, 429
Cibotium, 511
Cichorium, *713, 716
Cicuta, *680, 682
Cilia, 328
Cimicifuga, *633
Cinchona, 704, *705, *706
Ciucinnus, *129, *130
Cineraria, 718
Cinnamomum, 639. 749
Circaea, 674
Circulation, 13
Circumnutations, 336
Cirsium, 713
Cissus, tendrils, 354
Cistaceae, 647
Cistern epiphytes, 185
Cistiflorae, 646
Citrullus, 709, *710
Citrus, 652, *653, 654
Cladodes, 171
Cladonia, 471, *473, 474
Cladophora, *77, 78, 404, *406 ; cell of,

*17, *25 ; chloroplast of, *18 ;

polarity, 284
Cladostephiis, *79, 409
Cladothrix, *371, 375
Clavaria, *463
Clavarieae, 463

Claviceps, 443, 444 ; sclerotium of, *41
Cleistogamous flowers, 561
Cleistogamy, 561
Clematis, *98, 636
Climbers, anomalous secondary growth,

182

Climbing plants, 182
Clivia, 726
Closterium, 393, *394
Clostridium, 259, 372
Clove, Eugenia caryophyllata
Clover, Trifolium
Club Mosses, Lycopodinae
Cnicxs, 713, *714
Cobaea, tendrils, 354
Cocci, 370

Coccolithophoroideae, 380
Cocconels, 391, *392
Cochlearia, 646

782

BOTANY

Cocoa tree, Theobro'ma Cacao

Coco-nut Palm, Cocos nucifera

Cocos, *739, *740, *741

Coenogametes, 429

Co/ea, 704, *707

Coffee plant, Co/ea

Cohesion, mechanisms, 334 ; theory, 237

Cola, 651

Colchicum, *722, 724, 726 ; seed of, *5SO

Coleochaete, 404, *405

Collective species, 322

Collema, 474 ; carpogonium, *473

Collenchyma, 61, *62

Colleter, *57, 176

Colletia, 657

Colloidal solutions, 15

Colouring matters, 268

Colours of flowers, 554

Coltsfoot, Tussilago Farfara

Columella, 483, 492

Columniferae, 647

Combinations, 325

Comfrey, Symphytum

Commelina, 730

Commelinaceae, 730

Commiphora, 655

Companion cells, 158

Compass plant, Lactuca Scariola

Compass plants, 351

Compensations, 297

Complementary tissue, 59

Compositae, 711

Conducting tissues, 62

Conduction, 243

Conferva, *397

Conidiospores, 195

Coniferae, 592 ; microspores of, 566

Conium, *678, 682, *683 ; ovary of, *549

Conjugatae, 392

Conjugation in Spirogyra, 396

Connecting threads, *44

Connective, 546

Consortium, 469

Contact, stimulus of, 292

Contortae, 687

Contractile roots, 180

Convallaria, *100, *107, 725

Convergence of characters, 174

Convolvulaceae, 691

Convolvulus, 691, 693

Copalfera, 669, 670

Cora, 470, *474

Coralliorrhiza, '*191, 256, 746

Cor chorus, 649

Cordaitaceae, 604

Cordaites, *604, 605

Cordyline, *143, 725

Corethron, *390, 391

Coriandrum, *678, 683

Cork, *10, 58, *59, *160, *161 ; stone, 58

Cork cambium, 58, 162

Cork cells, 162
Cork oak, 162

Cormophytes, 73 ; gametophyte of, 83
Cormus, 83 ; adaptations of, -165 ; con-
struction of the typical, 84 ; secondary
growth iu thickness of, 140

Cornaceae, 678

Cornelian Cherry, Cornus mas
Cornus, *678

Corolla, 546

Coronilla, 672, *673

Correlation, 296, 310, 314

Corsinia, sporogonium, *480

Cortex, 92

Corydalis, *642, 643 ; seed of, *581

Corylus, 611 ; catkin of, *553

Cosmarium, 393, *394

Cotton, hairs of, 54, *55

Cotton-grass, Eriophorum angustifolium

Cotyledons, 117, 565, 575 ; number of, 588

Cowberry, Vaccinium iritis idea

Crambe, *643, 646

Crassula, 658

Crassulaceae, 658 ; respiration, 271

Crataegomespilus, 299

Crataegus, 661 ; leaf of, *109, *608

Craterellus, 463

Crenothrix, 371, 376

Orepis, 716

Cribraria, 384

Cribraria rufa, *382

Crinum, 726

Crocus, *728

Crossotheca, *535, 536

Cross-pollination, 201, 558

Croton, 625, 627

Crown-gall, 373

Cruciferae, 643

Crustaceous lichens, 470

Cryptogams, 366

Cryptomeria, 606

Cryptomonadinae, 380

Cryptomonas, *380

Cryptospora, *443

Cucumber, Cucumis sativus

Cucumis, 709

Cucurbita, 95, 709 ; pollen-grain of, *36 ;
sieve-tubes, *63 ; tactile pits, *353

Cucurbitaceae, 707 ; tendrils, *354

Cupressineae, 596

Cupressus, 597

Cupuliferae, 611

Curcuma, 745

Curvature, 327

Cuscuta, 189, *190, 259, 693

Cuticle, 50

Cutinisation, 38, 39

Cutis tissue, 57

Cutleria, *413, 414

Cutleriaceae, 414

Cuttings, 284

INDEX

783

Cyanophyceae, 376
Cyathea, 506
Cyatheaceae, 509
Cyathium, *624, 625
Cycadaceae, 589
Cycadeae, male cells, 562
Cycadeoidea, *605, 606
Cycadiuae, 589
Cycadites, 605
Cycas, 589, *590, *591
Cyclamen, *686, 687
Cydonia, 660, 661
Gylindrocystis, *393
Cynara, 713
Cyperaceae, 730
events, 730, 731
Cypress, Cupressus sempervirens
Oypripedium, 746 ; embryo-sac, 572
Cystocarp, 424
Cystodintum, *386, 387
Cystolith, 36, *37
Cystopus, 432
Cytisus, 671, 673
Cytology, 10

Cytoplasm, 11, 15 ; division of, 24 ; in-
clusions of, 28

Dactylis, 734

Dahlia, 717 ; root-tubers, *178

Dammara, 606

Dandelion, Taraxacum officinale

Daphne, 673, *674

Darwinism, 212

Date Palm, Phoenix

Datura, 697, *699, 703

Daucus, 682

Day-position, 357

Deadly Nightshade, Atropa Belladonna

Death, 220

Deciduous trees, 305

Delesseria, *79, 422, 427

Delphinium, 638 ; ovary of, *547

Dendri'ibiuiiii 749

Dentaria, bulbils, *194

Dermatogen, 86

Descent, theory of, 206

Desert, 219

Desmidiaceae, 393

Desmids, movements, 328

Desmodium, movement, 337

Determinants, 296, 317

Determination of sex, 314

Deutzia, 659

Development, 217, 278 ; commencement
of, 304 ; course of, 301 ; factors of,
288 ; external factors, 288 ; internal
factors, 296

Developmental physiology, 278

Diageotropism, 342

Dialypetalae, 629

Dianthus, 627

Diapensia, ovary of, *548

Diastase, 264, 265

Diatomeae, 387 ; Centricae, 389 ; Pennatae,
391 ; movements, 328

Diatoms, Diatomeae

Dicentra, 643

Dichasium, 127, *129, *130

Dichogamy, 559

Dichotomosiphon, 407

Dichotomous branching, 119

Dicksonia, 506

Diclinous flower, 545

Dicotylae, 608

Dicotyledons, secondary thickening of,
143 ; systematic arrangement of, 607 ;
wood of, 154

