Descriptive and physiological botany

THE

CABINET CYCLOPADIA.

Lonnon:

Printed by A. SPOTTISWOODE,
New-Street- Square.

CABINET CYCLOPAEDIA.

CONDUCTED BY THE

REV, DIONYSIUS LARDNER, LL.D. F.R.S. L. & E.
M.R.ILA. ERAS. F.L.S. F.Z.S. Hon. F.CP.S. &. &.

ASSISTED BY

EMINENT LITERARY AND SCIENTIFIC MEN.

atural istorp.

DESCRIPTIVE AND PHYSIOLOGICAL
BOTANY.

BY THE

REV. J. S. HENSLOW, M. A.

PROFESSOR OF BOTANY IN THE UNIVERSITY OF CAMBRIDGE
4

A NEW EDITION.

LONDON:

PRINTED ‘FOR
LONGMAN, ORME, BROWN, GREEN, & LONGMANS,
PATERNOSTER-ROW ;
AND JOHN TAYLOR,

UPPER GOWER STREET,

1837.

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N. PATERNOSTER ROW

AND JOHN TAYLOR, TPPER GOWER STREET.

1835.

CONTENTS.

INTRODUCTION.

Objects of Botanical Investigation (2.). — Descriptive and Physiological
Botany — Sub-divisions (3.). — Advantages of our Pursuit (4.). — Un-
organized and organized Bodies (5.).— Distinction between Animals and

Vegetables AF) - - a a Page 1

PART I.

DESCRIPTIVE BOTANY.

SECTION I.

ORGANOGRAPHY AND GLOSSOLOGY.

CHAPTER I.
ELEMENTARY ORGANS AND TISSUES.

External Organs — Conservative and reproductive (9.).— Internal Struc-
ture; Elementary Texture; Chemical Composition (12.). — Elementary
Organs; Cellular and Vascular Tissues (13.). — Compound Organs —
Investing and complex (28.).— Primary Groups or Classes GIT ye?

K

CHAP. Il.

NUTRITIVE ORGANS.

Fundamental Organs (38.). — Root and Appendages (39.). — Stems (Aërial)
(43.). — Internal Structure (45.).— Forms and Directions (53.). — Buds
(56.).— Branches (58.). — And their Modifications (61.).— Subterranean
Stems and Branches (62.).— Tubers and Bulbs; their Affinity (63.).—
Appendages to the Stems (67.) h ;

CONTENTS,

CHAP. III.
NUTRITIVE ORGANS — continued.

Leaves, simple and compound (69.).—~ Vernation (71.). — Forms of Leaves
(74.).—-Phyllodia (75.).— Transformation of Leaves (78.).— Venation
(81.). — Disposition and Adhesion (82.), — Nutritive Organs of Crypto-
gamic Plants (84.) - - < - Page 59

CHAP. IV.
REPRODUCTIVE ORGANS.
Flower Buds (85.). — Inflorescence — Modes of (86.). — Floral Whorls—

Perianth (92.). — Glumaceous Flowers (96.). — Stamens and Pistils (97.).
— Disk (101.). — Floral Modifications (102.). == Æstivation (104.) =~- 79

CHAP. V.

REPRODUCTIVE ORGANS — continued.

Fruit — Pericarp (105.),— Forms of Fruit (1(8.). — Seeds (109.). — Embryo
(111.). — Reproduction of Cryptogamous Plants (114.) = - 102

CHAP. VI.
MORPHOLOGY.
Abortion (115.).—Degeneration (116.).— Adhesion (118.), — Supernu.
merary Whorls (119.).— Normal Characters (120.).— Spiral Arrangement

of foliaceous Appendages (121.).— Tabular View of Vegetable Organiz-
ation (129.) ° - - ” - - 116

SECTION IL.

TAXONOMY AND PHYTOGRAPHY. |

CHAP. VII.

Natural Groups (131.). — Values of Characters (132.). — Subordination of
Characters (133.).— Natural Orders (135.).— Artificial Arrangements
(136.). — Linnzan System (137.).— Application of it (140.) - ` - 135

i

CONTENTS.

PART II.

PHYSIOLOGICAL BOTANY.

CHAPTER I
VITAL PROPERTIES AND STIMULANTS,

Vegetable Life (139.).— Properties of Tissues (141.): —Endosmose (144.).
— Vital Properties (145.). == Stimulants to Vegetation (152.) =- Page 155

CHAP. II.
FUNCTION OF NUTRITION — Periods 1, 2, 3, 4.

Absorption (160.). — Ascent of Sap (163.).— Causes of Progression (165.).
— Exhalation (169.).— Retention of Sap (172.). — Respiration (173.).—
Fixation of Carbon (176.). — Organizable Products — Gum (177.).—
Etiolation (179.). — Colours and Chromatometer (182.). — Results of
Respiration (189.) - = į -E

CHAP. III.
FUNCTION OF NUTRITION — continued — Periods 5, 6»

Diffusion of proper Juice (189.). — Intercellular Rotation (193.). — Local
Circulations (195.). — Vegetable Secretions (196.). — Fecula, Sugar,
Lignine (197.).— Proper Juices (202.). — Taste and Scent. (210.). — Ex-
cretions (212.). — Rotations of Crops (218.). — Extraneous Deposits
(219.) - =- = - - ~ 203

CHAP. IV.

FUNCTION OF NUTRITION — continued — Period 7.

Assimilation (223.). — Pruning (225.). — Grafting (227.). — Development
(230.). — Nutrition of Cryptogamic Plants (233.).— Parasitic Plants (234.).
— Duration of Life (235.). — Vegetable Individuals (236.).— Longevity
of Trees (239.) - - -= - = 227

CHAP. V.

FUNCTION OF REPRODUCTION — Periods.1, 2, 3.

Propagation (243.).— Origin of Flower-buds (245.). — Flowering (246.). —
Functions of the Perianth (252.).—- Development of Caloric (254,).—

viii CONTENTS.

Fertilization (255.).—Formation of Pollen (261.). == Maturation (265.).
— Flavour and Colour of Fruit (273.) - & Page 248
CHAP. VL.

FUNCTION OF REPRODUCTION = continued — Periods 4, 5.

Dissemination (275.). — Modes of Dissemination (279.). — Preservation of
Seed (281.). — Germination (283.).— Vitality of the Embryo (290.).—
Relation of Bud and Embryo (291.).— Proliferous Flowers (292.).— Hy-

brids (295.) - = - a a

~ 276

CHAP. VII
EPIRRHEOLOGY, BOTANICAL GEOGRAPHY, FOSSIL BOTANY.

Epirrheology (298.).—- Direction of Roots and Stems = . — Botanical
Geography (302.). = Fossil DU (315.) - = 290

THE PRINCIPLES

OF

DESCRIPTIVE AND PHYSIOLOGICAL

BOTANY.

INTRODUCTION.

OBJECTS OF BOTANICAL INVESTIGATION (2. ). — DESCRIPTIVE AND
PHYSIOLOGICAL BOTANY — SUB-DIVISIONS (3.).— ADVANTAGES
OF OUR PURSUIT (4.). — UNORGANISED AND ORGANISED
BODIES (5.). — DISTINCTION BETWEEN ANIMALS AND VEGE-
TABLES (7. ).

(1.) Or the advantages which accrue from the culti-
vation of the natural sciences, sufficient has been said in
the treatise of Sir J. Herschel, forming our fourteenth
volume; and Mr. Swainson, in his discourse, which
forms our fifty-ninth volume, has further exposed the
importance of the study of Natural History in general,
and more particularly of that department which he so
successfully cultivates. In introducing the science of Bo-
tany to the general reader, for whom more especially this
volume is designed, rather than for the scientific adept,
it will be right that we should follow the example which
has thus been set us, and say a few words by way of
introduction to our present subject. Whenever we are
about to enter upon any science which is new to us, it
B

2 PRINCIPLES OF BOTANY.

is always advantageous to take a general survey of the
limits within which it is restricted, and to obtain some
notions of the objects of which it professes tu treat.
We shall, therefore, offer a few remarks upon the
position which Botany holds with respect to other
kindred branches of Natural History ; and point out
the separate and subordinate departments into which it
may be advantageously divided.

(2.) Botany.—In the most extended sense of the
term, Botany may be considered as embracing every
inquiry which can be made into the various phenomena
connected with one of the three great departments into
which the study of nature is divided, and which is
familiarly styled the Vegetable Kingdom. And this
inquiry should extend as well to the investigation of
the outward forms and conditions in which plants,
whether recent or fossil, are met with, as to the exa-
mination of the various functions which they perform
whilst in the living state, and to the laws by which
their distribution on the earth’s surface is regulated.
We may conveniently arrange these several phenemena
under two heads. The one may be called the
“ Descriptive” department of the science, being de-
voted to the examination, description, and classification
of all the circumstances connected with the external
configuration and internal structure of plants, which
we here consider in much the same light as so many
pieces of machinery, more or less complicated in their
structure; but of whose several parts we must first
obtain some general knowledge, before we can expect
to understand their mode of operation, or to appreciate
the ends which each was intended to effect. In the
“* Physiological,” which is the other department. we
consider these machines as it were in action; and we
are here to investigate the phenomena which result
from the presence of the living principle, operating in
conjunction with the two forces of attraction and
affinity, to which all natural bodies are subject.

(3.) Subordinate departments. — Each of the two

INTRODUCTION. 3
departments mentioned in the last article admits of
subdivision ; and the several subordinate departments
thus formed become a register of special observations.
Thus, the descriptive department will include a “Glosso-
logy,” or mere register of technical terms — composing a.
conventional language, by which the description of
plants is facilitated, and a comparison of their forms
and peculiarities rendered clear and precise, without
any periphrasis or unnecessary prolixity. It will also
include an “ Organography,” containing a particular
account of the several parts or organs of which plants
are composed. A third subordinate department ‘is
styled “ Phytography,” in which a full description of
plants themselves is given: and lastly, we have the
“Taxonomy” of this science, in which plants are
classified in a methodical manner, according to some
one or other of those various methods or systems,
which serve to facilitate our knowledge of the forms
and relations of the numerous species already discovered.
We do not, however, propose to treat our subject with
so much technicality. In descriptive botany we shall
chiefly restrict ourselves to the more general details of
Organography, and include in this department what-
ever we may find it necessary to say on Glossology.
The reader may then consult the general index at the
end of the volume, whenever he meets with a word
which requires explanation, and he will be referred to
the page and article in which such explanation is
given, Phytography is entirely subordinate to Taxo-
nomy, or Systematic Botany, which forms no part
of our scheme, beyond what is necessary to give the
reader some general notions of the manner in which `
plants are described and classified in the most cele-
brated systems of systematic authors. We shall enter
somewhat more fully into the details of Physiological
Botany, as this subject possesses a more general inter-
est, owing to the numerous and striking phenomena.
of practical and economical importance, which it ena-
bles us to explain.

B2

4 FRINCIPLES OF BOTANY.

Tt is more usual, indeed, to restrict the term Botany
entirely to the descriptive departments, in which,
as might have been expected, and as the nature of the
case requires, much greater progress has been made
than in the physiological. It is, in fact, only very
lately that any successful attempt has been made to
connect the numerous facts which have been long
accumulating relative to the various phenomena which
attend, and the laws which regulate, the functions
performed by the living vegetable,

(4.) Advantages of our pursuit.—The old and by-
gone sneer of “cui bono,” by which the naturalist. was
formerly taunted, now offers no serious impediment in
the way of those who are willing to inquire for them-
selves. Even the few who still think that no’ advan-
tage would result from the encouragement of natural _
history as a branch of general education, no longer at-
tempt any very decided opposition wherever they meet
with others prepared to uphold it. Our pursuit has
been so often and so satisfactorily shown to be produc-
tive of direct practical benefit to the general interests
of society, that nothing further need here be said on that
topic. But we would more especially recommend it as
a resource which is capable of affording the highest in-
tellectual enjoyment ; and as much worthy of general
notice for mental recreation, as air and exercise are for
our bodily health. All who feel an unaccountable
delight in contemplating the works of nature 3 who
admire the exquisite symmetry of crystals, plants, and
animals ; and who love to meditate upon the wonderful
order and: regularity with which they are distributed ;
possess a source of continued enjoyment within them-
selves, which is capable of producing a most beneficial
effect upon their temper and disposition, provided they
do not abuse these advantages by making such studies

too exclusively the objects of their thoughts and care.
Above all, they must beware of pampering the ridiculous
ambition of surpassing others in the extent of their col-
lections, or of fostering an absurd and captious jealousy

INTRODUCTION. ERS

‘

about maintaining the priority of their claim to this or
that particular observation or discovery. We do not go
so far as some persons, who seem inclined to believe
that these pursuits are of themselves capable of produ-
cing a decided improvement in our moral sensibilities š
but we hail that joy which is felt in the pursuit of such
occupations, as a sacred gift, which may be compared
to the rain from heaven, sent for the benefit of all:
for increasing the temporal welfare both of the just,
and of the unjust: for procuring blessings equally to
the good and to the evil; but which the former only
know how thoroughly to appreciate, and to apply to the
highest and best advantage.

Botany has its peculiar interest, from embracing the
study of natural bodies which form the connecting link
between the animal and mineral kingdoms. If plants
ceased to grow, animals would cease to exist. No
animal derives its food immediately from unorganised
matter ; and though there are many which prey upon
other animals, yet the victims have always been them-
selves nourished by some plant. Nothing can exceed
the wonderful manner in which provision is made
for the constant supply of those myriads of animated
beings which people the earth, ocean, and atmosphere.
Most of them are not content with every chance vege-
table that may be growing in their path ; and many are
to be fed, and can only be fed, upon some one or two
kinds of vegetable, and would inevitably starve upon
every other besides! When, then, we seek to investi-
gate the laws by which the distribution and the very
existence of animals is regulated, it is of consequence
that we should not overlook even the minutest moss
or fungus that we can detect. It is by such plants
that the first step must often be made towards rendering
the barren and desolate rock a fertile and productive soil,
and converting a spot apparently destined to eternal si-
lence into a scene of lively bustle and delight.

(5.) Unorganised Bodies.—The most prominent dis-
tinction that subsists between the various natural bodies

B 3

0

PRINCIPLES OF BOTANY.

that surround us, is derived from their possessing or
being destitute of an organised structure. The want
of organisation is the peculiar characteristic of mere
brute matter, and affords an evidence of the absence of
the living principle ; and is a clear proof that it has not
been present in those bodies during their formation or
increase. On the other hand, the slightest trace of or-
ganisation discoverable in any natural body is a com-
plete proof that life is, or at least was once, present in
that body. The separate particles of which unorgan-
ised bodies are composed, are either elementary atoms,
or compound molecules, in which certain elementary
atoms are united together by the force of affinity
in a definite proportion. When these separate parti-
cles, or “integrant molecules” as they are termed in
mineralogy, are allowed gradually to coalesce from a
state of solution or of fusion, they then arrange them-
selves into various regular geometric forms, called crys-
tals. These crystals can increase in size only by a
further juxtaposition of similar molecules added to
them externally. When the peculiar circumstances
under which they may be placed do not allow these in-
tegrant molecules to arrange themselves into crystal-
line forms, they may still be able to combine together
into shapeless masses, which possess the same homo-
geneity of character as though they had been regularly
crystallised. All such combinations of unorganised
matter are termed “simple minerals.” Compound
minerals, such as rocks and stones, the ocean, the atmo-
sphere, are merely heterogeneous admixtures of simple
minerals, which naturally exist under a solid, liquid,
or gaseous form. When aggregated into large masses,
_ these “ compound minerals” constitute our earth, and
probably also all the various heavenly bodies.

(6.) Organised Bodies. — Although organised bodies
are made up of the same elementary atoms as those
which compose unorganised ‘bodies, yet are they dis-
tinguishable from these latter, not merely by the pre-
sence of the living principle, but completely and satis-

INTRODUCTION. 7

factorily by the manner in which they increase. The
various parts or organs of which such bodies are composed
are not homogeneous in their structure, like those of sim-
ple minerals ; and their increase is effected by an assimi-
lation of certain particles adapted to its growth, which
are received into the system through certain cavities, or
vessels, from whence they are elaborated, by a peculiar
process, into specific compounds, adapted to the nutri-
tion and development of the individual. These effects
depend upon the presence and activity of a distinct
force, peculiar to the condition under which organised
matter exists, viz. that mysterious principle which we
call “ life,” — a something totally different in its mode
of action from any of the forces to which unorganised
bodies are subjected ; and capable of controlling, and, to
a certain extent, of counteracting, the effects of those
forces. One striking peculiarity in the vital force is its
variable condition, and ultimate secession from all or-
ganised bodies whatever. However effectual, for a
time, in counteracting the influences of the two other
great forces of nature, attraction and affinity, a period,
sooner or later, does always arrive, in which it ceases
to operate, and abandons to silence and inactivity the
dust and ashes which it had for a little while collected,
and employed in forwarding the high interests of ani-
“mated nature.

(7.) Animals and Vegetables. — We may distinguish
organised bodies into animals and vegetables; and our
daily experience is sufficient to satisfy us of the pro-
priety of such a division. Yet is it extremely difficult,
and has hitherto baffled the attempts of naturalists,
to point out the precise limits which separate these two
kingdoms of organised nature; and no definitions of
what is a plant, and what is an animal, have yet been
framed sufficiently guarded and precise to satisfy all the
conditions under which different organised bodies are
found ; but, to-this day, there are some objects’ which
it is very doubtful under which class they ought to be
arranged. Among the higher tribes of organised bodies,

B 4

8 : PRINCIPLES OF BOTANY. >

indeed, there is no difficulty in pointing out numerous
lines of demarcation between the two kingdoms; but, as
we descend in the scale of each, we find an increasing
similarity in external characters, and a closer approxi-
mation between the analogies existing in many. of
those functions which mark the presence of the living
principle, both in the animal and in the vegetable king-
doms. Perhaps, until the contrary shall be distinctly
proved, we may consider the superaddition of “ sen-
sibility” to the living principle as the characteristic
property of animals ; a quality by which the individual
is rendered conscious of its existence or of its wants,
and by which it is induced to seek to satisfy those wants
by some act of volition. It has been supposed — and
both analogy and experiment appear most fully to con-
firm the supposition—that a sense of pain is very nearly,
if not entirely, absent in the inferior tribes of animals.
Even in the higher tribes, certain parts of the body are
incapable of receiving pain; and there seems to be no
absurdity in considering that an animal may be endowed
with just so much sensibility as may be sufficient to
prompt it to select its food, though at the same time its
body may be so organised as to be incapable of transmitting |
painful sensations. But the most constant, if not uni-
versal, distinction, and one which we can readily appre-
ciate, between animals and vegetables,—consists in the
presence or absence of those internal sacs or stomachs,
with which the former alone are provided, for receiving
their food in its crude state, previously to its being
elaborated by the organs of nutrition. pees

PART I.

DESCRIPTIVE BOTANY.

SECTION I.

ORGANOGRAPHY AND GLOSSOLOGY.

CHAPTER I.

ELEMENTARY ORGANS AND TISSUES.

EXTERNAL ORGANS— CONSERVATIVE AND REPRODUCTIVE (9.).
— INTERNAL STRUCTURE ; ELEMENTARY TEXTURE ; CHEMICAL
COMPOSITION (12.). — ELEMENTARY ORGANS ; CELLULAR AND
VASCULAR TISSUES (13.).— COMPOUND ORGANS — INVESTING
AND COMPLEX (28.). — PRIMARY GROUPS OR CLASSES (33.).

(8.) Organs. — Tue various parts of which a plant is
composed have been called its “ organs ;” and this term
is equally applied to those external portions, which may
readily be recognised as being subordinate to the whole,
such as its leaves, roots, flowers, &c., as to certain mi-
nute cells and vessels, of which its internal structure
consists. De Candolle has included every inquiry, both
into the external and internal organisation of plants,
under the title of ‘ Organography ;” although such
details as belong to their external characters have a more
exclusive reference to our descriptive department, whilst
those which relate to their internal organisation are more
especially introductory to our physiological.

(9.) External Organs.— The principal external or-

a

10 DESCRIPTIVE BOTANY. PART I.

gans of which a plant is composed are familiar to every
one. They are, the root, stem, branches, leaves, flowers,
&c. These organs may be conveniently grouped under
two heads, characterised by the nature of the functions
which they are severally destined to perform. The
root, stem, branches, leaves, and some other appendages
to each of these, are concerned in carrying on the func-
tion of nutrition, or that act by which the life of every
separate individual is maintained; and these are, in
consequence, styled the ‘ Conservative” organs. The
flower and fruit, with their various appendages, are
connected with the function of reproduction, by which
the continuance of the species is provided for; and
these are, therefore, named the “ Reproductive” organs,

(10.) Conservative Organs. — The conservative or-
gans, again, may be separated into two series. Every
one is acquainted with the fact, that the stems of most
plants are above ground, and that they affect a more or
less erect position, and are constantly being developed
upwards, whilst the roots of most plants penetrate the
soil with an evident tendency downwards. An imagin-
ary plane, intersecting the plant at the point whence
these opposite tendencies originate, is called the neck :
the stem, and the various organs which accompany it,
are styled the “ ascending,” and the root and its ap-
pendages the “ descending” series. But these defin-
itions do not exactly represent the truth, since there are
certain stems which are strictly subterranean, and have ,
a tendency to creep below the surface of the soil; whilst
there are also certain roots which are aérial, and some
of these scarcely indicate any downward tendency. The
terms employed in defining the two series must, there-
fore, be considered as indicating certain facts, which are
very generally, though not universally, applicable to the
several organs included under each.

(11.) Reproductive Organs.— The reproductive or-
gans may also be classed under two series. The first
is the ‘ Inflorescence,” which includes the flower and
the various appendages to that part of the stem on

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 11

which it is seated ; and the second is the “ Fructifi-
cation,” which embraces the seed, and the different en-
velopes by which it is surrounded, and which collectively
are termed the fruit. This latter series, indeed, consists
of organs which had previously belonged to the former
series during the early stages of their development ; but,
as a very material alteration takes place in their con-
dition after the flower has expanded and faded, they
are considered as having so far changed their character
as to merit a different name from that which they before
possessed. But here, again, our definitions do not apply
to the whole mass of vegetation, since no flowers
or seeds are ever produced by the lowest tribes of
plants ;, but they are propagated by little bodies
termed “ sporules,” which do not require any previous
process for securing their fertility, similar to that which
we shall hereafter show to be essential to the perfection
of true seeds.

(12.) Internal Structure.— Before we enter more
fully into further details respecting these and the other
external organs, we propose to examine the internal
structure of plants; especially as there are certain in-
vesting or cuticular organs, which cannot well be de-
scribed without referring to the elementary organs, of
which the whole structure of the vegetable is composed.

The great simplicity of the vegetable structure, when
contrasted with the complexity of that of animals, is very
remarkable; and whilst every separate function performed
by the latter, seems to require an organ of a peculiar con-
struction, the functions of vegetation are all carried on by
-the intervention of a few simple tissues of the same kind.
Probably, however, this extreme simplicity is much
overrated ; for as yet we know very little of the nume-
rous slight modifications which different plants exhibit
in the arrangement of the several parts of their tis-
sue, and it may be reasonably conjectured, that every
modification of this sort, however slight, implies some
corresponding alteration in the mode of performing the
function. If we cut or fracture any portion of a living

Po- DESCRIPTIVE BOTANY. PART k

plant, we find it to be made up of solid and fluid parts,
and with the aid of the microscope we may observe the
manner in which these parts are disposed. The solid
portions appear somewhat like a spongeous body, pene-
trated by minute cavities, through which the fluids are
dispersed. If we now take a very thin transverse slice
of some succulent stem, as of a cucumber (fig. 1.), and

examine a portion of it under lenses of high powers, it
will present the form of a distinct network, the meshes
of which consist of angular figures, differing in the
number of their sides, and in the degrees of regularity
with which they are disposed. In some cases the regu-
larity of their form and disposition is very remarkable ;
and they are frequently hexagonal. The meshes in
some parts of the slice are much smaller than in others,
especially where they are observed to surround certain
circular openings of a different appearance from the rest
of the cavities. If another slice he taken longitudinally
through the stem ( fig. 2.), and a portion of this be
2

examined in a similar manner, the netlike tissue pre-
sents a somewhat different appearance. The meshes
are for the most part quadrilateral, or nearly so, and ge-
nerally elongated in the direction of the axis of the stem.
The circular openings observed in the former fig. (1.)

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 13

are found to be the sections of tubes, which are often
variously marked by dots, lines, and, in some instances,
are composed of a spirally twisted filament. These
appearances evidently show us that the vegetable struc-
ture is composed of polygonal cells and cylindrical
tubes, so arranged that they lié with their greatest
lengths parallel to the axis of the part in which they
are found. Among the lowest tribes of flowerless plants,
which form an extensive class, no tubes are observable,
and their whole mass is composed of cells alone.

(13.) Elementary Textures.—I1f we now examine the
materials of which these cells and tubes are constructed,
we find them to consist of a delicate, homogeneous
membrane, of extreme tenuity, generally colourless, and
without any distinct traces of organisation. Besides
this, there is a fine cylindrical fibre, which might be com-
pared to transparent catgut ; and this is often spirally
twisted and variously ramified upon the surfaces of the
cells and tubes, in a manner which we shall presently
describe. It is supposed that all the modifications ob-
servable in the internal organisation of plants result
from the various combinations which take place be-
tween these two elementary textures, “Membrane” and
< Fibre.” k ~ i

(14.) Chemical Composition.—It has not been ascer-
tained whether these two organic elements of the vege-
table structure are identical in chemical composition, or
whether, indeed, the membrane and fibre which com-
pose the cells and tubes in different parts of plants are
always of the same kind. The inquiry would be one
of extreme difficulty, if not of absolute impossibility,
with the present resources of chemistry. All that is
known of the composition of these textures has been
derived from experiments made upon the gross mate-
rial, imperfectiy separated from the various matters
which the cells and tubes contain. In this state it is
found to be composed of the three elements, oxygen,
hydrogen, and carbon ; but the exact proportion in
which these are united is uncertain, if, indeed, it be

14 DESCRIPTIVE BOTANY. PART I,

always the same. In the several products of vegetation—
woods, gums, resins, &c.—the proporticns between
these three elements vary considerably; and even a
fourth element, azote, enters as a fundamental ingre-
dient into some of them. It should seem that the
atoms which compose the organic molecules in. the
elementary textures of vegetables, are held together by
some vital property, rather than by the laws of chemi-
cal affinity ; for although these substances may, with
certain precautions, be long preserved in much the same
State as that in which they were left when the vital
principle was first abstracted from them, yet there ap-
pears to have been no very definite chemical union
between their atoms, which are no sooner abandoned to
the influence of surrounding media, than they enter into
new combinations distinct from that under which they
existed in the living plant,

(15.) Elementary Tissues. — There are two element-
ary tissues, which are respectively composed of the two
kinds of elementary organs, the cells and tubes already
noticed. ‘The one is called the “ cellular” tissue, and
consists entirely of cells, and constitutes the chief bulk
of every vegetable: the other is the “vascular” tis-
sue, and is made up of tubes 3 but this latter tissue is
found only in certain families of plants. The vascular
penetrates the cellular tissue in thin cords, which are
composed either of single tubes, or more frequently of
bundles of tubes, running continuously throughout the
plant, and passing into the leaves, where the tubes
separate, and diverge in various directions, and form
the veined-like appearance which these organs generally
present. s ;

(16.) Cellular Tissue. — If a fragment of any plant
be allowed to macerate for some days in water, or if
it be subjected to the action of nitric acid, the several
elementary organs of which it is composed will sepa-
rate from each other, and may then be examined in an
isolated state. When thus detached, the cellular parts
are found to have been made up of minute vesicles, or

SECT. I. ~ ORGANOGRAPHY AND GLOSSOLOGY. .

bladders ( fig. 35): In some
cases these vesicles are nearly
` spherical (a); and, in others,
they approach the form of short
cylinders (b); andin others,again, [|
they are lengthened out, and, *\ J Ld
tapering at each extremity, pre- Nis
sent a fusiform or spindle-shaped appearance (e).
The shortest diameters of those cells which are more or
less spheroidal, vary from the —.1__ to the gly Of an inch ;
but are more frequently found between the soo and s4,.
The fusiform cells, sometimes termed «< closters,” which
abound in the woody fibre of trees, vary in breadth, at
- their thickest part, from the 51,5 to the zy Of an inch.
It is, therefore, entirely owing to the close packing and
mutual compression of these vesicles, that they assume
a polygonal form in the integral state of the tissue.
We may compare the general appearance of this tissue
to a mass of froth, obtained by blowing bubbles in
soap suds or gum water. The bubbles, by mutual
pressure, assume a polygonal structure towards the
centre of the mass, but have spherical surfaces towards
the outside. In the cells which are thus formed,
however, each cavity is separated from its neighbour by
only a single partition ; whilst, in the vegetable tissue,
each partition is of course double. As the cellular
tissue alone, without tubes, exists in a large class of
plants, it is evident that the most general functions of
vegetation must be carried on by it: but, as such an
inquiry belongs to the physiological department, we
need not say any thing concerning it at present.
(1 7.) Polygonal Structure.— If 4.

we place a number of equal circles
in contact, on a plane surface,
each circle may be touched by
six others; and if we suppose
them to be so pressed together,
that the curvature of each circle
at the points of contact may pass

DESCRIPTIVE BOTANY. PART 1.

into straight lines, the circles will become hexagons
(fig. 4.). Ifa number of spheres, of equal size, be in
contact, each may be touched by twelve others
(fig. 5. a); and if

the whole be subjected

to pressure, so that ,

their surfaces may be- \

come flattened at these

twelve points, the

spheres will become

rhomboidal-dodecahedrons (fig. 5. b). But, as the vesi-
cles which compose the cellular tissue are never exactly of
the same dimensions, the polygonal forms which they
assume will not be so strictly regular as the geometric
figure we have just mentioned. Still, there is often a
very marked approximation towards such a regularity ;
more especially in those parts of the plant which are the
best developed, or have been most securely defended,
as in the case of the pith, from the influence of disturb.
ing causes. Where the vesicles are elongated, the dode-
cahedrons assume the character of rectangular prisms,
terminated by four-sided pyramids, whose faces replace
the angles of the pyramids at various degrees of inclin-
ation to the axis ( fig. 6.). If sections be made through
these, by planes paral- ,,

lel and perpendicular to A

the faces of the prisms, f \

they will exhibit either 4

hexagonal or quadran.

gular surfaces, accord.

ing to circumstances, as

a simple inspection of the diagrams will be sufficient to
show. Cells of these forms may be so aggregated
(fig. 7.) as to fill space as completely as the hexagonal
prisms of the honeycomb; but as the extreme regularity
here delineated is never actually attained in nature, the
cellular tissue becomes every where penetrated by small
cavities, by which an intercellular communication is
maintained throughout the mass. These channels are

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 17

termed “ intercellular passages,’
in some portions of the tissue,
but are not to be detected in ,
others. The forms under ¥
which the vesicles appear, a
on making a section through
the cellular tissue, are much

: i
influenced by local pressure,
distension, and the more
obscure causes which depend
upon the specific qualities of |
each plant; and these forms
are detailed with greater minuteness, in works which
professedly treat of this part of our subject, in a more
elaborate manner than our limits will afford.

(18.) Striated and dotted Cells. — The separate vesi-
cles which compose the cells, frequently exhibit mark-
ings upon their surface, whose origin it is not always
easy to account for. Many of these appearances were
formerly mistaken for open pores through the mem.
brane, by which a communication was supposed to
Subsist between two contiguous cells. Some observers

ave considered them to be glands ; and others have
described them as nascent vesicles, generated within
the surface of the old cells, and which are afterwards
developed, and thus are formed into new tissue. The
best representations of these various appearances, is given
by Mr. Slack, in the forty-ninth volume of the “ Trans-
actions of the Society of Arts;” and he is inclined
to refer the greater part of them to one common origin,
viz. the Modification of the conditions under which
the elementary fibre is developed on the inner surface
of the vesicles. In some vesicles, this fibre is spirally
coiled over the whole surface, and the contiguous coils
are blended together, so as to render it very difficult to
distinguish them: in others, the coils are wide apart,
and distinctly visible (io 8.0). — In sommes casey the
fibre is branched (b); and in others, the branches
graft together, and the surface of the vesicle then appears

c

“and are very evident

r —
taste ladle rrr i

18 DESCRIPTIVE BOTANY. PART I.

reticulated ; whilst it sometimes happens, that the coils
of aclosely developed
spiral become sepa-
rated at intervals,
and then close to-
gether again, so as to
leave openings which
look like slashes and
dots in the vesicle itself (c). There are some cases, how-
ever, in which the dots on the vesicles appear to be
thickened spots; and especially those which abound
on the elongated cells, forming the woody fibre of
Coniferous, and some few other trees. These are very
peculiarly marked by large dots of a glandular aspect,
with a dark spot in the centre (fig. 9.); which latter
circumstance, however, may probably be owing to the
manner in which the light is refracted s
through them. It is a remarkable fact,
that these appearances are strictly imitated
in many fossil woods; and botanists are
thus enabled, by the inspection of a small
fragment of such plants, to pronounce with
certainty, upon the Class and Order to which
they have belonged. In some cases it hap-
pens, that theelementary fibre alone remains
entire, like a skeleton to the tissue, whilst
the membrane which originally formed the walls of the
cells has been obliterated. It is unnecessary to dwell
further upon the various appearances which the cellular
tissue presents, especially as nothing whatever is known
of the way in which a dissimilarity of structure, is con-
peed with any modification in the functions performed
yit.

(19.) Contents of the Cells. — The cellular tissue is
every where replete with juices, containing minute gra-
nules. of amylaceous, resinous, and other qualities,
which appear to be the result of peculiar secretions,
` formed by the vesicles themselves. Those which com.
pose the woody fibre, secrete an abundance of a car.

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 19

bonaceous material, which ultimately fills them, and
gives consistency to the stem. The juicy contents of
some cells are highly coloured; and even contiguous
cells often contain liquids of different tints, although
there is no apparent difference in their structure,
which might indicate some cause for such diversity.
Indeed, the brilliant hues of flowers, and the various
. tints of the foliage, all depend upon the coloured juices,

or the globules floating in them, which are contained in
the vesicles of the cellular tissue, and have been elabo-
rated by them; but they never depend upon the cr-
ganic membrane itself, of which they are composed,
and which is always colourless, or, at best, only slightly
tinged with green. i

(20.) Raphides. — But, besides the strictly organic
compounds, there are also certain chemical combinations
whose results appear in the form of minute crystalline
spiculæ, which have been deposited from the heteroge-
neous admixture contained in the cells. These have
been termed “ raphides,” and were originally considered
to be organised bodies. One of most common occur-
rence, is the oxalate of lime, the crystals of which are
Sometimes of such magnitude, and their forms so com-
plete, that the law of their crystallographic structure —
may bé readily recognised.

(21.) Cavities in the Tissue.— Besides the intercel-
lular passages mentioned above (art. 17.), there are
other well-defined cavities in the cellular tissue, which
serve either for the reception of various secreted matters,
as resins, oils, &c., or else contain air. ‘The former are
termed “ receptacles,” or “ vasa propria,” and are com-
monly of a spheroidal, cylindrical, or oblong form, the
result of an enlargement of the intercellular passages,
or of a rupture in the tissue itself, The latter are
termed “ air-cells,” or “lacune ;” and, although these
are most frequently very irregular in their form, they
are often constructed in a more definite manner than
the receptacles, and then consist of extremely regular

¢ 2

80 DESCRIPTIVE BOTANY. PART I,

and well-defined spaces, of hexagonal and other geo-
metric forms. In these cases the cellular tissue is so
arranged as to separate the lacune from each other,
both by vertical and transverse di-

visions ( fig. 10.) ; and the whole is

placed round the axis of the stem

in a beautiful and symmetrical man-

ner, The stems and leaf-stalks of

aquatics are every where filled with

lacune, and the air contained in

them serves the purpose of elevating

these parts towards the surface of the water.

(22.) Vascular Tissue. — This tissue consists of
tubes, which are also formed of membrane, to all ap.
pearance identical with that which composes the vesi-
cles of the cellular tissue. Some of these tubes bear a
close resemblance to the elongated cells already de-
scribed, and may certainly be considered as mere mo-
difications of that form of tissue; and, indeed, all
tubes, whatever be their length, appear to taper off
at each extremity into conical and closed terminations
(fig.11. a). A communication evidently subsists be-
tween some of these tubes, at the
point where they overlap each other
and are about to terminate, form-
ing an oval perforation of large di-
mensions. Some tubes are derived |
from the apposition of cylindrical | |
cells, base to base (b), and the sub-
sequent obliteration of the terminal
portions of their membrane. In cer-
tain cases this membrane remains
wholly, or in part, in the form of
transverse septa or diaphragms, and
then these organs present a tissue in-
termediate between the cellular and rm
vascular. The true vessels, or long tubes, which more
strictly compose the vascular tissue, are distinguishable
into two kinds, between which, however, there are cer-

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 21

tain intermediate forms, which establish the fact of a
most intimate connection, and even appear to indicate
a common origin. The two kinds of vessels alluded
to, are the spiral vessels and the ducts.

(23.) Spiral Vessels. — These are generally termed
“ trachee,” from the resemblance which they bear to
the windpipe, and more especially to the air-cells of
insects, which are called by the same name. They
consist of a membranous tube, on whose inner surface

a cylindrical fibre is spirally coiled (fig.12. a); and
the whole so completely

united, that if the vessel
be ruptured, and the thread
uncoiled, no trace of the
membrane is to be. seen,
excepting towards the co-
nical extremity of the ves-
sel, where the coils of the
fibre are wider apart. In
some trachee, indeed, the
successive coils are not in
contact with each other,
and then the investing
membrane is sufficiently
apparent. Sometimes. the
fibre branches into two

threads (b), and each continues its course in separate
but contiguous coils; and instances may be found,
where the contiguous coils of separate threads range (c)
between this number and twenty-two! The diameters
of these vessels vary from the sso up to the 545
of an inch. They may be detected with the greatest
facility upon tearing asunder the leaves of many plants,
and especially are very visible in some species of Ama-
ryllis, when they form a set of parallel fibres, nearly as
conspicuous as the threads in a spider’s web, and are
Strong enough to support the weight of a considerable
portion of the leaf. By carefully unravelling them,
they may sometimes be extended to eighteen inches in
c 3

292 DESCRIPTIVE BOTANY.. f FART I.

length. When the stems of the Plantain and Banana
are cut into slices, the tracheæ in which they abound
unravel before the edge of the knife, and form floc-
culent masses, which may be collected, and wrought
into a material possessing certain advantages superior to
those of cotton, for the manufacturer. The expense,
however, of collecting this delicate substance has been
found too great to admit of its being applied to any
really useful purpose ; as an entire plantain does not
yield above a drachm and a half of tracheæ.

Trachee have been detected ina very few of the flower-
less plants, and only among the higher tribes of them,
such as ferns and club-mosses.

(24.) Ducts. — The elementary fibre divides and
ramifies on the inner surface of some tubes which com-
pose the vascular, just as it does on the vesicles which
compose the cellular tissue (art. 18.), and forms linear,
dotted, and reticulated markings upon them. Some
tubes are true trachee in one part of their course,
whilst in another the fibre becomes ruptured at intervals,
and the detached portions, uniting at their extremities,
form .rings; and where the ruptures are more frea
quent, these fragments of the fibre present linear and
dotted markings adhering to the surface, and following
a spiral course (fig. 13.). 13
The name of ducts, is gene-
rally given to all varieties of
tubes composing the vas-
cular tissue, which are not,
strictly speaking, true trachee;
and they are separately named
according to the appearances
which the markings on their
surface assume ; ‘such as É
dotted, striped, and reticulated K
ducts. Some authors, how. &
eyer, include all the marked
tubes, together with the spi-
ral vessels, under the general

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. — 23

name of tracheæ. The diameters of most ducts are
generally larger than those of the true trachee, be-
longing to the same ‘plant ; and the dotted ducts, espe-
cially, are very distinctly visible to the naked eye, and
even large enough to admit of a delicate hair being thrust
into them, where they are divided by a transverse sec-
tion of the stem.

(25.) Woody Fibres and Layers.—When a piece of
wood is split longitudinally, or in the direction of the
stem, it cleaves more readily than when it is broken
transversely. And many kinds of wood may be thus
split in the direction of the grain, into very thin
layers, and these again be subdivided into fibres of ex-
treme tenuity. The fibres obtained by macerating flax,
hemp, and other plants used for cordage, are of this
description. If these fibres are examined under the
microscope, it will be seen that they do not consist of
continuous tubes or filaments alone, but are composed
of various combinations of vascular and cellular tissue.
Every separation in the direction of the fibves (fig. 14.
ad) occasions the disunion of i
contiguous tubes or vesicles, but
any transverse fracture (b b^)
can be obtained only by the ac-
tual rupture of these organs
themselves. It is upon this cir-
cumstance that the strength of
woody fibre depends, which is
very different in different plants.
It has been experimentally ascer-
tained, that the strength of silk,
New-Zealand flax (Phormium
tenax), hemp, and flax, are re-
spectively as the numbers 34 : 234: 161: 113.

As the cells and tubes are of different lengths, their
extremities overlap each other, and thus as it were
dovetail the mass together. Wherever a transverse
fracture is most readily produced, as in the suture by
which a seed-vessel opens, or at the scar which is

c 4

i
{
i
A
pE
t

Aee e e a S

aoa aaan aee hema

Ss SOF Seni? ee aa Aa i aaa

J4 DESCRIPTIVE BOTANY. PART I.

left where the leaf falls, we may conceive the vesicles
which are contiguous to the plane of separation on
either side, to be so arranged, that all their ends lie in
this plane (fig. 14. ¢ ey

(26.) Contents of the Tubes.—A considerable diver.
sity of opinion exists as to the probable uses of the vas-
cular tissue in those plants in which it is found. Some
observers consider the trachee destined to convey air
through various parts of the plant; and support their
opinion by the fact, that air is very commonly to be
observed in them, at least during certain seasons of the
year. Others consider all vessels to be channels for the
sap and nutritious juices. That most of them contain
liquid matter is sufficiently evident, but what may be
the precise use of each in particular is at present very
uncertain.

(27.) Vital Vessels.—Besides the tracher and ducts,
just described, there is found in certain plants, and
possibly in all where the vascular tissue is most de-
veloped, a sort of network formed of anastomosing tubes
(fig. 15.) and situate a little way beneath the surface of

15 the bark, through which fluids cer-

| tainly pass, in a manner we shall

d hereafter describe. These tubes are

| termed “ vital vessels,” or “ ducts of

the latex,” by their discoverer, M,

Schultz. They are by far the smallest

of all the tubes, and extremely diffi-

cult to be detected in young shoots,

but may be seen with tolerable fa-

cility as they become older. They are

i 44 entirely without markings of any kind,

a all parts of the plant, from the roots
to the leaves,

(28.) Compound Organs.—The organs hitherto de..
scribed, may be considered as the organic elements out
of which plants are constructed, just as we say that
minerals are formed out of certain integrant molecules,
We have next to notice the various compound organs,

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 25

` which result from different combinations of these ele-
mentary organs. These may be considered as of two
kinds. The first includes such as are found on the
surface of the several external organs, of which in fact
they are only subordinate parts, just as the.skin, hair,
feathers, &c. clothe the body and particular members of
animals. We may call these superficial organs, the
“ Investing organs.” The other kind may be styled
the ‘Complex organs,” and will include all those
which we have already classed under the ascending and
descending series, alluded to in art. 10., and of which the
investing organs form only subordinate parts.

(29.) Epidermis.—The surface of all parts of plants
(except the spongioles and some stigmata to be described
hereafter) is covered, at least when young, with a thin
skin, which may easily be detached, especially from the
leaves, and most readily after these organs have been
allowed to macerate for a few days in water. This
skin is termed the “ epidermis,” or “ cuticle,” and
when placed under the microscope, it exhibits a
delicate network (jig. 16.), whose meshes are either

quadrangular, hexagonal, or of other polygonal forms;
or else they are irregularly bordered by waved and
sinuous lines, extending over the whole surface. Very
frequently also, a set of pores may be observed, hav-
ing a sort of glandular border (a), which are scat-

tered over the epidermis at intervals, These pores

are termed “stomata.” It was not until very lately
that the real structure of the epidermis was well under-
stood; but M. A. Brongniart has shown, in the

26 A DESCRIPTIVE BOTANY, PART 1.

Ann. des Sciences for February, 1834, that a lengthened
maceration causes it to separate into three parts (fig. 17.).
The outermost of these, consists of an extremely de-

licate homogeneous pellicle (a), without any very
decided traces of organisation, though occasionally
somewhat granulated in its appearance, and also marked
by lines, which are merely the spaces left between the
impressions made upon it by that portion of the cellular
tissue with which it was in contact. It is generally
perforated by small oval slits, at the places where
the stomata exist. A lamina of flattened vesicles (6),
is closely united with this pellicle, and forms the second
portion of the epidermis; the vesicles occupy the ,
spaces included between the linear markings observed
upon the surface. Sometimes this part contains more
than, one lamina of flattened vesicles. The vesicles are
in close contact, excepting immediately under the spaces
occupied by the slits in the pellicle. The third part
alluded to, consists of the stomata (c), which are placed
a little further from the pellicle than the lamina of cells
last mentioned, and which, as we stated, is in immediate
contact with it. : ;

(30.) Stomata.—Each stoma is most generally com-

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY- 2

posed of two lunate vesicles (fig. 18. a), which may
be detached by maceration in- water, but in the epi-
dermis are in close contact at their extremities, and thus
form a sort of border round the area occupied by the
slits in the outer pel-

licle. The space be-

tween these vesicles

may be contracted or

completely closed, by

an alteration in their

position. Some sto-

mata appear to con-

sist of a single annular vesicle (b), which may pos-
sibly be occasioned by the blending of two; or this
may be owing to an optical illusion. In some cases,
the stomata are square (c); in others, the orifice ap-
pears dark, but whether from the interposition of a
peculiar membrane, or merely by the deposit of se-
creted matters, seems to be doubtful. As the vesicles
of the stomata contain granular matter, they appear to
be more nearly related to those of the cellular tissue
in the substance of the leaf beneath the epidermis,
which contain a similar matter, than to the flattened
cells which compose this organ itself, and which are
generally without grains, and perfectly transparent.
Stomata do not occur on flowerless plants, excepting
among their higher tribes, and which also possess tra-
chee (art. 23.). They are also absent on the sub-
merged parts of aquatics, and are not to be found on
certain parasitic plants.

(31.) Pubescence.—There are great varieties in the
forms under which certain prolongations of the cellular
tissue occur, on the surface of different parts of plants.
To the naked eye, such appendages to the epidermis re-
semble hair, silk, bristles, scales, &c., and have received
these names in descriptive botany. Under the micro-
scope, they are all found to be composed of cellular
tissue ; sometimes of a single vesicle, at others of

2 ST EEE

e a n veer

28 DESCRIPTIVE BOTANY. PART I.

several united ( fig. 19.). In some, the vesicles are
rigid, elongated, and sharp spicule ; in others they

“constitute a globular mass of a glandular structure
( fig. 20.), and secrete various juices of glutinous,

\
N

Dion

MEL OAs

Sweet, acrid, and other properties. Stings are sharp-
pointed hollow bristles, perforated at the extremity, and
seated on a glandular mass of cellular tissue which
secretes the poison (fig. 20. a). When the hand is
gently pressed against them, the delicate point pene-
trates some pore of the skin, .at the same time the
bristle is forced against the gland at its base, and the
poison rises into the tube in a manner strictly analogous
to that by which a discharge of venom is effected from

£ f~

A a,

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. | 29

the fangs of a serpent’s tooth. The

bristles have sometimes a stellate NV Z
form (fig. 21. a); and sometimes bs O3 i
the pubescence is composed of little AAS ZY
plates or scales (b). i
(32.) Complex Organs.—Although the epidermis and
several of the other investing organs are of a compound
character, they are still constructed in a much more
simple manner than the organs which they invest. We
have proposed, therefore (art, 28.), to separate the
latter under the name of “ complex organs,” which
will include all that have been already enumerated
under the name of external organs (art. 9.), together
with various appendages to be found on some of them.
These latter are not so generally noticed by casual ob-
servers ; but it will be necessary for us presently to de-
scribe them, when we treat of the forms and structure of
these organs themselves. But we shall here postpone
for a while the descriptive details of these organs, in
order that the reader may first obtain some general
notions of the three great natural divisions under which
all plants may be arranged. Although this method -of
treating our subject may seem to indicate a great want
of system, it appears to us highly convenient that every
one should be acquainted. with these divisions as early as
Possible before he enters on certain details which can-
not be so weli appreciated or discussed without an
occasional reference being made to them. It must be
remembered that we have not proposed to ourselves any
very methodical discussion of the several departments
of our science, which would have required a series of
separate treatises, but that we aim chiefly at conducting
the general reader, by such steps as may seem suffi-
ciently adapted to the purpose, to the ready comprehen-
sion of some of the best established facts in vegetable
physiology, and to give him an idea of what botany
proposes to attempt,
(33.) Primary Groups.—We apply the term ‘“‘ spe-
cies” to an assemblage of individuals which have sprung

30 ; ; DESCRIPTIVE BOTANY. PART I.

from seeds of the same common stock. Where these
individuals differ in certain respects among themselves,
they are termed “varieties;” but all varieties of the.
same species may, under particular circumstances, be
produced from the seeds of one plant. When different
species bear a striking resemblance to each other, they
are classed together in a group which is termed a
“genus ;” and such genera as agree in several points,
form a higher group called an “order ;” and those
orders which are most nearly related, constitute our
chief or primary groups, termed “ classes.” Minor
groups of subordinate value may be formed in each of
these ; but we do not consider it necessary at present
to enter into further details of this kind. We merely
propose to explain some of the chief characters by
which all plants may be grouped under three distinct
classes. The considerations upon which these groups
depend, do not rest upon any one solitary fact relative
to the structure or functions of all the species they
contain ; for there is no leading characteristic in either
class which is not liable to some objection, if it were to
be considered as the only distinguishing mark for de-
ciding the claims of a species to be included in that
class. But where one leading characteristic is deficient
in one species, and another in another, it is from the
aggregate of such as are present that we must de-
cide upon the class to which each should be referred,
With very few exceptions, however, nearly all plants
may be referred by any botanist, at a single glance, and
with unerring -certainty, to their proper class ; and a
mere fragment even of the stem, leaf, or some other
part, is often quite sufficient to enable him to decide
this question. The names of .these three classes are
derived from one of the chief characteristics which
prevails through nearly all the species included under
each of them separately. This we shall presently ex.
plain ; but the reader may understand these names to
be Dicotyledones, Monocotyledones, and Acotyledones ;
and that the two former of these classes have respect-

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. Si

ively the names of Ewogene and, Endogene. The
former names are derived from peculiarities connected
with the structure of the seed ; the latter, from a con-

sideration of the internal organisation of the plants
themselves.

(34.) Dicotyledones, or Exogene. —
(1-) Structure of the Seed.

Beans, peas, almonds, the kernels of our stone fruits,
&c. afford us familiar examples of the structure of the

seeds of dicotyledonous plants (fig. 22.). When the

outer skin is removed, we find that they are composed
of two large fleshy lobes (a), termed “cotyledons,”
which are attached toa small rudimentary germ (b),
almost entirely concealed between them. The entire
mass forms the “embryo,” and the skin which invested
it is termed the “seed-cover.”. After the seed has

been sown, and germination has commenced, the two

cotyledons expand and represent (what in fact they
are) a pair of imperfect leaves, but differ in many
respects from the leaves which are subsequently de-
veloped. One extremity of the little germ to which
the cotyledons are attached, is termed the «< radicle,”
and this descending into the ground becomes the root.
The other extremity is termed the < plumule,” and
consists of the rudimentary leaves and stem. In these
examples, where the embryo occupies the whole space
within the seed-cover, the fleshy cotyledons contain. the

ee

Ser tes get = ers <= — s
PRO RE, REIT a a a SAT E a

32 DESCRIPTIVE BOTANY. PART I.

nutriment on which the young plant subsists until the
root is sufficiently developed to support it. But there
are other cases, as in the seeds of the castor_oil plant
{Ricinus communis), the marvel of Peru (Mirabilis
Jalapa), &c., where the cotyledons are thinner and
more leaf-like (fig. 23. a), and the embryo is wholly

` or partially imbedded. in a nutritive matter termed the
“albumen ” (b), which serves to develope the plant in
the early stages of its growth. The few exceptions
which occur in the dicotyledonous character of the
embryos of this class, will be noticed when we enter
into further details concerning seeds in ‘general.

(2.) Organisation of the Stem.

The most important characters in the organisation
of most stems of this class, depend upon the manner in
which they increase in thickness. In young and suc.
culent stems, we find a solid cylindric or prismatic
mass composed of cellular tissue, and termed the
£ pith:” this is surrounded by a ring of vessels, consisting
of tracheæ and ducts, and named the “medullary sheath.”
The whole is coated by the epidermis. Afterwards,
a further development both of cellular and vascular
tissues takes place between the medullary sheath and
epidermis, and these form one layer of wood, and also
one layer of bark, by the time that a stem of one year’s
growth is completed. During the second year, a fresh
development takes place between the wood and bark
previously formed. This fresh matter appears at first
as a semifluid or viscous mass termed “ cambium,”

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 33

which is gradually organised, and ultimately separates
into two layers—one making an addition to the wood, and
the other to the bark, which had been previously formed.
Hence a layer of new wood forms a ring round the old
wood, and a layer of new bark round the new wood;
whilst the old layer of bark, being necessarily thrust out.
wards, is ruptured and withers, though it still continues
to form an outer coat over the whole stem. A layer of
fresh wood and another of fresh bark are in this way de-
posited every year ; and in many cases, we may ascertain
the exact age of a tree by the number of the concentric
zones observable upon making a transverse section of its
stem. Thus, in fig. 24., a is the pith, b represents three
layers of wood, and ¢ an a,

equal number of layers SAWI | Wien
of bark. Besides these
concentric zoned appear-
ances on the surface of £
the section, there are also
other traces running in
straight lines, radiating -

from the centre to the “~ a ob
circumference, which are formed of cellular tissue,
and termed. “ medullary rays.” Either of these three cir-
cumstances, then— the existence of a pith, the appearance

c

of concentric zones ;

or the presence of medullary rays -—
affords a sufficient ¢

haracteristic by which we recognise
the structure of dicotyledonous plants. The plants of
this class are further named *“Exogene,” from the cir-
cumstance of their stems increasing in thickness by fresh
materials, which are arranged “ externally” with respect
to the old layers. The oldest and hardest parts of such
stems lie towards the centre, as may be readily seen in
any tree growing in our temperate zone,

(35.) Monocotyledones, or Endogene, —
(1.) Structure of,the Seed.
The general structure of the seeds of this class may
be exemplified by an examination of a grain of Indian
D

34 DESCRIPTIVE BOTANY. PART I.

corn, wheat, &c.; or of a seed of an onion, lily, &e
(fig. 25.). An albuminous mass (a). forms the mair

|
i

bulk of most of these seeds, and the embryo (b) is
placed within it towards the centre, or on one side.
The embryo is not so distinctly ‘developed in the seeds
of this class as in those of the last, and its several
parts cannot always be readily recognised before
germination has commenced. Its general character is
that of a cylindrical body, tapering more or less at the
extremities, from one of which protrudes the radicle, and
from the other arises a single, conical, and almost solid
cotyledon. This elongates, and is ultimately pierced
by a leaf, rolled into a conical form, and which was at
first completely invested by the cotyledon.

>

(2.) Organisation of the Stem,

In Monocotyledones, there is no distinction between
pith, wood, and bark ; but their stems consist of a cy-
lindrical mass of cellular tissue, through which bundles
of vascular tissue are distributed in a scattered manner
(Jig. 26.). Every fresh 25 ATER
development of new mat. fii fie Cee a SM
ter is carried towards the no
centre of the stem, and, as fie = te
the stem elongates, the (igi mn Wa
outer parts become more WMI | | l l | PIY:
and moresolidified, whilst ee nn | i
the inner remain soft. I ne a HE
These stems possess no traces of medullary rays,

hp

ST a ae ea eae eae

~

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 35

plants of this class are termed “ Endogene,” from the
circumstance of the newly formed materials being always
developed towards the innermost part of their stems. A
piece of cane is a familiar example for illustrating this
structure ; but we have no woody plants in-our climate
belonging to this class,and very few even which possess -
herbaceous stems, if we except the hollow culms of the
grasses, where the development of the materials towards
the centre is not sufficiently rapid to keep pace with the

elongation of the stem, and the tissue is in consequence
ruptured.

(36.) Acotyledones. —
(1.) Structure of the Sporules.

The class to which we now refer, includes an ex-
tensive series of plants, grouped under several orders,
which differ considerably in many particulars. The
whole agree, however, in the important circumstance of
never bearing flowers, like those of the two former
classes : hence they are termed “ cryptogamic,” in con.
tradistinction to “ phanerogamic,” which is applied to

all flowering species. Having no flowers, they produce
no true seeds ; but, in lieu of them, are furnished with
what certainly bear a considerable resemblance to seed,
viz. small minute granular bodies capable of becoming

distinct plants. The manner in which these “ sporules,”
as they are termed, are produced, is very various in the
different orders of this class, but forms no part of our
present inquiry. They are also variously shaped, but
generally spherical or spheroidal, and are not separable
into distinct parts, with radicle and cotyledon, like the
seeds of phanerogamous plants. In germinating, the
sporules are developed by an increase
of cellular tissue, which appears in the
form of rounded masses and filament.
ous chords (fig. 27.). Among the
higher tribes, roots are afterwards
produced ; and a part which is more
or less elevated above the soil

» is the representative
D2

DESCRIPTIVE BOTANY. PART I.

both of the stem and leaves of phanerogamous plants
combined. In the lower tribes, however, there is sel-
dom any separation of parts into distinct organs, but
the functions of nutrition are carried on in an obscure
manner by the general mass.

(2.) Internal Organisation,

The internal organisation of acotyledonous plants, is
not sufficiently uniform in the different orders, to allow
of their being characterised by any appellation derived
from their mode of development, as in the case of the
Exogene and Endogene. But acotyledonous plants
may be separated into two groups: the one, termed
“ Ductulose,” characterised by the existence of a vas-
cular tissue, and by a mode of development much re-
sembling that of the Endogene; the other, termed
“ Eductulose,” or “ Celulares,” is entirely composed
of cellular tissue. De Candolle even considers the for-
mer group, in spite of their cryptogamic character, to
possess a monocotyledonous mode of development in
the germination of their sporules, and keeps them se-
parate from the others, as a distinct class. The latter
group may be strictly termed ‘ Cellulares,” from their
being composed of cellular tissue alone, and thus sepa-
rated from the “ Vasculares,” which will include the
rest of vegetation (as well cryptogamic as phanero-
gamic), possessing a vascular structure. The class Aco-
tyledones is, however, very readily recognisable by its
external appearance alone; and the general characters of
the several orders which it embraces — ferns, mosses,
lichens, seaweeds, fungi, &c.— ere pretty ‘familiarly `
known as examples.

(37.) Tabular View.—In the very slight sketch here
given of the primary groups under which all plants may
be arranged, we have not pretended to notice many
terms which different botanists have applied to them ;
but we shall now collect the substance of what we
have said in the form of a table, which may serve
to assist the memory of the reader in fixing any of

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 37

the terms here employed, which may chance to be new
to him. ?

Primary Groups, characterised by certain Considerations
taken from particular Parts.
Embryo. Structure. Fructification.

1. Dicotyledones. Exogenz.
2. Monocotyledones. Endogene. | Phanerogame.

3. Ductulosæ.
x } Acotyledones. Ga, } Cryptogamæ.

CHAP. II:
NUTRITIVE ORGANS.

[j
FUNDAMENTAL ORGANS (38.). — ROOT AND APPENDAGES (39. ).
— STEMS (AERIAL) (43.).— INTERNAL STRUCTURE (45.).
— FORMS AND DIRECTIONS (53.). —BUDS (56. ).-— BRANCHES
(58.)— AND THEIR MODIFICATIONS (61. ). — SUBTERRANEAN
STEMS AND BRANCHES (62.).— TUBERS AND BULBS; THEIR
AFFINITY (63.). — APPENDAGES TO THE STEMS (67.).

(38.) Fundamental Organs. — Wx may refer back to
articles 8, 9, &c. for a general notice of the complex
organs, which we are now about to describe more in.
detail, though we do not propose to enumerate all the
varieties of form which these organs assume. There
are , certain appendages both to the stem and root,
(or ascending and descending “ axes” of vegetation),
which are of very little importance in carrying on
the function of nutrition, These appendages, as the
thorns, scales, tendrils, &c. found on some stems,
have without doubt their respective uses; but as the
plant may be deprived of them, and still continue to
vegetate as freely as when they were present, they are
evidently not to be considered as fundamentally essential
-to the support of life. Moreover, they may in all cases
be referred to certain modifications and metamorphoses,
which have taken place in one or other of the three
D 3

88 DESCRIPTIVE BOTANY. PART I.

organs — the root, stem, and leaf,—which are more es.
pecially considered to be the ‘ fundamental organs” of
nutrition. The presence of neither of these can be
dispensed with without injuring vegetation, and ulti-
mately involving the destruction of the individual; unless
where some means have been provided (as we shall see
in the case of parasitic plants) to supply their deficiency,
or where (as in the lowest tribes of cryptogamic plants)
they are probably so blended and confounded together
that we are not'able to distinguish them.

(39.) Root.— The most common position for the
roots of plants, is at the base of the stem, from whence:
they descend into the ground, gradually tapering to a
point, and giving off filamentous branches on all sides,
in an irregular and indeterminate manner. These
branches of the roots are termed “ fibrils,” and are
composed of ducts and cellular tissue, and covered by an
epidermis, except at their extremities where the cellular
tissue is exposed. It is here that the true absorbents of
the root exist, termed its “‘ spongioles.” The structure of `
the main trunk, “ caudex,” or “ tap” of the root (when
well developed) is strikingly analogous to that of the
stem, except that in dicotyledonous plants there is no
pith, and in all cases the epidermis is without stomata. i
The medullary rays, however, are present; and the
bark generally bears a much larger proportion to the
whole mass, than in the stem. This latter circumstance
is owing to its being kept moist by its underground
position, which renders it more capable of disten-
tion, In the carrot, this is well exhibited by a differ-
ence in the colours of these parts. The concentric woody
layers are not distinguishable, and it very seldom hap-
pens that trachee are found in roots. They are very
rarely of a green colour, excepting some of those which
are developed above ground ; and even then it is seldom
_ more than the spongioles which are thus partially
tinted. Where the root has: no descending caudex,
which in some plants soon dies away, the fibrils are
given off from below the neck, or from a flattened dise

\
SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 39

which represents the caudex, as, for instance, in the
bulbs of hyacinths. Roots, however, may be developed
from any part of the stem and branches, if these are
` duly subjected to the influence of moisture and shade ;
and some plants of tropical climates constantly produce
roots from their stems and branches, which descending
into the ground become fixed, and serve to support the
superincumbent vegetation, and thus enable it to ex-
tend over a large tract of ground. The most celebrated
example of the kind is the banyan-tree of the East
Indies (fig.28.). In this case, it appears that when
mee aS “7

=)

the roots have reached the ground, the exposed portion
assumes the character of a stem. It has, indeed, been
asserted that the stem and root are so entirely distinct,
that the latter is never capable of assuming the cha-

racter of the former. But it is not uncommon to find
ash-trees which have grown on the stumps of pollard
willows and have sent their roots through the decayed
wood into the ground ; the exposed roots of the ash, when
the willows have fallen to pieces, become coated with
a green bark, and do not appear to differ in any respect
from the trunk itself. At all events, many roots are as
capable of producing stems or branches, as these are of -
D 4

DESCRIPTIVE BOTANY. PART I,

forming roots: this is often the case with the white
poplar, and certain elms which throw up their nu-
merous suckers, to the great detriment of the pasturage
when planted in meadow land.

