An introduction to vegetable physiology, with references to the works of De Candolle, Lindley, etc

AN INTRODUCTION TO
VEGETABLE PHYSIOLOGY

WITH REFERENCES TO

THE WORKS OF DE CANDOLLE

LINDLEY ETC.

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r

N". IX.

AN INTRODUCTION TO

VEGETABLE PHYSIOLOGY

WITH REFERENCES TO THE

WORKS OF DE CANDOLLE
LINDLEY ETC.

r

LONDON

WILLIAM PICKERING
1845

tlllSWICK:

i KIM I Ii I1Y C.

IF a person whose life, from infancy to man-
hood, had been passed in some volcanic
island, where scarcely a lichen covered the rock,
should be suddenly removed into a region of
luxuriant vegetation, his wonder and admiration
could not fail to be excited by the scene around
him. The return of spring would indeed appear
to him as an " annual miracle," and he would
probably inquire earnestly into the causes by
which the vernal leaves and flowers were pro-
duced. Habit has so familiarized us with these
beautiful objects, that many of us forget to bestow
a thought upon them ; and we eat our bread,
wear our linen, or sail the ocean in our majestic
vessels, without a recollection of the growth of
the corn, the flax, or the oak. In this, as in
many other matters, King Solomon has set us a
wiser example. Monarch, statesman, and phi-
losopher as he was, he nevertheless found leisure
to make himself acquainted with " every plant,"
" from the cedar of Lebanon to the hyssop on

2091 037

the wall ;" and " a greater than Solomon " vin-
dicated the claim of this exquisite part of the
creation to be studied and admired, when he
declared that the Monarch of Israel, " in all his
glory," was not arrayed like one of the lilies of
the field ; while at the same time he instructed us
how to draw from the study its most consoling
and important inference, that " if God so clothe
the grass" his fostering love will assuredly be
bestowed in full measure on us, his rational
creatures.

There is one point of view from which the
acquaintance with any of the works of creation
assumes its highest moral aspect, God is Truth ;
the one only source from which no error ever
flows ; and whenever we have arrived at the
undoubted knowledge of any facts in nature, we
have made a fresh approach to truth and to the
" Fountain of Truth." Let the subject of in-
quiry be what it may, this assertion will be found
to hold good. What God has not disdained to
make, we may surely think it time well bestowed
to examine, and coming to that examination in a
right spirit, we may indeed find " tongues in
trees," and even in what man, in his insolence,
has called the meanest weeds.

In one of the former " Small Books" some
insight has been afforded into the wonderful
chemistry perpetually going on, in the vegetable
as well as in the animal department of the great
laboratory of nature. It is the object of the
present little treatise to give a general idea of
the structure, nourishment, and reproduction of
the plants themselves ;— of Vegetable Physiology
in short, — and although the compass of this
work is too small to admit of much technical
detail, it is hoped that enough information may
be conveyed to increase the interest with which
its readers will henceforth view the vegetable
world around them, and to excite a wish in those
who may have leisure to pursue the subject at
some future day.

The following Treatise makes no pretension
to originality, being a compilation chiefly from
the works of M. de Candolle, Alphonse de Can-

dolle,— sometimes almost literally translated,

Professor Lindley, &c. carefully put together with
a view to afford an enlarged idea of the general
nature of the subject, and to justify the assertion
of the first named physiologist, that from the
apparently humble functions of vegetable life, we
may raise our thoughts to the contemplation of

the universal order that exists in the natural
world.*

Let us now return to our imaginary personage,
who has inhabited a volcanic island destitute of
vegetation, and has been supplied with food for
both man and beast from elsewhere. He has
seen rocks, and locomotive, sentient beings, and
nothing else. He quits his island, and lo I the
earth is covered with grass, and trees, and
flowers, and fruit, whose use soon becomes appa-
rent from the myriads of living creatures which
find their food there, — but what is this new
appearance? Is it the rock shooting up into
crystals under the influence of the sun and rain,
as salt crystallizes from sea water ? But the
rock, when broken, retains its characteristic
forms and substance unchanged; our islander
pulls a herb or cuts a branch, he finds moisture
exuding from it, like blood from the flesh of an
animal ; and the uprooted, or cut portion withers
and decays. It has then, in common with the
animal, some interior mechanism for the trans-
mission of fluids, and some principle by which

* To the recent works of Dr. Carpenter on Animal
and Vegetable Physiology, and to Professor Henslow's
'« Principles of Descriptive and Physiological Botany,"
the writer thankfully acknowledges much obligation.

this mechanism is regulated : for though not one
particle of the severed portion be injured by the
cutting off from the tree, it can exist no longer
than while it forms part of an individual ; and
the mechanism which nourished it is useless
when removed from the influence of that indi-
vidual principle : this principle is something dis-
tinct from mere tubes and fibres, and its operation
appears closely to resemble what is called life in
animals. Our inquirer therefore will soon re-
solve that the vegetable is more nearly allied to
the animal than to the rock, and he will ask
himself again, what is the difference between the
rooted animal and the rooted vegetable ? Is not
the vegetable, the lowest grade of living beings,
akin to the coral and other such tribes of animal
plants ? He will find an organism resembling
in many cases the lower kind of animals, vessels
transmitting moisture upwards, and carrying it
downwards,— while others are charged with the
supply of air : and the fibres and cellular tissue
are formed from the circulating liquid, as the
muscle from the blood. The substance of the
vegetable, when examined chemically, affords
fibrine and albumen, the components of blood :
its ultimate elements are mainly the same as
those of animals, i. e. oxygen, carbon, hydrogen,

and nitrogen, the residue of ashes alone affording
a small portion of other elements, chiefly alkalies.
Is there then any real difference between the
non locomotive animal and the non locomotive
plant?

For a long time the answer to this question
was in the negative, and the world heard of the
links of the chain all through nature, the vege-
table, the animal, and the intellectual kingdoms
blending like prismatic colours, so intimately,
that it was impossible to mark the boundary.
But our inquirer, with the aid of modern research,
will not allow himself to be influenced by theo-
ries, however plausible ; he will expect to have
the means of proof ere he acquiesces in any
scientific view, and he will soon perceive one
marked difference between the plant and the
animal ; for the root of the former is furnished
with organs for the reception and assimilation of
nourishment, while that of the latter is a simple
means of attachment to one spot ; and the nou-
rishment, instead of being derived from the rock
on which it is fixed, floats to the mouth or mouths
of the rooted zoophyte, and is of a totally different
nature. The plant feasts on unorganized matter,
imbibed in & fluid state by the roots and leaves,
and never collected into any common receptacle ;

7

the animal requires organized matter in a solid
state, which is received by a mouth into a
stomach, where it is reduced to a semifluid mass ;
and not till then does the process of assimilation
begin. The distinction is broad and clear, and
our inquirer will now go on to admire the beau-
tiful mechanism by which the rock, disintegrated
by the action of the air, and dissolved by the
rain, passes into the vessels of the plant, and
there becomes organized, so as to fit it for the
stomach of the animal ; where it undergoes still
farther changes ; and finally, produces an organ
fitted for the use of a higher order of beings :
for it cannot now be doubted that the brain,
which is the finest product of animal organi-
zation, never is fully called into action till it
becomes part of an individual of a yet higher
grade. The potass, &c. of the volcanic rock is
in great measure inert till it passes into the
absorbent vessels of the plant, and the plant is
of no use in creation further than it supplies the
nourishment for sentient organism, and the use
of the sentient organism, finally, is only demon-
strated when a fresh agent is introduced, and
the intellectual Will crowns the fair work of
Creation.

To an observer such as is above described,

that link of the chain which connects man with
the rock will have a deeper interest than the
mere examination of any mechanism, however
curious, could inspire : for the announcement
that man is formed from the dust of the earth
has a deep truth in it which modern science
alone can fully appreciate. It is from this dust,
that, after the various chemical combinations
effected in the cells and vessels of plants and the
inferior animals, man derives his corporeal frame,
and is, in fact, as far as that portion of his nature
is concerned, part and parcel of the earth he
moves on ; the first step, therefore, in this extra-
ordinary metamorphosis well deserves a careful
examination.

(JYS GYD GYt> GYS GYD GYD GYD GYS <

*/*0^» fc^o^* v^/^ fcp^jVrf 4^r\j fc^o*^ *^CT* «^*v*

VEGETABLE PHYSIOLOGY.

CHAPTER I.

STRUCTURE AND PROPERTIES OF VEGETABLE
TISSUE.

1.

T7EGETABLE Structure — " chemically
composed of oxygen, hydrogen, and car-
bon, to which nitrogen is always superadded," *
consists, in common with that of all organized
beings, of

1. The matter which forms the actual sub-
stance of the plant itself.

2. One or more liquids, either contained
in, or secreted by, its organs.

3. Other substances, more or less solid,
deposited during the passage of those liquids
through the different portions of the body.

The researches of modern investigators, aided
by the improved powers of the microscope, have

* Lindley's Elements of Botany, p. 1.

10 STRUCTURE AND PROPERTIES

shown that the solid structure of plants consists
of, Cellular Tissue, Vessels, Fibres, and Skin.
2. Cellular Tissue (contextus cellulosus), is
a membranous tissue, very similar in arrange-
ment and form, to a honeycomb, being com-
posed of detached cells, as its name denotes,
which are closed, and adhere more or less nearly
together — it is found universally in all plants,
and many of the lower tribes, such as lichens,
mosses, &c. are entirely formed of it. It sur-
rounds the vascular parts so that in the vege-
table as in the animal conformation, no vessel is
ever exposed and bare. The diameter of the
cells, or vesicles, which is perhaps their more
correct appellation, varies considerably, from
the thirtieth to the three thousandth of an inch ;
their shape also is much diversified, but the
normal form appears to be round, and it is pro-
bable, indeed almost certain, that the variety
depends on the pressure of one part of the plant
on another during its growth. ' The vesicles
seem to originate from a point, called by mo-
dern writers a cytoblasl,* which sometimes con-
tinues visible after they have reached maturity.
The property of uniting firmly together, pos-

* Probably from KVTOQ a cavity or hollow point, /3Xa<ro£
a branch or sprout.

OF VEGETABLE TISSUE. 11

sessed by the cells which compose this tissue,
forms a very important part of the history of
vegetation, for it is to these adhesions in the
cellular tissue, that all the seams in the various
organs of a plant are owing. The term paren-
chyma is applied to the cellular tissue, consi-
dered as a mass, to distinguish it from those
parts which abound in vessels. Cellular tissue
" is self productive, one cell not only having the
power of generating another on its surface," but
cells frequently produce others, — generally in a
definite number, — within their own cavities, on
the complete development of which, the parent
cell generally perishes or is re-absorbed.

3. Vessels, or Vascular Tissue. This term is
applied to tubes, nearly or quite cylindrical,
which are observed in the greater number of
plants. They are now usually distinguished as
Spiral Vessels and Ducts.

A. Spiral Vessels,or Tracheae, resemble a rib-
bon which has been rolled round a cylinder, and
which by its spiral convolutions forms a con-
tinuous tube. These vessels are very apparent
in the young shoots of plants, particularly those
which can be readily broken without tearing,
such as the rose, &c. They are formed in the
medullary sheath (27) in the nervures of leaves,

12 STRUCTURE AND PROPERTIES

&c. ; but are usually wanting in wood and bark,
and are never seen in any of the lower tribes of
plants. Their diameter varies from the three
hundredth to the three thousandth of an inch.

B. Ducts are transparent tubes, the sides of
which are marked with rings, bars, or transverse
streaks. They differ essentially from Tracheae
by being inelastic, and incapable of unrolling.
They are found in the wood of phaenogamous
plants, and of Ferns and Lycopodia?.

4. " The office of all the ducts is the same —
that of conveying fluid. It is only in the true
spiral vessel that we find air."* And even here
at certain periods of the existence of a plant,
fluid has also been found by recent observers ;
though if a branch be cut asunder whilst in a

* Carpenter's Elem. Veg. Pliys. p. 66.

"The functions ' of the Ducts' have not been accu-
rately determined. It is probable that they act as spiral
vessels when young ; but it is certain that they become
filled with fluid as soon as their spires are separated."
(Lindley's Elements of Botany, p. 6.)

"There are some large Ducts which appear to have
originated from cells, which have been placed together
end to end, and whose partitions have been so broken
down as to form one continuous tube. These are the
largest vessels (if they may be truly so considered) in
the whole vegetable fabric, and are of the class called
' dotted ducts:' — through them the sap principally rises."
See Dr. Carpenter's Vegetable Physiology — § 84, et

OF VEGETABLE TISSUE. 13

soft state, no juice is ever seen to issue from the
orifice of a spiral vessel; and though, as the
lymph is found to ascend in the stalks of mosses,
&c. which do not possess these vessels, we may
probably conclude that they are not requisite to
the transmission of fluid, though occasionally so
employed.

The Laticiferous Tissue consists of very de-
licate and anastomosing tubes, principally oc-
curring in the young bark, and on the under
sides of young leaves. They convey the fluid
called Latex, or proper juice ; which constitutes
the nourishment of the young organs, and in
which a curious oscillation of globules is visible
in the bright sunshine, with a powerful micros-
cope.*

seq. — The line of demarcation between the form of the
true spiral vessel, and some of the ducts, is sometimes
difficult to find ; in some vessels there are ohscure traces
of spiral form, interrupted in places, and covered by
membrane. — " In Ferns, (which have no true spiral
vessels) we find Ducts, which very closely approach the
spiral vessel in character, having an unbroken coil of
spiral fibre throughout their whole extent ; but besides
the important difference that these ducts are long, con-
tinuous tubes, they are further distinguished by the
brittleness of the spire, which snaps when we attempt
to unrol it." Ibid. § 82.

* For a further account of this and other local circu-
lations, see Appendix (A).

14 STRUCTURE AND PROPERTIES

5. Fibres and Layers. When a branch of a
vascular plant is cut transversely, a certain
number of points are observed, which are of a
more compact character than the rest of the
structure. If the branch be divided length-
wise, we shall perceive that these points are the
ends of so many longitudinal threads, which will
separate from the rest of the tissue more readily
than they will themselves break. These threads
are called fibres. With a microscope we can
see that each fibre is composed of bundles of
vessels, bound up and intermixed with cellular
tissue. If we macerate the branch in water,
after some time the fibres separate of themselves,
as in the case of hemp, flax, &c. This separa-
tion in reality disorganizes the vegetable struc-
ture; the water first dissolves the softer parts,
i. e. the true cellular tissue, and so releases the
fibres which it held together, and if the process
be continued, the disorganization proceeds still
farther, and a homogeneous pulp alone remains,
as is seen in the manufacture of paper, where
the fibres which had formed the thread are ar-
tificially torn and reduced to a pulp, in which,
however, a good microscope will still shew us
the remains of a fibrous structure. This des-
cription of the structure of fibres explains why

OF VEGETABLE TISSUE. 15

they are more difficult to break across than to
rend asunder lengthwise, this is what workmen
call following the grain of the wood. These
fibres constitute what is termed Woody Tissue,
or Pleurenchyma. It is also found in the young
bark, and in the nervures of leaves, " and gives
strength to the vegetable fabric." * When many
fibres are distributed circularly round an axis,
whether real or imaginary, the whole together
is called a Layer. It is thus that the annual
rings of Dicotyledonous trees are formed.