Dicranophyllum, 605

Dictamnus, 652

Dictyonema, 474

Dictyostdium, 385

Dictyota, *76, 79, 409, *414, 415 ; grow-
ing point of, *80

Dictyotaceae, 415

Diervilla, 706

Diffusion, 224, 243

Digitalis, *702, 703, 704

Dihybrids, 322

Dilatation, 160

Dill, Anethum

Dimorpha, *381

Dimorphothfca, 718

Dinobryon, *378, 379

'Dinoflagellatae, 386

Dionaea, *187

Dioon, 589 ; fertilisation, 564 ; pro-
embryos, *565

Diospyrinae, 686

Diospyros, 686

Dipsaceae, 706

Dipsacus, 706, *709

Dipterocarpaceae, 647

Dischidia, *184, 690

Discomycetes, 445

Distephanus, *379

Distomatineae, 381

Divergence, 89 ; angle of, 89

Dodder, Cuscuta

Dogwood, Oornus sanguinea

Dominance, rule of, 321

Dorema, 683

Doronicum, 718

Dorsal suture, 547

Dorstenia, 618

Dracaena, 725, *726, 749

Drepauium, *130

Drimys, 632

Drip -tip, 168

Drosera, *185, *186, 195 ; chemonastic
movements, 359

Droseraceae, 639

Drupe, 584

784

BOTANY

Dryas, 663

Dryobalanops, 647

Dryopteris, *497, 506, *507, *509, 511

Dry Rot fungus, Merulius lacrymans

Dudresna.ya, 425, *426

Duration of life, 309

Early wood, 153

Ebenaceae, 686

Ecballium, *709

Eccremocarpus, tendrils. 354

Echinocactus, 629

Echinodorus, *720

Echinops, 713

Echium, *694

Ecology, 3 ; of flower, 551

Ectocarpus, 409, *413

Edelweiss, Leontopodium

Egg-cell, 199

Elaeagnaceae, 673

Elaeagnus, 673 ; nodules, 261

Elaels, 740

Elaphomyces, 442

Elaphomycetaceae, 442

Elasticity, 60

Elder, Sambucus

Elementary species, 322

Elettaria, 745 ; seed of, *581

Elodea, 721

Elongation, phase of, 284

Embryo, 202, 575

Embryo-sac, 539, *57l

Embryonic rudiments, 282

Emergences, 56

Empusa, 435, *436

Enantioblastae, 730

Encephalartos, 589, 606

Enchanter's Nightshade, Oircaea

Endive, Cichorium endivia

Endocarp, 583

Endocarpon, 471

Endodermis, 57, 94, 135

Endophyllum, 459, *460

Endosperm, 565, 580 ; development of,

574 ; nucleus, 574
Endospores, 195
Endothecium, 481, 546
Energy, liberation of, 273
Enteromorpha, 402, *403
Entomophilous plants, 553
Entomophily, 556
Entomophthorineae, 435
Enzymes, 264

Ephedra, *602, *603 ; prothallia, 569
Epidermal system, 49
Epidermis, *49, 92
Epigeal germination, 589
Epigynous flower, *549, 550
Epilobium, 674
Epipactis, 746 ; cell of, *25
Epiphyllum, 629

Epiphytes, 183, 228

Epipogon, 191, 256, 746

Epithema, 113

Equisetaceae, 502, 51 7

Equisetinae, 517

Equisetum, *86, *87, 95, 517, *518, *519,

*520, 522 ; germination of the spores

of, 290

Ergot, 443, 444
Ergot, Claviceps purpurea
Erica, 686
Ericaceae, 684
Ericinae, 684
Erigeron, 716
Eriobotrya, 661
Eriophorum, 730, *731
Erodium, fruit of, 334
Erophila, 646
Erysibaceae, 438, 440
Erysibe, 440, 441
Erysiphe, *27
Erythraea, 689
Erythroxylaceae, 652
Erythroxylon, *652
Escholtzia, 642
Ethereal oils, 30, 268
Etiolation, 289
Eucalyptus, 235, 675, 676
Eucheuma, 428
Eudorina, 399, 400
Eugenia, 675, *676
Euglena, *380, 381
Euglenineae, 380
Eumycetes, 436

Euphorbia, *174, *623, *624, 625, 626
Euphorbia Cyparissias, 294
Euphorbiaceae, 623
Euphrasia, 191, 259, 704
Eurotium, 441
Euryale, 632
Eusporangiatae, 503
Everlasting flowers, Helichrysum
Everlasting Pea, Lathyrus
Evolution, 2

Excretion of water, causes of, 234
Exine, 541
Exoasceae, 449
Exoascus, 449
Exobasidiineae, 461
Exobasidium, *460, 461
Exocarp, 583
Exodermis, 135
Exogonium, *693
Exospores, 195
Exothecium, 546
External factors, purposiveness of the

reactions to, 295
External segmentation, 71
Extrorse, 546
Exudation, 232, *233
Eye-spots, 20

INDEX

785

Fagopyrum, 621 ; achene, *583 ; ovary
of, *549

Fagus, 612, *613, *614

False Acacia, Robirtia

Fascicular cambium, *144

Fats, 30, 266

Fegatella, antheridium, *477

Fennel, Foeniculum

Fermentation, 269, 274 ; bacteria of, *373 ;
products of, 276

Ferns, Filicinae

Ferns, venation of, *500

Fertilisation, 202, 314

Ferula, 683

Festuca, *733, 734 ; flower of, *554

Ficus, 617, *618

Fig, Ficus carica

Filago, 717 *

Filament, 546

Filamentous bacteria, Trichobacteria

Filamentous lichens, 470

Filices, 502, 505

Filicinae, 501, 503

Filicinae eusporangiatae, 502

Filicinae leptosporangiatae, 502

Flagella, 328

Flagellata, 378

Flagellates, Flagellata

Flax, Linum usitatissimum

Floral axis, 549

Floral diagrams, 551

Floral formula, 551

Florideae, 421 ; climbing parts, 356

Flowers, conditions of the formation of,
312 ; morphology and ecology of,
544 ; protandrous, 559 ; protogynous,
559

Foeniculum, *678, 682, 683

Foliaceous lichens, 470

Foliage leaf, diagram of, *109

Follicle, 583

Fomes, *464, 465

Fontinalis, 496

Food materials, assimilation of, 247 ; in-
dispensable, 239

Fool's Parsley, Aethusa cynapium

Foreign organisms, effect on development,
294

Forget-me-not, Myosotis

Formative tissues, 46

Fossil Angiosperms, 749 ; Gymnosperms,
604

Foxglove, Digitalis

Fragmentation, 24

Fragraria, 663

Fragraria monophylla, 325

Frangulinae, 657

Fraxinus, 687, *689

Free cell formation, 26

Free nuclear division, 26

Freycinetia, 737 ; pollination of, 558

FritiUaria, 726

Fruit, 582 ; collective, 582 ; dehiscence
of, *583 ; indehiscent, *583 ; partial,
582 ; ripening of, 269 ; spurious, 584

Fruttania, 488, *489

Fmticose lichens, 470

Fucaceae, 410, 416

Fucoxanthin, 19

Fucus, 410, *411, *416, *417

Fidigo, 384

Fumaria, nut, *583

Fumariaceae, 643

Funaria, 494, 496 ; archesporium, *481 ;
antheridium, *477 ; chloroplasts, *18 ;
included starch grains, *24 ; proto-
nema, *476 ; sporogonium, *481

Fungi, nitrogenous food, 258

Funiculus, 539

Funkia, egg apparatus, *572 ; embryos in,
y/o

Furze, Ulex

Galanthus, 726

Galeopsis, *695

Galium, 704 ; schizocarp, *583

Galls, 294, 295, 614 ; histoid, 295 ;

organoid, 295
Gametangia, 199, 369
Gametes, 198, 369
Garcinia, 647
Gases, absorption of, 244, 245 ; movement

of, 246

Gasteromycetes, 467
Gaultheria, 686
Geaster, 468
Geitonogamy, 201
Gelatinous lichens, 470
Gelidium, 428
Gelsemium, 688
Gemmae, 193, 194
Generative cells, 542, 561
Genes, 317
Genetic spiral, 90
Genista, 671

Gentiana, 688, 689, *690
Gentianaceae, 688
Geographical distribution, 209
Geophytes, 177 ; movement, 327
Geotropic curvatures, 341
Geotropic movement, *341
Geotropic position of rest, alteration of

344
Geotropism, 339, 340, 346 ; negative,

340; a phenomenon of irritability,

346 ; positive, 342
Geraniaceae, 651

Geranium, *651 ; flower of, *552
Germination, 202, 304, 305, 587
Genm, 663

Gigartina, 422, *423, 427
Ginger, Zingiber officinal*

786

BOTANY

Ginkgo, 591, *592, 606 ; male cells, 562 ;

pollen-grain, *562 ; ovule of, *563
Ginkgoaceae, 591
Ginkgoinae, 591
Girders, 93
Gladiolus, 730
Glandular cells, 70
Glandular epithelium, 70
Glandular hair, *70
Glandular scale, *70
Glandular tissue, 70
Glaucium, *642
Gleba, 468
Glechoma, 696

Gleditschia, 670 ; stem-thorn of, *174
Gleicheniaceae, 509
Globoid, *31
Gloeocapsa, *40, 377
Glucosides, 29, 268
Glumiflorae, 730
Glycogen, 28
Glycyrrhiza, 672, 673
Gnaphalium, 716
Gnetaceae, 602
Gnetinae, 602
Gnetineae, microspores, 569
Gnetum, 602, *603 ; embryo-sac, *569
Gooseberry, Riles grossularia
Gossypium, *55, *648, 649
Graft hybrids, 299
Grafting, 297, *298
Gramineae, 732
Grand period of growth, 280
Grape Vine, Vitis vinifera
Graphis, 471

Grass -haulm, geotropic erection of, *342
Grass-wrack, Zostera marina
Gratiola, *701, 703
Gravity, effect on development, 291
Grijfithia, 427
Grindelia, 718

Ground-nut, Arachis hypogaea
Growing point, 84, 282, *307
Growth, 217, 278, 306 ; and cell division,

306 ; distribution of, 280 ; grand

period of, 280 ; measurement of, 278 ;

phases of, 282 ; rate of, 279, 281
Growth in thickness, primary, 140, 286 ;

secondary, 142
Gruinales, 651 .