Besides the important purpose which the root is more
especially destined to serve, of absorbing nutriment, it
_ Is generally so placed as to take firm hold in the ground,
and thus enables the plant to maintain its position in
one and the same spot during its lifetime. There
are, however, certain plants, as the common duck-
weeds (Lemne, fig. 31. b), which float on the surface
of ponds, whose roots are suspended in the water
without ever reaching the bottom. There are others
termed “ air-plants” (some of the Orchidee), whose
roots cling closely to the branches of trees, and derive
their nutriment from the moist atmosphere perpetually
hanging over a tropical. forest 3 and these plants could
not live long if they were planted in the ground.

(40.) Forms of Roots. —'The various forms which
roots assume need not be dwelt upon here ; they are
such as may be readily learnt in any elementary work,

but their description would involve us in details fo;
which we have not space.

(41.) Appendages to the Root.—There are not many
distinct appendages to be found on roots. In some
fibrils, there are swollen nodosities (fig. 29.), and on

_ others there are little tuberous excrescences. In
some, the fibrils become very fleshy, and are swollen
into masses (fig. 30.), having an ovate (a), palmate

\

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 41

(0), or fasciculate (c) appearance, as in many of the
Orchidee. All these swollen portions serve as reser-

voirs of nutriment for the future use of the plant, but
they should not be confounded with certain analogous
modifications of the underground portions of stems,
which we shall describe when we speak of. the real
“ tuber.”

The extremities of some aérial roots, as in the Panda-
nus, are coated by exfoliations of the epidermis ; and
the same may be observed on those of the hyacinth.
The little Lemne, or duckweeds (fig.31. b), whose roots
hang suspended in the 7
water, have a distinct
cup-like appendage at- g3
tached to their extremi-
ties. In the early state
of their development this
formed a membranous
sheath (a), which com-
pletely enveloped them,
but which became rup-
tured at the base as they elongated, and was then carried
downwards as they continued to grow.

(42.) Bladders. — The roots of certains aquatics be-
longing to the genus Utricularia, are furnished with ap-
pendages, in the form of little membranous bladders

31

42 DESCRIPTIVE BOTANY. PART I.

( fig. 32.) which are partially filled with air, and serve to
float the plant, in order that 3
it may be enabled to flower
above the surface of the water.

(43.) Lenticelle.—On the ~
stem and branches of trees,
and very conspicuously in those
of the alder, birch, and willow,
there occur certain roughish
prominent tracings, of alenticular shape (fig. 33.), which
look as if they were fissures in the bark, having their
edges turned outwards. These
are termed “ lenticellæ ;” and
it is at these places that roots
are protruded whengver the
stem is placed a condi
stances calculated to give rise
to them.

(44.) Stems. — As the cau-
dex, or main trunk of the
root, is. not much extended A
downwards in many plants, so 77"!
there are many stems which x
are never much developed up- ’;
wards; but the flower-stalk
and leaves appear to rise immediately from the crown of
the root. Plants possessing this character are called
“‘stemless.”’ Strictly speaking, however, there are no
phanerogamous plants which are entirely without this
fundamental organ, although it is often reduced to a
mere flattened disc. Occasionally it assumes a bulb-
like form, as in the Cyclamens (fig. 34.), where
the large woody mass from whence the flowers and
leaves arise, is a true stem. In some plants, the stem
is wholly beneath the surface of the ground, forming
the “ subterraneous stem,” or “ rhizoma;” but ‘most
frequently it rises above it, and. composes ‘“ the aérial
stem,” which is called a “ trunk,” “culm,” &c. ac-
cording to its structure.

ee
SECT. I. ORGANOGRAPHY AND. GLOSSOLOGY. 43

(45.) Aérial Stems.—The stem is said to be “ herb-
aceous,” when it continues soft, and lasts only for
a short time; dying soon after the flower has ex-
panded, and the seeds ri-
pened. It is called “woody,”
when it continues to increase
for several years. Herba-
ceous stems belong to “ an.
nuals,” < biennials,” and
* perennials,’ which are , M
thus named, according to {f
the several periods which WN
their roots continue to live. \

Woody stems areconfined to

shrubs and trees; the former

having many stems rising

from the surface of the

ground, and the latter possessing one main trunk, which
branches or not, according to the nature of the species
to which it belongs. An “undershrub,” is where the
branches are partly woody and partly herbaceous, so
that a portion only dies back every year. Besides these,
there are the “ succulent” stems, so called from the
highly developed state of their cellular tissue, which
often remains replete with juices for many years, without
hardening into wood.

(46.) Internal Structure of Stems and Roots.— In
arts. 34, 35. we have given an account of the leading
differences, observable in the internal composition of the
stems of dicotyledonous and monocotyledonous plants ;

and we have now to explain a few more particulars
respecting them.

(47.) Dicotyledonous Stems.—In some stems of
dicotyledonous trees it is difficult, and in others im-
possible, to distinguish any separation of the wood into
concentric layers. This is especially the case with
trees of tropical climates, where vegetation is not liable
to the periodic checks which it receives in colder regions.
In a few examples, also, the medullary rays. are not

4A DESCRIPTIVE BOTANY. PART I,

clearly distinguishable, but the pith and bark are never
wanting.

(48.) Pith. — The vesicles of the pith are larger
and more regularly arranged than those of other parts.
It continues to increase in diameter as long as it re-
mains succulent, and in some trees, as the elder, it be-
comes more than half an inch thick ; but generally it
is much smaller. After it has lost its succulency and be-
come a dry spongy mass, it scarcely diminishes in size ;
but where the branch is much distended, the pith is
ruptured, and in some cases appears to be nearly ob-
literated. The stems then become hollow, as in many
umbelliferous plants. It always forms a continuous
mass through the whole stem ; but in some cases it is
so much condensed and hardened as to resemble wood
at the places where the leaves are attached, as in the
horse-chestnut.

Although it is generally without any fibres of vascular

tissue, such are found in some ‘plants, as in the elder,
where they may be seen, in a transverse section, forming
a circle of red dots, a short dis- sg
tance within the medullary sheath.
In Ferula communis there are so
many of these dispersed through
it, that the stem has the appear-
ance of belonging to a monocotyle-
donous plant ( fig. 35.).

(49.) Medullary Sheath.—The
fibres which compose the medul-
lary sheath, appear to retain their
Vitality for a long time after the pith has been exhausted
and become dead ; and the trachee which abound in it
may even be unrolled in old and dry wood.

(50.) Wood.—The woody layers seldom, if ever, con-
tain perfect trachee ; but they are composed principally
of elongated cellular tissue, traversed by ducts of various
kinds. As the tree becomes aged, the innermost layers
grow darker and more solid, and are then termed the
_ © Heart-wood,” or “ Duramen.” The outer layers,

SECT, I. ORGANOGRAPHY AND GLOSSOLOGY. 45

which are called the “‘ Alburnum,” remain soft and
pale, and are rejected by workmen as being unsuited to
economic purposes. The variously coloured fancy woods
employed by the turner consist of the heart only, the
alburnum in the ebony, even, being quite white.

Each zone is principally composed of cellular tissue
towards its inner, and of vascular tissue towards its
outer parts: and each is supposed to be a repetition
of the parts formed during the first year’s growth, In
the common sumach (Rhus typhinum), especially, the
cellular or inner part of each zone has precisely the
same appearance as the pith, which is here of a pecu-
liar brown colour and easily recognised. But as there
are no trachee among the vessels in the outer part of
the zones, whilst these are abundant in the medullary
sheath, the analogy alluded to is not perfect.

Some woods contain scarcely any ducts, as many Coni-
fere ; and the delicate material of which rice-paper (as
it is called) is composed, consists entirely of cellular
tissue. This curious substance is procured from the
herbaceous stems of a species of Æschynomene, growing
in China. The whole stem is about an inch thick, and
resembles a mass of pith covered b
dermis. There is, however, a
central column of real pith run-
ning through it. By means of
some sharp instrument, the stem
is cut spirally round the axis into
a thin lamina (fig. 36.), which is
then unrolled, and may be made
up into sheets containing about a
foot square of surface.

(51.) Médullary Rays (see fig. 24.).— These form
what carpenters term the “ silver grain” in wood, and
are generally distinctly traceable in dicotyledonous trees. ‘
They may be seen passing in straight lines from the centre
to the circumference, but cannot be traced continuously
to any great extent in a vertical direction. They ap-

46 DESCRIPTIVE BOTANY.

pear rather as isolated patches of cellu-
lar tissue, arranged in lamine of one
or‘:more cells in thickness, placed
at right angles to the concentric woody
layers ( fig. 37.). The cells are elong-
ated in the direction of the rays. +) |
In some climbers, where the stem is ff || (S2
twisted, the rays are curved from the ti F TN
centre to the circumference. 2

(52.) Bark.—The layers which compose the bark,
are formed on a reverse plan to that of the woody
layers, their outer portion being chiefly cellular, and
their inner more vascular. The last formed or inner-
most, is termed the “ Liber,” the rest bear the general
name of “‘ Cortical layers.” These layers are capable of
. greater or less distension, according to the nature of the
tree ; and in some cases the fibres are so far separated as
to represent a sort of lace-work, as in the Daphne lagetto.
In the lime tree, the inner layers, when separated by
maceration, form the common bass, or matting, used
by gardeners. The outer layers of the birch, beech,
and other trees, are thrown off in thin membranous
lamine. In oaks, elms, and a multitude of others,
the old bark remains in a rugged cracked state. The
absence of trachee is a nearly universal characteristic
of the bark ; but Dr. Lindley has detected them in great
abundance in that of the pitcher-plant (Nepenthes dis-
tillatoria).

(53.) Monocotyledonous Stems.—The complete want
of monocotyledonous trees in our climate, has debarred
botanists the opportunity of examining their structure
so particularly as they have that of « Dicotyledons ;
and, perhaps, even yet, the exact course of the woody
fibres distributed through the trunk, is not accu-
rately understood. It was supposed until lately, that
the newest fibres were placed nearer the centre than
the old ones, throughout the whole of their length
( fig. 38. @) ; but M. Mohl has recently shown that this
cannot be the case. He observes that the fibres cross

ORGANOGRAPHY AND GLOSSOLOGY. AT

each other before they pass into the leaves; and there-
fore supposes that the newest fibres are always nearer

to the circumference than the old ones, at the bottom of
the trunk, but that they cross them as they ascend, and
then curve outwards and pass into the leaf (b).

Those monocotyledonous stems which have no
branches, and are supplied with nutriment entirely from
the leaves at the summit, continue of nearly equal thick.
ness throughout their whole length, as in the lofty palms

fig. 39.), whose trunks are a long cylinder, crowned by
a splendid mass of foliage. But those which are
branched, become thicker below than above, as in dico-
tyledonous trees, The same may be said of such Mo-
nocotyledons as the grasses, whose stems are clothed
with leaves throughout their whole length. It has,
indeed, been generally asserted that the trunks of many
monocotyledonous trees do not increase in thickness
after they have risen above the surface of the soil ; but
such an assertion does not appear to have received a
satisfactory confirmation. It is easier to believe that
their increase is very slow, and that the fresh materials
are always equally distributed from the top to the
bottom—the diameter of the terminal bud increasing: as

[F

pa

ee : Lite io Cn ETG DA
a a a Tie ty ee S
, ps

Lema eet m i

48 | DESCRIPTIVE BOTANY. PART 1.

the trunk lengthens. We find that even the trunks of
old dicotyledonous trees, below the part where the boughs

set on, are nearly cylindrical, or frustra of very elongated
cones, when compared with the portions above them.
Mirbel has: figured the trunk of a monocotyledonous
tree which has become completely invested by a climber
whose branches have grafted together into a reticu-
lated cylindrical mass. This specimen has been consi-
dered to illustrate the fact, that the stem could not have
increased at all in thickness after it: had become so
closely embraced. But something of the same sort may
occasionally be observed even in dicotyledonous trunks,
where they have become completely invested by ivy,
whose branches intertwine and graft together, though

SECT. L ORGANOGRAPHY AND GLOSSOLOGY. _ 49

vg

Perhaps not so completely as in the case of the creeper
alluded to. That Monocotyledons increase very slowly
in thickness may readily be conceived, but so do the
` trunks of dicotyledonous trees, after they have acquired

channelled ( fig, 40.). This is frequently owing to

Some peculiarity in the development of the cellular
Ussue of which the bark is composed.

55.) Directions of Stems. — The original tendency

of aérial stems, is vertically upwards; but many are
too weak to support themselves in that position, and,
m Consequence, either trail upon the <-

ground, or cling to the surrounding
herbage, by means of tendrils, hooks,
and, various other appendages ; which
are frequently modifications of the leaf.
There are certain stems, also, which,
by continually twisting in a spiral man- W
ner, twine themselves round the trunks gif
and branches of neighbouring trees and
shrubs, and are thus Supported to a great a
height. The spiral which these stems describe, is

E

termed

50 DESCRIPTIVE BOTANY. PART I.

“right-handed” (fig. 41.5), or “left-handed” (a),
according as its coils appear to rise from left to
right, or from right to left, to a person supposed
to be placed in its axis; or, if we were to hold the
spiral in an upright position before us, then the coils of
a right-handed spiral will seem to descend from the
left towards the right, and those of a left-handed spiral
to descend from the right towards the left.

(56.) Knots, Internodia, and Joints.— Many stems
are swollen at intervals, where the leaves are at-
tached, and such swellings are termed “ knots.” . The
space which intervenes between two knots, is an “ in-
ternodium.” Joints” are also swollen parts, where
-the tissue is less firm than elsewhere (see art. 25.), and
may easily be fractured. They often occur immedi.
ately below the knots.

(57.) Buds. — As branches always originate in the
development of “ buds,” we shall. here describe these
bodies, before we proceed with further details concerning
stems, of which the branches appear to form, as it were,
mere subdivisions. Buds usually consist
of several scales, or rudimentary leaves,
closely wrapped round an axis; and
within these are other leaves, in a
still more rudimentary state, which |
are destined to assume a more highly
developed condition than the outer
scales of the bud. It is the outermost
scales which thus serve to protect the
innermost and more delicate parts, from
the inclemencies of the weather. Some
are covered with down, which may,
as some suppose, be effective.in pre-
serving them from the intensity of
cold ; others, as the horse-chestnut,
are coated over with gluten, which is
certainly a more effectual protection
against moisture ; and perhaps this is the end which
these scales best fulfil in most cases, as their closely im-

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 51

bricated condition, would Seem to indicate. Buds are a

Sort of nascent germ, originating within the stem, from

the surface of which they ultimately protrude, and are

developed ( fig. IAR
In ordinary cases, buds are formed about the places

where the leaves unite with the stem; and they are

most frequently situate immediately above the “axil”

of the leaf—or place where this union occurs (fig. 42. a).

In some plants, however, the buds are produced on the

sides of the axils; and, in Some, even within the space

covered by the leaf-stalk, Where, conse-

} quently, they lie concealed until the leaf falls.

Buds may, however, be developed, under pe-

{ culiar circumstances, from any part of the

` stem ; and such are called “ adventitious ”

“buds, to distinguish them from those which
are formed in the ordinary w
(58.) Shoots. — In the
their development,
“ shoots ;” and,
ground stems, a
form of Scales, a

ay.

3 but buds are formed and

branches proceed from the axils of the

scales.
(59.) Branches

especially in di

furnished wit

a draco)
y are developed after-

anches have precisely

em; and they may,

zk 2

52 DESCRIPTIVE BOTANY. PART Je

in fact, be considered as so many partial stems en-
grafted into the main trunk. Originating, as we have
stated, from buds, their disposition round the stem
must depend upon the arrangement of the leaves, to
which we shall allude when we treat of those organs.
We may, however, remark, that branches are never
| so symmetrically arranged as leaves; because a great
many buds are never developed at all. This arises
from the unfavourable circumstances under which many ,
are placed, for receiving a sufficiency of air, of moisture,
and more especially of light. The consequence is, that
those which originate on the lower parts of the stem, are
either much stunted, or become abortive.

(60.) Development of Branches. —When a branch
is not developed, where a bud has been formed, the
latter still continues to live; and, in dicotyledonous
trees, is carried outward- with the increasing bulk of
the stem, and awaits at the surface for a proper op.
portunity, when a sufficient quantity of light, or of
some other requisite, may enable it to “break” into
a branch. This fact is familiar to every horticul-
turist, and is the foundation of the principle upon which
he regulates the pruning of his trees. If a section of
the stem be made at the point where an undeveloped
bud is seen to protrude, it will show the course which
the bud has followed in passing from the centre outwards,
marked by a line or wake,
which traverses the several
layers (fig. 44.). Hence,
branches of the same
age, may have origin-
ated from buds which
have been formed at very
different periods of the
tree’s growth, This is
a further cause, tending
to destroy the symmetry
which they might other- i
wise have exhibited in their arrangement round the axis

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 53

of the stem. In the annexed diagram (fig. 45.), @ Te-
presents a bud, developed on
a branch which is one year g
old ; and this branch is seated Ẹ
on another which is two years @
old, and which originated f
from a bud of the same age §
as b, which has not yet been $
developed. :

(61.) Direction of branches. |
— The general contour given
to the whole foliage of trees,—-which bears the name
ues cyma,” depends upon the angle which the branches
make with the stem at their point of union, combined
with ‘the degree of rigidity which they possess. When
they stand out at various angles, more or less approach-
ing to a right angle, they are termed ‘ divergent ;”
and, when such branches are rigid, a rounded form is
given to the cyma, as in the oak and elm. When the
angle is more obtuse, they are said to be “ patent,” or
“spreading.” If they rise at a very acute angle, and
are packed close together into the pyramidal forms
assumed by the cypress and Lombardy poplar, they are
called “ appressed.” When they are very long, and so
flexible as to bend by their own weight, they are
“pendant,” as in the weeping willow. But in that
variety of the common ash, which is also called “ weep-
ing,” the branches’ are rigid, and possess a natural `
tendency downwards, from their very origin, and are in
this case termed. <“ depressed.”.

(62.) Modifications of Branches.—

Thorns. -— When a bud is imperfectly developed,
it sometimes becomes a short branch, very hard and
sharp at the extremity, and is then called a “ thorn.”
We must not, however, confound the “ prickle”
with the thorn. The former of these is a mere
prolongation of cellular tissue, from the bark, and
may be considered as a compound kind of pubescence
(art. 31.); whilst the thorn, containing both wood and

E 3

54 DESCRIPTIVE BOTANY. PART I,

bark, is an organ of the same description as the branch
itself. “Spines” originate in the transformation of
leaves, &c. (see art. 78.).

Runners. — These are branches which trail along
the ground, striking root at intervals, where the buds
develop and give rise to young plants, as in the straw.
berry.

. Suckers are branches originating below the surface
of the soil, and their base in consequence soon emits
roots. Any branch may be made to assume this cha-
racter artificially, by confining a portion of it below the
surface ; as the horticulturist is aware when he forms
his “ layers.”

(63.) Subterranean Stems and Branches. — There are
some stems and branches, which, instead of rising up-
wards, continue under ground, and creep horizontally
below the surface of the soil. These are very generally
mistaken for roots, and are usually termed “ creeping
roots ;” but they may readily be distinguished from
roots, if not by their internal structure, at least by their
external appendages. They are mostly furnished with
scaly processes, or other traces of a degenerated and
modified form of the leaves; and they produce buds,
and often throw up branches which rise above ground ;
or else they themselves ultimately take a tendency up-

' wards, and become true aérial stems ; a good example
of which occurs in the common reed (Phragmites com-
munis, fig. 46.). The swollen rhizomata of this plant
run. among the turf of our fens, forming large tubes
through the masses cut for burning. They are furnished
at intervals with pale membranous scales, or rudimentary
leaves ; and fibrous roots are given off from all the knots.
So soon as the rhizoma takes an upward tendency, it
contracts its dimensions, and ultimately rises above ground
as a slender stem, invested with long green leaves. The
term “ rhizoma or root-stalk,” is equally applied to pro-
strate stems, as in the iris tribe, and in some ferns, where
the upper surface gives rise to the leaves, and the lower
to the roots; and also to the completely subterraneous

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 55

stems which throw up stalks and leaves at intervals
\

p

(fig. 4'7.), as in the Carew arenaria, Elymus arenarius,
&c.—plants of inestimable utility in certain regions,

where they serve to bind the shifting sands of the sea
Shore, which would otherwise drift before the wind,
and form irruptions over the neighbouring land. The
common but noxious couch grass is another familiar ex-

56 DESCRIPTIVE BOTANY. PART L

ample of the kind, equally interesting to the botanist,
though not treated with a like consideration by the agri-
culturist. .

(64.) Tubers.—Some subterranean stems or branches
terminate in swollen nodosities, analogous to those which
we have described as formed on the roots of some
plants (art. 40.).. The common potato (fig. 48.) is a,

familiar example of this kind. These are called “* tubers,’
and form magazines of nutriment which serve for the
development of the buds or “ eyes,” seated upon their
surface. In general, the distortions produced by the
formation of the tuber, destroy the symmetry which the
buds onthe surface of this portion of the stem would other-
wise exhibit, in their mode of arrangement ; but still they
may, in many cases, be observed to. follow a spiral
course, characteristic, as we shall hereafter see, of the dis-
position of the leaves. In one peculiar variety of this
tuber, termed the “ pine-apple potato,” this disposition
of the buds is very striking; each is subtended by a
swollen projection which represents the base of the
leaf-stalk, in whose axil we may consider it to have
been formed. In turnips, radishes, &c., this tuberous
development originates in the lowest portions of their
stems, which are placed either wholly or partially
below ground; whilst in the Kohl-rabbi (a variety of

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 57

cabbage), the effect is produced on a part of the stem
which is entirely above ground.

(65.) Bulbs. — The buds of some plants are subject
to a peculiar modification. Instead of expanding into
branches and leaves, in the usual way, the rudimentary
parts of which they consist, become depositaries of

bulbs depend upon the rudimentary leaves of which
they are composed, being either in the form of succulent
or fleshy scales (a), as in the lily; or in concentric
coats (b) which completely surround the axis, as in

58 DESCRIPTIVE BOTANY; PART I.

the onion ; in the latter case, also, some of the outermost
lamine are thin and membranous. The young bulbs,
or “cloves,” as gardeners term them, are produced, as
we should expect, by the development of fresh buds
in the axils of the scales or lamine of the old bulb.

(66.) Cormus.— The name of
“ cormus,” is given to the swollen
base of some stems of mono-
cotyledonous plants, or rather to
the condensed state of the whole
stem (fig. 50.) ; which is deve- MK
loped underground, and assumes K "A
the general appearance of a coated Y
bulb, as in Crocus and Colchicum,
where it is sometimes erroneously
termed a “solid bulb ;” or else it
resembles a tuber, as in the common
Arum maculatum.

(67.) Affinity of Bulb to Tuber.— There is evidently
a great affinity between the tuber and the bulb; each
consisting of the same organs, peculiarly modified, and
adapted to analogous purposes. In the tuber, the de-
` position of nutriment has taken place mainly in the stem,
whilst the leaves, having received none, have disap-
peared. But in the bulb, on the other hand, the leaves
have generally received the greatest portion of the
deposited nutriment, whilst the stem is slightly, or not
at all, distended. This affinity is strikingly exemplified
by the little tubers which are sometimes produced on
the stalks’ of potatoes, and which are evidently modi-
fications of the buds in the axils of their leaves; the
bulbs on the stalks of the orange-lily alluded to in
art.64., are equally modifications of the leaf-buds of
that plant.

(68.) Appendages to the Stem. — The various organs
which we have just been describing, ought rather to be
considered as “modifications,” of certain parts of the
stem, than as distinct appendages to it: but we have now
to mention a long list of organs, situate on some part or

Wy / — Ap -|
lf LY ma Uf

SECT. I, ORGANOGRAPHY AND GLOSSOLOGY. 59

other of its surface, which are properly styled “ ap-
pendages” to the stem or ascending axis. Diversified as
these organs are in their forms, andevenin their func-
tions, they may all be considered as modifications or
transformations of one fundamental organ, of very ge-
neral, though not universal occurrence, viz. the leaf.
In order to obtain a general notion of the varied appear-
ances assumed by this organ, we must suppose that some
of the materials which compose the stem have become
detached from the rest, and are then given off at the
Surface, in the form of distinct organs.

CHAP. III.

NUTRITIVE ORGANS — continued.

LEAVES, SIMPLE AND COMPOUND (69.).— VERNATION (71.).
— FORMS OF LEAVES (74. ). — PHYLLODIA (75. ). — TRANS-
FORMATION OF LEAVES (78.). —VENATION (81.). — DIS-
POSITION AND ADHESION (82.). — NUTRITIVE ORGANS OF
CRYPTOGAMIC PLANTS (84.).

(69.) Leaves. — In by far the greater number of
plants, these organs consist of thin flattened expansions,
in which the vascular portion, termed “ veins,’ or
“ nerves,” is arranged in a kind of network, having the
interstices filled up with cellular tissue—here termed the
“ parenchyma ;” and the whole is invested with the
epidermis. In Dicotyledons, the vessels proceed imme-
diately from the medullary sheath. In a few rare ex-
amples, as in the Dracontium pertusum (fig. 51.), the
parenchyma imperfectly fills up the interstices between
the veins, and large holes are left through the leaf (a).
In the most curious and interesting Hydrogeton fenes-
tralis ( fig. 52.), an aquatic of Madagascar, the paren-

60 DESCRIPTIVE BOTANY. PART I.

chyma is so little developed, that the leaf appears to
consist entirely of the veins, and resembles those skeletons
of leaves which are sometimes pre-
pared by maceration in water. A
large proportion of trees produce
fresh leaves in the spring, which
afterwards fall in the autumn ;
such are termed “ deciduous,” in
contradistinction to “ evergreens,”
which are never entirely divest-
ed of leaves. No plant, how-
ever, retains its leaves for more
than two or three years; but as |
the leaf-fall in evergreens is par-
tial, consisting perhaps of one
half or one third at a time, there
are always a sufficient number left
on the tree, to keep it clothed with l ily h
perpetual verdure. ; ! la

In succulent plants, the ves- ii
sels which quit the stem to form the leaf, diverge in
different planes, and the leaves in
consequence consist of solid fleshy
massesof cylindrical and other solid
forms, instead of flattened lamine.

The complete leaf consists of
two parts: the leaf-stalk, or
< petiole ;” and the expansion,
or “limb.” There is often an
alteration in the colour and tex-
ture of the petiole at the point
where it is attached to the branch,
and sometimes a slightly swollen
protuberance. This is termed an
“ articulation ;” and it is at that |
part that a disunion takes place at the period of
leaf-fall, and a “scar” is left upon the stem. But:
where no articulation exists, the withered petiole re-

a
i
|!

\ | Wy H
ee

i

o jas jm a 0%
PZN
t

ED

SECT. I- ORGANOGRAPHY AND GLOSSOLOGY. 61

mains a long time attached to the stem before it falls off
and leaves the scar. Some petioles are termed “ clasp-
ing,” when they are attached for some extent around the
stem; and they form “ sheaths,”
when they wholly embrace it, as in
the grasses. In some, a membranous
limb-like expansion occurs on each
side of the petiole, which is then said
to be“ winged.” The limb in gene-
ral is similarly constructed on each
side of the midrib ; but to this there
are striking exceptions, as in the leaves
. Begonia ( fig. 53.), Epimedium,
c

(70.) Simple and compound Leaves.
— The most obvious classification of
leaves, is into “ simple” and “compound.” Thelimb of the
former consists of one piece \
only (fig. 54.), which may
either be entire at the mar-
gin (a), or variously indent-
ed (b); and attached to the
stem with or without the in- /
tervention of a petiole: in §
the latter case it is said to
be “ sessile.” Compound
leaves (fig. 55.) are made up
of one or more pieces, called
“ leaflets,” each of which
is articulated to the petiole ;
and the degree to which it is
compounded, depends upon
the number of times in which
the main petiole branches, before the leaflets are attached
to its ramifications. Hence we have the simply (a),
doubly, triply (b), &c. compound leaf.

(71.) Venation or Nervation of Leaves.—The distri-
bution of the vascular tissue through the limb of the

62 DESCRIPTIVE BOTANY. PART I.

~

leaf is termed its “venation” or ‘ nervation” — the
course of the vessels bearing some resemblance to the
distribution of veins and nerves in certain parts of the
animal structure. The bundles of vessels which com-
pose the veins, maintain a nearly parallel course in

their passage through the petiole, and are closely con-
densed together ; but on arriving at the limb, they
separate, and are distributed in various ways ; all of
which may, however, be referred to one or other of
two classes, called the “ angulinerved,” and the “ curvi-
nerved,” disposition. The former of these is eminently,
though not exclusively, characteristic of dicotyledonous
plants ; and the latter equally predominant among such
as are monocotyledonous.

(72.) Angulinerved Leaves.—In these, the vessels,
after entering the limb, either branch off immediately
from the apex of the petiole, and form several strong
velns ; or they form one midrib, from which secondary
veins are given off on either side, and which at their
origin, maintain a straight course for a short distance,

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 63 f

however they may afterwards be curved (fig. 54.). The
angle at which they diverge is generally acute, towards
the apex of the limb, and their mode of ramification
bears a resemblance to the branching of trees. This
kind of nervation may be subdivided into four sub-
Ordinate groups, which are important in regulating
the conditions upon which some of the principal forms
of leaves depend.

(a.) Penninerved.— Here the midrib is continued to

the extremity of the limb, and the primary nerves
branch off from it on either side, throughout its whole
length (fig. 56.). The breadth of the leaf is chiefly
Yegulated by the size of the an- 56
gle at which the nerves quit the
midrib, being narrower in pro-
portion as this angle is more
acute. The contour of the limb
is also defined by the proportion
which the different nerves bear
to each other on quitting differ-
ent parts of the midrib. This
form of nervation is by far the
Most usual, and regulates the
Structure of many compound
leaves. In these the main petiole
may be likened to the midrib of a
Simple leaf, with its parenchyma `
only partially developed round the secondary nerves, so
that it becomes split up into separate leaflets. Compound
€aves are pinnate, bi-, tri-, &c. pinnate, according
to the degree of subdivision to which the branching of
the petiole extends. But when the limb of a leaf is
Merely subdivided, without being completely separated
into distinct leaflets, the terms applied to designate the
degree of subdivision are “ pinnatifid,” “ bi-, tri-, &e.
Pinnatifid.” In pinnate leaves, the leaflets are fre-
quently arranged in pairs, on opposite sides of the
petiole, with or without a terminal leaflet.

64 DESCRIPTIVE BOTANY. PART I.

The intimate relation which subsists between simple
and compound leaves, is well exemplified in some
cases, Where two or more contiguous leaflets become
grafted together, and thus reduce the usual extent of
the subdivision to a lower degree. This may be often
seen in seme species of Gleditsia (fig. 57.), where dif-

ferent parts of the same leaf assume a simply, doubly, or
triply compound character. It is difficult in some cases
to decide whether a leaf should be considered compound,
or simple ; and it is usual to account all leaflets which
are articulated to the petiole, as parts of a compound
leaf, even though they may be reduced to one in num-
ber, as in the case of the orange; but those which are
not articulated, even though they may be otherwise dis-
tinctly formed, are considered as subdivisions only of a
simple leaf. Where these articulations exist, each
leaflet falls separately from the main petiole, when
this also becomes detached from the stem ; but where
the leaflets are not articulated to the petiole, the limb
falls entire, with the petiole attached.

(b.) Palminerved.—Instead of forming a midrib, the

SECT. I. ORGANOGRAPHY’ AND GLOSSOLOGY. 65

vessels here diverge from the extremity of the petiole
into several (usually three or five) equally strong nerves,
Which are afterwards
subdivided in a penni-
herved manner (fig.58.),
The whole system of
venation here resembles
that of a compound
penninerved leaf, whose
leaflets have become
grafted together into
one limb. This nerv-
ation stamps the character of the palmate leaves.
(c:) Peltinerved.—The vessels in this case diverge in
a plane which is inclined to the
direction of the petiole; and in
proportion as the angle of inclin-
‘ation approaches a right angle, the
limb of the leaf is more symmetri- ‘
cally formed, round the point where

the petiole isattached to it (fig. 59.).

Where the angle is acute, the

nerves which diverge on the side

nearest to the petiole are the short- .

est, and the limb is proportion-

ably contracted. From this neryation originate the
peltate leaves.

(d.) Pedalinerved.—In this case there is no decided
p

66 DESCRIPTIVE BOTANY.

PART i.

midrib, but the vessels diverge in two strong lateral

nerves, from which branches are
given off, on that side only which is
` towards the apex of the leaf (fig. 60.).
This form of nervation is far less com-
mon than either of the preceding. The
pedate leaves are thus nerved.

(73.) Curvinerved Leaves. — In
these leaves, the nerves are more or
less curved at their base, or point
whence they diverge ; and they retain
a certain parallelism among them-
selves, as. well as a simplicity of
structure, which very readily distin- |
guishes them from the angulinerved
leaves. This mode of nervation may
be subdivided into two classes. ©

(a.) Convergent. — Where several
nerves, curved at the base of the

limb, run nearly parallel to its margins, and proceed

gradually converging towards its apex
» GE).
Me AE catia the ves-
sels collectively form a midrib to
the limb, and numerous simple nerves
diverge from it in a pinnate manner,
but maintain nearly a parallel, or some-
what curvilinear course (fig. 62.).
(74.) Forms of Leaves.— It will
easily be understood, how very much
varied the forms of leaves may be-
come. Their contour is principally
determined, by the distance to which the
ramifications of the nerves extend ;
and the shape of the margin is modi-
fied, by the degree to which the paren-
chyma is developed between them.
Thus, in ovate leaves (fig. 63.), the

margin of a, which is only slightly indented. is said to ©

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 67

- be “ toothed ;” that of b, which has the indentations `

deeper, is called “divided,” or “ineised;” and cis

termed “ partite.” Where the 6s

limb is almost severed into se-

Parate segments, each portion,

when tolerably large, isalso termed

a “lobe,” and the angle at which j

the lobes meet is the “sinus.” ) ,

When the teeth are large and?

regular, they are termed “ ser-

Tatures;” and when these are œN

rounded, “ crenations.” Thus,

a vast number of terms, most of

them of very simple construction, and easy compre.
ension, are used, for expressing a variety of different

Modifications, by which these and other organs of plants

May be accurately defined.

The leaves on different parts of the same plant often
differ in shape ; and even those on the same part are
Sometimes subject to great modifications, according as
they are influenced by the peculiar circumstances under
Which they are developed. Thus, we may occasionally.
find three varieties, among the radical leaves on the same
Plant of horse-radish (Cochlearia armoracia), where the
Marginal indentations vary as much as in fig. 63. In ge-
neral, however, the leaves of the same plants, or at least on
the same parts of a plant, retain a ‘sufficient constancy
n their character, to enable us to use them for the pur-
Pose of discriminating between species which are very
Closely allied. It would not be in character with
Sur present undertaking, to enter more minutely into
any description of the forms of leaves; but we recom-
Mend all who wish to pursue this subject further, and
to become acquainted with those technicalities of the
Science which are necessary for the purposes of accurate

scription and descrimination of species, to notice the
dependence which the forms of leaves possess upon the
Conditions of their venation. In the first place, they
should remark the general contour of the. limb, without
$ F2

DESCRIPTIVE BOTANY. PART I.

reference to its marginal incisions ; then they should
consider the character of the incisions, and the relation
they bear to the disposition of the veins. In com-
pound leaves, the degree to which the subdivisions
of the petiole take place must be considered, and the
analogy noted, which exists between the disposition of
the partial petioles and the venation of simple leaves.
Thus the student will soon learn to fix in his memory
the numerous modifications of form which leaves pre-
sent.

(75.) Phyllodium.—There are some plants, as many
of the acacias of New Holland, in which the limb of
the leaf is not developed, but the petioles themselves are
laterally compressed, and so much flattened out as to
assume the appearance of a limb ; except that they affect
a vertical position instead of a horizontal one, and that
there is no apparent difference between their two sur-
faces in colour, or other characters. In young plants

of this description, however, and occasionally also in old
ones which have been freely pruned, we may observe all
the intermediate states or varieties between a doubly

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 69

compound leaf (fig. 64. a) and the simply expanded
petiole just described (6); the latter being more dilated
m proportion as the leaflets of the limb are fewer in
Number. These flattened pétioles are termed “ phyl-
lodia,” and the character of their venation corresponds
very closely with that

of the. curvinerved

leaves of monocoty-

ledonous plants. The

Non-development of

the limb is also com-

mon in some species -

of Monocotyledons,

which are never-

theless, capable of

producing one. The

Sagittaria sagittifolia

(fig. 65.), an aquatic

of this class, has the agai

limb developed at the summit of those leaves only,
which reach above the surface of the water, all the rest
consisting merely, of strap-shaped expansions of the pe-
tioles.

De Candolle considers the greater number of sheathing
leaves, which are not furnished with distinct limbs, to
be only petioles; and although such are found in
Several Dicotyledons, asin Ranunculus gramineus, La-
thyrus nissolia, the whole genus Bupleurum, and some
others, yet they are more especially characteristic of Mo-
Nocotyledons, where he supposes the development of a
true limb to the leaf to be comparatively rare ; though
it certainly occurs in the Arum tribes, Sagittarie, and
Some others. Some limbless petioles are cylindrical and
Pointed like the leaves of a rush.

(76.) Foliaceous Branches.—The phyllodium is not
the only substitute which nature provides, to supply the
absence of a perfect leaf. In some plants, the leaf is com-
pletely abortive, and becomes a small dry scale, incapable

¥ 3

70 DESCRIPTIVE BOTANY. PART I.

of performing any of the proper functions of this
organ. In these cases, the branches themselves be-
come flattened, and assume the appearance of leaves
(fig. 66:). In the com-
mon __ butchers’-broom
(Ruscus aculeatus), and
others of this genus,
the flowers are seated
in the middle of the
upper surface (a) of
these flattened branches.
In the genus Xylophylla
they are placed round
the edges of similar or-
gans. (b).
(77.) Stipules. —
At the base of some
leaves, and on each side
of their axils, there are
appendages of a foliaceous character, sometimes resem-
bling the leaflets of compound leaves, and sometimes like
small membranous scales (fig. 67. a a). These are

termed “ stipules,” and are very characteristic of certain
groups of plants, but are entirely wanting in others.
They are never found on any Monocotyledons, or on

- SECT. L. ORGANOGRAPHY AND GLOSSOLOGY.

any dicotyledonous plant where the -petioles are
“ sheathing.” .

(78.) Spines. — Some leaves, which do not freely
develop in the usual manner, assume a dry hardened
appearance, and pass into spines, as in the common
furze; just as some abortive branches have been stated
to assume the character of thorns (art 62.). In the
berberry (fig. 68.) all the intermediate states (s) be-

{ $

Ş

tween a well-developed leaf and the hard spine, may
be distinctly traced, on vigorous suckers of a year’s
growth. i

'(79.) Tendril. — In some leaves, the midrib is pro-
truded beyond the apex of the limb, in the form of a
filamentous chord, and, in many cases, the limb entirely
disappears, and the whole petiole is transformed into
what is termed a “tendril.” These organs serve to
Support the weak stems of certain plants, by twisting
round the branches of others, in their neighbourhood.

j F 4

Ga; DESCRIPTIVE BOTANY.

In the Lathyrus aphaca ( fig. 69.)

all the leaves become tendrils,

except the first pair in the

young plants, which are com-

pound, and have two'or ‘three

pairs of leaflets. Occasion- ‘

ally an odd leaflet (b) is de-

veloped on the tendrils, in a

later stage of growth, which

further indicates the origin of

the organ on which it is seated.

A provision is made for sup-

plying the want of leaves in this

plant, by an unusual development of the stipules (a),
which are so large that they might readily be mis-

taken for real leaves. All tendrils, however, do not
originate in the modification. of the leaf; but some
are derived from an altered condition of the stipules, as
in the cucumber ; others, from a transformation of the
branches or peduncles, as in the vine (fig. 70.). \In
fact, they may result from any of ‘the caulinar append-
ages, which become lengthened out at their extremi-

SECT. 1. ORGANOGRAPHY AND GLOSSOLOGY. 73

ties into filiform flexible cords, more or less spirally
twisted.

(80.) Pitcher. — Of all the metamorphoses which
the leaf is found to undergo, the singular productions
called “ pitchers” are the most curious. The annexed

cut (fig. 71.) represents three different forms of these
organs.

(a.) In the genus Sarracenia, nearly the whole leaf
resembles a funnel, with the upper extremity crowned
by a membranous expansion, tapering to a point.

(b.) In the Nepenthes, or true pitcher-plant, the
pitcher (b) is placed at the extremity of a tendril, ter-
minating a winged petiole. It is crowned with a mem-
branous lid, which is closely shut in the early stages of
its growth, but is afterwards raised, and does not again
close the aperture. These pitchers, in some species,
are six or seven inches in length, and have the lower
portion of the inner surface, of a glandular structure,
which is constantly secreting a subacid liquid. In
this liquid a number of insects are continually drowned ;

74 DESCRIPTIVE BOTANY. PART 1-

and, strange as the idea may seem, it has been conjectured,
that the providing of such animal manure for the plant,
is one object which these singular appendages were in-
tended to accomplish. There is, certainly, a striking
analogy between this result, and the still less equivocal
object effected by the fly-traps of the Dionea, to which
we shall have occasion to allude when speaking of the
irritability of plants.

(c.) In the Cephalotus follicularis, the pitchers (c)
are about two inches long, and are seated round the
base of the flower-stalk, intermixed with the radical
leaves. Though so much smaller, they are perhaps
still more curious and striking than those of the Ne-
penthes.

(81.) Vernation of Leaves. — Before the leaves ex-
pand, they are compactly folded together in the leaf-bud ;

72

So

1 NOCO

Jee e

and the various modes in which this takes place, is called
their “ vernation.” The folds or plaits either lie in a
longitudinal direction, parallel to the midrib; or they
are transverse, so as to bring the apex and base towards
each other. Different terms are applied to the various
modes of vernation, some of which, however, are seldom

_ employed in descriptive botany. The appearances re-
presented in the annexed cut (fig. 72.) are among the

SECT. 1. ORGANOGRAPHY AND GLOSSOLOGY. 75

most striking and important, and are obtained by
making a transverse section through the leaf-buds of
different plants: a, plicate ; b, equitant ; ¢, imbricate ;
d, involute ; e, revolute ; f, obvolute ; g, circinate.
(82.) Disposition of Leaves. — Although the term
“radical leaves,” is applied to those which are seated
close to the ground, and appear to spring from the
summit of the root itself, yet all leaves do, in fact,
originate upon the stem or branches. In a general
way we may refer their disposition to one or other of
two modes: either “ verticillate,’” when more than
one is attached to the stem at the same altitude, or
about. the same horizontal plane ; or “‘alternate,” when
they are so dispersed upon the stem that no two are
seated precisely in the same horizontal plane. When the
number of leaves in the same plane does not exceed two,
and these lie on contrary sides of the stem, they are said
to be “opposite.” Leaves are frequently so arranged,
one above another, as to form two or more ranks down
the stem; and sometimes they appear to follow the
direction of spiral lines which coil round it. These

different appearances receive appropriate names in de-
scriptive botany, which it does not fall in with our
plan to dilate upon ; but, before we have concluded this

re £0

TO DESCRIPTIVE BOTANY. PART I.

part of our subject, we shall enter somewhat more fully
into the details of a theory, which has been proposed
for reducing under general laws, all the modes which are
observable in the distribution of foliaceous appendages.
(83.) Adhesion-of Leaves. — In some species where

the leaves are opposite, we find them “ connate,” or
grafted together by ‘their bases (fig. 73. a), so as
completely to surround the stem ; and in other species,
_where they are alternate, and without a petiole (sessile),
the edges at the base of the limb extend round the
stem (b), and are united together. Both these
cases are termed “ perfoliate ;” the stem seeming as it
were to penetrate the leaf. In some plants, the middle
of the leaf adheres to the

stem, through a greater

or less extent, whilst its

edges are free (fig. 74.).

The leaf is here said to

be “ decurrent,” and the

stem “ winged.” 7

(84.) Nutritive Organs

of Cryptogamic Plants.—

In art. 36. we have al-

ready stated nearly all

that it will be necessary for

us to mention respecting

the organs of cryptogamic

plants; a more particu-

lar account would involve

us in descriptive details,

which belong rather to

the department of phytography and systematic botany,
with which we do not profess to interfere. The higher
tribes of these plants, contained in the division ‘‘ Duc-
tulosæ,” have green expansions, much resembling leaves
in their general appearance, and like them possessing
stomata; but differing from them very considerably in
some respects, especially in bearing the fructification
upon their surface. These have therefore received a

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. “ae

distinct appellation, and are called “ Fronds ;” and that
part of a frond which is analogous to the petiole, is

5 SR ete A

termed the “ Stipes.” In some cases, as in the tree
ferns of tropical climates (fig. 75.), the bases of
the decayed fronds form a tall trunk, which is termed
their “ caudex ;” but when this portion creeps upon the
ground, as in the humbler forms of our own climate, it
has received the name of “rhizoma.” In several
tribes the fronds possess nerves, but in many cases they
are composed entirely of cellular tissue. The vernation
of the fronds of most ferns is peculiar, and termed
“ circinate ” (fig. 72. g). It consists in having all
the extremities of its different subdivisions, as well as

"8 DESCRIPTIVE BOTANY. PART I.

the whole frond itself, rolled inwards. The lower
tribes of cryptogamic plants, included in the division
e Cellulares,” are very homogeneous in their struc-
ture, and of different degrees of consistency — from
‘highly gelatinous, to tough and leathery. When they
consist of a plane membranous lamina, as in the Lichens,
this is termed a “ thallus” (fig. 76.) ; but when more

or less branched, the name of frond is retained. They
` are either terrestrial, aquatic, or marine. - Many of
them are parasitic, seldom green, and without stomata.

SECT. I. ORGANOGRAPHY AND GI.OSSOLOGY.

CHAP. IV.

REPRODUCTIVE ORGANS.

FLOWER BUDS (85.). — INFLORESCENCE — MODES OF (86.).—
FLORAL WHORLS—PERIANTH (92. ).— GLUMACEOUS FLOWERS
(96.).—STAMENS AND PISTILS (97.). — pisk (101.).—
FLORAL MODIFICATIONS (102.).—- asTIvatIon (104.).

(85.) Flower Buds. Numerous examplesare perpetually
occurring, in which the attentive observer of nature may
catch a glimpse of the mysterious connection which
subsists between the organs of nutrition and reproduction,
in plants. Instances continually present themselves, of
flowers whosé separate portions are singularly charac-
terised, by possessing an intermediate condition, partly
leaf-like, and partly like those variously coloured append-
ages which constitute the blossom. By an accurate ex-
amination of these and other “monstrosities,” as all
deviations from the ordinary conditions of vegetation are
termed, it has been clearly ascertained, that the organs
of reproduction and nutrition are merely modifications
of some one common germ, which may be developed
according to circumstances, either in the form of a
flower-bud, or of a leaf-bud. In the latter case we have
shown, how this body becomes a branch and leaves ; and
we have now to explain the conditions and characters of
those several organs which are developed from the flower-
bud, and collectively termed the “ inflorescence.” It
would be equally erroneous for us to call the flower-
bud. a metamorphosed state of the leaf-bud, as to say
the leaf-bud was an altered condition of the flower-bud ;
and we are nearer the truth, when we consider each of
them to be a peculiar modification of the same kind of
germ, adapted in the one case to perform the functions
of nutrition, and in the other, those of reproduction.

Ga IRTP Ge mao

a I a a

80 DESCRIPTIVE BOTANY. PART I.

Flower-buds ought consequently to make their appear-
ance on similar parts of the stem and branches with the
leaf-buds, viz. in the axils of the leaves ; and the de-
velopment of each will present us with analogous
phenomena. However different in their external cha-
racters, still the various parts of the inflorescence must
bear a strong affinity to those of the foliaceous append-
ages on the branch.

(86.) Inflorescence.—In this term we include, not
merely the flower which proceeds from the development
of the flower-bud, but also the stalk on which it is
placed, and any of those other various appendages upon
it, which are always.more or less distinct from true leaves.
The more general term for the flower-stalk is ‘‘ pedun-
cle,” but the term “pedicel” is also used in a re-
stricted sense, where there are partial flower-stalks seated
upon a common peduncle. The flower-stalk is more
or less dilated at the apex, when there are several flowers
closely crowded upon it, and without distinct pedicels,
as in the order Composite. Such dilatations of the
flower-stalks receive the general name of “receptacles,”
but other terms are specially applied to some of their mo-
difications. The foliaceous appendages on the peduncle,
which more or less resemble the stem-leaves, but which
are also sometimes reduced to the condition of mere
scales, are called “bracter.” The flower terminates
the pedicel, and is composed of certain foliaceous ap-
pendages, which are still further removed from the
character and condition of leaves, than the bractee. —
The analogy which exists between the various parts of
a leaf-branch and those organs which compose the in-
florescence, is very oftenexhibited in certain monstrosities
of the rose; where we find the central parts of the flower,
instead of assuming their usual character, become deve-
loped as a branch. It sometimes happens that this
monstrous development will again make an effort to pass
to the state of a flower, and then the central parts will
a second time assume the condition of a branch. In the
Water-avens (Geum rivale, fig. 77.) this description of

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 81

monstrosity is particularly frequent ; and, indeed, it may
be often seen in many other flowers.

(87.) Modes of Inflorescence—From what we have
said, it will be evident that the term inflorescence, is
either applied to the appearance presented by the general
disposition of all the flowers on a plant taken collect.
ively, or it is confined to certain groups of flowers
which are found on different branches; or, lastly, it
is restricted to solitary flowers produced from sepa-
rate buds. In order to understand the general law,
which regulates the distribution of flowers under every
form of inflorescence, according to the vague appli--
cation of this term in descriptive botany, it will be
well to consider the manner in which we may conceive
it possible, for a succession of buds to become developed
upon the main stem, or any of the branches. Assuming
any bud (fig. 78.) from which the stem or given branch
is developed, to be the “ primary” bud (No. 1.) of

G

82 DESCRIPTIVE BOTANY- PART I.

the series we are investigating, then “secondary” buds
(Nos. 2.) are developed from the axils of the leaves or
bractee ; and when these become branches, “ tertiary ”?

buds (Nos 3 .) are similarly developed from them ; and so
on. In this way a plant may be considered capable of
indefinitely multiplying the number of its branches, and
also of extending them to any length, by the continued
development of the terminal bud at the extremity of
each of them. ‘Trees continue to develop a succession
of buds in this manner for many years together, without
producing flower-buds ; but some trees, and all herb-
aceous plants, soon produce flower-buds, and then the
branches on which they occur are abruptly terminated.
Now, it appears to be a general rule, that when the
buds of one order cease to develop as branches, by
becoming flower-buds, then the buds of the next order,
which are developed round the axis of the former, like-
wise terminate in flower-buds. Thus, if No. 1., after
developing a branch and leaves, ultimately becomes a
flower-bud, then every bud (Nos. 2, 3, 4, &c.) which
terminates the branches developed round its axis, will
also ultimately terminate in flowers. Now, in the com-

9

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 83

mon definition or notion of Inflorescence, we either in-
clude only a certain aggregation of Branehek, all of which
terminate in flowers, or else we include one or more of
those branches, honed terminal buds still continue to
develop as leaf-buds, without ever becoming flower-
buds. It has been supposed, indeed, that fe are two
distinct modes of inflorescence, in one of. which the
terminal bud does, and in the other it does not, become
a flower. But this depends merely upon the vague
manner in which we include under our definitions of in-
florescence, a greater or less number of buds of different
orders of development. If we admit a bud which does
hot terminate in a flower, to be the primary bud in.
cluded in the inflorescence, then we have what has
been termed the “ Indefinite inflorescence,” because the
main axis continues to develop indefinitely, whilst the
lateral buds alone terminate in flowers. But if the main
axis, of what we choose to include within the inflo-
rescence, terminate in a flower, then the “ Terminal
inflorescence” is the result, There are numerous modi-
fications of both these kinds of inflorescence, which either.
depend upon the disposition of the leaves or bractee, in
Whose axils the flower-buds originate, or else upon the
partial abortion, or peculiar de-
Velopment, of some or of all the
Secondary, tertiary &c. buds;
and also upon other circum-
Stances.

(88.) The Terminal Inflores-
cence. — The principal axis in-
cluded in this inflorescence, ter-
Minates in a flower-bud, and the
Secondary buds are developed in
the axil of each leaf or bractea,
Situated at the base of that
Portion. of the branch which
becomes a peduncle, and must
therefore be placed immediately a y

between a leaf and a flower (fig. 79. ). If the second-
G2

~~

84 DESCRIPTIVE BOTANY. PART í.

ary bud is not developed, the inflorescence must consist
of a solitary flower (a). If the leaves are placed alter-
nately on the axis, the peduncle of the flower will bear
a single bractea at its base. If the secondary bud is de-
veloped (b No. 2.), it will terminate in a flower with a
bractea at the bottom of its peduncle, bearing a ter-
tiary bud in its axil; and this (No. 3.) may develop
like the former; and so on. In this case, all the
flowers will appear to stand opposite the leaves or
bractee, upon a stem which seems to develop inde-
finitely ; but which is, in reality, composed of a succes-
sion of branches or peduncles, originating from different
orders of buds. Since No.1. is the real termination
‘of the main axis, and Nos.2, 3, &c. are further and
further removed from it, the order in which the
flowers expand is from the centre outwards, and this
has in consequence been termed the ‘‘ Centrifugal inflo-
rescence.” ;

When the leaves or bracteæ are opposite or verticillate,
in the terminal inflorescence, this is called a “ cyme.”
When each secondary bud is developed from the axils of
a pair of opposite bracteæ, and the tertiary buds origin- -
ate in the same manner, and so on, the cyme is styled
«c dichotomous” ( fig. 80.a). If there be a whorl of three

bractee, the cyme is “ trichotomous,” &c. If, how-
ever, one bud only is developed in the dichotomous

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 85

cyme, and always on the same side of the axis, it as-
sumes a peculiar character, termed “ scorpioidal” (b).
(89.) Indefinite Inflorescence. — Here the terminal
bud, of the main axis included in the inflorescence, con-
tinues to develop as a leaf-bud, until sooner or later it
is exhausted, and the branch stops ; but it does not pass
to the condition of a flower-bud. If we first consider
the case where the leaves are alternate, then the second-
ary buds in the axils of the leaves or bracteæ may either
become flowers immediately (fig.81. a); or they may be

3
2

\

partially developed as branches (b) which give rise to
tertiary buds ; and these may become flowers, or branch
in the same way as the secondary buds. When the
Secondary buds become flowers, without previously
branching (a), the inflorescence is termed a “‘ raceme,”
or “ cluster,” provided each flower has a pedicel ; but
it is called a “spike,” if the flowers are sessile, or
Without pedicels. Where the secondary buds become
branches, bearing flowers produced from tertiary buds,
the raceme is called “ compound” (b). A few of the
subordinate varieties of these forms may here be noticed.
In such plants as the willow, hazel (fig. 82.), and

GO

DESCRIPTIVE BOTANY. PART I.

oak, the peculiar spike in which the flowers are
arranged is termed a “ catkin.” In the
tribe to which the common arum belongs
(Aroidee), the fleshy mass which forms
the axis round which the flowers are
aggregated in a spike, is termed the “ spa-
dix” (fig. 88. b). The small spikes in
which the flowers of grasses are aggre-
gated, are termed “ spikelets” (fig. 95.
c); and these, again, are arranged round
a common axis into a compound spike.

In this kind of inflorescence, those
secondary buds which are seated lowest
on the main axis are the first formed,
and their flowers expand the earliest.

As these are also the outermost, with

respect to the terminal bud, the order

of expansion is from the circumference

inwards, or contrary to that which takes

place in the terminal inflorescence; and hence this
has been called the “ Centripetal inflorescence.”

When the leaves are ver--
ticillate, the secondary buds
may either become flowers, or
produce branches, on which
buds of a lower order be-
come flower-buds. This kind
of inflorescence is generally
called “whorled,” and is either
simpleor compound ( fig.83.).

(90.) Modifications of
Inflorescence. — It will be
seen from what has been
said, that the application of
the term “ inflorescence,” is
as indefinite as the use of
the word “organ,” which
we equally employ, to signify ;
the several parts of a plant, as well as the subordinate

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 87

portions of which those parts themselves are composed.
And thus, in some cases, we term a single fiower the
inflorescence ; in others, an aggregation of flowers ; or
even include some buds which produce no flowers.
Perhaps we might find terms, which would express
more definitely the different orders of buds, included .
in our notion of inflorescence: and then, the flowers —
of all terminal inflorescences would be subordinate to
buds of the first order; whilst the flowers of those
which are styled indefinite, would commence only from
buds of a second, third, &c. order. Each kind of inflo-
rescence might be considered as simple, or as doubly,
triply, &c. compound, according as one or more orders
of buds were developed in the form of flowers. It
might happen, that a terminal inflorescence, in which
several orders of buds were developed (as fig. 79.),
would contain fewer flowers than an indefinite inflo-
rescence, in which one order only (as fig. 81. a) was
developed. Both kinds also include several forms, strik-
ingly similar in their general appearance, and which,
in descriptive botany, have received the same names,
Of these forms we may enumerate the following :

“ Panicle.” — When the se-
condary, tertiary, &c. buds are
developed on long peduncles and
Pedicels, so that the flowers are
loosely aggregated, or, as it”
Were, scattered round the axis
(fig. 84.).

“Corymb.” —When the main
axis soon terminates, and the
secondary, tertiary, &c. buds
form peduncles of such lengths,
that the flowers which terminate.
them stand at nearly the same
level. The peduncles are, of
course, of different lengths, those towards the summit
being the shortest (fig. 85.).

«< Umbel.”? — When the main axis is so contracted

G A

88 DESCRIPTIVE BOTANY. PART I.

between the bractee, that all the secondary buds are
crowded together, and developed from one point at its

summit (fig. 86.). The pedicels are of the same
length, so that all the flowers stand at the same level,
as in the last case. When several small, or “ partial”

umbels, are themselves arranged in an umbelliferous

manner round a common axis, the inflorescence is called
a “ compound Umbel.”

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 89

An umbellate form, may evidently result also from
a terminal inflorescence, where the leaves are whorled,
and the secondary buds become flowers without pro-
ducing tertiary buds. It often happens (as in the
genus Euphorbia) that the main axis is crowned by an
umbel of this deseription, whilst the lower part pos-
Sesses the character of a raceme.

“€ Capitulum.” — This
form bears much the same
relation to an umbel, that
the spike does to the va-
Ceme ; the pedicels of the
Single flowers being want-
ing, or scarcely distinguish-
able. The flowers are, in
Consequence, crowded into
a dense head (fig. 87.).

(91.) Bractea. — We
have said, as the flower-
_ bud expands, a succession
of various kinds of append-
ages, which depart more or less from the leafy struc-
ture, are developed round the peduncle, and that all of
these would have become true leaves, if the bud had
been impressed with the character of the leaf-bud.
Of these appendages, the “bracter,” as we stated
(art. 86.), exhibit the closest approximation to the
leaf itself, and, in many cases, are only nominally dis-
Unguishable from it, by their position alone. In general,
Owever, they are of much smaller dimensions than the
€aves, and are often reduced to mere scales. Some-
times they approach the appearances presented by the
Parts which compose the flower, and are brilliantly
Coloured. In the “cone” (fig. 137.), which is a
Modified form of the spike, having the flowers very
Closely arranged together, the bractee become large
Scales. These, in the fir tribe are coriaceous, and mem-
ranaceous in the hop. `

When the bractee are arranged in a distinct whorl

GU DESCRIPTIVE BOTANY. PART I.

round the peduncle, it is termed an “involucrum al
and in some cases they cohere by their edges, and
thus form a single piece. Where the bractea, or rather
involucrum, is very large, and completely envelopes the
flowers, as in the Aroidee, it is called a “ spathe”
(fig. 88. a). In the extensive order
Composite, the little florets are crowded on

a highly dilated receptacle, as in the com-

mon daisy and dandelion; and they are

closely surrounded by an involucrum

(fig. 87. a), composed of many bractee,

which are either free, or adhere together,

and the whole head has the appearance of

a single flower. The cup in which the

acorn is placed, is an involucrum, com-

posed of several whorls of bractee, all

adhering, and blended together into a solid

mass (fig. 118.).

(92.) Floral Whoris.— The foliaceous
appendages which succeed the bracteæ in
the order of development, are brought close together,
by the non-extension of the axis, so as to crown the
summit of the flower-stalk with a series of whorls,
partaking still less of the leafy character than the bracteæ
(art. 86.). These whorls constitute the flower; and
the portion of the axis on which they are seated, is
termed the torus, which bears the same relation to
a single flower, as the receptacle does to a head of
flowers.

In flowers which possess the greatest number of
whorls, such as those of the natural order Ranuncu-
lacee, we may distinguish four different kinds of organs ;
two of which, composing the outermost whorls, are col-
lectively termed the “ perianth;” and these are not
essential to the fertility of the plant; but the two
kinds which make up the innermost whorls, are abso-
lutely requisite to secure the perfection of the seed. Itis
not necessary, indeed, that both the latter kinds should

E tH
NR a a a r E]
= = = SSS ii
` i
th
|

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. gi

be found in the same flower, or even in different flowers
Seated on the same individual plant; but unless both
exist, and can be subjected to a mutual influence, the fer-
tility of the seed is never secured. A more accurate notion
of these several whorls may be obtained, if we now exa-
Mine the blossoms of a common ranunculus in greater
detail ( fig. 89. a). Here, the outermost whorl of the
SF 89

perianth consists of five parts, of a greenish yellow
colour, and is sufficiently distinguished from the next
whorl, to admit of its receiving a specific appellation ;-
it is therefore termed the “calyx” (b); whilst its
subordinate parts are called “ sepals.” The five parts
which compose the next whorl are of a bright yellow
colour, and are termed “ petals” (c), or, collectively,
the “corolla.” The calyx rarely consists of more than
one whorl of sepals, but the corolla is frequently com-
posed of more than one. Next, within these, are
Several whorls of “stamens,” one of which is repre-
Sented at (d). These are the fertilising organs of
the flower, composed of threadlike stems, surmounted
by oval cells, or pouches, which contain a fine powder,
named pollen. Lastly, we have several whorls of
“carpels” (e), which are little ovate bodies, containing
the « ovule,” or young seed. The carpels, like the
Sepals, are not often ranged in more than one whorl,
though they are so in this instance; but the stamens
frequently occupy several. When the carpels adhere

92 DESCRIPTIVE BOTANY. PART I.

together, so as to form one mass, this is termed a com-
pound “ pistil;” but when they are distinct, as in the
present case, each forms a separate pistil. Having
given a general notion of the various parts of the
flower, we must now enter a little more fully into a
description of the several whorls, and mention some
of the numerous modifications which they present ;
also premising, that although it is not necessary for
flowers to be composed of all the four kinds of organs
here enumerated, and that some contain only one or
other of the two innermost, yet, wherever more than
one kind are present, these always maintain the pre-
cise order of collocation, which we have stated above
— the calyx outermost, then the corolla, next the sta-
mens, and the carpels in the centre.