6. Skin, called also Cuticle, or Epidermis.
The whole surface of the plant, wherever it is

* " A peculiar form of woody fibre is found in the stems
of resinous woods, especially the Pine and Fir tribe.
The diameter of its tubes is much greater than that of

any other woody tissue it is by a peculiar

set of dots, seen along their course, that these woody

tubes may be readily distinguished from all others

\V hatever be their character, they are of great interest
as tending to establish the true nature of coal.

" That this substance had a vegetable origin has long
been generally admitted ; but from the comparative fre-
quency and perfection, with which the remains of Ferns
occur in it, it has been supposed to have been produced
by the decay of vast forests of this tribe of plants. As
Ferns do not form resins however, this hypothesis would
not account for the large quantity of bituminous matter
which coal contains ; and hence it was supposed that

16 STRUCTURE AND PROPERTIES

exposed to the air, with the single exception of
the stigma, is covered by this membrane, which
may generally be separated from the rest of the
tissue, and is seen under the microscope to be
formed of a range of flattened cells, distinct
from those of the Parenchyma.

7. Stomata, or Pores, are exceedingly mi-
nute oval-shaped orifices, capable of expansion
and contraction, which are easily visible with
the assistance of the microscope on the cuticle
of the herbaceous surfaces of plants. They
exist more or less in all the leafy surfaces of
vascular plants, but are wanting in all roots, in
old stems, in fleshy fruits, and in all the organs

coal must have been formed from resinous woods, even
though the remains of such were very scanty and im-
perfect. Now on applying the microscope to transpa-
rent sections of such fragments of coal as most distinctly
exhibit the fibrous structure it is seen that they present
the character which has been described, as peculiar to
the resinous woods — the glandular form of woody fibre,
as it has been technically termed, and hence it is estab-
lished beyond doubt that the immense masses of coal
which now contribute so much in every way to the com-
fort and social improvement of the human race, are but
the remains of vast forests, probably the growth of many
successive centuries, which chiefly, if not entirely, con-
sisted of trees of the Pine and Fir kind." (Carpenter's
Veget. Physiology, pp. 65, 66.

OF VEGETABLE TISSUE. 17

of cellular vegetables, — with the exception of
certain mosses, in which recent observers have
detected them, — and are rarely found in seeds.
These stomata are distributed at nearly equal
distances ; their principal use appears to be that
of effecting the aqueous transpiration, a view of
their office which is strongly confirmed by the
•facts that they are very abundant in those plants
with membranous leaves which transpire freely,
and wanting in those which transpire little ; and
that they are closed during darkness, when no
transpiration takes place, and open in sunshine,
when it is most copious. It is probable that in
addition to these visible stomata, the superficies
of plants may be studded with other pores, too
small to be detected by the highest powers of
the microscope, and whose existence is only sus-
pected in consequence of physiological pheno-
mena— for instance, if a portion of a plant, known
to be devoid of visible stomata, is exposed to the
air, it gradually loses weight ; and consequently
the liquid it contained must have found some
exit.

8. Spongioles are certain exterior portions of

vegetable tissue, which, without offering under

the microscope any appearance of a peculiar

organization, have a very strong disposition to

c

18 STRUCTURE AND PROPERTIES

imbibe moisture, and seem to act like small and
very absorbent sponges. The radical spongioles
are situated on the fibrous extremities of the roots,
and it is by these extremities only that the absorp-
tion of juices by the roots takes place.* Senebier
placed two roots in such a manner that in the one
the extremity alone touched the water, while
the whole surface of the other root was covered
by it, except the point, which was out of the
fluid : the former took up water in the ordinary
manner, the other imbibed no sensible quantity.
The root fibre and its spongiole may be well
observed in the common duckweed, in which it
hangs from the under surface of every leaf.
Spongioles are found on the stigmas and on the
seeds of plants.

9. The name of Lenticular glands has been
given to a peculiar kind of spots observed on the

* Dr. Carpenter, in his Vegetable Physiology (§ 106),
mentions a strong instance of the practical value of an
acquaintance with the nature and structure of the spon-
aioles, in the removal of some vines from Shropshire into
Norfolk, which was effected without the smallest injury
to the plants by first digging a trench round them at such
a distance as included all their roots, and then removing
the earth " not with spades and trowels, but with the
fingers; every fibril being thus uncovered without in-
jury." The vines bore an abundant crop in the following
season.

OF VEGETABLE TISSUE. ]9

bark of trees. These spots are in the first in-
stance oval lengthwise, then round, and after-
wards transversely elongated. They present a
remarkable and very smooth surface, as if the
cuticle were dried up : they often become swollen,
and end by splitting asunder. Below the cuticle
is a substance, sometimes green, sometimes white,
which appears to be composed of detached cells,
in the form of egg-shaped bladders. It is from
these organs that such roots are put forth, as
shoot from branches, whether spontaneously, or
when plunged in earth ; they may with truth be
called root buds. They differ from the ordinary
buds which produce leaves or flowers, both by
their form and position : they absorb nothing
from without, as the spongioles do, nor do they
appear at all to serve the purpose of evaporation,
like the stomata.

10. Glands, in the animal economy, signify
those organs which have the power of elaborating
some peculiar fluid from the nutritive juices of
the body. The word preserves the same mean-
ing when applied to vegetable anatomy.

11. Hairs (pili, villi). — Vegetable hairs are
prolongations of one or many cells, which by
their length rise above the surface: they are
principally glandular and lymphatic ; the former

20 STRUCTURE AND PROPERTIES

being the supporters of separate little glands, and
the channels by which the fluid secreted by a
gland passes off. It is worthy of remark, that in
all glands furnished with excretory hairs, the
juice secreted is of an acrid nature, and is only
directed towards the exit prepared for it, when
the gland, pressed on by some exterior force,
suffers the fluid to escape; the juice then flows
through the excretory canal, which by its pointed
extremity punctures the skin of the animal which
has incautiously touched the plant, and deposits
its fluid beneath it. This defensive organization
closely resembles the structure of the venom bag
and tooth of serpents, and is well illustrated in
the common nettle. Lymphatic hairs are much
more abundant than the preceding ; they are of
very various forms, and are only found on those
parts of plants which are exposed to the air.
Their office is probably that of preventing evapo-
ration in certain portions of the plant, and of pro-
tecting the more delicate organs against cold,
moisture, insects, &c. ; and in support of this view
of their use, it will be found that the tender bud is
often defended by these hairs, which, when the
shoot approaches to maturity, either drop off en-
tirely, or become thin and widely scattered.
12. Air Cavities. The cellular tissue is often

OF VEGETABLE TISSUE. 21

distended in such a manner as to form cavities
filled with air. They are sometimes composed
of large cells regularly arranged, in which case
they are essential to the species, as in water-
plants ; in other instances they are merely occa-
sioned by the distension of the cellular tissue.

13. Articulations and Dehiscences. At cer-
tain parts of a plant, the cells or vessels instead
of being, as usual, dovetailed together, so as to
afford the greatest strength, are all arranged in
one plane, and consequently easily disunited ; at
these points, called articulations, all parts of
plants which naturally fall of, as the leaves of
deciduous trees for example, separate; where
these articulations do not exist, the parts may
perish, dry up, and be destroyed by degrees, but
are never detached entire. The surface left ex-
posed by the fall of the organ which was attached
to the plant by such an articulation, is called a
cicatrice or scar. Dehiscence consists in a de-
terminate and regular rupture, such as takes
place when fruits, arrived at maturity, burst open
(the beech-mast, for instance) ; the lines which
mark the direction these separations will take
are often rather prominent, and may be observed
before the ripening of the part— the term suture
has been applied to them.

22 STRUCTURE AND PROPERTIES

14. Two grand classes are obvious on con-
sidering the foregoing organography, viz. Cellu-
lar and Vascular plants. The first being wholly
composed of cellular tissue, the last of both
cellular tissue and vessels. Vascular plants
may again be divided into two principal kinds —
those whose vessels and cells extend longitudi-
nally, and whose growth takes place towards the
centre of the stem ; which from this circumstance
have been termed Endogenous : * and, secondly,
those which have vessels or bundles of elongated
cells, taking either a longitudinal or transverse
direction, and in which the growth is always
towards the circumference of the stem — these
are called Exogenous.-f-

15. Having shewn what the general structure
of plants is composed of, without reference to
those particular organs on which their growth,
nourishment, and reproduction depend, it may
here be desirable to give some idea of the pro-
perties inherent in vegetable tissue, before the
organs, which are modifications of that tissue,
and of course partake of its properties, are more
especially noticed.

Organized beings are, like all other bodies,

* From tv£ov, within, and jiyvofiai, to produce.
t From i£u>, without, and ytyvo/»eu.

OF VEGETABLE TISSUE. 23

subject to the laws of physical and chemical
action ; we must therefore inquire, in the first
place, concerning every fact of their existence ;
whether it is merely a consequence of those laws,
or whether that consequence be modified by the
structure and condition of their organization.
The first case will come under the class of
simple chemical or physical facts ; the other will
range itself among those which are denominated
properties of tissue ; that is, properties which are
not indeed strictly vital, but which arise from the
peculiar structure of living bodies. Other facts,
which we cannot include under either of the
above heads, are the direct consequences of that
mysterious state called life. The distinction of
these three classes is the basis of all true physi-
ology.

16. Vegetable tissue possesses three proper-
ties which deserve attention, viz. Extensibility ;
Elasticity ; and the power of imbibing moisture.

17. Extensibility. All organic tissues have
in a greater or less degree the power of extend-
ing themselves even in the act of growth. This
property is greater in proportion as the tissue has
received fewer solid deposits, diminishes as it
becomes older, and at a certain period ceases
altogether. If we watch the development of a

24 STRUCTURE AND PROPERTIES

branch, we shall find that its cuticle stretches
during a considerable period, after which it
breaks, and is replaced by an epidermis : the
same thing occurs in all cases in which we can
follow the growth of any organ ; and if plants
appear to increase indefinitely, it is because fresh
organs are perpetually added to the former ones,
and the older parts fall sooner or later into that
inert state in which they are no longer capable
of extension.

18. Elasticity of vegetable tissue is that pro-
perty by which each membrane is enabled to
resume its proper position when deranged by any
external force. It implies a certain degree of
rigidity, and is consequently less sensible when
the tissue, having received but few deposits, is
still in a semi-fluid state, than when it is of older
growth. This property is worthy of remark,
because it occasions certain movements, which
might be mistaken for vital action. It is very
variable in intensity. Every one must have ob-
served that a branch, if bent out of its natural
course, returns to it of itself ; but in certain cases
this is not so — the dracocephalum-moldavicum
has pedicels which may be turned from their
natural direction, and will remain in that which
has been forced on them. The plant, on account

OF VEGETABLE TISSUE. 25

of this deviation from the ordinary law of elas-
ticity, has been called cataleptic. The elastic
movements of plants are sometimes determined
byjan arrangement of the organs, which once
deranged, although spontaneously, have never-
theless no power to return to their original state ;
thus the four stamens of the parietaria tribes have
their filaments turned inwards before flowering ;
but as this process advances, and the filaments
enlarge, a moment arrives when they no longer
adhere together, but burst open with considerable
force : this is facilitated by the tubercles which
are formed in the inside of the filament ; the
anthers, shaken by this sudden movement, scatter
their pollen, the filaments die, and the phenome-
non can never be repeated. All these effects are
consequent on the manner in which the parts are
arranged, which indeed is connected with the life
of the plant, but must not be confounded with
those movements which are really dependent on
vital action.

19. The power of imbibing moisture exists in
both organic and inorganic substances ; thus
deliquescent sails, as they are called, are so emi-
nently hygrometric, that their own particles are
in the end dissolved in the water they have im-
bibed. The effect cannot be carried to this extent

26 STRUCTURE AND PROPERTIES

in organized bodies, being limited by their na-
ture ; thus hair, whalebone, &c. though capable
of being employed to indicate the state of com-
parative dryness or dampness of the air, from
their power of attracting moisture to a certain
extent, are nevertheless, under ordinary circum-
stances, insoluble in water. It is the same with
several vegetable productions, which can, conse-
quently, be similarly employed. Vegetable tissue
is in general more hygrometric in proportion as
it is less loaded with extraneous substances : the
woody fibre is, in this respect, very different from
the bark ; this latter being scarcely hygrometric,
while the woody fibre imbibes moisture with great
facility. This absorption of water occasions an
enlargement of the woody portion, which thus
presses itself, as it were, against the bark, and it
is in consequence of this pressure, that the gums
contained in and under the bark of certain trees
are forced outwards, as in the cherry, plum, &c.
Senebeir has greatly exaggerated the effects of
this power in attempting to account by its agency
for the ascent of the sap, and for some of the
most important phenomena of vegetation. The
fact, that the sap ascends in plants which live
in water, and that it does not rise in dead plants,
might alone prove his theory to be erroneous.

OF VEGETABLE TISSUE. 27

20. " Connected with the hygroscopicity of
vegetable membrane, we may here mention 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 micro-
scope, it appears to possess a perfectly homo-
geneous texture, without pores of any kind ; and
yet water, milk, and other fluids, placed under
certain circumstances, are capable of passing
through it with considerable facility. The con-
dition required for producing this effect are
these: — Any two fluids which exert a mutual
affinity towards each other, being placed on oppo-
site sides of a membrane, their immediate inter-
mixture 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, a portion of
the treacle will soon be found to have exuded,
while a still larger quantity of water will have
penetrated into the bladder ; and this action will
continue until the fluids have acquired the same
density. The remarkable circumstance attend-
ing this phenomenon is the fact of the lighter

* This property is called Endosmosis.

28 STRUCTURE AND PROPERTIES

fluid having penetrated the membrane with
greater velocity than the denser fluid." (Hens-
low's Principles of Botany, p. 159-60.)

21. Vegetable existence has been supposed to
possess three vital properties, so termed from
their analogy with the powers similarly named in
the animal economy; viz. 1. Excitability. 2.
Irritability, and 3. Sensibility : by the first is
understood that peculiar state of the vegetable
tissue, which enables it to resist decomposition
by water much more energetically while living
than after death, and which also renders it
capable of supporting the action of air and heat
during life, in a manner totally different from
that in which their agency affects it afterwards.
Many phenomena common to all plants concur
to prove that this difference is inexplicable with-
out the admission of vital excitability ; such are
the rapid mounting of the sap in the living plant,
compared with the slow absorption of water in
the lifeless tissue ; the influence of light on the
ascent of the sap, &c.