Guard cells, 52, 53 ; movements of, 231
Guiacum, 652
Gum-resins, 268
Gutta-percha, 268, 689
Guttiferae, 647
Gymnadenia, 746
Gymnodiniaceae, 386
Gymnospermae, 589
Gymnosperms, 542 ; flowers of, 544 ;

secondary thickening of, 143 ; sexual

generation, 561 ; wood of, 150

Gymnosporangium, *457
Gynaeceum, 546, 547
Gynandrae, 745
Gynostemium, 745
Gyromitra, 447

Haastia, 716

Hadrome, 68

Haemanthus, 726

Haematococcus, 398, *399

Haematoxylin, 158

Haematoxylon, 158, 670

Hagenia, 661, *662, 664

Hairs, 54 ; scale, *56 ; stellate, *55 ;

stinging, *57
Halasphaera, 397
Halimeda, 406
Halophytes, 169
Hamamelidaceae, 623
Hamamelidinae, 623
Hamamelis, 623
ffancornia, 689
Haplobacteria, 371, 372
Haplomitrieae, 489
Haplomitrium, *489
Haptotropisin, 353
Hart's-Tongue Fern, Scolopendrium
Harveyella, 427
Haustoria, *77, 191

Hawthorn, Crataegus (Mespilus) oxycantha
Hay bacillus, Bacillus subtilis
Hazel, Gorylus avellana
Head, 127
Heart- wood, 158
Heat, production of, 276
Heather, Calluna vulgaris
ffedera, 678
Hedychium, 745
Helianthemum, *646, 647
ffelianthus, *713, 717 ; embryo-sac of,

*575

Helichrysum, 716
Heliotropism, 348
Ifelleborus, 636 ; foliage leaf, *119
Helobiae, 719

Hemerocallis, anther of, *541
Hemicelluloses, 37
ffemidesmus, 690
Hemlock, Conium maculatum
Henbane, Hyoscyamus niger
Hepaticae, 475, 482, 483
Herbs, 141 ; annual, 180 ; perennial, 176
Hercogamy, 560
Heredity, 316
Heterocontae, 396
Heteroecious, 458
Heteromerous lichens, 470
Heterophylly, 116, 308
Heterostyly, 560 ; dimorphic, 560 ; tri-

morphic, 560
Heterotrophic cormophytes, 188

INDEX

787

Heterotrophic plants, 254

Heterotype division, 205

Heterozygotes, 317

Hevea, 626

Hexoses, 38

Hibernacula, 194

Hibiscus, 649

Hieracium, *713, 716 ; apospory in,

*579

Hilum, 579
Hippocastanaceae, 657
Hipiiophae, 673
Hippuris, *87
Histology, 40
Holcus, 734
Holly, Ilex aqu (folium
Homoiomerous lichens, 470
Homotype division, 205
Homozygotes, 317

Honeysuckle, Lonicera peridymenum
Hoodia, 690
Hop, Humid us lupulus
Hordeum, 733, 734, *735 ; apex of a

root, *133

Hornbeam, Carpinus Bet id us
Hornea, 501

Horse-chestnut, Aescidus hippoca-stannm
Horse-tails, Equisetineae
Hoya, 690
Humulus, 618, *619
Hyacinthus, 725
Hyaloplasm, 15
Hybrids, 317 ; inheritance in, 319 ; in

nature, 317
Hydathodes, 71, 168
Hydneae, 463
Hydnophytum, 704
Hydnum, *463
Hydrangea, 659
Hydrastis, *638
Hydrocharis, 194, 721
Hydrocharitaceae, 721
Hydrodictyon, 401
Hydrophilous plants, 553
Hydrophytes, 165
Hydropterideae, 502, 512
Hydrotaxis, 332
Hydrotropism, 352
Hydrurus, 379
Hygrophytes, 167
Hygroscopic movements, 333
Hymenogastreae, 468
Hymenolichenes, 474
Hymenomycetes, 461 ; clamp connections,

461

Hymenophyllaceae, 509, 510
Hyoscyamus, 697, 699, *701, 703; seed

of, *581 ; stamen of, *547
Hypanthium, 550
Hypericum, 647
Hyphae, *77

Hypholoma, basidium, *452 ; cell of, *16

Hypnodinium, 387

Hypochnus, 462

Hypocoty], 565

Hypogeal germination, 589

Hypogynous flower, *549, 550

Hypophysis, 575

Iberis, 646

Ilex, 655, *656

Illicium, 632

Imbibition, 223 ; mechanisms, 333

Immunity, phenomena of, 295

Indian Hemp, Canndbis sativa

Indusium, 508

Inflorescences, 125 ; diagrams of, *128

Initial cells, 46, *80

Initial layer, 144

Inorganic material, oxidation of, 274

Insectivorous plants, 185, 258

Integuments, 539

Intercellular spaces, 44, 246 ; lysigenous,

45 ; schizogenous, 45
Intercellular system, 45
Interfascicular cambium, *144
Internal differentiation, 287
Interuodes, 88
Intine, 541

Intramolecular respiration, 272
Introrse, 546

Intussusception, growth by, 35
I aid a, 716
Inulin, 28, 265
Iodine, 240
Ipomoea, 693
Iridaceae, 726
Iris, *728, *729, 730 ; diagram of, *551 ;

seedlings, *588
Irritability, 215
Isatis, 644, 646
Isoetaceae, 502, 530
Isoetes, 523, 530, *531
Isogamy, 198, 369
Isosmotic solutions, 224
Ithyphallus, *468
Ivy, Hedera Helix,

Jasione, 709

Jasminum, 687

Jateorhiza, 638

Jerusalem Artichoke, Helianthus tuberosus

Juglandaceae, 609

Juglandiflorae, 609

Juglans, 609, *610 ; fertilisation, *574

Juglans regia, chalazogamy, *573

Juncaceae, 721

Juncu.s, *721

Jungennannia, 489

Jungermauniales, 488

Juniperus, *97, *595, *596, 597, 602

788

BOTANY

Kandelia, 674 ; seedling, *588

Karyokinesis, 21

Kickxia, 689

Kidney Bean, Phaseolus

Kidney-Vetch, Anthyllis

Kieselguhr, 392

Klinostat, 340, 350

Knautia, 707

Knight's experiments, 339

Krameria, *668, 670

Labiatae, 694

Laboulbeniaceae, 438, 450

Laburnum, *668, *671, 673

Laburnum Adami, 299, *300

Laburnum, Laburnum vulgare

Lachnea, 438, *445

Lactaria, 466, 467

Lactuca, 716

Ladies' Slipper, Cypripedium

Laelia, 749

Lagenostoma, *535, 536

Lamarckism, 210

Lamina, 108

Laminaria, 409, *410, *415, 416, 418

Laminariaceae, 409, 416

Lamium, *694, 695

Landolphia, 689

Lappa, *712, 713

Larch, Larix europaea

Larix, *600

Late wood, 153

Lateral branches, direction and intensity

of growth of the, 125
Lateral branching, 120 ; types of, 125
Lateral buds, position of the leaves of,

122

Lateral root, origin of, *138
Latex, 68, 268
Lathraea, 704
Lathyrus, 672
Laticiferous cells, *68
Laticiferous tubes, 69
Laticiferous vessels, 69
Laudatea, 474
Laurel, Laurus nobilis
Laurus, 638, *641
Lavandula, *695, 696
Leaf arrangements, 88 ; alternate, 88 ;

main series of, 91 ; verticillate, 88
Leaf axil, 120
Leaf-base, 108, 115
Leaf-blade, 108 ; external form, 109 ;

functions of, 114
Leaf-cushions, 115
Leaf mosaic, 115
Leaf, pitchered, *187
Leaf-gfears, 119
Leaf-sheath, 108, *116
Leaf-stalk, 108, 115
Leaf-thorns, 172