(93.) Perianth.—In the bracteæ, we often find a
striking resemblance to the leaf ; but in the several parts
of the perianth, this becomes so much slighter, that in
most cases the close affinity between these organs would
scarcely be acknowledged, were it not clearly perceptible
in some flowers ; and also established by those cases of
monstrous development, where the several parts of the
perianth assume a leafy appearance. In many cases, and
especially in monocotyledonous plants, the several whorls
of the perianth so nearly resemble each other, that no
distinction can be drawn between calyx and corolla,
and the separate parts are described as “segments of
the perianth.” In those Dicotyledones where the pe-
rianth consists of a single whorl, it generally assumes
the usual characters of a calyx; and is always so con-
sidered by most modern botanists, though Linneus and
others, have described it as a corolla, in many species
where it happens to be coloured. Stomata exist both
on the calyx and corolla, but more especially on the
former.

(94.) Calyw.— Although the calyx very frequently
** persists,” — or remains whilst the fruit ripens, after
i the corolla has fallen, — it is in some instances very
fugacious. The sepals frequently cohere by their edges

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 93

into a tube, and the calyx is then ‘ monosepalous, ”
or “‘monophyllous,” or more correctly “ gamosepalous.”
In proportion as this cohesion extends from the base
towards the apices of the sepals, the several modifi-
Cations which it presents receive different appellations.
It is termed “partite,” when the cohesion extends but
a short way; “divided,” when it reaches about half-
Way up; “toothed,” when it is nearly complete; and
“entire,” when the’ sepals are completely united to the
very summit. In this last case, the number of the
Sepals can only be ascertained by their venation, each
Separate sepal being indicated by the position of its
midrib ; but in the other cases, which are most usual,
the free apices of the sepals readily point out their
number. Some sepals are so firmly united by their
apex into one piece, that no separation 90
takes place in this part, as the corolla gy
enlarges. The calyx is then ruptured
round the base, or transversely across
the middle, and is thrown off in the
form of a little cup, as in Eucalyptus
(fig. 90.). When the cohesion is more \ l
perfect between some sepals than others, so as to form
two lobes to the calyx, it is termed “lipped.” An
analogy is frequently maintained be-
tween sepals and the leaves, in’ such
plants as bear stipules. This is indicated
by the presence of little scales, re-
Sembling bracteæ, seated on the outside
of a monosepalous calyx, and alternating
With the sepals themselves, as in Poten-
tilla ( fig. 91.).

(95.) Corolla.— The petals are generally even less
leaf-like than the sepals, more highly coloured, and
More variously modified in shape. Like the sepals,
they are either free, or cohere by their edges, forming a
is monopetalous” corolla. In many cases, the petals may i
e divided into two parts —the “ claw,” which is ana-
logous to the petiole of the leaf; and the “limb,” which

94 DESCRIPTIVE BOTANY. PART Ie

corresponds to the limb of that organ. By the cohesion
of the claws, a tube is frequently formed, whilst the
limbs continue more or less free, and appear as a border
round the top of it. In some cases, the petals adhere
at the base and apex, but are free in the middle, as in
Phyteuma. An irregularity in the cohesion, produces a
lipped corolla, as in the case of the calyx. We will
here enumerate a few of the most important forms
which the corolla assumes, the most remarkable of
which are among such as are monopetalous. _

1. Regular monopetalous Corolle. — Where the
several parts are symmetrically arranged round the
axis, the forms are named after certain appearances
which they are supposed to resemble ; as the bell-shaped
(fig. 92. a), funnel-shaped (b), salver-shaped (e);
rotate (d).

2. Irregular monopetalous Corolle. — Where the
petals cohere, but one part of the corolla is differently
modified from another ; asin the “lipped” or ‘ labiate”
flower (fig. 93.), which has two
lobes forming the limb; and the “ per-
sonate” flower (fig. 131. a), formed ÑA
on somewhat the same plan, but where
the mouth of the tube is closed. In
these, and in other cases of irregular
monopetalous corolle, it is not always
easy to distinguish the precise number
of petals which cohere together, al-
though we may generally do so by
examining the venation, or by observing the apices of

SECT. 1. ORGANOGRAPHY AND GLOSSOLOGY. 95

the petals, which are free, and project beyond the
Margin. ;
3. Irregular polypetalous Corolle.
— One of the. most prominent of
this class is the “ papilionaceous”
flower ( fig. 94.), composed of five pe-
tals; which, however, are not always |
free at their base ; but in a few cases
Cohere by their claws into a tube.
The large single petal is termed the
“standard” (a) ; the two lateral, the
“wings” (b); and the two others,
Which often cohere into one, form the
“keel” (c). These flowers belong ex-
Clusively.to certain groups of the
extensive order ‘ Leguminose,” of which beans and
Peas are familiar examples.

There is a vast variety among the irregular poly-
Petalous corolle, originating in peculiarity of shape,
and in the proportion and numbering of the several parts.

(96.) Glumaceous Flowers.—The grasses (Graminee)
and sedges (Cyperacee) have their flowers constructed
in $0 peculiar a manner, that it will be necessary to
describe them somewhat more particularly. Their peri-
anth consists of membranous scales termed “ glumes,”
Which are referable to a modification of bractee, rather
than of those more or less
flaccid and foliaceous organs,

Which we have described as

Sepals and petals. In thell

“xample selected for fig. 95.,

there is a pistil (a), com-

Posed of an ovarium which

©ontains a single ovule, and |
8 surmounted by two \Viil why,
Stigmas. At the basearetwo Wilf fi
Scales (Jodicule.) There

‘re three stamens. These

Parts are included between two glumes (palee) (b), one

D
u
‘f

WN

BA
z ANNA Ý
a

SAY
b

96 DESCRIPTIVE BOTANY. PART I.

of which is towards the stalk, or “ rachis,” on which
the flower is seated; and this glume appears by its
nervation to be composed of two united ; this is further
indicated by a little notch at its apex. The other, or
outermost glume, is furnished with a bristle-shaped pro-
jection at the back, termed an “‘ awn.” Several of these
flowers are closely ranged on opposite sides of a stalk,
and form a “spikelet” (c), which is itself contained
between two glumes (glume) at the base. When several
of these spikelets are arranged alternately on the main
rachis, they form a spike, as in wheat. Some flowers
are solitary, and on separate pedicels, as in the oat;
and the lax branched inflorescence assumes the form of
a “panicle” (fig. 84.). Some grasses have only two
stamens, and some have only one glume ; others, three at
the base of each spikelet.

In the Cyperace (as in fig. 96.) we have only one
glume to each flower (a). The
pistil (b) is inclosed in a mem-
branous bag (at a), composed of
two glumes united. The stamens
are two or three, as also are the
stigmas. The flowers of many of
the Cyperacee are unisexual, and
arranged in spikelets and spikes,
much in the same way as in the
grasses. These two orders, although
so closely allied, are readily distinguishable ; for be-
sides the different character of their inflorescence, the
grasses have round, hollow, and jointed stems (culms),
whilst those of the sedges are more or less angular, and
solid.

(97.) Stamens.—These organs are generally com-
posed of two parts: the “anther” (fig. 97.4), which bears
an analogy to the limb of the leaf, and is a sort of pouch
containing a fine powder termed the “ pollen ;” and
the filament (e) or stalk upor which it is seated, ana-
logous to the petiole, or leaf-stalk. The latter part,
however, is sometimes wanting, and then the anther is

SECT. 1. ORGANOGRAPHY AND GLOSSOLOGY. 97

Consequently sessile. Sometimes the filaments cohere, and
orm a tube round the carpels, and the stamens are then -
termed “€ monadelphous.”
(Jig. 97. a). When they
cohere into two separate
undles, they are said to
be « diadelphous ;” and
when they appear in more
than two, “polyadelphous.”
n some orders, but more
Particularly in the extensive order of the Composite,
Where this circumstance is universal, the filaments are
free, whilst the anthers alone cohere, and form a ring
round the pistil (b). This disposition of the stamens is
termed “syngenesious.” In some plants the filaments
are dilated and closely resemble petals (c), to which
organs they also frequently adhere through a greater or
ess extent. y
(98.) The Anther generally consists of two separate

lobes or pouches, which contain the pollen (fig. 89. 4);
‘nd this, when fully ripened, escapes through a fissure.
Vhen the fissure is closed, excepting at one extremity,
the opening is a mere pore (fig.98.a). In avery few
stances the pollen escapes 2
through vales, formed on `
the face of the anther (b).

That part of the filament

Y which it is connected
With the lobes of the anther,
18 termed the “connective ;” and although more frequently
Obscure and of small dimensions, yet in some species it
Spreads, or branches laterally, and keeps the two cells
Wide apart (e). The cells themselves assume various
aPpearances, and sometimes only one is perfected. Tn
its earliest state, each is subdivided by a partition, which
afterwards disappears ; but in some cases it remains, and
then each lobe contains two cells.

(99.) Pollen. — The grains of pollen (fig. 99.) are
Minute vesicles composed of one or two membranous

H

<=

SS

SSS SSS

DESCRIPTIVE BOTANY. PART Í:

coats, and are generally spherical or spheroidal, and
often have determinate markings, warty projections, and

minute bristles upon their surface. Some of the largest
grains do not exceed the tyor $y part of an inch
in diameter ; and in some species they are not so much
as the zgo In several species, the grains approach
‘a tetrahedral shape; others are very singularly modi-
fied, of which the few examples ‘represented in the an-
nexed cut may serve as a specimen. In some tribes
of the remarkable order Orchidee, the grains ad-
here together in waxy “masses,” which fill the anthers.
Each grain of pollen contains a quantity of minute
« granules,” the largest of which do not exceed the
as$o0 part of an inch, These are occasionally inter-
spersed with oblong particles, two or three times larger
than the granules, We reserve further details for the
physiological department, when we shall speak of the
manner in which the grains act upon the stigma, in se-
curing the fertility of the ovule.

(100.) Pistil. — The parts which compose the in-
nermost whorl or whorls, are termed carpels, as we have
already stated (art. 92.) ; and when they are not united
together, each is also considered as a * pistil.” This
pistil, whether simple or compound, consists essentially
of an “ ovarium” or “ germen,” containing the young
seed or “ ovules ;” and of a “ stigma,” or glandular
summit, which is either seated immediately upon the
ovarium, or on a sort of stalk, called the “ style,”

‘SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 99

interposed between them. The construction of the
compound pistil will be more readily understood, by
_ Considering the manner in which the carpels themselves
May be supposed to originate. Each carpel is an
Organ, analogous to a leaf folded inwards upon its mid-
rib, so as to bring the edges into contact, which cohere
and form the “ placenta,” and upon this the ovules are
Produced. In general, the carpels may be likened to
a sessile leaf ; but in a few cases they are fur- — 100
nished with a support (thecaphore) analogous
to the petiole. When two or more carpels
are placed closely in contact, and adhere to-
8ether by their sides, the compound ovarium
will contain’ two or more “ cells” (fig. 100.)
And if the styles and stigmas also cohere, the
Pistil will assume the appearance of a simple
organ, although, in fact, compounded of
More carpels. Where there
1S more than one row of
arpels in the composition
of a pistil, this will con-
‘ain more than one tier
of cells ; as in the fruit of
the pomegranate ( fig. 101.).
The stigma is variously
Modified in different spe-
“les. It consists of vesi-
Cles of cellular tissue de-
nuded of the epidermis,
excepting in a few cases,
Where the thin pellicle which we have stated to form

the outer skin of this investing organ, appears to cover
lt.

(101.) Disk.—The term “ disk,” is applied to a
Portion of the torus between the calyx and pistil,
When it assumes a glandular, swollen, or fleshy appear-
ance. This is always supposed to proceed from the
abortion, or imperfect development of some of the pe-

H2

100 DESCRIPTIVE BOTANY. PART I.

tals and stamens. The disk, therefore, is not properly
a distinct organ; but merely a modification of one
or other of these. As connected with the develop-
ment and modification of the torus itself, we may here
describe three conditions of the flower, which are con-
sidered of the greatest importance in systematic botany,
and which we will explain by referring to the annexed
diagram (fig. 102.). When that part of the torus from

which the petals and stamens originate, is limited to the
space immediately between the calyx and pistil, the
corolla ‘and stamens are necessarily seated below the
ovarium, and are in consequence termed “ hypogy-
nous” (a). But when the torus is so developed, that it
becomes partially extended over the inner surface of the
calyx, the corolla and stamens appear to arise from, and
are seated upon, this organ, and they are then termed
“ perigynous” (b). When the torus, modified as in the
last case, also extends up the sides of the ovarium, the
pistil is closely united with the calyx ; and the corolla
and stamens are placed near the summit of the ovarium,
and are then styled “ epigynous” (c). In this case, the
ovarium is also said to be ‘“ inferior,” with respect to
the other parts of the flower, and these again are called
“ superior,” with respect to it. In the perigynous and
hypogynous corollz, the reverse is the case, the ovarium
being superior and the other parts inferior. There are
a few other modifications which cannot exactly be re-
ferred to either of these three. In the white Water-lily
(Nymphea alba), the petals and stamens are attached to
the sides of ‘the ovarium, though the calyx is perfectly

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 101 |

free. In the passion-flowers, the stamens adhere to
the ovarium, and the petals to the calyx.

(102.) Floral Modifications. — As an illustration of
these, we may state, that the orders of the class Dicoty-

edones, are thrown into four principal groups, two of
Which are characterised by the cireumstances alluded to
in the last article. The first of these, the Thalamiflore,
includes those flowers which have their several whorls de-
tached, or not adhering together — each whorl occupying
a distinct position on the torus, as in fig. 89. The sepa-
tate parts of the several kinds of whorls, however, may
Or may not adhere together. This group can strictly
include only hypogynous flowers. The next, or the Ca-
Yciflore, includes those orders whose flowers have their
Petals and stamens adhering to the calyx, whether in
the perigynous or epigynous form of the flower. In both
groups, all the four floral whorls are almost universally:
Present. Each, however, contains a few examples which
Cannot be separated from their congeners, but in which
the petals are wanting, or are very rarely developed.

Of the two other groups, one is termed Corolliflore,
Where the corolla is monopetalous, and the stamens ad-

ere to the inside of its tube. This includes only

Ypogynous flowers. ‘The last group is termed Mono-
Chlamydee, where the perianth consists of only one
Whorl, which is almost universally recognised as a
Calyx,

(103.) Nectary.—The word “ nectary,” is of very
Seneral application, and is used to express some pecu-
lar modification in the sepals or petals, by ‘which they
assume an unusual form; but more especially, when there
is some alteration of structure, by which they are wholly
Or partially converted into secreting organs, and exude ~
a saccharine, glutinous juice.

(104.) „Æstivation. — As the condition of the leaf
whilst yet in the bud, is termed its vernation, so the man-
Ner in which the several parts of the flower lie folded in
the flower-bud, is termed their “ estivation.” Of this

H 3

102 DESCRIPTIVE BOTANY. PART L

there are several kinds ; the most important distinctions
depending upon whether the edges of two contiguous
sepals or petals meet without =

overlapping — when the esti-

vation is called “ valvular ”

(fig. 103. v) ; or whether the

one overlaps the other — when

it is termed ‘‘ imbricate ”

(fig. 103. 1). The various

modifications to which the

estivation is subject, is rea-

dily seen, by making a trans-

verse section through the flower-bud. Thus, the “ con-
duplicate” (fig. 104. c), is

1
where the edges in the valvu- Ț er ide
lar estivation, are rolled ine
wards beyond the line of

hd

contact. The “contorted”

r “twisted” sstivation (T),
‘when the parts of an imbricate estivation are so
curved, that each is partially wrapped round one,
and at the same time is partially enveloped within
another. These examples are sufficient to afford a ge-
neral notion of this phenomenon.

CHAP. V.

REPRODUCTIVE ORGANS — continued.

FRUIT — PERICARP (105.). — FORMS OF FRUIT (108.). —
seeps (109.). — EMBRYO (111.). — REPRODUCTION OF
CRYPTOGAMOUS PLANTS (114. ).

(105.) Fruit.— ImmeDIareLY after the flower has
become fully expanded, several of its parts begin to

SEOT. I. ORGANOGRAPHY AND GLOSSOLOGY. ce lala

decay ; but the ovarium, sometimes the calyx, and
Other parts continue to grow, and ultimately assume a
Very different appearance from what they possessed in
the flower. This altered condition of these parts is
termed the “ fruit.” In many cases, the fruit is not
ripened unless the ovula are subjected to the fertilising
influence of the pollen; but if this process be com-
pleted, then these bodies undergo certain remark-
able changes, and pass to the condition of “seeds.”
Certain fruits, however, will ripen freely enough, al-
though they produce no seed, as some varieties of
Oranges, grapes, pineapples, &c.

(106.) Pericarp.— The part of the fruit immedi-
ately investing the seed, and which originally formed
an ovarium, becomes the “ pericarp.” When the
Carpels are separate, the fruit is termed “ apocarpous ;”

ut when composed of several adhering carpels, it is
said to be “ syncarpous.” The pod of a common pea,
is a familiar example of a simple pericarp, with a
structure not very dissimilar to that of a leaf folded
longitudinally inwards, with the seeds attached along
the margins, united and forming a swollen placenta.
De Candolle has given a figure, in his ‘“ Memoir on

105

1

the Leguminosæ,” of a monstrosity, where the pericarps
H 4

104 DESCRIPTIVE BOTANY. PART I.

have manifested a decided tendency to develop in
the form of leaves, and where the position of the
ovules is marked on their edges by small projections
( fig. 105.). hs

If we suppose five carpels, formed
on the same general principle as
that of the pea-pod, to be ar- (
ranged round an axis, and to be en- `
veloped in a mass of pulpy matter,
contained in a swollen calyx (as
in the apple blossom), we have such
syncarpous fruits as apples, pears, &c. ( fig. 106.).

A multitude of examples might be adduced, where the
compound structure of the pericarp is easily referable
to an aggregation of several carpels. In such cases,
each carpel forms a distinct “ cell ;” and the wall of se-
paration between two contiguous cells, is termed a “ dis-
sepiment”’ (fig. 107.). There are, however,
many pericarps, which, in their naséent state,
possess this’ structure, but become further
modified as they ripen, by the rupture and
subsequent obliteration of the dissepiments;
at the same time the placente coalesce round
the axis, so that the ripe fruit consists of a single cell,
formed by an outer shell, which is entirely detached
from a, central placenta bearing the seed (fig. 108.).
This is the case in the seed-vessels of pinks, 108
primroses, &c. In some cases, the edges
of the adhering carpels do not extend so far
inwards as to reach the axis, and then the
dissepiments are not complete, as in the
poppy (fig. 109.). In other cases, the edges
of the contiguous carpels meet without ex-
tending inwards at all, and then the placente
are said to be “ parietal,” because they are
placed on the inner surface of the shell
which forms the one-celled capsule, as in the violet
(fig. 110.). The pericarp is essentially composed of
three parts, analogous to those in the leaf—two skins, and

SECT. 1. ORGANOGRAPHY AND GLOSSOLOGY.

the cellular matter between them. The outer skin forms
the “ epicarp,” the inner the “ en- “See
docarp,” and the intermediate por-
tion is the “ sarcocarp.” In many
Pericarps, these parts are not well
defined ; but in such as are fleshy,
as in the stone-fruits, peaches, maim
Plums, &c., it istheendocarp-which Urmu
develops into the <stone;” the epi- Vj
Carp forms the “ skin,” whilst the
Sarcocarp becomes the delicious and
edible portion of the fruit.
_ (107.) Dehiscence: — W hen the
"pened pericarp divides spontane- J
ously, in any definite manner, it is said to be “ dehis-.
Cent,” and the line of division is termed ee
the “c suture,” whilst the separate parts
are called “ valves” (fig. 111.). In ge-
Neral, the suture tallies either with the
adhering edges of the carpels, or with
a line parallel and midway between them,
in the position of the midrib or nerve of i
cach carpel. In the former case, the dehiscence 1s
termed “ septicidal” (a), as 1
in the Colchicum piini a AN agi
and in the latter, which is the {9° On
Most usual, “loculicidal” (6), « Æ Wa
as in the tulip. In a few
plants, as in the common pimpernel (Anagallis arven-
sis), the suture is transverse to the lines
formed by the edges of the carpels ; such
a pericarp is termed a “ pyxidium ” (fig.
112.). In some cases, the dehiscence is so
limited, that it merely forms pores or small \
valves, at the extremities of the pericarp.
In many pericarps there is no particular
line of suture ; but they rupture irregu- j
arly, to permit the escape of the seed ; or else they
decay and gradually rot without bursting.

106 DESCRIPTIVE BOTANY. PART I.

(108.) Form of Fruits. — It would be impossible
in this treatise to enumerate the vast variety of forms
and characters which different fruits present. Some
are soft and pulpy ; others are very hard, woody, dry,
or membranaceous. It is sometimes one part, and
sometimes another, of the inflorescence, which becomes
developed into a succulent and nutritious form, in dif.
ferent fruits; and a casual observer might easily
overlook these distinctions, in the general resem-
blance which they bear to one another (fig. 113.).

The raspberry (a), the strawberry (b), and perhaps
the mulberry (c), may be mentioned, as bearing a
considerable general resemblance to each other. In
the first, however, the juicy part consists of nume-
rous distinct and globular pericarps, each enclosing a
single seed, which are seated on a spongy unpalatable
torus. In the second, it is the torus which becomes
pulpy, whilst the pericarps remain dry, and are scat-
tered over its surface in the form of little grains, com-
monly considered as naked seeds. In these two cases,
the fruit is the produce of a single flower ; but in the’
mulberry, the structure is altogether different. This
tree is moncecious ; and the small fertile flowers — or
such as contain pistils, and no stamens — are disposed
in a dense spike. It is the calyx of each flower which
becomes succulent, and thus the fruit is made up of.
the aggregate mass of these altered calyces, each of
which invests a dry pericarp, containing the seed.

SECT. Ie ORGANOGRAPHY AND GLOSSOLOGY. 107

We shall very briefly notice a few of the most im.
portant forms which fruits assume, but cannot pretend
to enter into any details on so extensive a subject. Dr.
Lindley’s _“ Introduction...to.Botany.“may be advan-
tageously consulted for further information, and Gert-
ner’s invaluable works for the fullest details.

SIMPLE PERICARPS.

1. Follicle. — Where the pericarp is dry,
and dehiscent only along the suture formed
by the union of the edges of a foliaceous carpel,
it may be considered as composed of a single
valve: as in the monkshood (Aconitum napel-
lus), and- larkspur (Delphinium consolida,
fig. 114.).
2. Legume.—This form is familiarly illus-
trated in the pericarps of peas and beans. In |
many cases, it presents a near approach to the leafy struc-
ture,and may be considered as a modified condition of the
leaf, folded longitudinally on its midrib, with the edges
adhering, and forming a suture (fig. 115. a), Another

suture is also formed along the midrib or dorsal nerve,
so that the legume separates into two valves. In
some species, however, the sutures are so firmly closed,
that the legume becomes indehiscent. Its varieties
are yery numerous. In the genus Astragalus, it is

108 DESCRIPTIVE BOTANY. PART I.

divided into two spurious cells (b), by the back of the
legume becoming doubled inwards until it reaches the
placenta. In some cases, the legume is divided by
transverse partitions (c), formed by the agglutination
of the opposite parietes, so that each seed appears
to be contained in a separate cell; and in some cases
the pericarp is pinched between each seed, so that
the sides nearly meet, when it is termed “ lomen-
taceous” (d). In some cases it falls to pieces at these
transverse contractions, and breaks up into as many
detached cells as there are seeds. In the genus Medi-
cago, the legume is curiously twisted in a spiral manner,
and somewhat resembles a snail-shell (e).

3. Drupe.— This form may be illustrated by the
plum, cherry, and other stone-fruits, where the peri-
carp has a thickened and pulpy mesocarp, with a stony
endocarp. It contains two seeds in the early state ;
but one of them is most frequently abortive, and withers
completely before the fruit is ripe. The numerous
small drupes, or ‘‘ drupels,” of the raspberry, and other
Rubi, are closely aggregated on a spongy convex torus
(fig. 1158. a).

4. Nut. — This is a bony pericarp, containing a
single seed, to which it is not closely attached ( fig.
116.). The strawberry has a fleshy succulent torus,
covered with small nuts (fig. 113.). 116
The torus of the rose, coats the interior
of the tube of the calyx, and its nuts
are placed round the sides and at the bot-
tom of this tube. This form of the pe-
ricarp must not be confounded with the fruit usually
called a nut, and which belongs to the “ glans,” pre-
sently to be described. _

Pericarps simple by Abortion.

5. Cariopsis. —'This pericarp is a thin, dry, and
indehiscent membrane, closely investing, and in-

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 109

deed adhering to, the seed—as in corn, and other Gra-
mine., As these pericarps bear two or three stigmas,
the seed is probably simple by abortion, and there-
fore the fruit, strictly speaking, is compound.
6. Akenium.—This may be con- 17
sidered as a cariopsis, with the su- ©
Peraddition of the calyx, adhering to
the pericarp, and forming a single
skin round the seed — which, in this
case also, is simple by abortion. The %9
fruit of the ‘‘ Composite” are formed
(fig. 117 ne
7. Glans. — Acorns (fig. 118.),
hazel nuts, and chestnuts, are exam-
ples of this form. The base of the
fruit is enveloped by an involu-
crum, which at first contains several
flowers, but one of them alone per-
fects its seed. The pericarp is tough
or woody, indehiscent, adhering to
the perianth, one-celled by abortion,
and containing one or more seeds. S
8. Capsule. — This is a very general term, for dry
fruits composed of two or more carpels, variously com-
bined and modified. k
9. Gourd. — The carpels
are not complete, but united
by their edges so as to form
a single cell with parietal pla-
centæ. The pericarp is thick
and fleshy, with the outer coat
hard (fig.119.).
_ 10. Berry. — This term
1s applied to very liquid fruits,
` Which are covered with an in-
dehiscent skin, as the grape,
gooseberry, and others. In
the gooseberry the carpels are incomplete, and form one
cell with parietal placente (fig. 120. a); and the calyx

110 DESCRIPTIVE BOTANY. PART I.

adheres to the pulpy pericarp; but in the grape
(fig. 120. b), the calyx is free, and forms no part of the
fruit; the carpels are complete, and the placente central.

11. Pomum.— Several membranous, or bony carpels
are: embedded in a fleshy
mass, which is the swollen
calyx. Apples (fig. 106.),
medlars (fig. 121.), quinces,
&c., are examples.
12. Samara. — The peri-
carp is here extended into a
flat wing-like appendage, as
in the sycamore (fig. 122.)
and ash ; the fruit of which
trees is commonly termed a “ key.”
13. Siliqua. — This is the name given to the bi-
locular and bivalvular seed-
vessels of the Crucifere.
The seeds are attached to
lateral placente ; the dissepi-
ment is formed by a thin
- membrane, which is appa-
rently a prolongation of the
inner skin (endocarp) of the two carpels (fig. 123.).
_ (109.) Seed. — It would be impossible to obtain a
just notion of the seed, without first tracing the ovule
through the several alterations which it undergoes, after
it has been subjected to the fertilising influence of the
pollen ; but, as such details are more especially con-

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 111

nected with the physiology of our subject, we. shall for
the present confine ourselves to a few
general observations on the ripe seed.
Every seed is attached to the placenta,
by what is termed a “ funicular, or um-
bilical cord ;” and when the seed has
fallen from the pericarp, it is marked by
a scar or “ hilum,” at the place where
this cord was attached to it. In very
Many cases, this cord is small, and
Scarcely distinguishable, but in some it
is well marked ; and in the genus Mag-
Nolia, when the pericarp bursts, the seeds
hang out for some time, and to a con-
Siderable distance, by means of their
umbilical cords, before they become de-
tached and fall to the ground (fig.124.).
In a few plants, the funicular cord is
Unusually developed ; and, rising round
the seed, forms a distinct skin or covering to it,
termed an “ arillus.” The
nutmeg (fig. 125.) is thus
enveloped by an arillus,
Which is the “mace” of com-
Merce. In the spindle-tree
Euonymus europeus), the
Seeds are invested by an arillus,
of a fleshy consistency and
bright scarlet colour.
In its ripe state every seed
18 essentially composed of an
Outer skin, or “ spermoderm,”
and a “ kernel” within it. The
Spermoderm, however, is not
a distinct organ, but is rather
the dry and exhausted remains of two or more coats,
With which the embryo was invested in its earliest
State, but which have ultimately united, and form
à single skin on the ripe seed. The kernel consists

112 DESCRIPTIVE BOTANY. PART L

of the “ embryo;” and, in many cases, also con-
tains a peculiar substance termed the

« albumen,” which is a nutritious mat-

ter secreted for the use of the embryo,

and is either of an oily, farinaceous,

or hard and horny, consistency. This

substance is always wholesome ; and in

many seeds, especially in corn, forms an

important article of human food. In

some cases, the embryo is completely

invested by the albumen, as in the

cocoa-nut ; in others it is only partially embedded, as
in wheat and other corn (see figs. 23. and 25.). Ina
multitude of seeds, however, there is no trace of this
substance, in a detached form ; but then we often find the
cotyledons themselves much swollen, and abundantly
supplied with a similar material. This is the case in
peas and beans, whose cotyledons are very large, and
contain a nutritious material, which serves to develop
the young plant in the early stages of its growth. Some
few seeds, as the orange, contain more than one em-
bryo; a fact which has been considered analogous to
the phenomenon of double fruits, and to be explained
on the supposition that two or more ovules have adhered
together in the earliest state of their development.

(110.) Forms of Seeds. — The forms which seeds
assume are very various, and their surface is either
smooth, rough, or, in some cases, furnished with pe-
culiar downy or membranous appendages. The various
appendages, however, which assist the dissemination of
the seed, are more frequently attached to the pericarp ;
and afford abundant instances of an adaptation of means,
admirably calculated to secure the end for which the
seed is destined — the preservation of the species upon
the earth.

(111.) Embryo. — We have already described (arts.
34, 35.) the two principal distinctions, which subsist be-
tween the embryos of flowering plants, and which es-
sentially separate them into two great classes. To those

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 113

remarks, we may add the following: —The embryo
May be either straight or curved ; placed in the centre of
the albumen, where this substance exists in a separate
form, or else laterally disposed with respect to it. The
Parts of which it is composed are, 1. The “ radicle,”
Which is the conical extremity, afterwards developed
into a root; and, 2. The “ plumule,”— consisting of the
“cotyledon or cotyledons,” and the “ gemmule,” or
first leaf-bud, which is afterwards evolved in the form
of stem and leaves.

The position of the embryo is determined by the
direction of its radicle, the point of which is constantly
turned towards the “ foramen,’ — a small hole pierced
through the outer coat of the seed, and of which we
shall speak more particularly hereafter. Now, the posi-
tion of the foramen varies with respect to the hilum,
and may be either on the opposite side, or placed
Near it, on the same side of the seed. The radicle will,
consequently, either point from or towards the hilum,
and the embryo become “ inverse” (fig. 120. a) or

126

“erect” (b) accordingly ; or the embryo may lie “ trans-
Verse” (c), when the apex is on one side of the seed, and
the radicle cannot be said to point either towards or
from the hilum. Some authors, however, make the
direction of the embryo to depend also on the position
of the seed itself, which may be either erect or pendent
Within the pericarp ; but this is a circumstance which
can merely modify the direction of the embryo with
tespect to the pericarp, and not with respect to its po-
‘ition in the seed.

(112.) Cotyledons. — In many plants, the cotyledons `
have comparatively little resemblance to leaves, but 1

i

1i4 DESCRIPTIVE BOTANY. PART I.

others they alter their character very considerably after
germination has commenced ; they then become green,
and expand in a form which closely resembles the or-
dinary leafy structure. Some cotyledons, however, whilst
still in the seed, have the appearance of miniature leaves,
are extremely thin, and delicately veined (fig. 23s a) ;
and no one could for a moment consider them in any
other light, than as these organs in a young and un-
developed state. In many Dicotyledons, the embryo is
a cylindrical body, with nothing more than a notch at
one end, indicating the position of the cotyledons ; but,
in a few species, there is no appearance of any division,
and then it is presumed that the cotyledons adhere
together; or rather, if we judge from analogy, that
they are entirely abortive. Their stem consists merely
of a slender filament which twines itself round other
plants, from which it extracts its nutriment by means
of suckers provided for this purpose.

Here and there we find a young plant of several
dicotyledonous species, which have three, or even more
cotyledons, instead of two. The common sycamore
( Acer pseudoplatanus) affords frequent examples, where
this unusual number appears to have originated in some

ations from the usual character, in species where the
cotyledons are most frequently two in number, may
serve as a connecting link between them and plants
of the coniferous tribes (the fir trees), which possess
several cotyledons.

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 115

An attempt has been made, to establish an affinity
between the embryonic structure of dycotyledons and
monocotyledons, by supposing the single cotyledon in
the latter class, which completely envelopes the
rest of the embryo, to be in reality compounded.
of two cotyledons, united by their edges into one
mass, In some cases this occurs in dycotyle-
dons ; and the annexed figure (128.) represents
a monstrosity, observed in a young plant of the
‘sycamore, which exhibits something like suchan
approximation to the condition of a monocoty-
ledon, at the commencement of its germination :
the two cotyledons having adhered by one of
theiredgesnearly throughout their whole lengths.

The truth however seems to be, that the cotyledon of a
monocotyledon is a single folded leaf.

In all monocotyledons, it is more difficult to determine
the several parts of which the embryo is composed, than
in dicotyledons. It generally consists of a nearly cylin-
drical fleshy mass, without any external traces of organis-
ation ; but if it be cut longitudinally, the position of the
radicle and the gemmule may then be seen, traced by a
faint outline, indicative of a separation in the substance
of the embryo (fig. 25.).

(113.) Reproductive Organs
of Cryptogamic Plants. — The
sporules mentioned in art. 36.
are contained in peculiar cells,
placed on the surface, or em- |]
bedded in the substance of | |
the plant, among the crypto- ©
gamic tribes. Among the higher families of this class,
the cells assume a distinct capsular form, 130
termed “theca” (fig. 129.) which has |
various characters, ‘in the ferns (4), Equi-
seta: (b), mosses (c), &e. The cells,
or cases which contain the sporules, among
the inferior families of this class, are more
simple in their structure, and often re-

p 4

i

116 DESCRIPTIVE BOTANY. PART I.

semble short closed filamentous tubes, or sacks (fig. 130.),
which ultimately discharge their contents by the rupture
of one of their extremities.

CHAP. VI.

MORPHOLOGY.

ABORTION (115. ):— DEGENERATION (116. ).— ADHESION (118. ).
— SUPERNUMERARY WHORLS (119.).— NORMAL CHARAC-
TERS (120.). — SPIRAL ARRANGEMENT OF FOLIACEOUS
APPENDAGES (121.). — TABULAR VIEW OF VEGETABLE OR-
GANIZATION (129.).

(114.) Morphology. — Ir is an observed fact, that the
subordinate parts which make up the floral whorls of
very many plants, are symmetrically arranged round the
axis, and that the parts of each separate whorl are placed
alternately with those of the contiguous whorls. Con-
nected with these facts, it has been remarked, that the
flowers of certain species, whose parts are not-symmetri-
cally arranged, and which do not alternate in the manner
described, do nevertheless occasionally assume a per-
fectly regular structure, by the development of super-
numerary parts. As an illustration of our meaning, we
may select the common snapdragon ( Linaria vulgaris) ;
in which, as well as in some other species of this and of
the allied genus Antirrhinum, the phenomenon we are
about to describe may occasionally be observed. The
common form of the flowers of this plant is termed
“personate” (fig. 131. a); the corolla is monopetal-
ous, and divided into two large lobes, closed in front,
and presenting somewhat the appearance of an animal’s
face. The upper portion of the corolla is prolonged
backwards, into a tubular “spur ;” it contains four
stamens, arranged in pairs of unequal length (didy-

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 117

namous) : the calyx is subdivided into five segments,
Indicating the adhesion of as many sepals ; the pistil

is a two-celled capsule, with the seeds arranged on
a central placenta. In short, the flower is highly un-
symmetrical and irregular, in all its parts. Now, there
is an interesting variety of this plant, termed “ Peloria,”
in which the corolla is strictly symmetrical, consisting
of a conical tube, narrowed in front, and elongated
behind into five spurs (b). It contains five stamens of
equal length. In this state, therefore, we have a flower
composed of five sepals, adhering through a considerable
portion of their length, constituting a five-toothed mo-
nosepalous calyx ; five petals, adhering into a monope-
talous corolla ; five stamens ; but a pistil which is com-
posed of only two carpels, as in the irregular flowers.
- The three first whorls are therefore strictly symmetrical,
and the parts are also arranged in an alternating order
round the axis. It should seem, that the ordinary
irregularity of this flower is somehow connected with
the disappearance of the fifth stamen, involving a
Partial suppression, as well as modification, of four
of the petals: Other specimens may be seen in every
intermediate condition, between the regular and irre.
gular forms here described; some having two, others
three or four spurs, to the corolla (c). If we connect
these and similar facts, with the observations already
detailed, viz. that the subordinate parts of the flower-
bud are analogous to those which compose the leaf-bud,
1 3

118 DESCRIPTIVE BOTANY. PART I.

and consequently that all these parts are only analogous
to so many leaves, which under other circumstances
would have developed regularly round the branch on
which they grew—then may every deviation from the
symmetrical arrangement in the parts of the flower, be
ascribed to the operation of certain modifying causes,
connected with some peculiarity, inherent in the several
species themselves. These causes may be arranged under
the heads of “ Abortion,” “Degeneration,” and “ Ad-
hesion.”

(115.) Abortion.— This term is used, wherever some
organ is ‘wanting, to complete the symmetry of the
flower ; in which case, such organ is supposed to lie
dormant under ordinary circumstances, though capa-
ble of development under other and peculiar condi-
| tions. As the latter are of accidental occurrence,
/ they only give rise to those various monstrosities, or
deviations from the ordinary form, which are frequently
(as in the case of the Linaria above mentioned (art.
114.) so valuable), in determining what is considered
to be the “normal” structure, or regular condition, to
which various unsymmetrical flowers may be referred.
Portions of the inner whorls are more often abortive
than those of the outer ; and thus the number of carpels
is far less frequently in accordance with the normal
structure, than the number of the stamens. All uni-
sexual flowers, may be considered as resulting from the
complete abortion of one or other of the two innermost
whorls.

(116.) Degeneration, is where the abortion of an
organ is not fully completed, but where it has become
imperfectly developed, or very differently modified from
its usual state. In many instances, we find certain
anomalous appendages, which occupy the place of some of
the subordinate parts belonging to one or other of the
floral whorls, and which are consequently considered as a
monstrous or incomplete state of those parts. Perhaps
the stamens are more especially subject to this condition
of degeneracy than any other organs. They frequently

SECT. 1. ORGANOGRAPHY AND GLOSSOLOGY. 119

assume the form and structure of secretory glands, and
of various processes and appendages, of an anomalous
character, In many cases, the parts which have
degenerated from their usual condition, assume 4
highly developed structure, and become more leaf-
like. Thus, we find double flowers are often formed
by the stamens having put on the appearance, and
all the characters of petals, — organs which are usually
of larger dimensions, though of inferior importance
in the floral economy. In some plants, as the com-
mon white Water-lily (Nymphea alba), the transition
from the character of a petal to that of a stamen, is so
very gradual (fig. 132.), through successive whorls of

i

these organs, that it is hardly possible to determine where
one set begins and the other terminates.

(117.) Causes of Abortion and Degeneration. — An
inquiry into the causes of abortion and degeneration,
more properly belongs to our physiological department,
but may as well be alluded to in this place. The par-
tial or total abortion of certain organs, is very frequently
occasioned by accidental circumstances — from some
impediment thrown in their way, from a deficiency of
light in a particular direction, and many other external
causes. In these cases, when the influence is removed,
the suppressed organ will sometimes appear, and assume
its proper character. Thus, in trees, it seldom happens
that all the buds generated in the axills of the leaves,
are developed into branches ; but many of them remain
dormant, especially about the lower parts of the stem ;
and it is not until a better supply of light and air is

1 4

= a ae le a ac A
oe =

120 DESCRIPTIVE BOTANY. PART 1.

afforded them by the pruning knife, that they are
enabled to grow. Sometimes the development of an
organ is impeded or prevented, by the want of a suffi-
cient supply of nutriment 3 and this often arises from
the abstraction of what was naturally destined for it,
by the more vigorous growth of some neighbouring
portion. Hence the different characters which dis-
tinct individuals of the same species assume, depend
upon the various. degrees of influence which those and’
many other external circumstances have upon them.
J From such causes as these, we find the leaves of a
tree gradually dwindling into membranous scales ; the
calyx of the florets in the Composite becoming a
downy pappus (fig. 117.). The thorny prickles of
the wild plum are merely stunted branches, and by
culture readily disappear, — an effect which Linneus
| fancifully termed, the taming of wild fruits. But
besides these merely external influences, which may all
be considered as accidental causes, tending to produce
the abortion of particular parts, there are others of a
more subtle and incomprehensible description, which
are in constant operation within the plant ; and which,
acting from the very earliest periods in which certain
organs begin to develop, tend to suppress or modify
them; and thus produce that infinite diversity of
forms and characters, which we find even among those
which are destined to perform the very same function.
And sometimes the altered organs are so far changed
from their original character, as to become adapted only
to serve some new secondary purpose, distinct from
that for which they were primarily intended. Thus,
the spines of the common furze (Ulex europeus), are
merely modified leaves. In the common berberry
(Berberis vulgaris), the transition may be readily traced
(see fig. 68.).

/ C118.) Adhesion.—If to the operation of the two
causes already noticed, we add the“ adhesions,” which
take place between the contiguous parts of similar or
different organs, we introduce a third cause, in very

SEOT. i. ORGANOGRAPHY AND GLOSSOLOGY. 121

general operation, which serves to modify the normal
condition of the several parts of the separate whorls.
For example, the Phlox amena has a monopetalous

tubular corolla (fig. 133. a), expanding into a flattened

border at the summit, and forming what is called a
salver-shaped” flower. But a monstrosity of this
plant has been observed, where the corolla is split up
into five distinct petals, resembling those of a pink
(Dianthus). This shows us, that the ordinary mono-
petalous condition of the corolla in this flower, has
resulted from an adhesion of the five subordinate parts
of which it is composed; and some blossoms have
been found, in which this adhesion has only taken place
partially, some of the petals being cemented half-way
up the tube, whilst others adhere nearly throughout its
whole length (b).

' Not only may the several parts of the separate
whorls contract adhesions of these kinds, but two or
more of the whorls may be grafted together, throughout
a greater or less extent.

The causes here enumerated, as modifying or dis-
guising the several parts of which flowers are composed,
are brought into operation at such early stages of their
development, that it is very seldom we can trace the
successive steps by which the metamorphosis has been
effected. In many cases, however, we find the number
of ovules in the ovarium, far exceeding the number of
ripened seeds in the pericarp; and the obliteration of

——

amen EL me maare S aa

122 DESCRIPTIVE BOTANY. PART Is

those which have become abortive, may be some-
| times traced to the circumstance of there having been
| more ovules originally formed than could possibly be
| contained, as ripened seeds, in the pericarp, which would
be too small to hold them all. It is easy, therefore, to
conceive, that those parts of a flower which are only
exhibited in cases of monstrous development, may in
like manner have been choked by the compression of
some contiguous parts, which got the start of them in
the progress of their growth. It is equally easy to
comprehend, that two contiguous parts may be con-
stantly predisposed to graft together, long before we
can trace them in a detached state. We perpetually
see apples, peaches, and a variety of other fruits,
become double, owing to the great facility with which
their tissues graft together, when brought into close
contact; and we can readily imagine that the tissues
of two contiguous organs, whilst they are yet in their.
nascent state, must be in a condition even still better
adapted for receiving this impression, than they would
be at a later period of their growth.

In those cases of adhesion where the union is most
perfect, it generally happens that some portions have
necessarily become suppressed, and thus a monstrous
form is produced, in which the number of its parts will
lie between the regular number in a single flower, and
some multiple of that number. Now, that which is so
evidently the result of a natural grafting of contiguous
parts, in these monstrous cases, may be conceived also to
exist in other instances, where the same cause may have

‘been in operation, previous to the very earliest stage of
development to which the existence of the flower can
be traced. i

(119.) Supernumerary Whorls.—It sometimes hap-
pens, that a supernumerary development takes place,
of one or more entire whorls, or of the parts of a
whorl. In this way, certain flowers become double ; but
such are not necessarily barren,as is the case where double
flowers have resulted from the transformation of the

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 123

Stamens and pistils into petals. The various parts of
these supernumerary whorls alternate with those which
precede them in the series.

(120.) Normal Characters.—It will readily be un-
derstood, how numerous may be the modifications
which can be referred to the same normal condition
of the parts of a flower, —if we suppose the three
Causes which we have enumerated, capable of acting
Separately, or together. If, for instance, the normal
Character of a flower consisted of five sepals, five
petals, five stamens, and five carpels; and these several
Parts were so arranged, that all those which were
in any one whorl, alternated in position with those in
the contiguous whorls —this arrangement would consti-
tute a highly regular flower, such as we meet with in
the genus Crassula (fig. 134.). By simultaneously sup-
Pressing one, two, three, or four 134
Parts of each whorl, we may con- iat
ceive four other flowers to be 4
formed, equally symmetrical with #7

e original, but disagreeing with |
this normal type, in not possessing
@ quinary arrangement of their
Parts. Irregularity might now be
Introduced, by suppressing certain
Parts of some whorls and not of others, or by form-
ing adhesions between two or more parts of one whorl,
Whilst the other parts remained free ; or by supposing
Some of the parts of one whorl to degenerate, and
assume a variety of distorted shapes. In this way, an
Infinite variety of forms may be supposed to result
from a few normal types; and it is by detecting these,
that the systematic botanist is enabled to ascertain the
affinities of certain species, which at first sight appear
Widely separated.

_ Whenever the parts of one whorl are placed. opposite,
instead of alternate with, the parts of the contiguous
Whorls, this circumstance is considered to indicate a
Want of regularity in the flower, although there may be

124 DESCRIPTIVE BOTANY. PART i.

no real want of symmetry in the arrangement; and
such a state of things is always supposed to have
originated in the abortion of one or more of the whorls.
These whorls may possibly be still developed under
certain conditions, and then the regularity of the
flower would be restored, and the normal condition ex-
hibited. In the annexed figure (135.) there are five
whorls ascribed to the normal
condition of certain organs,
which “alternate ” with each
other in some flower; and by
suppressing the parts in the
second and fourth whorl, those $
in the first, third, and fifth
are brought “opposite” to
each other. Where two con-
tiguous whorls are abortive,
no irregularity would be ap-

parent, and the existence of the suppressed parts might
not be suspected, unless it were indicated by some ana-
logy in other allied species.

It is a remarkable circumstance connected with these
inquiries, that the normal condition of dicotyledonous
plants, appears most frequently to involve a quinary
arrangement, in the disposition of the subordinate
parts of the several whorls; whilst that of Monocoty-
ledons, equally affects a ternary. In a multitude of
examples, where the parts or organs of the class exceed
these numbers respectively, they are still observed to be
some multiples of them — 10, 15; 20, &c., or 6, 9, &e.5
and many deviations from this rule, are clearly referable
to the abortions of some of the parts, and the adhesions
of others; so that a considerable approximation has
apparently been made, towards the discovery of some
general laws on this subject.

(121.) Spiral Arrangement of foliaceous Append-
ages.—The variety exhibited in the disposition of leaves,
and other foliaceous appendages to the stem, or other

1

135

SECT, I. ORGANOGRAPHY AND GLOSSOLOGY. 125

axes, may be reduced to a general mode of expres-
Sion, by a method proposed by M. Schimper, and
Subsequently elucidated by M. Braun. Even in those
Cases where their distribution does not seem to be
regulated by any law of symmetry, this may be con-
Sidered to be owing to the various disturbing causes
Which are perpetually modifying the conditions under
Which their arrangement would otherwise have taken
Place. As the mineralogist refers the crystalline
forms of his minerals, to certain geometric solids,
Whose angles at least are the same as those on the
Crystal; so we must here neglect the accidental displace-
Ments, produced by the unequal development of those
Parts to which the foliaceous appendages are at-
tached, or some other circumstances, and look only to
the primary conditions upon which their distribution
depends. If in those cases, even, where the leaves are
Most scattered on the plant, we were to draw a line
from any one which is seated lower down the stem
or branches, to another next above it, and so on,
this line will be found to follow a spiral direction ; and
thus we ultimately arrive at a leaf, which is seated ver-

tically above that from which we started. The usual
Mode of expressing this, is to name the number of the

126 DESCRIPTIVE BOTANY PART I-

leaf which ranges vertically over the first on this spiral,
but without any reference to the number of coils which
the spiral makes before this happens. Thus, in each of the
annexed figures (fig. 136.), No.8. ranges vertically over
No. 1.; but, in A, this happens after one coil ; and in
B, not until after three coils of the spiral. The
numbers are ranged at equal intervals, indicated by
the eight vertical lines drawn on the surface of the
cylinder. 7

(122.) Divergence of generating Spirals. — M. Braun
proposes to note the nature of this arrangement, by
giving it a numerical value, which shall be expressive of
the angular distance between two successive leaves on
the spiral, when they are projected on a plane perpen-
dicular to the axis. The expression obtained, is termed
the “ divergence ” of the generating spiral. Thus, the
divergence in A, is the angular distance between 1° and
2 (viz. 1 of the circle) ; but the divergence in B,
is 3, as may be seen by inspecting the summits of the
two figures. The numerators of these fractions also
express the number of coils which the generating spirals
make, before one leaf ranges vertically over another ;
and their denominators, are the number of leaves distri-
buted upon this interval — which is called the “length”
of the spiral. It is further evident, that the leaves
arrange themselves along as many lines drawn parallel to
the axis, as there are leaves on one length of the spiral,
viz. seven-in each of these figures.

Where the coils of the spiral are not very close, and
the numbers succeed each other at short intervals, it is
easy to trace its course round the axis; but, in many
cases, the coils are so close together, and the leaves, of
other appendages, so disposed upon them, that all traces
of its course are either obliterated, or much confused.

(123.) Secondary Spirals. — But still, the symmetry
with which the leaves are really disposed, is now ma

-nifested by the appearance of several ‘ secondary”
spirals, which may be traced in various directions
This is well exhibited in the arrangement of the scales

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 127

of a fir-cone (fig. 137.) ; and we shall endeavour to
Show, how the real dispos-

ition of the scales on the

“ generating” spiral may be

readily ascertained, from

merely inspecting the ap-

Pearances presented by these

Secondary spirals. Thus, in

the spruce fir (Pinus abies),
It is easy to trace several sets

of spirals, running parallel to

1,9, 17, 25, &c.; and other

Sets parallel to 1, 6, 11,

16, &c. ; and others to 1, 4,
7, &e,, and so on. In the
Present example, there are twenty-one

e drawn through those scales which are ranged ver-
tically over the others, as 1, 22, 43, &c., 14, 35, 56,
&c. and so on. This number, as was before shown of
the seven verticals, in A and B (fig. 136.), indicates the
Number of scales that are ranged upon one length of the
Spiral. But the course of the generating spiral is not
apparent, and, consequently, the numerator of the frac-
tion which expresses the divergence is unknown.
(124.) To fix Numbers to the Scales. — We may

easily observe, that the numbers on the scales which
form the different secondary spirals, are in arithmetical
Progression ; and we shall presently show, in the next
article, that the common differences in these progressions,

. ālso indicate the number of similar secondary spirals
| Which range parallel to each other. Thus, there are

$

j

| Sight parallel spirals, 1, 9, 17; &e., O, 14, 22; &e.,
| Where the arithmetical progressions have all the same

Common difference —eight. Hence we see a ready means
of numbering the scales on the cone, without the necessity
of previously ascertaining the course of the generating
Spiral. Fixing on scale (1) for a beginning, and count-
ing the number of parallel spirals (viz. eight) which
run in one direction, as above, we can fix the numbers

sh GRD MRT E

128 DESURIPTIVE BOTANY. PART I,

1, 9, 17, &c. on one of these spirals; then counting
the number (viz. five) which lie parallel with 1, 6, 11,
&ec., and which run in a contrary direction, we can
also fix those numbers, upon that spiral: and it is easy
to see that, as these two sets of spirals intersect one
another, we may fix numbers to every other spiral
parallel to each of them, that is, to every scale; and
thus the position of the generating spiral becomes ap-
parent, by observing the scales on which the numbers
1, 2, 8, &c. occur, in succession. We may easily count
the number of parallel spirals of the same class, even in
a mere segment of a cone, by observing the intersections
which they make with a circle drawn round it ; and, where
the cone is complete, they may be counted, by observing
how many lie between the coil which completes a length,
in one of them. Thus the spiral 1, 6, 11, 16... 38,
46, 51, 56, has four others lying parallel to it, and
between two of its successive coils ; there are, therefore,
five such spirals in all, and, consequently, the common
differences on them are five. Looking to the truncated
edge, we might ascertain the same fact, by observing
that five such spirals meet it in the scales 59, 61, 58,
&e. Also eight parallel spirals meet it in the scales
54, 59, 56, 61, 58, &c. But even without numbering
many of the scales, we may ascertain first the deno-
minator, and then the numerator, of the fraction which
expresses the divergence. We need only place the num-
bers 1, 9, 17 in one direction, and then pass from 17 to
22 in another direction, and we arrive at the scale
placed vertically over number 1 ; and thus we know that
21 is the denominator of the fraction. To find the nu-
merator, we must fix the scales 2 and 23 — the latter
ranging vertically over the former ; and then fixing all
the scales that lie between the verticals (1, 22,) and (2,
23), which we shall find to be 9, 17, 4, 12, 20, 7,
15 — through each of which other verticals may be
drawn — we obtain the angular distance between
any two vertical lines, viz. 2 of a circle: and this
gives the number 8, fo~ the required numerator. This

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 129

may perhaps be rendered more evident by an inspection
of the annexed figure ~
(138.), which shows the
relative position of the
Scales on one Jength of
the spiral, seen in the
direction of the axis.

(125.) Number of se-
Condary Spirals. — Al-
though the number of
Secondary spirals which
are readily distinguish-
able, is limited, yet it is
evident that we may really
establish the existence of any number, however great,
by merely passing~a line successively, from No.1 to
any other scale, and so on to that scale next beyond
it, which has the same relative position towards it, as
it has to No.1. In other words, we may have arith.
Metical progressions with all possible common differ-
€nces, which shall represent different secondary spirals ;
and these spirals may be coiled, some to the right, and
Others to the left. We proposed to show (what we
took for granted in the last article) that the number
of parallel spirals of the same class, was always equal
to the common differences, of the progressions,on these
Spirals. It is clear that the generating spiral, passing
Successively through 1, 2, 3, &c., must be unique:
ut the secondaty spiral, which passes through the
odd numbers, 1, 3, 5, &c., leaves the even numbers, 2,
4, 6, &c., which form a second spiral, of the same
class ; that’ is to say, there are two secondary spirals,
Where the common difference is 2. There are three
Spirals, in the same manner, which pass through 1, 4,
7, &e., 2, 5, 8, &e., 3, 6, 9, &c., where the common
difference is 3; and so on of all the rest. Several
Other properties, of a mathematical nature might be.
Mentioned; but sufficient has been said, to show the
Simplicity of the investigations necessary for obtaining

K

130 DESCRIPTIVE BOTANY. PART I.

an expression for the divergence, which is all that the
botanist requires.

(126.) Irregularity of Divergence. — Although the
appendages on one part of a plant, may be arranged
according to one law of divergence, it does not follow
that those of another kind, and on another part, possess
the same law; and even the same kind of appendages
are not all subject to the same law: thus, a few cones
on the same fir tree often possess a. different diverg-
- ence. from the rest, and even different parts of the
same cone are sometimes differently disposed. Many
of these anomalies originate in disturbing causes, which
it is not difficult to appreciate; such, for instance, as
some slight torsion of the axis, or the abortion of some of
the parts, &c. It is also common to find the generating
spiral turning to the right in some cones, and to the
left in others, upon the same tree.

(127.) Examples of Divergences.— From what has
been said, it will readily be seen, that the disposition of
foliaceous appendages may be conveniently and accu-
rately expressed, in terms of the divergence of the
scales on the generating spiral, unless they happen to
be so irregularly disposed as to lose all traces of a sym-
metrical arrangement. Thus, where the appendages
range in a line along one side of the axis, the divergence
is = 4; where they are ranged in two rows, on opposite
sides of the axis (distichous, fig. 139.), the 139
divergence = $; when in three rows
(trifarious), the divergence may be 4 or
2: the latter, however, may be considered
the same as 1, turning round the axis in
an opposite direction. One of the most
common, the “ quincunxial” arrangement,
where the appendages range in five ranks,
may be produced by four different diverg-
ences, represented on the circles in the an- ;
nexed figure (fig. 140.); but here also it will `}
be seen, that two of them are the same as
other two, only that the spirals turn in opposite

SECT. I; ORGANOGRAPHY AND GLOSSOLOGY:. 131

directions. And always, where the denominator of the
fraction is a prime number,
there will exist one number
less than that of thedivergences,
„according to which the gener-
ating spiral may be construct-
ed — and a similar number of
Vertical ranges will still be the
result. But where the deno-
Minator is not a prime number,
then some of the fractions which
express - these different diver-
Sences, are not. in their lowest
terms; and these divergences
represent the very same spirals
@s'when such fractions are so
teduced. Thus, when there are
Six vertical’ ranges (fig. 141.), ‘ aae
the divergences may be taken a í

EA 3, 4, 2; but 4=4, and 4 = 4, both of which

h

D
+.
`~
Oe
<2
i] Pa

P
y~, o
nee ee O

Pete aR)
usb
Sanar’

a
Sameena”

Pee eer N
$
7:
o
oe
Gs
a,

L
r

v
%,
“M

wg,

.

represent the trifarious arrange- : ia

- Ment ; also 3=4, which is the
di A 4 = TA P
istichous. Hence 4 and $ are °,/ ,

m

ua

the only divergences which // /
represent the hexafarious ar- |
rangement, and even these may

be reduced to one kind, only \\
the spiral would be turned in NNC
°pposite directions in the two

Cases,

132 DESCRIPTIVE BOTANY. PART I.

h wa
Examples of various Forms of Divergence among cer-
tain Species of the following Genera, selected from a
long List given by M. Braun.

Acotyledones.

Asarum ; Tilia ;/Spikes of all Graminez ; Fissidens; Didymodon
Vicia; Orobus./Cyperus;Acoruscalamus.| capillaceus.

Cactus triangu-|Carex.; Colchicum au-|Gymnostomum aestivum;
Jaris. tumnale, y Jungermannia tricho-
phylla.

Common in this|Scirpus acicularis ; Common,
class. Schoenus fuscus. -

Laurus nobilis ;| Lilium candidum; Scire|Commonest in mosses;
Ilex aquifolium.| pus lacustris. Lycopodium Selago.

Euphorbia sege-| Agave Americana ; Orthotrichum affine ;
talis; Convol-| many Orchis. t Aspidium filix mas. |
vulus tricolor.

Isatis tinctoria ;|Orchis conopsea; many|Hypnum `alopecurum ;
Plantago lan-| Yuccæ, ‘f Polytricum piliferum.
ceolata.

-| Euphorbia _czs-| Yucca aloefolia; Orni-[Sphagnum; Politrichum
pitosa; Plan-| thogalum pyrenaicum. formosum.
tago media.

Cactus corona-
rius.

(128.) Mode of examining the Divergence.— To the
above list we will add a complicated example, in the
spinous bractee which compose the
involucrum of Carduus Eriophorus,
and explain the manner in which
the divergence may be ascertained.

It is easy to observe two sets of
spirals respectively parallel to 4 B
and C D (fig. 142.), of which there
are 34 of the former, and 21 of
the latter. Fixing the Nos. 1, 35,
69, in one direction, and 90 in
the other, as in art. 124., we ar-
rive at the bractea which ranges vertically over No.1.

EE

I

SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 133

Also, No. 35 is evidently nearer than any other bractea
to the vertical line through 1 and 90. To con-
Struct the figure which represents the projection of one
length of the generating spiral, we may thus proceed.
Place No.1 in the circumference
of the circle (fig.143.), and di-
Vide it into 89 equal parts; place |
No. 35 on the part nearest to “|
No.1: and 34 is the com- os
mon difference on that secondary
Spiral, which is more nearly
Perpendicular than any of the
Others. The series on this
Spiral is, therefore, 1, 35, 69,
103, &c, of which we may
place 69 on the next’ division
to 35 ; but as 103 belongs to a
Second length of the generating
Spiral, we must subtract 89 from it, and thus we shall
obtain No. 14, which ranges vertically below it, and
is, consequently, within the first coil of the generating
Spiral itself, and therefore succeeds No. 69, on the circle.
From No. 14 then, we may begin with another secondary
Spiral, whose common difference is the same as the last ;
and, consequently, we place the Nos. 48, 82, next in
succession to 14; but 106 rises into the second length
of the generating spiral, and we must subtract 89 as
before, which gives us No. 17, for the next number in the
circumference of the circle which represents only the first
length. And so on until we arrive at No. 2. We shall
thus ascertain that No. 2 is placed at 55 intervals from
No. 1, and, consequently, that the divergence in this
example is =55. It may readily be understood, by any
Person accustomed to mathematical investigations, that
the first term common to the two arithmetical series, 1,
35, 69, &c., and 2, 91, 180, &c. (and which is 1871),
will be the number on the bractea intersected by
that spiral, which is represented by the first of these
K 3

143

a.
134 DESCRIPTIVE BOTANY. PART I.

arithmetical series, and the vertical line through No. 2,
represented by the second ; and also that one less than
the number of terms in the first series represents the
angular distance of 2 from 1. Several other interesting
mathematical considerations might be given, but they

would appear to be misplaced in a treatise of this de-
scription.

(129.) Tabular View of Vegetable Organs.— In con- —
cluding this part of our subject, we shall. present the
reader with a tabular view of the various organs we have
been describing, so arranged as to display the subordin-
ation which subsists between them; giving a reference
to the separate articles in which each is described.

I. Exementary Orcans (15.).

Ee. ;

in Vesicles (16.) Cellular tissue (16.

Membrane (13.) Tracheæ (23.) + Vascular tissue (22.)
: i Ducts (24.)

Fibre (13.) ši Vital vessels (27.})-

II. Comrounp Oreans (28.).

Pellicle (29.) ; ia (OC

Stomata (30.) ? ? coli 29.)
Stings (31.}
Glands (31.)

III. Comrrex Oreans (32.).
* Nutritive (38.).

Spongioles (39.)
Fibrils (89.) } Bogie ©.)
Appendages (41.)

Pith (48.) Thorns (62.)
Medullary sheath (49.) A pu pe (65)
Woody layers G0) | stems (ayana uns)
Medullary rays (51.) Branches (59.) Runners (62.)
Liber (52.
Cortical layers (52.) Phyllodia (75.)
yllodi ;

‘ Spines (78.)
Leaf (69.) Tendrils (79.) ek
Stipules (77.) Pitchers (80.)

Petiole (69.)
Limb (69.) i

7
SECT. I. TAXONOMY AND PAYTOGRAPEHY.

** Reproductive (85. ).
Bractea Involucrum (91.)
(91.3 t

Sepals — Calyx

“Petals — Corolla

(95.)
Fovilla Pollen 2 Anther |
(99.) Grains (98. i.

Granules 1 )
(99.) Stamen (95.) Flower (92)

Filament
aE (100) ¢
Carpels (100.) Ovarium i v7 § Pistil
Ovules (112.) Style to.) 2 (100.)
COMPOSITION OF THE RIPE Froiv (TOS: E

Pericarp
(106.)

Embryo

(111.) ;

Spermoderm Seed (109.)
(109.)

Cotyledon (112.)

Radicle (111.)
Plumule (111.) ?

SECTION II.

TAXONOMY AND PHYTOGRAPHY.

CHAP. VII.