22. The quality to which the term Irritability
has been applied by some physiologists, is that
by which certain portions of some plants respond
to the agency of external objects, in a manner
somewhat similar to the sudden contraction of

OF VEGETABLE TISSUE. 29

the muscles in the animal body ; for example,
when the base of the stamen of the Berberis is
pricked with a needle, it is seen to depress itself
towards the pistil. If the hairs of the Drosera
are irritated, they press themselves close to the
leaf ; and one instance, especially, must be fami-
liar to most persons, viz. the closing of the leaves
of the Mimosa pudica, or sensitive plant, on the
slightest touch. It has, however, been conjec-
tured that all this class of facts may be referred
to vital excitability alone ; and with respect to
the third quality, which some persons have attri-
buted to plants, sensibility, or more properly
sensation, until much more positive proof of it
shall be adduced than has yet been offered,
it can only be classed with those phenomena
which are referrible to excitability. The same
argument, from analogy, which leads us to sup-
pose that the lower orders of animals are far
less sensitive than the higher, is against the idea
that plants, wholly unprovided as they are with
any apparatus of nerves, can be susceptible of
those impressions, whether of pain or pleasure,
which in the animal economy we have every
reason to refer to a particular portion of the
nervous system : — nor can we see in the general
order of things any sufficient cause to lead us to

30 STRUCTURE AND PROPERTIES

an opposite conclusion. Although it may be a
poetical and an agreeable idea to imagine the whole
vegetable world welcoming and rejoicing in the
return of spring, and basking in the warm beams
that are so congenial to our own nature and
necessities, yet the satisfaction this notion might
afford would be far more than counterbalanced
by the reflection that we could not pluck a rose
or gather a peach without inflicting pain ; and
that the pruning knife was an instrument of tor-
ture. One strong reason to conclude against the
sensibility of plants, arises from the great contrast
between the provision made for them and for
animals during the winter. It is known that
animals liable to exposure to cold are well de-
fended against it by their fur or down ; while
trees, stripped bare at the season when all sen-
tient beings look for shelter, would indeed un-
dergo a heavy penalty if they could feel the chill
blasts that howl around them.

23. It was formerly supposed that vital ex-
citability was seated exclusively in the vessels,
but M. de Candolle's reasoning is conclusive
against this theory, as he shews that the power
is possessed by plants wholly formed of cellular
tissue ; that is to sav> they offer the same facts
from which the existence of vital excitability in

OF VEGETABLE TISSUE. 31

vascular plants has been deduced. The imme-
diate cause of these phenomena appears to be
that the cells and vessels of the tissue are endued
with a contractile power, analogous to that of the
heart in animals, or rather, perhaps, to the con-
traction and dilatation observed in certain micro-
scopic infusoria : there are cases in which this
action (though ordinarily confined to parts so
minute as to escape observation) becomes visible :
for instance, if a branch of the Euphorbia, or
any other milky plant, be cut across, the milky
juice exudes from both surfaces. If it flowed
by an impulse given either from below or from
above, it would only appear on one half of the
severed plant ; if it issued forth by its own weight
by the law of gravity, it could only flow when
turned downwards, and if the lower half were
held upright,-the fluid would stand as in a cup ;
but it exudes let the branch be held in whatever
direction it may, and it must therefore be owing
to some contractile power within.

The agents which occasion or modify vegetable
excitability are light, heat, and perhaps elec-
tricity ; and in addition to these, accidental causes
of excitement, such as blows, the action of certain
chemical substances, &c. will in some cases pro-
duce the phenomena by which it is manifested.

CHAPTER II.

NUTRITION.

24.

THE general structure and properties of
Vegetable tissue having been explained,
it becomes desirable briefly to describe the or-
gans by which plants are nourished, and enabled
to perform the functions of growth and secre-
tion, as the physiology of this part of the sub-
ject, which is in fact, nothing more than the
active agency of those organs, cannot be well
understood without some distinct idea of their
form and nature.

The organs which are indispensable to the
nutrition of all vascular plants, are three, i. e.
the Root, the Stem or Trunk, and the Leaves.
In cellular plants these are often so united that
the parts are scarcely distinguishable. It will
be desirable to consider them in detail as they
are found in vascular plants, in which they are
generally well defined.

25. -The Root (radix). This terra is com-

NUTRITION. 33

monly applied to that part of a plant which is
beneath the earth, but this is not an exact defi-
nition, as there are roots which exist out of the
soil altogether,* it may be more correctly de-
scribed as that portion which vegetates down-
wards. The point of junction between the stem
and the root bears the name of the neck, or
crown :— from this point they proceed in oppo-
site directions, so that the part the nearest to
this is, in both organs, the oldest, and in gene-
ral the thickest. The office of the root is
double, it both serves to fix the plant in the soil,
and to imbibe its requisite nourishment. Roots
are never green excepting at their extremity where
it has been shown (8) that they perform their
function of absorbing water through their spon-
gioles. As soon as a plant begins to exist, a
principal, or tap root, may always be perceived,
growing in an opposite direction to the stem :

* Such are the curious braces as they may be called
sent out by the Pandanus, or Screw Pine— this stem is'
smaller at the bottom than it is above, and ae this form
is of course unfavourable to the steadiness of tlie plant
in the ground, it sends out roots at various distances up
the stein which find their way into the earth, and thus
act as buttresses for its support. Such is also the well
known method by which the Banyan, from a single tree
becomes a grove.

34 NUTRITION.

it is very remarkable in the seed, and is there
called the radicle; this principal root, after
having sent out branches in all directions, often
perishes, and the ramifications frequently take a
horizontal course. Besides affording nourish-
ment by direct absorption from the soil, the roots
are often storehouses of nutritive matter. Such
are those of the Dahlia, which abound in starch,
the orchis, &c. &c. such roots are generally
much swelled or thickened. In their anatomi-
cal structure roots principally differ from stems
by the absence of stomata, and, in the Exo-
genes, by the want of a central pith or medulla
(27).

26. The Stem (caulis). This organ is never
really wanting in vascular plants, though in
some it is hidden beneath the earth. " The
stem is produced by the successive development
of leaf buds (35), which lengthen in opposite
directions." The stems of Exogenous plants
possess the most complicated organization, but
as they are much better understood than those
of the Endogenous and Cellular tribes, and as
the Exogenes comprise all the trees of our own
part of the globe, they are more interesting to
us.

Four distinct parts are observed in Exoge-

NUTRITION. 35

nous trees — the Pith, or Medulla, in. the centre;
the Wood surrounding the pith ; the Bark which
envelopes the whole, and the Medullary Hays,
which run horizontally across the wood and
bark, from the centre to the circumference. To
these may be added the Medullary Sheath which
is but the first annual layer of wood.

27. The Pith, or Medulla, is composed of
cellular tissue, whose cells are large, regular,
and spongy, it contains starch which is after-
wards converted into mucilage,* and its office
seems to be that of nourishing the young buds ;
when this function is performed it perishes.
Around it is the Medullary Sheath which differs
from the succeeding annual layers only in
having its vessels usually capable of being un-
rolled, and consequently truly spiral, it enve-
lopes the pith like a case, and its fibres often
branch into the substance of the pith itself,
where they appear as scattered spiral vessels.
The medullary sheath has been supposed to be
the channel by which oxygen, liberated by the
decomposition of carbonic acid, is conveyed to
the leaves.

* See " Introduction to Practical Organic Chemistry,"
P- 49, $ 36.

36 NUTRITION.

28. The Wood immediately surrounds the
central pith, and is formed of concentric layers
of vessels, or ducts, and of fibre, annually depo-
sited outside each other. It consists of two
parts, namely :

1. The central layers which are harder,
more coloured, and evidently older than those
near the circumference : these form what
workmen call the heart of the wood, and na-
turalists, true wood, or lignum.

2. The external layers, which being incom-
pletely formed, are softer, whiter, and younger
than the former, and constitute what is called
the Alburnum.

In some trees, especially in those which are
not very hard, the line of demarcation between
the true wood and the alburnum is not very
perceptible ; in the hard woods it is well marked,
both by texture and colour, as in ebony, in
which the wood is jet black and the alburnum
white.

Every layer both of the wood and alburnum,
if we except the medullary portion, is composed
of vessels and fibres intermixed with elongated
cellular tissue. The sole organic difference be-
tween the wood and the alburnum, is, that in
the former, the interior of the cells and perhaps

NUTRITION. 87

of the vessels, is encrusted, while in the latter it
is empty or only filled with juices scarcely so-
lidified. M. Dutrochet has proved that the
different degrees of hardness between divers
woods, and between the wood and the albur-
num, is owing to the nature of the juice con-
tained in their tissue, and not to the tissue it-
self, which is identical in both. The tissue of the
box and the poplar, though these woods differ so
much in density, become perfectly similar when
the matter they contain has been dissolved out
by nitric acid. The spaces which after mace-
ration appear to exist between the woody layers,
are not really such ; but were filled with cellu-
lar tissue, analagous, for each annual layer,
to the central pith of the first year's growth.
Each woody layer, being, in the Exogenous
trees of cold or temperate climates, the produce
of one year, the number of concentric zones in
a transverse cutting of a stem will show the
number of years during which that part of the
tree has existed. To know the entire age of
the tree itself, it must be cut exactly at the
crown, since of course the higher portions of the
stem were not in being when the deposits on
the lower were formed, An inscription graven
on the trunk of a tree, and penetrating to the

38 NUTRITION.

Alburnum, becomes covered by new woody
layers, and may be discovered unaltered: thus
Reisel found in 1675, some capital letters in
the centre of a beech tree.* The nourishment
of the tree being entirely 'performed by the
young or sap wood (the alburnum) is carried on
when age and decay have deprived it of its heart
wood. Thus we see the hollow trunk of an oak
or willow capable of sustaining large branches
and putting forth foliage almost as luxuriant as
when in its prime.

29. The cortical system (or Bark) of Exo-
genes is organized in a manner analogous to
that of the central, or ligneous system — every
stem acquiring a cortical, as well as a ligneous
zone annually; but while each fresh woody
layer is deposited on, and externally to, that of
the year before, each layer of the bark is pro-

* There is a singular illustration of the manner in
which the older portions of a stem are completely en-
veloped in the later deposits of woody matter, to be
seen in a part of the stem of the Wellington Tree, pre-
sented to the British Museum by Mr. Children. A
chain had been passed round the trunk when it was a
sapling, and was so entirely buried in the layers of suc-
ceeding years, that it was only by the violent resistance
the chain made to the tools of the workmen who were
sawing the tree, that its existence was discovered.

NUTRITION. 39

duced on the inner side of that previously
formed. The younger and more flexible por-
tion is called the Liber, and is deposited on the
alburnum of the wood ; the older layers are
pushed outwards, and are the cortical layers, or
true bark : they represent in the bark, what the
heart wood is in the central portion, but with
this great difference, that the woody layers
being deposited beyond each other in the order
of their formation, remain perfectly entire ;
while the layers of bark, acquiring fresh zones
from within, undergo considerable distension —
thus, although the number of cortical layers
equals those of the wood, their fate is very dif-
ferent: those of the bark, distended by the
growth of the tree after the first year, always
present more or less flexuous fibres, and this
tendency augments with age, while on the con-
trary the fibres of the wood continue straight
and rigid. The woody layers remain in the
state of alburnum till they have acquired their
proper hardness, — the layers of bark on the
contrary, soon lose their freshness, and never
attain the same degree of solidity. The first,
placed beyond the reach of atmospheric influ-
ence, preserve the appearance of life ; the lat-
ter, exposed to the action of the air and light,

40 NUTRITION.

soon dry up and split. This* difference in the
mode of growth accounts for the different re-
sults of such experiments in this part of the
tree, as were before mentioned as having been
tried in the wood — if an inscription be made on
the bark only, the letters without lengthening,
gradually become thicker, larger, further apart,
and are at last effaced. The secretions of a
plant are often deposited in the bark.

30. The Medullary Rays, formed of com-
pressed parallelograms of cellular tissue, connect
the centre and circumference of the trunk : they
strengthen the tissue, and convey secreted nu-
tritive matter in a horizontal direction. They
are distinctly perceptible in a section of a woody
stem. Sometimes they can be traced from the
central pith to the extreme circumference, but
ordinarily the line is interrupted.

31. Stems vary extremely in appearance in
different plants — sometimes they run under the
ground, and are improperly called creeping
roots; occasionally they lie prostrate, and send
roots into the earth underneath them ; — the

* It will be therefore observed tbat, strictly speaking,
it is the woody portion only of Exogenes to winch the
term applies, as the bark follows the laws of the Endo-
genous tribes.

NUTRITION. 41

term rhizoma is then applied to them ; — and
sometimes they are much swollen, and called a
tuber; — or if they (or rather their leaf buds) (35)
thicken below the ground, a corm. All these
forms of stem have been called roots ; but there
are two marked distinctions between these and
true roots. They have what are termed nodes,
which are the points at which the leaf buds are
formed, as well as leaf buds, which are never
found on roots properly so called. Scales being
the rudiments of leaves, no proper root can be
scaly.

32. The stems of Endogenous plants, consi-
dered generally, have as their common charac-
ters.

1. They are composed of one single homo-
geneous mass.

2. They have no true medullary channel
nor distinct medullary rays.

3. Their older fibres are on the circumfe-
rence, and the newer deposits in the centre,
from which latter circumstance they take their
name.

They are less marked in character, and pre-
sent less regularity of structure than the Exo-
genes. Tims one species, the Palm, will afford
a sufficient idea of the whole class. This stem

42 NUTRITION.

is generally upright, strong, simple, regularly
cylindrical, and crowned at its summit with
a bunch of leaves : transversely divided, it ap-
pears to be composed of scattered fibres, mixed
with cellular tissue, which unites them together.
At a glance it is obvious that the fibres of the
circumference are more close, of a firmer consist-
ence, and older than the inner ones, which are
distant, soft, and surrounded by a loose cellular
tissue. Each fibre consists of a bundle of tracheae,
and rayed and dotted vessels. The difference in
consistence between the circumference and the
centre of the trunk is always perceptible, some-
times very remarkable : for instance, there are
some palms whose exterior is so hard that a
hatchet can make no impression on it, while the
inside is a loose spongy tissue, quickly decaying
in a humid air. The circumference of the palms
corresponds to the wood of our trees, while the
centre is a species of alburnum. It is from this
central alburnum that the leaves and flowers
spring, or in a word, it is from the centre that the
development of all the parts takes place. Im-
mediately on the appearance of the plant a first
row of leaves is put forth, attached to the crown
by a layer of fibres — the next year a second row
is produced within the former, and distends them

NUTRITION. 43

— it is the same with the succeeding seasons, till
the period when the outer layer having acquired
by age the hardness of perfect wood, and no
longer admitting of further distension, is in-
capable of any increase of diameter.