Leaves, bracteal, 117 ; deciduous, 119 ;
development of, 106 ; different forms
of, 108 ; duration of life of, 118 ;
evergreen, 119 ; foliage, 108 ; internal
structure, 111 ; median plane of, 121 ;
scale, 117 ; transverse section of,
*113 ; venation of, 110

Lecanora, 474

Lecithins, 258, 266

Ledum, 685

Legume, 583

Leguminosae, 664 ; root-tubercles, 260

Lemon, Citrus limnnum

Lens, 672

Lentibulariaceae, 704

Lenticels, *59

Lentil, Lens

Leocarpus, *383

Leontodon, flower-head, *357

Leontopoditim, 716

Lepidium, *643

Lepidocarpon, 533

Lepidodendraceae, 503, 533

Lepidodendron, *532, 533

Lepidostrobtis, *533

Lepiota, 466

Leptome, 68

Leptosporangiatae, 505; antheridia, 510;
archegonia, 510

Leptothrix, 371

Lessonia, 410

Lettuce, Lactuca sativa

Leucin, 258

Leucobryum, 492

Leucqjum, 726, *728

Leuconostoc, 373

Leucoplasts, 19, *20, 32, *33

Levisticum, 682

Lianes, 182

Lichen acids, 469

Lichenes, 469

Lichens, LicJienes

Licmophora, *388

Life, active, 220 ; conditions of, 218 ;
duration of, 309 ; essential phenomena
of, 215 ; latent, 220

Light, adaptations for obtaining, 181 ;
effect on development, 289 ; produc-
tion of, 276

Lignification, 38, 39

Ligulatae, 530

Ligule, *116

Ligustrum, 687

Liliaceae, 724

Liliiflorae, 721

Lilium, 725 ; diagram of, *551 ; embryo-
sac, 572 ; fertilisation of, *575 ;
pollen-grain of, *570

Lilium martagon, germination of, *180

Lime, Tilia

Limnanthemum, 689

INDEX

789

Limodorum, 746

Linaceae, 652

Liiiaria, 703

Linnaeus, classification, 365

Linum. *652 ; gynaeceum of, *548

Liquidambar, 623

Liquorice, Glycyrrhiza

Liriodendron, 632

Listera, 746

LitoreUa, 704, 710

Liverworts, Hqpaticae

Lobaria, 474

Lobelia, 710, *711 ; ovary of, *548

Lobeliaceae, 709

Loganiaceae, 688

Lolium, 734, 735, *738

Lonicera, 706

Lophospermum, tendril-like petioles, *355

Loranthaceae, 620

Loranthiflorae, 620

Lorantkus, 620

Lotus, *669, 670, 672

Lovage, Levisticum

Lunaria, *643

Lupinus, 670, 671

Luzula, 724

Lycoperdon, 467, 468

Lycopersicurn, 697

Lycopodiaceae, 502, 524

Lycopodinae, 523

Lycopodinae biciliatae, 524

Lycopodinae. plv.riciliatae, 524

Lycopodium, *99, 523, *524, *525, *526,

527 ; bifurcating shoot, *120 ; stem

of, *499

Lygiiiodendron, *534, *535, 536
Ly thrum, 673

Macrocystis, 409, *410

Macrosporangia, 501

Macrospores, 501

Macrozamia, 589

Magnolia, 632

Magnoliaceae, 632

Mala it th cm u m . 7 25

Main-root, 140

Maize, Ze« mais

Malacophilous plants, 558

. *647, 648; pollen grain of,
*547

Malvaceae, 648

Mummlllaria, 629

Mo. ug if era, 655

Mangroves, 167

Manihot, 626

Manures, 2 44

Maranta, 745

Marantaceae, 745

Marattiaceae, 503

Marcgrai-ia, inflorescence of, *558 ; polli-
nation of, 556

Marchantia, 484, *485, *486, 487 ; air-
pore, *82; antheridium, *476 ; arche-
gonium, *478 ; rhizoid of, *36

Marchantiales, 484

Marsh Marigold, Oaltha palustris

Marsh plants, intercellular spaces of, 166

Marsilia, *512, *516, *517

Marsiliaceae, 512, 516

Martensia, 423

Mastigamoeba, *381

Matricaria, *712, 713, *715, 718

Matthiola, 645

Maximum, 219

Mechanical influences, effect on develop-
ment, 292

Mechanical tissue system, 60

Mechanism of development, 278

Mecurialis, 625

Median plane, 72

Medicago, 672

Medick, Medicago

Medlar, Mespilus germanica

Medullary rays, 95, *146, 156 ; primary,
146 ; secondary, 146

Meiosis, 24, 205

Melaleuca, 676

Melampyrum, 191, 704 ; embryo-sac of,
*577

Melica, 734

Melilot, Mdilotus

Mdilotm, 672

Melon, Cucumis Mdo

Mendel, laws of inheritance, 319

Mendelian rules, validity of, 322

Menispermaceae, 638

Mentha, 696

Menyanthes, 689

Mercurialis, *623

Meringosphaera, 397

Meristems, 46 ; primary, 46 ; secondary,
47

Merulius, 465

Mesembryanthemum, 628

Mesocarp, 583

Mesocarpus, cbloroplasts, 330

Mesophyll, 112

Mesotaeniaceae, 393

Mespilus, 661

Metabolism, 217, 220

Metals, assimilation of, 262

Metaphase, 23

Metroxylon, 740

Metzgeria, 81, 488, 489 ; apex of, *82

Miadesmia, 533

Micrasterias, 393, *394

Micrococeus, 374

Microcycas, 589

Micropyle, 539, 579

Microsomes, 15

Microsporangia, 501

Microspores, 501

790

BOTANY

Mildew fungi, Erysibaceae

Milfoil, Achillea

Millet, Andropogon Sorghum

Mimosa, *664, 667 ; movements *360 ;

seismonastic movements, 359 ; state

of rigor, 361
Mimosaceae, 664
Mimusops, 686
Minimum, 219
Mirabilis, hybrid, *320
Mistletoe, Viscum album
Mitochondria, 16
Mixo-chimaera, 301
Mnium, *83, 491, *493, 494, *495 ;

archegonium, *479 ; peristome, *496
Modifications, 211, 322
Monarda, 696
Monascus, 438, 439
Monkshood, Aconitum napellus
Monoblepharideae, 430
Monoblepharis, *199, 428, *430
Monochasium, 128, *129
Monochlamydeae, 609
Monocotylae, 718
Monocotyledon flower, 550
Monocotyledons, secondary growth in

thickness of, 142
Monopodium, 75
Monosporangia, 423
Monotropa, 191, 256
Monstera, 740 ; perforations, 284
Moraceae, 617

Morchella, *447 ; hymenium, 439
Morphology, 7 ; experimental, 9
Morus, 617 ; inflorescence of, *584
Mosses, Musci
Moss-plants, origin of, 475
Movement, 218, 326, 332; conditions of,

329 ; hygroscopic, 333 ; nastic, 356 ;

of orientation, 338 ; paratonic, 337 ;

periodic, 358 ; of protoplasm, 328 ;

seismonastic, 359 ; tactic, 329
Movements of curvature, 332 ; autonomic,

335
Movements of locomotion, 327 ; mechanism

of, 327
Mucilage, 28
Mucilage tubes, 69
Mucor, *434, 435, *436
Mucorineae, 434 ; heterothallic, 435 ;

homothallic, 435
Mucuna, stem of, *148
Mullein, Verbascum
Multicellular formation, 26
Musa, 743
Musaceae, 743
Muscari, 725
Musci, 475, 482, 489
Mutations, 325
Mutisieae 712
Mycelium, 77, *78

Mycobacterium, 373, 374

Mycorrhiza, 191, 256

Myosotis, 694

Myristica, *632 ; seed, *581

Myristicaceae, 632

Myrmecodia, 704

Myroxylon, *669, *670, 671, 673

Myrtaceae, 674

Myrtiflorae, 673

Myrtle, Myrtus communis

Myrtus, 674, *676

Myxamoebae, 383

Myxobacteriaceae, 385

Myxococcus, *385

Myxogasteres, 382

Myxomycetes, 13, 381

Narcissus, 726 '