NATURAL Groves (131.).— VALUES OF CHARACTERS (1382.)
— SUBORDINATION OF CHARACTERS (133.). — NATURAL OR-
DERS (135. )- — ARTIFICIAL ARRANGEMENTS (136.).— LIN-
NAAN SYSTEM (137.).— APPLICATION OF IT (140. ).

(130.) Taxonomy. — Wx have no space to devote to

any extended review of the various methods and sys-

tems which have been proposed for the classification

of plants; and it is not necessary for us to explain
K 4

\

136 DESCRIPTIVE BOTANY. PART 1.

the uses which a systematic arrangement of natural
bodies is intended to serve. This subject has been
thoroughly and sufficiently discussed by Mr. Swainson,
in our sixty-sixth volume. We may just remark, that
the number of species already named and classified in
- works of botany, amounts to about 60,000; and this
fact alone must- satisfy us, how necessary it is that
botanists should possess those means of intercommuni-
cation, which a systematic classification alone can afford
— whenever they wish to announce the discovery of a
new species, or to refer, with certainty, to one which has
been previously noticed. But, if we have the higher
object in view, of searching after the laws and princi-
ples which regulate the structure and fix the properties
of plants, then it is a necessary and immediate conse-
quence of every discovery of this kind, that we thereby
obtain a nearer conception of those affinities by which
plants approach, and of those differences by which they
recede from each other.; and this, in fact, amounts to
a closer insight into that hitherto undiscovered system, or
plan, upon which we must feel satisfied that the Author
of nature has proceeded in creating all natural objects.
(131.) Natural Groups.-—— We have already (art.
33.) mentioned the leading characteristics of the three
primary groups, or classes, into which plants seem
to be naturally divisible. Each of these, again, admits
of subdivision into minor groups, which severally con-
tain such species as are more nearly related to each
other than to those of other groups. By further sub-
divisions of this kind, a subordination of groups, of
smaller and smaller dimensions, is obtained, until we
arrive at those groups which do not readily admit of
further subdivision, and which are termed “genera.”
It must, however, be obvious that this method, of
analysis, is not the actual process in which the primary
groups were originally established. This was effected
by a synthetical mode of procedure — by comparing
separate individuals, and by selecting those which most
nearly resembled each other; and thence establishing, .

SECT. II. TAXONOMY AND PHYTOGRAPHY. 137

in the. first place, the limits within which a given
Species might be supposed to vary. Then, by com-
Paring different species, and selecting those which had
the greatest resemblance, a genus was constructed.
Then the genera were grouped into orders; and lastly,
those orders which possessed only a few general but im-
Portant points of resemblance, were arranged under the
three classes alluded to. But when these several groups
Were once established, a further refinement in their
Classification could be made; and the principles upon
which this was effected, may be explained by the ana-
lytical process to which we have just had recourse,

hen we said that all species are comprised, first, in a
Class; secondly, in an order, or family ; and thirdly,
ina genus. In very many cases, a further subordination
may be established. among the several groups; and,
from various considerations, they may either be aggre-
gated into larger, or subdivided into smaller groups ; to
which other names are applied, of which we have
given an example in art. 102. When any group is
subdivided into larger groups than those which it
is supposed to contain under the system of subordin-
ation already described, these are generally recognised
by the addition of the word “ sub” to the name of
the original group; thus we have sub-classes, sub-
Orders, and sub-genera. Certain groups are also termed
“Tribes,” “ Cohorts,” “Sections,” and “ Divisions ;”
and some of these terms are used indiscriminately for
Subordinate groups among the classes, genera, and even
Species. When a “ variety” of any species is repro.
ducible by seed, and retains its peculiarities pretty
Steadily, without returning to the more common type,
it is termed a “ race;” but when its distinguishing
characters are transient, and may be modified. by a
change of soil or situation, it is only a “ variation.”
In this way then, we establish a subordination among
the natural groups into which plants may be arranged,
and which may be exemplified by the following in-
Stance,

138 DESCRIPTIVE BOTANY. PART I.

J. Class - > - Dicotyledones.
* Sub-class ` Calycifloræ.

II. Order Leguminosæ.
i Sub-order Papilionaceæ.
MENDE Loteæ
*** Sub-tribe Genistee.
AII. Genus - - Anthyilis.
* Sub-genus (or Section) Vulneraria.
IV. Species - é Vulneraria.
* Variety Dillenii
** Race - Floribus coccineis.
*** Variation - - Foliis hirsutissimis.

(132.) Value of Characters.—In determining the
particular group to which a plant belongs, it is neces-
sary to compare its “ characters” with those of other
species. By the term “ characters,” we mean the pecu-
liar appearances presented by different organs. Thus,
a leaf may be round, lanceolate, &c. ; the petals may
be united, abortive, &c.; and these adjectives denote the
peculiar characters of these organs. It will readily be
understood, that some characters must be of much
greater importance than others, in determining the
affinities of different species. Thus, the first degree
of affinity in phenogamous plants, is almost always to
be ascertained by a single character, residing in the
embryo ; and we may determine at once, to which of
the two primary groups it belongs, by attending to this
circumstance alone. But even here, this primary cha-
racter may be so far disguised or modified, as inevit-
ably, in some instances, to lead us into error, if it
were not possible for us to check our observations by
other considerations, of secondary importance in most
cases, but which, in the present instance, are quite
sufficient. to correct our judgment, and to satisfy us
of the real affinities of the plant in question. Thus,
in the genus Cuscuta, the character of the flower,
the structure of the stem, and other circumstances,
clearly indicate that it belongs to the class “ Dicotyle-
dones”—although the embryo has no cotyledons, and the
stem is leafless. ‘The inference to be drawn from these

SECT. II. TAXONOMY AND PHYTOGRAPHY. 139

facts is, that the cotyledons and leaves are abortive ;
and hence we might expect, if ever such a phenomenon
Should occur as a leafy Cuscuta, that its cotyledons
would certainly resemble those of other Dicotyledones.
When the class of any plant has been determined by
the presence of some one character, or by the combin-
ation of several, we next renew our search for other
characters of a less general description, to ascertain the
€ order” to which it belongs. And when we have found
the order, we must descend to still more minute particu-_
lars for fixing the “ genus.” It is, therefore, of the
Utmost consequence to these inquiries, that an accurate
subordination of characters should be established ; and
for this purpose a few rules have been framed, which
are the result of an extended examination of facts, or
the deductions of common sense. We must remark,
that a direct comparison can only be made between
two organs which belong to the same class of functions:
the nutritive organs must therefore be compared toge.
ther, and the reproductive together, in order to esta-
blish a subordination in each series respectively. We
May, however, afterwards determine, whether one of
these two functions can not be considered more im-
Portant than the other ; and then we shall also be able
to establish something like a fresh relation, between the
Several degrees which had been previously settled for
the two series of organs. Suppose, for example, it were
determined, that the cotyledons are among the organs
of most importance to the nutritive system, and the
root among those of the next degree. Suppose, also,
the stamens were determined to be organs of the highest
importance to the reproductive function, and the co.
rolla among those of the next. Now, if it were also
determined that the nutritive function was of more im-
Portance than the reproductive, then the cotyledons will
be of more value than the stamens. But, although the
root may be of more importance than the corolla, it
does not follow that it is necessarily of more than the
Stamens ; it may be of equal or less importance. In

140 DESCRIPTIVE BOTANY. PART I.

this latter case, we are comparing an organ of second-
rate importance in the one series, with one of first-rate
in the other.
If we could determine the natural affinities of all
_ plants, from a comparison of the characters deduced
from one series alone, and could likewise determine their -
natural affinities from characters belonging to the other
series, it is evident that the two arrangements thus
established would strictly coincide. In the establishment
of the minor groups, botanists have recourse almost
exclusively to the reproductive organs; as their cha-
racters are much better defined, and more varied than
those of the nutritive organs. The larger groups, how-
ever, are chiefly determined by characters belonging to
the nutritive and elementary organs, as we have shown
(art. 33.), where the exogenous structure tallies with
the dicotyledonous embryo, and the endogenous with the
monocotyledonous,

(133.) Rules for fixing Subordination of Characters.
— The following rules may be advantageously con-
sulted, for determining a subordination of characters in
one or the other series.

1. Where two organs, belonging to different classes .
of functions, have the same relative value in their re-
spective series, that organ will possess the greatest value
which belongs to the most important function.

2. Those organs of the same series, are of the
greatest value, which are of most general occurrence.
Thus the cellular tissue, which is universally present, is
the most important element in vegetation.

8. The adhesion which frequently subsists between
an inferior and a superior organ, serves to point out the
relative value of any two of the former ; since it will
be the same as that which was previously established
for those of the latter, to which they respectively adhere.

4. The greater degree to which an organ is liable
to vary, indicates an inferiority in its value. Thus
the shape of the leaves, is of little importance beyond
determining the specific distinctions of plants, and in

SECT, 11. TAXONOMY AND PHYTOGRAPHY. 141

many cases is even of no further use, than in discrimi-
Nating certain varieties of the same species.

5. The relative periods at which different organs
are formed and developed, may also be taken as- some
test of their relative importance ; those which are the
earliest formed, being considered more important than
Others with which they are immediately connected, and
of the same class.

By attention to these and a few other rules of less
Seneral application, a subordination of characters has
been established, of which the chief results are exhibited
m the following table : —

Relative
alues.

l. Cellular Tissue —

2, Vascular Tissue } Embryo and
(a) Tracheæ Sporule
(b) Ducts (a) Cotyledons
Stomata - (b) Radicle
(c) Plumule

f Root, . Stem,
Leaf, Frond,
Thallus

Elementary. Nutritive. Reproductive.

. Pistils.
2) Fruit, Peri-
carp, Theca.
Perianth.
(a) Corolla.
(b) Calyx.
Inflorescence,
Torus, Nectary,
Bractea, Invo-
lucre.

fi Stamens and
(

—

_(134.) Relative Importance of similar Organs. — Be.
Sides the relative values of different organs, established.
in this table, we may estimate the relative value which
two organs of the same kind bear to each other, in dif-
ferent species. This will depend upon the greater or less
Perfection which they exhibit in their respective modes
of development ; also, upon their position, connection
With other organs, and numerous other particulars which
t is impossible to define with any degree of precision.

PEI ET OO RES ™
eye Ne ee

142 DESCRIPTIVE BOTANY. PART I.

and which practice alone can enable the systematic
botanist duly to appreciate.

(135.) Natural Orders.—As we make no pretensions
in this volume to enter upon the details of systematic
botany, we do not consider it advisable to present the
reader with a bare enumeration of the characters of thé
natural orders which have been hitherto established in
the most recent works. We shall content ourselves with
explaining the connection which subsists, between the
principal groups under which Jussieu arranged the

- natural orders, so far as they had been established in

his time, with the principal groups in the recent system
of De Candolle, under which this eminent botanist has
arranged the natural orders as they are at present un-
derstood. Jussieu threw the natural orders or families
with which he was acquainted, into fifteen groups,
which he termed classes, and these he further com-
bined into six principal groups or divisions ; of which
four belonged to Dicotyledones, and one each to Mono-
cotyledones and Acotyledones. De Candolle has also
four groups for the Dicotyledones and one for the Mo-
nocotyledones, but somewhat differently arranged ; and
he has split up the Acotylodones into two parts, one of
which (although cryptogamic like the other) he classes
with the Monocotyledones, and retains the other only
as Acotyledones. He further arranges the whole of
vegetation under two principal heads, according as plants
possess, or are entirely without, any portion of a vascular
structure.

SECT. 11. TAXONOMY AND PHYTOGRAPHY. 143

Comparative View of the Systems of De Candolle and
Jussieu.

i f |
oA EPA | Subordinate Gr |
Py imary Divisions of De} (Classes Of. Bay 4 Primary Divisions
: Candolle. | common to both. of Jussieu.

net SE E

* Vasculares sew Cotyle-
donee.

A. Dicotyledonez seu C. Dicotyledones.
Exogene.

L Thalamiflore. . Hypopetale

. Peripetale

. Epipetale
. Epicorolle corisan-
Il. Calyciflore. there

. Epicorolle = II. Monopetale.

TII. Polypetale.

: there
. Pericorolle
IMI. Corolliffore. \ 8. Hypocorolle
. Hypostaminee
i .- Peristamineæ
Epistamineæ
. Diclines
Angiospermæ
Gymnosperme

I. Apetale.

IV. Monochlamydex i
! IV. Diclines.

B. Monocotyledoneæ sew B. Monocotyledones,

Endogenæ
. Monoepigynæ

V. Phanerogamæ . Monoperigynæ
~ Monohypogynæ
A. Acotyledones.

yI. Cryptogamæ
| Gellniares seu Aco-

yledonez

vu. Cellulares

. Acotyledones

We have explained in art. 102. the meaning of the terms
Which designate the principal gíoups of De Candolle in
the first column of this table; and we shall now explain
those which have been proposed for the classes of Jussieu,
in the second column, as their etymology may assist the
reader in recollecting them. “They are combinations
of words expressive of the three modes of floral arrange-
Ment described in art. 101., applied respectively (in the
Dicotyledones) to the “petals,” when these organs do
Rot cohere together ; to the “ corolle,” when they are mo-
Nopetalous; and to the “stamens,” when the perianth is
Single. Thus, Epicorolle indicates, that a monopetalous
Corolla is epigynous in the 10th and 11th classes; which
are further distinguished from each other by the anther

144 DESCRIPTIVE BOTANY. PART Í.

being united together (cv) in the 10th, and separate
(xoeis) in the 11th. The term Diclines indicates the
flowers of the 15th class to be unisexual ; and in the
two subdivisions of this class, the seeds are contained in
a pericarp or distinct vessel (ayyss) in the one, and are
without it, or naked (yuyves), in the other. The deri-
vation of the classes of the Monocotyledones is evident.
(136.) Artificial Arrangements.—Anartificial arrange-
ment proceeds upon the fact, that certain organs, in nearly
all the species included under the same genus, have a
great degree of constancy as to their number, relative
size, position, and other characters ; and these organs
are selected as the basis of the systematic arrangement.
Thus, for example, every species of the genus Ranun-
culus has more than twenty stamens, and these organs
are similarly circumstanced with respect to the other
floral whorls. The species of the genus Papaver, have
their stamens arranged like those of the last-mentioned `
genus, and they are also numerous. These two genera
belong to different natural orders, but they and many
others are thrown together into the same artificial class,
characterised by the species having their stamens nume-
rous, and not attached to the calyx, the flowers also
containing both stamens and pistils.
The natural groups, then, which we term genera, and
which are the lowest in the rank of subordination, are
not subdivided to suit the purposes of an artificial arrange-
ment; but it is the higher groups only which are so.
There are certain cases, however, where it is advisable to
break through this rule, and to retain under the same
artificial class, several genera of a natural order, which do
not agree with the rule laid down for fixing their posi-
tion in the system. In other words, it would be too great
a violation of the natural: group to which such genera
belong, to separate them from it. Thus, for example,
the greater number of those genera of the natural order
Leguminose which have papilionaceous flowers, forming
the tribe Papilionacee, have their filaments united round
the pistil, so thatnine are blended together, and one stands

SECT. 11. TAXONOMY AND PHYTOGRAPHY. 145

by itself (see art. 97.) ; and an artificial class (Diadel-
Phia) has been constructed to admit all flowers which

ave their stamens united into two bundles. Now, there
are a few genera of the Papilionaceez, where the union

Of the ten filaments is complete; and these therefore

Strictly belong to another artificial class (Monadelphia),
-Raracterised by this circumstance. But in this case
the natural affinity is so striking, that the artificial
arrangement is broken through, and they are all classed
together. We shall presently explain how the diffi-
culty of such a false position is, to a certain extent,
obviated. (Art. 138. bis.)

An artificial system which should disregard the con-
Struction of genera, and group species according to
he principles of that system, would be the most per-
fect; but this would be descending to a degree of
Precision unnecessary for obtaining the sole purpose for
Which an artificial system should be employed, viz.
the detection of the name of a plant; and the devices
adopted for referring the anomalous species to their
Proper genus, and the anomalous genera to their pro-
Per class, are sufficient to counteract the smaller in-
Convenience of establishing a system at variance with
these few cases.

(137.) Linnean System. — The most celebrated of
the several artificial systems which have been proposed,
'S that which Linneus established, from considerations
duced from the number and disposition of the sta-
Mens and pistils ; these organs maintaining a greater
eneral resemblance in all the species of the same
Senus, and through many genera of the same natural
Stoup, than any others. They are at the same time
“ufficiently modified in different groups, to allow of
these being thrown into several orders and classes, cha-
řacterised by some definite and striking peculiarity.
his system has been styled the sexual system. In
18 arrangement, Linneus established twenty-four
“lasses; the last of which embraces the whole of
the natural class of Acotyledones, or flowerless plants,

L

pn

ma saa a a Aiia

Se

an

146 DESCRIPTIVE BOTANY, PART Ie

The Dicotyledones and Monocotyledones are distributed
unequally throughout the other twenty-three classes 5
some of these consisting entirely, or chiefly, of the
one, and others of the other, whilst several of them
are made up from both of these natural classes. The
fundamental principles upon which his arrangement
proceeds, are of the simplest possible description, but
in the practical application of them, the beginner
will unfortunately meet with several anomalies, and
without repeated caution he is sure to be misled-
The following table exhibits the names of the classes
and orders of the Linnean system; and we shall
explain their etymology, as this is intended to con-
vey the leading characteristic upon which each de-
pends.

Tabular View of the Classes and Orders of the
Linnean System.

Classes. Orders.

Monandria. povos. } Monogynia.
Diandria. dts. Digynia.
Triandria. TpELS. Trigynia.
Tetrandria. retpas. | Tetragynia.
Pentandria. mevre. | Pentagynia.
. Hexandria. et. Hexagynia.
. Heptandria, énta. >Heptagynia.
. Octandria. oxrw. | Octogynia.
. Enneandria. evvea, | Enneagynia.
. Decandria. deka. Decagynia.
. Dodecandria. Swdexa. | Dodecagynia.
. Icosandria. eost. | Polygynia.
. Polyandria. modus. J

CHNIAAR LYS

. Didynamia. ienesa
ngiospermia,

4 Siliculosa.

. Tetradynamia. Siliquosa.

16. Monadelpbia. }

Triandria, &c. as in

17. Diadelphia. Classes

18. Polyadelphia.

TAXONOMY AND PHYTOGRAPHY. 147

Polygamia equalis.
superflua.
frustranea.
necessaria. _
segregata.

Monogamia.

6 Gynandria. Monandria, &c. as in the
à Moneecia. à Classes.

Diæœcia. ; k
. Polygamia. Monecia, Diœcia, Triœcia.
. Cryptogamia. Filices, Musci, &c.

. Syngenesia.

(138.) Linnean Classes. — The first eleven classes
are. characterised by the “number” merely, of the
Stamens, which the species (or nearly all of them) in
the respective genera contain ; and their names are a
Compound of.two Greek words, one of which signifies

at number, and the other is ayo (a man). The
Number eleven is not employed, as no flowers are found

possess that number of stamens. In the first ten
Classes, the species are pretty constant in the num-

t of stamens by which their class is designated ;

Ut in the eleventh class the number is not so certainly

üxed, There are, however, very few species included
it; and when the genera to which they belong have
been once pointed out, the student is not afterwards
Kely to refer them to
Nother class..

Although the name of
€ twelfth class would
dicate that the species
p erred to it contained 4

Yenty stamens, while
E- of the thirteenth

ntained more than that
number, the real dis-

“ction between these l
WO classes depends more upon the position, than
Pon the number of these organs. In both classes
a are ics — that is to say, are above a
n number ; but in Icosandria they adhere to the

L 2

- 148 DESCRIPTIVE BOTANY, PART E

calyx (fig. 144.), or are perigynous (see art. 101.) ;
whilst in Polyandria they are free from the calyx, oF
are hypogynous.

The fourteenth and fifteenth classes are characterised
by a twofold consideration, — the number and relative
lengths of the stamens, In Didynamia there arè
four, and in Tetradynamia there are six; but the
former is distinguished from Tetrandria, by two of the
stamens being always shorter than the other two ; and
the latter from Hexandria by two being shorter that
the other four. This is expressed by the word dway%s
(power), signifying that some of the stamens have a?
ascendancy over others, and this is combined with the
word which expresses their number. These circum-
stances are not always readily recognised by begin- |
ners; and they should take into consideration a few
other particulars which may enable them to correct
their judgment. Thus, in Didynamia, the four stamens
are not symmetrically disposed round the axis, but are
thrown together on one side of the flower, which is
always monopetalous, and never strictly regular. The
lipped flowers (Labiate, art. 95. and fig. 93.) form: 4
large portion of this class, except-

‘ing a few of them, as the genus
Salvia, in which two stamens are
abortive, and which is there-
fore placed under Diandria. T he
class ' Tetrandria is readily re-

~ eognisable, from the circumstance
of all its species having six sta-
mens, but only four petals, and
four sepals. It agrees precisely
with the natural order Crucifere,

-so named from the petals being dis-

posed in such a manner as to re-

present a cross (fig. 145. a). (b)
shows the relative position of the floral organs.

The names of the three next classes indicate that tH?
filaments are united into bundles, expressed by the

|

SECT. 11. TAXONOMY AND PHYTOGRAPHY. 149

Word œdeàgog (a brother); these bundles or brother-
hoods of stamens, being either one, two, or more than
two respectiyely. Where there is only one (in Mona-
delphia), the filaments must necessarily form a cylin-
drical. tube round the pistil (fig. 97. a). The greater
Portion of Diadelphia is composed of a large section of
4 natural tribe, the Papilionacee, belonging to the natural
der Leguminose. (See art. 136.) A small section of
the Papilionacee, in which the filaments are perfectly
free from any adhesion, is classed under Decandria,
in the same way as a few of the Labiate are placed
Under Diandria. The remainder of this artificial class
is almost entirely composed of the few genera which

long to the Fumariacee and the Polygalee; the
former having six, and the latter eight stamens, united
to two bundles.

The class Polyadelphia is exceedingly small, (the genus

Ypericum forming its most prominent feature,) and
the stamens are here placed in little tufts or bundles
tound the pistil. .

The nineteenth class is also strictly natural, like the
fteenth, coinciding with the natural order Composite,
80 named from the inflorescence being composed of a
dense mass of small flowers, or florets (as they are
ere termed), closely invested by an involucrum. The
Whole head, in popular language is called a single
flower. (See fig. 87.) The name of the artificial class
Signifies that the anthers are united, ovy ( together, ) and
Yevecis (generation).

Although the several parts of the florets are very
Minute, and the adhesion of the anthers into a tube
round the style not readily recognisable, yet there is
Very little difficulty in referring any species of this —
lass to its right position. There are a few flowers in
Some other natural orders, arranged in heads resem-
ling those of the Composite, but their anthers are
ree,

The twentieth class is named from yun (a woman),
and awp (a man) ; the centre of the flower not

; L 3

150 DESCRIPTIVE. BOTANY. PART I

having the pistils and stamens separate in distinct
whorls, but grafted together into one column, on the
summit of which the anthers are seated near the
stigma. This class is principally made up of the
natural order Orchidee, which includes all those sin-
gular flowers commonly known by the name of orchises
and air-plants.

The next two classes are characterised by having
unisexual flowers, expressed by the word omas (a house) ;
intimating that, in Moncecia, flowers of both sexes
are found on the same plant; whilst in Dicecia the
stameniferous flowers are on one plant, and the pistili-
ferous on another. i

In Polygamia, yauoç (marriage), we have three
kinds of flowers, which may all, or some only, be
placed on the same plant. In these cases, it should
seem that the flower in its most perfect form contains
both stamens and pistils; and that in those flowers,
where either of these organs is wanting, it is from abor-
tion, and not that any difference of construction pre-
cludes its development.

And lastly, Cryptogamia, from putes (hidden),
and yayuos (marriage), there being no flowers apparent
from whence seeds are produced.

(139.) Linnean Orders.— The orders of the se-
veral classes depend upon circumstances, connected either
with the stamens or pistils.

In the thirteen first classes, the orders are fixed en-
tirely by the number of the pistils, and this is expressed
by the word yy (a woman) in composition with the
Greek words signifying the number ptesent. In some
compound pistils, however, this number is calculated
from the number of the styles or stigmas rising from
the top of the ovarium, when those organs happen to be
remarkably distinct.

In class fourteen, there are two orders, characterised
by the manner in which the ovaria are developed into
seed-vessels. One (Angiospermia) is named from ayy%
(a vessel) and omepua (a seed), and in this case the

SECT. 11. TAXONOMY AND PHYTOGRAPHY. 151

pericarp is composed of two carpels blended together
into a single two-celled capsule, containing many seeds
attached to a central placenta. The other order (Gym-
Nospermia) was so named from a mistaken opinion
that the seeds were destitute of any pericarp, or naked
(yvuvec). In this order the pistil is composed of four
Carpels, each containing a single seed, and agglutinated
together into a compound ovarium with one style.
As the fruit ripens, the carpels separate, and ulti-
mately become four nuts, seated at the bottom of
the calyx. The two orders are, therefore, readily dis-
tinguished, by the former containing only one seed-
vessel with many seeds, and the latter four seed-vessels
which resemble four naked seeds.

The fourteenth class also contains only two orders,
which are characterised by the comparative lengths of
the seed-vessels. They are composed of two carpels
United by their edges, and are divided into two cells by a
transverse membranous partition (see art. 109. fig. 123.).
When the length of the seed-vessel exceeds its breadth

three or four times, it is termed a siliqua, and the

order to which it belongs is named “< Siliquosa.” When
the length and breadth of the seed-vessel are nearly the
same, the order is named “ Siliculosa.” ‘These dis.
tinctions are apparent in the flower, from the earliest
stages of the ovarium, and long before it becomes a true
Seed.vessel.

In the sixteenth, seventeenth, and eighteenth classes,

the orders depend upon the number of the stamens ;
and in this respect they resemble the thirteen first
Classes themselves.

The nineteenth class was originally divided into six
orders; in five of which the flowers were aggregated
into heads, and thence distinguished under the name
of “Polygamia ;” whilst the sixth contained those simple
flowers, whose anthers, as in the violets (Viole), were
More or less united. But this last order has been abolished
by the universal consent of botanists; and the species
which it contained, are now referred to their position in

L4

il E a a aaa iania ei ih sn n
i A as a a a ee

a Is a TSS ae

a a a

152 DESCRIPTIVE BOTANY. PART b

the system, without regard to the syngenesious cha-
racter of their anthers. Of the five orders, then, which
it now possesses, the first, “ qualis,” is so named from
all the florets being “ alike ;” each containing both
stamens and a pistil (fig. 146 a). In “ Superflua,” the
outer florets have a pistil Jagi :

but no stamens; whilst Ų è < c
the florets in the centre Í

contain both (b). In this

case, the outer florets, as in
the daisy, are “ligulate,”
or “ strap-shaped,” and constitute what is termed the
“ray ;” whilst the inner florets are all “ tubular,” or
“ floscular,” and form the “disk” of the capitulum.
The inner florets being the most perfect, and sufficient
to secure the production of seed, the outer florets ap-
pear as it were ‘‘ superfluous,” from whence the name
has been given totheorder. In “ Necessaria,” (c) the outer
florets contain pistils only ; and the inner, stamens only ;
and consequently both are ‘ necessary ” for perfecting
the seed. In “‘Frustranea,” (d) the central florets are per-
fect, or contain both stamens and a pistil ; whilst those
in the ray contain neither, and hence appear to be
formed, as it were, in “ vain” (frustra), as regards the
pertecting of seed. The corolla of the latter florets
is generally very highly developed, and assumes 2
handsome appearance, as in the genus “ Centaurea ”
(fig-87.). In “Segregata” (1), each floret is surrounded
with a distinct and well-defined involucrum of its own:
which “ separates” it completely from the other florets
in the same capitulum. In the diagram ( fig. 146.), these
different arrangements of the pistils and stamens are
represented, and the capital letters further refer to the
kind of florets of which the capitula are composed, viz..
H (hermaphrodite), M (male), F (female), N (neuter),
I (involucrate). i
In the two next classes, Moncecia and Dicecia, the
orders depend upon the number and arrangement of
the stamens, precisely. as in the several classes al-

SECT. 11, TAXONOMY AND PHYTOGRAPHY. 153

Teady enumerated ; whilst in Polygamia the orders
are characterised by the flowers being moneecious,
dicecious, or tricecious.

There is no connection between the nomenclature
of the orders of the class Cryptogamia, and the charac-
ters of the plants they contain ; but some of them are
familiar to most persons, as the ferns (Filices), mosses
(Musci), seaweeds (Alge), mushrooms (Fungi).

(138. bis?) Application of the Linnean System.—Not-
Withstanding the apparent great simplicity of this
System, there are many anomalous cases to which it
cannot be directly applied. In order to meet these,
Linneus made use of an expedient by which such
Species as do not strictly belong to the class and
order under which their genus is arranged, may still be
ascertained. Their names are placed in Italics at the end
of the order to which they really belong, and in which
they would naturally be sought for ; so that the student,
who has not been able to detect them among the genera
there enumerated, may refer to the index, and search
among these anomalous cases. Thus, for example, the
genus Gentiana is classed under Pentandria Digynia ;
but Gentiana campestris has generally only four sta-
mens, and would be sought for under Tetrandria Di-
Synia. Not being found among the genera there
enumerated, it must be one of the few anomalous
Species, whose names are mentioned ; and these must

all referred to, before it can be determined which
of them it may be. The very unequal distribution
of the classes is another inconvenience in this system.
The great bulk. of plants are included in about one

alf of them, whilst the others contain comparatively
few, If, however, attention be paid to the general
form of the flowers, the relationship which usually

Subsists between the divisions of the perianth and the

number of the stamens, in such as have a regular
Corolla, and a few other particulars, the knowledge of
which a little practice alone can bestow, these diffi-
culties are soon greatly diminished, and many large na-

NE e n

err a

154 DESCRIFTIVE BOTANY. PART I.

tural groups will be instantly referred to their proper
class and order, without the necessity of searching
for the characters upon which their arrangement de-
pends. It will be soon seen that Triandria, Hex-
andria, and Gynandria contain the great bulk of
the Monocotyledones, and that there are very few
of this natural class among the other artificial classes.
This circumstance is connected with the ternary ar-
rangement of the subordinate parts of the floral
whorls, to which we have alluded (art. 120.). On the
other hand, the great bulk of Dicotyledons are included
in those classes where some trace or other of a quinary
disposition is observable. Thus, Pentandria, Decan-
dria, Icosandria, and Polyandria are large classes an-
swering to this description; and Syngenesia, which
is the largest of any, has always five stamens, and the
corolle generally exhibit a tendency to a subdivision
into five separate petals, indicated by five teeth at the
end of the florets. Didynamia is eminently irregular ;
but even here, the normal character of the species seems
to repose upon a quinary arrangement, which is some-
times manifested by a monstrous development of the
suppressed organs, as in the varieties termed “ Peloria,”
of the genera Antirrhinum and Linaria (see art. 114.)
Tetradynamia is not unsymmetrical, but equally irregu-
lar, as regards the more usual characteristic of a dico-
tyledonous flower,

PART II.

PHYSIOLOGICAL BOTANY.

CHAPTER I.

VITAL PROPERTIES AND STIMULANTS.

VEGETABLE LIFE (139,).— PROPERTIES OF TissuES (141.).—
ENDOSMOSE (144.).— VITAL PROPERTIES (145.). — STIMU-
LANTS TO VEGETATION (152. ).

(139. bis.) Vegetable Life — Hırnerrto we have been
Occupied with the forms only which the various organs
of plants assume, and the manner in which they may

considered to be mutually related. We have been
examining merely some of the details of that exquisite
Mechanism by means of which the vital principle is
enabled to act and may be acted upon; and thus
Produce all the varied and complicated results which
the phenomena of vegetation present. In this second
Part of our treatise, we propose to examine the vegetable
Machinery in a state of action, and to search for
indications. of those laws by which vegetable life
enables the organic bodies to which it is united to
Stow and multiply. It would be an unnecessary
Waste of words to offer any proof that plants are
Organised bodies endowed with life. No one is so
ittle observant, as to be ignorant of the more ge-
Neral phenomena of vegetation, that plants originate
from seed, that they are gradually developed, and,

156 PHYSIOLOGICAL BOTANY. PART Il.

after having attained perfection, that they as gra-
dually decay, die, and are decomposed. In fact the
general phenomena of life and death, are scarcely less
striking in the vegetable than in the animal king-
dom; and probably the vital principle, considered
apart from sensibility, is something of the same kind,
if not the very same thing, both in animals and vege-
tables. This similarity or unity in essence must lead
us to expect, what experience has shown to be the fact,
that a considerable analogy exists between the functions
of animal and vegetable life. Although every argu-
ment which may be derived from this analogy, cannot
- be too severely scrutinised before we admit the particular
conclusion which it may seem to establish, yet we may
confidently reckon upon the certainty of its existence, as
one of the best guides which we now possess, towards
obtaining a more perfect elucidation of the general laws
of physiology.

(140.) Vital Stimulants. — Life, though at the best
of only temporary duration in organised bodies, cannot
be maintained in them at all, without the continued
application of certain stimulants. All require peculiar
kinds of food, according to their respective natures; 4
sufficiency of air, of moisture, of heat, &c. If entirely
deprived of these stimulants, they soon die ; and even
when they are only partially subjected to their influence,
in a less proportion than is requisite for a free exercise
of their functions, they languish and become sickly.
But, besides the various salutary influences to which
all living bodies must be submitted, in. order to secure
for them a due and healthy performance of their
several functions, there are others to which they
may be subjected, which are decidedly noxious under
all conditions, and which must ultimately prove fatal
to them, if they had not the power of escaping from
their presence, or at least of modifying their effects»
In proportion as a living being possesses a greater
power. of choice, either in profiting by those circum-

Hi

CHAP. 1. VITAL PROPERTIES AND STIMULANTS. 157

Stances which are favourable, or in avoiding those
~ which are hurtful to its existence, we may con-
sider it to be more elevated in the scale of nature, and
further removed from the condition of mere brute
Matter. Most animals, by the faculty which they pos-
sess of locomotion, have a great advantage in this
respect over plants ; and even those among the very
lowest tribes of animals which are permanently fixed to
One spot during the whole period of their existence, still
possess a certain power of selecting their food, and re-
jecting what is noxious to them, which vegetables have
hot. The consequence is, that the continued influ-
ence of external agents, is found to be far greater
in modifying the characters of plants than of animals.
As a sort of compensation however, the vital prin-
ciple in’ plants is so much less energetic than in’
animals, that they are not so readily affected as these
latter, under any merely casual or temporary altera-
tion in the external conditions under which they may
be placed.

(141.) Properties of Tissue. — Before we describe
the functions performed by the vegetable tissues, it will
be necessary to remark upon a few of the properties
which these tissues themselves possess. In the com-
plex phenomena which vegetation furnishes. it is very
difficult to separate so much of each result as may be
strictly ascribed to the operation of the vital principle,
from such as may be due to the action of purely physical
Causes, the chemical effects of affinity, and the mere
mechanical properties of the tissue. The most obvious
means which we can employ, for ascertaining the precise
properties of the tissue, is to perform experiments upon
it in the dead vegetable, and as nearly as possible
before any chemical change may have taken place in it.
It will not be necessary for us here to notice all the
Properties which the vegetable tissues possess in coms
Mon with other substances; but there are two on
Which we shall make a few remarks, as the pheno-
mena to which they give rise might in some cases

158 PHYSIOLOGICAL BOTANY. FART It.

be attributed to the operation of the vital force: these
are, the elastic and hygroscopic powers of some vege-
table tissues.

(142.) Elasticity of Tissue. — This property is
eminently conspicuous when the tissue is distended with
fluid; and, unless its effects be duly appreciated, we
might be misled, and inclined to consider certain phe-
nomena as the direct result of an irritability residing in
the plant, whilst, in fact, they may be easily accounted
for by the action of elasticity alone. Thus, in the flowers
of the common nettle (fig. 147.a), the filaments are at

When the flower is completely expanded, the filaments
have become highly elastic; but are still retained in
their original curved position by the mutual pressure
which they exert upon each other. If this state of
equilibrium be disturbed, either by slightly displacing
the anthers with the point of a pin, or by the further
progress made in vegetation, the stamens are suddenly
thrown back by the elasticity of their filaments, the
anthers burst and the pollen is scattered by the shock
(b). This appearance is very like that of some other
sudden motions, which, as we shall hereafter show,
must be referred to the direct influence of some stimulus
upon the vital principle. Many seed-vessels when
fully ripe, burst as it were spontaneously, by the in-
creased elasticity of their tissue, and the seeds are often
scattered to a considerable distance by this means; but
although all the organs of plants when replete with
fluid, are generally elastic, a remarkable exception o€-
curs in the pedicels of Dracocephalum moldavicum.

CHAP, I, VITAL.PROPERTIES AND STIMULANTS. 159

When these are turned in any particular direction, they
tetain the position in which they are placed, without
any effort to return again to that in which they were
Previously disposed.

(143.) Hygroscopicity of Tisswe.—The hygroscopic
Properties of some tissues are very great, and are the
cause of certain motions, which might be mistaken for
the direct effects produced by the vital force. If the
awn or bristle of the wild oat be moistened, it imme-
diately untwists ; the teeth of mosses suddenly collapse
When moistened by the breath, and readily expand upon
drying again. In estimating the hygroscopic properties
of the tissue, we must distinguish between the action of
the whole mass, and the property of the membrane
Which forms the separate vesicles and tubes. of which
the tissue is composed. It seems easy to account for
the hygroscopicity of the mass of the tissue, when we
temember that it is penetrated in all directions by inter-
cellular passages, and thus resembles a sponge, which
absorbs moisture by the common properties of capillary
attraction. This action is found to be much more
Powerful in proportion as the vegetable tissue is but
slightly charged with foreign matter. Some plants, as
the mosses, readily imbibe water, however long they
May have been dried ; and reassume an appearance of
freshness nearly equal to that which they possessed in a
living state; but, in these cases, the effect is most pro-
bably due to the hygroscopic action of the elementary
Membrane composing the vesicles, and not to the capil-
arity of the tissue itself. The immediate result of any

Ygroscopic action upon a portion of the tissue is to
enlarge it; and consequently, where two portions
are in contact, one of which is more hygroscopic than
the other, there exists @ tendency to separation.

hen, however, they do not separate, the portion
Which is the least hygroscopic, becoming less dis-
tended than the other, necessarily produces an incurv-
ation of the mass upon that side on which it is placed.

(144.) Endosmose.— Connected with the. hygro-

160 PHYSIOLOGICAL BOTANY. |. PART IL

scopicity of the vegetable membrane, we may here men-
tion a property of all membrane, which has probably a
considerable influence in the economy both of animal
and vegetable life. When a membrane is viewed under
the highest powers of the microscope, it appears to
possess a perfectly homogeneous texture, without pores
of any kind; and yet water, milk, and other fluids,
placed under certain circumstances, are capable of pass-
ing through it with considerable facility. The con-
ditions required for producing this effect are these : —
Any two fluids which exert a mutual affinity towards
each other, being placed on opposite sides of a mem-
brane, their immediate intermixture will commence,
each ‘of them passing through the substance of the
‘membrane. If, for instance, a little treacle be enclosed
in a piece of bladder, and this immersed in water, 4
portion of the treacle will soon be found to have exuded,
whilst a still larger quantity of water will have pene-
trated into the bladder; and this’ action will continue
until the fluids have acquired: the same density. The,
remarkable circumstance attending this phenomenon, is
the fact of the lighter fluid having penetrated the mem-
brane with greater velocity
than the denser fluid. In
consequence of this, the
bladder becomes distended.
By a simple contrivance,
styled an endosmometer,
we may measure the degree
of force or velocity by
~ which the current of water
exceeds that of the current
of the denser fluid. In
fig. 148 a is a glass
funnel with ‘the mouth
downwards, and covered
with a piece of bladder.
The other end of this funnel is fornished with a tube
twice bent, the stems of which are vertical; treacle

rarer ie

VITAL PROPERTIES AND STIMULANTS. 161

's placed in the body of the funnel,. and the mouth
immersed in water ; mercury is poured into the open
extremity of the tube, and ascends in the other stem
Until it meets the fluid in the funnel. So soon as the
endosmose commences, the rising fluid pushes the mer-
Cury before it ; and the amount of the force by which
this is effected, is ascertained by pouring in more mer-
tury until the further rise of the fluid is checked. The
eight of the column of mercury affords an estimate of
the pressure of the ascending fluid, which is of course
due to the force of the endosmose. In this way it may
shown, that a syrup three times the density of water
Produces an endosmose capable of sustaining a pressure
equal to the weight of three atmospheres.
(145.) Vital Properties. — After abstracting all that
ĉan reasonably be allowed to the physical properties of
the tissue, and to the chemical or other effects which
Operate in modifying every vital phenomenon, whatever
Still remains unaccounted for in the functions of ve-
Setation, must be ascribed to the direct operation of the ©
Vital force itself. What life is, whether it is a simple
Quality, the effects of which are variously modified ac-
cording to the nature of the tissue in which it resides,
and by means of which it acts, or whether it possesses
Severa] distinct properties, which are severally capable of
acting only upon and through particular tissues, is quite
Unknown to us. For the sake of convenience, and pro-
“sionally merely, the physiologist considers animal life.
to be compounded of certain properties, and that its
Various functions are performed by these properties,
acting through the intervention of different kinds of
- tissue, There are three of these properties attached to
‘himal life, which may be styled respectively its ex.
“tability, irritability, and sensibility.
(146.) Excitability. —The excitability of animal life,
Which is also termed the “ vis formativa,” is manifested
rough the cellular tissue, by which the function of
Nutrition is carried on ; it is that property by which
1S tissue takes cognizance of the action of external
M

SRE

162 PHYSIOLOGICAL BOTANY. ` PART Ib

influences upon it, and by which it resists those mechan-
ical and chemical efforts which otherwise would soon
succeed in decomposing its substance. The existence
of such a property is equally evident in the vegetable as
in the animal kingdom. No one will deny that ve-
getables live; and we may perhaps believe, that the
general law of life by which they resist destruction, is
the very same in kind, however different it may be in
degree, as that by which animals are also maintained in
a state of existence, In animals indeed, the intensity
with which this vital property acts is greater than in
vegetables ; but, as a sort of compensation, we find that
vegetables are much more tenacious of life than animals.

- A plant may be mutilated to a very great extent, and

its separate parts will still live, and are frequently ca-
pable of becoming distinct individuals ; and, although
there are certain creatures possessing a compound struc-
ture, among the lowest tribes of, animals, yet even in
them this property does not reside in so eminent 4
degree as in certain vegetables, every elementary orga?
of which appears capable of ‘existing in a detached,
form, and of reproducing an individual, similar to the

original of which it formed a trifling and subordinate

part. This therefore, the “ excitability” of life as it
has been termed, is a property which we may consider
common to both kingdoms of organised nature.
(147.) Tenacity of Life. — A plant may lose
nearly half its weight by drying, and yet be restored
by care. De Candolle has recorded an instance of 4
Sempervivum cespitosum, which had been placed in 2
herbarium for eighteen months, and from which he
afterwards detached a living bud and reared a plant
But the tenacity of vegetable life is best exhibited
in the property which seeds possess, of retaining
their powers of germination after having been expose
to very considerable extremes of heat and cold. Somé
also, which have partially gerininated, may be again
dried and kept for months, without losing the power Ô
germinating afresh, although they are sensibly weaken

CHAP, I. VITAL PROPERTIES AND STIMULANTS. — 163

by such treatment. The revival of plants among the
*ryptogamic tribes, after a very long suspension of the
Vital functions, is well authenticated.
(148.) Jrritabilityx— Besides the excitability of ve-
Setable life, there are certain striking phenomena ex-
ibited by some plants, which seem to indicate the
Presence of a property analogous to that of animal
" irritability.” A closer examination, however, of the
circumstances under which this “ vegetable irritability”
Manifests itself, rather inclines us to believe with De Can-
Olle, until sufficient proof be brought to show the con-
rary, that these are only extreme cases of the operation
of the property of excitability. The sudden inclination
Of the stamens in the berberry towards the pistil, when
the filaments are touched near the base on the inside,
the well-known phenomena exhibited by the sensitive-
Plant, and several other singular movements of particular
rgans in some other plants, are the phenomena which
ave led to the conclusion, that séme few vegetables are
endowed with an irritability analogous to that which
€xists in all animals. But on the other hand it has
en observed, that in animals this property is confined
the muscular fibre, whilst in vegetables there does
Not appear to be any particular tissue to which it is
peculiarly restricted. In animals, again, the effects of
Writability are apparent during the whole course of their
lfe, and are not destroyed by repetition of the experi-
Ments by which they are elicited ; whereas this property
fan be traced only under peculiar conditions of vege-
table existence, and then only in certain organs of a
Very few species.. Several of these instances, also, are
only special modifications of certain actions, which are
“onstantly produced by the operation of more general
Causes, For instance, the folding of the leaflets of the
“ensitive-plant, which takes place when we touch them,
'S the very same sort of effect which we daily witness
M a vast number of other plants, where it is elicited
Y the agency of light, only in a more gradual and
M 2

164 PHYSIOLOGICAL BOTANY. PART Ii

imperceptible manner. In these latter cases, the effect
is denominated the sleep of plants, and may be more
especially witnessed in the leguminose tribes, whose
leaves remain folded during a certain portion of the
day, and assume an appearance of languor and inaction
singularly analogous to the periodical state of repose
exhibited in the animal kingdom. In cases therefore,
where similar effects are brought about by the action of
certain stimuli, in a yet more violent or rapid succession,
we may imagine that they are nevertheless: the results
of the same vital property, which is here exhibited
under some peculiar degree of excitement.

(149.) Examples of Vegetable Irritability. — AS
some of the phenomena exhibited by vegetable irrita-
bility are very striking, we shall here insert a brie
notice of a few of the most interesting examples.

(1.) Sensitive-Plants. — There are several species
of sensitive-plants, which
possess the property of
moving their leaves
when they are touched,
or otherwise stimulated.

The most common is an
annual (Mimosa pudica),
with compound digitate
leaves, with four pinnules
( fig-149.);—each partial
petiole being furnished
with numerous pairs of
leaflets, expanded hori-
zontally as at (a). One
of the most striking
means of eliciting the phenomenon in question, is by .
scorching a single leaflet in a candle, or by concede
trating the sun’s rays upon it with a lens. Ths
leaflet. will immediately move, together with the one
opposite to it, both bringing their upper surfaces
into contact, and at the same time inclining forwards:

NS

sa

m
7]
3

CHAP, fi. VITAL PROPERTIES AND STIMULANTS. 165

or towards the extremity of the partial petiole on
Which they are seated (b). Other pairs of leaflets,
Nearest to the one first stimulated, will then close in
Succession in a similar manner ; and at length the
Partial petioles themselves fold together, by inclining
Upwards and forwards. Last of all, the influence is
transmitted to the common petiole, which bends down-
Wards with its extremity towards the ground (c); in
a direction the reverse of those which were taken in
the former cases. The effect is next continued to the
Other leaves nearest to the one first stimulated, and
they fold their leaflets and depress their petioles in
a similar manner. When the plant is shaken, all the
eaflets close simultaneously, and the petioles droop
together ; but if the agitation be long continued, the
Plant will at length become accustomed to the shock,
and after a lapse of some time, the leaflets expand
again, The mechanism by which these movements
ae produced resides in the thickened or swollen joints,
Seated at the bottom of each leaflet and petiole; for
if the upper part of these swellings are cut away,’
the leaf remains erect; but if the lower part is re-
moved it continues depresséd. Hence it appears that
the elevation and dépression of the leaf, is owing to
the elasticity of the tissue of which the swollen joint is
Composed ; and that the stimulus eniployed to produce
Motion, tends to weaken the upper parts of these joints
in the case of the leaflets and partial petioles, but the
Ower part of those belonging to the main petioles —.
the contrary sides continuing elastic, as before. But
‘how the effect is produced, and what may be the law
Which regulates its action, is not known. The causes
are active from the earliest stages of the plant’s exist-
Ence ; the cotyledons themselves exhibiting the property
50 soon as they have expanded. The transmission of
the stimulus from one leaf to another along the stem
of the plant, has been shown by Dutrochet to take
Place through the intervention of the ducts contained in

166 PHYSIOLOGICAL BOTANY. PART Il-

the woody parts. For, if both the pith and the corti-
cal portions are removed, the effects are not stopped 5
whilst, if the woody parts are abstracted, which con”
tain the ducts, they cease entirely.

(2.) Desmodium gyrans.— The Desmodium gy-
rans is another plant of the same natural order as the
sensitive-plants, the motion of whose leaflets is still
more striking than in the latter ; for here the motion
is continued, without the necessity of applying any
external stimulus. The
leaves are composed of a f
pair of small leaflets, and }

a terminal one of larger

dimensions (fig. 150.).

The motion consists of a

succession of little jerks,

produced at intervals of

a few seconds. One of

the two lateral leaflets

is gradually elevated,

whilst the other is de-

pressed; and when both

have attained the maxi-

mum amount of movement in one direction, they begi®
to proceed in the opposite. At the same time the
erminal leaflet becomes inclined by similar inter-
rupted movements ; first on one side, and then on thé
other.

(3.) Common Berbery. — The flowers of the com-
mon Berbery contain six stamens, which surround 2
single pistil. When first expanded, the stamens até
inclined back upon the petals or away from the pistil-
If the filaments are touched near the base on the in-
side, they immediately start forward towards the pistil,
so that the anther is brought close to the stigma. In #

. little time they recover their original position, and may
be again stimulated as before. When the anther is
ripe, the violence of the motion causes it to burst, and
the pollen is projected on the stigma; and we may

CHAP, I, VITAL PROPERTIES AND STIMULANTS. 167

Unquestionably consider the mechanism by which this
effect is produced as designed for effecting this very
Purpose.

(4.) Dionea muscipula. — The leaves of the Dio-
Rea muscipula, or Venus’s Flytrap, consist of a flat-
tened petiole (fig. 151. a), at the extremity of which
are two fleshy lobes (b),

Which lie when ex-
Panded in the same
Plane with the petiole.
hese lobes are capable
of being elevated and
brought together in-
to a position perpen-
cular to the surface
of the petiole (e).
hey are furnished
With “cilie,”or bristles,
round their margins,
Which stand nearly at
Tight angles to their
Upper surface; and
there are besides these,
Upon the upper surface of each lobe i
Order, When a fly or other insect, crawling over the
Surface of the lobes, touches either of these latter
ristles, the irritability is excited, the lobes suddenly.
Close, and the insect is imprisoned like a rat in a com-
Mon gin. Some little time after the death of the
Msect, the lobes unfold and wait for another victim.
The only plausible conjecture which has been made,
to account for the use and intent of this singular con.
trivance, supposes this plant to require animal manure
or the healthy performance of some function or other ;
and in corroboration of this opinion, it has been stated
that Mr. Knight, after having secured some plants from
the possibility of providing themselves with flies, fur-
Nished some of them with scraped beef, and left the
test without any such provision. The result of the
m 4

+

1 68 PHYSIOLOGICAL BOTANY. PART Il-

experiment showed the more flourishing condition of
the provisioned specimens.

(5.) Sundews. — To the above list we may add one
more example, taken from a British genus of plants,
the Drosere or Sundews, of which three species are
natives of this country. The leaves of these plants are,
furnished on their upper surface with long hairs, tipped
with glandular and viscous globules. When an insect
settles upon them it is retained by the viscosity of the
gland, and in a little while the hairs exhibit a consider-
able degree of irritability, by curving inwards, and thus
holding it secure. `

(150.) Sensibility. — If we do not consider it clearly
established that plants are endowed with an irritability
strictly analogous to that which exists in animals, there
seems still less reason for supposing them to possess that
“ sensibility,” by which all animals, but more espe-
pecially the higher tribes, are so eminently characterized.
In them this property resides in their nervous system,
to which there appears to be nothing analogous among
vegetables. Even in the lower tribes of animals, their
hervous system is so little developed, that they may be
mutilated and otherwise injured, to an extent which
would speedily cause their death, if the intensity of
the pain which they felt were at all proportionable to
what animals of a higher grade experience under si-
milar treatment ; and yet they scarcely appear to suf-
fer any inconvenience. If there were no better ar-
gument to satisfy us that plants are utterly devoid of
sensibility, we have the general consent of mankind,
founded on their daily observation, in favour of the
non-existence of such a property. The only plausible
arguments in support of the probability of plants being
endowed with something analogous to a nervous system,
rest upon the effects produced on them by different
poisons. When corrosive poisons are imbibed into
their system, they destroy the tissue much in the same
way as in the animal frame ; but when narcotic poi-
sons are imbibed, although they kill the plants, they do

CHAP, I. VITAL PROPERTIES AND STIMULANTS. 169

not appear to have produced any derangement or disor-
ganisation in their tissue. But it has been argued that,
as these latter poisons act upon the nervous system of
animals, we may suspect something analogous to this
System to exist in vegetables also. A long list has
been given of substances which act as poisons on
Plants ; and it has been ascertained that very nearly
all such as are deleterious to animal are so likewise to ve-
fetable life, and many others besides, which animals may
take with impunity. Some of those which it is necessary
to administer in large quantities in order to produce
death in animals, are sufficiently powerful to kill plants
when.given in very smali doses — as alcohol, ethers,
and oils ; whilst on the other hand, the oxides of lead
and zinc, which poison animals when administered in
small portions, produce little or no effect on plants,
Probably because they are incapable of being absorbed
by the spongioles. Most vegetable extracts and ex-
Cretions act as poisons on all plants (even upon those
from which they were obtained) when they are imbibed
by the roots. Gases diffused in water are harmless.
Many salts are highly noxious, but most of the salts of
lime produce no effect. Fortunately for the permanence
of vegetation on the surface of the earth, the natural
Poisons are not very generally diffused in places where
Plants are likely to grow. :

(151.) Periodicity. —In tracing the various ana-
logies which exist between the phenomena of animal.
and vegetable life, we find a remarkable example in
what may be termed the individual temperament, or
idiosyneracy of a living organic being. Besides that
general resemblance between the manner in which the
Same functions are performed by all individuals of the
Same species, there are certain modifications in the re-
Sults which are peculiar to particular individuals, end
which must be attributed to some peculiarity in their
temperament. This is remarkably exhibited in the
differences observable among separate individuals of
the same species, as regards their periods of leafing

170 PHYSIOLOGICAL BOTANY. PART I.

or flowering ; for although it is evident that the re-
gular return of the seasons stimulates all plants to a
periodic execution of these functions, and although
the great majority of individuals of the same species
and under the same circumstances perform them at
nearly the same time, yet it often happens that some
individuals are considerably retarded or accelerated’ in
these respects. But further than this, the functions
themselves, independently of the action of any external
stimuli, appear to have a natural inherent tendency to
periodic returns of activity and repose. Thus in the
animal kingdom, the return of night and day are met
by a desire to sleep and to be awake ; and although
these desires may be so modified in different individuals
that some require less sleep than others, there are cer-
tain limits beyond which it is not safe to carry any
unnatural attempts to live without it. Now as in
these cases we do not attribute the periodic desire
to sleep to the regular return of night, but to the cha-
racter of the function itself; so in the case of the
diurnal opening and closing of flowers, the phenomenon
must primarily be ascribed to some inherent quality
in the plant, assisted indeed by the stated returns of
the stimuli to which it is subject.

(152.) Functions of Vegetation. — Whether we con-
sider life in the vegetable kingdom as possessing more
than one property or not, the various operations which
result from its action, upon and through the instru-
mentality of the several organs of which plants consist,
are termed “ functions of vegetation.” Although there
are a multiplicity of operations carried on in different
parts of the vegetable structure, they may all be con-
sidered subordinate to one or other of the two general
functions of nutrition and reproduction. By the former
the life of each individual is preserved, and by the latter
the continuance of the species is secured.

(153.) Stimulants to Vegetation. — Life, in order
to act through the instrumentality of the vegetable
structure, requires to be stimulated by the influence of

CHAP, I, VITAL. PROPERTIES AND STIMULANTS. 171

external agents. Unless such be present, the vital force
remains dormant, even where it is not extinguished.
Thus for example, seed will not germinate unless it be
Placed under peculiar circumstances with regard to
Moisture, temperature, and the atmosphere ; but when
a sufficient supply of these three stimulants is provided,
the seed swells, bursts, and the plant is gradually de-
veloped. The principal stimulants to vegetation are
light, heat, air, and water ; and the conjoint action of
at least three of these four is generally requisite to se-
cure a healthy condition to most plants.

(154.) Light.— The action of light, as we shall show
More distinctly when we are describing some of the
functions of vegetation, is of the greatest importance.
We shall here notice only one phenomenon, to which
we have already alluded (art. 148.), where the presence
of this stimulant exerts a decided influence.

(155.) Sleep of Leaves.— The phenomenon to which
we allude is termed the sleep of plants. This consists in
a periodic change in the position of an entire leaf, or of
the several leaflets of which a compound leaf is formed.
The petioles, or leaf stalks, either bend upwards or
downwards, so that the flattened surface or limb of the
leaf is elevated or depressed. There are about a dozen
different modifications in the manner in which the
leaves are inclined to the stalks on which they grow ;
some raise their leaflets so that their upper surfaces are
brought into contact, and others depress them so that
the under surfaces meet together. . This phenomenon
is best exhibited by various species of the two natural
Orders, the Leguminose (which includes both the pea.
flowering plants, as clover, &c., and the acacias and
mimosas, &c. which have regular flowers) and the
Oxalideæ. These phenomena depend upon a special
Physiological law, subject in some degree to the sti-
Mulating effects of light and heat, which elicit and
Control them, but which are not themselves the pri-
Mary causes of these effects. When the sensitive-plants
are confined in a dark room, their leafiets periodically

172 PHYSIOLOGICAL BOTANY. PART II-

fold and open as usual, excepting that the periods
are somewhat lengthened; on the other hand, when
they are exposed to a continued light, these periods are
shortened. When exposed to strong lamplight by
night, and excluded from all light by day, their periods
of sleep become extremely irregular for a time ; but,
in the end, the specimens generally close their leaves
during the day, and unfold them at night. The
alternate opening and closing of flowers is a similar
function to that of the sleep of leaves. The time of
day in which flowers close is very different for different
species, and even differs for that period during which
the leaves are asleep on the very same plant. Bertho-
let mentions an acacia in the garden at Orotava in
Teneriffe whose leaflets closed at sunset and unfolded
at sunrise, whilst its flowers closed at sunrise and
expanded at sunset.

(156.) Electricity. — Nothing very decisive is
known of the effects which so important an agent as
electricity produces on vegetation. It is, indeed, sup-
posed to act as a stimulant, and the supposition is
countenanced by the increased vigour with which plants
are observed to grow during the prevalence of stormy
weather. It seems to be not unlikely, that some
trees are more liable to be struck by lightning than
others ; but they are all so constructed as to present
numerous conducting points in the extremities of their
branches, well adapted for drawing off the electricity
in the clouds. }

(157.) Temperature. — The influence of temper-
ature on vegetation is a very important consideration,
whether we regard the physical or physiological effects
which it produces. When the temperature is below
the freezing point plants can obtain no nutriment, be-
cause the water in which it is conveyed is solidified.
But further, it is essential to the healthy condition of
every plant that its internal temperature should be sup-
ported within certain limits, which differ for different
species, The opposite extremes of temperature under

CHAP. I, VITAL PROPERTIES AND STIMULANTS. 17s

which different plants are capable of existing are widely
apart. Some flourish within the influence of hot springs,
where they are stated to be constantly exposed to a tem-
Perature of 62° R., or 1714° F., and even to 80° R.,
which is equivalent to 212° F.; whilst the oak sustains
the rigours of a winter in latitudes where the thermo-
Meter falls to -25° R., or —244° F., and the birch will
resist a cold of —36° R., or -49° F. The latter is well
Protected against the effects of extreme cold by the man-
Ner in which its trunk is defended with several loose coats
of epidermis. The chief protection, however, against
the sap freezing in the trunks of trees, is the circum-
Stance of its being contained in extremely minute ve.
Sicles and capillary vessels ; for it has been shown that
Water will resist a temperature of —7° R. or 161° F.
Under similar circumstances; and all viscid fluids are
Still more difficult to freeze than water. Whenever
the sap does freeze, it produces the effect technically
termed “ shakes” in timber trees, which consists in a
tendency in.the separate layers of wood to disunite.
(158.) Internal Temperature. — In animals, _the
function of respiration is the means by which caloric is
Set free, for the purpose of maintaining the temperature
of their bodies at a sufficient elevation to protect them
against the influence of cold, and perspiration cools them
When they are exposed to excessive heat. As vegetables
Perform two functions of a similar kird, we might per-
haps be led to expect that the influence of similar
effects would regulate their internal temperature. But,
if such be the fact, the results are on too minute a
Seale to be rendered sensible by our instruments ; and
in the winter, when these functions nearly cease, we
Cannot suppose that they operate at all in resisting any
atmospheric changes which might be injurious to vege-
tation. Still it has been observed as a general law, that
the temperature of a tree is higher between autumn and
Spring than the average temperature of the air, and
that it is lower between spring and autumn. But
there are physical causes which seem to be sufficient

174 PHYSIOLOGICAL BOTANY. PART II.

to account for these facts without the necessity of as-
cribing them to the results of any physiological action.
The roots penetrate the earth to a depth where the soil
is always warmer than the atmosphere in winter and
cooler in summer, and the moisture which they imbibe
will consequently partake of this influence. Hence it
has been observed, that the internal temperature of trees
is about the same as the soil at one-half the depth to
which their roots penetrate. The maintenance of an
internal temperature distinct from the external is as-
sisted by the nature of the wood itself, which is a bad
conductor of heat; and also by the property which it
possesses of conducting heat better in a longitudinal
than in a transverse direction. As an example, we may
mention that the milk of the cocoa-nut is kept cool
during the hottest part of the day by the thick fibrous
coating of the pericarp, which is a very bad conductor
of heat. i

CHAP. II.

FUNCTION OF NUTRITION — Periods 1, 2, 3, 4.

ABSORPTION (160.).— ASCENT OF SAP (163.). — CAUSES OF
PROGRESSION (165.)e — EXHALATION (169.). — RETENTION
OF sap (172.). — RESPIRATION (173.). — FIXATION OF CAR-
BON (176.).—-ORGANIZABLE PRODUCTS — GUM (177.). —
ETIOLATION (179.).— COLOURS AND CHROMATOMETER (182, ).
— RESULTS OF RESPIRATION (189.).

(159.) Function of Nutrition. — Tax first of the two
general functions (art. 152.), that of nutrition, may

conveniently subdivided into about seven distinct
Processes or subordinate functions, which are all car-
tied on simultaneously in different parts of the vege-
table structure, more especially during those seasons
of the year in which the powers of vegetation are
the most active. Sometimes, only one of them is
n activity, whilst the rest are either partially or
€ntirely suspended. But as the whole of the materials
Which serve to nourish the plant’ must have been
Subjected to these several processes in succession,
We may consider the function of nutrition to be
Carried on during as many successive periods, be-
Ore it is completed. We will briefly mention what
these successive processes are, before we enter upon
the details necessary for the more accurate description
of each of them. In the first place, plants absorb
their nutriment by the roots ; this nutriment is then
conveyed through the stem into the leaves; there it
‘8 subjected to a process by which a large proportion
of water is discharged; the rest is submitted to the
action of the atmosphere, and carbonic acid is first
Seherated, and then decomposed by the action of light :

176 PHYSIOLOGICAL BOTANY. PART Il.

carbon is now fixed under the form of a nutritive ma-
terial, which is conveyed back into the system ; and this
material is further elaborated for the development of all
parts of the structure, and for the preparation of certain
secreted matters, which are either retained within or
ejected from the plant. These several processes may
he designated: 1. Absorption; 2. Progression of sap 3
3. Exhalation; 4. Respiration; 5. Retrogression of
proper juice; 6. Secretion ; 7. Assimilation.