33. A Leaf has two distinct parts — the Pe-
tiole, or stalk, and the Lamina, called also the
blade or limb ; the former consists of fibres pro-
ceeding from the stem, and enclosed in a cellular
integument ; the latter is formed by the ramifi-
cations of the fibres of the petiole, and the expan-
sion of its cellular tissue. In exogenous plants
the veins branch in various directions, so as to
form a kind of network ; in the endogenes they
run parallel to each other, and are simply con-
nected by transverse veins. When the petiole
becomes lengthened so as to curl up, it is called
a tendril, and many curious forms, such as that
of the Pitcher Plant, are but expansions of this
portion of the leaf. The limb of a leaf presents
three distinct parts; the superior and inferior
surfaces, and the mesophyllum, or substance con-
tained between the nervures. Both the surfaces
are ordinarily furnished with stomata, the under
side much more abundantly than the upper ; but
in leaves which rest by their under surface on
the water, this relation is reversed, their upper

44 NUTRITION'.

surface (that which is exposed to the air) being
alone furnished with stomata. In like manner,
leaves which are constantly immersed have no
stomata. The nervures of the superior surface
are supposed to be the channels by which the
juices are conveyed from the stem to the limb ;
those of the lower surface conduct them back to
the bark. If we attempt to twist a leaf so that
the naturally superior surface shall be undermost,
it endeavours to regain its original situation;
and if the force used prevent it from doing so,
the leaf quickly perishes.

34. Stipules. This name has been given to
small leafy organs, whose only essential character
is their lateral position at the base of the leaf.
They are occasionally changed into true leaves,
and one of them is sometimes wanting; they
vary exceedingly in appearance.

35. Leaf Buds are those vital points, sur-
rounded by scales, which are usually found in
the axils of the leaves, and from whose growth
a branch is formed.* The scales, as the vege-

* " Leaf-buds are always formed from the cellular
portion of the stem or brandies, on which the function
of extending the growth of the individual seems espe-
cially imposed. They may be distinctly traced, in young
branches, to the pith ; and where this has dried up, they
may be seen to arise from the medullary rays." (Car-
penter's Veg. Phy. p. 197.)

NUTRITION. 45

tation proceeds, are replaced by leaves. When
leaf buds are found under ground, and become
swollen and large, like the crocus, &c. they are
called bulbs or conns (31). In both cases young
bulbs are produced in the axils of the scales, and
feed on the old bulb. Some of the latter tribe
raise themselves out of the earth by a very
curious process. " In some Gladioli," says Pro-
fessor Lindley, " an old corm produces the new
one always at its point ; the latter is then seated
on the remains of its parent, and being in like
manner devoured by its own offspring, becomes
the base of the third generation." Leaf buds
are divided into regular and adventitious, the
former being always found in the axil of the
leaves, none of which, in fact, are ever really
without them, though in some cases they are
undeveloped; so that the arrangement of the
branches of a plant would always be the same as
that of its leaves, were it not that the buds are
very unequally matured : and this regularity is
found to exist in reality through every part of a
plant, although from the obliteration of some
portions, and the non development of others, it
cannot always be traced throughout. " It has
been distinctly proved, that while roots are pro-
longations of the vertical or woody system, leaf

40 NUTRITION.

buds universally originate in the horizontal or
cellular system."

36. The nutritive organs of cellular plants are
far less defined than those of the vascular tribes,
and it even appears as if the whole mass of the
former were composed of one homogeneous sub-
stance, capable of taking diverse forms, and ful-
filling different functions, without being sepa-
rated into distinct organs. They are analogous
in many cases to those of vascular plants, but
never consist of vessels. They vary so much in
the different species of the cellular tribes, such
as the Mosses, Hepaticae, Lichens, &c. that it
would be impossible to describe them here with-
out entering into details far exceeding the limits
of this work.

37. On considering the phenomena of vege-
table nutrition, one fundamental principle meets
us at the outset ; viz. that no aliment ever pene-
trates the plant, unless water serve it for a
vehicle. Without water there is no vegetation.
The first thing then to inquire is how it enters
into the system. The habitual and vital absorp-
tion of water is performed by the spongioles of
the roots (8), although under certain conditions,
such as rain, heavy dew, artificial watering, &c.
the surfaces of the leaves have also the power of

NUTRITION. 47

imbibing it. Plants being utterly without loco-
motion, and unable to seek their own food, it
follows that their nourishment must be so abun-
dant in nature as to be almost universally within
reach, and so easy of absorption as to offer no
resistance to their comparatively feeble powers
of action. These necessary conditions are beau-
tifully fulfilled by the spongioles and by the
nature of water. The spongioles make no selec-
tion of healthy material for the nourishment of
the plant : and the absorption of fluid through
their medium appears to be regulated merely by
the readiness with which certain solid substances
held in solution can be received along with the
water. Thus the action of the spongioles sepa-
rates a portion of the water from a solution of
gum arabic, leaving the gum behind in the re-
maining solution, in an increased state of satu-
ration ; but sulphate of copper in solution — one
of the substances most injurious to vegetation —
is rapidly absorbed. Dr. Carpenter, however,
mentions an exception to this, in the power which
some plants exert of taking up certain mineral
substances which seem peculiarly requisite for
them. He says, " if a grain of wheat and a pea
be grown in the same soil, the former will obtain
for itself all the silex, or flinty matter, which the

48 NUTRITION.

water can dissolve; and it is the deposition of
this in the stem which gives to all the grasses so
much firmness. On the other hand, the pea will
reject this, and will take up whatever calcareous
substances (or those formed of lime and its com-
pounds) the water of the soil contains, these
being rejected by the wheat." (Carpenter's Veg.
Physiol. p. 89.) On this subject Professor Dau-
beny has made many curious experiments.

38. Plants, then, absorb water by their roots ;
but is it pure water only they require ? Modern
chemistry has decided this question in the nega-
tive. Water in its absolute purity, such as we
obtain it by distillation, does not exist in nature :
if exposed to the influence of the atmosphere it,
holds some of it in solution ; if it is in contact
with the soil it will imbibe saline, or organic
particles, and thus the water which reaches plants
is always more or less charged with other sub-
stances.

39. When water, accompanied by the soluble
matter it contains, has entered the spongioles, it
becomes a part of the juices of the living plant,
is propelled forward with great force, and re-
ceives the name of sap. This sap rises in the
plant, and probably in its course furnishes the
air with which the vessels are filled. The rapidity

NUTRITION". 49

with which the sap rises has been proved by
several curious experiments. Hales introduced
the root of a vigorous pear tree into a glass tube
hermetically sealed at the top, with a lute quite
impervious itself to air ; this tube was filled with
water, and placed in a cup of mercury ; in six
minutes the mercury had risen eight inches in
the tube, to replace the water that had been
absorbed. From other experiments on the force
with which the sap rises, Hales drew the con-
clusion that it is five times greater than that
with which the blood is thrown into the crural
artery of a horse. " If a piece of bladder be
tied over the surface 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 indi-
cate the pressure of a powerful force, a ' vis d
tergo,' residing in the lowest extremities of the
roots, by which the propulsion of the sap is regu-
lated. Although these results so closely resemble
those of endosmosis (20), 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 com-
posing the spongioles, and the water in the soil
E

50 NUTRITION.

which surrounds them, by the ordinary operation
of endosmosis, 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
material is obtained for carrying on the endos-
mosis, 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 renewed, and without
which the endosmosis would of necessity soon
cease." (Henslow's Principles of Botany, pp.
181-2.)

40. It would seem natural here to observe
what course the sap takes in its rise in the plant,

NUTRITION. 51

but the question of the channels through which
it is propelled is by no means one to which an
indisputable answer can be given. " The great
difficulty," says Professor Henslow, " in deter-
mining the precise channel through which the
progression of the sap takes place, must be as-
cribed to the perfect transparency of the vege-
table membrane, and the extreme minuteness of
these organs themselves. By 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 regularly traced ; but on exam-
ining microscopically 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.

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 . . .
.... The probability seems to be, that the
crude sap rises, at least in woody stems, through
the intercellular passages, where it bathes the
surface of the cells and vessels, all of which are
so many distinct organs destined to act upon
it." (Henslow's Principles of Botany, p. 179.)

52 NUTRITION.

Many excellent observers, however, deny the
general system of intercellular passages, or of
consequence the passing of the sap by these
means; the question must therefore be consi-
dered as undecided.

41. Heat and light exercise great influence
on the ascent of the sap. A plant exposed to
the light takes up a sensibly larger quantity of
water than one kept in darkness. The leaves
exhaling moisture in great abundance (to the
amount of about two thirds of the water taken
up) and consequently requiring and receiving a
proportionate supply, tend largely to promote
the direct ascent of the sap, and a terminal
bunch, such as is always left by mulberry grow-
ers when the leaves are picked, determines the
rise of the sap to the top of the tree, whereas if
the summit be left bare, the juices will scarcely
be active enough to reach it, and in addition to
this vertical action, the cellular envelope which
surrounds the branches, and which communi-
cates with all the woody and cortical layers by
the medullary rays, draws the sap, by the ac-
tion of the living cellules, in a transverse direc-
tion. In Endogenous plants, in which there
are no medullary prolongations, the sap is ne-
cessarily drawn to the summit by the leaves,

NUTRITION. 53

and it is only in youth that the cellular envelope
of the branches, can receive a small quantity of
moisture : as soon as the action becomes har-
dened, further lateral growth is impossible. The
powerful action of the leaves, &c. as here de-
scribed, in determining the ascent of the sap, is
a much more probable account of that pheno-
menon than any propulsive vis d tergo like that
supposed in the extract from Professor Hen-
slow in paragraph 39, to be resident in the
lowest extremities of the roots.

42. It is well known that fresh plants ex-
posed to the air part with a considerable por-
tion of their moisture. This exhalation is not
performed equally all over the plant, but is in
exact proportion to the quantity of stomata on
any given part, and it is curious that this fact
was established by the experiments of Guillard,
Saint-Martin, Bonnet, and Senebier, before the
existence of stomata was known. Light has
great influence in increasing the transpiration of
plants. This exhalation may sometimes be ob-
served in the form of drops of water resting on
the leaves, &c. when circumstances preclude
the possibility of their arising from rain or dew.
" The manner in which the stomata act is un-
known ; and consequently we are compelled to

54 NUTRITION.

ascribe the function which they perform to the
immediate operation of the vital force." (Hen-
slow.)

43. The influence of the atmosphere on the
nourishment of plants, or in other words, their
respiration, is the most complicated and perhaps
the most important of all the processes of vege-
table economy. Animal respiration, which is
in effect, that process by which the blood is ex-
posed to the action of the air, may shew us by
analogy how necessary it must be to consider
the relations of the nutritious juices of this class
also of organized beings with atmospheric action
in order to comprehend their physiology. Thirty
years after Bonnet (then occupied in researches
on the uses of the foliage of plants) had first
observed that air was given out by living green
leaves, Priestley's attention was turned to the
subject ; and he submitted the air thus obtained
to analysis : it proved to be either pure oxygen,
or to contain that gas in a much larger propor-
tion than atmospheric air does : other chemists
confirmed the details of Priestley's experiments.
The phenomenon is evidently connected with
the life of the plant, since leaves though still
green but no longer living, give out no gas at
all until the commencement of decomposition.

NUTRITION. 55

The direct rays of the sun are necessary to the
effect : no other light, however strong, will suf-
fice. The course of the phenomena connected
with the respiration of plants appears to be the
following. The water which enters the plant
by the roots contains carbonic acid, which is
carried with it into the green parts ; it is there
decomposed under the influence of the sun's
rays — the carbon is fixed in the plant, and the
oxygen escapes. The carbonic acid which is
formed from the oxygen of the air in all those
portions of the plant which are not green, is
partly dispersed in the atmosphere, partly dis-
solved in water, which water at last reaches the
plant again, and thus is ultimately absorbed by
the roots, drawn up to the leafy parts and there
decomposed. The water taken up by the roots
holds besides its carbonic acid, a certain quan-
tity of soluble matter containing carbon : this
carbon is also carried with the sap into the
green parts, it combines during the night with
the oxygen which had been previously absorbed
by them, and the following day such of this car-
bonic acid thus formed in the leaves as has not
been given out during the night is decomposed
by the solar light, as if the carbon could not be
usefully deposited in the nutritive juices unless

56 NUTRITION.

it proceed from the decomposition of carbonic
acid gas. Thus the whole of this important
function, i. e. vegetable respiration, appears to
have for its object the fixing carbon in the
plant, while the result of animal respiration is
to diminish its quantity in the body, or in other
words, to supply animal heat by its combustion.*
It is well remarked by Mr. Hunt, that "The
animal kingdom is constantly producing car-
bonic acid, water in the state of vapour, nitro-
gen, and, in combination with hydrogen, ammo-
nia. The vegetable kingdom continually con-
sumes ammonia, nitrogen, water, and carbonic
acid. The one is constantly pouring into the
air what the other is as constantly drawing from
it, and thus is the equilibrium of the elements
maintained.

" Plants may be regarded as compounds of
carbon, vapour, oxygen, hydrogen, and nitrogen
gases, consolidated by the all-powerful, all-per-
vading influences of the solar ray ; and all these
elements are the produce of the living animal,
the conditions of whose existence are also greatly
under the influence of those beams, which are

* See Introduction to Practical Organic Chemistry,
p. 61.

NUTRITION. 57

poured in unceasing flow from the centre of our
system. Can any thing more completely dis-
play a system of the loftiest design, and most
perfect order, than these phenomena?"*

44. It has been shown that the watery
juices, pumped up as it were, by the roots, have
been drawn to the leafy parts ; a large part of
the water is there evaporated, green matter is
formed, and the decomposition of carbonic acid,
ammonia, and water, fixes carbon, nitrogen, and
hydrogen in the residuum. From these changes,
to which the term assimilation has been given,
results the formation of a new and descending
juice whose existence is perhaps less palpable
than that of the ascending sap, but concerning
which there can be no doubt. If a circular in-
cision be made in the bark of an exogenous tree?
a tumour will in a short time appear above the
wound ; this tumour increases, and if the cut be
very narrow, it soon reaches the lower lip of
the wound, the communication is restored, and
the tree lives on as usual, but if the wound be
too wide to admit of this junction, the tumour
continues to increase till the branch (or the
tree, if the main trunk have been operated on)

* Researches on Light, p. 200.

58 NUTRITION.

perishes in a longer or shorter time according
to circumstances. If the ascending current were
impeded, it is obvious the accumulation which
causes the tumour, must take place on, or below
the lower lip of the incision. This descending
sap, or proper juice, — whose chemical composi-
tion appears to be water and carbon, — and which
itself principally in the form of gum, is capable
of being, by very slight modifications, trans-
formed into fecula (starch), sugar, and lignine,
quits the leaves during the night, and traversing
the bark and pith in exogenous, and the wood
in endogenous plants, reaches the roots. In its
progress it deposits nutritious matter, which,
more or less mixed in the woody portions with
the ascending sap, or absorbed with the water
which is taken up through the medullary rays
by the cellular envelope, is imbibed by and elab-
orated in the cells. It meets in its course and
especially in the bark, glands and glandular
cells, which imbibe it and form in their cavities
peculiar secretions (51) most of them incapable
of nourishing the plant, and destined to be re-
jected or carried into the substance of the
tissue.

The water which rises from the roots to the
foliage is almost as pure when it reaches it, as

NUTRITION. 59

at its entrance into the plant, if its course has
been rapid through the older wood,* where the
particles are slightly soluble ; that on the con-
trary which has traversed those younger por-
tions in which there is much cellular tissue filled
with nutritive particles, slackens its course,
mixes with and dissolves them, and arrives at
the higher parts of the plant loaded with nou-
rishment. The cells appear to be the true
organs of nutrition, in which the decomposition
and assimilation of the juices takes place. In
each cell ligneous matter is deposited which
coats its walls, and the inequalities of this depo-
sit in many cases appear to have given rise to
the idea that the cells were perforated — the
thinner portions being so r transparent, that
under the microscope they have the appearance
of pores. It is evident from the above detail
that there is no circulation in plants strictly
similar to that of animals, but that there is an
alternate ascent and descent of the sap.