Nastic movements, 338, 356

Natural selection, 212

Natural system, 365

Navicula, *391, 392

Nectaries, 71, 550

Nectria, 442

Nelumbium, 632

Nemalion, 424, 427

Neottia, 191, 256, 746

Nepenthaceae, 639

Nepenthes, *187

Nepeta, 696

Nephromium, 474

Nerium, 689, *691

Nerves, 110, 111

Neuropteris, 536

Nicotiana, 697, 699, *700 ; gynaeceum

of, *548

Nicotiana tabacum virginica apetala, 326
Nightshade, Solanum nigrum
Nitella, 14, 419, 421
Nitophyllum, 423, 427
Nitrate-bacteria, 254, 274, 375
Nitric acid, assimilation of, 257
Nitrite bacteria, 254, 274, 375
Nitrobacter, *375
Nitrogen, assimilation of, 256
Nitrosomonas, *375
Nodes, 88
Nopalea, 629
Nostoc, *377, 378
Nucellus, 539
Nuclear cavity, 17
Nuclear division, 21, *22 ; direct, 24;

indirect, 21
Nuclear membrane, 17
Nuclear plate, *23
Nuclear sap, 17
Nucleolus, 17
Nucleus, 11, 16
Nuphar, 631
Nutations, 336
Nutmeg, Myristica fragrans

INDEX

791

Nutrient salts, 237, 243 ; absorption of,
240 ; and agriculture, 243 ; transport
of, 242

Nutrient substances, absorption of, 222

Xuts, 583

Xyctiiiastic movements, 356

Nyctinasty, 357

Nymphaea, *631 ; seed of, *581

Nymphaeaceae, 630

Oak, Quercus

Oat, Arena saliva

Ocean currents, distribution of seeds by,

586

Ochrea, 116
Ochrolechia, 475
Odonlites, 704
Oedogonium, 403, M05
Oenanthe, *681, 682
Oenothera, *674
Oidium, 441
Olea, 687, *688
Oleaceae, 687
Olive Tree, Olea, europaea
Olpidiopsis, 430
Ol-pidium, *429
Onagraceae, 674

. 672

Ontogeny, 2
Oogonium, *199, 369
Oomycetes, 430
Oosphere, 199, 369
Ophiocytium, 397
Ophioglossaceae, 504
Ophioglossum, *504, *505
Ophrys, 746

Opium Poppy, Paparer somniferum
Optimum, 219
Opuntia, *173, 628, 629
Orchidaceae, 745
Orchis, *746, *747S *748 ; root-tuber,

*179

Organic acids, 28, 268
Organic bases, 258
Organography, 71
Organs, 71 ; vegetative, 73
Origin of species, 316
Ornithogalum, *723, 725
Ornithophilous plants, 557
Ornithophily, 556
Ornithopus, 672
Orobanchaceae, 704
Orobancke, 191, *703, 704
Orthosticbies, 89
Orthotropous, 72, 123
Oryza, 734, 735, *736
Oscillarid, *377
Osmometer, 224
Osmosis, 224

Osmotic pressure, 224 ; high, 227
Osmunda, *509

Ostrich Fern, Struthioptens germanica

Ourouparia, 705

Ovaries, transverse sections of, *548

Ovules, 198, 539, 540 ; position of, 549

Ovum, 567

Oxalis, movement, 337

Oxygen, 244 ; evolution of, *248

Padina, 415

Pae&nia, 638 ; flower of, *197, *545
Palaeontology, 209
Palaeostachya, *521, 522
Palaquium, *685, 686
Palisade cells, 112
Palmae, 738
Pandanaceae, 737
Pandanus, 737, *741
Pandorina, 399
Panicle, 126, *127
Panicum, 734
Pantostomatineae, 381
Papaver, 95, *642, 643 ; seed of, *581
Papaveraceae, 640
Papilionaceae, 670
Papillae, *54

Parasites, 188, 255, 256, 259
Parastichies, 90, *91
Paratonic movements, 337
Parenchyma, 48 ; assimilatory, 49 ; con-
ducting, 49 ; water- storage, 49
Paris, 725, 726, *727
Parmelia, *47l, *472
Parnassia, 659
Parsley, Petroselinum
Parsnip, Pastinaca

Parthenocissus, *182, 658 ; tendrils, 355
Parthenogenesis, 193, 316, 577
Partial parasites, 191
Passiflvra, ovary of, *548 ; tendrils, 354
Pastinaca, 682
Paullinia, 655
Pavetta, 704
Payena, 686
Pea, Pis urn

Pea, reserve material, *580
Peach, Prunus persica
Pear, Pyrus communis
Pectic substances, 38
Pediastrum, 401, *402
Pedicularis, 191, 259, 704
Peireskia, 628
Pelargonium, *651
Pellia, 488, 489
Peltigera, 472, 474
PenicUUum, *78, 441
Pentacyclicae, 684
Pentosanes, 37
Perception, 338
Perianth, 545
Periblem, 86
Pericarp, 583

792

BOTANY

Perichaetium, 492

Periclinal cell walls, 307

Pericycle, 95, 136

Periderm *160, 162

Peridineae, 386

Peridiniaceae, 386

Peridinium, *386, 387

Perigone, 546

Perigynous flower, *549, 550

Periodicity, 304

Periplasm, 500 '

Perisperm, 581

Peristome, 495

Perithecium, 439

Periwinkle, Vinca minor

Peronospora, *77, *433

Peronosporeae, 431

Persea, 639, *640

Personatae, 696

Petals, 197

Petasites, 718

Petiole, 108

Petroselinum, 682

Petunia, *697

Peziza, *445

Phaeocystis, 380

Phaeophyceae, 409

Pliaeosporeae, 412

Phaeothamnion, 380

Phalloideae, 468

Phallus, 468

Phascum, 496

Phaseolus, 673 ; pulvinus of, *337

Phelloderm, 162

Phellogen, 162

Phelloid tissue, 59

Philadelphia, 659

Phleum, 734

Phloem, 68

Phobophoto taxis, 330

PJwenix, 740

Phormium, *112

Phosphorescence, 277

Phosphoric acid, assimilation of, 262

Photonasty, 357

Photosynthesis, 254

Phototaxis, 330

Phototropic perception, localisation of,
351

Phototropism, 348, *349, 351 ; a pheno-
menon of irritability, 351 ; transverse.
350

Phmgmidium, 455, 456, 457, *458, *459,
460

Phycocyan, 19, 423

Phycoerythriu, 19, 423

Phycomyces, 435

Phycomycetes, 428

Phycoxanthin, 411

Phyllactinia, 440, 441

Phyllocactus, 629

Phylloclades, 171

Pliylogeny, 2

Physalis, fruit of, *584

Physarum, *384

Physiology, 215 ; object of, 215

Physostigma, 673

Phytelephas, 740

Phyteuma, 70?

Phytolacca, 95

Phytopathology, 303

Phytophthora, 431, *432

Picea, *599, 600 ; embryo, *568 ; ovule

of, *567i
Picorhiza, 704
Picrasma, 654

Pilobolus, 434 ; phototropism, 349, *350
Pilocarpus, 654
Pilostyles, *189
Pilularia, *512, 516, 517
Pimenta, 676

Pimpinella, *678, 681, 683
Pinaceae, 593, 596
Pine, radial section, *152 ; tangential

section, *153 ; transverse section, *151
Pinguicula, 186, 704
Pinnularia, *74
Pinus, 600, *601, 602, 606 ; archegonium

of, *567 ; embryo, *568 ; germination,

*587 ; male flower, *544 ; pollen-
tube, *566
Piper, 95, *622, 623
Piperaceae, 621 ,
Piperinae, 621
Pistacia, 655
Pisum, 672
Pith, 95

Pithecoctenium, winged seed of, *585
Pits, *35, *42, *43 ; bordered, 65 ; tactile,

353

Pitting, 43
Placenta, 539, 547
Placentation, axile, 548 ; free central, 548 ;

parietal, 548

Plagiochila, 80, *81, *488, 489
Plagiogeotropism, 342
Plagiotropous, 72, 123
Plankton, 74
Planktoniella, *388
Plant geography, 244
Plantaginaceae, 704
Plantago, 704 ; inflorescence of, *559
Plantain, Plantago
Plants, chemical composition of, 220 ;

organs of, 71 ; perception in, 338 ;

sensation in, 338 ; size of, 281 ;

stability of, 60
Plasmodesms, *44
Plasmodiophora, 385
Plasmodiophoraceae, 385
Plasmodium, 13, 382
Plasmolysis, *226