FIRST PERIOD OF NUTRITION.

(160.) Absorption. — That plants absorb moisture
from the soil in which they grow admits of easy proof.
The extremities of the fibres in which their roots ter-
minate, are not covered with an epidermis like the rest
of the surface, and consequently the cellular texture is
there exposed, and constitutes the “ spongiole,”’ or,true
absorbing organ. As plants do not possess the power
of locomotion, it is essential that their food should ke so
universally distributed that they may run no risk of
perishing from want of a constant supply. It is further
requisite that their food should be offered them in a
fluid form ; for it is an established principle in ve-
getable physiology, that the spongioles are incapable
of absorbing any matter in a solid state. Whatever
therefore, is to be received into the system for the pur-
pose of nutrition must be held in a state of solution
in water. The three most important ingredients to be
found among the products of vegetation, are oxygen,
hydrogen, and carbon (see art. 14.) ; the two former are
the elements of water, and the third is an element of
carbonic acid, a gas which is every where present in the
atmosphere, and which may be detected in almost all
springs and other waters on the. surface of the earth-
Water, again, in a state of suspension inthe air, is als0
present every where. Plants, therefore, receive a constant
supply of these three elements wherever they are placed
on the surface of the earth, in situations adapted to theit

CHAP, 41, FUNCTION OF NUTRITION. 177

Stowth. Besides the three elementary substances, oxygen,
ydrogen, and carbon, essential to the composition of all
Organized matter, whether animal or vegetable, there
are other elements to be met with in slight proportion
mM some vegetables. Azote is an element more espe-
cially essential to the formation of animal substances ;
Sut it seems probable, that it is also a fundamental
Mgredient in certain vegetable compounds, in which
it exists in considerable abundance. As this gas
also forms a component part of the atmosphere, plants
May as readily be furnished with it, as with either
of the other three ingredients universally essential to
‘heir nature. Whether the other elements occasion-
ally found in plants ever constitute an essential part
of their structure, is uncertain. Several of them exist
ünder combinations, such as common salt for example,
Which appear to be useful to some plants ; possibly as a
Stimulus necessary for the preservation of their health,
Since they languish and die. when wholly removed from
their influence. In all cases, however, whatever be the
Nature of the various saline, earthy, metallic, and other
“Ompounds found in small quantities in the ashes of
Plants, they must have been introduced in a state of so-
ution through the spongioles.

(161.) Cause of Absorption. — This absorption by
the spongioles continues during the lifetime of the plant,
ànd it becomes a question for the physiologist to deter-
mine, upon what cause the action depends ; whether it
May be ascribed, for instance, to the known hygroscopic
Powers of the cellular tissue, or whether it be wholly or
Partly due to a vital action. This question can scarcely

Considered as satisfactorily settled. If we suppose
€ plant capable of removing the imbibed fluid as fast
as it is absorbed by the spongioles, then we may imagine
the Possibility of a supply being kept up by the mere
Ygtoscopic property of the tissue, much in the same
ay as’ the capillary action of the wick in a candle
Maintains a constant supply of wax to the flame by
N

LR OEE

SE SSS

Fa eT REE ns b sac

178 PHYSIOLOGICAL BOTANY. PART 1

which it is consumed. This view is further sup-
ported by the fact, that the facility with which dif-
ferent liquids are absorbed, appears to depend entirely
upon their degrees of fluidity ; and thus even the most
noxious materials will be more readily imbibed than such
as are nutritious, provided they are presented to the
spongioles in the more fluid state. Now if their ab-
sorption were the result of a vital action, we might havé
expected that a greater degree of energy would havé
been exerted in favour of the more nutritious matte",
and: that the noxious ingredient would have been ab-
sorbed with difficulty. ;

(162.) Stimulants to Absorption.— Whatever be the
immediate cause of absorption, it does not depend upo”
the action of light; for plants absorb by night as well
as by day, and the absorbing organs are most frequently
placed under ground, and in the dark. In an indirect
manner, however, light does certainly exert a consider-
able effect upon the quantity of fluid absorbed ; becaus¢
it is the stimulant by which a large portion is con-
tinually removed by the function of exhalation ; and
we consequently find that when plants are placed in the
dark, although the absorption continues it is consider-
ably checked, so that the water imbibed accumulates
until they become dropsical, and their leaves fall off upo’
the slightest touch. ‘An increase of temperature aug“

' ments the quantity of water absorbed ; but this agait

may depend upon some local stimulus upon anothe
function. Thus if a branch from a, plant growing
in the open air be introduced within a stove during
the winter, it will immediately begin to push its leaves
and become the remote cause of accelerating the ab-
sorption of the sap, which had been going on very 1a?”
guidly.

SECOND PERIOD OF NUTRITION.

(163.) Ascent of the Sap.—The fluid introduced bY
the absorption of the spongioles bears the general nam? ,

CHAP, I. FUNCTION OF NUTRITION. 179

of sap or “lymph?” Essentially, this sap is nearly pure
Water ; but in order that it may become effective in
Nourishing the plant, it must contain carbonic acid, or
at least some carbonaceous material capable of being con-
Yerted into carbonic acid by a subsequent process, which
We shall presently describe. In Dicotyledonous woody
Stems, it has been clearly ascertained that the course of
the sap is up the woody fibre, and especially through the
alburnum, but that it does not ascend in any appreciable
quantity through the pith or bark. It is then carried
Onward through the branches and into the leaves, In
the internal parts of old trunks, the sap accumulates in
arge quantities about the spring of the year, and is there
retained under a certain degree of compression ;. for if
the tree be felled at this season, it flows most readily
tom those central parts which have ceased to possess
any vitality, and sometimes it even issues ina jet during
a few seconds, when the trunk is first severed. Whether
or not any distinct modification takes place whilst the
Sap is moving onward, analogous to the effects of diges-
tion in animals, has not been clearly ascertained. It is
Certain, indeed, that if a tree is tapped at different
heights, when the sap is rising with the greatest energy,
the liquid obtained from the lower parts of the stem is
Purer than that which is derived from the upper parts.
But this may be ascribed to the complete admixture
Which takes place between the juices previously elabo-
tated and the ascending sap, which thus becomes thick.
ned by them as it moves onward.

`- (164.) Channels for the Sap.—Some authors suppose
the sap to be propelled through the vascular system,
Whilst others consider it to rise through the intercellular
Passages, and others again imagine that it passes from
fell to cell, through the elementary membrane of
Which they are formed. The great difficulty in de-
termining the precise channel through which the pro.
Stession of the sap takes place, must be ascribed to the
Perfect transparency of the vegetable membrane, and the
extreme minuteness of these organs themselves. By

N 2

180 PHYSIOLOGICAL BOTANY. PART Ib

placing a branch in coloured fluids, such as a decoction
of Brazil-wood or cochineal, they are absorbed and the
course of the sap through its whole passage into the
leaf may be readily traced; but on examining micro-
scopically the stains which have been left, it is scarcely
possible to feel satisfied whether they are on the outer
or inner surface of the vessels and cells which they have
‘discoloured. The mutilated state of the stem, when
subjected to experiments of this description, has also
introduced errors into the results, and the coloured
liquids have been observed to rise up certain vessels
which under ordinary circumstances appear destined t0
convey air. Since there are many plants which possess
no vascular structure, in them at least we must allow the
cellular tissue to be the true channel through which the
sap is conveyed. But whatever may be the manner i?
which the effect is produced in the more succulent parts
of plants, it seems to be unquestionable that a more di-
rect mode of progression than that of a gradual trans-
mission from cell to cell, must exist in the older parts
of woody stems. If for instance we take a long branch
of the vine and bend it in the middle, the sap imme-
diately exudes at the extremities, but chiefly on those
sides which are towards the concave surface produced by
the flexure; which not only indicates a continuity, but
also a rectilinear course in the channels through which
the sap is conveyed. It is further evident that a general
intercommunication must subsist between these several
channels ; for the stem may be notched to the very
centre, at different altitudes and on different sides, so a5
completely to intercept every rectilinear communicatio?
between the lower and upper parts, and the sap wi

still find its way into the leaves. The probability
therefore seems to be, that the crude sap really rises,
at least in woody stems, through the intercellular pas-
sages, where it bathes the surface of the cells and ves-
sels, all of which are so many distinct organs destine

to act upon it—and more especially when it has after-
wards become intermixed with the proper juices of the

\

CHAP, Ir, FUNCTION OF NUTRITION. 181

Plant. If this view of the subject should prove correct,
then the intercellular passages must be considered ana-
ogous to the stomachs of animals, mere recipients of a
Crude material, which is afterwards modified and ren-
dered available for the purposes of nutrition.

(165.) Cause of Progression. — The progression of
the sap appears to be influenced by several causes. De
Candolle supposes it to be carried forward through the
Intercellular passages by successive contractions and dila-
tations of the cells. Butthere appears to be no warrant
for the supposition ; on the contrary, it seems impos-
sible that such an effect could be produced in cells
Which are replete with an incompressible fluid. If
Contraction were to take place, an expulsion of the con-
tained fluid must ensue, and every dilatation of the cells
Would require that the ambient fluid should enter them.

hether therefore the sap rises or not through the in-
tercellular passages, the hypothesis which he has framed
to explain its progression appears to be inadmissible.

_ (166.) Propulsion of the Sap. — The first and most
important cause of the rise of the sap, resides in the
Spongioles. The water imbibed by them, is also by
them propelled forward with considerable force, and
the effects are strikingly analogous to those exhibited
by the endosmometer (art. 144.). Hales cut off the
Stem of a vine in the spring, when the sap rises with
the greatest velocity, and luted a tube to the top of the
Stump, bent in the manner we have described in the
Construction of the endosmometer. As the sap rose into
the tube, mercury was introduced at the open end ; and
a measure of the force of the rising sap was thus ob-
tained, and found to equal the pressure of an atmosphere
and a half. If a piece of bladder be tied over the sur-
face of a vine-stump, when the sap is rapidly rising,
it soon becomes tightly distended, and will ultimately
burst. These effects manifestly bespeak an action very
different from the ordinary results of capillarity, and
Mdicate the presence of a powerful force, a “ vis à tergo,”
n 3

182 PHYSIOLOGICAL BOTANY. PART II:

residing in the lowest extremities of the roots by which
the propulsion of the sap is regulated. Although these
results so closely resemble those of endosmose, there
still exists a difficulty in connecting the two phenomena ;
for whilst we may admit the possibility of an inter-
change between the contents of the vesicles composing
the spongioles, and the water in the soil which sur-
rounds them, by the ordinary operation of endosmose,
it is difficult to explain how the sap may be propelled
forward so violently as it appears to be, in the open
channels through the centre of the stem, which contain
crude sap of nearly the same specific gravity as water
itself. It would be further necessary to account for the
manner in which a continued supply of fresh materials
is obtained for carrying on the endosmose, which must
otherwise soon cease when the fluid within has become
much diluted. We shall find, however, that a constant
supply of fresh material is actually provided by the
direct action of the vital force, during a subsequent
period in the function of nutrition ; and hence it is not
impossible, though it has not been proved, that both
the propulsion as well as the absorption of the sap may
principally if not entirely be owing to the operation
of mechanical causes ; dependent however for their
lengthened continuance upon the existence of the vital
energy by which those conditions are perpetually re-
newed, and without which the endosmose would of neces-
sity soon cease. Although therefore it is quite evident
that the immediate effects of the vital force must be some-
where present, and co-operative with the two pheno-
mena we have described, these themselves may be only
the secondary results, and not the direct effects of its
action.

(167.) Adfluzion. — Another cause which promotes
the rise of the sap, is the continued discharge of moisture
which takes place from the surface of the leaves and
other parts, by a process to be described presently (art.
168.). This effect produces a constantabsorption from be-
low ; and thus a branch placed in water gradually imbibes

CHAP, I FUNCTION OF NUTRITION. 183

a large quantity at its cut extremity. This “ adfluxion ”
Of the sap, as it has been termed, is clearly the result

of a different cause from that of its propulsion, explained
Mn the last article. :

- THIRD PERIOD OF NUTRITION.

_ (168.) Evhalation. — A large portion of the water
Mmbibed by the spongioles is afterwards discharged at
the surface of the leaves, in a manner analogous to the
insensible perspiration of animals. This discharge may
be attributed to the operation of two distinct causes. A
Very small portion is carried off by the ordinary
effects of evaporation, but a far greater quantity by
a process which has been named “ exhalation,” and
Which is ascribed to the immediate action of the
Vital force. That a certain portion of the discharge
Must be due to the evaporation of the contained
fluid through the membranous coats of the vesicles, is
Proved by the gradual desiccation of the succulent
Parts of dead plants, and by the effects observed in the
Preservation of pulpy fruits. But still, the effects of
evaporation alone are scarcely perceptible, when com-
Pared with the rapid manner in which the fluid is dis-
charged from the surface of the leaf. It has been
ascertained that a common sunflower of three feet in
height, will exhale about twenty ounces of water every
day ; and a common-sized cabbage discharges moisture
at the same rate: so that the surfaces of these plants
exhale at a rate which is seventeen times greater than
that at which the insensible perspiration is given off
from the surface of the human body.

(169.) Ewhaling Organs. —By comparing the effects
Produced by the leaves of different species, it has been
found that those exhale the most which possess the
greatest number of stomata; whilst those surfaces which
Possess none, produce very little or no effect beyond the-
ordinary loss sustained by evaporation. It is quite as
evident therefore that the stomata are the true exhaling

N4

184 PHYSIOLOGICAL BOTANY: PART Il

organs of plants, as that the spongioles are their real
absorbing organs. As the under surfaces of leaves are
in general more plentifully supplied with stomata than
their upper surfaces, the exhalation is there the most
abundant. Plants which live under water have no sto-
mata; but as they have no true epidermis either, they
rapidly fade when exposed to the air, from the more de-
cided effects of evaporation alone.

(170.) Stimulants to Ewhalation. — The manner in
which the stomata act is unknown ; and consequently
we are compelled to ascribe the function which they
perform to the immediate operation of the vital force-
The stimulus by which their activity is sustained, is
mainly if not entirely due to the influence of light ; for
the exhalation ceases when the plant is carried into 2
darkened chamber, and is restored upon its return tO
the light. Even lamplight is, to a certain extent, suf-
ficient for maintaining this action. The effects of ex-
halation are remarkably apparent about sunrise, when
the temperature is low, and the moisture exhaled is not
readily carried off; it then accumulates, and is deposited
in innumerable drops upon the surface and edges of the
` leaves, and is generally mistaken for the effects of dew :
but as it collects equally on plants which are under shel-
ter as on those which are openly exposed, this cannot be
the true cause. It is by no means clear that an elevation
of temperature has any effect in modifying this func-
tion ; but since it undoubtedly increases the quantity of
the evaporation, it becomes difficult to decide whether
any portion of the result is due to an increased ex-
halation also. ‘The manner in which the direct rays of
the sun act in stimulating this function, is well know?
to those who are aware how necessary it is in order to
preserve the beauty and freshness of a nosegay, to keep ít
constantly in the shade. There are certain succulent
plants which possess so few stomata that they may be
preserved out of the ground for many days and even
months, without perishing from want of moisture ; and
it will frequently happen that Sedums, and other plants

CHAP, II. FUNCTION OF NUTRITION. 185

of this character, will even push considerable shoots
whilst placed under pressure, when preparing for the
herbarium: such specimens should first be killed by
immersion for a few seconds in scalding water.. As
juicy plants require most light to secure for them a
regular discharge of moisture, we may mention as a
Piece of practical information, the propriety of exposing
as many leaves as possible in the melon frame to the
action of the sun’s rays, at the same time providing
against the accumulation of moisture in the confined
Situation in which such plants are placed.

The operation of transplanting should be carried on
either in the spring or autumn, when plants are des-
titute of leaves ; otherwise the exhalation is too strong
at a time when the absorption has been checked, owing
to injury sustained at the root. Provided the plants
are well watered, the latter inconvenience may to a
Certain extent be obviated. The water exhaled is so
Nearly pure, that scarcely any trace of foreign matter is
discoverable in it, certainly not more than would be
found in distilled water prepared with the greatest care.
Even that which is exhaled by aromatic plants is scarcely
tainted by any odour. The stomata are in fact the
Most perfect and delicate stills to be met with in the
aboratory of nature.

(171.) Retention of Sap. — About two thirds of the
fluid imbibed by the spongioles is thus exhaled by the
Stomata, and consequently about one third must be
Still retained in the plant. As this portion now in-
cludes all the saline, earthy, carbonaceous, and other
Materials, which happened to be dissolved in the sap
When it was first absorbed, the obvious effect produced

Y the exhalation is to condense these matters, so
that the sap becomes a comparatively denser fluid
than it was before. As many of the materials thus
Mtroduced are not adapted to the purposes of nutrition,
they are deposited in those parts where the exhalation
as been going on ; but the various carbonaceous ma-
terials, furnished chiefly by decomposing animal and

ae x a
a aE S

186 PHYSIOLOGICAL BOTANY. PART I

vegetable substances, are brought into a situation favour-
able for receiving a peculiar modification, which we
shall describe in the fifth period of nutrition. Of the
three elements more especially essential to the compo-
sition of all vegetable matter, we find that two of them,
the oxygen and hydrogen, may be furnished by the

water retained after the process of exhalation has bee?
completed.

FOURTH PERIOD OF NUTRITION.

(172.) Respiration. — The first actual change pro-
duced in the sap is effected by a process analogous tO
animal respiration. The air is inhaled by the leaf and
the fresh surfaces of other parts of the plant, an

„p, its oxygen then unites with the carbonaceous matters
“contained in the sap, and the result is the formation of
na ¥ “"earbonic-acid. The greater part of this gas is the?
« «4 held in solution by the sap; and the whole or very nearly
yer) all the azote which was separated from the oxyge™
, P yg
: is exhaled. Besides the carbonic acid thus formed bY
the plant itself, the trifling proportion every where
found in the atmosphere is also inhaled; and a still
larger quantity is introduced in the water absorbe
by the spongioles. Hence it appears that a threefold
provision is made for maintaining a supply of this ne-
cessary ingredient. So long as plants remain in the
dark, no fresh change takes place in this condition ©
things ; the carbonic acid is retained, but is not fixe
in the form of an organic compound. This furthe!
result requires the additional stimulus of light, and ther
the decomposition of the carbonic acid is effected, the
carbon becomes fixed under the form of an orgaņisab!?
compound, which we shall presently describe (art. 176.)
and all or nearly all the oxygen with which it was unite®
is exhaled into the atmosphere. So long then as plants
continue to vegetate in the dark they tend to vitiate th?
atmosphere by abstracting its oxygen, and also by the

CHAF. 13, FUNCTION OF NUTRITION. 187

Emission of some portion of the carbonic acid which
they generate ; but when they are exposed to the light,
they not only restore the oxygen which they had pre-
Viously abstracted from the atmosphere, but also give
Out another portion of this gas, which they set free by
the decomposition of the carbonic acid contained in the
air, as well as that which was in the water imbibed by the
Spongioles. In animal respiration, the carbonic acid is
immediately expelled from the lungs as soon as it is
formed, and the function is then considered complete ;
and perhaps it would be more logical to divide the
function of vegetable respiration into two processes, one
of which should comprise the formation, and the other
the decomposition, of carbonic acid.

(173.) Formation of Carbonic Acid.— The formation
of carbonic acid takes place in the leaf, beneath the
€pidermis; but whether the air penetrates through the
Stomata or not, is still uncertain. That it cannot uni-
Versally be introduced through these organs is apparent,
Since many leaves have no stomata; and in these cases
at least, the action takes place through the intervention
of the delicate membrane of which the vesicles of the
Cellular tissue are composed. If a section perpendicular
to both surfaces of a leaf be examined under the highest
Powers of the microscope ( fig. 152.), the interior will be
Observed to be chiefly
Made up of cellular
` Matter, or “ paren-

Chyma,” whose vesi-
tles are loosely ag-
Stegated, so that large
Mtercellular passages
exist in communica-
tion with each other,

rough its whole sub- ;
Stance, That these passages are filled with air is readily
Shown by placing a leaf under water, and beneath the re-
ĉeiver of the air-pump. Upon exhausting the recéiver, the
“tr contained in the leaf will be seen to escape through the

188 PHYSIOLOGICAL BOTANY. ' PART IL

petiole ; and upon removing the receiver, the water will

then find its way into the leaf, and occupy the in-

terstices which were originally filled with air. This

effect is rendered particularly striking in those leaves

whose under surfaces are of a paler colour than their

upper, in consequence of the larger dimensions of the

intercellular passages in those parts. When the water

is introduced and occupies the whole of these passages,

the two surfaces become equally coloured. ;
(174.) Air Cells.— Besides the air in the leaves, some

also is found in the stems and other parts of plants, where

its precise use has not been fully ascertained. In many

aquatics, indeed, it is contained in large cavities, terme

“lacune,” as we have stated (art.21.). The obvious use

of such reservoirs as these, is to float the leaves and other

parts in which they exist. The Pontideria crassipes

has its petioles (fig. 153 a.) remarkably distended with

air. The roots of the Utri-

cularie are furnished with a

multitude of little bladders

(fig. 32.) by which they are

floated to the surface during

the season of flowering ; and

a number of other instances

might be mentioned where

some provision or other of

this kind exists. But, be-

sides the mere mechanical

effects which are thus pro-

duced, it is probable that

the air introduced into the

system may in many instances serve some physio"

logical purpose. It seems to be sufficiently ascet”

tained, that some portions at least of the vascular syste?

are destined to convey air from one part of the plant es

another. The spiral vessels and some ducts are ofte”

found filled with it; and in these positions, according a

some experimenters, it contains rather more oxyg”

CHAP, II. FUNCTION OF NUTRITION. 189

than the atmosphere. At present so little has been
ascertained of the conditions under which this air has
been introduced into the vessels, or of the peculiar office
which it is destined to perform, that we can do no more
than just mention the, fact, and state the opinion of
Some botanists, who have considered it probable that in
these situations also it is subservient to the process of
respiration, and who conclude that it is not impossible
there may exist a strong analogy between the manner
in which this function is performed by plants and by
Some of the inferior tribes of animals. Insects for
example breathe by introducing air through several
Spiracles ranged along each side of their abdomen,
and which open into certain ducts or pipes, singularly
resembling in their general appearance the trachee or
Spiral vessels of plants.

(175.) Fixation of Carbon. — When all those parts
of plants which are capable of assuming a green tint, but
more especially the leaves, receive the stimulus of light,
they immediately decompose the carbonic acid contained
in the sap. The result of this action is the retention of
the carbon, and the expiration of the greater part of the
Oxygen into the surrounding atmosphere. The most
Obvious effect produced by this fixation of carbon is the
appearance of that green colour which we find in nearly
all leaves, and in some other organs. In the few
Cases which militate against this rule, we may reason-
ably imagine the existence of some other cause in
Operation which speedily modifies the initial result.

hus for instance, the peculiar tinge assumed by the
leaves of the red-beech, may possibly be owing to the
Presence of an acid secreted simultaneously with the
fixation of the carbon, which converts the green to
ted. The fixation of the carbon by plants appears
. to be the first step in that elaborate process by which

tute matter is converted into an organisable compound ;
that is to say, into a material capable of being afterwards
assimilated into the substance of an organised body.

,

190 PHYSIOLOGICAL BOTANY. PART IL

Many effects, popularly ascribed to the action of air, are
in fact due to the agency of light. Thus trees which
grow in elevated or in isolated situations, are more
vigorous than others of the same species which grow in
forests or in shady ‘places; and those on the skirts of a
wood are finer than those in the interior. When fields
are arranged into alternate strips of fallow and crop,
the produce is much greater from a given portion 0
land than where the whole field is regularly sown, and
this effect must be attributed to the increased in-
fluence of light in such cases. The loss of light in
stoves and green-houses, by diminishing the effects 0-
exhalation, renders plants more liable to be frozen tha
others of the same description which are growing in the
open air.

(176.) Organisable Products.—W hen we proceed tO
inquire in what form the carbon appears after it has be-
come fixed, the subject assumes a degree of uncertainty:
which it seems almost hopeless to get rid of in the pre-
sent state of our knowledge. Since this fixation is effected
by the leaf and other green parts of the plant, it is coP-
sequently in them that we may expect to find the orga?-
isable product, whatever it be, which is the primary
and immediate result of this action. Now unluckily
for our inquiry, there are so many different compounds
contained in solution among the sap and various juices
of plants, — such as gums, sugars, resins, oils, acids,
alkaloids, &c., all of which are composed of different
modifications of the same three elements, carbon, oxygem™
and hydrogen, —that it becomes a task of the greatest
delicacy to” determine which of them ought to be coP-
sidered as the immediate result of the process of fixation.
If we may presume that this result is the same in al
plants, or so nearly the same that we may designate #
(like the blood of animals) by some name which e™-
braces all the subordinate modifications, we must ©"
pect to find it among those products which are thé
most generally dispersed in vegetables, and which are

CHAP, II. FUNCTION OF NUTRITION. 191

also known to be eminently beneficial to them. These
requisites will at once exclude a large class of com-'
Pounds, to be met with only in certain families of plants,
as well as several others which are known to exercise —
Noxious effects upon vegetation, And thus we find,
Upon careful inquiry, that our choice is restricted to
about four substances, all of which possess nearly the
Same chemical characters, and which are the most uni-
Versally present among the juices of plants. These are
: um, sugar, fecula, and lignine. The first of these ap-
Pears by far the most universally diffused, and has been
Obtained from nearly every plant in which it has been
Sought for ; and moreover as it possesses decidedly nutri-
tious qualities, it may be considered with every proba-
bility in its favour, as the first or proximate organisable
Compound formed by the action of vegetable life, acting
Under the stimulus of light. The other three substances,
Which so nearly resemble gum in chemical composition,
appear to be slight modifications of it, which have re-
Sulted from some further elaborations perfected by the
Vesicles in different parts of the vegetable structure, and
We shall defer their description to our account of the
Sixth period of nutrition.
(177.) Gum exudes naturally from certain trees,
‘nd especially from some acacias, which furnish the
“ommon gum-arabic of commerce. It is purer when
Obtained in this way than when it has been separated
Y some chemical process from the sap. Its specific
Stavity varies from 1'316 to 1:482. It is extremely
Soluble in water, but is insoluble in alcohol, ether,
nd oil. It possesses slight modifications in its qua-
ltles, according as it is extracted from different plants ;
Md the following analysis will show its composition, as
it has been stated by three eminent chemists : —
Thénard. | Berzelius. | Prout.
Carbon - - 42°23 41-906 Al*4
Oxygen - 50°84 51:306 52°]
Hydrogen - 6:93 6:288 6:5

192 PHYSIOLOGICAL BOTANY. PART II-

For the present then, we may consider this substance
as most probably the material which is primarily pre-
pared for the nourishment of all parts of the vegetable
structure, and which is afterwards further modified by
the different vesicles and glands distributed through the
system, according as the nature of different parts may
require. 3

(178.) Etiolation.— When any part of a plant capa-
ble of decomposing carbonic acid is entirely excluded
from the light, it remains white. This “etiolation,”
as botanists term the phenomenon, consists in a combin-
ation of an excess of water with the vegetable matter
previously prepared ; so that the quantity of carbon
already fixed becomes as it were diluted, and diffused
over a wider space. If the etiolated parts are exposed
to the light, the green colour makes its appearance in
less than eight-and-forty hours, and the plant gradually
assumes a natural and healthy character. The parts
which have once become green are incapable of being
completely etiolated afterwards. Among the various
vegetable matters used by man as food, those which
are the least sapid are among the most alimentary ;
whilst the more highly flavoured are generally more O"
less deleterious, and some of them extremely poisonous:
In order to obtain a food which shall be both whole-
some and grateful, the horticulturist contrives by vary-
ing his mode of culture to moderate the proportion i?
which the deleterious ingredients are naturally secreted;
and thus renders them harmless. ‘The most commo”
mode of producing this effect is by removing the sti-
mulus of light from such parts as are intended to be
eaten; this both diminishes the activity of the organ’
employed in secreting the deleterious matters, and at the
Same time causes them to absorb a superabundant supply
of moisture. In this way the blanched stems of celery»
which in its natural state is a poisonous plant, become ĉ
grateful food. The leaves of the endive, and mary
others which would be far too bitter or tough in thei

CHAP. I1. FUNCTION OF NUTRITION. 193

natural state to be eaten, are rendered useful and agree-
able additions to our salads.

(179.) Action of Sun’s Rays. — Although the decom.
Position of carbonic acid by the green parts of plants,
1S perpetually carried on under the stimulus of. diffused
ight, and its effects may even be rendered apparent by
the action of lamp-light, which gives a slight tinge of
8teen to plants when grown ina cellar, vet in these cases
the process is carried on too slowly to allow of our col-
“cting the oxygen which is set free. But when plants
are placed in the direct rays of the sun, the action is so
Much more rapid, that the oxygen may then be collected
sufficient quantity to produce a striking result. If a
Plant be immersed in pump water, under an inverted
Slass jar placed in the direct light of the sun, in a
“Mort time the surface of its leaves becomes covered with
Minute bubbles, which presently collect at the top of

€ jar, and are found to be nearly pure oxygen. When

oiled or distilled water is used from which all the

“trbonic acid has been. expelled, no such effect takes
Place, But if another jar filled with carbonic acid be
aiso inverted over the same pan in which the jar con-
“ining the plant is placed, and the surface of the
Water in the pan protected by a coat of oil, to prevent

© escape of the gas as it is gradually imbibed by

è water, it will then be decomposed as before, and the
*Xygen will collect in the upper part of the jar which |

tains the plant, whilst an equal bulk of carbonic |
àcid will disappear from the other jar. It does not ap- |

“ar that the epidermis is essential to the success of
'S experiment, and the decomposition of the carbonic |
acid is equally effected by leaves which have been de-
Prived of it, |

(180.) Action of Oxygen.—A certain portion of free
XYgen is necessary for the formation of the carbonic
ad generated by the process of respiration ; but when
fhis carbonic acid is decomposed and the carbon fixed,
© same oxygen which is set free, will serve again
r a fresh formation of carbonic acid so long as there

o

194 PHYSIOLOGICAL BOTANY. PART U-

yemains any carbonaceous materials in the sap. This
may assist us in explaining an interesting fact described
in the “ Gardener's Magazine,” vol. x. p. 208. It #8
there stated that many plants, especially ferns, hav?
been readily grown in the smoky atmosphere of Lon-
don, by placing them in boxes furnished with glass
coverings hermetically sealed. In this state they hav?
lived and increased in size during several years, without
any immediate communication with the atmosphere
The same mode of treatment has been successfully
practised in transporting plants during a long voyag®
the influence of the sea breeze charged with saline pa!”
ticles forming the greatest obstacle to their safe co?
veyance. When performing experiments to ascertain the
decomposition of carbonic acid by the process of respi"
ation, great precaution is necessary to ensure accuralé
results. The plants being placed under conditions
which are not strictly natural, are’ soon apt to becom?
sickly and exhibit a tendency to decompose. Wher
this is the case the formation of hydrogen, water, and
other substances takes place, and vitiates the results
Those who are anxious to pursue these researches in
further detail may peruse the admirable treatises °
De Saussure and Ellis, where they will find a multitud?
of experiments recorded and a patience of investigatio”
exhibited, which has been rarely surpassed by the la-
bours of other philosophers. ;

(181.) Vegetable Colours.—Not only the green colou!
of those parts which decompose carbonic acid, but ?
the various colours of plants, depend upon the present?
of minute grains of matter contained in the vesicles
of the cellular tissue. The grains which give t
green tinge to the leaf are termed “ chromule,” 2”
it is probable that all the others are only modification
of the same substance. From observations made up”
the leaf at different seasons of the year, it appears tha"
towards autumn this organ ceases to give out oxyge?
day though it continues to imbibe it by night; 9
hence it seems highly probable that the chromule passe?

CHAP, II, FUNCTION OF NUTRITION. 195

nto different states of oxidation, each of which possesses
Some peculiar tint, as in the case of the various oxides
of iron. Although carbon is the principle ingredient in
the composition of chromule, it is not likely as some

ave supposed to be this substance in a perfectly pure
State. Although different colours in plants appear to
depend upon that action of light which effects the de-
Composition of carbonic acid, yet we find that many
Sea-weeds are intensely coloured when they grow at a
depth where the illuminating power of the sun’s rays is
Some hundreds of times less than it is at the surface of
the earth. Humboldt mentions having obtained the
Fucus vitifolius from a depth of 190 feet, where the
ight which it received was two hundred and three
times less than that of a common candle placed at the
distance of one foot from the object illuminated. All
| White flowers are only different tints extremely diluted
‘| a fact of which the celebrated flower painter Redouté
availed himself. By placing the flower on a white
Sheet of paper he could observe the exact tint, however `
delicate, which ought to form the ground of his drawing.
All blacks on the other hand are only intense shades
of some of the darker colours, or of grey.

(182.) Colours of Flowers. — Colour is (generally
Speaking) of very little importance as respects the de-
termination of species among flowering plants; but it
ften furnishes characters of considerable value for the
iscrimination of many among the cryptogamic tribes.
n some other branches of natural history it is of much
Steater consequence; and we shall here explain a method
Y which an accurate and comprehensive nomenclature
May be established for defining colours, so far as may be
tequired in the description of objects of natural history,

‘he scheme is little more than a modification of a plan
Suggested by M. Mirbel; and consists in referring al]
natural colours to certain absolute tints and shades my

termined according to fixed rules.

(183.) Composition of Colours.—All colours may be

* By “shade” we here mean the depth or intensity of a tint,

196 _PHYSIOLOGICAL BOTANY. PART Dv

referred to different degrees of mixture between three
colours, which are considered as “ primary.” These
we may assume to be red, blue, and yellow. A mix-
ture of red and blue makes purple; of red and yellow
makes orange ; of blue and yellow makes green ; a0

innumerable binary compounds may be formed by unit-
ing the primaries two and two in different proportions:
Innumerable shades also of each of these may be ob-
tained, between the deepest that.can be formed and
the faintest, by diluting each colour. to a greater or
less extent. In order that we may consider every
colour to be formed on some regular principle, We
divide a circle into three equal parts (fig. 154. in-
nermost), and place the Blue (B), Red (R), and Yellow

(Y), in each of them re- 154

spectively. Around this

circle a second is de-

_ scribed, and divided into

six equal compartments

containing respectively

the three primaries, and

also those three binaries

which are exactly inter-

mediate between them ;

viz. the Orange (R + Y),

the Purple (B + R), and

the Green (B + Y); as- :

suming these also of the same shade as before. Anothe!
circle containing twelve equal compartments is describe

round the last, and in these are placed the last sik
colours, together with six new ones formed by uniting
each contiguous pair in the same way as before. Av-
other circle would contain twenty-four colours 4”

so on; each fresh addition being always formed fro”.
the combination of two contiguous colours in a forme”
circle, and between which it is to be exactly intet-
mediate ; and the whole is then’reduced to a unifor™
shade. By proceeding in this way it is evident t je

we may form every conceivable binary compound, ý

CHAP, IL FUNCTION OF NUTRITION. 197

2

“ pure colour.” Butas the colours in contiguous com-
Partments will differ less and less from each other as
We extend our circles, it will not be necessary that we
Should proceed further than we are able readily to ap-
Preciate their difference. Now it is considered that
the third circle of twelve colours will satisfy the re-
quired purpose, and these we name the fundamental or
“ basial” colours of our scheme. Their composition
18 expressed in our diagram ( fig. 154.), and the usual
names employed to designate them would be —

B. Blue. l
2B + R. Bluish Purple, or Purplish Blue.
B + R. Purple.
2R +B. Reddish Purple, or Purplish Red.
R. ‘Red.
2R + Y. Reddish Orange, or Orange Red,
R + Y. Orange.
2Y +R. Yellowish Orange, or Orange Yellow.
Y. Yellow.
2Y + B. Greenish Yellow, or Yellowish Green.
Y + B. Green.
2B + Y. Bluish Green.

(184.) Pure Colours. — It may be here observed
that if the three colours purple, orange, and green,
or any other three taken at equal intervals round a cir-
Cle constructed on the above principle, had been assumed
às our three primaries, and these had been combined
two and two, we should have obtained all the pure
Colours as before, and among them the three former
Primaries (blue, red, and yellow) under the character
of binary compounds. This will be apparent when we
Tecollect that the union of three primaries in equal pro-
Portions forms white light with the colours of the
SPectrum, and a grey or neutral tint (N), when ma-
terial colours are employed.

Now, Green + Orange=(B + Y)+ (R+ Y) = (B+ R+Y)+Y
Orange + Purple=(R + Y) + (B+ R)=(B Y)
Green + Purple=(B+ Y) + (B+ R) = (B i

o 3

198 PHYSIOLOGICAL BOTANY. PART IL

_ In these three mixtures of the binaries, we have respect-
ively the three original colours, Y, R, B, combined with
N. And thus, if N be white light a restoration of the
three original primaries is effected, but if (N) répresent
grey, obtained by mixing material colours, then the
three primaries will appear dull or “‘impure.” This dull
appearance always results from the mixture of any tw?
material colours, however brilliant or “ pure” they may
naturally be. These remarks are perhaps sufficient tO
show that all brilliant or “ pure” colours may be con-
sidered equally as primaries or binaries, combined with
a greater or less proportion of white light; whilst all
dull or “impure” colours result from mixing pure
colours with grey. In order to obtain any truly bril-
liant tint we must procure our colour from some na-
tural substance and not form it by admixture, Such:
pure colours are comparatively rare in nature, and evel
those which approach the nearest to brilliancy gene-
rally contain more or less grey. Although it is par-
ticularly difficult to obtain either of the three colours
which we have adopted as our primaries perfectly pure
from admixture with one of the other two, we may
state our theory and then we must practically contrive
to make as close an approximation to such a scheme aS
the nature of the case will admit.

It will be evident, that any pure colour in nature,
when reduced to the same shade as those in our scale
(fig. 154.), will either exactly coincide with one of the
twelve basial colours or lie between two which ate
contiguous. Thus a colour whose composition is 5
+ 3 Y, lies between (B + Y) and (2 B + Y), and if
exact position may be ascertained, by forming fresh
combinations between these two colours and their te
sultants as before described, Thus,

Since (2 B + Y) and (B + Y) are contiguous‘in the third circle,

So will (2 B + Y) —(3 B + Y) — (B + Y) be in the fourth, in

And (2 B + Y)—(5 B + 3 Y)—(3 B + 2 Y)— (4 B + 3 Y)—(B + Y)
the fifth, &c.

CHAP. II, FUNCTION OF NUTRITION. 199

This colour therefore is one of forty-eight pure co-
Ours which would compose a fifth circle constructed
on the plan alluded to. We may remark that any
two colours arranged in opposite compartments added
together make white or grey, and are hence styled
Complementary colours. Thus (2B + Y) is exactly
posite to (2 R + Y), and these added together
Make up (2B +2R +2Y) or 2N; and so of any
Others,

_ (185.) Impure Colours. — From what we have said
it appears, that every tertiary or other compound among
Material colours, that is to say every dull or “impure”
Colour, must be some pure colour mixed with a greater
or less proportion of grey. Thus, a colour com-
Posed of (9B + 7Y + 4 R) is the same as (4B + 4
Yi4 R) + (5B+3Y), which is the same as (4 N)
+(5B+3/Y), ora combination of grey (4 N) with
the pure colour represented by (5B + 3 Y) which is
ne of the bluish greens. Many ternary compounds have
Obtained specific names; thus the different “ browns”
tesult from various proportions of grey mixed with some
Pure colour of which red is a constituent part ; and the
s Olives” are some of the greens similarly rendered
impure.

In order to conceive how every possible impure colour
May be formed by combining the pure colours with
grey, we may take the deepest shades of all the former
and having placed them in the compartments of a circle
divided as before, combine them with all the shades
of grey beginning with the palest in the centre and
Proceeding to the darkest in the circumference ; and
then in another circle concentric with the former, com-

ine every shade of all the brilliant colours with the

deepest shade of grey. This double arrangement gives

Us every possible mixture between the basial colours and

Srey; that is to say every possible ternary compound or

Impure colour. Thus in the annexed figure (155.), if the

deepest shade of blue extends from (a) to (b), and the
Oo 4 .

200 PHYSIOLOGICAL BOTANY. PART II.

deepest shade of grey from (b) to (c), then all the
shades of grey may be 3
added, increasing in

their intensity from

(a) to (b), and all

those of blue from (0)

to (c), and the re” w

quired results will be

obtained for this single basial colour. The impure C0-
lours thus formed will also be of their deepest shades.

As we have assumed twelve pure colours out of the
innumerable sets which might be formed so we may
assume two impure colours corresponding to each of
our basial colours, as sufficient for representing the
tertiary compounds. Those may be selected which lie
exactly intermediate between (a) and (b), and (b) and
(e) (fig. 155.). The former will evidently contain 2
double proportion of a pure colour mixed with one ot
grey; and the latter a double proportion of grey
mixed with one of pure colour. Thus we shall have
one set of “impure” and another of “ very impure”
colours.

(186.) Chromatometer.— It will be seen that we
have considered the construction of twelve “ pure
colours, twelve “impure” colours, and twelve “very im-
pure” colours to be sufficient for our scheme. But we
may further adopt three separate shades of each of
these thirty-six colours, to which we may also refer the
shades of all natural colours; and this gives us 108
different shades, If to these we add three correspond-
ing shades of grey we shall have in all 111 to complete

aight ME '

he scheme. These may be
termed a ““Chromatometer,” which will serve for purposes

CHAP. II: FUNCTION OF NUTRITION. 201

of immediate reference whenever we wish to describe
any colour. The annexed figure (156.) may be taken as
a representation of one of its sectors, containing the three
shades of grey (a b), and those of the “ very impure”
(bc), “impure” (c d), and “ pure” (d e) blues. If
the other eleven basial colours were similarly disposed
round the same centre the chromatometer would be
complete.

It seems unnecessary to include in this scale the
different tinges commonly ascribed to white, black, and
grey ; as these after all are only very faint or dark
Shades of some defined colour, and may be recognised
by comparison with the nearest shades expressed in the
chromatometer.

(187.) Limitation of Colour. — It has often been
Observed by horticulturists, that among different va-
rieties of the same species a limited number of colours
is found, among which are not more than two out of
three of the basial colours similarly disposed upon the ,
chromatometer. Thus there are blue and red hyacinths, ©
but none that are pure yellow; there are yellow and |
red dahlias, but none that are blue. The rule is not ;
free from exceptions, still less does it apply to those |
flowers which have different bands of colour on their |
Corolla. It has been conjectured that those colours |
Which pass from green through yellow to red arise from |
Combinations of oxygen with the chromule in its”
green or neutral state; whilst those which pass from
green through blue to red contain a less proportion of
Oxygen than the green chromule itself. But as these
two series meet in the same colours at both ends of
Such a scale it is not easy to understand how this can
be the case, since the red would equally result from a
Union of the chromule with a maximum and with a
Minimum of oxygen.

(188.) Results of Vegetable Respiration. — From
What has been said it seems necessary to conclude
that carbon, in order to be fixed in vegetation must be
Presented to a plant in the form of carbonic acid ; and

\

202 PHYSIOLOGICAL BOTANY. PART Il.

that the decomposition of this gas by the direct oper-
ation of the vital principle furnishes the first step to-
wards the organisation of brute matter.

The ultimate effects of vegetable respiration being the
reverse of those which result from the analogous func-
tion in animals, have been often regarded as a remark-
able provision against the gradual deterioration of our
atmosphere. But the effects produced by the respiration
of animals, by combustion, and by various other processes
by which carbonic acid is added to the atmosphere, are
of too trifling a description to enable us to appreciate
their consequences under the lapse of many ages. The
continued spontaneous decomposition of a large portion
of dead vegetable matter, is also perpetually counter-
acting some portion of the beneficial effects which the
fixation of carben by plants might produce. Still it
is evident that every particle of carbon in living vege-
tables, and likewise all that exists in ‘those fossil bodies,
coal, jet, &c. which are the altered remains of primeval
vegetation, must have resulted from the decomposition of
carbonic acid whose oxygen has been set free during
the process of vegetable respiration. To this we may
also add whatever carbon is found in animals, since
this has been derived from their food primarily ob-
tained from the vegetable kingdom. We should possess
something like a measure of the extent to which vege-
tation has been active in altering the state of our atmo-
sphere, if we could obtain an estimate of how much
oxygen would be required to convert into carbonic acid
all the carbon now fixed in organised beings, recent and
fossil; and hence we might ascertain whether the at-
mosphere thus modified would still be fitted for our
respiration or not. But in other respects there can be
no doubt of the. important results to which the respiration
of vegetables gives rise. It is this process which pre-
pares the organizable materials from whose subsequent
elaboration are derived those infinitely varied conditions
of organized matter which are essential to the develop-
ment of the numerous tribes of plants which gladden

CHAP, 1, * FUNCTION OF NUTRITION. 203

the fair face of nature, and serve to nourish the
Myriads of animated beings which people the earth,
the ocean, and the atmosphere. And lastly and most
incomprehensibly, from these same materials are con-
i structed those organized substances which seem to
Stand as portals to the intellectual and spiritual world
~ channels of direct communication by which reason
and revelation may tell the frail tenants of a few mould-
ring atoms, of that more glorious condition which will
as certainly be their heritage hereafter as their hopes
and yearnings after immortality are within the actual
Xperience of their present state.

CHAP. III.
PUNCTION OF NUTRITION CONTINUED — Periods 5 An

DIFFUSION OF PROPER JUICE (189.). — INTERCELLULAR ROTA-
Tion (193.). — LOCAL CIRCULATIONS (195.). — VEGETABLE
SECRETIONS (196.). — FECULA, SUGAR, LIGNINE (197.): —
PROPER JUICES (202.) — TASTE AND SCENT (210. ). EX-
CRETIONS (212.).— ROTATIONS OF CROPS (218:) == EX-
TRANEOUS DEFOSITS (219. ).

FIFTH PERIOD OF NUTRITION.

(189.) Diffusion of proper Juice.— Tue crude sap hav-
ing been subjected to the action of the atmosphere and
the carbonic acid decomposed, the result is termed the
X Proper juice” or elaborated sap of the plant. This
liquid has now to find its way back again into the
System for the purpose of nourishing and develop-
ing the various parts. There are three distinct kinds
of movement to which the proper juices of plants

a
204 PHYSIOLOGICAL BOTANY. PART Il.

are subjected. The first of these is its descent and
transfusion ; the second is a very singular rotation
of the juices contained in the vesicles and short tubes
of some plants; and the third is a sort of actual
though local circulation more nearly resembling the
circulation of blood in animals. We propose to describe
each of these under the present period, though certainly
they can hardly be all considered as subordinate pro-
cesses of the same function.
(190.) Descent of Sap.— When a ring of bark is re-
moved from a stem or branch of a dicotyledonous plant
a tumour is formed at the upper edge of the ring, which
indicates a stoppage to have taken place in the descent
of the elaborated sap. This stoppage by causing 2?
excess of nutriment to accumulate above the ring, oper-
ates in improving the size and quality of fruits, an
will even occasion a tree to flower and produce fruit
when it would otherwise have developed nothing but
leaves. No increase or at most a very slight one takes
place in the diameter of the trunk below the ring ; but the
part above it is more developed than it otherwise would
have been. If a potato be ringed in this way the buds
in the axille of its leaves are developed in the for™
of little tubers, whilst none are produced on the under-
ground stems or rhizomata. Similar effects are produce
by a tight ligature; and most persons have observed the
appearance which a woodbine causes on the branches 0
trees by twining round them. A spiral protuberap©?
is formed immediately above and below the stricture
but more especially above it, and in process of tim?
these swellings often become so large as to meet com-
pletely over the woodbine and embed it in the sud-
stance of the tree. The parts which lie above a ri08
or ligature become specifically heavier than those whic
are below it as Mr. Knight found in the oak, the
wood above having a specific gravity of 1°14, and that
below only 1:11. All these facts seem to indicat?
that the chief passage of. the descending sap is dow?
the bark, and towards the surface of the stem. It w#

CHAP, IIT. - FUNCTION OF NUTRITION. 205

Supposed by some persons that an important advantage
might be taken of this circumstance ; and that by
Stripping a tree of its bark some time before it was
felled, the sap would be forced to descend along the
Newly formed wood and thus ripen or harden it more
speedily than would have been the case in the natural
Course of things. But experience has shown that such
timber is very brittle and unfit for the purposes of
building. .

_ (191.) Progression of the Sap.— Although the proper
juice appears to descend more especially by the bark
and those portions of the tree which are towards the
Surface, and which are in fact the parts where the
Vitality of the trunk resides, there still appears to be
@ very general diffusion of the nutritious juice con-
tinually taking place throughout all parts of the tree,
Sometimes in one direction and sometimes in another.
This may be shown by a

contrivance of M. Biot (fig.

157.). A wooden wedge boiled

in wax and oil to render it

Impervious to moisture, has a

groove cut in the upper part,

and is then driven into a ca-

Vity which it exactly fits in the

trunk of a tree; a space is

hollowed out both above and

below this wedge ; the roof of

the cavity above it shelves

towards the middle, so that

the descending sap collects there and drops into the
pen extremity of a pipe placed in the groove to re-
Ceive it, The ascending sap rises into the lower cavity
Which is also cut into a groove, and it is there re-
feived into another pipe placed in the bottom. In
this manner a flow of sap is obtained either simul
taneously from both pipes, or at separate times and in
ifferent proportions according to the state of the at-
Mosphere, season of the year, and other circumstances

206 PHYSIOLOGICAL BOTANY. PART II

which influence the flow. It is observed that the de-
scending current is generally denser and more saccharine
than the ascending, although the reverse is occasionally
the case after violent rains. Light appears to be the
principal agent in modifying the conditions of the flow-
Mild weather promotes the ascent, and a sudden cold
succeeding causes a rapid descent by contracting the
trunk of the tree. If the cold continue and the ground
become frozen, the sap is again forced to ascend. When
a thaw succeeds a frost the exhausted roots are to be
replenished, and the downward current is re-established:
The rapid ascent which commences in spring when the
buds are beginning to burst, ceases as soon as the leaves
are completely expanded. After midsummer the power
of the solar rays being less energetic, and the deposition
of earthy particles having obstructed the vessels of the
leaf less sap is exhaled from them and the tree attains
a state of plethory, indicated by an increasing flow at
the upper tube of the instrument.

{192.) Causes of Progression. — Although these ex-
periments of M. Biot clearly indicate that there is a”
influence produced by a change of temperature and
probably also by other atmospheric causes on the pro-
gression of the sap, it is neither to these nor yet to the
effects of gravity that we must entirely attribute the
descent and general diffusion of the nutritious juices-
We find that if a branch is ringed and its extremity
bent towards the ground, the tumour now is produced
upon that edge which is the lowest in position thoug?
furthest from the root, and consequently the return-
ing sap has been compelled to rise into the pendent
branch. Its progression is decidedly facilitated bY
mechanical causes, such as the wind continually agitat-
ing the stem and branches. Mr. Knight confined the
Stem of a tree so that it could vibrate only in one
' Plane ; and at the end of some years he observed that
7 Section was an ellipse, whose greater axis lay in this
plane.

(193.) Intercellular Rotation. — In the ascent,

CHAP, III. FUNCTION OF NUTRITION. 207

descent and general transfusion of the sap, we can
trace the operation of physical causes modifying and
controlling to a considerable extent, if indeed they do
not originate and entirely regulate these movements.
We have now to describe a more remarkable movement of
the juices of some plants, which more decidedly evinces
a vital action. This movement consists in a constant
rotation of the fluid contained in their vesicles and tubes,
ana rendered apparent by the presence of minute glo-
bules of vegetable matter floating in it. The original
disovery of this phenomenon was made about a century
ago by Corti, who first observed it in the Caulinia fra-
gilis, a maritime plant found on the shores of Italy.
His observations appear to have been generally neg-
lected until lately, when the re-discovery of the pheno-
Menon in other plants has excited the attention of
botanists. It may readily be seen with a good lens
in Valisneria, Hydrocharis, Potamogeton, and other
aquatic genera, but more especially in the genus Chare.
It has also been observed in the terrestrial genera Cu- '
curbita, Cucumis, Pistia, and others ; and is more es-
Pecially observable in the hairs of many species. It
appears to be a universal property of the cellular
tissue though it is impossible in many cases to de-
tect it, either on account of the want of sufficient
transparency in the membrane or from the absence of
the granular matter by whose presence alone the ro-
tation of the fluid itself can be observed. We shall
explain the phenomenon as it may be seen in the
Chara with a lens of about the tenth of an inch focal
distance or even of less power.

(194.) Rotation of Fluid in Chara. — This genus
May be divided into two sections, which are considered
as distinct genera by Agardh. In one of them, the
true Chara, the stems are composed of a central tube
jointed at intervals and surrounded by a row of smaller
tubes. In the other section, or genus Nitella, the
Stems consist of single tubes jointed as before. If we
Select a species of the first section it will be necessary

208 PHYSIOLOGICAL BOTANY. PART IL

to clear away the outer tubes which are always more
or less encrusted with carbonate of lime, in order t
expose the inner tube in which the rotation of the
fluid may be seen. This is an operation requiring some
little delicacy ; and the choice of a
species of the other section (Witella) is
to be preferred, in which the tubes are
generally very transparent and require
no preliminary preparation to clean their
surface. At the joints of the stem are
whorls of branches (fig. 158.) com-
posed also of short tubes, in each of
which the same rotation of the con-
tained fluid may be seen. If an entire k
tube occupying the space between two U
joints be detached and placed under the microscope,
its inner surface appears to be studded with minute
green granules arranged in lines, which do: not ru!
parallel to the axis of the tube but wind in a spiral
direction from one extremity to the other. They are
studded over the whole of the interior, with the exception
of two narrow spaces on opposite sides of the tube form-
ing two spiral lines from end to end. The globules of
- transparent gelatinous matter dispersed through the fluid
are in constant motion, being directed by a current UP
one side of the tube and back again by the other. The
course of this current is regulated by the spiral arrange-
ment of the granules, and it moves in opposite directions
on contrary sides of the clear spaces on the inner surface 0
the tube. The rotation continues in a detached portion,
for several days; and if the tube is tied at intervals
between the joints the fluid between two ligatures sti
continues to circulate, even though the extremities of thé
‘tube should be cut away. The motion here describe
is precisely similar to what takes place in the tubes 0
Corallines, and must unquestionably be considered #°
the result of. a vital action. À

(195.) Local; Circulations. — It was in the ye?
1820, that a distinguished naturalist, M. Schultes»

ip

CHAD, II. FUNCTION OF NUTRITION. 20G

first announced his discovery of a peculiar movement
the juices of plants, which more nearly resembles
the circulation of the blood in animals than any thing
Which had formerly been observed. The existence
of such a circulation had been strongly suspected be-
fore ; but as the experiments upon which his actual
detection of the phenomenon depended were difficult to
Verify, his account was much disputed until recently
When he obtained the prize which the Academy of
Sciences at Paris had proposed for the purpose of elicit-
mg further investigations on the subject. His memoir
as not, hitherto we believe made its appearance ; but
the committee appointed to examine its merits have
Made a favourable report of its contents published
M the “Archives de Botanique” vol-ii.p.505; and from
‘his and a former paper in the “Annales des Sciences,”
We have gleaned the following particulars: — The
liguia, whose movement is described and which M.
Chultes terms the “ latex,” is sometimes transparent
d colourless but in many cases opaque, and either
Mmilk..white, yellow, red, orange, or brown. The
“olours depend upon the presence of innumerable mi-
Mute globules which are constantly agitated as if by
à spontaneous motion, and appear to be alternately
“tracted and repelled by each other. This liquid
'S considered to be the proper juice of the plant
Secreted from the crude sap in the intercellular pas-
‘ages and consequently analogous to the blood of ani-
mals as was long since suggested by Grew, who
“Urther likened the lymphatic or crude sap to their
ayle. It is contained in delicate, transparent, mem-
řanous tubes, which become cylindrical when iso-
“ted, but when packed together in bundles assume a
Polygonal shape. In young shoots it is difficult to de-
Ct them, on account of their extreme transparency and
‘enuity ; but they may be extracted with considerable
àcility from older parts. They have been observed very
Seherally in Monocotyledons and in Dicotyledons, ex-
P

210 PHYSIOLOGICAL BOTANY. PART Ib

cepting in the few species in which no tracheæ have bee?
hitherto noticed. They frequently intereommunicate F
anastomose by means of lateral branches, and sometimes
form a regular network (see art. 27. fig. 15.). They
occur in the woody fibre, in the bark, occasionally
even in the pith, and very frequently surround the
tracheæ. They exist in greatest complexity in the
root, from whence they proceed in parallel lines UP
the stem into the leaves and flowers and then retur”
again to the root, the ascending and descending branches
anastomosing throughout their course. The movement
of the latex can be witnessed only in those parts whi¢

happen to be very transparent; and it has not bee?
actually seen in many plants. The Ficus elastic
Chelidonium majus,. and Alisma plantago, are the
species upon which most of the observations hither!
recorded have been made. Distinct currents are 09-
served traversing the vital vessels, and passing through the
lateral connecting tubes or branches into the princip?
channels. These currents follow no one determinat?
course, but are very inconstant in their direction —so™?
proceeding up and others down, some to the righ
and others to the left; the motion occasionally stoP-
ping suddenly, and then recommencing. In detache

fragments of the plant it will continue from five minute
to half an hour, according to circumstances ; but M:
Schultes has been able so to adjust his lens as to witne”
the flow in the growing plant. The action is su%
denly checked by cold, and again recommences W*

an elevation of temperature. The effect does not see
to depend upon a contractile power of the tubes, be-
cause the latex flows chiefly or entirely from one &

of a tube even when it has an orifice open at b?

extremities. The appearance is very similar to i

circulation of the blood in the fcetus contained i? ê
bird’s egg before the heart is formed ; but is more °-
pecially analogous to the circulation of some of the
lowest tribes of animals, as in the Diplozoon paradoxu™ 4
which may be divided into two parts and the blom™

CHAP, IIT. FUNCTION CF NUTRITION. 2Ti

still continue to circulate for three or four hours in each.
By a strong electric shock, the force by which the latex
18 propelled is paralysed, and its motion arrested.

SIXTH PERIOD OF NUTRITION.

(196.) Vegetable Secretions.— In describing the pro-
fess by which we have supposed the first step to be
Made towards the organisation of those materials which
nter into the vegetable structure, we have considered
gum to be the immediate result of the fixation of car-
bon in combination with the two elements of water ;
and that this substance is formed by all those parts of
Plants which almost universally acquire a green tinge.

e further stated that there were three other sub-
Stances nearly allied to gum in chemical composition,
Which might also be considered as destined for the
Nourishment of the plant. It is probable that these
Substances are only slight modifications of gum, produced
9y its subsequent elaboration in the cellular tissue. It
ts impossible, however, to point out the specific organs
Which are appropriated to this office. In some cases
à distinct glandular structure is very apparent, and
the immediate secretions effected by it ‘are collected in
an isolated form ; but in others there is no apparent

lfference between the organisation of those parts in
Which the secretions are produced and the rest of the
*ellular tissue.

(197.) Fecula.— The first of the three alimentary
Products which we shall further notice is fecula. This
Substance forms minute spheroidal grains in the cellu-
“ar tissue, and must be considered rather as a dis-
tinctly organised product than as a secreted matter.

ach grain consists of an insoluble pellicle or integu_
Ment, containing a soluble substance which seems to
.© pure gum, or some material scarcely differing from

m any essential character. These grains are not

ER

PA es FHYSIOLOGICAL BOTANY. PART Ue

altered by the action of alcohol, ether, or cold water »
but in hot water the pellicle bursts, the contained
matter exudes, and the whole mass becomes a paste
The specific gravity of fecula is about 1:53., It
may be obtained from the pulp of fruits, tubers, succU-
lent stems, and other parts of various plants. That
which is derived from corn and the potato is fami-
liarly termed starch. Sago (from the stems of a palm)
tapioca (from the tubers of the Jatropha manihot)»
arrow-root (from the rhizomata of the Maranta arun-
dinacea), are all so many varieties of fecula, THIS
substance is highly alimentary and is largely store
up in various parts of vegetables where it forms
magazines of nutriment, apparently destined for the
future development of the buds and ripening of the
seed. It is a material of all others the most im
portant as an article of human food, and is provider-
tially provided for our use in the greatest abundan¢e
It bears a striking analogy to -the fat of animals, eve?
in the general structure of its component parts accore-
ing to some, but more evidently in the uses to whic?
it is subservient in the economy of vegetation. The
formation and subsequent re-absorption of fecula 5
rendered very evident, by comparing the different qua?”
tities found in plants of the same species at differe?
seasons of the year. The following table shows ™
the gradual accumulation which takes place in 1
pounds of potatoes between August and November, 4
the subsequent diminution from March to May :—

Aug. Sept. Oct. Nav. March. April. May.
10 ee 4 a 17 13} 10

(198.) Plants containing Fecula. — The followins
list contains a few of the principal plants which furm!®

giv’

fecula in the greatest abundance, and the figures fait
YO

the percentage yielded by the several organs
which it is extracted. These numbers may also
considered to a certain extent indicative of the deg”
of nourishment which each is capable of affording : g

ees

,
CHAP, III. FUNCTION OF NUTRITION.

=- 80 to 92)
- 80 to 85
- 70 to 77

French beans. -
Kidney beans

Lentils - A
Amomum curcuma
Dioscorea triloba -
Potato 4

26 "
rhizoma.

tuber.

Tapioca (Jatropha manihot) 13:5 | root
Sweet Potato (Ipomea batatas) 13°3 x
Arrow-root ( Marantaarundinacea) 12:5 | ioe
Canna coccinea ” - 12° ;
Breadfruit (Artocarpus incisa) - 3'2 fruit.

(199.) Sugar. — There are numerous modifications
of sugar, all of which may be referred to two general
heads. The one class, as the sugars of the sugar-
Cane and beet-root, contains a less proportion of water
in combination with an equal quantity of carbon than
the other class, which includes the sugars extracted
from raisins, manna, &c. ‘Some are erystallisable
Others not. The purest obtained from the sugar-cane
has a specific gravity of 1-605, and. is composed cf
about 42 per cent. of carbon and 58 of water. In the
East Indies the canes yield about 17 per cent., and
in America 14 per cent, of sugar; but in our hot-
houses they produce scarcely any. All sugars are
řeadily soluble in water but less so in alcohol, into
Which latter fluid they may themselves be converted
by the process of fermentation ; thus the quantity of
ardent spirits which may be extracted from any vege-
table is in proportion to the sugar it contains. This
Substance bears a striking affinity to gum in its che-
mical composition, and is very commonly dissolved

P 3

‘
214 PHYSIOLOGICAL BOTANY. PART Ib

in the juices of plants. After it has been formed
it is again very easily altered during the progress of vege-
tation ; a fact of considerable importance to the cultivator,
who must be cautious to collect the produce of his canes
at the season when the sugar is most abundantly gener-
ated and before it sustains such alteration. The flowering
of the cane exhausts the sugar in the stem; and that
which is so abundantly contained in the cortical sys-
tem of the root of the beet is ultimately carried int?
the upper parts of the plant, and similarly exhausted
during its inflorescence.

(200.) Lignine. — This substance is contained i?
the elongated vesicles termed closters (art. 16. fig. 3. c), of
which the woody fibre is composed. It does not ap-
pear that it has ever been submitted to a careful analy-
sis, or accurately examined in a detached form. After
various matters have been abstracted from the woody
fibre, such as certain salts, gummy particles, and others,
` there ‘then remains about 96 per cent. of an in-
soluble substance, composed of nearly equal propor-
tions of water and carbon. But this is a compout
material, consisting both of the thin pellicle which
formed the vesicles themselves as well as of the lignine
which they contained. The resemblance which lignine
bears to gum is not so striking as in the case of the tw
materials just described, nor does it appear to answer any
ulterior purpose of nutrition after it has become secreted;
but it remains unchanged in the cells, and imparts
to wood the varied qualities and colours which different
species present. Its specific gravity varies being 1°49
in the maple, and 1-534 in the oak.