45. It will be gathered from the account of
the course of vegetable nutrition just given that

* It has been proved by colouring the water with co-
chineal, that the ascent of the sap certainly takes place
through the ligneous system, though the particular chan-
nels may be doubtful.

GO NUTRITION*.

the oxygen, hydrogen, carbon, and nitrogen, of
which plants are chemically composed (1) are
thus derived. The oxygen is abundantly fur-
nished by the decomposition of carbonic acid,
by the surrounding atmosphere, and by the
water taken up into the system. The carbon,
which constitutes so large a part of the texture
of plants that it retains the form and character
of the species when the other portions have
been separated from it, and it alone remains as
charcoal,* is also mainly derived from the de-
composition of carbonic acid. The hydrogen is
partly obtained from the water the plant takes
up by its roots and leaves, and also from the
same source as the nitrogen, which although so
abundant in our atmosphere as to constitute
four fifths of its whole composition, does not
appear to be thence imbibed in its simple form
by plants, but to be supplied to them combined
with hydrogen in the form of ammonia, the
great ingredient in those animal manures so
important in agriculture. " It appears," says
Dr. Carpenter, " from recent inquiries, that the

* A remarkable instance of this may be noticed in
the triangular pith of the alder used in the manufacture
of gunpowder.

NUTRITION. 61

organized tissues of plants, that is, their cells,
fibres, vessels, &c. freed from their contents, are
composed of a substance which every where
possesses the same composition ; and that this
consists of 24 carbon, 20 hydrogen, and 10 oxy-
gen, without any nitrogen ;" ... " on the other
hand the substances into whose composition ni-
trogen enters, though very generally diffused
through the tissues of the plant, do not seem to
undergo organization, but to form part of the
contents of the cells, vessels, &c. of which these
tissues are composed. It is curious to remark
that precisely the reverse is the case with ani-
mals ; their tissues being composed of a sub-
stance containing nitrogen, and substances which
are destitute of it being never found in their
bodies in an organized state, but only existing
there in the cavities of their cells, tubes," &c.
(Veg. Physiology, p. 117, § 163.)

46. It is obvious from the nature of the nou-
rishment which plants require, that the condi-
tion of the soil in which they are grown is a
matter of great importance. This subject has
already been noticed in the " Introduction to
Organic Chemistry," which forms the fourth
Number of these " Small Books," § 27, &c.
There is scarcely perhaps a stronger proof in

62 NUTRITION.

the history of human progress, of the light which
Truth sheds on every thing within its influence,
than the improvement that modern agriculture
has derived from the science of Chemistry. The
earth has been in some sort cultivated from
the time when Adam was sent forth to till it,
yet not until the last half century,* had the
advantages the husbandman may derive from
an acquaintance with the composition of the
soil of his fields, been known, and little could
the landowners of the days in which the alche-
mist, half empiric and half enthusiast, was pre-
paring the way by his toilsome and blind gro-
pings for the more enlightened researches of his
successors, imagine that the time would come
when chemistry should, at least metaphorically,
teach him how to turn earth into gold. The
subject is worthy of all attention, not merely
from the pecuniary advantage the scientific cul-
tivator may reasonably expect to gain, but from

* Sir Humphrey Davy, in his first lecture before the
Board of Agriculture, delivered in the year 1802, says,
" Agricultural Chemistry has not yet received a regular
and systematic form. It has been pursued by competent
experimenters but for a short time only ; the doctrines
have not as yet been collected into any elementary trea-
tise," &c.

NUTRITION. 63

the mental exercise which he may thus obtain,
while labouring in his proper calling. The
words of Sir Humphrey Davy in concluding his
volume on this subject are admirable: "The
same energy of character, the same extent of
resources which have always distinguished the
people of the British Islands, and made them
excel in arms, commerce, letters, and philoso-
phy, apply with the happiest effect to the im-
provement of the cultivation of the earth. No-
thing is impossible to labour, aided by ingenuity.
The true objects of the agriculturist are likewise
those of the patriot. Men value most what
they have gained with effort ; a just confidence
in their own powers results from success ; they
love their country better, because they have
seen it improved by their own talents and in-
dustry; and they identify with their interests,
the existence of those institutions which have
afforded them security, independence, and the
multiplied enjoyments of civilized life."

CHAPTER III.

GROWTH AND SECRETIONS.
47.

^ I ^HE progress of the growth of a plant, and
-»- the annual course of vegetation remain to
be considered, but it must be borne in mind, to
use the words of Professor Henslow, that " of
the precise manner in which the assimilation of
nutriment takes place we know nothing, and the
first steps towards the formation and develop-
ment of any organized being are entirely con-
cealed from us." New cells, fibres, and vessels
are most undoubtedly formed, or the leaf buds
must remain for ever undeveloped, but we are
ignorant of the immediate cause, and of the first
commencement of the effect ; for when we say
that the vital action is excited (whether in the
growth and nourishment of a plant or an ani-
mal,) what do we more than state a fact, whose
course we may indeed follow when we have
once observed it, but whose origin is, in the
present state of our knowledge, beyond our

GROWTH AND SECRETIONS. 65

reach ? — The course of growth, however, as
far as we can trace it, seems to be the following.
When a leaf bud begins to be developed, it is
seen to be formed of a short axis surrounded by
many leafy folds or scales. This axis begins to
lengthen ; the ascending sap is consumed by the
developing leaves, which separate from each
other by nearly equal distances, proving that
the shoot increases through its whole length.
The power of extensibility which is inherent
in vegetable tissue, especially when young, is
now probably an agent in the growth ; — the as-
cending sap, which is partially decomposed in
its upward course, supplies some nutritive matter
to the young cells, and, it may be conjectured,
stimulates them to that method of increase by
the spontaneous formation of one cell on the
surface of another, of which mention was made
in describing the cellular tissue. The young
leaves now begin to perform their office, they
exhale water, decompose carbonic acid gas, and
the formation of a descending current com-
mences. This descending sap, depositing in its
course such nutritive materials as are proper
for the formation of wood, gradually solidifies
the new shoot. If the ascent of the sap be aug-
mented by placing the plant so that it may ab-

68 GROWTH AND SECRETIONS.

sorb a large quantity of water, or if the current
of the descending sap be materially lessened, as
will occur if it is in total darkness, then shoots
are obtained extraordinarily long and herbace-
ous ; as in the weeping willow, and in the
blanched plants of flax, cultivated for the finest
Flanders thread. On the contrary, if the quan-
tity of water be diminished, and the plant ex-
posed to the influence of such circumstances as
will increase the fixation of carbon, we obtain
shoots which are short, firm, and woody ; as
are seen in the dry and light situations of south-
ern climates and high mountains. It appears
from the above facts that the lengthening of the
shoots depends on the influence of the ascend-
ing sap, while from the richness of the descend-
ing current, and consequent deposition of nu-
tritive matter, arises its solidification and the
diminution or cessation of vertical growth.
Those plants which have the greatest tendency
to form wood, attain proportionately the soonest
to that state of hardness which arrests the
lengthening of the shoot; thus it is seen that
there is a sensible relation between the slowness
of increase in height in each tree, and the quan-
tity of carbon which it furnishes to combustion.
In herbaceous perennials, the nourishment,

GROWTH AND SECRETIONS. 67

which would in trees serve to form ligneous
matter, is deposited in their roots, as gum, starch,
or sugar, and serves to feed the young shoots of
the following year. The newly formed branches
of exogenous trees do not grow much in diameter
till they have attained their length.

48. It cannot be said that the ascent of the
sap is absolutely null during the winter, but it is
then much weaker than in the remainder of the
year. In the early spring two phenomena occur ;
the heat of the sun begins to be felt on the bark,
or cellular envelope, and the more strongly in
proportion to the youth of the plant ; the vital
action is excited, and the sap begins to rise from
the roots, whose spongioles, at this epoch of
vernal vegetation, rouse from their lethargic
state.* Besides this effect, a second occurs, less
visible indeed, but highly important : during the
depth of winter, the earth has been warmer than
the air ; this comparative warmth is felt by the
roots, in which all the accumulated nourishment

* Perhaps from the circumstance that during the
winter the roots being full of the sap, which has been
there stored up, are incapable of imbibing more until that
begins to rise, which it does as soon as the influence of
the sun is felt on the bark.

68 GROWTH AND SECRETIONS.

of the preceding year remains ;f their vitality is
excited, and towards the end of winter radical
fibres are formed ; these, being fresh and vigor-
ous, begin to act, and pump up moisture from
the soil : thus, the revival of vegetation is effected
by the concurrence of two causes — the activity
of the roots, and of the cellular envelope. The
sap arriving at the leafy parts* promotes the
development of the buds ; it first reaches those
at the summit of the branches, either because it
moves more readily in a vertical than in a lateral
direction, or because the wood and bark of the
extremity of the branches, being young and
herbaceous, the cells have there retained a
stronger vital action. When the action of the
leaves has furnished a certain quantity of nutri-
tive juice, it descends through the laticiferous
tissue, supplies the material from which the
tissues and secretions of the plant are formed,
and which " being poured out between the bark
and the newest layer of wood, is the viscid sub-

t If a had preceding year has rendered the quantity of
nourishment small, the vegetation of spring is propor-
tionally weak.

* If the sap, as it rises, finds any fissure in the wood,
it flows from it as from a fountain, as may be observed in
what are called the tears of the vine when pruned.

GROWTH AND SECRETIONS. 69

stance called cambium ; in which the rudiments
of the cellular tissue that is to form part of the
new layer of wood, after a time present them-
selves. Even if this cambium be drawn oif from
the stem, its particles shew a tendency to arrange
themselves in a form resembling that of cells
and vessels ; though no perfect tissues are pro-
duced by this kind of coagulation."* When
this cambium is formed, the tree is said to be in
sap. The gradual solidification of the tissues
then proceeds, but the leaves continue to take up
nourishment, till, after some months of spring
and early summer, they are loaded with earthy
and carbonaceous particles, and then the buds
which are situated at their axils become com-
paratively more active than the leaves them-
selves, and now absorb the sap, while the leaf
wholly or in part ceases to do so. This effect,
taking place before the year is sufficiently ad-
vanced to check the second vegetation (or mid-
summer shoot, as it is called), continues, and
fresh branches are developed. At length the
leaves in autumn, being too much encumbered
with solid matter to retain any activity, cease to
perform their functions, and finally die. Then

* Carpenter's Veg. Phys. p. 208.

70 GROWTH AND SECRETIONS.

if, as has been shewn (13), they are articulated,
they fall off ; if not, they are destroyed by the
inclemency of the air. The leaves of what are
called evergreens form no exception, although
they endure longer than those of deciduous
plants, and instead of all falling off together in
the autumn, are renewed at various intervals ;
yet each individual leaf undergoes the ordinary
course of growth and decay. The change of
colour which withering leaves present is a very
curious subject, and one which the recent experi-
ments of Sir John Herschell and others have
tended to explain. Mr. Hunt thus expresses his
views of this phenomenon : " The change in the
colour of leaves appears to be entirely dependent
upon the absorption of oxygen, which all the
green parts of plants have the power of absorb-
ing, particularly in the dark. This true case of
chemical affinity, it would appear, goes on equally
with the spring or the summer leaves, but during
these periods the vital force, under the stimulus
of light, is exerted in producing the assimilation
of the oxygen for the formation of the volatile
oils, the resins, and the acids. In the autumn
the exciting power is weakened ; the summer sun
has brought the plant to a certain state, and it
has no longer the vital energy necessary for

GROWTH AND SECRETIONS. 71

continuing these processes : consequently, the
oxygen now acts in the same manner on the
living plant, as we find in experiment it acts upon
the dried green leaves, when moistened and ex-
posed to its action : they absorb gas and change
colour." (Researches on Light, p. 201.)

To the fall of the leaf succeeds the dormant
wintry state : there is no absorption of moisture
from the air, except through the cellular en-
velope ; the roots have not yet formed the young
radicles, and are in their least active state ; and
on account of these concurring circumstances,
this is the most favourable period for trans-
planting.

49. Cellular plants have, as has been said
before, no true vessels ; their fibres, if they may
be so called, are composed only of elongated
cells, and are never identical with the ligneous
fibre. The formation of the elongated cells,
when such exist, determines the direction of the
juices ; thus in the mosses, for instance, the stem
receives the water at its base, and by its radical
fibrils, and transmits it in a longitudinal direction
to the leaves, which direction is determined by
the elongated cells. These plants are likewise
nearly devoid of stomata, and can therefore only
exhale the superabundant water slowly, and

72 GROWTH AND SECRETIONS.

almost imperceptibly, and as a simple effect of
the porous nature of the tissue. The nourish-
ment of the cellular tribes appears then to be
thus accomplished ; the water which reaches
them penetrates either at given points, or by the
whole surface, and reaches the cells, where it is
elaborated by each, separately, in its own cavity.
50. As the blood of animals performs two
distinct offices, first, depositing throughout the
whole body the materials necessary for the
nourishment of each organ ; and, secondly, un-
dergoing in certain particular organs, named
glands, an operation which is called secretion,
and from which results the formation of par-
ticular juices ; so in the vegetable economy, the
sap, besides affording the general sustenance
which has been considered above, experiences a
peculiar action in certain organs, and furnishes
peculiar secretions as the result. These secre-
tions never form any part of the tissue of a
plant, and are either excrementitious, i. e. those
which are thrown off ; or special secretions, which
remain, in most cases, where they are formed,
and are seldom removed from one organ to
another ; but in others pervade the whole plant,
and, as in the case of Tannin, impregnate
the soil around them. The excretions are ex-
tremely various, and are probably a provision

GROWTH AND SECRETIONS. 73

for the removal of some material which is use-
less or injurious to the plant. One of the most
singular is that of the fraxinella, though this is
probably of the same class with the volatile oils to
be mentioned presently. If at the close of a dry,
hot day, a light be held near the top of that plant,
the vapour which surrounds it takes fire, and
burns with a lambent flame, without injury to the
plant. This vapour appears to be of the nature
of an extremely volatile oil, which escapes from
the small glands that cover the surface of the
plant, for the white fraxinella, which has fewer
glands than the red, exhibits the phenomenon in a
slighter degree. Other excretions are acid, some
are caustic, some glutinous (such as the leaves
of the gum cistus). Some plants secrete a waxy
matter from their surface ; others saline or sac-
charine particles. Manna is one of these excre-
tions, it both exudes naturally, and is also ob-
tained when artificial incisions have been made
in the tree. It would be impossible to describe,
or even enumerate, all the excretions of plants in
this treatise, the above may convey an idea of
their nature.