INDEX

793

Plasmopara, 432, 433

Plastids, 11

Platanaceae, 623

Platanthera, 746

Platanus, 623

Platystemon, 642

Plectasciueae, 441

Plectonema, *78

Pleiochasium, 127

Plerome, 86

Pleuridium, 496

Pleurocarpi, 496

Pleurocladia, *412

Pleurosigma, 391, 392

Plum, Prunus domestica

Plumbagella, embryo-sac, 572

Plumeless Thistle, Garduus •

Plumule, 565 *

Pneumatophores, 167, 246

Poa, 734

Pocket- leaves, 185

Podetium, 471

Podocarpus, 593 ; ruycorrhiza, 261

Podophyllum, 638, *639

Podospora, 442 ; perithecium, *443

Podostemaceae, 576

Poisons, 294

Polarity, 72, 282, 291, *292, 305;

establishment of, 74
Pollen-chamber, 563
Pollen grains, 197, 540
Pollen sacs, 197, 540, 546 ; cohesion

mechanisms, 335 ; development of,

541

Pollen-ttibe, 201, 541
Pollination, 201, 545 ; of flower, 551
Polyangium, *385
Polycarpicae, 629, 639
Polygala, *655
Polygalaceae, 655
Polygamy, 546
Polygonaceae, 621
Polygonatum, *719, 725, 726 ; geotropism,

*345 ; rhizome of, 119
Polygoninae, 621
Polygonum, *621 ; embryo-sac in, *571 ;

ovary of, *572
Polyhybrids, 322
Polypodiaceae, 508
Polypodium, 507, 509, *511
Polyporeae, 463
Polyporus, 465, 467
Polysiphonia, 427
Polytoma, *399
Polytrichaceae, 495
Polytrichum, *491, 492, 494, 496 ;

antheridium, *479
Pond-weed, Potamogeton natans
Poplar, Populus
Populus, 615,^*616
Porogamy, 573

Potamogeton, *720, 721

Potamogetonaceae, 721

Potentilla, 663

Presentation time, 348

Primula, *686, 687 ; heterostyled flowers,
*560

Primulaceae, 687

Primulinae, 687

Pro-embryo, 565, 568, 575

Promycelium, 455

Prophase, 23

Prop roots, 140

Prosenchyma, 48

Protandry, 559

Proteid crystals, 30

Proteids, hydrolysis of, 267

Prothallium, 567

Protococcales, 400

Protogyny, 559

Protomastiginae, 381

Protonema, 475, *476, 490

Protoplasm, 218 ; movements of, 13, 326,
328 ; permeability of, 241

Protoplasts, 11 ; chemical properties of, 14 ;
connections of, 43 ; inclusions of, 27 ;
main vital phenomena of, 13 ; origin
of the elements of, 21 ; structure of
the parts of, 15

Prunus, *107, *660, *663, 664

Psalliota, *464, 466

Pseudo-parenchyma, 437

Pseudotsuga, 598

Psidium, 675
I Psilophytales, 501
I Psilophyton, 501

Psilotaceae, 502, 527

Psilotum, 527

Psychotria, 704, 705

Pteridium, *498, 509

Pteridophyta, 496 ; classes of, 5QJ. ;
embryo, 498 ; gametophyte, 497 ;
heterosporous, 501 ; homosporous,
501 ; prothallium, 497 ; sexual repro-
duction, 200 ; sporangia, *197, 499 ;
spores, 499 ; sporophylls, 499 ; sporo-
phyte, 498 ; suspensor, 498 ; vascular
bundles, 499 ; vascular system, 105

Pteridospermtae, 503, 534

Pteris, *101 ; apex of a root, *132 ;
embryo, *497

Pterocarpus, 673

Ptyxis, 87

Puccinia, *456, *457, 458, 459

Pulvinus, *115, 336, *337, 351

Pumpkin, Cucurbita Pepo

Punica, 676, *677

Punicaceae, 676

Pure line, 322

Pycnidia, 443

Pycuoconidia, 443

Pycnospores, 443

794

BOTANY

Pyrenoids, 18

Pyrenomycetes, 442

Pyronema, 438, 439, 445, *446, *447

Pyrus, 660, 661 ; flower, *550

Pythium, 433

Quassia, 654, *654

Querciflorae, 609

Quercus, *614, *615, 749 ; cupule, *613

Quillaja, 660, 664

Quince, Cydonia vulgaris

Raceme, *126

Radial vascular bundle, 136

Radicle, 565

Radish, Raphanus salivus

Rafflesia, 189

Rafttesiaceae, 639

Rainalina, 471

Ramenta, 54

Ranunculaceae, 633

Ranunculus, *633, *634, *635, 636 ;
flower, *550 ; root of, 136 ; vascular
bundle, *104

Raoulia, *170, 716

Raphanust 646

Raphe, 579

Raphides, 30, *31

Raspberry, Rubus idaeus

Ravenala, 745

Reaction-time, 347

Receptacle, 508

Red Algae, Rhodophyceae

Red Currant, Ribes rubrum

Reduction division, 24, 203, *206, 369

Regeneration, 164, 282 ; in Bryophyta, 481

Regulation, capacity of, 217

Reindeer Moss, Cladonia rangiferina

Rejuvenation, 21

Reparation, 282

Reproduction, 192, 217, 310; asexual,
193 ; conditions of, 311 ; digenetic,
193 ; monogenetic, 193; sexual, 193,
315 ; organs of, 192 ; vegetative, 193

Reseda, multicellular formation. *26

Reserve materials, 263 ; mobilisation of,
263 ; regeneration of, 268 ; transport
of, 267

Resins, 30, 268

Respiration, 269, 273 ; experiment to de-
monstrate, *271 ; intramolecular, 272

Respiratory coefficient, 270

Respiratory roots, *167

Rest-Harrow, Ononis

Resting condition, 303 ; awakening from,
305

Restitution, 164, 282 ; stimulus of, 305

Rhabdonema, 392

Rhamnaceae, 657

Rhamnus, *657, 658

Rheum, *621

Rhinanthus, 191, 259

Rhipidium, *130

Rhipsalis, 629

Rhizoids, 80

Rhizomes, 177

Rhizomorphs, 466

Rhizophora, *168, 674, *675

Rhizophoraceae, 674

Rhizopus, *433, 434, 435

Rhododendron, 685 ; ovary of, *548

Rhodomela, 427

Rhodophyceae, 421

Rhoeadinae, 639

Rhubarb, Rheum

Rhus, 655

Rhynia, 501

Ribes, *659

Riccia, 80, *81, *487

Ricciaceae, 487

Rice, Oryza saliva

Richardia, 740

Ricinus, *625, *626, 627 ; endosperm of,
*31

Rigidity against bending, 93, *94

Rigor, 361

Robinia, *174, 672

Roccella, 471, 475

Rock Rose, Helianlhemum vulgare

Root- cap, 131

Root-climbers, 182

Root-hairs, *54, 134, *134, *227

Root- pockets, 131

Root-pressure, *234, 236

Root-system, appearance of, 139

Root-thorns, 172

Root-tubercles, *260

Root-tubers, 179

Roots, 131, 139 ; borne on shoots, 139 ;
branching of, 138 ; external features
of, 132 ; geotropic curvature of, *342 ;
growing point, 131 ; growth in thick-
ness of, *147 ; mechanical tissue of,
*137 ; primary structure of, 134

Rosa, *660, 664 ; fruit of, *582

Rosaceae, 660

Rose of Jericho, Anastatica hierochunlica

Rosiflorae, 658

Rosmarinus, 696

Rotation, 13

Rowan, Sorbus (Pyrus} aucuparia

Royal Fern, Osmunda regalis

Roziles, 467

Rubia, 704

Rubiaceae, 704

Rubiinae, 704

Rubus, 663 ; collective fruit of, *584

Rumex, 621

Runners, 194

Ruppia, 721

Ruscus, cladode, .*173

Rush, Juncus

INDEX

795

Russula, *461, 467

Rust Fungi, Uredintae

Rust of Wheat, Puccinia graminis

Ruta, 652, *653

Rutaceae, 652

Rye, Secale cereale

SabadUla, 725

Saccharomyces, *27, 449, *450
Saccharomycetes, 449
Saccharum, 734
Saffron, Crocus satin/ s
Sagittaria, 719, *720, 721
Salicaceae, 614
Saliciflorae, 614
Salicornia, *173
Salix, 615, *616