(201.) Vegetable Products. — Besides the four ma-
terials gum, fecula, sugar, and lignine, which W°
consider as the simplest modifications which the nutri-
tious and organisable materials found in the’ vegetable .
structure can assume, there is an interminable catalogu?
of other substances which may be extracted from the
juices of different plants, all of which have been forme
by secretion in some part or other of their structure

CHAP, IIL FUNCTION OF NUTRITION. 215

Some are the results of disease, whilst others are more —
abundantly formed when the plants which produce
them are placed in peculiar soils and situations. Some
Occur in a very few species only, whilst others are
Characteristic of whole families. None of them are
80 abundantly diffused as the four nutritive sub-
Stances already described ; and they all materially
differ from these, by having either the oxygen or the
ydrogen which they contain in greater excess than
Would be necessary to form water. These may there-
fore be termed hyperoxygenated and hyperhydrogen-
ated products, when contrasted with the others.
Little is at present known of the exact manner in
Which these various products are formed. Their com-
Plete enumeration belongs to the department of che-
mical Botany ; and we can here pretend to do no
More than point out some of the principal groups, and
Mention a few of their most striking peculiarities.
(202.) Proper Juices. — Several of the products
elaborated in the leaves and cortical parts, are dissolved
m those proper juices of plants which in art. 195.
We described as the latex or vital fluid, analogous to
the blood of animals. But as these juices are very
different in their characters in different species, as they
ate not clearly defined in some and above all as they
act as poisons when imbibed by the roots, De Candolle
Magines that they ought more properly to be con-
sidered as secretions of a recrementitial nature, ana-
gous to the bile and others in the animal economy.

Ome of these products even contain azote, and by
this circumstance are brought into closer resemblance
With animal matter. The more remarkable materials
found in the proper juices of plants are milks, resins,
and oils.

' (203.) Milks. — These are generally of an opaque
White, though some are variously coloured. They
bound in many species, and are highly characteris-
tic of certain natural families, as the Euphorbiacee,

p 4

216 PHYSIOLOGICAL BOTANY. PART I

Apocynee, Artocarpeæ, &c. They differ very remark-
ably in their characters; for although a large portion
are noxious, and even highly poisonous, some on thé
contrary are wholesome and nutritious. There are
several substances found in the composition of these
milks, of which we may mention the following : — ;

1. Caoutchouc, or Indian rubber is abundant 1}
some of them, and may be readily obtained from severa
trees of different families growing in tropical climates:
All that is requisite for the purpose of procuring this
material, is to receive the milk into suitable vessels 25
it flows from a wound in the bark and to allow i
aqueous particles to evaporate, when the caoutchouc 1e-
mains in a solid form. ;

2. Opium is procured by inspissating the milk of
the poppy, and is also found in other plants.

3. The Cow-Tree.— One of the most remarkable
phenomena of the vegetable world is the cow-tre®
described by Humboldt in the following terms, 2
growing in the Cordilleras of South America: — “ O”
the barren flank of a rock grows a tree with dry and
leather-like leaves ; its large woody roots can scarcely
penetrate into the stony soil. For several months 1”
the year not a single shower moistens its foliage. Jt
branches appear dead and dried ; yet as soon as th?
trunk is pierced, there flows from it a sweet and not-
rishing milk. It is at sunrise that this vegetable foun-
tain is most abundant. The natives are then to Be
seen hastening from all quarters, furnished with large
bowls to receive the milk, which grows yellow a
thickens at the surface. Some empty their bowls unde"
the tree, while others carry home the juice to the!
children. The milk obtained by incisions made in the
trunk is glutinous, tolerably thick, free from all act!
‘mony, and of an agreeable and balmy smell. It w4®
offered to us in the shell of the tutuno, or calabash
tree. We drank a considerable quantity of it in the
evening, before we went to bed, and very early in te
morning, without experiencing the slightest injurious

CHAP, III. ' FUNCTION OF NUTRITION. 217

effect. The viscosity of the milk alone renders it some-
what disagreeable. The negroes and free labourers
drink it, dipping into it their maize, or cassava bread.”
Mr. Lockhart has subsequently afforded the following
additional particulars concerning this tree: — “ The
Palo de vaca is a tree of large dimensions. The one
that I procured the juice from had a trunk seven feet
in diameter, and it was one hundred feet from the root
to the first branch. The milk was obtained by making
a spiral incision into the bark. The milk is used by
the inhabitants wherever it is known. I drank a pint
of it without experiencing the least inconvenience. In
taste and consistence it much resembles sweet cream,
and possesses an agreeable smell.”

_ (204.) Receptacles for Milk.—All the various milky
juices reside in the bark and leaves, and are not found
in the wood. They are contained in distinct receptacles,
and may be extracted by means of incisions chiefly
in the upper parts of plants, and which do not ex-
tend deeper than the bark; otherwise they would be
diluted and impoverished by mixing with the as-
cending sap. M. Bertholet has recorded a remarkable
Instance of the harmless quality of the sap in the
interior of -a plant, whose bark is filled with a milky
Proper juice of a poisonous nature. . He describes the
Ratives of Teneriffe as being in the habit of removing
the bark from the Euphorbia canariensis, and then
Sucking the inner portion of the stem in order to
Quench their thirst, this part containing a consider-
able quantity of limpid and non-elaborated sap. The
reservoirs which contain the milky juice of the wild
lettuce (Lactuca virosa) are so remarkably irritable
that the slightest touch is sufficient to cause it to be
ejected from them with considerable force. When
this plant is about to flower, if an insect happens to
Crawl] over the surface of the stalk any where near its
Summit a jet of milk is propelled. In general plants
Which secrete these milky juices love tne light; few
re found to affect shady situations, and none are aqua-

le OE ES

218 PHYSIOLOGICAL BOTANY. PART If:

tics. By cultivation, their noxious properties may be
greatly subdued.

(205.) Resins. — This class contains certain sub-
stances separated from the proper juice by some pro-
cess of secretion ; and not having any peculiar channels
appropriated to their reception, they form cavities a0
force passages for themselves in the cellular tissue. OC-
casionally they exude from the surface of the stem ; but
this must be considered accidental and not the result 0
any provision made for their excretion, as is the cas¢
with some substances which exude from certain glands
on the surface.

(206.) Oils. — There are two classes of oils secreted
by plants: the one contains the highly volatile or essen”
tial oils as they are termed, which impart the fragrant
or disagreeable odours peculiar to different plants ; an
the other the fixed oils, such as those extracted from
the fruit of the olive, the seeds of flax, &c.

(207.) Volatile Oils. — The first kind are gener-
ally contained in spherical or oblong cells in the leaves
and cortical parts of plants; when held to the light
these parts appear as if they were punctured, owing
to the superior transparency of the receptacles i
which the oil is deposited. The St. John’s-wort
(Hypericum perforatum) and any of the myrtle tribe
are familiar examples of this fact. In the Umbellifer®
the oil accumulates in oblong club-shaped receptacles,
termed “‘vitte,” which are placed between the coats °
the seed-vessel ; and it is remarkable that their num-
ber and general appearance is so constantly the sam®
for each separate species that important generic cha-
racters are derived from this circumstance.

(208.) Camphor is deposited upon the evaporation of
certain volatile oils, especially those extracted from som?
of the Labiate, as the common lavender. :

(209.) Fixed Oils. — These are rarely found in the
Cortical parts like the others, but are for the mos
part extracted from the seed or its envelopes, 4”
sometimes from the pericarp, as in the olive. Jn

CHAP, III. FUNCTION OF NUTRITION. 219

these cases they are readily convertible by some natural
Process into a nutritious emulsion; and then appear to
be destined to feed the young plant during the early
Stages of its development. £

_The following table shows the percentage of fixed
oil obtained from the seeds of a few plants :—

Nut =
Cress -
Walnut -

Poppy ~
Almond. -

(210.) Taste and Scent of Plants. — It will readily
be conceived that the peculiar tastes and odours met with
in different species, must depend entirely upon the nature
of the various matters which are secreted by them,
Attempts have been made to classify the various im..
pressions which are thus made upon the sensorium, and
odours have been arranged into classes, under the
terms aromatic, fœtid, acrid, alliaceous, musky, &c.
Such classifications at the best are highly empyrical,
and any arrangement which could be founded on an
accurate knowledge of the chemical nature of these
Substances would be far preferable ; but our extreme
ignorance on these points will not justify the attempt
at present. The delicate perfumes emitted by certain
flowers, as well as the more powerful and often disagree-
able scents afforded by the herbage of some plants,
generally depend upon the diffusion of a volatile oil.
n some cases this oil is magazined in the stalks and
leaves, and is rendered more sensible the more these
Parts are rubbed or bruised. In the flower especially,
the oily particles which produce the odour seem to be
diffused as fast as they are secreted ; and hence it hap-
Pens that the greater number of plants are more power-
fully scented at one particular part of the day and
that almost all flowers are most fragrant towards night.
There are some, specially termed “ night-scented,”
which are extremely powerful after sunset though

PHYSIOLOGICAL BOTANY. PART Ib

ing a peculiar brown and lurid tint. The flowers of
the splendid Cereus grandiflorus begin to expand about
seven o'clock in the evening, attain their full beauty
and put forth their powerfully fragrant odour before
midnight, and are completely faded before sunrise-
Some of the singular tribe of Stapelias are disgustingly
nauseous in the scent which they emit, strongly resem-
bling the most offensive carrion ; so much so indeed
that even flies and other carnivorous insects are de,
ceived by the similarity, and very frequently deposit
their eggs in their blossom.

(211.) Impressions made by Odours. — The scents
emitted by certain flowers make very different impres-
sions upon the nerves of different people; and some
persons can readily perceive a powerful odour wher
others are nearly or entirely insensible to its impressio™,
although they may not be defective in other instances 1”
the sense of smelling. ` Very deleterious impressions 4°
made on some constitutions by the odours of strong-
scented flowers. The most dangerous symptoms hav
occurred in persons especially females with weak nerves,
merely by their remaining in a room where certain
flowers have been placed; and even violets are 20!
exempt from a bad reputation. Instances of deat?
have been recorded which were considered to have
been occasioned by effects of this kind; and Linneus
_ mentions a case where the odour from the Rose-bay
(Nereum oleander) was supposed to have proved fat
to the constitution of one person. Prussic acid may
be instanced as abounding in the leaves of the commo”
laurel (Prunus lauroceratus) to so great an extent
that if one of them be cut into small pieces and place
under a wine-glass, and a wasp or other insect be iP-
troduced under the glass it will be completely stupefie
in two minutes.

(212.) Eweretions. — We have still to allude t°

CHAP. III. FUNCTION OF NUTRITION. 2a}

a class of substances which are excreted from plants by
Various glands seated on the surface of their stems,
leaves, and other organs. Many of them are of the
Same description as those which are formed within
the plant by internal secretions, such as acids, oils, &c. ;
but some of them are peculiar. They may be con-
Sidered as more strictly analogous to the various ex-
Crementitious matters ejected by animals than those of
the former class; and the glands by which they are’
formed are for the most part more complex and
better defined than those which are seated in the
interior of plants. The external glands (see art. 31.
and fig. 20.) by which these matters are excreted often
form a sort of clammy pubescence upon the epidermis.
T hey frequently resemble hairs tipped with a little
globular mass by which the excreted matter is more
especially elaborated.

(213.) Frawinella.— The common Fraxinella is
covered with minute: glands which excrete a volatile
oil. This is continually evaporating -from its surface,
and on a calm still evening forms a highly inflammable
atmosphere round the plant. If a candle be brought
Near it, the plant is enveloped by a transient flame
Without sustaining any injury from the experiment.

(214.) Stings. — The stinging plants prepare a
Caustic juice which is contained in a cellular bag sur-
mounted by a hollow bristle. When the bristle is
gently pressed the fluid is forced through it and flows
out at the summit through a minute orifice, as we have ,
Stated (art. 31. and fig-20.'a). If the bristle enters a pore
of the skin, the caustic fluid is introduced and produces
the painful sensations familiar to all who haveever handled
a common nettle. ‘The Loase have stings which give
a still more irritating sensation than the nettles. The
Malpighie are furnished with a multitude of doubly
Pointed bristles which lie parallel to the surface of their
leaves, to which they are attached by a short hollow stem.
These contain a slightly caustic fluid.

(215.) ‘Glue.—The gummy excretions on the stems of ;

999 PHYSIOLOGICAL BOTANY. PART Ib

certain plants, as the fly-catching Lychnises (Lychnis
armeria and others) appear to be composed of 4
material of the same nature as common birdlime’

extracted from the bark of the holly. Several kind of

leaf-buds, as those of the horse-chestnut, are coated
over with a glutinous insoluble excretion apparently
intended to secure them from the ill effects of moisture
(216.) Wax—is a very abundant excretion from
mapy-plants. It forms a delicate powder on the sur-
face of certain fruits, as the substance termed the
“bloom” on the plum. It is so plentiful on the sur-
face of poplar leaves, that a manufactory was at-oné
time established in Italy for the purpose of procuring
it from them as a material for commerce. It is very
abundantly furnished by some palms in tropical countries,
where it is advantageously employed for economical
purposes ; but the Myrica cerifera is the plant which
affords it in the greatest abundance. Its fruit i
completely enveloped in a coat of wax, and whe?
thrown into boiling water the wax melts and floats t°
the surface where it is skimmed off. It has a slightly
green tinge which can be removed by chlorine, and it
may then be formed into candles resembling spe
maceti. This fruit yields about one ninth per cent. 0
its weight in wax. All the kinds of vegetable wax at
closely allied to common bees’ wax in several prope!
ties, though essentially distinguished from it by others-
(217.) Radical Excretions. — But of all excretions
proceeding from plants, some of the least-known at
perhaps the most important in an economical point 0
view. It was not until very recently that their pro-
perties had been made a subject of experimental in-
quiry, or even that their existence had been cleatly
established ; but the partial results hitherto obtaine
have opened a wide field for speculation. The exere-
tions to which we allude. are discharged from the
root, and may be detected by a very simple experi-
ment. If young French beans, for example, be place
in a glass containing distilled water, at the end °

oh ok D O O at eb ot O af fs

CHAP, III. FUNCTION OF NUTRITION. 223

a few days this. water will be found strongly im-
Pregnated by a matter excreted from the roots. A
fresh plant should be placed daily in the water, to avoid
the effects which might otherwise be produced by an
Incipient decomposition. It is also found that the
Matters thus procured from plants of different families
are dissimilar. Thus that which is excreted by the
Leguminose contains an abundance of mucilage, whilst
that which exudes from the Graminee has very little.
The Chicoracee excrete a bitter matter analogous to
Opium; the Euphorbiacee a gum-resinous matter, &c.
(218.) Rotation of Crops. — So far as observations
have hitherto been made, it appears probable that
the excretions given out by plants of different fami-
lies possess very different qualities, and act differently
upon other plants. It had been long known to gar-
deners that flowers and fruit-trees will not prosper so
Well when they have been planted in a situation where
others of the same kind had previously grown, as if
they were planted in situations where they succeeded

to others of a different kind. It is also a well-esta~ ,
blished fact in forestry, that when a wood principally |

Composed of one species of timber trees has been
Cleared, the trees which then spring up spontaneously
and supply the place of the former growth are for
the most part of a different species. And lastly,
the agriculturist has established a rotation of crops
upon experimental proof that grain of one kind suc-
ceeds better when it follows certain other kinds, than
when it is sown immediately after a crop of the
Same plant. The various theories which had formerly
been proposed to account for these facts were all liable
to serious objections ; but M. De Candolle has suggested
the probability, that the excretions of any one plant
although they may be noxious to others of the same
Species, genus, or family, may nevertheless be per-
fectly harmless or even beneficial td plants of other
families, In this manner he would account for the
fact, that plants of the natural order Leguminose (as

Daisaku- nakatiis tate Se

294, PHYSIOLOGICAL BOTANY, PART Il

vetches, tares, &c.), prepare or improve the soil fot
those of the Graminee (various kinds of corn, &c.).
the farmer by further experimental research should
ever be able to establish an extensive series of facts of
this description, he may expect to grow a succession
of crops with comparatively little manure and without
ever being obliged to let his land lie fallow. In the
present state of this inquiry it would be idle t
say much upon the possible advantages which may
be expected from the confirmation of this theory;
but it must be.evident to the most prejudiced admiret
of old customs, that we cannot expect to make any real
progress in the various branches of human knowledg®
agriculture among the rest, until we have obtaine
clearer notions and a sounder theory respecting the
fundamental principles upon which the successful prat-
tice of any pursuit depends.

(219.) Eatraneous Matters. — Besides those numer-
ous products directly secreted by plants, and which are the
immediate results of vegetable action, there are many
others which have either been accidentally absorbed
with the water that enters through the spongioles an
pores, or else have resulted from subsequent combin-
ations chemically effected between matters so introduce
and the undoubted products of vegetation. All matters
however which are accidentally introduced, form only
avery slight per centage of the weight of the whole mass-
They compose the various earthy, saline, metallic, a?
other ingredients found in the ashes of plants, afte?
combustion has dissipated all the purely vegetable pro” -
ducts. They generally exist in the greatest quantity ™
those plants, or parts of plants, where the process of ¢*-
halation has been carried on with the greatest rapidity.
Hence they abound more in the leaves than in othet
parts, and more in the bark than in the wood. Herba-
ceous plants for similar reasons furnish more ashes
than trees, te é

(220.) Earths.— Lime is the earth which is most w1-
versally present in the ashes of plants, generally in t#°

CHAF. III. FUNCTION OF NUTRITION. 225

form of a carbonate, but also in union with other mineral
and vegetable acids. Carbonate of lime is largely deposit-
èd in the stems of some of the Chare, which it completely
incrusts with stony matter. — Silica is the earth which
Next to lime occurs in the greatest abundance, especially
among some of the monocotyledonous tribes. The glossy
Surfaces of canes, reeds, and other grasses, are com-
Posed of a very large percentage of it ; and if two canes
be rubbed together in the dark, they emit a flash of light
Similar to that which is obtained by the friction of two
quartz pebbles. When a stack of corn or hay has been
rapidly consumed, the ashes are fused into a semi-vitri-
fied mass: the straw abounding both with silica and an
alkali, the two chief ingredients necessary to the form-
ation of suth a compound. In the hollow portions
of the stem between the joints of the bamboo, a sub-
Stance named tabasheer is deposited in lumps which
Very much resemble fragments of opaque and semitrans-
Parent opal. This remarkable deposit contains 70 per
Cent. of pure silica, and possesses very peculiar and
Curious optical properties. Silica is also deposited in
ittle semi-crystalline lumps along the angles of the
Stems of some species of Equiseta, especially the Equi-
Setum hyemale or Dutch reed, which from this circum-
Stance is serviceable to watchmakers and others in
Polishing their work.

(221.) Salts. — The salts of potash are particularly
abundant in most plants, but the salts of soda are more
pecially confined to such as grow near the sea. It is

Owever remarkable, that plants which abound in the
Salts of soda whilst growing in these latter situations,
Secrete the salts of potash when they are no longer
Within the influence of the sea. In such plants, it is
difficult not to believe that the presence of one or other
Of these alkalis is in some way beneficial to their health,
ven though it may not form any essential part of their
Structure. The common soda of commerce is a carbon-
ate obtained from the incineration of several maritime

Q

yas

296 PHYSIOLOGICAL BOTANY. PART Ue

plants and sea weeds, and is largely prepared on the
shores of the Mediterranean for the European market.
(222.) Origin of extraneous Deposits. — The various
other products, such as oxides, metallic salts, &c., whic
occur in small quantities in the ashes of plants, have ®
been either derived immediately from the soil or intt0-
duced in some way by absorption from the atmosphere:
_ It seems clearly established that none of them ought 10
be considered as the direct product of any vegetative
function, as was once supposed ; and it has been satis
factorily shown that however carefully the experime? j
may have. been made which favour such a theory, 4!
however cautiously the means may have been taken 10*
excluding all foreign matters from access to the grow-
ing plant, error was unavoidable. The extreme ™I-
nuteness of the elementary organs of plants, and t
more delicate manipulations of a natural chemistry, are
capable of separating the minutest portions of foreig®
matters from the materials with which they are broug
in contact, however carefully and accurately these M%
terials may have been purified and cleansed by artificl#
processes. It seems to be impossible for instance
provide even distilled water so pure, but what some
traces or other of foreign matter may be detected in it

CHAP. IIL FUNCTION OF NUTRITION.

CHAP. IV.

FUNCTION OF NUTRITION CONTINUED — Period 7.

ASSIMILATION (223.). — PRUNING (225.). — GRAFTING (297.).
— DEVELOPMENT (230.). — NUTRITION OF CRYPTOGAMIC
PLANTS (233.). — PARASITIC PLANTS (234.). — DURATION OF
LIFE (235.1). — VEGETABLE INDIVIDUALS (2363): — LONGE-
VITY OF TREES (239.).

SEVENTH PERIOD OF NUTRITION.

(223.) Assimilation. — Tux chief end and object of
the various processes which we have been describing, is
the manufacture of the materials which are ultimately
© be assimilated into the vegetable structure, and by
Which it is to be nourished and developed in all its
Parts. Of the precise manner in which the assimilation
of this nutriment takes place we know nothing, and
the first steps towards the formation and development
of any organised being are entirely concealed from us.

e may indeed observe when a gradual organisation of
Matter is taking place; but there is no stage in the
Process from whence we may not refer back to some
Previous state, out of which it appears to have emerged.
imperceptibly and inexplicably ; and it is utterly im-
Possible to note with any degree of accuracy, either the
Precise manner or exact time when the first traces of
any new condition of organisation commenced. In other
Words, as soon as we can distinguish an organ it already
exists in a developed form, however faintly its subor-
dinate parts may be indicated.

(224.) Growth of the Tissues,—In dicotyledonous
trees, as we have observed (art. 34. 2.), the new tissue
Makes its appearance between the old wcod and old

Q 2

tsa i acai anor

ee

=

. 228 PHYSIOLOGICAL BOTANY. PART Iie

bark. In the earliest stage in which it is discoverable
it appears as a thick clammy fluid termed the cambium,
which gradually assumes the character of a new!y
formed cellular tissue intermixed with vessels which ar?
disposed longitudinally through the stem. It shoul
seem that the cellular tissue at least is developed fro™
the old tissue, as may be shown experimentally by
grafting a branch containing a wood of one colour 0?
tree whose wood is of a different colour as a peach OP
a plum. The new wood retains the distinctive cha-
racters of the parts round which it is formed, the gra J
increasing by pale-coloured layers and the stock by layers
of a reddish colour, even though these latter have bee?
nourished by the descending sap elaborated in the leave
of the former. Different theories have been proposed 1”
order to account for the manner in which the cellula"
tissue increases. Some suppose that the young cells
are developed within the old ones, which they ulti-
mately rupture and replace; but of this there is n°
good evidence. Others consider the opaque dots dis-
-cernible on the surface of some cells to be nascent
vesicles, which are afterwards developed on the outsia€
of the old ones ; and this is a more probable hypothes#
than the last. According to a third opinion, an 0%
cell becomies separated into compartments by the form-
ation of a transverse diaphragm, and each compati-
ment afterwards develops into a separate cell. The
formation of the fresh vessels is still more ambiguo”?
than that of the cells. One theory considers them a24
logous to descending roots proceeding from the bud’
‘placed in the axille of the leaves, and supposes the
to be continuous throughout the whole length of tne
longest stems. But as vessels are formed, though ”
small dimensions, in those parts of the stem which are
below the place where a ring of bark has been remov®’’
this supposition is untenabie. It seems more proba
that the vessels have a common origin with the vesicles»
or are modifications of them ; and that a long vessel W?
originally composed of several parts.

CHAP, IV. FUNCTION OF NUTRITION. 229

(225.) Effects of Pruning. — The objects to be ob-
tained by pruning are various. The gardener employs
this resource as the means of improving the general
form which he wishes his ornamental shrubs to assume ;
and he prunes his fruit trees in order that they may
bear fruit of larger size and improved flavour. With
these questions we have nothing to do in this place.
The results of pruning which we propose to notice
are such as are produced internally at places where
the knife has been employed, particularly for the pur-
Pose of improving the quality of timber. This is at-
tempted by removing superfiuous branches, which com-
pels the main trunk to become a straight clean shaft. The |
effect of every wound of this kind is to expose a portion ;
of the older or innermost parts of ‘the woody layers
Which are incapable of generating fresh tissue. The
Consequence is that such parts cannot be healed over
excepting by the growth of the newest tissue round the
edge of the wound. This tissue gradually extends
itself from the edges over the whole surface of the
Wound until the opposite sides meet, and then grafting
together unite into one continuous mass: but the new
Wood contracts no union with the surface of the old
Wood exposed by the operation of pruning. As the
growing tissue which coats over a’ wound depends
Upon the returning sap for its supply of nutriment, no
Wound produced by cutting off a branch at some dis-
tance from the main trunk can ever heal. In this case
there are no leaves beyond the exposed surface to supply
‘It with proper juice, and whatever descends from the
Main stem is carried into the branch, and consumed
in developing the buds and tissue on the lower part
of it before it can arrive at its extremity. But where
the branch is lopped near the trunk and a “snag”
(as it is technically termed) has been left, the descending
Sap flows into this stump in sufficient abundance to
enable the tissue to close over the exposed extremity.
As the trunk increases these snags are completely em-

edded and greatly injure the timber ; especially as they
a 3

if

ay
TR
EPE
Ai,
1 i
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a j
di

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230 PHYSIOLOGICAL BOTANY. PART Ii-

generally become more or less rotten at the exposed
extremity before the new tissue has had time to coat it
over. Of all descriptions of wounds those which ar
the nearest to the main stem heal the quickest, 22

this shows us the propriety of pruning as close as pos-
sible to the trunk, whenever a branch is to be remove

for the purpose of improving the timber. The new
tissue increases with great rapidity chiefly from abov®
downwards, but also from the sides of the wound, a?

a little likewise at the base, until it has spread over thé
whole surface. The extent of the injury introduce

into the timber is best seen by forcibly separating the
new wood from the surface over which it has spread ;
when the latter will always be found exactly as it wa
left at the time it was covered up, with the mark of the
knife upon it or with any portions of decay which may
afterwards have taken place. This is sometimes see?
in trees upon which deep inscriptions have been carved.
Wherever the letters have penetrated below the bark
into the woody layers an impression is left in them ; a?

however long the new wood may have been forme

over them, they will be found beneath it whenever the
outer portion is removed. Birds’ nests, stags’ horns»
an image of the Virgin Mary, and many other articles

_are described as having been found in the very heart 0

some trees, where they were unquestionably embedded
by the enlargement of the stem in the way we have de-
scribed.

(226.) Precautions to be observed in Pruning.—
From what we have stated it is evident, that wherev@
a branch has been pruned off a blemish is inevitably
mtroduced ; and consequently where pruning can ”
avoided it should never be resorted to; but where it
is really necessary it should be performed as early 4
possible, before the branch has attained any consider-
able dimensions. Even rubbing off the buds should be
preferred to regular pruning. The cut also should be
made close to the stem, and as nearly vertical as po
sible; the latter precaution prevents the accumulatio®

CHAP. IV. / FUNCTION OF NUTRITION. 231

of water upon the surface of the wound, after the newly
developed wood has formed a swollen border round its
edges. If the cut is perfectly smooth it will be the
Sooner healed ; and its surface may. be protected by
some compost (such as that which is known by the
name of Forsyth’s mixture) whenever the wound is un-
avoidably large. An opinion has gone abroad that it is
Possible to diminish the blemish which pruning neces-
sarily occasions in timber, by lopping the extremities of a
branch and causing them to die and rot off in a natural
Manner. Supposing it were true that a branch thus
treated always did die,—which is by no means a neces-
Sary consequence, —all that could be gained by such a
mode of proceeding would be the introduction of the
rotten stump of the lopped branch into the heart of the
tree instead of the clean scar which close pruning pro-
duces, It is not true, as some suppose, that any na-
tural sloughing off of the decayed part takes place
or that the old and new wood can ever completely
Unite together ; but in all cases it will be found that
the new wood has grown over the old wound, and that
the surface of the latter is preserved exactly in the
state in which it was embedded. The knots in deal
and other timbers are defects produced by the process
of “natural pruning,” as it has been termed, and such
defects are inevitably greater than those which result
from artificial pruning performed on branches of the
same dimensions and cut off close to the stem.

(227.) Grafts. — Every one is acquainted with the
fact, that certain portions of some plants may be grafted
upon others, and that the tissues of the “ graft” and
s stock” as the two are named will completely unite
and vegetate together as though they were parts of the
same individual. The effects thus artificially produced
are occasionally observed to take place naturally : two
branches of the same tree being sometimes found
grafted together, where they have been wounded by
Mutual attrition. When ivy has grown to a consider-
able size its branches often interlace and graft together

Q4

ine aa r

zsm
ata Lg aiii

234 FHYSIOLOGICAL BOTANY. FART Il-

thorn is capable of sustaining a greater degree of cold
than it otherwise could. In some cases the crop of
fruit is increased, in others it is diminished ; and some
plants which are naturally climbers become more
bushy, &c.

(230.) Development. — The process of development
never appears to be entirely stationary in the living
plant, not even during winter when the repose of vege-
table life is the most marked ; but a slight progression
of the sap is still going on and a trifling enlargement of
the buds is gradually taking place. As the spring ad-
vances the vital energies revive and vegetation seems
to awaken ; a sudden and rapid flow of the sap towards
the extremities takes place, and the buds begin to de-
velop with great rapidity. It is evident that the in-
creased temperature of the atmosphere is a stimulating
cause in producing these effects ; and they may be par-
tially accelerated or retarded by artificial means.
for instance a branch of any tree growing in the ope?
air is introduced into a hothouse during the wintet>
the buds upon it swell and put forth leaves although
the rest of the tree continues bare.

(231.) Vernal Development. — The different degrees
of vigour with which buds burst forth in spring 1?
different years, is probably regulated by the quantity
of nutriment which has been prepared and laid up 1 ~
the stem during the previous summer ; so that a moré
rapid development will take place after a fine seaso!
than after a bad one. The extraordinary activity which
vegetation evinces in the spring, appears to depend upo”
the great freshness of those parts by which the severa
processes of nutrition are then conducted. New fibres
have been formed at the roots during the winter, a!
their absorbing powers now act with the fullest energy $
the young leaves have their vessels and vesicles quite
fresh, and unobstructed by the deposition of those
earthy matters which are afterwards found in the™
when the exhalation of moisture from their surface
has been going on for some time. If a branch of the

CHAP, IV. FUNCTION OF NUTRITION. 235

Vine, sycamore, and many other trees be cut off at this
Period, the sap often flows with sufficient rapidity to
fill a bottle in a few hours. As the summer advances
this action gradually diminishes ; but in the autumn it
is again partially renewed.

(232.) Autumnal Development. — The buds formed
in the axils of the leaves of many plants have attained
by autumn a sufficient size to attract the sap towards
them, and then they undergo a partial development,
which however is soon checked on the approach of
winter. In a few cases, as in the Lombardy poplar, this
autumnal development is sufficient to furnish the ex-
tremities of some branches with leaves which remain
for some time after the older leaves have fallen. This
always takes place in mulberry trees in those countries
where they are stripped for the purpose of feeding silk-
worms. The buds then become the centres of attraction
to the rising sap, and soon developing furnish the trees
with fresh leaves which replace those that have been
removed. Such a tree lives as it were two years in
one, but is always proportionably stunted and injured in
its growth.

(233.) Nutrition of Cryptogamic Plants. — The
higher tribes of cryptogamic plants possess true roots
and leaves; and we may suppose their function of nu-
trition to be carried on in a way which differs little
from that in which it proceeds among phanerogamic
Species. But the manner in which the lower tribes
whose nutritive organs are not distinguishable into roots
and leaves complete the function is in great obscurity,
and few attempts have hitherto been made to elucidate
the subject. .

(234.) Parasitic Plants. — There are certain plants
which are without the means of providing nutriment
for themselves or of elaborating the crude sap into
proper juice but obtain their nourishment immediately
from other plants to which they attach themselves,
and whose juices they absorb. Such plants are true
“ Parasites.” They are distinguished from “ Epi-

a

Sapte ee ee

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ane oe ns ea SR ER SES EE
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F39 PHYSIOLOGICAL BOTANY. PART Ib

in various places, till the whole forms a rude network
upon the trunk of the tree up which it has climbed.
Although it is so easy for two parts of different in-
dividuals of the same species to graft together, it
requires great care and precaution to secure such 4
union between two different species. In dicotyledonous
plants the two alburnums and the two libers must be
placed in contact, and then the line of junction betwee?
the two cambiums will also be complete and the newly
formed tissues wili readily unite. De Candolle thinks it
likely, in contradiction to the common opinion, that the
ascending sap being attracted by the graft will first
produce a union between the two alburnums, and that
the descending sap then effects the union of the tw?
libers. The chief requisite in this operation is the
near relationship of the two species; and it never suc-
ceeds excepting between such as are of the same genus
or at least between allied genera of the same family-
The ancients were of a very different Opinion, and cor-

sidered it possible to graft any two plants together

Thus Virgil: —

“ Et steriles platani malos gessere valentes :
Castanee fagos, ornusque incanuit albo
Flore pyri ; glandemque sues fregere sub ulmis.”

Pliny has recorded a marvellous instance of a grafted
tree bearing a variety of different fruits, which he tells.
us he himself saw. ‘ Tot modis insitam arbore!.
vidimus, omni genere pomorum onustam: alio ram?
nucibus, alio baccis, aliunde vite, ficis, piris, punicis,
malorumque generibus. Sed huic brevis fuit vita.” *
As we must not doubt that Pliny saw the specime?
to which he here so pointedly alludes, we cannot other-
Wise explain the fact, than by supposing him to have
been imposed upon by a practice which it is said is sti
resorted to in Italy, for amusement or deceit. The
French have termed it the “ Greffe des Charlatans
It consists in cutting down a tree, as the orange, tO

* Lib. xvii. ch. 17. sect, 26.

CHAP. IV. FUNCTION OF NUTRITION. 233

within a short distance of the ground ; then hollowing
out the stump and planting within it several young
trees of different species and families. In a few years
the whole grow up together so as completely to fill the
cavity, and on a superficial observation appear to have
become blended or grafted into a single stem. ‘The
deception is still more perfect if a few buds have been
left upon the stump to keep this alive also.

(228.) Kinds of Grafts. — M. Thouin has de
scribed about a hundred different ways in which the
process of grafting may be varied. These may however
be referred to the three following general classes.

1. By Approach. — Two plants are placed near
each other, and their boughs grafted together whilst
they are still on the stems. When they have become
completely united, one is then severed from its own
stock and left to grow on that of the other.

2. By Slips. — A shoot is taken from one tree and
placed on the extremity of a branch of another properly
prepared to receive it. The branch is cleft and the
graft inserted into the notch in various ways, which
more peculiarly form the study of the gardener. This
graft is made in the spring when the sap is rising.

3. Budding. — A piece of bark is removed from a
tree at a place where there is a bud ; and a’piece of the
same dimensions is taken from another tree also con-
taining a bud and is then placed on the exposed alburnum
of the former tree. The branch is tied tightly above
the graft in order to force the rising sap into it. This
graft is practised both in spring and autumn.

(229.) Effects of Grafting. — It does not appear that
the graft produces any decided effect upon the stock, as
we have already remarked (art. 224.) ; but in certain
instances the reverse seems unquestionably to be the case,
The influence is rather to be attributed to some dif-
ference in the mode of growth in the two subjects,
than to any dissimilarity between the two saps of the
stock and graft. Thus the lilac grafted on the ash be-
comes a tree, and the Mespilus japonica on the haw-

i

236 PHYSIOLOGICAL BOTANY. PART I `

phytes,” which also grow on the stems and branches
of trees, but do not penetrate their bark or absorb
their juices. There are a vast number of cryptogamic
plants among the ferns, mosses, and lichens, which
are epiphytic, as are also several species of certain
phanerogamous tribes. This is particularly the case
with those Orchidee which are termed “ air plants,”
whose roots imbibe moisture from the atmosphere as
we noticed in art. 39. Among the true parasites,
some cryptogamic species live wholly within the plant
and may be considered analogous to intestinal worms ;
whilst such as are external (both cryptogamic and
phanerogamic) may be likened to the ticks and lice
which infest. animals. Different species are parasitic
on different parts of plants as-on the root, stem, OF
leaves. Some of the cryptogamic species are highly
destructive to our crops, as those which cause the
“smut” and “rust” in corn. It is difficult to as-
certain in what manner the impalpable powder into
which their sporules disperse is introduced within the
very substance of the plants attacked ; but it seems not
improbable that it may be imbibed with water by the
roots. Some suppose it may be introduced through the
stomata, but this is not so plausible an opinion as the
former. All the phanerogamic species except those of
the natural order Loranthee (to which the common
misseltoe belongs) are destitute of green leaves; these
organs appearing only in the form of small brow?
scales without stomata, and incapable of performing
the functions of respiration. Hence these plants have
a livid and discoloured appearance. They are furnished
with suckers which penetrate the bark and absorb the
proper juices of the plants on which they grow, and
which are always dicotyledonous. It is remarkable,
that the flower of largest dimensions hitherto discovered
is a parasite of this description. This is the Rafflesi@
Arnoldi (fig. 159.) whose corolla measures a yard i?
diameter and is fifteen pounds in weight. It grows i?
the island of Sumatra upon the woody stems and roots

CHAP. Iv. FUNCTION OF NUTRITION. 237

of a trailing plant (Cissus angustifolia). In our own
country the genera Orobanche, Cuscuta, Lathrea, Mono-

tropa, and Epipactis afford us leafless parasitic species.
These do not appear to be very injurious to any woody
plants which they attack; but such as grow on herba-
ceous species are highly mischievous. The species of
c Cuscuta” are among the most curious of this kind.
When they first germinate they have a stem formed
like a delicate thread, which is leafless and soon coils
itself round the stem of some plant growing in the
neighbourhood. To this it adheres by means of suck-
ers formed of wart-like protuberances at intervals along
its stem. When it has obtained firm hold of the plant
round which it has coiled, its root decays and the
stem ceases to have any connection with the soil, but
vegetates and produces flowers at the expense of the
proper juices of the plant to which it is attached. The
common misseltoe and other Loranthex being furnished
with green leaves are “able to elaborate crude sap into
proper juice ; but as they are destitute of any true
root they possess the property of penetrating through
the bark of the trees to which they are attached, and
of fixing the base of their stems into the wood be-
neath. Thus they absorb the rising sap in its progress
towards the leaf. It is asserted that a branch of mis-
séltoe when placed in water has no power of absorbing
this fluid, but that when the branch to which it is still

————

eee
core.

ote sa

Eer

238 PHYSIOLOGICAL BOTANY PART H-

attached is immersed, then the water is readily ab-
sorbed and penetrates into the misseltoe itself.

(235.) Duration of Life. — Some plants exist only
for a few days or weeks, others for about a twelve-
month or two years, and others again for a very length-
ened period. Some when they have once flowere
and perfected their seeds immediately die; and these
in consequence are termed “€ Monocarpeans.” Others
annually produce a fresh crop of seeds, and are termed
“ Polycarpeans.” The difference between them is more
apparent than real ; for although in the ordinary course
of things the Monocarpeans soon die, the natura
period of their existence may be considerably extended
beyond the usual period, by merely preventing the form-
ation or development of their seed. This shows U
that it was the effort of the plant to form seed which
checked the functions of nutrition, and not that the
period of its existence was necessarily so limited 2$
its early death would seem to indicate. Some plants
which are annuals in our stoves are perennials in their
native country. The American aloe (Agave american@
is a striking example of a plant, the ordinary period
of whose existence may be very considerably extended
by preventing its flowers from developing. In its na-
tive climate it comes into blossom when four or five
years old, and afterwards dies; but in our greenhouses
it continues to vegetate for fifty or a hundred years
without showing any symptoms of putting forth its
flowers. If then we make abstraction of those checks
which are given to the vital function by the process 9
fructification, and which do not appear formidable in
any degree to the life of perennial species, we migh
imagine it possible for plants to continue vegetating for
a much longer period than they naturally would; a?
that the life of some might be extended indefinitely,
provided the external or accidental causes which tend ©
produce decay and death were continually removed. BY
this we mean, that certain plants never die from the
effects of old age in the same sense in which we apply

CHAP, IV. FUNCTION OF NUTRITION. 239

this term to animals, but are as well qualified to perform
all their functions with vigour and precision after they
have existed for many years as when they were young.
The causes why such plants perish are not merely those
common accidents which result from the influence of
the weather, the ravages of animals, and the like ex-
ternal accidents, but likewise the continually increasing
difficulty they meet with in procuring sufficient nutri-
ment. The increasing length of their branches affords
greater hold to the wind, and renders them proportion-
ably more liable to be broken off and rottenness to be
introduced in consequence. But in speaking of the dura-
tion of life in plants, we ought to have some definite
notion of what we mean by a vegetable individual.
(236.) Individuality of elementary Organs. — Some
persons consider every vesicle and other elementary
organ of which plants are composed, to possess a dis.
tinct and separate existence of its own; and therefore
they look upon every specimen as an aggregate of ve-
getable individuals, closely packed, together and con-
stituting a compound individual, The main facts upon
which this singular hypothesis reposes are the follow-
ing. — There are certain plants among the lowest tribes
which consist of only one or at most of very few distinct
vesicles, which indicates the possibility of a single de
tached vesicle existing as a separate individual. It
may be observed however that these plants are among
some of the most minute objects of organised matter,
and that we know very little of their actual history
and scarcely any thing of 4heir physiology. Another
argument in favour of the individuality of each vesicle
is deduced from a belief that the cellular tissue in every
part of the vegetable structure is capable of producing
buds or gems, each of which is able to exist separate
from the plant on which it was developed, and by
Proper treatment to become an individual plant similar
to its parent. M. Turpin has recorded a very in-
teresting and remarkable instance of this description,
where a leaf of an Ornithogalum after it had been

QAO PHYSIOLOGICAL BOTANY. PART 15-

placed between some sheets of paper for the purpose of
being dried for the herbarium, threw out a multitude
of minute bulbs from ali parts of its surface. He con-
cludes that each separate bulb was only a more deve-
loped state of a single cell, and hence he would draw
the inference that each cell must be a distinct individual.
But if this conclusion were admitted, the same thing
might be asserted of every organ which produces 4?
embryo of any kind. It would perhaps have been more
logical to have considered each cell as an embryoni¢
sac, capable of originating a distinct individual of the
same complicated form and structure of which it was
itself only a subordinate organ. If each vesicle wer
an individual plant, its offspring if we argue from
analogy ought to resemble itself, and to be a vesicle
and not a bud with a complicated arrangement ©
parts representing in miniature the several organs of the
entire plant. This hypothesis of the individuality of
each vesicle according to our acceptance of the ter™
appears to be untenable.

(287.) Individuality of Buds.— A second hyp.
thesis considers each bud as a separate individual, pos-
sessed of a vitality independent of that of the whole
plant. This view is considerably supported by the
great analogy which exists between the structure °
a plant considered in this light and that of some °
the lower tribes of animals. The reproduction of pe
lypi is effected by means of little bud-like protuber-
ances on their surface, which having attained a cer-
tain degree of development quit the body of the pare?
and become separate individuals. Thus also if t e
buds on the stem of a tree are removed and treaté
with proper precaution, they will grow and become
trees themselves. Some buds are detached by a natur?
process, and the plant is ordinarily propagated by this
means, Thus the death and decay of the orange lily
(Lilium bulbiferum) causes the little bulbs which a?
produced in the axils of its leaves to detach from the
stem ; and these upon falling to the ground become?

t

CHAP. IV. FUNCTION OF NUTRITION. 241

so many individual plants. The runners of the straw-
berry decay when the buds at their extremities have
Obtained a firm root in the ground, and thus the
Parent plant becomes separated from the numerous;
Progeny scattered around it. But the closest ana-
logy between a plant, considered as an aggregate \
of individuals, and any living animal, is that which |
exists in certain marine tribes still lower in the scale of i
Organisation than the polypi to which we have referred. d
A number of these animals are grafted and blended to-
gether into a compound mass, in which each still
Possesses its separate individuality, and is capable of
existing in a detached form. It is by the joint labours
of these compound animals that a coral reef is raised
from the bottom of deep seas to the surface. The
innermost and oldest parts of the reef consist of the
Untenanted cells of those animals which have died,
Whilst a fresh crop is continually developing towards
the surface. Thus also in a tree, the oldest parts of
the trunk and branches is composed of matter in a dead
or dying state, and it is the newly developed portions
alone which contain the living materials capable of per-
forming the functions of vegetation. As these latter
Portions originate from successive crops of fresh buds,
the analogy alluded to is very complete,

It has been further observed, that if each bud be not
a separate individuality, we might, by grafting several
buds on the same stock, produce a tree composed
of a multitude of species; which would be an ab-
Surdity. .

(238.) Individuality of Plants.— Any cutting, layer,
or bud, which has been detached from a plant, and
grown in an isolated state, always retains the exact pe-
Culiarities of the individual plant from which it was
Obtained ; but a seedling, raised from the same plant,
will frequently deviate more or less from the original
type, and present us with certain peculiarities of its
own, ‘This fact appears to favour another hypothesis,

R

242 PHYSIOLOGICAL BOTANY. PART Ie

distinct from the two already explained, which con-
- siders the vegetable individual, in the most usual ac
ceptation of the term, as an entire plant which has
originated from the development of a single seed. But
this definition of an individual involves the seeming
absurdity, that an organised being may consist of severa
detached portions, each of which may exist apart from
the others. Thus a cutting from a tree is a part of
the individual from whence it was taken; and thoug
it may also become a tree, it is no more than the
developed state of a portion of the former. Since al
the weeping willows in Europe, for instance, are sait
to have originated from cuttings taken from a single
tree; according to this hypothesis, there is no more that
one weeping willow in Europe, and that also can only
be a portion of one which may be still growing in Asia-
But whatever be the speculations of physiologists, W?
must admit the truth of the remark, “ that in ordinary
parlance we require some more precise mode of express”
ing ourselves, when we would speak of the individu
weeping willow which shades the grave of Napoleo®
at St. Helena, as bemg the same plant which decorates
the tomb of J.J. Rousseau at Ermenonville, althoug”
each may probably have originated from the same em
bryo.” But if we cannot, in the present state of know-
ledge, exactly determine the requisites which constitute
the individuality of vegetables, and may possibly co”
sider as a separate existence what in reality constitute?
the duration of a succession of individuals ; yet whilst
we choose to put such a limitation to our ideas, we may
speak of the duration of life in a plant as the real €¥
istence of an individual, whether this plant may have
- originated from a seed, bud, cutting, or from any othe”
mode by which it could be propagated.

(239.) Longevity of Trees.—When we consider each
separate plant as an individual being, there is this m3-
nifest and important distinction between the mode il
which its life is maintained, and that in which oF
continued in any animal ; — the plant annually renew?

CHAP. IV. FUNCTION OF NUTRITION. 243

all the different organs by which its various functions
are carried on, and which are consequently as vigorously
performed in the oldest tree as in the youngest. But
although the organs which every animal possesses are
continually sustaining a certain degree of repair, yet
they are gradually wearing out, or ultimately become
choked up in old age; and thus a definite period is
naturally allotted to the existence of the individual
from this cause alone. But the period of life to which
plants attain is no way dependent on these conditions ;
but is regulated by a combination of external causes
and internal influences of a very different kind. Those
trees are most likely to endure the longest, which grow
the slowest, and which attain the least height in pro-
Portion to the diameter of their trunks ; and the anti-
quity of some trees of this description appears to be
prodigiously great.

(240.) Estimation of the Age of Trees.—— It is only the
ages of Dicotyledons which can be ascertained with any
degree of certainty. In Monocotyledons the diameter of
the tree is not enlarged by annual additions of fresh
cylinders of wood, as is the case with the former, whose
ages may be accurately ascertained by inspecting a
transverse section of their trunks. By placing a strip
of paper upon this section from the centre to the cir-
cumference, and marking it along the edge where it
intersects the concentric circles on the section, a con-
venient register may be obtained, not only of the ages
of different trees, but of their comparative rates of in-
crease at different periods of their growth. As the pith |
is seldom exactly in the centre of the tree, the best mode
of obtaining the average annual growth is by measuring
the circumference of the trunk, and then calculating for
the mean thickness of each layer by dividing the semi-
diameter by the whole number of layers. These mea-
Surements should be made at a little distance above the
Soil, generally about four feet, where the trunk is free
from protuberances and of an average thickness.

. R 2

DAA PHYSIOLOGICAL BOTANY. PART Il-

Where a complete section cannot be obtained, a la-
teral incision may be made, and by counting the number
of rings in the portion exposed, an approximation may
be made to the whole number ; care being taken to make
allowance for the more rapid increase of the trunk in
the early stages of its growth.

In other cases, some judgment may be formed of the
ages of very old trees, by ascertaining the rate at which
others of the same species have increased within know?
intervals of time, and by then applying the rule thus
obtained to the tree in question. The observer must
be cautious when he is examining very large trees, lest
he should be deceived by several trunks having become
blended into. one.

(241.) Examples of Longevity in Trees. — As ex-
amples of the mode in which approximations have been
made towards the ages of very old trees, we may men-
tion certain individuals of the lime, yew, and baobab.

1. The Lime. — A tree of this description was
planted at Fribourg in Switzerland, on the day whe?
the news of the victory of Morat arrived, in 1476.
In 1831, this tree was 13 feet 9 inches in circum-
ference, which gives 13 lines in diameter per annum
as the mean raté of its increase. But as this tree
is confined in a town, we may allow 2 lines per a!-
num as the rate of increase for other trees more freely
exposed, whose ages we may wish to ascertain. Now,
there is a lime near Neustadt on the Kocher, in the
kingdom of Wurtemberg, which was of large dimer-
sions in the year 1229 ; since it is stated in ancient
records, that the city was rebuilt after its destructio”
in that year, “near the great tree.” A poem, bearing t $
date of 1408, describes this tree as having its branches
at that time supported by 67 columns. Evelyn, n
1664, mentions the number of columns then to have
been 82; and in 183r they had increased to pon
At this period, the trunk was 37 feet 6 inches an
3 lines (Wurtemberg measure) in circumference, be-
tween 5 and 6 feet from the ground. This, upor an

`

CHAP. IV. FUNCTION OF NUTRITION. . 245

estimate of 2 lines per annum for its growth, would
make it to be between 700 and 800 years old. - But as
it is certain that it has not increased for some centuries
at so rapid a rate, it may fairly be considered as above
1000 years old.

2. The Yew. — M. De Candolle ascertained, by in-
specting three yews which had been felled, that they
had grown at the rate of 1 line in diameter per annum
during 150 years ; and that one of them had in-
creased somewhat less rapidly during the succeeding
century. The rate thus obtained, he applies to the
growth of some English and Scotch yews, whose di-
mensions were given by Evelyn in 1666, and Pennant
in 1770. Among these, is a yew which the former
describes as growing in the churchyard of Braburn in
Kent, which was 58 feet 9 inches in circumference, or
2890 lines in diameter ; indicating by the above rule, as
many years for its age. If now living, this tree, according
to such an estimate, would be more than 3000 years old.
It may be doubted from the following account, whether
the rate at which the yew increases in England is not
more rapid than in France. There are two fine healthy
trees of this kind in the churchyard at Basildon in
Berkshire, which, according to the parish register, were
planted in 1726. In #834 they were very nearly of the
same dimensions, and the largest measured 9 feet 3 inches
in circumference at 4 feet from the ground : this gives
444 lines for its diameter, or 4 lines per annum as the
mean rate of increase for a century. It appears how-
ever by some other entries in the same register, that
the tree had grown more rapidly during the former
half of this period than it has done latterly. Taking
these data as a guide for estimating the ages of some
old yew trees in the churchyards of two neighbouring
parishes, it would seem that De Candolle’s calculations
should be reduced by about one third, in order to ob-
tain a more correct approximation than that which he
has given for trees of this description. It was found,

R 3

246 PHYSIOLOGICAL BOTANY. PART Il.

for instance, that the layers of wood at different depths,
in a hollow yew tree at Cholsey, Berkshire, varied con-

_ siderably in thickness ; and that some of those which —
had been very recently deposited were 24 lines, whilst
others, which were more than a century older, were
only half a line in thickness. This tree is between 14
and 15 feet in circumference ; and there is another in
_ the churchyard of the neighbouring parish of Aldworth,
which is more than 19 feet in circumference, which,
estimated by De Candolle’s rule, ought to be above 900
years old; but may rather be considered as nearer 600
years.

3. The Baobab (Adansonia digitata.) — The last ex-
ample which we shall select, is that of the enormous
baobabs, or monkey-bread trees of Senegal, whose great
ages Adanson has attempted to estimate from the fol-
lowing data.

Thevet mentions, in his “ Voyages aux Isles Ant-
arctikes,” in 1555, some “‘ beaux arbres,” which Adan-
son found to be 6 feet in diameter in 1749. He
judged, from Thevet’s expression, that these trees could
not have been less than 4 feet in diameter at the time
when he saw them ; and this opinion was strengthened
by observing the extent to which the letters of certain
inscriptions upon them had become deformed, and which
inscriptions were dated from the fourteenth and fifteenth
centuries. Allowing therefore that these trees had in-
ereased 2 feet in diameter during two centuries, he
estimated their age at 600 years. But there are trees
of this species which are 30 feet in diameter ; and these,
at the above rate, would be 3000 years old. But
if the age of these trees be calculated upon mathematical
principles, it should seem that they must be much
older even than this. Thus, Adanson having ascer-
tained that a tree of 1 year old was 5 feet in height
and 1 inch in diameter, and a tree of 30 years was
22 feet high and 2 feet in diameter, he applied these
data to construct a table, which should give the heights

CHAP. IV. FUNCTION OF NUTRITION. 247

and diameters of trees from 1 year to 5000 years old.
From this we shall make the following extract : —

Age. Height. Diameter.
1 year. 5 feet. -fz feet.
30 22
100 29
210 40
660 53
1050 58?
2800 67
5150 73

It will be observed, according to this table, that the
ages of trees whose diameters are 6 feet would be no
more than 210 years; whereas it was satisfactorily
shown that those which Thevet had described must at
least be 600. So far then this table would underrate
rather than exaggerate, the ages of these trees. It
must be confessed that the estimate given for those of
the largest dimensions is too startling to be received
with implicit confidence ; and that we need further
evidence to satisfy us that these calculations are good
approximations to the truth. Be this as it may, it
seems to be sufficiently proved that the world is pos-
sessed of living monuments of antiquity, whose ages
surpass those of the most stupendous fabrics which
the labour of man has reared to perpetuate the memory
of his folly or his superstition.

(242.) Tables of Longevity of certain Trees. —
From various sources of information — some the re-
sults of direct observation, others the approximate values
obtained from the kind of inferences which we have
referred to — De Candolle has furnished us with the
' following list of remarkable trees, whose ages he con-
siders that he has succeeded in ascertaining with some

degree of precision : —

R 4

PHYSIOLOGICAL BOTANY. PART Ile

Years.

Elm - 335.

Cypress - 350 (about).

Cheirostemon 400 (about).

Ivy - 450.

Larch > 576.

Orange - 630.

Olive . 700 (about).
© Oriental plane 720 (and upwards).
. Cedar z 800 (about).
. Lime 1076—1147.
. Oak - 810—1080—1500,
. Yew ~ 1214—1458—2588—2820.
. Baobab - 5150 (in 1757).
. Taxodium - 4000 to 6000 (about).

CHAP. Y.

FUNCTION OF REPRODUCTION. — Periods 1, 2, 3.

PROPAGATION (248.). — ORIGIN OF FLOWER-BUDS (245.)- —
FLOWERING (246.).— FUNCTIONS OF THE PERIANTH (252+)
— DEVELOPMENT OF CALORIC (254.). — FERTILISATION
(255.). — FORMATION OF POLLEN (261.). — MATURATION
(265.). — FLAVOUR AND COLOUR oF FRUIT (273.).

(243.) Propagation.— Turns are two distinct modes,
according to which the propagation of the vegetable species
is naturally secured, viz. “ subdivision” and “‘reproduc-
tion.” In the first the individual plant may be subdivided
into several parts, each of which when detached from thé
parent stock is capable of existing as a separate individual.
A familiar example of this mode of propagation may
be seen in the common strawberry, to which we have
alluded in art. 237. It is very common to find elms;
poplars, and other trees throwing up suckers from thelf

CHAP. V. FUNCTION OF REPRODUCTION. — 249

roots at a distance from the trunk, all of which are
capable of becoming so many distinct trees, under fa-
vourable circumstances. Man has availed himself of
this property, to extend the means which nature has
provided for the propagation of the species ; and by
placing cuttings, slips, and buds under proper treat-
ment, he forces them to throw out roots; or he grafts
them on other stems, where they adhere and develop
as so many separate and independent individuals. The
process by which any detached portion of a plant be-
comes a distinct individual, similar to that from which
it was derived, depends upon the power it possesses
of reproducing those organs or parts in which it may
be defective. Thus the ascending organs develop roots ;
and these again, produce buds from which the ascend-
ing organs proceed.

(244.) Reproduction. — But although the propa-
gation of many plants may be effected by the means
here alluded to, and although some species are more,
frequently and readily propagated by subdivision, than
by the method which we are about to describe, yet
the greater number of plants, and at least all those
which bear flowers, secure the continuation of their
species by a distinct process, of a very different nature.
This constitutes the function of “ reproduction,” pro-
perly so called; which consists in the formation of
seeds, containing the germs of future individuals. This
function of reproduction is to the species, what life is
to the individual —a provision made for its continued
duration on the earth. The more minute details of the
process by which the function of reproduction is carried
on, and the germ or “ embryo” of the future plant be-
comes generated in the seed, were never understood till
of late. years; nor are they even yet so completely
ascertained as we may one day hope to find them.
The general function of reproduction may be consi-
dered as completed in five different periods; much in the
same manner as we ascribed seven periods or processes
to the function of nutrition.

950 PHYSIOLOGICAL BOTANY. PART IL

(245.) Origin of Flower-buds.— We find some buds
capable of developing into branches and leaves, and others
destined to produce fiowers: but it is beyond the limits
of our present faculties to ascertain by what law they are
thus specially inclined, in their nascent state, to as-
‘sume the one rather than the other of these characters:
That leaf-buds and flower-buds have fundamentally the
same origin, is apparent from an extensive review of
those singular deviations from the ordinary productions
of nature, which are termed Monstrosities, as we have
already stated in art. 85. The organs developed from
a flower-bud serve a temporary purpose, of a very dif-
ferent description from that assigned to those which
are developed from a leaf-bud ; and when that purpose
is completed, they soon decay. The causes which pre-
dispose the plant to produce a flower-bud rather than 4
leaf-bud must begin to operate long before we are able
to detect any traces of the bud itself ; and from the very
earliest period that we can perceive its existence, it has
already assumed the peculiar characters with which it is
destined to develop. It is asserted that in some palms;
the flower-buds which are to produce flowers during
seven successive years may all be detected at one time
in the inner parts of the stem. We may further notice
the manner in which the Lemne (Duckweeds) are pro-
pagated, as affording a striking argument in favour of
the common origin of all buds. Each plant is a little
green lenticular and frond-like mass, which produces 2
long pendent root from its under surface (fig. 31-)+
Its usual mode of propagation is by a bud or gem, which
makes its appearance on the edge of the frond, an
when fully developed, detaches itself and becomes 4
Separate individual. In some seasons however, 22
under circumstances suitable to such an event, thes?
plants put forth diandrous flowers, which originate
Precisely in those spots where the gems are usually de
veloped.

CHAP. V. FUNCTION OF REPRODUCTION.

FIRST PERIOD OF REPRODUCTION.

(246.) Flowering. — When the flower-bud is dis-
tinguishable, the parts of which the flower is com.
posed are in a very rudimentary state. The perianth
especially, continues for some time very small in pro-
portion to the anthers, which are more early deve-
loped. A gradual enlargement of all the parts of the
flower continues to take place till the period of ex-
pansion arrives. This expansion may be likened to
the age of puberty in animals; and when completed,
terminates the first period of the function of reproduc-
tion. In herbaceous plants, it is very frequently effected
the same year in which they have germinated from the
seed; but there are some which do not flower until the
second year, and others not until later, Some under-
shrubs also begin to flower within the year; others
not until after a second, third, or fourth has elapsed.
Shrubs and trees, with very few exceptions, never
flower before the second or third year at least, and
very many of them attain a considerable age before
they show any symptom of flowering. It may be as-
serted of trees, almost as a general rule, that the period
when they commence flowering is protracted in pro-
Portion to the slowness of their growth.

(247.) Stimulants to Inflorescence. — Although we
cannot comprehend the primary causes upon which
the formation of the flower-bud depends, we can con-
nect several phenomena which attend its development
with the operation of specific influences. For instance,
an increase of temperature accelerates, and a dimi-
nution retards the period of flowering ; and accord.
ing to the nature of the individual, these causes also
Operate in predisposing its buds to assume the cha-
racter of leaf-buds or flower-buds. Many plants, when
removed from a warm climate to a cold one, or vice
versé, will flourish without ever producing flowers ; and
Others which are able to flower, never perfect their

252 PHYSIOLOGICAL BOTANY. PART Il.

fruit. A superabundance of moisture retards the flower-
ing, and also affects the formation of flower-buds ; and
it is generally observable, that where the functions of
nutrition are forced into a state of unnatural excite-
ment, the plant has an increased tendency to produce
leaf-buds rather than flower-buds. Hence it is re-
marked, that when the fruit trees of temperate climates
are transplanted to the warm and moist regions of the
tropics, they frequently become barren, although. they
continue to push their shoots with vigour. To coun-
teract this effect, a practice is resorted to in the East
Indies, of laying bare some part of the roots, which
checks the growth, causes the leaves to fall, and thus
predisposes the plant to form flower-buds instead of
leaf-buds. At the period of flowering, the vital energies
of the plant seem to be called into extraordinary activity;
and the organs of inflorescence are developed with
great rapidity. An Agave fætida which had vegetated
in the Paris garden for nearly a century, and during
that period had scarcely shown any signs of increase,
during a warm summer began to show signs of flowering:
In eighty-seven days, it had grown twenty-two feet
and a half, and during one portion of this interval Ít
increased at the rate of nearly one foot per diem.

- (248.) Periods of Flowering. — The precise periods
at which a species commences flowering in different
years, range within certain limits, dependent partly
upon the state of the weather ; but it is very difficult
to appreciate all the causes which concur in modifying
them. It is evident that the annual distribution 0f
temperature produces a marked effect upon the perio

of flowering, and that this operates more decidedly 0”
those plants which flower in the spring, than on such
as flower later in the year. The almond, flowers at
Smyrna in the early part of February, in Germany
about the beginning of April, and in Christiania not
until the beginning of June. The vintage, howeve?
takes place at Smyrna the beginning of September, 3?

CHAP. V. FUNCTION OF REPRODUCTION. 253

in Germany about the middle of October ; a retardation
in this case which is less than in the former.