51. The Special Secretions are liquids secreted
in the bark, or some other organ. Their prin-
cipal characters are,

1. That they are all composed of two or

74

GROWTH AND SECRETIONS.

more principles, which can be separated, and
are not homogeneous, like the nutritive juice,
which, although it may of course, by chemical
analysis, be resolved into its elementary con-
stituents, presents no such peculiar principle
as do the special secretions.

2. These latter contain (in addition to their
carbon) oxygen and hydrogen, not in the pro-
portion in which they combine to form water,
but with a preponderance of one or the other
of those gases, and some of them, and those
the most important to man, also contain azote,
i. e. nitrogen.

3. All these secretions, if they are absorbed
by the roots of living plants, even by those
which produced them, act on them as poisons.
A sufficient proof of their not being intended
to percolate the plant in the manner of the
nutritive juices.

They consist principally of four divisions : —
1, Milky, and 2, Resinous Juices, 3, Volatile,
and 4, Fixed Oils,* and the local secretions,
properly so called. The milky and resinous
fluids, which form the first two classes, are some-

* With the fixed oils should perhaps be classed the
vegetable tallows and butters.

GROWTH AND SECRETIONS. 75

times expelled from the plant by accident or
disease, and are almost always capable of removal
from one portion of the plant to another. Pro-
fessor Henslow gives among the milky juices the
following curious instance of a tree called the
Cow Tree, from Humboldt : " On 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
in the year not a single shower moistens its
foliage. Its branches appear dead and dried ;
yet as soon as the trunk is pierced, there flows
from it a sweet and nourishing milk. It is at
sunrise that this vegetable fountain is most abun-
dant. The natives are then to be seen hastening
from all quarters, furnished with large bowls to
receive the milk, which grows yellow and thickens
at the surface. Some empty their bowls under
the tree, while others carry home the juice to
their children. The milk, obtained by incisions
made in the trunk, is glutinous, tolerably thick,
free from all acrimony, and of an agreeable and
balmy smell." The milky juices are contained
in the bark and leaves, the volatile oils in closed
cells, from which they are probably only exhaled
in consequence of the permeability of the tissue,
whence it happens that the organs which secrete

76 GROWTH AND SECRETIONS.

these oils are in general strongly odorous. The
fixed, or fat oils, as they are called, are formed
in cells, from which they never escape by any
natural process, but must be artificially extracted.
The caoutchouc (India rubber) is an instance
of a milky secretion, as are also our common
spurge, and opium, the well known product of
the white poppy. Most of the juices to which
the name of milky has been applied are tchife,
but not all of them, for instance, the lactic secre-
tion of our English celandine is of a brilliant
orange colour. Of the resinous juices one ex-
ample, common resin, is familiar to every one.
Of this class are the true balms, Gum Benzoin,
&c. Examples of volatile or essential oils, as
they are otherwise called, such as those of the
rose, &e. will readily occur to every one's recol-
lection ; and the fixed oils, those, for instance, of
the nut, the almond, linseed oil (the product of
the seed of the flax), olive oil, so useful for both
food and light to the inhabitants of the south of
Europe, with many others, are too well known
to need more particular notice here. The prin-
cipal chemical distinction between the volatile
and fixed oils is that the former are powerfully-
odorous, slightly soluble in water, with which
they pass over in distillation, communicating

GROWTH AND SECRETIONS. 77

their flavour to it ; and that they are volatilized
by heat without decomposition. The fixed oils,
on the contrary, are inodorous and insipid, sup-
port two or three hundred degrees of heat with-
out volatilizing, and are decomposed at a higher
temperature. In a physiological point of view
their difference is equally striking. The volatile
oils are found in the leaves or in the cortical
system, the usual place of the secretions ; the
fixed oils are either situated in the seeds them-
selves, or more rarely in the tissue of the peri-
carp.

52. There are many local secretions, of which
a detailed account belongs more properly to a
chemical treatise than to one that, like the pre-
sent, is only physiological, and also too brief to do
more than glance at the other sciences immedi-
ately connected with the subject : it will there-
fore only be possible to notice these secretions
slightly here. They consist of acids, such as
citric, malic, acetic, &c. prussic acid (remarkable
by the absence of oxygen) which is found in
peach and laurel leaves, &c. of Gluten, Albumen,
Tannin and Colouring matter, of which indigo
is one of the most important, and a variety of
other secretions or principles, each confined to
the particular vegetable in which it is found,

78 GROWTH AND SECRETIONS.

such as Asparagin, whose name denotes its origin
from the asparagus.

53. Besides the above, substances are found
in plants which are purely mineral, and which
are principally lime, magnesia, silica, alumina,
and perhaps barytes. Potash and soda are found
in very large quantities. Iron, manganese, and
copper* have been observed, and besides the
above there are occasionally found in plants
chlorine, iodine, sulphur, and phosphorus. The
reader is referred to No. 4 of these little trea-
tises f for further particulars on the chemical
part of the subject.

54. Those whose leisure permits, and whose
inclination leads them closely to examine into
the simple yet marvellous chemistry by which
compounds, absolutely essential to the animal
economy, but which it has no direct power of
preparing for itself, are formed for it in the
vegetable organism, will perceive how true it is
that the more we search into those phenomena
which we daily and hourly witness and experi-

* Copper was found by M. Bischoff, Dr. Meissner
and M. Sarzeau. See De Candolle, Phy. Veg. vol. i.
p. 389.

t " Introduction to Organic Chemistry."

GROWTH AND SECRETIONS. 79

ence, the more we shall see that nothing has
been made in vain, and the more resistless will
be the proof that such a chain of causes and
effects as may be traced from one end of creation
to the other, could only have had their origin in
that One Mind to which every thing is ever
present, and who, in the very " constitution and
course of nature," has stamped too deeply to be
effaced, even amid the moral disorder man's folly
has introduced, the "image" of his own perfec-
tion, and the " superscription " that the work of
his hand is " very good" To God then let all
" render the things that are God's," by a full
acknowledgment of his wisdom and goodness in
thus supplying what they need, and by making
such a use of those gifts as may best prove their
gratitude, and most tend to the glory of the
Giver.

CHAPTER IV.

REPRODUCTION OF PLANTS.
55.

THE reproduction of plants from seed is the
chief object of all those wonderful organs,
a description of which will now be given, and it
would be difficult if not impossible to find in
the whole of the beautiful world around us, any
thing more admirable than the organization by
which that object is attained ; while the parts
are, in many instances, so minute as to require
the assistance of the microscope to discover
them at all. It has been said above, that the
chief office of that lovely portion of the vege-
table kingdom, the flowers which glow like gems
in our sight, is to reproduce the species; but it
would be ingratitude to assert that they have no
other end to answer. The mere purpose of re-
production might doubtless have been effected
with no beauty to charm the eye, but it pleased
Him who made that exquisite organ, also to

REPRODUCTION OF PLANTS. 81

furnish it with objects that should delight it,
and we can scarcely behold these jewels of the
field, and not say of them as the son of Sirach
did of the brilliant bow whose tints they emu-
late, "Look on the 'flowers' and praise Him
who made them, very beautiful they are in the
brightness thereof."

56. Plants are distinguished, with reference
to the organs of fructification, into two great
classes,— phanerogamic, or those which have
their flowers visible to the naked eye, and are
more or less symmetrical ; and cryptogamic, in
which the flowers, if they exist, are invisible
except by the microscope, and are little, if at
all symmetrical. In the former group the seed-
bearing and fecundating organs are very dis-
tinct ; in the latter they are not so.— The first
include all the Exogenes, and the greater part
of the Endogenes, the second all the cellulares
and some of the Endogenes.

57. At a longer or shorter period before a
Phanerogamic plant is about to put forth blos-
soms, points appear called Flower Buds, sur-
rounded like the Leaf Buds above described, by
developed or undeveloped leaves, and like them
really situated at the axil of a leaf, though that
leaf may have been rudimentary and oblite-

82 REPRODUCTION OF PLANTS.

rated,* — these points in due time expand into
the perfect flower — and if a transverse section
be made of them they will be found to be most
exquisitely folded together in the state to which
botanists have applied the term (estivation.

When the Flower Buds are unfolded and have
expanded into flowers, they are seen to be com-
posed of one or more whorls of leaves, sur-
rounding and protecting the organs of repro-
duction.-j- In anatomical structure they do not
differ from true leaves. Situated immediately
within the inner whorls of these leaves, if more
than one be present, we find the organs of fruc-
tification, the Stamens and Pistils.

58. Each Stamen consists of two parts, the
anther, and the filament ; the latter is a slender

* The subject of symmetrical arrangement in the
parts of a plant is a very curious one, but involves too
much technical and botanical detail to be properly in-
troduced here. Whether it really exist to the extent
that botanists have supposed, or not, there is ample
proof that the general law is that of symmetry, and the
deviations from it the exceptions : thereader who wishes
for detailed information on this point is referred to the
6th chapter ("Morphology") of Professor Ilenslow,
" Principles of Descriptive and Physiological Botany."

t If but one whorl exists it is always considered by
botanists as a Culyx, whether it be green or coloured, —
if more than one whorl is present the outer one is always

REPRODUCTION OF PLANTS. 83

stalk by which the stamen is attached to the
flower, but is not an essential portion of the or-
gan, and is sometimes wanting ; it is formed of
spiral vessels, surrounded by cellular tissue — on
the top of this filament, or occasionally, though
rarely, sessile on the flower, is the Anther,— -a.
case of cellular tissue, usually consisting of two
lobes, which contain the Pollen. This is the
indispensable part of the fructifying organ.

59. The Pollen* is a collection of minute
cases, " containing a fluid in which float grains
of starch and drops of oil. It is furnished with
apertures through which its lining is protruded,
in the form of a delicate tube, when the pollen
comes in contact with the stigma." f The shape

the calyx, — the inner whorls being the Corolla,— while
the general term Perianth, is applied to the whole floral
envelope together,— any more minute notice of the forms
and divisions of the calyx and corolla would be incon-
sistent with the intention of the present treatise, which
does not profess to be an Introduction to Botany.

* Any one who wishes to study minutely the wonder-
ful varieties in form, &c. of the Pollen will find the sub-
ject illustrated by most exquisite microscopic drawings
in the German work by Fritzsche (" Ueber den Pollen'')
and in another in the same language (" Ueber das Pollen
der Asclepiadeen") by Ehrenherg.

t Lindley, El. Bot. pp. 47, 49, 50.

b4 REPRODUCTION OF PLANTS.

of the pollen grains varies extremely ; " its func-
tion is to vivify the ovules." *

60. The Pistil occupies the centre of the
flower, and consists of three parts ; the ovary,
the style, and the stigma. " The ovary is a hol-
low case enclosing ovules (or young seeds). It
contains one or more cavities, called cells. The
stigma is the upper extremity of the pistil. The
style is the part that connects the ovary and
stigma ; it is frequently absent, and is no more
essential to a pistil, than a petiole to a leaf, or a
filament to an anther." -j- The pistil, or ova-
riuin, is frequently composed of several carpels,
(61) each having its separate ovary, style, and
stigma.

61. Carpel. The pistil, anatomically consi-
dered, is in reality a modified leaf, or whorl of
leaves, and a carpel " is formed by a folded
leaf, the upper surface of which is turned in-
wards and the lower outwards ; and within which
are developed one or a greater number of buds,
which are the ovules."

* Lindley, El. Bot. pp. 47, 49, 50. t Ibid.

J Lindley 's Elements of Botany, p. 50.

Professor Lindley has made the subject of the carpels
so clear in his " Ladies' Botany" that it may be well to
add his explanation to what is given above. " Next to

REPRODUCTION OF PLANTS. 85

62. The Ovule, as has just been seen, is con-
tained within the carpel, and becomes the germ
of the new plant ; it is either naked or enclosed
in a covering, sometimes sessile, sometimes
stalked : in its most complete state it consists of
a nucleus, surrounded by two coats or integu-
ments.

63. The Fruit is the mature state of the pis-
til or carpels.

the stamens, and occupying the very centre of the flower"
(the common Ranunculus, or Buttercup, is the one he
takes as his example) " are a number of little green grains,
which look almost like green scales ; they are collected
in a heap, and are seated upon a small elevated recep-
tacle ; we call them carpels. They are too small to be
seen readily without a magnifying glass ; but if they are
examined in that way, you will remark that each is
roundish at the bottom, and gradually contracted into a
kind of short bent horn at the top ; the rounded part is
the ovary, the horn is the style ; and the tip of the style,
which is rather more shining and somewhat wider than
the style itself, is named the stigma: so that a carpel
consists of ovary, style, and stigma. At first sight you
may take the carpels to be solid, and, if you already
know something of botany, you may fancy them to be
young seeds; but in both opinions, you would be mis-
taken. The ovary of each carpel is hollow and contains
a young seed called an ovule, or little egg; so that the
carpel, instead of being the seed, is the part that con-
tains the seed." (Letter I. p. 7.)

86 REPRODUCTION OF PLANTS.

64. The ovary of the pistil becomes what bo-
tanists call the Pericarp of the fruit ; it has a
great variety of names, dependant on the num-
ber of carpels, their situation, the quality of their
texture, &c.

65. The Seed is the perfected ovule, it is co-
vered with an integument, which is sometimes
curiously spread out so as to form wings, and
contains the embryo lying in it as the embryo
chick is in the egg, and often similarly sur-
rounded by the albumen which affords its nou-
rishment.

66. Spores. The principal organs of repro-
duction in those plants, called Acrogens or Floiv-
erless, which are destitute of stamens and pistils,
are called spores, these are cells which are seen
by a microscope to be analogous to a grain of pol-
len ; the cases containing them are termed thecff-
or sporangia.

Sori are clusters of thecae, and the Indusiwm
is a portion of the epidermis which encloses
them.

67. The reproduction of plants is of two
kinds, that by seed and that by division, which
is either natural or artificial and will afterwards
be noticed. When the flower is fully developed,
— a period which arrives in different kinds of

REPRODUCTION OF PLANTS. 87

plants at very different times, — in some for in-
stance, in the first, in others in the second year
of their existence, — a process occurs by which
that contact between the pollen (59) and the
stigma (60) takes place, which in all the phane-
rogamic plants is absolutely essential to the re-
production of the species by seed. This con-
tact or impregnation is thus effected. " The
pollen emits a tube of extreme delicacy, which
pierces the stigma and style, and passing down-
wards into the ovary," * thus reaches the ovule.
The result of this process is the gradual deve-
lopment of the embryo which becomes the fruit :
or, in other words, the pistil, after this impreg-
nation, arrives at maturity, and the ovary of
the pistil becomes the pericarp of the fruit.
This main fact remains in all cases unaltered,
though in consequence of the non-development
or obliteration of some of the parts, the identity
of the fruit with the original pistil is sometimes
difficult to recognize. Various names have been
applied to fruits according to their form, nature,
&c. — All, however, are receptacles for the seed,
which is the perfect state of the ovule, as the
fruit generally, is of the pistil.

* Lindley's " Elements of Botany," p. 56.