Salvia, *696 ; pollination of, 555, *556
Salvinia, *513, *514, *515
Salviniaceae, 512, 513
Sambucus, 706 ; flower of, *547
Sangnisorba, *660, 661
Santalaceae, 620
Santalum, 620
Sapiudaceae, 655
Sapindinae, 655
Saponaria, 627, *629
Sapotaceae, 686

Saprolegnia, *35, 430, *431 ; course of
development of, 311 ; zoospores, *196
Saprolegniaceae, 430
Saprophytes, 255, 256
Sarcina, 375
Sargassum, 410
Sarothamnus, 671
Sarraceniaceae, 639
Sassafras, 638, *640
Savannahs, 219
Saxifraga, 659
Saxifragaceae, 659
Saxifrage, Saxifraga
Scabiosa, 707
Scalariform pitting, *66
Scale leaves, 118
Scandix, 682
Scenedesmus, 401, *402
Schistostega, *493, 496
Schizaeaceae, 509
Schizocarp, 584
Schizonema, 388
Schizosaccharomyces, 449
Schoenocaulon, 725
Sciadium, 397
Sciadopitys, 598
Scilla, 725
Scinaia, 427
iStewyMs, 730, *731
Scitaraiueae, 742
Sclerenchyma, 60, *62
Sclerenchymatous fibre, *61
Scleroderma, 467, 468

Sderopodium, *493

Sclerospora, 433

Sclerotium, 437

Scolopendrium, *508

Scorzonera, 716 ; seedlings, *588

Scrophulariaceae, 703 ; floral diagrams of,

•208

Scurvy Grass, Cochlearia qfficinalis
Sea lettuce, Ulva lactuca
Secale, 733, 734, *735
Sedum, 658, *659

Seeds, 193, 540, 579 ; distribution of, 584
Segregation of characters, 320
Seismonasty, 359

Selaginella, 523, 527, *528, *529, *530
Sdaginellaceae, 502, 527
Selection, 324
Selective power, 241
Self-pollination, 201
Self -sterility, 558
Semi-permeable membrane, 224
Sempervivum, 658 ; formation of the

flowers of, 312
Senecio, 711, 718
Sensitive Plant, Mimosa pudica
Sepals, 197

Sequoia, 235, 598, 599, 606
Serjania, *183
Sex, determination of, 314
Sexual reproduction, significance of, 315
Sexual reproductive cells, 198
Shaddock, Citrus decumana
Shade plants, 181

Shepherd's purse, Capsella bursa pastoris
Shoot-thorns, 172
Shoots, 84 ; adventitious, 122 ; aerial, 84 ;

axillary, 121 ; branching of, 119 ;

endogenous, 122 ; formed from roots,

306 ; normal, 122 ; order of sequence

of, 124 ; subterranean, 84
Shorea, 647
Shrubs, 141
Sieve-pits, 63, *64
Sieve-plates, 63, 159
Sieve-tubes, *63, *64, 158
Sigillaria, 532
Sigillariaceae, 502, 532
Silene, *630
Siler, *678
Siliceous earth, 392
Silicoflagellatae, 380
Silicon, 240

Silver Fir, Abies pectinata
Simarubaceae, 654
Sinapis, 645
Siphonales, 405
Siphonocladiales, 404
Siphonodadus, 404
Siphonogams, 542
Sisymbrium, *644
Sium, 682

796

BOTANY

Sleep-position, 357

Sliding growth, 48, *150

Slime fungi, Myxomycetes

Smilax, 725, 749

Smut Fungi, Ustilagineae

Sodium, 240

Soil, power of absorption of, 242

Solanaceae, 696

Solanum, 696, *697, 699 ; tuber, *177

Solerina, 474

Solidago, 716

Sols, 15

Sonneratia, *167

Sorbus, *660, 661 ; hybrid, *318

Soredia, 471

Sorrel, Rumex acetosa

Spadiciflorae, 737

Spanish Pepper, Capsicum annuum

Sparassis, 463

Sparganiaceae, 737

Spartium, 672, 673

Species, 322 ; origin of, 206, 326

Spermatogenous cell, 561

Spermatophyta, 539, 542 ; sexual repro-
duction, 200

Spermatozoids, 199, 369, 565 ; chemo-
taxis, 331 ; of Zamia, *563

Spermogonia, 455

SpJiaeria, 442

Sphaerococcus, 427

Sphaero-crystals, 34

Sphaeroplea, 404

Sphaerotkeca, 440, 441

Sphagnales, 493

Sphagnum, *490, 493

Sphenophyllaceae, 502

Sphenophyllinae, 522

Sphevophyllum, *522

Sphenopteris, 536

Sphere-crystals, 28

Spike, *126

Spinach, Spinacia oleracea

Spinacia, 627

Spiraea, *660»

Spirillum, 370, *371

Spirodinium, 387

Spirogyra, 395, *396 ; cell of, *25

Spirophyllum, 376

Spirotaenia, 393

Splachnum, 494

Splint-wood, 158

Spongy parenchyma, 113

Sporangial spores, 195

Sporangium, 195, *509 ; cohesion mechan-
isms, 334, *335

Spores, 193, 195, 369

Sporidium, 455

Sporodinia, 434, *435

Sporogonium, 196 ; hygroscopic move-
ments, 334

Sporophylls, 197

Sporothecae, 501

Spring wood, 153, 154

Stachys, 695

Stamens, 197, 540, 546

Staminodes, 546

Stangeria, 589

Stapelia, *174, 690 ; pollination of, 556

Staphylococcus, 374

Starch, 32, 252, *253, 264 ; assimilation,
32 ; reserve, 32

Starch grains, *33

Starch sheath, 94, 102

Statolith-hypothesis, 347

Statoliths, 346

Stelar theory, 106

Stele, 106

Stellaria, 627

Stem, primary internal structure of, 92

Stemonitis, *382, 384

Stem-tendrils, 182, *182

Stem-tubers, 177

Sterculiaceae, 650

Stereoine, 60

Stereum, 463

Stigma, 201, 548

Stigmatomyces, *450

Stimulus, 337 ; conduction of, 361 ; move-
ments, 337

Stinging Nettles, Urtica

Stink-horn, Ithyphallus impudicus

Stipa, section of the leaf, *172

Stipules, 108

Stock, Matthiola

Stomata, 51, *52, 230, 231, *246

Stomatal apparatus, 51, 52, *53

Stoneworts, Characeae

Storage parenchyma, 148

Stratification, *35, 41

Stratiotes, 194, 721

Strawberry, Fragraria

Strelitzia, 745 ; ornithophilous flower of,
*557 ; pollination of, 556

Streptochaeta, 732

Streptococcus, 373, *374

Striation, *37|

Strickeria, *443

StrophantJms, 689, *692

Struggle for existence, 212

Struthiopteris, 508 ; spermatozoid, *510

Strychnos, 688, *689

Style, 548

Styracaceae, 686

Styrax, 686

Suberisation, 38, 39

Subtending leaf, 121

Succisa, 707, *709

Succulent stems, *174

Suction force, 237

Sugar-cane, Saccharum ojficinarum

Sugars, 28

Sulphur bacteria, 254, 274, 376

INDEX

797

Sulphuric acid, assimilation of, 261

Sunflower, Helianthus annuus

Surirella, 391

Suspensor, 565, 575

Swarm spores, 196

Sivertia, 689

Symbiosis, 469

Symmetry, 282, 306 ; dorsiventral, 75 ;

planes of, 72 ; relations of, 72
Sympetalae, 684
Symphytum, 694
Sympodium, 127
Synandrae, 707
Syncarpous gynaeceum, 547
Synchytrium, 429
Synedra, 392
Syringa, 687, *687

Tabernaemontana, 689

Tactile pit, *353

Taeniophyllum, *175

Tamarindus, *666, *667, *668, 669, 670

Tannin, 29, 268

Tapetum, 500

Taphrina, *449

Tap-root, 140

T:'.ritxaci(m, 712, 713, *714, 718 ; modi-
fications, *323

Taxaceae, 593

Taxodium, 596, *597, 606

Taxus, *97, *593, *594, 602; embryo-
sac, *566

Teak-tree, Tectona grand is

Teazel, Dipsacus

Tectona, 694

Teleutospores, 455

Telophase, 23

Temperature, effect on development, 288

Tendril climbers, 182

Tendrils, *181, 182, 353 ; points of
reversal, 354

Teratology, vegetable, 303

Terfezia, 442

Terfeziaceae, 442

Terminal bud, 121

Ternstroemiaceae, 647

Tetracyclicae, 687

Tetraspores, 423

Teucrium, 695

Thalictrum, 95

Thallophyta, 367 ; phylogenetic connec-
tions of, 368 ; reproduction of, 369 ;
sexual reproduction, 198