When a perennial has once begun to flower, it is
subject to periodic returns of this function. The period
of the year in which the flower expands, is regulated in
all cases by the peculiar character of each individual;
and it is very nearly the same for all plants of the same
species. There are, however, remarkable exceptions to
the laws by which the periods of flowering in different
Species are regulated. Advantage is taken of this cir-
cumstance ; and by propagating from such individuals /
as are both the earliest and latest in producing their |
seeds, peculiar “ races ” are gradually established, which |
secure to the cultivator a longer succession of a given |
crop than he could otherwise have obtained. De Can- |
dolle mentions an instance of a horse-chestnut at.
Geneva, which always flowers a whole month before |
the rest in its neighbourhood, without any apparent
cause for such precocity. These anomalies indicate
some peculiarity of constitution, or « idiosyncrasy, in `
the separate individuals ; but they determine nothing
against the existence of a general law, by which each
species is supposed to be regulated in producing its
flowers at a certain period of the year. A very abun-
dant crop of fruit generally absorbs so much of the
nutriment prepared in the stem, as to diminish, and
often entirely to prevent the formation of flowers
in the following season; and hence, some trees in
orchards- bear abundantly only on alternate years. As
double flowers produce no fruit, their stems are
not so thoroughly exhausted ; and perennials of this
description generally flower earlier in the season than
Single flowers of the same species. By far the greater
number of plants flower in the spring, and several
do so even before they expand their leaves. - In these
cases, the nutriment which has been prepared for the
development of the flower, must have been wholly
provided by the leaves of the preceding season, and
have been magazined through the winter in the stem.

254 PHYSIOLOGICAL BOTANY. PART It.

The peach, apple, and almond are familiar examples-
It sometimes happens, when the leaves have been de-
stroyed by drought or other causes, that a second crop
of flower-buds is developed late in the year ; the trees
having sustained a check in their vegetation, similar tO
what takes place in the winter, break out again as if it
were a second spring.

(249.) Periodic Influences. — The periods at which
the flowering of plants commences in different years, at
a given spot, appear to depend upon the mean distri-
bution of temperature per month, rather than upon the
mean annual temperature. Since some process or other
of the function of nutrition is carried on throughout the
year, and even in winter this is not entirely dormant,
there may very likely be a critical season, when some
defect of moisture, light, or temperature would be fatal
to the progress and perfection of a particular process;
and retard or completely prevent the flowering of
the plant at the proper time. When by a com-
bination of circumstances — partly dependent on the
peculiar constitution of the individual, partly on the
character of the species, and partly on external influ-
ences — the periodic return of a plant’s flowering has
‘been fixed within certain limits, to a given month i?
the year, it requires a certain lapse of time before
any alteration in the external circumstances to which
it may be subjected, can effect a decided change in this
period. Thus, it is observed that plants which are
transported from the southern to the northern hemi-
sphere, do not immediately accommodate themselves tO
the opposite condition of the seasons in which they are
placed, but for a while continue to show symptoms of
flowering, at the same period of the year in which they
had been accustomed so to do in their native climate. I”
some instances they are several years in accomplishing
_ the change, and sometimes even die before they ca"
effect it. The usual limits within which the periodie
returns of flowering in each species take place, are
always mentioned in the Floras of a given district ; a0

. CHAP. V. FUNCTION OF REPRODUCTION. 255

Linnæus and others have prepared tables of different
plants, which flower in each month of the year, under
the title of Flora’s Calendars.

(250.) Horary Expansion.— As the flowering of
different species takes place at different seasons of the
year, so also many species open their flowers only at
certain hours of the day. The greater number are
hot subject to any very marked law in this particu-
lar ; and their flowers, when once expanded, continue
open until they decay. Some flowers, as those of the
purple horned-poppy (Remeria violacea), expand early
in the morning, and their petals are so very fugacious,
that they are mostly fallen two or three hours before
noon. But there are many plants, as the Convolvulus
nil, which retain their corolla for several days, and
regularly open and shut it at certain hours. Linneus
prepared tables to express these facts, which he fanci-
fully termed Flora’s clocks. The following list may
Serve as a specimen.

re ae
Convolvulus nil.

Papaver nudicaule.
Convolvulus tricolor.
Sonchus oleraceus.
Anagallis arvensis.
Calendula arvensis.
Ornithogalum umbeilatum.

12. Mesymbrianthemum.

2. Scilla pomeridiana.
5—6. Silene noctiflora.
6—7. Nyctago jalapa.
7—8. Cereus grandifiorus.
10. Convolvulus purpureus.

He named those flowers “ Ephemeral,” which open |
Once only at a given time, and decay within the period
of a day; and those “ Equinoctial,” which open and
Close for several days at the same hour. Of these,

256 PHYSIOLOGICAL BOTANY. PART Il-

some are diurnal, others nocturnal. ‘ Meteoric”
flowers are such as are influenced by the state of the
atmosphere. A few of these as the Calendula pluvialis
close at the approach of rain; others as the Campanula
glomerata when the sky is clouded.

(251.) Stimulants to Expansion. — Light and not
heat appears to be the chief stimulus which regulates
the expansion of the blossom; and the influences of
moisture alone do not seem to affect it greatly; at least
plants when wholly immersed in water expand as
freely as in the open air. The phenomenon of their
alternately expanding and closing, is allied to the sleep
of the leaves (art. 155.), and like the periodic returns 0
flowering, appears to be regulated by the joint operation
of several causes, among which we must allow that the
peculiar idiosyncracy of each individual plays its part.
For independently of the effect produced by the external
stimulus of light, if a plant accustomed to flower at 2
given period of the day be removed to a dark room it
will still make an effort to expand its flowers at the
wonted hour. De Candolle proved this by shutting uP
some of these equinoctial plants, as Linneus terme
them, in a dark chamber by day and exposing them by
night to strong lamp-light. This treatment occasione
for a while the greatest irregularity in their periods 0
expanding ; but at length they became accustomed to the
change, and closed their petals by day and opened the™
by night. In some cases the expansion of the flower
is evidently influenced by the effects of light, heat, a2
moisture. The common dandelion (Leontodon tarat-
acum), when closed on a cloudy day, upon being
brought into the stove will immediately expand its plos-
soms, though it may now be exposed to less light 2?
more moisture than before. On the other hand, if the
same plant be exposed to the light of the sun, it will als?
expand though the temperature may be lower tha?
on a cloudy day, when it would continue shut.
has been often asserted and as frequently denied, that
the common sunflower will continue to turn its blos-

CHAP, V. FUNCTION OF REPRODUCTION. ZOT

soms to the sun during his diurnal course through the
sky. That such is not always the fact is easily seen,
for it often happens that a single plant is covered with
blossoms, which face all quarters of the heavens. It is
possible there may be some foundation for the opinion,
and that under a more genial climate this may be the
fact ; or perhaps the notion may have originated in some
confusion of ideas connected with the name of the plant,
which seems at least as much entitléd to its appellation
from the appearance of its flowery disk surrounded by
the glory of its golden rays, as from the very doubtful
property which has been assigned to it. An effect
of the kind alluded to is sometimes strikingly exhibited
in such flowers as Hypocheris radicata, and Apargia
autumnalis; which may often be seen in meadows
where they abound, most evidently inclining their
blossoms towards that quarter of the heavens in which
the sun is shining.

(252.) Functions of the Perianth.— The universal
Presence of the stamens and pistils in every species
of flowering plant, and the frequent want of a corolla
and in some cases of a calyx also, appear to indicate
that the functions of the two outermost whorls of
the flower forming the perianth, are not so essential
to the perfecting of the seed as the two innermost. In
Many cases indeed, where these whorls are not deve-
loped, some traces of their existence are nevertheless
apparent in the form of glandular protuberances or
Nectaries ; andit is possible that these may still perform
Whatever “function” more especially belongs to the
Perianth ; just as the green surfaces of stems which
do not develop leaves, perform the function of respir-
ation. One obvious use of the calyx and corolla,
When they are present, is to protect the inner whorls
from injury in the early stages of their develop-
Ment. It seems not unlikely that they may pri-
Marily be destined in some way to modify the ma-
terials which are provided for the formation of the
Pollen and ovules. In addition to the purpose which

ER

258 PHYSIOLOGICAL BOTANY. PART I

the calyx and corolla serve, of protecting the stamens
and pistils in the early stages of their development,
they occasionally perform a similar office at a later
period in protecting the seed. In some cases they
remain. attached to the seed-vessel in the modified
form of membranous or chaffy appendages, which
serve as sails to waft the seed to a distance. Some
of the most familiar and effectual contrivances of this
description are to be seen in the Composite ; such
as the common dandelion and thistles. In these cases
the down attached to each seed is only a modified for™
of the calyx.

(253.) Functions of the Nectary.— As the nectary
has been noticed in not fewer than seventy-two families,
and is found in a vast number of species, its use 15
probably of some importance in the general economy of
reproduction, though we do not know what this may
be. The most plausible conjecture that has bee?
offered supposes the secreted matter or nectar to be
discharged by the organ on which it is seated
near which it is placed, whilst it is elaborating the
juice for the use of the inner whorls. An important
secondary purpose which it serves is to allure bees 4?
other insects, which crawling over the flowers, and pass
ing from one to the other, facilitate the dispersion q
the pollen, and thus promote the fertility of the plant
in the way we are about to mention under our seco?
period.

(254.) Development of Caloric.—At the time of the
flower’s expansion a considerable development of heat
takes place in certain species, and there is also a rap!
formation of carbonic acid. This phenomenon is m0*
strikingly exhibited by some of the Arum tribe. The
spadix of the common arum (Arum maculatum) 2%-
tains a temperature of 7° R. or 4739 Fahr. above th?
of the atmosphere, and the Arum cordifolium in the
Mauritius has been observed to attain a temperature a
44° to 49° R. or 131° to 1421° Fahr. that of the sure
rounding air being at 19° R. or 742° Fahr. Thes?

CHAP. V, FUNCTION OF REPRODUCTION. 289

effects take place once only for each plant, and it seems
most likely that they are the result of some chemical
action, rather than of any physiological property.

SECOND PERIOD OF REPRODUCTION.

(255.) Fertilization. — Great progress has been made
within the last few years towards attaining an accurate
knowledge of the process by which the fertility of the
seed is secured. It had been long ascertained, that the
action of the pollen was somehow essential to this pur-
pose, and that the effect was also produced through the
intervention of the stigma; but the manner in which it
took place was not understood. Even the ancients had
obtained some vague notions on the subject, although
their speculations regarding this as well as most other
minute details in natural science were -replete with
error and absurdity. The general fact had forced itself
upon their attention in the cultivation of the date-
palm. As the blossoms of this tree are dicecious, the
distinction between those individuals which continued
barren and such as always bore fruit was of course
soon remarked ; and it was found to be necessary that
either some of the barren kinds should be cultivated
in the neighbourhood of those which bore fruit, or
else that bunches of their flowers should be suspended
near them, otherwise the fruit never attained per-
fection. Hence originated the custom of cultivating
only fertile plants, and of annually bringing bunches of
the sterile flowers from the wild trees—a practice
which has prevailed from the earliest periods of history
to the present day in Egypt, and those countries of the
East where the date forms a most important article of
human food. When the French were in Egypt in
1800, the events of the war prevented the inhabitants
from procuring the blossoms of the sterile or male
plant (as it is considered) from the deserts, and none
of the cultivated plants in consequence bore any fruit.

(256.) Erroneous Theory of the Ancients.— A prac-

s2

260 PHYSIOLOGICAL BOTANY. PART Il

tice has long prevailed in certain countries of the East
with respect to the cultivated fig, of a similar description
to that which is employed to fertilize the date, and
although the results are very different in the two cases;
it is only lately that this fact has been suspected.
Both phenomena were always considered of the same
class ; and an erroneous theory was formerly founded où
the mistake. Bunches of the flowers of the wild fig
are brought from the woods and suspended over the
cultivated plants, when a small insect (the larva of @
eynips) imported with the wild flowers punctures the
young fruit of the cultivated individuals, and accelerates
' their ripening — in the same way that we find a similar
effect produced in some apples and pears by the punc-
ture of the caterpillar of a small moth, which causes them
to ripen before the rest, and to fall sooner from the
tree. In consequence of the earlier ripening of the
figs occasioned by the practice alluded to, and which is
styled the caprification of their fruit, a second crop is
secured which might otherwise have failed, from being
produced too late in the season to allow of its attaining
perfection. It was in attempting to generalise from the
facts observed in the caprification of the young fig, that
the ancients asserted that a maggot (wy) was the effi-
cient cause of fertility in the date, and that this insect
crept from the sterile into the fertile blossoms before
the development of the fruit could take place.

The existence of a sexual distinction between indi-
vidual trees in such species as the date and some othet
dicecious plants, gave rise to another erroneous opinion,
and it was supposed that even plants where the stamens
and pistils were contained in the same flower were
nevertheless unisexual. Thus Claudian asserts —

« Vivunt in venerem frondes,omnisque vicissim
Felix arbor amat; nutant ad mutua palme

Foedera;populeo suspirat populus ictu ;
Et platani platanis, alnoque assibilat alnus.”

(257.) Vegetable Sewes. —A more careful research
and the results of direct experiment have supersede

CHAP. V. FUNCTION OF REFRODUCTION. 201

the vague conjectures of the old philosophers; and it
is now clearly established that the two innermost floral
whorls, the stamens and pistils, are the organs essen-
tial to the fertility of the seed. In the case of double
flowers where all the stamens have assumed. the condi-
tion of petals, seed is never produced ; but if the pistil.
be perfect, it may be supplied with pollen from another
plant of the same species, and will then ripen its ovules.
Some apparent anomalies are recorded among the various
experiments which have been made to prove the necessity
of the action of the pollen in securing the fertility of the
seed. The females of certain dicecious plants have ma-
tured their seeds although they were carefully excluded
from the action of the stameniferous individuals; but
in some of these cases, this was probably owing to the
fact that dicecious plants are frequently partially mo-
neecious, and that a stameniferous flower is here and
there developed on the fertile plants, which may have
furnished sufficient pollen to set the fruit. Accord-
ing to some recent experiments, however, the universality
of a law which establishes the necessity of the pollen’s
action has been rather shaken, unless there be some
error which it is difficult to account for. If they are
correct, it seems to have been proved that hemp and
a few other annual dicecious species are capable of ri-
pening their seed without the action of the pollen having
taken place. Even if the fact should be satisfactorily
established it will in no way disprove the general neces-
sity of the pollen’s action, or the sexual distinctions of all
phanerogamous plants. But such isolated exceptions
may possibly be considered analogous to the case of the
Aphides, in which insects a single impregnation is suf-
ficient to enable several generations to become fertile.
But after all we have such marvellous accounts of the
distance to which the pollen may be carried and yet
Preserve its proper influence, that it seems hardly pos-
sible to feel quite certain that the plants in question
May not have been fertilized from others growing in
the neighbourhood. It is stated that in the year 1505
s 3

262 PHYSIOLOGICAL BOTANY. PART Il

there was a female date-palm growing at Brindes,
which flowered regularly but never bore fruit. At
length a male plant of the same species growing
thirty miles off at Otranto, having attained a sufficient
height to overtop the trees in its neighbourhood, its
pollen was then wafted by the wind across the inter-
vening space, and the tree at Brindes produced its
| fruit. The poet Pontanus who flourished at the time,
has also recorded the fact. The late colonel Wilkes
when governor of St. Helena, procured some pollen
from dates growing on the continent of Africa, with
which he fertilized some trees on the island that ha
never before perfected their fruit. It is certainly not
necessary that the ripe pollen should immediately be
brought into contact with the stigma; and instances
are recorded of its having been sent in a letter from oné
part of the country to another and still retaining its
activity. Dr. Graham mentions that a female specime?
of the Chinese pitcher-plant (Nepenthes distillatori@)
was fertilized in the Edinburgh Botanic Garden, bY
pollen thus procured from a male plant which happené
fortunately to be in flower in another part of Scotland.
(258.) Dispersion of Pollen. — Before the pollen is
scattered from the anther, some plants seem to make
preparation for increasing the certainty of its taking
effect, by bringing the stamens nearer to the pistil.
This is remarkably evident in the Grass-of-ParnassU®
(Parnassia palustris), whose stamens on the first €¥-
pansion of the flower are inclined away from the pistil,
but are afterwards brought in succession towards it
when their anthers are about to burst. In Geraniu™>
Kalmia, &c. the filaments bend until the anther is place
immediately over the stigma. In the berberry (as W°
have described in art. 149. 3.), the filament may be
caused to incline suddenly towards the stigma by gen#Y
touching it near the base on the inside. The genus
Stylidium affords one of the most singular examples 0
this kind of floral irritability ; though in this case the
object is not so clearly to be perceived, since the anthers

CHAP. V. FUNCTION OF REPRODUCTION. 263

are at first close to the stigma, and the pistil is sud- | { €
denly removed from them. m,
But independently of any means which some species
employ for assisting the dispersion of the pollen and se-
curing its contact with the stigma, we find that the
mere conditions in which the flower is placed are often
such as are most likely to secure these results with-
out further contrivance. Thus, when the flower is
erect and the stamens are longer than the pistil, the
pollen on falling from the anthers is most likely to
come in contact with the stigma placed immediately
below them ; so also where the flower is pendent and
the stamens shorter than the pistil, the same effects
will be produced. In cases where the flower is erect
and the stigma stands higher than the anthers, there is
often a closer aggregation of the flowers as in the nu-
merous order Composite, so that the chances are greatly
increased whereby the pollen from one flower may be
brought into contact with the stigma of another, either
by the action of insects crawling over them or by the
mere agitation of the wind. These and a thousand
other instances might be adduced of a provision made
for securing the perfect success of an operation of so
much consequence to the preservation of the species.
(259.) Protection of Pollen.— It is further essential
that the pollen should be protected from the influence
of moisture ; and, consequently we find that aquatics,
as the water-lily (Vymphea alba), elongate their flower-
stalks until the blossoms float upon the surface of the
water. In the water-soldier (Stratiotes aloides), water-
violet ( Hottonia palustris), and others, the entire plants
float to the surface of the water during the period of flower-
ing, but live submerged at other times. In the Zostera
marina the flowers are arranged within a cavity filled
with air: and thus, although they are developed beneath
the surface, they are protected from the immediate
contact of the water. But of all instances that might
be mentioned, where the action of the pollen is secured
by some singularity of structure or contrivance, the
s 4

264 PHYSIOLOGICAL BOTANY. PART IL #

Valisneria spiralis is one of the most remarkable. This
is an aquatic, native of the south ot Europe. Its
flowers are dicecious. The females are attached to
long peduncles which at first are spirally twisted, s0
that the buds are completely submerged. They after-
wards untwist until the buds reach the surface, and the
flowers expand. The males on the other hand have
very short peduncles, and their buds are in the form
of little bladders which easily detach themselves from
the peduncle and float to the surface of the water when
the pollen is ripe. Here they surround the female blos-
soms and then expand. The peduncles of the female
plants coil up again, the flowers are submerged and the
seed is then ripened below the surface of the water.
(260.) Certainty of Reproduction. —No one who
feels as he ought the lessons which the study of nature
is calculated to convey, but must be struck with admir-
ation at witnessing the multifarious resources, combined
with an extreme simplicity in the means employed, for
effecting that unity of purpose which is manifested in
the preservation of the numerous species that clothe
and beautify the surface of the earth. Independently
of that security which every species possesses in its
reproduction by seed against the probability of utter
annihilation, some are further enabled to maintain their
) position by means of creeping stems. Many aquatics, as
` the potamogetons, are thus extensively propagated at
the bottom of rivers and lakes and their perpetuity
secured, even though the conditions necessary to en-
able them to perfect their seed should never be ful-
filed. On the other hand the occasional produc-
tion of seed in such plants seems to be necessary;
if we remember that their native bed may possibly
be drained in the lapse of ages by one of those
events which characterise the geological history of our
planet; when the only chance which they would possess
of being preserved must consist in the probability of
some of those seeds which they had ‘cast upon the
waters,” finding a new station equally congenial to

|
CHAP. V. FUNCTION OF REPRODUCTION. 265

their growth. The chances which threaten the fail-
ure of seed.in dicecious species are diminished by the
occasional. development of a few flowers of an oppo-
site sex among those which otherwise characterize
the separate individuals; and it is well authenticated
that cases occasionally occur, where willows which for
many years had borne flowers. of one sex only, have
afterwards changed their character and begun to bear
only those of an opposite sex.

(261.) Formation of Pollen.—Before we describe the
action of the pollen, we shall say a few words upon its
formation. In this case, as in the whole account of the
fertilization and development of the ovule, we are es-
pecially indebted to the admirable researches of Adolphe
Brongniart, who in a memoir published in the “ Annales
des Sciences,” has combined an extensive series of
original observations with whatever was previously
known on the subject ; and placed the main facts of this
interesting and curious question beyond the possibility
of successful contradiction. To Robert. Brown also in
this as in every department of botany, we are pre-
eminently indebted for important and accurate details.
His invaluable papers on the fecundation of Asclepia-
dee and Orchidee form an important epoch in the
progress of general physiology,

So soon as the anther can be distinguished in the flower-
bud, its cells are filled with a mass of cellular tissue, each
vesicle of which contains one or more grains of pollen.
As the anther ripens these grains enlarge and ultimately
rupture the vesicles ; and the débris of the cellular tis-
sue then forms loose fibres intermixed with the pollen.
In general the grains are separate, but in some plants (as
the heaths) three or four grains always adhere together.
There is no appearance of any thing like a pedicel to the
Separate grains, nor any scar upon them like the hilum on
the ovule, which might indicate an original attachment to
the sides of the vesicles within which they were formed.
In most plants each grain is composed of two membranes ;
the exterior presenting the various appearances de-

266 PHYSIOLOGICAL BOTANY. PART Il.

scribed art. 99.; and the interior being an exceedingly
delicate homogeneous pellicle. Whatever may be the
ultimate determination of botanists, respecting the form-
ation and origin of pollen, yet as its grains in a very
early stage of their development are free and unattached
to the inner walls of the anther, it should seem that from
this period at least their growth must depend upon the
absorption of nutriment through their surfaces.

(262.) Action of Water on Pollen.—If ripe pollen
be placed in a drop of water and examined under 2
microscope, in a few seconds it will be seen to dilate,
burst, and violently expel a cloud of
minute granules (fig. 160.). These
granules are still contained within (777
the inner membrane of the pollen (0,
grain protruded through the rup- \e
tured outer membrane, but which is
difficult to be observed, on account
of its extreme tenuity. It thus forms
a sort of rude sack, termed a “ pol-
len tube,” and contains a liquid, the “ fovilla,” in which
are dispersed a number of very minute “ pollen gra-
nules.” The outer skin of the grains is ruptured irre-
gularly in most Monocotyledons ; but in Dicotyledons
there are one or more determinate points on its sur-
face where a regular dehiscence takes place, and it is
through these that the inner membrane then protrudes:
In consequence of the effect thus produced on pollen by
water, it is liable to injury in rainy seasons and the fer-
tility of the seed is often impaired. Although the gra-
nules are destined to convey that influence to the ovule
which is necessary to secure its fertility, yet their violent
expulsion from the grains is not the manner in which this
effect is produced. This process constitutes one of the
most curious phenomena which have been observed 0
late years among the many wonders which the micro“
scope has brought to light. Considering the minuteness
of the objects and the delicacy of the manipulations T€-
quisite for these investigations, we must feel surprise

CHAP. V. FUNCTION OF REPRODUCTION. 267

at the progress which this inquiry has already made,
although much yet remains to be done before a complete
elucidation of all points can take place.

(263.) Granules. —With a lens which magnifies
about 300 times in linear measure, the form of the gra-
nules in the fovilla may be clearly distinguished. Whilst
still in the pollen tubes they are often in motion, like
the globules in the stems of the Chara (art. 194.). A few
larger molecules are found dispersed among them, appa-
rently of an oleaginous nature. In the same species
all the granules are nearly of the same size and shape,
but they differ in different species. They are always
more or less spheroidal or cylindrical. They are cer-
tainly to be considered as the direct agents employed in
securing the fertility of the ovules.

(264.) Action of the Stigma. — When the grains of
pollen fall upon the stigma, they become attached to it
by means of a glutinous exudation with which it is
covered. No immediate action takes place, and the
grains are not violently exploded with the pollenic
tubes as when they are placed in water ; but after they
have remained for a few hours, and in some Cases even
for a few days on the stigma, each grain protrudes one
or more delicate pollenic tubes which penetrate be-
tween the vesicles of the cellular tissue of the stigma
(fig. 161.2). These tubes increase rapidly in length,
growing as it should seem by
means of thenourishment which
they derive from the granular
matter abounding in the inter-
stices or intercellular passages
between the vesicles of the
style. In some cases if not
in all, the pollen tubes become
extended down thewhole length
of the style, and penetrate into the cavity of the
ovarium, where they run along the surface of the pla-
centa, and surround the ovules. At (b) we have the
section of a stigma on whose surface are numerous pol-

268 PHYSIOLOGICAL BOTANY. PART II

len grains each protruding a tube and appearing like
pins on a cushion. In certain families, as the Orchi-
dee (fig. 162. a) and Asclepiadee (b), the grains
contained in one cell of each anther are agglutinated
together into waxy masses, so that when the action
takes place, a number of tubes are

protruded together and form a thick-

ened cord (as at c); and thus

they penetrate into the ovarium “en

masse.” Even some grains which

are composed of only one vesicle, A

exsert. more than one pollen tube. A

In some cases the tube originates \

in a swelling on the surface of the grain, which then
seems to be formed of one skin only, or perhaps the
two may be united.

THIRD PERIOD OF REPRODUCTION.

(265.) Maturation.— After the action of the pol-
len has taken place, the ovules contained in the ovarium

begin rapidly to increase, and the fruit swells and
ripens. But in order to understand the several parts of
which the seed is composed, it is necessary to trace
the changes which the ovule undergoes, from the
earliest period in which it is distinguishable in the
young flower-bud, up to the time when the complete
maturation of the fruit is effected.

(266.) Origin of the Ovule.— When the ovules can
first be seen (as in some T
species of the cucumber or
gourd), theyare small pus-
tules or wartlike excres-
cences formed upon the
inner surface of a cavity in the ovarium; and are with-
out any distinct traces of organisation (fig. 163. a)-
Soon after their first appearance we find them lengthen-
ing (b), and assuming traces of an organised structure (e).
They are observed to consist of an internal mass of cel-

CHAP. V. FUNCTION OF REPRODUCTION.

lular tissue termed the “nucleus” (fig. 164. a), in-
vested by two coats or skins (b), open at their lower
extremity, and allowing a portion of the nucleus, called
its “ apex,” to protrude through them. This open-
ing is termed the * fora-
men.” Shortly afterwards
these skins close over the
nucleus, and leave only a
small orifice to the fora-
men (c). The outermost z
of these skins is termed
the “testa” or “primine,”
and the innermost the

‘ tegmen” or “f secun- :
dine.” Sometimes there is only one skin, or more
probably the two are so blended together that they are
not distinguishable. As the ovule enlarges, the nucleus
itself is also found to be a closed sack, of a thick or fleshy
consistency ; and within this and towards its apex, an-
other small sack or vesicle makes its appearance called the
“embryonic sack” (fig.165. a). The ovule may there-
fore generally be considered in its early

state to be composed of two closed sacks

which together constitute the nucleus,

and of two open sacks which form its

integuments. In some cases the two

outer skins appear to be blended to

gether, for one only can be seen. The

number of sacks which compose the nu-

cleus sometimes also amounts to three ;

so that the whole number contained in

the ovule is as many as five, and these

have received the several names of pri-

mine, secundine, tercine, quartine, and

quintine —reckoning from without, inwards. Whilst
the enlargement of the ovule proceeds, a change of
position also takes place in the relation of its parts,
owing to an unequal development. of the sides of the
primine, The apex, which at first was on the side of

164

270 PHYSIOLOGICAL BOTANY. PART Il.

the ovule opposite the part by which it is attached to
the ovarium, has now by some torsion of the mass been
brought close to its base. In this case the point where
the secundine is attached to the primine (and which is
called the “ Chalaze” b) is distinct from the “ Hilum,”
or place where the funicular cord is attached to the
primine. The vessels which penetrate the funicular
cord, are then extended through the substance of the
outer integument from the hilum to the chalaze and
form a vascular bundle termed the “ raphe” (c). Figure
166. represents a section of the developing ovules O
plums, almonds, and other stone fruits,

and may serve as a further illustration of
the facts detailed in this article. When
the embryo (a) makes its appearance in
the embryonic sack (or quartiney (b), this
latter organ is observed to be connected
with three or four other large vesicles in
communication with the raphe where it
joins the chalaze (c); the hilum being at

d). The testa and tegmen already appear as one skin
(f). The thick nucleus (e), together with the embryonic
sack, are ultimately exhausted by the development of
the embryo, and the spermoderm is then composed of
the débris of the four integuments.

(267.) Modifications of the Ovule. — When the
hilum and chalaze are contiguous and the foramen at
the opposite extremity, the ovule is called ‘‘ Ortho-
tropous” (fig. 167. 0), and this is the condition of all
ovules in their earli- i

an :
est state. In many // \\ ff
cases the integu- j sg
ments and nucleus | N
develop more rapidly \ J \ )
o e

i6

on one side than on
the other, and a pe-
culiar torsion takes place in the body of the seed, by
which means the apex is brought near the hilum. The
ovule is then termed “ Campulitropous” (0). When the

CHAP. V. FUNCTION OF REPRODUCTION. 270

chalaze is removed from the hilum, so that the whole
nucleus is inclined upon the axis, as described in art.
266. the ovule is termed “ Anatropous” (a). It
more frequently happens that the chalaze is immedi-
ately opposite to the hilum, and the foramen near. it
(as at a); but sometimes the former is placed on one
side, at about a quarter of the circumference of the
ovule. ‘

(268.) Formation of the Embryo.— Such is the
state of the ovules previous to the action of the pollen
upon the stigma. Sooner or later after that action, the
embryo makes its appearance under the form of a
minute vesicle, attached to the summit of the inner-
most or embryonic sack, with the radicle directed
towards the foramen, and the cotyledons towards the
chalaze. It gradually enlarges, and the whole ovule
also continues to increase.

(269.) Formation of Albumen.— Whilst the ovule
is increasing, the testa and tegmen gradually part with
their juices, for the support and increase as it should
seem of the nucleus; and these two integuments are
‘ultimately blended together, and their debris then forms
only a single skin over the ripe seed. The nucleus
itself is sometimes exhausted in a similar manner;
whilst, in some cases, a deposition of nutritious matter
takes place within the tercine, and round the quartine
or embryonic sack. In some kinds of seed the nutri-
ment thus provided for the embryo is secreted within
the embryonic sack, and in others there is a secretion
of this description going on simultaneously within this
sack and the tercine also. In many cases this nutri-
ment, or “ amnios,” as it is styled in its earlier state,
is not wholly absorbed by the ripening ovule; and it
ultimately becomes the “ albumen” or “‘ perisperm”’ of
the seed, and is then farinaceous, hard, or oily. This
- superabundant supply of albumen is of further ser-
vice to the embryo during its germination, and supplies
it with nutriment in the early stages of its develop-
ment, before the roots have sufficiently enlarged to

Se

272 PHYSIOLOGICAL BOTANY. PART IL

absorb the sap from the surrounding soil. Butin many
cases there is no separate provision of albumen in a de-
tached form, but this material, or something like it, is
diffused through the substance of the cotyledons.
(270.) Development of the Ovule.— So soon as the
embryo makes its appearance it becomes a centre of
vital action, attracting the juices of the plant and be-
ginning an independent existence. It continues tO
increase at the expense of its several envelopes, and in
the end constitutes the bulk of the seed. The seed
then consists of this body enveloped by a single skin
(the spermoderm, art. 109.), which is composed of the
débris of all the envelopes blended together, and in some
cases there is also superadded a store of albumen.
Those ovaries which are not fertilized soon wither up ;
but still it often happens that the ovaria containing
them do not perish. On the contrary in some fruits,—
asin the cultivated varieties of the pine-apple, where the
ovules are universally abortive, — the ovary is developed
into a fleshy pericarp ; although such is not the case with
the wild plants which possess ovules. The same is
true also of the bread-fruit. In some oranges whose
ovules happen to be abortive, the flavour of the fruit is
much improved ; but in many plants, when the ovules
are abortive the ovary does not increase. In ovaria
which contain numerous ovules it often happens that
some only are fertilized ; and sometimes only one ovule
arrives at perfection, the rest being either starved for
want of sufficient nutriment, or choked by the more
rapid growth of that which becomes a perfect seed.
| In the oak for example, five ovules out of six are con-
| stantly abortive. In the horse-chestnut it seldom hap-
pens that more than one arrives at perfection, though the
pericarp originally contained six; and though all of
them, for some time after their fertilization was se-
cured, had every appearance of health and vigour. I”
the stone fruits — plums, peaches, &c. — we generally
find only one ripe kernel, though two ovules are
always present in the early stages of the fruit; the

CHAP. V. FUNCTION OF REPRODUCTION. Ors

other may be seen in a withered state attached to
the inner edge of one suture of the stone, whilst the
perfect seed is attached to the other.

(271.) Maturation of the Fruit. — Whilst the fruit
continues to swell, the sap is drawn with increased `
energy towards those branches on which it hangs, and
a rapid exhaustion takes place of the nutritious materials
previously deposited in the stem. As these materials
are distributed among the whole of the fruit, the ad-
vantage of thinning it early is evident, as the share
which each will receive must be proportionably in-
creased. We may compare the maturation of the fruit
to the period of gestation in animals ; and it is of very
varied duration in different species. The greater num-
ber of plants ripen their fruit considerably within a
year from the time when the flowers first expand, and:
some require only a few days for this purpose. But
there are certain trees, as some oaks, which require
eighteen months; and the fruit of the juniper, and. the
cones of many of the fir tribe, hang above a twelve-
month. The cedar requires twenty-seven months to
bring its seed to perfection.

The following list contains a few other examples of
the different periods required by some plants for the
maturation of their seeds :—

13.
14.

16-—36;
Months 2.

Panicum viride.

Avena pratensis.

Most other Graminee.

Raspberry, Strawberry, Cherry, Elm,
Poppy, &c.

3. Bird-cherry, Lime, Reseda-luteola.

Days

A

5—6.

ji

8-—9.
10—11.

Whitethorn, Horse-chestnut.
Vine, Pear, Apple, Walnut, Beech.
Olive.

Colchicum autumnale, Missletoe.
Most Fir trees.

No uncombined water is found in the seed when it is
completely ripe; but it is now chemically united in
T

Q74 . PHYSIOLOGICAL BOTANY. PART Ib.

their fecula, oils, &c., and the proportion of carbon also
is then ata maximum. Hence it acquires an increase
power of resisting decomposition, and of preserving its
vitality under every temperature to which it is likely t°
be naturally exposed.

Most ripe seeds are of greater specific gravity than
water, unless (as in the common Indian cress, Tropæolu™
majus) air ħappens to be contained in their envelopes
when they will float.

(272.) Stimulants to Maturation.— An increase of
temperature materially accelerates the period in whic
fruits ripen, and also improves their flavour. Advan-
tage is taken of this fact to wrap fruit in thin bags, to
place it under glass, or upon slates of a dark colour:
That elaboration of the juices by which the fruit 1°
ripened is a local operation, and takes place within the
fruit itself, This is clearly shown where a tree, whos?
fruit possesses a peculiar flavour, has been grafted upo”
the stock of another kind whose fruit possesses a very
different quality: no alteration is produced upon the
graft. Also where fruit has been gathered before it
was quite ripe it will nevertheless ripen, as every one $}
aware is the case in apples, oranges, and many others,

The process of ringing the branches or stems of fruit
trees, already alluded to in art. 190., considerably acc”
lerates, as well as secures the maturation of the fruit.
In the vineyards of France this has been practised on j
large scale, and a peculiar instrument invented for t Z
purpose ; and the results have shown that the operatio?
accelerates the ripening of the grapes from twelve x
fifteen days. De Candolle mentions a vine near Genev?
which regularly flowered every year, but had never pri
duced fruit until this operation was performed upon it 5
and then the fruit set, and proved to be the sm
Corinth grape, which in commerce is known under the
name of dried-currants or plums.

(273.) Flavour of Fruit-—We are wholly un?
quainted with the physiological causes upon which t j
different flavours of fruits depend. In the earlier state

CHAP. V. FUNCTION OF REPRODUCTION. 215

of the pericarp, its functions are analogous to those of
the leaf; but when this organ possesses no stomata and
becomes succulent, at first there is a superabundance of
water, but in ripening, an increase of saccharine matter
takes place accompanied with a diminution of the
water.

The percentage of water and sugar in the following
fruits, in their unripe and ripe state, has been thus
stated, viz. : —

biae e SUGAR.

Unripe. | Ripe. ||Unripe. | Ripe.
Apricot -| 89.39 | 74.87 6.64 | 16°48
Peach - -| 90.31 | 80.24 = poi
Red Currants -| — — 0°52 | 6:24
Cherries (royales) -| — pen 1:12 | 18°12
Plums (reine-claude) wits ae 17°71 | 24°81

The solid portion of succulent fruits consists of lignine ;
and their liquid parts are chiefly water mixed with gum,
malic-acid, malate of lime, colouring matter, and vegeto-
animal matter. The whole is flavoured with an aroma-
tic substance peculiar to each fruit. Much wet weather
renders these fruits insipid; and many autumnal fruits
acquire more flavour if they are detached from the tree
before they are perfectly ripe.

(274.) Colours of Fruit.— The peculiar colours of
fruit depend upon some local secretions, of which we
are not able to give an account, any more than of those
which produce the colour of the flower. These two
phenomena have this property in common, that those
parts which are usuaily coloured may become white in
certain varieties, which may be propagated by slips
and cuttings ; even races of white-flowered and white-
fruited varieties may to a certain extent be established
by seed. The colours are deepened by the action of
light.

/

PHYSIOLOGICAL BOTANY.

CHAP. VI.

FUNCTION OF REPRODUCTION CONTINUED. — Periods 4, 5-

DISSEMINATION (275.). — MODES OF DISSEMINATION (279.) ——
PRESERVATION OF SEED (281.).— GERMINATION (283.).—
VITALITY OF THE EMBRYO (290.). —- RELATION OF BUD AND
EMBRYO (291.).— PROLIFEROUS FLOWERS (292.). — HY-
BRIDS (295.).

FOURTH PERIOD OF KEPRODUCTION.

(275.) Dissemination. — Tae manner in which the
ripe seed is disseminated, forms a more important ele-
ment in the history of the preservation of species than
might at first be imagined. It may be considered ana-
logous to the period of labour in the animal kingdom,
and still more strietly to the laying of eggs among such
as are oviparous. If the different modes of dissemina-
- tion were not in harmony with the peculiar character ot
the species, we might expect in the lapse of ages that
4 some combination of circumstances would arise which
\ should so far interfere with the reproduction of a give?
| species that it would disappear from the earth. This
\is guarded against by some peculiar adaptation of the
mode in which the seed is disseminated to the con-
ditions under which each species naturally thrives the
best. In some cases, the seed falls immediately around
the parent plant; and where many seeds are contained
in the same seed-vessel, the young plants come up in
a crowded manner and occupy the soil in society, t°
the exclusion even of more robust species. Other seeds
and seed-vessels are furnished with the means of beizg
transported by the influence of the wind or by some othet
cause to a considerable distance.’ The great diversity #
the means by which the dissemination of the seed is na-
turally secured forms one important inquiry to the bota-

CHAP. VI. FUNCTION OF REPRODUCTION. 207

N

nical geographer; and a complete description of the
various appendages by which their dispersion is assisted
would form an interesting topic of inquiry. We may
just refer to three forms of fruits which are more espe-
cially connected with the physiology of our subject, and
which exercise a marked influence on the dissemination
of the seed.

(276.) In pseudospermie Fruits.—In this class we
may include all fruits whose pericarp is so closely
attached to the seed, that it cannot readily be distin-
guished from one of its integuments. These are often
erroneously considered as naked seeds, and not as com-
plete fruits. To this class belong the various kinds of
corn ; the seeds of the umbellifere, as carrots, parsnips,
&c.,; and of the composite and others. In these cases,
the seed is sown together ‘with the seed cover (or peri-
carp), and the young plant has this additional obstacle to
overcome before it can grow. Many fruits of this kind
are furnished with wing-like appendages, as in the ash
and sycamore; or with down, as in the valerian, but
more especially in some of the composite, as the dande-
lion, thistles, and others. All these contrivances are

manifestly intended to assist in the dissemination of the |
seed ; but in many cases the pseudospermic seeds haye |
no such provision, and are even“so arranged on the |
plant as to secure it against any very extended dis- |

persion.

(277:) In fleshy Fruits——The soft pulp which sur- {

rounds the seeds of fleshy fruits does not appear to ac-

celerate their growth when sown with them ; and by’

its tendency to rot, it prevents them from keeping so
long as when they are divested of it. As a sort of
compensation for the injuries which they might receive
on this account, many seeds of pulpy fruits are encased
in a hard stone or bony envelope which resists the action
of moisture, and protects them from the influence of
the rotting pulpy mass on the exterior. All fruits ot
this kind fall to the ground close to the plant which
bears them, and must depend upon accident for their

t 3
’

i ea

278 PHYSIOLOGICAL BOTANY. PART It.

dispersion ; but as nature has destined these fruits to
be the favourite food of many birds and other animals,
they become instrumental in doing this. Animals after
swallowing these fruits digest the pulp only, whilst the
seed is voided by them in a state better fitted for ger-
mination than it was before.

(278.) In capsular Fruits.—Under this denomina-
tion may be included all fruits whose pericarp consists
of a dry cover, which generally becomes detached from
the seed, and bursts regularly along a line of suture,
separating it into distinct valves. Most of these fruits
are many-seeded, and their dispersion is commonly ©
effected by the agitation of the wind, which shakes 2
few at a time from the capsule. In some cases they
are so arranged that their dispersion is necessarily
| protracted, whilst in others it is speedily accomplished.
Some fruits retain their seed long after they are ripe,
as though it were necessary they should be thoroughly
dried. Some capsular fruits project their seeds to @
distance, by the elastic force with which their valves
suddenly burst when thoroughly ripe. The Balsams
(Impatiens) are a familiar instance of this, in which
the effect is accelerated or suddenly stimulated by the
slightest contact of the finger. The genus Owalis has
. the seeds covered with an elastic arillus, which sud-
denly bursts after the capsules have opened, and turning
the inside outwards projects the seed to a considerable
distance. i

(279.) Peculiar Modes of Dissemination. — The
ordinary effect produced by moisture upon the valves of.
a seed-vessel is to keep them closed ; but there are
some remarkable exceptions to this law. In the Ona-
| grarie, which grow naturally in moist places, the valves
open in moist weather, and the seeds are then scattered.
There is a small annual cruciferous plant, called the
Rose of Jericho (Anastatica - hierochuntina), which
grows in the driest deserts. When the seeds are ripe
the plant withers and the branches coil together, £0
that the whole mass forms a sort of ball. As the root

CHAP. VI. FUNCTION OF REPRODUCTION.

is very small and unbranched, it is easily torn up by
the force of the wind, and the plant is then blown
along the surface of the soil until it happens to arrive
at some pool of water, when the branches imbibe
moisture and unrol: the pericarps also burst and the
seeds are disseminated in a spot where they are able to
germinate.

(280.) Hypocarpogean Fruits. — There are some
plants which possess the singular property of ripening
their seed under the ground. In some of these the
blossoms expand in the air, and then the pericarp is
drawn down or forced underground by the incurvation
of the pedicle, as in the Antirrhinum Cymbalaria,
Cyclamen, &c. The Trifolium subterraneum, a small
species of clover not uncommon in the sandy districts
of England, has its flowers arranged four or five ina
head: the end of the pedicel emits some succulent
spinous processes, which soon harden, and the whole is
eradually thrust under the surface of the soil, where
the seeds ripen and germinate.

Some plants possess two distinct modes of flowering,
the one aérial and the other subterranean ; and these
either perfect the fruit on both stems, as in the Vicia |
amphicarpos ; OY else that which is un- |
derground stems alone arrives at perfection, ps in the | X
Arachis hypogæa, or ground-nut. Lo Carn yg

(281.) Preservation of Seeds. — Notwithstanding —“
the ample provision which is made for securing a super-
abundant crop of seeds, infinitely beyond the number
of individuals destined to spring up from their disse-
mination, there is another circumstance to be noticed in
their history, which most materially diminishes the
chance of any species being extirpated. This is the
property which seeds possess of resisting decomposition,
and of retaining their vitality whenever they are placed
under circumstances favourable to their -preservation.
Seeds are capable of being longer preserved in propor-
tion as they have been more thoroughly matured ; and
hence it is advisable to allow them to remain for a

eT A A

AS

i UA

ao Asmaan
k- en eee
Ain

nae aasa ni:

oe

rT ù hi

mam

280 PHYSIOLOGICAL BOTANY. PART Il.

certain time in the pericarp after they have been ga-
` thered, in order that they may more completely elabo-
rate the provision there prepared for their use. When
thoroughly mature many seeds may be preserved for 2
very great length of time, provided they are not exposed
to the influences of those causes which determine their
germination, viz :— a certain elevation of temperature,
the presence of oxygen, and the influence of water.
There are some however which very soon lose the
faculty of germinating after they are ripe, though they
may be preserved in a state fit for food for a long time.
The seeds of coffee, for instance, will not germinate
unless they are sown within the space of a few weeks
after they have become ripe.
The fact’ that seeds retain their vitality for very
many years is well authenticated. De Candolle tells us
that a bag of seeds of the sensitive-plant gathered about
sixty years ago, has regularly supplied’ the Paris gar-
den with fresh plants every year since then. Young
plants have been raised from seeds of a French-bean
which were taken from the herbarium of Tournefort,
where they must have lain for more than a century.
These examples are remarkable exceptions to the more
general rule, that seeds cannot be artificially preserved
in a living state for many years together. It is cer-
tain that most of those found in ancient tombs, and
in the catacombs of Egypt, have entirely lost their
vitality ; and although recent accounts have been pub-
lished to the contrary, the fact, does not seem to have
been thoroughly established, and may possibly have
been founded on some mistake, or perhaps imposition
practised upon the credulity of the traveller by the
cunning of the natives. M. Rifaud, a recent and labo-
rious investigator of the antiquities and natural history
of Egypt, brought to Europe a large collection of various
seeds, bulbs, and other parts of plants, which he had.
found in the catacombs, and all of these were deprived
of any vegetating power. Many of them have pre-
served to a great extent the appearance of freshness.

CHAP. VI. F NOTION OF REPRODUCTION. 281

Some spikes of maize, obtained from the tombs of
an ancient and extinct race in South America, still
retain their original colours, the pericarps being either
red or yellow; the variety is also much smaller, and
in other respects different from those at present in cul-
tivation. But although it is generally impossible to
secure the vitality of seeds by artificial means for such
very lengthened periods, it should seem that naturally
and under peculiar circumstances, they can retain the
power of germinating for many ages. It is very.
common, upon turning up the soil from great depths,
or on breaking up a tract of ground which has lain
uncultivated within the records of history, to find a
crop of plants spring up from. the newly-exposed sur-
face, whose seeds must have lain dormant for centuries.
In the fens of Cambridgeshire, after the surface has been
drained and the soil ploughed, large crops of our mus-

tards (Sinapis arvensis and alba) invariably spring up.,
‘Ray mentions the appearance of Sisymbrium Irio upon
the walls of the houses immediately after the great fire’

of London, though the plant was not before known to
exist in the neighbourhood. We must be cautious in
not confounding such facts as we have here referred to,
with the delusive effects sometimes produced upon soil
which has been brought up from a great depth, and
taken from strata which have never been disturbed be-
fore. The seeds of plants which spring up in such soils
have been accidentally conveyed to them by the wind.
We may also account for some cases where plants have
appeared spontaneously on soils obtained from undis-
turbed strata at great depths, by supposing the seed to
have been carried there by the percolation of water.
(282.) Artificial Preservation of Seed. — It is a
vulgar notion that some seeds, as those of the melon
and cucumber, improve by being kept for a few years ;
and that the plants raised from them will produce more
fruit and fewer leaves than they would have done had
they been sown immediately ; but this opinion appears

to be without sufficient foundation. In an economical -

f

si il testa ie

282 PHYSIOLOGICAL BOTANY. PART It.

A

point of view, the preservation of fruits and seeds in a
state fitted for food is a subject of considerable import-
ance; and various plans have been proposed which
might combine both cheapness and the means of pro-
tecting them from the attacks of vermin, with security
against decomposition. Some wheat preserved at Zu-
rich for a space of 250 years was found to make ex-
cellent bread. One of the simplest and at the same
time most efficacious modes of preserving corn, is to
inclose it in wooden casks well pitched, and secured
against the influences of the weather. When fleshy
fruits are thoroughly ripe they become rotten, by the
oxygen uniting with their carbon and forming carbonic
acid. This effect may be prevented, and the fruit pre-
served for a considerable length of time in vessels her-
metically sealed, and from which the air, or at least all
the oxygen, has been previously expelled.

FIFTH PERIOD OF REPRODUCTION.

(283.) Germination. — When the maturation of
the seed is complete, all further development of the
embryo ceases, and it then enters into a state of tor-
pidity ; and thus it continues until it meets with that
peculiar combination of circumstances upon which the
last process of the general function of reproduction de-
pends. After the dispersion of the seed has been
secured, we might properly consider the function of
reproduction to be terminated ; but as the young plant
is still dependent upon the nutriment previously pro-
vided for it, and has not yet acquired the power of
preparing its own nutriment, we may perhaps be per-
mitted to include the process of “germination,” of which
we are about to speak, among the details of the repro-
ductive function. Germination commences with the
revival of the embryo from its state of torpidity, and is
considered’ to have terminated when the whole of the
nutriment previously prepared has been absorbed, and
the young plant is able to derive its nourishment in the

,

CHAP., VI. FUNCTION OF REPRODUCTION. 283

usual way. This period bears some analogy to that of
suckling in the Mammalia, or still more strikingly to
that of incubation in birds.

(284.) Stimulants to Germination. — There are
three requisites to germination, either of which being
wanting the process will not take place. These are
moisture, oxygen, and a certain elevation of temper-
ature. When the conditions requisite for the germina-
ation of a seed are satisfied, it imbibes moisture through
its integuments, the embryo swells, and the radicle is
protruded and tends downwards. The plumule or
terminal bud then expands and rises upwards; the
albumen, either free or contained in the cotyledons, is
soon exhausted ; the young plant takes firm hold on the
ground and commences its independent existence.

Although the period which elapses between the time
when seeds are sown and when they first begin to ger-
minate is very different even in the same species, ae-
cording to the external conditions under which they are
placed, yet if different seeds are subjected to precisely
the same influences, we find a still more remarkable dif-
ference between the periods which elapse before they se-
verally germinate. The following list exhibits the result
of some experiments made at the Geneva garden, on
seeds similarly watered and exposed to a common tem-
perature of 95° R. It was ascertained that about half
the species of the following families germinated after

the lapse of the number of days here mentioned, viz:——

Days.

9. Amaranthaces.

10. Crucifere.

11. Cariophyllacee, Malvacez.
12. Composite, Convolvulacee.
13. Polygonee.

14, Leguminose, Valerianee.
15. Graminee, Labiate, Solanes.
90. Ranunculacee.

92, Onagrarie.

93. Umbellifere.

oe

284 PHYSIOLOGICAL BOTANY. PART il.

(285.) Action of Moisture.—It has been found that
the quantity of water absorbed by seeds varies in pro-
portion to their bulk, and that all seeds absorb very
nearly @ weight of water equal to their own. If a co-
loured liquid be used, it will be found to traverse the
substance of the seed cover (spermoderm) until it col-
lects in the cellular tissue near the extremity of the
radicle. From this spot it is imbibed by the radicle, and
penetrates into the cotyledons of dicotyledonous plants,
along the minute and ramifying veins which traverse
them. The chief use of the imbibed water appears to
be, to dissolve whatever materials have been prepared in
the seed for the nourishment of the embryo, and to
convey them into its substance. Where the cotyledons
are leaflike and not fleshy, they contain very little nutri-
ment; and if there is no free albumen, the cotyledons
themselves are furnished with stomata, immediately ex-

pand, and begin to elaborate nutriment by decomposing
carbonic acid. When the albumen is free and surrounds
the cotyledons, it must in some way be absorbed by
their surface, though it is difficult to explain how. The
process bears a striking analogy to the suckling of the
young in animals, Seeds will not germinate in boiled
or distilled water, from which the oxygen has been ex- -
pelled ; and if they are placed in an atmosphere of hydro-
gen, azote, carbonic acid, or any gas which contains no
portion of oxygen, they are equally incapable of ger-
minating. They succeed best in a mixture of one part
oxygen with three of azote, and this is. not very far
removed from the proportion in which these gases are
united in the atmosphere. Where the oxygen is in
larger quantity it over-stimulates the seed.

(286.) Action of Oxygen.—One use of oxygen in ger-
mination is to unite with the superfluous carbon which
has been prepared during the process of maturation for
the better preservation of the seed: thus it appears that
the first step in the new process is to undo the last by
which the maturation was completed. Consequently it is

CHAP. VI. FUNCTION OF REPRODUCTION. 285

found that if the nearly ripe seed be sown immediately
it is gathered, it will vegetate more speedily than when
it has remained in the pericarp until the complete elabor-
ation of the juices has taken place. This fact seems to
account for the very rapid manner in which corn vege-
tates in moist and warm weather, after it has been cut
and whilst still in the sheaf, or even before it is reaped.

(287.) Action of Heat.—The degree of heat requisite
to produce germination is different for seeds of different
species; but, within certain limits, an increased tem-
perature acts as a stimulus upon all of them, the larger
and drier seeds requiring a longer time for the effect
to be produced. ;

(288.) Action of Light.— The action of light, though
not fatal is decidedly noxious to the. germination of
seeds ; and the cause why it is so is obvious. Seeds
require-to be freed from their superfluous carbon, by
this combining with oxygen; but light is the chief
stimulus which operates in the decomposition of carbonic
acid, and in the fixation of carbon in the green parts.

(289.) Action of the Soil.—After germination is
complete, most plants grow in some soil adapted to their
nature, which serves them! as a support, and more es-
pecially regulates the right proportion of moisture re-
quisite for their roots.

(290.) Vitality of the Embryo.—Ewvery part of the
perfected embryo appears to be equally endowed with

life ; for if any portion be cut off, the remainder con- .

tinues to germinate for a time, and will often repro-
duce the organ which has been detached. Thus the
radicle may be repeatedly cut away whilst it is de-
veloping, and the plumule will nevertheless elongate ;
or the plumule may be cut away and the radicle will
develop. There is of course a limit to these mutila-
tions, beyond which the young plant cannot be made to
grow ; but whilst it is still germinating, the vital force
cannot be said to reside in any one part of the indivi-
dual rather than in another.

(291.). Connection between Buds and Embryos. —We

a
=
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K ny ee doen a ore ee ae = a —= = ae = ~ -5 =
Se : cin aul si ita hati P S PAS a ” s Z ee nanos ni >

PHYSIOLOGICAL BOTANY. PART il.

have already given several instances of the close affinity
which subsists between the various foliaceous appendages
on the stem (art. 85.), and have further mentioned the
community of origin in the leaf-bud and flower-bud.
There also exists an evident and striking affinity be-
tween the leaf-bud and the embryo, inasmuch as
each of them when detached from the plant on which
they were formed, is capable of becoming a perfect in-
dividual. The chief distinction between them consists
in the former first developing its ascending organs and
then its descending organs, whilst the embryo first
emits the root and then develops the plumule.

(292.) Proliferous Flowers. — In “ proliferous Y
flowers especially, the identity of their origin is strik-
ingly exhibited. In these instances, every bud which
in ordinary circumstances would have been developed as
a flower, assumes the characters of a young plant. In
the onion tribe this description of monstrosity is very
common, and the little flowers which are aggregated
into heads become small bulbs, and germinate as young
plants even whilst they are still attached to the summit
of the stem. The same fact very often takes place in

certain grasses, and especially in some of those whieh
affect a mountainous situation. This appears to be
provision of nature, to furnish an additional security
against the chance of failure in the seed, at an elevation
where the cold might offer a serious obstacle to its being —
perfected. i

(293.) Buds on Leaves.—The Bryum calycinum
-furnishes one of the most satisfactory examples of the
connection which exists between the bud and the em-
‘bryo. Its leaves are very fleshy, and when they are
placed in a moist situation, and even whilst they are
still attached to the stem, little buds are formed at the
bottom of the crenations on their margins (fig. 168.)
and these buds soon develop into perfect plants.. Now
if we only suppose a leaf of this plant to be longitudi-
nally folded inwards, and that its margins become
grafted together, the buds will then correspond to the

CHAP. VI. FUNCTION OF REPRODUCTION. 287

ovules arranged on the placenta of a carpel— an organ .
which we have considered to be formed on this prin-
ciple (art. 100.).

(294.) Proportion between Seeds and Buds.— An
argument in favour of the common origin of the em-
bryo and bud is deduced from the observed fact, that
many plants which produce the one in abundance are
proportionally defective in the other kind. But this
after all may depend upon the plant not being able to
provide a sufficiency of nutriment for both.

(295.) Hybrids. —It the pollen of one species is
employed to fertilise the ovules of another, the seeds
will often produce plants which are strictly intermediate
in all respects between the two parents. Such produc-
tions are termed hybrids, and are manifestly analogous
to mules among animals. The conditions necessary for
the production of a hybrid are not ascertained, beyond
the fact that those species only are capable of forming
them which are nearly allied to each other, and are
either of the same genus, or of genera which scarcely
differ. It has been suggested that the possibility of
producing hybrids was limited to species whose pollen,
or rather whose pollen granules, were nearly of the same

288 | PHYSIOLOGICAL BOTANY. PART Il.

form and dimensions ; but this is at present mere con-
jecture. Not more than forty kinds of hybrids have
been found naturally produced in a wild state between
well-defined species, and all of these are described as
barren or incapable of perfecting their ovules ; so that
they can never be reproduced by seed, though they
may be propagated by other means. Numerous hy-
brids are @ontinually produced artificially by horticul-
turists, for the purpose of obtaining choice flowers and
fruit ; and it has been asserted that many of these are
capable of fertilismg their ovules, and thus of being re-
produced by seed. If this be really the case, it would
seem to. be impossible for us to draw any distinction
between true species and hybrids. But sufficient atten-
tion has not hitherto been paid to this intricate subject,
to enable us to feel quite satisfied that these supposed
| hybrids are any more than intermediate forms between
| marked varieties or races of the same species. It
“appears tö have been ascertained that hybrids may
be fertilised by the pollen taken from one or other
of the parent species, and that the seed thus obtained
will produce plants intermediate between that species
and the hybrid, and thus a return may gradually be
made to one of the original types. It has been equally
asserted of animals, that although mules never produce
young between themselves, yet a female mule may be-
come productive by a male of one or, other of the pya
species.

The rarity of wild hyba is , eaily accounted for
by the fact, that so soon as the stigma has been affected
by the contact of the pollen, it) becomes incapable of
transmitting an additional influence from any fresh
grains that may afterwards be applied to it ; and conse-
quently the chances of every .sfigma being first affected
by the pollen of its own stamens (if we except dicecious
species), is infinitely greater than its receiving any
influence from others. y

(296.) Permanence of Spettes. — Every thing that
has hitherto been written on the origin and limitation of

CHAP. VI. FUNCTION OF REPRODUCTION. 289

species, may be fairly stated as purely hypothetical.
Linneus supposed that only a few species or distinct
typical forms were originally created, and that a mul-
titude of others had since been derived from them by
repeated intermixture and crossings. He supposed the
` species of very different genera might be capable of in-
termixing and producing new species, and even new
genera. These speculations are wholly unsupported by
facts or experiments. De Candolle also supposes a de-
finite number of species or typical forms to have been
originally created, but he does not imagine any de-
cidedly new form or type to have ever originated from
them. He considers that certain hybrids can repro-
duce their kind, but that in such cases there exists a
constant tendency in the offspring to return again into
one or other of the original types from which they sprang.
Thus we should never have any strictly new type intro-
duced, or any form which differed very materially from
what was already in existence, but only a multitude of
minute shades of difference, in varieties which were alf
intermediate between the original species. In this way
he proposes to account for the endless varieties of some
of our long cultivated fruits, as apples, pears, &c. The
subject is one of great difficulty, and it will require
many accurate and careful experiments to be made,
before we can expect to ascertain the laws by which the
limitation of species and the production of hybrids are
regulated. We are quite certain that many forms, con-
sidered characteristic of particular species, have con-
tinued unaltered in their minutest particulars for the
last 3000 years at least. T his is proved by a careful
examination of the fragments of numerous plants found
in the catacombs of Egypt. An analogous fact is still
more strikingly established in the animal kingdom, and

for a much longer period ; since the forms of certain

existing species of shells have been found in those ter-
tiary deposits of which the geologist can say no more
than that they are comparatively recent in the history

ii |
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290 PHYSIOLOGICAL BOTANY. PART Il.

of our globe, though incalculably earlier than any date
to which we can refer by authentic records.

(297.) Origin of Varieties —The origin of varieties
is a phenomenon in some respects analogous to the
creation of hybrids; and it has been even supposed
that all races, or such varieties as are capable of main-
_ taining their peculiarities by seed, must have originated in
hybridity between two species. If such hybrids have
been fertilised by the parent species, and new hybrids of
the second and third degree been produced, these will so
closely resemble the parent plants that they will appear
to be mere varieties of it.

CHAP. VII.

EPIRRHEOLOGY, BOTANICAL GEOGRAPHY, FOSSIL BOTANY:

EPIRRHEOLOGY (298.). — DIRECTION: OF ROOTS AND STEMS
299.). — BOTANICAL GEOGRAPHY (302,).— FOSSIL BOTANY

K d
(315.). r

(298.) Epirrheology. — Tuis term has recently been
proposed, to express that branch of our science which
treats of the effects produced by external agents upon
the living plant. It can only be considered as a sub-
ordinate department of vegetable physiology, and one
indeed whose limits are not very strictly defined. For
we have seen that life itself requires the stimulus of
external agency, in order that its powers may be eli-
cited, and produce the various phenomena of vege-
tation included under one or other of the two functions
of nutrition and reproduction. But then these fune-
tions become variously modified, according as the ex-
ternal stimuli by which they are called into action are

CHAP. VII. EPIRRHEOLOGY.

permitted to operate with greater or less intensity. In
all cases, there is that happy mean which can so regu-
late the vital force as to produce a healthy and vigorous
condition of existence ; whilst every increase or dimi-
nution in the stimulus applied, only tends to injure or
greatly to modify the individual subjected to its long-
continued influence. Physiology might be considered
as embracing the investigation only of such phenomena
as resulted from the healthy condition of the vital
functions ; whilst epirrheology would take further cog-
nisance of such as resulted from an unhealthy condi-
tion of vegetation. Hence this department would lay
the foundations of another branch, termed the “ noso-
logy” of plants, or that science which treats of their
diseases ; and also of the extensive subject of “ Bota-
nical Geography,” which makes inquiry into those
causes which limit the distribution of various species
to certain spots upon the earth’s surface. But in a trea-
tise like the present we have not thought it necessary
to make any distinction between physiology and epir-
rheology, nor are we prepared to allow that such distinc-
tion is a very judicious one. In order to understand
the effects produced by the vital force, it is necessary to
trace its operations under various modifications of the
external stimuli by which it is controlled, and ever ren-
dered capable of acting at all. These inquiries relate to
the results of an action and reaction between opposing
forces, questions which cannot well be separated with-
out greater refinement than the subject seems to require.
There are, however, certain phenomena, the discussion of
which could not be conveniently introduced under either
of the two functions into which the vital properties were
arranged. Of these we may select as an example the
effects produced by the action of gravity upon growing
plants.