88 REPRODUCTION OF PLANTS.

The provisions for ensuring this necessary
contact between the pollen and the stigma, are
among some of the most curious in nature.
The stamens of many plants, by a spontane-
ous movement, approach the pistil at the sea-
son when fructification should commence. The
action of water on the pollen, which would be
injurious to it, is in some cases avoided by the
corolla closing on the approach of rain, and in
aquatic plants the organs of fructification are de-
fended from wet, by being produced in a cavity
filled with air, or by the flowers being raised
above the surface of the water. The Vallisneria,
whose flowers are diaeceous (that is, the pistil
is situated on one plant, and the stamens on
another) is a very remarkable instance of the
method by which the contact of the two organs is
effected. It grows in the waters of the south
of Europe, strongly embedded in the mud by
its roots. The pistils are situated in flowers
which are on long peduncles, spirally rolled up
at first, but which uncurl till they reach the
surface. The flowers which bear the stamens
have, on the contrary, a very short peduncle,
but the buds form little bladders, on which
they float, detached from their stems, around the

REPRODUCTION OF PLANTS. 89

pistilliferous flowers, they then expand, emit
their pollen, and die.

68. The seed itself consists, as has been stated
above (65), of an embryo, and of the albumen,
&c. which nourish and protect it. This embryo,
" the organized body that lies within the seed,
and for the purpose of protecting and nourishing
which the seed was created," " consists of the
cotyledons, the radicle, the plumule, and the
collar."* The cotyledons are those undeveloped
leaves which are seen to push their way above
the ground when a plant first makes its appear-
ance : they vary in number, but most usually
there are either one or two of them. If a plant
have but one cotyledon, it is said to be Mono-
cotyledonous, which is the case with all the
Endogenous tribes ; if there be two or more, the
plant is called Dicotyledonous, in which latter
division all the Exogenous tribes are found.
The Cryptogamia are all Acotyledonous — that
is, without cotyledons.

69. The ascending portion of the embryo plant
is called the plumule, and is sometimes hardly
distinguishable from the cotyledons ; the de-

* Liudley.

90 REPRODUCTION OF PLANTS.

scending portion is named the radicle, and forms
the future root, &c. : the collar is the line of
separation between them. " When the seed is
called into action, germination takes place. The
juices of the plant, which before were insipid,
immediately afterwards abound with sugar," as
in the conversion of Barley into Malt, " which
process consists in promoting the germination of
the seed by moderate heat and moisture, and
checking it by the higher temperature of the
kiln as soon as the largest possible quantity of
saccharine matter is formed. When the seed
has germinated, and sugar is produced, the period
of growth commences." This growth is in the
first instance caused by the absorption and de-
composition of water, whose oxygen combines
with the superfluous carbon of the seed, and is
expelled in the form of carbonic acid gas. When
the absorption of oxygen has removed a suffi-
cient quantity of carbon from the seed, " the
young plant begins to absorb food, and to grow
by the processes of assimilation and respiration
already described ;" and as soon as the seed is
once active it receives, by a special provision of
nature, a larger proportional share of the sap
than any other part of the plant. Probably the
heat produced by the consumption of its carbon

REPRODUCTION OF PLANTS. 91

is also essential to the welfare of the newly
formed plant, and may give the necessary stimu-
lus which brings its organs into action.

70. The fact that darkness is essential to
germination has long been known — " an em-
bryo, exposed to constant light, would not germi-
nate at all, and hence the care taken by nature
to provide a covering to all embryos in the form
of the integument of the seed, or of a pericarp."
Mr. Hunt has recently turned his attention to
this subject, and he remarks thus on it : " It is
not at present in our power to explain in any
thing like a satisfactory manner the way in
which the luminous rays act in preventing ger-
mination. The changes which take place in the
seed during the process have been investigated
by Saussure : oxygen gas is consumed, and car-
bonic acid gas evolved ; and the volume of the
latter is exactly equal to the volume of the
former. The grain weighs less after germination
than it did before ; the loss of weight varying
from one-third to one-fifth. This loss of course
depends on the combination of its carbon with
the oxygen absorbed, which is evolved as car-
bonic acid. According to Prout, malted and un-
malted Barley differ in the following respects :

92

REPRODUCTION OF PLANTS.

Unmalted

Malted

Resin . . .

. 1

1

Gum . . .

. 4

15

Sugar . . .

. 5

15

Gluten . .

. 3

1

Starch . . •

. 32

56

Hordein ... 55 12

100 100

This shows that the insoluble principle, hordein,
is, in the process of germination, converted into
the soluble and nutritive principles, starch, gum,
and sugar. We are therefore at present left in
considerable doubt; we can only suppose that
the luminous solar rays act, as indeed we find
them to do on many of the argentine prepara-
tions, in preventing those chemical changes
which depend upon the absorption of oxygen.
A like interference has been observed by Sir
John Herschell to be exerted by the red rays of
the spectrum ; and from the manner in which
germination is impeded in the seeds covered by
deep red media, we may trace a somewhat similar
influence." *

All Mr. Hunt's experiments prove " that the

* " Researches on Light," p. 192.

REPRODUCTION OF PLANTS. 93

process of germination is obstructed by the in-
fluence of light on the surface of the soil, although
the bulbs and seeds have been buried some depth
beneath it."*

" One very remarkable result," says Mr.
Hunt, " must be noticed ; under all ordinary cir-
cumstances plants bend in a very decided manner
towards the light. In all my experiments with
red fluid media, they hare as decidedly bent from

* " Researches on Light," p. 191.
t Ib. p. 319.

A very curious phenomenon which from its usually
taking place in the evening has been called the sleep of
plants, appears to be principally owing to the influence
of light. The fact itself is, that in certain plants the
leaves fold up, and sometimes grasp the stem. It occurs
also in some flowers which shut up periodically, and the
inference that light is probably the agent in producing
this effect, was drawn by M. de Candolle from the cir-
cumstance that he found the period of its occurrence
could be reversed by excluding the light from the plants
during the day time, and placing them in strong lamp
light at night. (De Candolle, Pliys. Veg. vol. ii. p.
860.)

It was remarked in an earlier part of this little work,
that the influence which the study of one science has on
many others, with which it appeared in the first instance
to promise no connection, was illustrated by the benefit
that agriculture derives from chemistry ; another proof of

94 REPRODUCTION OF PLANTS.

72. In whatever manner a seed may be placed
in the ground, it invariably shoots forth its plu-

the fact that in the observation of natural phenomena,
and the rational investigation of their causes, it is im-
possible to foresee or limit the beneficial results which
may follow, even where we have least reason to antici-
pate them, is afforded by the comparatively novel subject
of Photography. This, which at first appeared but an
ingenious application of a natural agency to the purposes
of art, is assuming, in the hands of some of our greatest
philosophers, the rank of a science, which promises to
lead to discoveries equally curious and important. The
true nature of that sunbeam, whose wonderful operation
can either call forth the vital energy of a plant, cause it
to perform its functions of growth and nutrition, yet
prove detrimental to its germination ; or delineate its
portrait with a fidelity and beauty unknown to the pencil
of man on the sensitive surface presented to it, has yet
to be fully ascertained ; but that it has other properties
than were supposed before the subject of Actino-Che-
mistry came under the investigation of Herschell and
others, seems already established ; and who shall assign a
limit to the possible results which may arise from a clearer
knowledge of the nature and operation of such an agent
in the universe. It may as yet seem to bear little on the
immediate subject of the present work, but it is impossible
to assert, that a further insight into the nature of a cause
whose effects on vegetation are so decided, may not prove
of great practical benefit ; and although its study is no
new branch of science in itself, yet the new aspect under
which it is now pursued may probably lead to unantici-
pated Truth.

REPRODUCTION OF PLANTS. 95

mule in an ascending, and its radicle in a de-
scending direction. Invert it as we may, the
result will be the same ; but on what vital energy
within the plant the constancy of this fact de-
pends, seems yet entirely uncertain. Whether
it arise from the tendency of upper portions of
plants to seek the light, or from any other cause,
the reason is equally obscure, and we can hardly
reckon on its being ascertained by the most
minute investigation ; it seems to belong to that
class of phenomena in nature whose ultimate
principles are too subtle for our grasp, and
appear to depend on that vitality which we can
indeed perceive most palpably in its effects, but
whose cause is known only to the Creator :
whether modern science will be permitted to
approximate nearer to the truth on this and
some few similar subjects must remain at least
doubtful : at all events we are not now in posses-
sion of any wholly satisfactory solution of the
difficulty.

" That gravity is an important agent in deter-
mining the difference between the directions
taken by the root and stem, is shewn 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

96 REPRODUCTION OF PLANTS.

be thrown off when a rapid rotatory motion was
given to the wheels. One wheel was disposed
horizontally, the other vertically, and both were
kept in constant motion while the beans were
germinating. The radicles of those beans which
germinated on the vertical wheel extended them-
selves outwards, or from the centre, and the
plumules inwards, or towards it. Those which
were placed on the horizontal wheel pushed
their radicles downwards and their plumules up-
wards ; but the former were also inclined from
and the latter towards the axis of the wheel.
This inclination was found to be greater as the
velocity of the wheel was increased. Now in
the vertical wheel the effects of gravity were
nullified ; since the beans were constantly chang-
ing their position with respect to those 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 effects of gravity, compelling the root to grow
outwards and the stem inwards, instead of down-
wards and upwards. The effect produced upon
the horizontal wheel is evidently the result of
the combined action of the forces — gravity in-
clining the root downwards, and the centrifugal

REPRODUCTION OF PLANTS. 97

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 directions 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,
while the stem continues to increase for some
time through 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 effect of gravity
alone. (Henslow's Prin. of Botany, p. 292.)

Is it not probable that we may find the agency
of light connected with the fact of the plumule
ascending ?

72. The reproduction of the tribes of the
Cryptogamia takes place in a very different
manner from that of the flowering plants. In
all of them it occurs spontaneously, and without
any contact between one part of the plant and
another. At the season of the year when the
H

98 REPRODUCTION OF PLANTS.

lowest tribes of all, such as the Red Snow, the
Confervas, &c. are to reproduce their species, a
number of small granules are liberated by the
bursting asunder of the cell which enclosed
them. They gradually develope themselves
into cells, acquire the size and form of the pa-
rent plant, and become distinct individuals ca-
pable in their turn of producing others like
themselves. The apparatus of reproduction, if
we may so call it, increases in complexity as it
approaches the higher orders, but in all except
the cells just mentioned, the immediate organ is
called a spore,* and is analogous to the seed of
the flowering plant.

73. It has been seen that in reproduction by
seed, each germ has the power of becoming de-
veloped, after fecundation, into a separate indi-
vidual plant, entirely distinct from that which
gave it birth. In addition to this accustomed
mode of increase, plants are also propagated by

* " It is in the spores that the power of increase re-
sides; every one of them will form a new plant, and
consequently they are analogous to seeds, but, as they
do not result from the action of pollen upon a stigma,
they are not real seeds, but only the representations of
those organs amongst the flowerless plants." (Lindley's
Ladies' Bot. p. 270.)

REPRODUCTION OF PLANTS. 99

division ; and this is either natural or artificial,
and depends on two circumstances : in one, the
ascending organs are first developed, or in other
words an adventitious leaf bud (35) is produced,
and these favour the subsequent development
of the roots ; in the other, roots are first formed,
and by their action promote the development of
the ascending system. The former is in gene-
ral the case when the germ is found surrounded
by a sufficient deposit of nourishment to sustain
it till it can push forth its roots : this nourish-
ment is furnished by the mother plant from the
descending juices. To this sort of buds may be
given the general name of tubercles, though bo-
tanists designate them by a variety of appella-
tions. In all tubercles a phenomenon occurs
which distinguishes their germination from that
of seed ; in the latter the radicle is always first
developed, while in the tubercle the ascending
part, — that which corresponds to the plumule, —
is first put forth. The common potato is an
instance of this mode of increase ; the tubercles
are detached towards the end of the year either
by the death of the stem on which they grow,
or by the slightest accident, and falling on tin-
ground, vegetation ensues. This single exam-
ple is sufficient for the present purpose ; the

100 REPRODUCTION OF PLANTS.

phenomenon exists in many other plants under
various forms. In the cases in which vege-
tation commences in the descending system,
that is, in which roots, whose development is
always effected through the descending juices,
are first formed, the result is produced in some
portion of the stem which is found to contain a
deposit of nutritive matter, and which is within
reach of moisture. This effect occurs naturally
in some stems, but is facilitated by any cause
which tends to arrest the nutritive juice in its
descent, and so to form an accumulation of it at
a given part. Thus in nature when a portion
of a stem containing such an accumulation, is
buried beneath a humid soil, and has a fleshy
bark, it tends to put out roots, which it does
naturally by what are called "suckers," and
man, profiting by this provision, adopts the me-
thod of increasing by layers, pipings, cuttings,
&c. since it is found that the part thus endowed
may be separated from the parent trunk, and
being composed of the two parts that constitute
an individual plant, a stem and a root, is capable
of an independent existence. In some instances
a leaf planted in the ground will vegetate from
its central nervure.

74. There is one great difference notwith-

REPRODUCTION OF PLANTS. 101

standing so much apparent identity, between the
products of the two methods of reproduction
above mentioned. In the case of propagation by
seed, the embryo is really, and from the first
moment of its existence, a being distinct from
the parent plant, the seed is furnished with all
the organs it requires ; the tubercle, on the con-
trary, is but a fragment of the plant that bore it,
and has gradually to form for itself the needful
organs. The seed, being entirely distinct, may
only resemble the original plant by the general
characteristics that belong to its kind ; while the
tubercle or the cutting, being actually portions
of the plant itself, preserves its minutest particu-
larities. A very curious instance of reproduc-
tion occurs in the lemna, or common duckweed.
If one of its little discs be placed in a saucer, we
shall soon see it send forth laterally a tubercle
which grows in a horizontal direction, puts out
a root underneath, and thus forms a second
plant similar to the former, but united with it.
This double disc continues to vegetate in the
same manner, and so on.

75. Besides the method of increase by cut-
tings, tubercles, &c. mentioned above, another
exists which is, as all gardeners well know, of
immense practical utility — that of grafting, —

102 REPRODUCTION OF PLANTS.

All parts of plants have the power of uniting
together by their cellular tissue, — thus we see
even in those which consist only of cellular sub-
stance, that such adhesions take place. The name
of graft has been especially given to one case of
adhesion, that in which the liber, and particu-
larly pith, of two plants unite so nicely together
that the part called the graft can receive its sap,
and thus live by the nourishment it derives
through the organs of the old plant ; thus arti-
ficially doing what parasitic plants, such as the
mistletoe, do by nature. There is, however, a
limit to this operation ; if we except parasitical
and some few natural adhesions, we shall find
that artificially it is only plants of the same na-
tural family that can be grafted together with
any thing like permanent success, and only those
of families strongly analogous in which any
union will take place at all. When they are
not of the same family the grafts are of short
duration in consequence of their physiological
difference from the tree to which they have been
united. Grafts are of three kinds — that ordi-
narily so called, in which a severed portion of a
stem is united to another tree, whose bark has
been cut away at the proper spot, — that by ap-
proach, which consists of drawing two branches

REPRODUCTION OF PLANTS. 103

or two trees together, each remaining in the
ground held by its own roots, and taking off the
bark of each at the point of contact ; the liber
and pith of the two plants soon unite by the de-
velopment of their cambium, and one of them
may then be cut away below the junction. The
third method is by the insertion of a portion of
a stem containing a bud in the axil of a leaf,
within the bark of the tree on which we desire
to ingraft it; the bud thus inserted receives nou-
rishment from the juices of the tree in which it
is placed, and is developed as it would have
been on the stem from which it was originally
taken.