Thallus, 73 ; internal structure of, 78

Thamnldium, 435

Thea, *646

Thecotheus, 439

Thelephorea°, 463

Theobroma, *649, *650, 651

Theory of descent, 1, 206, 326

Thermonasty, 356

Thesium, 191, 259, 620

Thigmotropism, 353

Thorn-apple, Datura Stramonium

Thorns, 171

Thuja, 596, 597 ; germination, *587

Thyloses, 158

Thymelaeaceae, 673

Thymus, 696

Tilia, *649 ; radial section of the wood
of, *157 ; tangential section of the
wood of, *156 ; transverse section
of the bast of, *159 ; transverse
section of a stem of, *154 : transverse
section of the wood of, *155

Tiliaceae, 649

Tillandsia, 185

Tilletia, *454

Tilletiaceae, 454

Tilopteridaceae, 414

Tissue-systems, 45

Tissue tensions, 286, *287

Tissues, boundary, 49 ; formation of, 40 ;
permanent, 47

Tmesipteris, 527

Tobacco, 697

Tolypellopsis, 421

Tone, alteration of, 345, 351

Toothwort, Lathraea squamaria

Topophototaxis, 330

Torsion, 91

Tozzia, 191, 259, 704

Tracheae, 64, *65 ; annular, 65 ; reticu-
late, 65 ; spiral, 65

Tracheides, 64, *65 ; annular, 65 ; reticu-
late, 65 ; scalariform, *66 ; spiral, 65

Tradescantia, *14, 730

Tragopogon, 716

Transpiration, 228 ; cuticular, 230 ;
stomatal, 230

Transpiration stream, 235
I Transverse geotropism, 342

Trapa, 674

Tree-ferns, 506

Trees, 141 ; longevity of, 310

Tremella, basidium, *452

Tremellineae, 460

Trentepohlia, 402

Tribonema, 397

Trichia, *383

Trichobacteria, 371, 375

TrichocauloH, 690
j Trichogyne, 424

Tricholoma, 466

Trichomanes, *510

Tricoccae, 623

Trifolwm, 672 ; movement, 337

Trigonella, 672

Triticum, 733, 734, *735 ; endosperm, *31

Tropaeolum, chromoplasts, *20

Tropisms, 338

Tropophytes, 175

798

BOTANY

Truffles, Tuberaceae

Trypanosoma, *381

Tuberaceae, 447

Tubers, 178, 194, 308, 447 *448

Tubiflorae, 690

Tulipa, 725 ; bulb, *178

Turgescence, *225

Turnip, Brassica napus

Tussilago, *716, 718

Twining plants, 182, 343, *344

Typhaceae, 737

Tyrosin, 258

Ulex, 672

Ulmaceae, 616

Ulmus, 616, *617 ; development of the

leaf, *108 ; ovule of, *573
Ulothrix, *199, 402, *404
Ulotrichales, 401
Ulva, *75, 402
Umbel, *127
Umbelliferae, 679
Umbelliflorae, 677
Uncinula, 440, *441
Unfolding buds, distribution of, 124
Unicellular bacteria, Hapldbacteria
Uragoga, 705, *708
Uredineae, 455
Uredospores, 457
Urginea, *723, 725, 726
Urtica, 619 ; hybrid, *321
Urticaceae, 619
Urticinae, 616
Usnea, 471, *472
Ustilaginaceae, 453
Ustilagineae, 452
Ustilago, *453, 454, *455 ; brand-spores,

453
Utricularia, *186, 704

Vaccinium, 685, *685

Vacuoles, 12

Valerian, Valeriana

Valeriana, 706, *708

Valerianaceae, 706

Vallisneria, 721

Vanda, 749

Vanilla, *747, 748

Variability, 316, 322

Variation curves, *324

Vascular bundles, arrangement, 95 ; bi-
collateral, 100 ; cauline, 96; collateral
100 ; common, 96 ; complete, 67 ; con-
centric, 99, *100, *101 ; course of,
96 ; foliar, 96 ; incomplete, 67 ;
radial, 99 ; structure of, 99 ; system,
67 ; system of tissue of, 67 ; termina-
tion of, *111

Vascular cryptogams, 496, 499

Vascular plants, 366

Vascular system, phylogeny of, 105

Vaucheria, *407, *408

Vegetable kingdom, phylogeny of, 365

Vegetative cone, *85, *86, *87

Vegetative form, periodic changes in, 307

Veins, 110

Velamen, 184

Velum, 465

Venation, 110

Ventral canal-cell, 567

Ventral suture, 547

Veratrum, 725, 726

Verbascum, *701, 703

Verbena, *694

Verbenaceae, 694

Vernation, 87

Veronica, 703

Verrucaria, 471

Vessels, 64, 148 ; pitted, 65 ; scalariform.

Vetch, Vicia
Vibrio, 370, *371, 374
Viburnum, 705, 706
Vicia, *668, 672, 673
Victoria, 632
Vinca, 689, *690
Vincetoxicum, 690, *693
Viola, *646 ; capsule, *583 ; flower of,

*552

Violaceae, 647

Viscaria, *630 ; diagram of, *551
Viscum, 192, 259, 620, *620
Vitaceae, 658
Vitis, *658

Viviparous plants, 589
Volva, 465
Volvocales, 398
Volvox, 399, *400

Wall, growth in thickness, 36
Wallflower, Gheiranthus Cheiri
Walnut, Juglans regia
Water, 222 ; absorption of, 223, 227 ;

assimilation of, 262 ; conduction of,

235 ; movement of, 228
Water cultures, 238, *239
Water- Ferns, Hydropterideae
Water-Hemlock, Gicuta
Water-net, Hydrodictyon
Water Nut, Trapa
Water-Parsnip, Slum
Water plants, 165, 228
Water-pores, *114
Water-stomata, 113, 233
Water-storage tissue, 113
Wax incrustation, *50
Weigelia, 706

Welwitschia, 108, *602 ; prothallia, 569
Wheat, Triticum
White Mustard, Sinapis alba
White Water Lily, Nympliaea alba
Whorl, 88

INDEX

799

Wild Cabbage, Brassica oleracea

Wild Cherry, Primus cerasus

WiUonghbeia, 689

Willow, Salix

Willow-herb, Epilobium

Wind-dispersal, seeds, 585

Winter buds, *176

Wistaria, 672, 673

Witches' -brooms, 449

Wood, 148 ; arrangement of the tissues in,
151 ; autumn, 153 ; grain of, 157 ;
heart-, 158 ; splint-, 158 ; spring,
153 ; subsequent alterations of, 157

Wood-fibres, 148

Wood parenchyma, 149

Woodsia, antheridium, *510

Wormwood, Artemisia Absinthium

Wounds, healing o$ 164

Xanthophyll, 19
Xenogamy, 201
Xerochasy, 333
Xeromorphy, 169
Xerophytes, 168
Xylem, 68

Yeast Fungi, Saccharomycetes
Yeast fungus, fermentation, 275

Yew, Taxus baccata

Yucca, 725 ; pollination of, 556

Zamia, 589 ; fertilisation, *565 ; formation
of spermatozoids in, *562 ; spermato-
zoids, *563

Zanardinia, 414

Zanichellia, 721

Zea, *92, 734, 735 ; vascular bundle, *102,
*103

Zingiber, *744, 745

Zingiberaceae, 745

Zoosporangia, 196

Zoospores, 196, 369

Zostera, 721

Zygnema, 395

Zygnemaceae, 395

Zygogynum, 632

Zygomorphic, 72

Zygomorphic flowers, geotropic orienta-
tion of, 343

Zygomycetes, 434

Zygophyceae, 393

Zygophyllaceae, 652

ZygosaccharomyceSy 449

Zygospore, 199, 369, 434

Zygote, 199, 369

Zymase, 275

THE END

Printed by R. & R. CLARK, LIMITED, Edinburgh.

14 DAY USE

RETURN TO DESK FROM WHICH BORROWED

This book is due on the last date stamped below, or

on the date to which renewed.
Renewed books are subject to immediate recall.

LD 21-40m-4,'64
(E4555slO)476

General Library

University of California

Berkeley

. vr

U.C. BERKELEY LIBRARIES

1250

UNIVERSITY OF CALIFORNIA LIBRARY

TRY

-uirs

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "Strasburger's Text-book of botany"

See other formats