(299.) Direction of Roots and Stems.— That the
reots and stems of most plants constantly develop in
opposite directions, is a fact too notorious to need a.
comment ; and any deviation from this general law is

u 2 :

202 PHYSIOLOGICAL BOTANY. PART I

considered an anomalous circumstance. It is not
strictly true to say that the tendency of all stems is
upwards, though it is more nearly true that all roots
take a direction downwards. The branches of the
weeping birch, weeping willow, and some others of this
character incline downwards, merely by the effect of
gravity, acting upon the long slender rods of which they
are formed. But there are some trees, as the weeping
ash, and weeping horse-chestnut, whose branches take a
decidedly downward tendency from their very origin.
Many plants also have underground stems (rhizomata),
besides those which they develop above ground. But,
neglecting these anomalies, it is generally true that the
stem has a tendency to develop upwards, and the root
downwards. There are two causes to which we may
ascribe these modifications in the directions of the
stems and roots. One is “ gravity,” and the other
“ light.”

(300.) Effects of Gravity on Vegetation. — That
gravity is an important agent in determining the differ-
ence between the directions taken by the root and stem,
is shown by an ingenious experiment of Mr. Knight.
He placed some French-beans on the circumference of
two wheels, and so secured them that they could not be
thrown off when a rapid rotatory motion was given to
the wheels. One wheel was disposed horizontally, and
the other vertically, and both were kept in constant
motion whilst the beans were germinating. The radi-
cles of those beans which germinated on the vertical
wheel extended themselves outwards or from the cen-
tre, and the plumules inwards or towards it. Those
which were placed on the horizontal wheel pushed their
radicles downwards and their plumules upwards; but
the former were also inclined from, and the latter to-
wards the axis of the wheel. This inclination was
found to be greater in proportion as the velocity of the
wheel was increased. Now in the vertical wheel the
effects of gravity were nullified, since the beans were
constantly changing their position with respect to those

CHAP. VII. EPIRRHEOLOGY. 2

parts which were alternately uppermost and lower-
most in each revolution. The only cause which
could have produced the effects described must be the
centrifugal force, which has here replaced the force of
gravity, compelling the root to grow outwards and the
stem inwards, instead of downwards and upwards. The
effect produced upon the horizontal wheel is evidently
the result of the combined action of the two forces —-
gravity inclining the root downwards, and the centri-
fugal force propelling it outwards; and the reverse
with regard to the stem. Although it is plain that
gravity is the efficient cause in establishing the direc-
tions of the stems and roots of plants, it is not so easy
to understand the manner in which it produces opposite
effects on these two organs. Various theories have been
formed to account for this, and the most plausible is
that which ascribes it to the different manners in
which the newly developed tissues are added to the
root and stem. In the root the addition is almost
entirely confined to the very extremity, whilst the stem
continues to increase for some time throughout its whole
length. Hence it is supposed that the soft materials
continually deposited at the extremity of the root must
ever be tending downwards from the mere effect of

avity alone. In the stem, gravity would cause a sub-
sidence of the denser and more nutritious materials to
the lower side, and this side would consequently be
more nourished than the upper, supposing the stem to
be somewhat inclined from the perpendicular. The
consequence of one side being better nourished than the
other, whilst the whole was in a growing state, would
be a greater extension of that side; and thus a slight
curvature upwards would be given to the stem, which,
being continually repeated as it develops, would always
send to keep it more or less in a vertical position. Per-
haps we want sufficient data to allow us to lav anv
great stress upon this explanation.

(301.) Effect of Light on Vegetation. — Light 1s

ty
°

another cause which produces a great effect in modify-
u 3

294 PHYSIOLOGICAL BOTANY. PART Il.

ing the directions of the stems of plants. When grown
in a chamber which admits the light on one side
only, they constantly incline towards it. This has been
supposed to be owing to a greater decomposition of
carbonic acid on the side which is towards the light,
and a necessarily greater deposition of carbon on that
side than on the other. This produces a greater rigidity
in those parts, and consequently a curvature on the side
which is towards the light. This effect is produced
only on the young green parts of plants, and does
not take place in the old woody portions; nor is it
observed in parasitic species, which are without the
means of decomposing carbonic acid. The missletoe
forms a most remarkable exception to the usual laws
which regulate the direction of the root. and stem.
If a seed of this plant be attached to a piece of glass
placed over a dark surface, the radicle invariably ex-
tends itself in.a direction opposite to the side in which
the light shines, from whatever quarter it may come.
The branches of this plant are also developed indiffer-
ently in all directions, without any obvious tendency
either upwards or towards the side from whence the
greatest illumination may proceed.

(302.) Botanical Geography. — We cannot dismiss
the physiological department of our subject, without
referring to that branch of it which treats of the
natural distribution of plants on the earth’s surface — in
other words, to “ Botanical Geography.” It is a fact
sufficiently familiar to every one, that different species
of plants affect peculiar situations; some love an ex-
posed aspect, others prefer shady places ; some are
found in mountainous districts, others in plains, im
Marshes, and even wholly submerged in lakes, or in
the sea. The various physical circumstances attend-
ing different spots in the same range of country
determine the “stations” in which the different spe-
cies of plants can grow. We know that different
plants require different degrees of temperature ; some
are calculated to live in cold or temperate climates,
whilst there are others which belong to the torrid zone ;

CHAP. VIL BOTANICAL GEOGRAPHY.

and these last we are obliged in our latitudes to preserve
in the stove or conservatory. The term “ habitation”
has been given to any tract of country throughout
which each particular species is found naturally distri-
buted in stations adapted to its growth. The deter-
mination of these stations and habitations of plants
leads: to an inquiry into the laws and circumstances
which regulate the distribution of species. We must
suppose that there exists a mutual relation between the
external conditions under which each species is naturally
disposed, and its own peculiar organization ; and this
relation must be sought for by a patient comparison of
the various species, genera, and families peculiar to dif-
ferent regions, with the precise conditions under which
they there exist. T he problem is one of a most com-
plicated description, and it cannot be said that any very
decided progress has hitherto been made towards its
solution. We shall mention some of the more obvious
conditions under which all inquiries of this description
must be regulated, and present the reader with some of
the conclusions at which botanists have already arrived.

Influence of external Circumstances on the Geographic
Distribution of Plants.

(303.) Temperature. — The influence of temper-
ature is the most decided of all the circumstances which
regulate the distribution of plants on the surface of the
earth. It seems evident, that each species is constitu-
tionally adapted to thrive best between certain limits of
temperature, and that every excess of heat or cold
(beyond these) is alike injurious to it. Hence, every
species must naturally be restricted within those geo-
graphical boundaries beyond which the temperature
either exceeds Or falls short of these limits. These
boundaries will not necessarily coincide with any de-
finite parallels of latitude; for it is well known that
the climate of different places having the same latitude
is very different. By drawing lines through those

u 4 i

296 . PHYSIOLOGICAL BOTANY. PART Il.

places where the mean annual temperature is found to
be the same, Humboldt established a series of “ Iso-
thermal” lines intersecting the parallels of latitude. But
these lines by no means show us what might be the
probable range of particular species. For an isothermal
line may intersect a range of country where the extremes
of heat and cold are very different 3 and the constitution
of different species, which may be equally adapted to a
given mean temperature, may not be equally suited to
these differences in the extremes. Thus many plants
which will live in the open air at Edinburgh, would
perish during the severer winters of more southerly
regions, whilst many that can stand greater cold than
that to which they would be exposed at Edinburgh,
require also greater heat in the summer than they would
find there, in order to bring their fruit to perfection, or
even to ripen their wood sufficiently to maintain them
in a healthy condition. In fact, the mean distribution
of temperature throughout the year, is a considera-
tion of much less importance than the distribution
per month, which perhaps most effectually regulates
the range of species. As annuals cannot maintain
their footing in any climate without yearly perfecting
their seeds, they are necessarily limited to more tem-
perate habitations than certain perennials; it is suf-
ficient for the latter, if they occasionally meet with
a season in which they may be able to do so. It has
been remarked that the western parts of continents are
more nearly equable in their temperature throughout
the year than the eastern, and the southern hemisphere .
than the northern; and~ that evergreens affect the
former, and deciduous trees the latter description of
climate. Maritime districts have always a more nearly
€quable temperature than such as are inland.

Besides the physiological relations which plants pos-
Sess with regard to temperature, there are others of a
physical character by which their distribution is con-
siderably affected. Where the temperature is so low
that water exists only in the form of ice, it cannot be
imbibed by the roots, and no plants can live there.

CHAP. VII. BOTANICAL GEOGRAPHY.

When the sap is frozen, the cells and vessels in which
it is contained are ruptured, and the parts subjected
to such an accident die. But trees possess a resource
against the effects of great cold, in their roots pene-
trating to a depth beyond that which the frost has
reached. Hence they obtain a supply of caloric, which
is not readily carried off, because their woody layers and
bark are bad conductors of heat. It has been observed
that the internal parts of large trees retain a temperature
which is about equal to that of the subsoil at one half
the depth of their roots.

The temperature of a tree, being always influenced by
that of the subsoil, will be greater than the surrounding
atmosphere during winter in high latitudes, and less
during summer in low latitudes. This is even more
remarkably the case than would at first be imagined, if
we were to refer the cooling and heating of the earth to
the effect of radiation alone. But it has been observed
by Von Buch, that the temperature of the subsoil is
mainly regulated by that of the surface waters, which
by infiltrating into the earth produce an effect far
greater than any which may be ascribed to the mere
conducting power of rocks and soils. Now, in the
frigid zone, no‘infiltration takes place during the winter,
when every drop of water is converted into ice or snow ;
and consequently the mean temperature of the subsoil
in very high latitudes, will be somewhat higher than the
mean temperature of the atmosphere ; but this is not so in
lower latitudes, where the infiltration continues during
a great portion of the winter. On the other hand, as
we approach the torrid zone, where rain falls only
during the coolest season of the year, the mean tem-
perature of the subsoil will be more cooled in propor-
tion than in those places where it also falls during the
hottest weather. Hence it happens that the mean tem-
perature of springs throughout the central and northern
parts of Europe, as far as Edinburgh, are much the
same as the mean temperature of the air; whilst from
the south of Europe to the tropic of Cancer, the difference
is gradually increasing in favour of the atmosphere

298 PHYSIOLOGICAL BOTANY. PART It.

But from the latitude of Edinburgh northwards, the
difference increases in favour of the subsoil. The
consequence is that certain plants which naturally
belong to the more temperate parts of our zone, are
enabled to extend themselves further north and south
than they could do if the mean temperature of the soil
and air were every where the same.

(304.) Influence of Light. — The influence of light
is less essential than that of temperature in fixing the
geographical limits of different species, though it is cer-
tainly of great importance in many cases. Light is, as
we have seen, the chief agent in stimulating the vital
properties, and its, effects are apparent in a great
number of vital phenomena, such as the absorption of
` the sap, the exhalation of moisture, and the decom-
position of carbonic acid. It is probable that each
Species requires a peculiar stimulus from different de-
grees of light as well as of heat, and we find that such
as are succulent, resinous, or oily, generally prefer situ-
ations where they can obtain most light ; whilst many
evergreens and others grow best where they are some-
what shaded. In these respects alpine plants may be
contrasted with maritime species, the former receiving
the greatest and the latter the least light, under the
same degree of latitude. Whilst the mean distribution
of light is more nearly equable for all latitudes than the
mean temperature, the variations in the mode of its dis-
tribution are much greater. Contrast, for instance, the
alternate long continuance of light and darkness at the
poles with their nearly equable daily distribution at the
equator. . .

(305.) Influence of Moisture.— The proportion in
which water is supplied, constitutes one of the chief
peculiarities of every “ station ;” and plants are very
differently constituted with respect to the precise supply
which they require to preserve them in a healthy con-
dition. Those which require most, have a loose and
spongy texture, with large and soft leaves, and little or
no pubescence, but many stomata; whilst such as grow
in arid districts are frequently firm and succulent, often

CHAP. VII. BOTANICAL GEOGRAPHY. 299 |

provided with long pubescence, but have few stomata.
‘An excess of water is apt to corrupt and dissolve the
outer texture, and hence we find many aquatics, as the
pondweeds (Potamogeton), protected by a superficial
varnish. Many Monocotyledons are coated with a
siliceous pellicle, and afford useful materials for thatch-
ing, as the common reed.

(306.) Influence of Soils. — Most soils are a very
heterogeneous mixture of different earths and other mat-
ters ; and hence it is not likely that any very decided
feature will be often impressed upon the flora of a given
district, by any peculiarity in’ the purely chemical
qualities which soils possess. That some chemical
action takes place in certain soils cannot be positively
denied, but has probably been greatly exaggerated.
For though certain plants seem to prefer particular
geological districts marked by the prevalence of pecu-
liar rocks, some especially abounding on limestone
and chalk, others on slate-rock ; yet it not unfre-
quently happens that many of these plants also occur
in equal abundance in some other localities where
the rocks possess a totally different mineralogical cha-
racter. It seems, therefore, more likely that such effects
may be attributed to mechanical rather than to chemical
causes; especially to the mode in which different rocks dis-
integrate, and are rendered capable of retaining a greater
or less abundant supply of moisture. It may indeed be
said, that these mechanical properties are generally the
direct result of the peculiar chemical qualities which the
rocks possess, though in some cases rocks of very different
mineralogical character certainly disintegrate in much the
same manner. Hence we find the same lichens and
some other plants growing on schistose rocks, whether
they happen to be argillaceous or cretaceous in their

composition. Various soils may be stated as generally .

retaining moisture in proportion to the quantity of alu-
mina which they contain, and parting with it more rea-
dily in proportion as they abound in silica. Siliceous
tracts require most rain, and clay soils least, to become

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300 PHYSIOLOGICAL BOTANY. PART II:

proportionably fertile. Sandy districts support only
such low or trailing plants as the wind cannot readily
root out, or those which have very deep and branching
roots ; whilst very tenacious clays are adapted only to
such species as have small roots, and which do not
require any great depth of earth.

(307.) Influence of the Atmosphere. — Although the
atmosphere is every where of the same chemical com-
position, its effects may vary in proportion to the density
which it possesses at different elevations, or according
to the materials (as moisture, gases, &c.) which may
be suspended in it; or lastly according to its mecha-
nical action, in the greater or less degree of violence
with which it is moved in different regions. It is pro-
bable that the difference in density which the atmosphere
possesses at different elevations above the surface of the
earth, produces little or no effect in comparison with
those which result from the modifications which the
temperature, light, humidity of the air, &c. undergo.
Since the mean temperature diminishes in receding from
the equator much in the same proportion as in ascending
a mountain, many plants peculiar to the plains of higher
latitudes are found on the tops of mountains in warmer
climates. Hence a very extensive range may be given
artificially to some plants, by cultivating them at
different altitudes in different latitudes. Humboldt —
has likened the earth to two great mountains whose
bases meet at the equator, and whose summits are the
poles; and, ceteris paribus, we may say that the
latitude at which a plant thrives best will vary as the
altitude above the sea at which it also flourishes under
the tropics. The potato offers an interesting illustra-
tion of this fact — growing in Chili, at an altitude of
eleven or twelve thousand feet above the level of the
sea, and being well adapted to summer culture in the
plains of the temperate zone as far north as Scotland.
The olive has a much less extended range, and can only
be cultivated as far north as 24°, and at an altitude of
twelve hundred feet in tropical cl'mates.

CHAP. VII. BOTANICAL GEOGRAPHY. 301

(308.) Botanical Stations. —The various peculiari-
ties which characterize different “ stations,” can scarcely
be appreciated. Those which possess a very general
resemblance, may still differ in some important cir-
cumstance by which the existence, or at least the pre-
valence of some peculiar species may be determined.
Thus a marsh may be formed by salt and fresh water
mixed in different proportions ; two tracts in other
respects alike, may be very differently exposed to the
prevalence of winds, or the influence of sea breezes,
&c. Independently of these modifying circumstances,
we may enumerate about sixteen tolerably well de-
fined stations, to one or other of which the different
plants of every flora will be found more particularly
attached. ,

1. Maritime.— Districts bordering on the sea and
influenced by the spray and sea breezes.

2. Marine. — Where plants are growing beneath
or on the surface of the sea itself.

3. Aquatic. — Freshwater rivers and lakes, where
the plants are wholly immersed or floating on the
surface.

4. Marsh.— Bogs and fens.

5. Meadows and Pastures.

6. Cultivated Lands. — These districts abound in
plants which have been introduced by the agency of
man, and have become completely or partially na-
turalized.

7. Rocks. — Lichens, mosses, and other crypto-
gamic tribes abound in rocky situations, but more
especially in the vicinity of springs and cascades. A
few phanerogamic plants also affect such situations,
even where there is little or no soil to support them.

8. Sands.

9. Barren Tracts, by road sides, &c. i

10. Rubbish. — There are many species which
seem to follow the footsteps of man, and spring up
wherever he scatters the rubbish and rejectamenta of
his dwellings.

= re anr aee ee = =

ani i mn

302 PHYSIOLOGICAL BOTANY. PART II.

11. Forests. — These districts may be considered
with respect to the trees which compose the forests, and
also with reference to the humbler species which seek
their shade.

12. Copses and Hedges.

13. Subterranean Caves.

14. Alpine.

15. Parasrrio. (See art. 234.)

16. Psrupo-parasitic. (See art. 234,)

. (309.) Botanical Habitations. — Greater uncertainty
prevails respecting the different habitations of plants
than their stations. If indeed the extent of their ha-
bitations were entirely dependent upon their range in
latitude, the difficulty of determining them would not
be so great; but it is a remarkable circumstance, that
the vast majority of species grow naturally within cer-
tain limits restricted in longitude as well as in latitude ;
that is to say, the limits within which they naturally
occur, are much more restricted than the regions through-
out which they might readily grow, so far as climate is
concerned in this question. There are indeed some
species which have a very extensive range in longitude
as well as in latitude, and are even found in both
hemispheres, but several of these have undoubtedly
become thus generally dispersed by the agency of man.
Others we may equally conclude to have been trans-
ported by natural causes, from the habitations to which
they were first restricted. But when we have made all
such allowances, we find the great majority of species
so far restricted in their range, as to lead us to the very
probable supposition that each was originally assigned
by the Creator to some definite spot upon the surface of
the earth, from whence it has wandered to a greater or
less extent in all directions, until it happened to meet
with such obstacles as were sufficient to check its fur-
ther progress. It may be worth while to consider the
nature of those obstacles which afford the most effectual
barrier to the migration of species from one part of the

CHAP. VIL BOTANICAL GEOGRAPHY. 303

earth’s surface to another ; and also the means by which
their migration is most effectually provided for.

(310.) Obstacles to Migration. —

1. Seas.—The salt of sea-water produces an in-
jurious effect upon the seeds of plants, and completely
destroys the vitality of those which are long subjected
to its influence. In proportion therefore to the extent
of sea which surrounds a tract of land, the chances are
diminished by which the seeds of plants may be wafted
to or from it in a state fitted for germination. This
is remarkably exemplified in the flora of St. Helena,
which is so peculiar, that not more than two or three
of its indigenous species have been found on the con-
' tinent of America, and not one of them on the con-
tinent of Africa. Generally speaking, the floras of all
islands resemble those of the continents to which they
are nearest, in proportion to their greater proximity to
those continents. England does not possess fifty species
which have not also been detected in France; and pro-
bably, the number peculiar to our flora is even still
less than this. The floras of the opposite shores of the
Mediterranean are very nearly the same.

2. Deserts.—These are a very effectual barrier to
the migration of species; and hence there are scarcely
any species described in the ‘ Flora Atlantica” which
are to be met with in Senegal; the great desert of
Sahara completely intercepting the botanical intercom-
munication of the two districts.

3. Mountain Chains. — Where mountain chains
possess lofty summits, the cold of those regions presents
a barrier to the migration of plants across them. In
general however they are not so effectual as seas and
deserts, on account of their being intersected by trans-
verse valleys. '

4. Partial Obstacles are offered by extensive forests
and marshes; for although there are numerous species
which prefer such tracts as “stations,” to which they
are best adapted, there are others which cannot live

304 PHYSIOLOGICAL BOTANY. PART Il»

under the influence of the moisture and shade which
prevail there.

(311.) Means of Transport. —

1. Currents. — Rivers and other currents of fresh
water are among the most effectual means of dispersing
the seeds of plants: even the sea may occasionally
serve a like purpose where the seed is protected from
its influence by some accidental circumstance.

2. Atmosphere. — Many seeds are provided with
downy and winglike appendages, by which their dis-
persion is secured ; but more especially the minute im-
palpable sporules of cryptogamic plants appear capable
of being wafted to very considerable distances by this
means. It has been supposed that two species of lichen
found on the coasts of Bretagne, have been brought
thither from Jamaica by the prevalence of the south-
west winds.

3. Animals. —Seeds often become entangled in the
hair and wool of many animals, and may thus be carried
by them to considerable distances from the spot where
they grew ; but more especially such as are furnished
with hard pericarps, or bony coverings to the kernel
(as in stone-fruits) are capable of resisting the digestive
powers of the stomach, and are thus conveyed by birds
from one region to another in a state fitted for germin-
ation. But man is most instrumental in the disper-
sion of different kinds of plants. , The seeds of some
he has carried intentionally from one quarter of the
globe to another; and others have been accidentally
transported by him in a thousand ways, and follow
his footsteps wherever he has penetrated.

(312.) Botanical Regions.—It seems to be a natural
consequence of our considering the geographical distri-
bution of every species to have taken place by its gradual
dispersion from one definite spot on the earth’s surface,
that some would be found only in one district, and
others in .another, provided these were separated by
some great physical feature, such as a chain of moun-
tains or a wide sea ; and that two such districts though

CHAP. VIL BOTANICAL GEOGRAPHY. 305

they might lie under the same parallel of latitude, would
contain few species common to both. Such districts are
termed “botanical regions.” These are spaces enclosing
particular species, distributed through them in the sta-
tions adapted to their growth ; but so encompassed by
physical obstructions, that the great majority of species
found within their limits are not to be met with else-
where. We do not as yet possess any very accurate
information respecting the number and exact extent of
the well-defined botanical regions into which the surface
of the earth may be mapped out. There are about
fifty whose floras have been partially examined, and of
which the following list has been given:—

1. Arctic. — Includes the northern parts of Asia,
Europe, and America. This region is not well defined
towards the south ; but may be considered as termin-
ating in that direction between lat. 62° and 66°.

2. European.— Included within a line drawn from
the north of Scotland, through St. Petersburg, the Ural
Mountains, to the north of the coasts of the Mediterranear
up to the Pyrenees.

3. Mediterranean. — Coasts all round the Medi-
terranean, with Italy, Dalmatia, Greece, Syria, and
Spain.

4. Red Sea.—Includes Egypt, Abyssinia, and part
of Arabia.

5. Persian. — Includes countries round the Per-
sian Gulf.

6. Caucasian. — Caucasian chain and countries
between the Euxine and Caspian.

7. Tartarian. — About Lake Aral. S

8. Siberian. — Between the Northern Ocean and
the Ural Mountains. Bounded towards the south by
the Altaic Mountains.

9. Nepaul. — The chain of the Himalaya.

10. Bengal.—The plains through which the Ganges
flows.

11. Indian. — The Peninsula and Ceylon.

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PHYSIOLOGICAL BOTANY. PART Il-

12. Birman empire.

13. Cochin- China.

14. Indian Archipelago.

15. New Holland, with Van Diemen, New Zealand,
New Caledonia, Norfolk Island.

16. Friendly and Society Islands, with those adjacent.

17. Sandwich Islands.

18. Mulgrave, Carolinas, Marian, &e.

19. Philippine Islands.

20. China, with Corea and Japan, Too little known
to be subdivided.

21. Aleutian Islands, and the north-west of America.

22, North-east of America. Canada and the United
States.

23. Mexico. — From California and T exas to the
Isthmus of Panama.

24. Antilles.

25. Venezuela, Carthagena, and the Oronoco.

26. New Grenada and Quito.—Includes every variety
of climate, from the sea-shore to the summits of the
highest Andes. |

. Guyana. — Cayenne, Surinam.

. Peru. .

. Bolivia.

. The Basin of the Amazon.

. North-east of Brazil.

. South-east of Brazil.

. West of Brazil.

. Argentine Region. — Between the Andes of
i, Paraguay, Brazil, and Patagonia.

. Chili, with the Island of Chiloe.

j. Patagonia.

. Ascension, and St. Helena.

. Tristan d Acunha, and Diego d Alvares.

. Prince Edward's, Marion, Kerguelen, and St-

. Cape of Good Hope, with all extra-tropical
Southern Africa.

CHAP. VI. BOTANIGAL GEOGRAPHY.

41. Madagascar, with the Mauritius and. Isle of
Bourbon.

42. Congo.

43. Guinea.

44 Senegambia.

45. Canaries, Madeira and Azores.

The centres of Africa, Asia, and other unexplored
districts probably afford several more regions.

Twelve of the regions enumerated belong to the
northern hemisphere, between the pole and tropic of
Cancer ; twenty-six are intra-tropical ; and seven are
extra-tropical, in the southern hemisphere. The first
are the largest, and approach each other the nearest ;
the second are less extended, and more frequently se-
parated by the ocean and deserts ; the last are very un-
equal in extent, and above all more dispersed, many of
_ them being small islands in the midst of an immense
ocean.

(313.) Relative Number of Individuals and Groups
in each Region. — In contrasting one botanical region
with another, inquiry may be made as to the number
of individuals which each may be supposed. to contain,
and also as to the number of species, genera, and fami-
lies. The result of the first of these inquiries must
depend upon the actual extent of country included in
the region, and upon the character of its climate. The
nature of the plants which grow in the region will also
form an important element in this inquiry, since a space
occupied by a single tree may contain many hundreds
of smaller plants, and those regions in which large
species prevail will not contain so many individuals as
those which abound in small ones. The greater or less
prevalence of particular species in a given region, may
be observed by noting the number of places in which they
occur ; and then representing by ciphers the relative

abundance in which they appear to exist in each spot, .

the sums of these ciphers will afford some approximation
to the relative abundance of each species, Those regions
O
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308. _ PHYSIOLOGICAL BOTANY. PART Ife

which embrace a greater diversity of stations will, ceteris
paribus, also contain a greater number of species. Those
which ‘are more strictly isolated from each other are
not so likely to interchange their species; and hence it
is observed, that a given space on a continent generally
contains a far greater number of species than an equal
space in an island. An elevation of temperature is
favourable to the greater number of species, as we find by

` the fact that the number at different latitudes increases
as we approach the equator. The genera and families
also seem to obey a similar law; but we scarcely possess
sufficient information to speak positively as to the pro-
portion in which the relative rate of their increase takes
place. It does not appear that the same proportion of
genera to species is maintained in different latitudes :
for instance, the species in Sweden are to those in
France as one to three; whilst the genera are as one to
two. š

(314.) Proportion of Species in each Class, in dif-
ferent. Regions.-—If a’ botanist collect indiscriminately
all the plants he meets with, in any region he may be
examining, he will most probably be soon able to obtain
a very close approximation to the relative proportion
which the species of each of the three classes, and
many of the orders bear to each other, long before he
has obtained an accurate notion of the whole number of
species which the region possesses. So far as calcu-
lations havehitherto been made, the following general
laws appear to be correct ; and it is not likely that they
will be modified by any additional information which
future researches may procure.

1. The proportion of cryptogamic to phanerogamic
species increases as we recede from the equator.

2. The proportion of Dicotyledones to Monocotyle-
dones increases as we approach the equator.

8. The absolute number of species, and also the
proportion of woody species to the herbaceous, increases
as we approach the equator.

4, The number of species either annual or biennial

CHAP. VII. BOTANICAL GEOGRAPHY.

(monocarpeans ) is greatest in temperate regions, and
diminishes both towards the equator and poles.

Many local circumstances produce remarkable mo-
difications in the relative proportions between the
species of different classes and orders, in regions under
the same parallels of latitude. Thus for instance, ceteris
paribus, the cryptogamic tribes flourish most in moist
regions. The places best adapted to the growth of
ferns are the islands in tropical climates, in some of
which, as in St. Helena, one half the flora is composed
of them. It is remarkable that in this respect, and as
regards the existence of arborescent species in this
order, the ancient flora of our coal-fields, appears to
approximate very closely to that of islands situate in
the midst of an extended ocean and in low latitudes.
The same causes which appear favourable to the in-
crease of cryptogamic species, seem also to produce
a diminution in the proportions which dicotyledons
bear to monocotyledons. Other relations of consi-
derable interest have been pointed out between the
species of different orders, occurring in different re-
gions ; but we cannot enter into the minutie of their
details, our object being rather to present the reader
with the principles on which such investigations depend,
than to acquaint him with the partial results which
have hitherto been deduced from them; several of
which must doubtless be greatly modified hereafter,
considering the little knowledge we at present possess
of the floras of many parts of the world.

The following table exhibits a few of those results
which appear to have been most satisfactorily esta~
blished. It gives the relative proportion which ten
well-defined orders, or families of plants, bear to the
whole of the phanerogamic tribes in the torrid, tem-
perate, and frigid zones respectively, and shows us in
which they occur in the greatest relative abundance,
decreasing as we recede from that zone towards the
others.

= ae

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10 PHYSIOLOGICAL BOTANY. PART Ite

| |
Equatorial. Temperate, | Frigid.; Maximum
Orders. Lat. 0—109 | 450—520 | 679—790| ~ ratio in

| Juncdee - sca
(Rushes) } Frigid.

Cyperaceze oe.
(Sedges) HE Frigid.

` Gramineæ 6

( Grasses) } Frigid.
1 Old World
Te À
1t New World Temperate
ee 15 Equatorial.

tz Old World :
5 Nod World Equatorial.
Equatorial.
Equatorial
Temperate.

{ | z Temperate.

(315.) Fossil Botany. — The history of vegetation —
could not be completed without some inquiry respecting
those plants which existed on the earth in its primeval
state, during the extended geological epochs which
elapsed before the establishment of the present order of
things. Traces of this ancient vegetation are very
abundant in certain strata, but more especially in the
“€ coal-measures,” the important mineral combustible
obtained from them being nothing else than vegetable
matter in an altered and fossilized state. In general, we
do not find the remains of plants so perfectly preserved
as the skeletons of vertebrate animals, or the testaceous
coverings of mollusca. It is also rare to meet with
those parts (the flower and seeds) upon which the dis-
tinction of species and their classification chiefly depend :
but still the fragments which remain often possess very
great beauty; and many specimens of wood are so exactly
preserved, that their tissue may be distinguished under @
microscope as completely as in recent species. As it is
principally from, these fragments of stems, and the im-
pressions of leaves, that any comparison between the

Composite -

Rubiacez

ol

Euphorbiacez
Malvacee -
Umbelliferze

Crucifere -

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CHAP. VII. FOSSIL BOTANY: 31i

ancient and present flora of our planet must be ‘insti-
tuted, it will be evident that such data must generally
be far too imperfect to ‘admit of any accurate deter-
mination of specific differences, though they may afford
us sufficient materials for ascertaining several truths of
high interest. The class, order, sometimes the precise
genus, may ke ascertained to which a fossil vegetable
belongs, even though we possess only a small fragment
of the plant. More frequently, these fossils bear an
analogy to some recent genera, which they closely re-
semble, but to which they cannot be accurately referred.
In such cases this resemblance is indicated by referring
them provisionally to a genus whose name is a modifi-
cation of the recent genus: thus “ Lycopodites” is a
genus of fossil plants allied to “ Lycopodium,” but too
imperfectly known to have its characters fully pointed

out.

(316.) Botanical Epochs. — It was soon remarked,
when the study of fossil vegetables began to attract the
attention of botanists, that those from the coal-measures
were distinct from the plants now existing on the sur-
face of the earth, and that they more nearly resembled
the species of tropical climates than such as grew in
the temperate zones. Subsequent researches have shown
that the species embedded in different strata likewise
differ from each other, and that on the whole there are
about fourteen distinct geological formations in which
traces of vegetables occur. According to Mons. Bron-
gniart they first appear in the schists and limestones
below the coal. These contain a few cryptogamic
species (about thirteen), of which four are marine
Alge, and the rest ferns, or the allied orders. In the
coal itself above 300 distinct species have been re-
cognised, among which those of the higher tribes of
cryptogamic plants are the most abundant, amounting
to about two thirds of the whole. Many of them are
arborescent, and parts of their trunks are found stand-
ing vertically in the spots where they grew. There are
no marine plants in the formation. A few palms and

x4

812 PHYSIOLOGICAL BOTANY. PART II.

Graminee are the chief Monocotyledones; and there are
several Dicotyledones which have been considered analo-
gous to Apocynee, Euphorbiacee, Cactee, Conifere,
&c. No great stress need be laid at present upon the
several proportions which species of these classes bear
to each other; as it is probable that subsequent re-
searches will considerably modify them. The great pre-
dominance and size of arborescentferns and other tribes of
Ductulose constitute the main feature of the formation.

Above the coal we arrive at the new red sandstone f-
in some of the formations subordinate to this series a
few species of fossil plants occur. In the oolitic series
they become more abundant, and some beds are re-
markably characterized by the prevalence of the genus
Zamia, together with some Conifere, Liliacee, and
many ferns, the latter being very distinct from those in
the former formations. In the green sandstone and
chalk few species have been hitherto found, and these
are almost all marine. Among the tertiary strata (or
those above the chalk) the Dicotyledones begin to pre-
_, yail to a far greater extent than they did before, and

‘the plants are entirely different, including terrestrial,

_ lacustrine, and marine species. Several fruits are
referable to existing genera, as Acer, Juglans, Salix,
Ulmus, Cocos, Pinus, &c.

It is remarkable that scarcely any species has been
found in more than one distinct formation, and none
have occurred in any two which are separated by a long
epoch. Hence it appears to be a natural conclusion, that
there have been successive destructions and creations of
distinct species. Mons. Brongniart has grouped the
Several formations in which vegetable remains are
found, under four great epochs, during each of which
no very marked transitions occur in the general cha-
racter of the vegetation ; but between any two of these
epochs, a striking and decided change takes place:
even most of the genera are different, and none of the
species are alike. These epochs include the periods
during which the following strata were deposited : —

‘CHAP. VII. FOSSIL BOTANY» 313

1. From the earliest secondary rocks to the upper-
most beds of the coal-measures.

9. 'The new red sandstone series.

3. From the lowest beds of the oolitic series to the
chalk inclusive.

4. The beds above the chalk.

Judging from analogy, from the characters and rela-
tive proportions of the species in different classes, the tem-
perature of those parts in which the plants of the first
period were growing must have been both hotter and
moister than the climates in any part of the earth at
present. It has been plausibly conjectured that the at-
mosphere was more charged with carbonic acid at those
early periods of our planet’s history, when gigantic
species of cryptogamic plants formed the main feature
of its vegetation. The abundance of reptiles, also,
without any Mammalia during the same epoch, appears
favourable to this supposition. Since the fossil plants,
which have been found in the arctic regions, are
analogous to those which now grow in tropical islands,
it seems likely, that not only must they have enjoyed a
higher temperature, but also a more equable diffusion
of light than those regions now possess. Speculations
of this description, imperfect as they confessedly are at
present, may one day lead to the most important re-
sults, and may teach us many truths respecting the
earliest conditions of our planet, which the science of
astronomy could never have suggested. And surely no
one ought to consider such inquiries too bold for our
limited faculties, needless for our present, or dangerous
for our future welfare. No naturalist, desirous of know-
ing the truth, can be so weak as. to fancy that any
search into the works of God, or any contemplation
of the wonders of his creation, can interfere with the
lessons he has taught us in his revealed and written word.
The commentator who wishes us to pay attention to
his interpretations of the sacred text, must not pro-
ceed upon the supposition that there has been any thing
written in the Bible for our learning, which can possibly

SEE S L

314 PHYSIOLOGICAL BOTANY. PART Il.

be at variance with the clear and undeniable conclusions
deducible from other and independent sources. If the
letter does not announce a particular fact revealed in
the works of the creation, a true believer will imme-
diately infer that the letter (though it have the au-
thority of inspiration) was not intended to teach that
fact. When the philologist has ably interpreted the
letter, the aid of the natural historian. may still be
needed before the divine can safely pronounce upon
the exact scope and meaning of the instruction which
it was intended to convey.

INDEX AND GLOSSARY.

The language of the botanist compri
compounded, from Greek and Latin,

ses many words adopted, or rather
which are seldom applied in their

strictly classical signification ; and some English terms are also employed in a
peculiar and technical sense. The derivation of many of these is here given,
that the reader may be the better able to remember them ; but further refer-

ence is made to the article and page,

where the fullest explanation of their

meaning occurs, in the body of the work.
* The figures in brackets refer to the articles, the others to the page. ,

A.

Aportion (115.), 118.

Absorption (160.), 176.

‘Acotyledones (æ, not ; nOTVANDwWY, A
seed leaf), (36.), 35.

Adfluxion (167.), 182.

Adhesion (118.), 120.

‘Adventitious buds (57.), 51.

‘Aerial-stem (45.), 43.

Æstivation (estiva, summer quar-
ters), (104.), 101.

Age of trees (240.), 243.

Air-cells (21.), 19.

‘Air-cells (174.), 188.

Akenium (a, not; yaa, to open),
(108. 6. fig. 117.), 109.

Albumen (albumen, the white of

an egg), (34. 1.), 32.

Albumen, formation, of (269.), 271.

Alburnum (alburnum, sap-wood),
(50.), 45.

Alternate (82.), 75.

Amnios (269.), 271.

Amylaceous (amylon,
food), like flour. $

Anastomose, (avec ropmcss, Passing
of one vein into another).

Anatropous (ava, overs ceerw ; to
turn), (267 ), 271.

Angulinerved (72.), 62. :

Annular (annulus, a ring), ringed.

‘Anther (aviegos, flowery), (97. and
98. fig. 98.), 96. Š

Apex (apet, the summit, pl. apices).

Apocarpous (avo, apart; xaueros,
fruit), where the carpels are not
united into a compound pistil,

103.

wheaten

Arillus (109.), 111.

‘Articulation (69.), 60.

‘Ascent of sap (163.), 178.
Assimilation (223.), 227.
Atmosphere, influence of (307.)s

300.

Awn (96.), 96.

Axil (axilla, the arm-pit). «The
angle at which a leaf or branch
unites with the stem,

Axis, imaginary line, drawn lon-
gitudinally through the middle
of an organ.

B.

Bark (52.) 46. i

Bell-shaped, or campanulate (95, 1.
fig. 92. a), 94.

Berry (108. 10. fig. 120.), 109.

Biennial, lasting two years.

Bladders (42.), 41.

Botanical geography (302.), 294.

Botanical habitations (309.) 302.

Botanical regions (312.), 304.

Botanical stations (308.), 301.

Bractea (bractea, a thin leaf of me«
tal), (91.), 89.

Branches (59.), 51.

Budding (228. 3.), 233.

Buds Gi), 50. 7

pong e gae (293. fig. 168.), 286.
uds and embryos, connecti
(291), 285. onh

Bulb (65.), 57.

INDEX AND GLOSSARY.

C.

Caloric, development of (254.),

8.
Calycifloree (102.), 101.
Calyx (calyx, the cup of a flower),
(92. and 94.), 91.
Cambium (34. 2.), 32.

Camphor (208.), 218.
Campulitropous (zeprvaAes, curv-
ed; seer, to turn), (267.), 270.
Capitulum (capitulum, a little head),

90. fig. 87.), 89.
a (capsula, a chest), (108. 8.),
109.

Cariopsis (zæen, the head; opis,
form), (108. 5.), 108.
Carpels (xægros, fruit), (92.), 91.

100.), 98.
Catkin, (89. fig. 82.), 86.
Caudex (caudex, a stem), (39.), 38.
Caudex (84.), 77.
Caulinar (caulis, a stem), attached
to the stem. p
Cellulares (36. 2.), 36.
Cellular tissue (16.), 14.
Centrifugal inflorescence (88.), 84.
Centripetal inflorescence (89.), 86.
Chalaze (voruge, tubercle in the
skin), (266.), 270.
Chara (194, fig. 158.), 207.
Character (132.), 138.
Chromatometer (xioa, colour ;
uerew, measure), (186.), 200.
Ciliæ (cilium, hair of the eyelids),
fringes of hair or bristles, 167.
ee Te mer rounded),
. 72. 8), 14.
aon (195.), 208.
Classes (33.), 30. >
Closters (16.), (xAwrrne, a spindle),
elongated vesicles of the cellular
tissue, 15.
Cluster. See Raceme.
Cohorts (131.), 137.
Colour (181.), 194.
Colour of fruit (274.), 275.
Complex organs (32.), 29.
Compound organs (28.), 24.
Cone (91. fig. 137.), 89.
Conduplicate (104.), 102,
Coniferous, bearing cones, as the
- _ fir tribes.
Connate (83. fig. 73. a), 75.
Connective (connecto, to join to-
gether), (98.), 97.
Conservative organs (10.), 10.
Contorted (contortus, twisted),
(104.), 102.
Cormus (66.), 58.
Corolla (corolla, a little crown), (92.
and 95.), 91.
Corolliflore: (102.), 101.
Corymb (zogumEos, a summit, or a
branch), (90. fig. 85.), 87.

Cotyledons (zorvAydov, a hollow
vessel) ; used in botany to signify
the seed-leaves (34. 1.), 31.

Cow-tree (203. 3.), 216.

Crenate, cut into rounded teeth.

Cryptogamic (xevrras, concealed ;
yueos, Marriage), (36. 1.), 35.

Culms (cu/mus, a stem), the stem
of grasses (96.), 96.

Curvinerved (73.), 66.

Cuticle (cuticula, the outermost
skin), (29.), 25.

Cuticular, belonging to the skin or
cuticle.

Cyma (cyma, a branch or sprout),

(61.), 5a,
Cyme (88.), 84.

D.

Deciduous (deciduus, liable to fall),
opposed to persistent.

Decurrent (decurro, to run down),
(83. fig. 74.), 76.

Degeneration (116.), 118.

Dehiscence (dehiscens,
(107.), 105.

Depressed (depressus, pressed
down), where the transverse sec-
tion of an organ is larger than >
the Jongitudinal.

Descent of sap (190.), 204.

Desmodium gyrans (149.2. fig.
150.), 166.

Development (230.), 234.

Diadelphous (dis, twice ; #dzAgos, a
brother), (97.), 91.

gaping),

Dichotomous (d:vorojeos, divided in

two), (88. fig. 80, a), 84.
Dicotyledones (dis, twice ; zorvAn-

day, a seed-leaf), (34.), 31.
Diffusion of proper juice (189.), 203.
a it muscipula (149. 4. fig. 151.)5

Disk (101.), 99.

Dissemination (275.), 276.

Dissemination, modes of (279.), 278,

Dissepiment (dissepio, to separate),
(106.), 104.

Distichous (fig. 139), 130.

Divergent, separating asunder.

Divided. See Incised.

Divisions (131.), 137.

Drupe (drupe, unripe olives), (108.)

8

3.), 108.
Drupel (108. 3.), 108.
Ducts (ductus, a pipe for water),
(24.), 22.
Ductulose (36. 2.), 36.
Duramen (duramen, a hardening),

(50.), 44.
Duration (235.), 238.

INDEX AND ‘GLOSSARY.

E.

Earths (220.), 224.

Eductulosæ (36. 2.), 36.

Elasticity of tissue (142.), 158.
Electricity (156.), 172.

Elementary textures (13.), 13.
Embryo (e&bguov, the foetus), (34. 1.),

Į.

Embryo (111.), 112.

Embryo, formation of (268.), 271.

Embryo, vitality of (290), 285.

Embryonic sack (266.), 269.

Endocarp (evdev, within; xaeros,
fruit), (106.), 105.

Endogenz (evdcy, within ; yesvoncs,
to beget), (35.), 33.

Endosmometer (144. fig. 148.), 160.

Endosmose (evdox, within; wopeos,
impulsion), (144.), 159.

Ephemeral flowers (250.), 255.

Epicarp (er, upon ; xaeros, fruit),
(106.), 105.

Epidermis (ersdeguis, the skin),
29,), 25.

Epigynous (ers, upon; yvvy, a WO-
man), (101.), 100.

Epirrheology (exigpon, an influx),
(298.), 290.

Equinoctial plants (250.), 258.

Equitant (equito, to ride), (fig.

. 5), 74.
Erect (111. fig. 126. b), 113.
Etiolation (178.), 192.
Excitability (146.), 161.
Excretions (212.), 220.
Exfoliate, to scale off.
Exhalation (168.), 185.
Exogene (skw, without; yésvopeas,
to beget), (34.), 31.
Expansion, stimulants to (251.),
256.
Extraneous matters (219.), 224.

F.

Farinaceous (farina, meal), formed
of meal-like powder.

Fasciculate (fasciculus, a bundle),
in bundles, (fig. 30. c), 41.

Fecula (197.), 211.

Fertilization (255.), 259.

Fibre (13.), 13.

Fibrils (39.), 38.

Filament (97.), 96.

Filamentous (filum, a thread),
threadlike.

Fixation of carbon (175.), 189.

Flavour (273.), 274.

Flocculent (jloccus, alock of wool),
wool-like.

Floral whorls (92.), 90.

Flower-buds (85.), 79,

Flower-buds (245.), 250.

Flowering (246.), 251.

Foliaceous branches (76.), 69.

Follicle (folliculus, a little bag),
(108. 1. fig. 114.), 107.

—_ (foramen, a hole), (1i1.),
113.

Foramen, (266.), 269.

Fossil Botany (315.), 310.

Fovilla (262.), 266.

Fraxinella (213.), 221,

Frond (frons, a leaf), (84.), 77.

Fruit (105.), 102.

Fugacious (fugax, fleet), lasting
for a very short time.

Functions of vegetation (152.),

Fundamental organs (38.), 37.
Funicular chord (funiculus, a little
rope), (109.), 111.
Funnel-shaped, or infundibuli-
form, (95. 1. fig. 92. b), 94.
Fusiform (fusus, a spindle), spin.
dle-shaped (jig. 3. c), 15

G.

Gamosepalous (yaos, marriage ;
sepalum, a sepal), where the se-
pals are united together.

Gemmule (gemma, a young bud),
(111.), 113.

Genus (33.), 30.

Germen (germen, a bud). See Ova-
rium (100.), 98.

Germination (283.), 282.

Germination, stimulants to (284.),.

283.
Glans (glans, an acorn), (108. 7.
ig. 118.), 109.-

Glue (215.), 221.

Glossology (yAwsræ, the tongue;
Aoyes, a discourse). The depart-
ment of Botany which contains
an explanation of the technical
terms used in the science (3.), 3.

Glumaceous (96. fig. 95.), having
the character of a glume, 95.

Glume (gluma, a husk of corn),
(96), 96.

Gluten, a tenacious substance ex-
tracted from flour.

Gourd (108. 9. fig. 119.), 109.

Grafts (227.), 231.

Granulated, having the appearance
of being composed of grains,

Granules of the polien (99.), 98,

Granules (263.), 267.

Gravity, effects of (300.), 292,

Growth (224.), 227.

Gum (177.), 191.

318 INDEX AND

H. `

Habitations (302.), 295.

Habitations (309.), 302.

Hair (81. fig. 19.), 27.

Heart-wood (50.), 44.

Heat, action of (287.), 285.

Herbaceous, of a soft and succulent
nature — opposed to the woody
structure of trees,

Hilum (hilum, the black on a
bean), (109.), 111.

Hilum (266.), 270.

Horary expansion (250.), 255.

OE) s (hybrida, a mongrel),

o) eS Ts

ey of tissue (143),

Hypocarpogean (ýro, beneath ;
xeeros, fruit; yn, the earth),
(280.), 279,

Hypogynous (úro, beneath; yyy,
a woman), (101.) 100.

L &J.
Incised (incisus, cut), (fig. 63. b),

Indefinite inflorescence (89.), 85.

Indehiscent (in, not; dehiscens,
cleaving open), where there is no
natural line of suture.

Individuality (236, 237, 238.), 239. A

Inferior (101.), 100.

Inflorescence (86.), 80.

Inflorescence, stimulants to (247.),

251.

Intercellular (17.), 17.

Internodium (56.), the space be--
tween two knots, 50.

Inverse embryo (111., jig. 126. a),
113.

Involute (énvolutus, folded in), (fig.
2. d), 74.

Irritability (148.), 163.

Joints (56.), 50.

K.
Kernel (109.), 111.
Knot, (56.), 50.

L.

Labiate (Jabium, a lip), (95. 2. fig.
93.), 94.

Lactne (lacuna, a hollow place), :
geo:

Lamina, a thin plate of any thing.

Latex (latex, Juice), (195.), 209.

Leaflets (70.) The subdivisions of
a compound leaf, 61,

GLOSSARY.

Left-handed spiral (55 fig. 41. a), 49

Legume (/egumen, pulse), (108. £.
fig. 115.), 107.

Lenticellez (43.), 42.

Lenticular, shaped like a lens,

Liber (52.), 46.

Light (154.), 171.

Light, action of (288.), 285.

Light, effects of (301.), 293.,

Light, influence of (304.), 298.

Lignine (lignum, wood), (200.),

14,

214.

Limb of a leaf (69.), 60.

Lime (220.), 224,

Linear, equally straight through-
out, the edges parallel to each
other.

Linnzan system (137.), 145.

Lipped. See Labiate.

Lobe, the separate divisions of a
leaf or other organ, between the
indentations on its margin.

Loculicidai (Zocudus, a little pouch),
(107. fig. 111. b), where the open-
ing is in the middle of the cell,
105.

Lodicula (95.), 95.

Longevity of trees (241.), 244.

Lomentaceous (108. 2. fig. 115. d),
where an organ, as the seed ves-
sel, or a leaf, is much contracted
at intervals, 108.

Lunate (luna, moon),
shaped.

Lymph (lympha, water), (163.), 179.

crescent-

M.

Macerate, to decompose by the at-
tion of water.

Maturation (265.), 268.

Maturation (271.), 273.

Maturation, stimulants to (272.),
274.

Medullary rays (34. 2.), 33,

Medullary rays (51.), 45. `

Medullary sheath (34. 2.), 32. -

Medullary sheath (49.), 44.

Membrane (13.), 13.

Meteoric plants (250.), 256.

Migration, obstacles to (310.), 303.

Milk (203.), 215.

Moisture, action of (285.), 284,

Moisture, influence of (305.), 2985

Molecules (5.), the smallest par-
ticles (simple or compound) of
which simple minerals are com-
posed, 6.

Monadelphous (coves, alone; adeA-
gos, a brother), (97. fig. 97. a)»
97.

Monocarpean (jzoves, alone; zagros,
fruit), (235.), 238.

Monochlamydezx (povos,
xAcmus, a toat), 101,

alone 3

INDEX AND

Monocotyledones (/oves, alcne ;
zorvanowy, a seed-leaf), (35.), 33.

Monocotyledonous stems (53.), 46.

Monophylious (eves, alone; QuArov,
a leaf).

Monosepalous (woyos, alone; sepa-
dum, a sepal).

Monstrosity (85.), 79.

Morphology (“2e¢n, form; Aoyos,
a discourse), (114.), 116.

N.

Nectary (103.}.

Nectary, functions of (253.), 258.

Nervation (71.), 61

Nerves (69.), 59.

Nodosities, knotted appearances.

Normal (normalis, right by the
rule), (115.), 118.

Nosology (voros, a disease; àoyos, a
discourse), (298.), 291.

Nucleus (266.), 267.

Nut (108. 4. jig. 116.), 108.

Nutrition (159.), 175.

O.

Obvolute (fig. 12. f), 74

Oil (206.), 218.

Opposite (82.), 75.

Order (33.), 30.

Organizable products (176.), 190.

Organized bodies (6.), 6.

Organs (8.), 9.

Organography (ogyæyov, an organ 5
yeggu, to write), (3.), the depart-
ment of Botany which contains
a description of the organs of
plants, 3.

Orthotropous (ogðos, straight 5
reexw, to turn), (267.), 270.

Ovarium and Ovary (ovwm, an
egg), (100.), the part of the pistil
containing the seeds, 98.

Ovate (ovum, egg)» egg-shaped,

. 30. a).
(ovum, an egg), (100.), the
young seed, 98.
Ovule, development of (270.), 272
Ovule, modifications of (267.), 270.
Ovule, origin of (266.), 268.

193.

Oxygen (180.),
= i (286.), 284.

Oxygen, action of

P.

Palea (96.), 95.

ak ni the hand), hand-
shaped, (fig. 30. b. and fig. 58.)

Palminerved (72. j

Panicle (90. fig. 84), 87.

e)s G4.

GLOSSARY.

Papilionaceous (papilio, a butter-
fly), (95. 3. fig. 94), 95.

Pappus (f. 117.), 109.

Parasites (234.), 235.

Parenchyma (69.), 59.

Paries (paries, the wall of a house),
(parietes, pl).

Parietal, belonging to the paries—

e wea tia to the paries.
artite (partitus, divided), (fig.
63. c), 67. ; )> We

Patent, spreading open widely.

Pedalinerved (72. d.), 65.

Pedate (pes. pl. pedes, a foot), (fig.
60.), a shape somewhat like a
foot, 65.

Pedicel (86.), 80.

Peduncle (86.), 80.

Pellicle (pellis, the skin), a thin
skin.

Peltate (pelta, a shield) ,(fig. 59.) 65.

Peltinerved (72. c.), 65.

Penninerved (pennatus, winged),
(72. a.), 63.

Perennial, lasting many years.

Perfoliate (per, through ; folium, a
leaf), (83. fig. 73. a, b), 76.

Perianth (regi, around; æybos, @
flower), (92, 93.), 90.

Perianth, functions of (252.), 257.

Pericarp (wees, around ; xagros,
fruit), (106.), 103.

Perigynous (ees, around; yun, a
woman), (101.), i

Periodic influences, (249.), 254,

Periodicity (151.), 169.

Perisperm (wee, around; TEGH
seed), (269.), 271.

Permanence of species (296.), 288.

Persistent, remaining when other
parts fall off.

Personate (persond, a mask, (95. 2.
fig. 131. a), 94.

Petals (rero, a leaf), (92.), the
subordinate parts of the corolla,

91.

Petiole ( petiolus, the stalk of fruits),
(69.), used in botany for the stalk
of leaves, 60.

Phanerogamic (¢avegos, evident ;
woos, marriage), (36. L) 39:
Phyllodium (gvrac, a leaf; £1005,

form), (75.), 68.

Phytography (¢urov, a plant ; yeagu,
to write), (3.), the department of
Botany which contains a descrip.
tion of the entire plant, 3.

Pinnate (pinnatus, feathered
winged), (72. a.), 63. z

Pinnatifid (72. a.), cut in a pinnate
manner, 63.

Pistil (pistédium, a pestle), (92, 100.),

925
Pitcher (80.), 73.
Pith (34. 2.), 32

pS PS

320

Pith (48.), 44.

Placenta (100.), 99.

Placenta (105.), 103. i
Plumule (plumula, a little feather),

INDEX AND

(34, 1.), 31.

Plumule (111.), 113.

Pollen (pollen, fine flower), (97. 99.
Jig. 99.), 96. |

Pollen, dispersion of (258,), 262.

Pollen, formation of (261,) 265.

Pollen tube (262.), 266.

Polyadelphous (rove, many ; ader-
gos, a brother), (97.), 97.

Polycarpean (roavs, many ;
fruit), (235.), 238,

Polygonal (rodvs, many; yown, an
angle), having many angles and
sides,

Pomum (108. 11. fig. 106. 121.), 110.

Preservation of seed (287.), 279.

Prickle (62.), 53.

Primary groups (33.), 29.

Primine (266.), 269.

Progression of sap (191), 205.

Proliferous (proles, the young ; fero,
to bear), (292.), 286.

Propagation (243.), 248.

Proper juice (202.), 215,

Propulsion (166.), 181.

Pruning (225.), 229.

Pseudospermic (4evòos, a falsehood;
oree, seed), (276.), 277.

Pubescence (pubescens,
OLS els

Pyxidium (rvéidioy, a little box),
(107. fig. 112.), 105.

Q.
Quincuxial (f. 140.) 130.

HOLTOSy

downy),

R.

Race (131), 137.
Raceme (racemus, a bunch), (89.
fig. 81. a), 85.
Rachis (gexis, spine of the back),
96.), 96.

Radical, proceeding from the sum-
mit of the root,

Radical excretions (217.), 222.

Radicle (radicula, a little root),
(34. 1.), 31.

Radicle (111.), 113.

Raphe (fag, a joint or suture),
(266.), 270.

pides (gagis, a needle), (20.)

Receptacles (21.), 19.

Receptacle to the flower (86.), 80.
Regions, botanical (312.), 304.
Reproduction (244.), 249.

Reproduction, certainty of (260.),

264
Reproductive organs (11.), 10.

GLOSSARY.

Resin (205.), 218.

Respiration (172.), 186.

Revolute (revolutus, turned back.),
(fig. 72. e), 74.

Rhizoma (psf, a root), (44.), 42.

Rhizoma (63.), 54.

Rhizoma (84.), 77.

Rhomboidal dodecahedron (fig. 5.
b), a regular geometric figure,
whose sides are twelve similar
and equal rhombs, or plain four-
sided figures, having their sides
equal, but their angles not right
angles, 16.

Rice-paper (50. fig. 36.), 45..

Right-handed, spiral (55. jig. 41. 5),

49.
Ringing (190.), 204.
Root (39.), 38.
Roots, direction of (299.), 291.
Rotate (rota, a wheel), wheel
shaped, (95. 1. fig. 92. d), 94.
Rotation (193.), 206.
Rotation of crops (218.), 223.
Runners (62.), 54.

S.

Salts (221.), 225.

Salver-shaped (or hypocrateriform)
(95. 1. fig. 92. c), 94.

Samara (108. 12. fig. 122.), 110,

Sap (163.), 178.

Sarcocarp (ræež, flesh ;
fruit), (106.), 105.

Scar (69.), 60.

Scent (210.), 219.

Scorpioidal (exzcgr10s, a scorpion ;
eos, form), (88. fig. 80. b), 85.

Secretion (196.), 211.

Sections (131.), 137.

Secundine (266.), 269.

Seed (109.), 110.

Seed-cover (34. 1.), 31.

Sensibility (150.), 168.

Sensitive plant (149. 1. fig. 149.), 164.

Sepals (92.), the subordinate parts
of the calyx, 91.

Septicidal (septum, a hedge or fence),
opening along the divisions be-
tween the cells (107. fig. 111. a),

05

HUETO,

Serrature (serra, a saw), having the
edge jagged or toothed like a
saw.

Sessile (sessilis, dwarfish), without
a stalk.

Sexes (257.), 260.

Shoots (58.), 51.

Silica (220.), an earth ; the basis of
flints, quartz, &c., 225. s
Siliqua (siliqua, a husk or pod), (108.

13. fig. 123.), 110.

Silver grain (51.), 45.

Simple mineral (5.), 6,

INDEX AND

Sinus (sinus, a bay), the indenta.
tions on the edge of a leaf.

Sleep (155.), 171.

Snag (225.), 229.

Soil, action of (289.), 285.

Soils, influence of (306.), 299.

Spadix (89. fig. 83. b), 86.

Spathe (ergin, a ladle), (91. fig. 88.),

Species (33.), 29.

Spermoderm (oxzgo, seed ; Dto puot,
skin), (109.), 111.

Spicule (spiculum, a dart), small
thread-like and sharp-pointed
bristles,

Spike (spica, arf ear of corn), (89.),

85.
Spikelet, a little spike (89. fig. 95.
c), 86.

Spine (spina, a thorn), (78.), 71.

Spiral-vessels (23.), 38.

Spongioles (spongia,

9.), 38.

Sporules (rrogæ, a seed), (36. 1.),
the reproductive organs of the
cryptogamic tribes, analogous to
the seeds of flowering plants, 35.

Spur, the prolongation backwards
of a sepal, petal, &c.,

Stamen (stamen, the chive of the
flower), (92. 97.), 91.

Stations, botanical (302.), 294.

Stations, botanical (308.), 301.

Stellate (stella, a star), star-shaped,
(fig. 21. a).

Stem (44.), 42.

Stems, direction of (299.}, 291.

Stigma (100.), 98.

Stigma, action of (264.), 267.

Stings (31. fig. 20. a), 28.

Stings (214.), 221.

Stipes (stipes, trunk of a tree), (84.),

a sponge),

‘ig

Stipules (stipula, husk round straw),
its. 70.

Stomata (crea, the mouth), (30.), ,
9

26.

Stock (227.), 238.

Striated, marked with stripes.

Style (arvAos, a style), (100.), 98.

Suckers (62.), 54.

Sugar (199.), 213.

Superior (101.), 100.

Suture (sutura, a seam), where a
division takes place naturally in
the fruit.

Syncarpous (suy, together ; zaeros,
“fruit), (fig. 106.), 103.

Syngenesious (syy, together ; yeveois,
generation), (138.), 149.

GLOSSARY.
T

Tap (89.), 38.. *

Taste (210.), 219.

Taxonomy (reZis, order; vomos, a
law), (130.), the same as sys-
tematic Botany, — The Depart-
ment of the science in which
plants are arranged and classified,
135.

Tegmen (zegmen, a
(266.), 269.

Temperature (157.), 172.

Temperature, effects of (303.), 295.

Tendril (79.), 71.

Terminal inflorescence (88.), 83.

Testa (zesta, an earthen pot), (266.),
269.

Thalamiflore (Saraumos,
chamber), (102.), 101

Thallus (84.), 78.

Theca (yxy, a sheath or case),
(113), 115.

Thecaphore (Syxn, a case; ¢&ew, to
bear), (100.), 99.

covering),

a bed.

_ Thorns (62.), 53.

Toothed (fig. 63. a), 67.

Torus (torus, a bed), (92.), 90.
Trachee (23.), 21.

Transport, means of (311.), 304.
Transverse, embryo (111. jig. 126.

Ch $

Tribes (131.), 137.

Tuber (tuber, an excrescence),
(64.), 56.

Turio (turio, a young branch),
(58.), 51.

Vi

Valve, a part which becomes de-
tached by means of a natural
rupture along a line of suture, as
in seed-vessels.

Valvular (104.), 102.

Variation (131.), 137.

, Varieties (33.), 30.

Varieties (131.), 137.

Varieties, origin of (297.), 290.

Vasa propria (21.), 19.

Vasculares (36. 2.), 36.

Vascular tissue (22.), 20.

Veins (69.), 59.

Venation (71.), 61.

Vernation (vernus, belonging to
spring-time), (81.), 74. i

Verticillate (verticulum, a whirl
for a spindle), (82.), 75.

Vesicles (vesicula, a little bladder),
(16), 14.

Viscous (v%scus, glue), clammy and
glutinous, 5

Vital vessels (27.), 24.

322 INDEX AND GLOSSARY,

Uz. W.

Umbel (90. fig. 86.), 87. j Wax (216.), 222.
Umbellate, in the form of an um- Winged (83. fig. 74.), 76.
el

bel. ‘ Wood (50.), 44.
Umbilical chord. See Funicular. Woody fibres (25,), 23,
Under-shrub (45.), 43.
Unorganized bodies (5.), the objects

of the mineral kingdom, 5.

LONDON :
Printed by A. SPOTTISWOODE,
New-Street-Square.

THE

CABINET

OF

NATURAL HISTORY.

CONDUCTED BY THE

REV. DIONYSIUS LARDNER, LL.D. F.R.S. L. & E.
| MRIA. FR.AS. F.LS. F.Z.S. Hon. F.CP.S. &c. &c.

ASSISTED BY

EMINENT SCIENTIFIC MEN.

DESCRIPTIVE AND PHYSIOLOGICAL
BOTANY.

BY THE
REV. J. S. HENSLOW, M. A.

PROFESSOR OF BOTANY IN THE UNIVERSITY OF CAMBRIDGE.

A NEW EDITION.

LONDON:
PRINTED FOR '
LONGMAN, ORME, BROWN, GREEN, & LONGMANS,
PATERNOSTER- ROW.
AND JOHN TAYLOR,
UPPER GOWER STREET.

1837.

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