76. There are various subjects of great inte-
rest connected with the reproduction of plants,
whether from seed or division, but which are
too numerous to be dwelt on in an elementary
work : among them is the production of hybrid
varieties by fertilizing the stigma of one plant
with the pollen from another, which may occur
accidentally, if the plants are in each other's
neighbourhood, or may be effected at pleasure
between those whose natural affinities are very
close. In this manner modern gardeners have
succeeded in raising numberless varieties of fa-
vourite genera. The effect of culture and care

]04 REPRODUCTION OF PLANTS.

generally, as is universally known, is to improve
the beauty and value of the vegetable produc-
tions by which we are so bountifully surrounded.
This subject, interesting as it is, can here be
only recommended to notice, without further
entering on it. Its details may afford to those
whose local situation enables them practically to
pursue them, an occupation at once healthy to
both body and mind, and so connected with che-
mistry and mineralogy, as to lead on from the
simple nurture of a pretty or useful plant, to the
study of some of the most important of the
sciences.

77. What great antiquity the method of
grafting may claim, we may gather from St.
Paul's exhortation to the Gentiles in the llth
chapter of his Epistle to the Romans, in which
the metaphor is used throughout with an evident
knowledge of the subject. Indeed the custom
appears to have been one with which practical
gardeners have been familiar for ages, and to
which attention has been at times particularly
turned.

In the Philosophical Transactions for 1675,
mention is made of a work by Abraham Hunt-
ing, printed three years before, which shows
that his attention was practically given to the

REPRODUCTION OF PLANTS. 105

cultivation of fruit trees, and to the improve-
ment of the sorts by grafting. " To obtain extra-
ordinary good, large, and beautiful apple fruit,"
he advises " by all means to graft good grafts
upon such apple stocks as are produced from
the seed, and have been deprived of their heart
root which shoots downwards" *

To the invaluable and long continued inves-
tigations and experiments of Mr. Andrew
Knight, however, and to his acute reasoning on
the subject, the present highly improved know-
ledge/of the best method of grafting trees, and
of the general nature of the subject, is mainly
owing. In a paper published in the Phil. Trans,
for 1795, Mr. Knight gives a very interesting
account of the experiments which convinced
him of the fact, so important in its practical re-
sults, that " every cutting taken from the apple,
and probably every other tree, will be affected
by the state of the parent stock. If that be too
young to produce fruit, it will grow with vigour
but will not blossom ; and if it be too old, it
will immediately produce fruit, but will never
make a healthy tree, and consequently never

* Phil. Trans, abridged, vol. xix. p. 192-3, " Account
of some new books."

106 REPRODUCTION OF PLANTS.

answer the intention of the planter." Having
suspected that the decay in some trees he had
seen recently grafted might be the consequence
of the diseased condition of the grafts, Mr.
Knight says, " I concluded that if I took scions
or buds from trees grafted in the year preced-
ing, I should succeed in propagating any kind I
chose. With this view, 1 inserted some cuttings
of the best wood I could find in the old trees,
on young stocks raised from seed. I again in-
serted grafts and buds taken from these on other
young stocks, and wishing to get rid of all con-
nection with the old trees, I repeated this six
years ; each year taking the young shoots from
the trees last grafted. Stocks of different kinds
were tried, some were double grafted, others ob-
tained from apple trees which grew from cuttings,
and others from the seed of each kind of fruit
afterwards inserted on them ; I was surprised to
find that many of these stocks inherited all the
diseases of the parent trees." — Mr. Knight came
at last to the conclusion which subsequent expe-
rience has fully confirmed, " that all efforts, to
make grafts from old and worn out trees grow,
are ineffectual," and that " the durability of the
apple and pear may be different in different

REPRODUCTION OF PLANTS. 107

varieties, but that none of either would vegetate
with vigour much, if at all, beyond the life of
the parent stock. I am confirmed in this opin-
ion by the books on this subject ; of the apples
mentioned and described by Parkinson, the
names only remain, and those since applied to
other kinds now also worn out ; but many of
Evelyn's still remain (1795), particularly the
red streak. This apple, he informs us, was
raised from seed by Lord Scudamore in the be-
ginning of the last century. We have many
trees of it, but they appear to have been in a
state of decay during the last forty years ....
. . . the durability of the pear is probably some-
thing more than double that of the apple."
Many of the readers of this paragraph will pro-
bably recall to mind the gradual and complete
extinction of the unrivalled " Golden Pippin,"
which has evidently afforded a proof of the truth
of Mr. Knight's deductions. His experiments
on seedling apples, while the excellence of seve-
ral of the sorts affords much encouragement to
gardeners and landed proprietors to imitate his
example, and endeavour to replace by new fruit
trees of equal goodness, the kinds wrhose limit
of duration may be pretty nearly guessed, also

108 REPRODUCTION OF PLANTS.

show the necessity in this, as in most pursuits,
of the valuable qualities of patience and perse-
verance which he must himself have possessed
in so great a degree, since of the seeds he sowed
he reckoned that one in a thousand came up
which was not a crab, and one in a thousand of
these became a good eating apple.

78. There is one more subject, connected
with reproduction by seed, which is too curious
to be passed over; the wonderful tenacity of
vegetable life. This, indeed, is shown in the
plants themselves in many instances, such as
the enormous longevity of some trees, particu-
larly the oak, the yew, and some of foreign
growth,* but it seems even more extraordinary
as it exists in seeds. The latter will remain
torpid for many months or even years without
injury. Corn grains enclosed in the bandages
which envelope the mummies, are said to have
occasionally germinated, though most of them
seem to have lost their vitality. There is no-
thing improbable in the fact ; but as the Arabs,
from whom the mummies are commonly ob-

* In the Appendix will be found translated a table
given by De Candolle of the presumed age of some cele-
brated trees (B.)

REPRODUCTION OF PLANTS. 109

tained, are iii the habit of previously unrolling
them in search of coins, &c. it is not always
certain that the seeds which have sprouted,
were really at first enclosed with the mum-
mies.*

* Carpenter's Veg. Physiol. § 451.

110 COMPARISON OF VEGETABLE

CHAPTER V.

COMPARISON OF VEGETABLE WITH ANIMAL
PHYSIOLOGY.

79.

IT is impossible to consider the subject of
Vegetable Physiology and organization,
without being struck by the analogy which it
presents in so many points to that of Animals.
— Yet, however strong may be that analogy,
it never in any instance becomes identity, and
the marked fact, noticed in the Introduction,
that the latter in all cases convey their food by
the mouth to a stomach, is alone sufficient to
establish a boundary between them ; * the com-

* There does indeed appear to be one group, about
whicb some doubt exists in the mind of some physiolo-
gists as to its reference to the animal or vegetable king-
dom. "They are mostly," says Dr. Carpenter, " formed
of cells jointed together, as the Confervae; but some of
them seem to possess a different interior structure ; and
others exhibit very curious motions, which can scarcely
be distinguished with certainty from those of animals."
(Carpenter's Veg. Pby. p. 44.)

WITH ANIMAL PHYSIOLOGY. Ill

parison, however, between the two, is so inter-
esting and instructive, that a few words may be
well bestowed upon the subject.

The whole range of functions both of animals
and plants, that is to say as far as nutrition and
reproduction are concerned, affords ample illus-
trations of the near approach to similarity in the
two kingdoms — a few examples of each may
prove the truth of this assertion, while the dif-
ference will also in general be equally percep-
tible. In the entire course of that function by
which the individual is nourished, the main
point holds good in both cases ; i. e. that mat-
ter fitted for its food is taken into the system
by the appointed organs, thence conveyed through
the necessary channels, assimilated and con-
verted into the requisite substance for continu-
ing and replenishing the tissue of the body, and
furnishing the needful secretions, while such as
is unavailing to any of these purposes, is ex-
creted. In the plant, however, the juices are
not conveyed to a single receptacle, there to be
elaborated, but, according to the process de-
tailed in the foregoing pages, are gradually in
their progress converted from the crude into
the nutritive sap. The circulation of this sap,
and the power of the glands to convert it into
peculiar secretions, suggests immediately to the

112 COMPARISON OF VEGETABLE

mind the idea of an analogy with the circulation
of the blood in animals, and a fanciful imagina-
tion might see a degree of further likeness to
the venous and arterial blood in the two states
of the sap. The similarity, however, though it
does exist, is but very partial, no one general
circuit of the sap throughout the system, as
there is of the blood originally propelled from
the heart, really taking place. Again the tissue
produced and nourished in the two kingdoms,
though very analogous in some respects, is by
no means identical : — the cellular texture of
animals differing from the cellular tissue of plants
by its structure, which is not actually composed
of individual cells, united together by the cohe-
sion of their walls, but of " a congeries of ex-
tremely thin laminae or plates, variously con-
nected together by fibres, and by other plates,
which cross them in different directions, leaving
cavities or cells."* This cellular texture, how-
ever, forms the essential material of the animal
fabric generally, as the cellular tissue does of
the vegetable. The important chemical diffe-
rence between animal and vegetable organized
tissue has already been noticed, viz. the pre-

* Roget's " Anim. and Veget. Physiol." vol. i. p. 99.

WITH ANIMAL PHYSIOLOGY. 113

sence of nitrogen in the one case and its absence
in the other (45).

80. Perhaps, however, the most curious and
interesting analogy between animal and vege-
table organization is that which relates to the
process of reproduction — which in some of the
lowest tribes of animals approaches more nearly
to identity with that of plants than in any other
function. In several of the most minute of
the Infusoria, in which nevertheless, small as
they are, the patient investigation of Ehren-
berg has discovered a series of stomachs, we
meet with frequent examples of multiplication
by the spontaneous division of the body of the
parent into two or more parts. " Many species
of Monads for instance, which are naturally of
a globular shape, exhibit at a certain period of
their development a slight circular groove round
the middle of their bodies, which by degrees be-
coming deeper, changes their form to that of
an hour-glass; and the middle part becoming
still more contracted, they present the appear-
ance of two balls united by a mere point. The
monads in this state are seen swimming irre-
gularly in the fluid ; as if animated by two dif-
ferent volitions ; and apparently for the purpose
of tearing asunder the last connecting fibres,

114 COMPARISON OF VEGETABLE

darting through the thickest of the crowd of
surrounding animalcules ; and the moment this
slender ligament is broken, each is seen moving
away from the other and beginning its inde-
pendent existence."* — Now although we have
not in the vegetable world any instance of this
voluntary division, yet, in the all but sponta-
neous action, the reproduction of plants by the
division of their parts bears a strong analogy to
it, and in the cases to be further mentioned, the
resemblance is still stronger. The Hydra, or
fresh water Polype, " is capable of indefinite
multiplication by simple division : thus, if it be
cut asunder transversely, the part containing a
head soon supplies itself with a tail ; and the
detached tail soon shoots forth a new head,
with a new set of tentacula. If any of the ten-
tacula, or any portion of one of them be cut off,
the mutilation is soon repaired ; and if the whole
animal be divided into a great number of pieces,
each fragment acquires, in a short time, all the
parts which are wanting to render it a complete
individual. "t In this same animal (the Hydra)
which is thus capable of being increased by

* Roget, Anim. and Veget. Physiol. p. 583.
t Ib. p. 586.

WITH ANIMAL PHYSIOLOGY. 115

what would in a plant be slips or cuttings, the
natural method of propagation is analogous to
that of many plants — such as the Duckweed :
" At the earliest period at which the young of
this animal is visible, it appears like a small tu-
bercle, or bud, rising from the surface of the
parent hydra ; it grows in this situation, and re-
mains attached for a considerable period; at
first deriving its nourishment as well as receiv-
ing its mechanical support, from the parent. . . .
this mode of multiplication, in its first period,
corresponds exactly with the production of a

vegetable by buds ; although at a later

stage, it differs from it in the complete detach-
ment of the offspring from the parent."* An
instance of reproduction occurs in the sponges,
which bears a near resemblance to the sponta-
neous fructification and bursting of the thecae
of many of the Cryptogamic plants. "The
parts of the Spongia panicea, which are natu-
rally transparent, contain at certain seasons a
multitude of opaque yellow spots visible to the
naked eye, and which, when examined by a mi-
croscope, are found to consist of groups of ova,
or more properly gemmules, since we cannot

* lb. p. 590.

116 COMPARISON OF VEGETABLE

discover that they are furnished with any enve-
lope. In the course of a few months these gem-
mules enlarge in size, each assuming an oval or
pear-like shape, and are then seen projecting
from the sides of the internal canals of the pa-
rent, to which they adhere by their narrow ex-
tremities. In process of time, they become de-
tached, one after the other ; and are swept along
by the currents of fluid, which are rapidly pass-
ing out of the larger orifices." * " When two
gemmules, in the course of their spreading on
the surface of a watch-glass, come into contact
with each other, their clear margins unite with-
out the least interruption, — in a few days we
can detect no line of distinction between them,
and they continue to grow as one animal. The
same thing happens, according to the observa-
tions of Cavolini, to adult sponges, which on
coming into mutual contact, grow together, and
form an inseparable union. In this species of
animal grafting we again find an analogy be-
tween the constitution of zoophytes and that of
plants." f

81. With respect to the higher orders of ve-

* Roget, Anim. and Veget. Physiol. p. 156.
t Ib. p. 159.

WITH ANIMAL PHYSIOLOGY. 117

getable life, the Phanerogamic, or flowering-
plants, the whole analogy in their method of
increase with that of the larger part of the ani-
mal creation has been so long known, and so
much insisted on, that it is superfluous to dwell
on it. Enough has been said to show how the
same analogy holds good in the lower tribes .
to multiply instances would swell these pages
unduly and unnecessarily. The paper* recently
read by Professor Forbes, at the meeting of the
British Association at York, contains, as far as
can be gathered from the abstract given of it in
the Literary Gazette, for October 19th, 1844,
some very curious information bearing on this
branch of the subject. From that abstract the
analogy between " the formation of the parts of
the flower out of transformed leaves," and a cor-
responding phenomenon in " one tribe at least of
composite animals," seems to be manifested

* " On the Mosychology of the Reproductive Sys-
tem of the Sutularian Zoophytes, and its analogy with
the Reproductive System of the Flowering Plants."
Prof. Forbes has a paper with a similar title in the 93rd
No. of the " Annals and Mag. of Nat. History" for Dec.
1844, and there are some curious observations on the
same subject also contained in a paper by Mr. Couch,
in the " Annals" for March, 1845.

118 COMPARISON OF VEGETABLE

strongly in the cases on which Professor Forbes
has grounded his novel views of the subject.

Connected also with this part of Vegetable
Physiology is a paper of Dr. Martin Barry's, in
the Phil. Trans, for 1842, Pt. 1 ;* in which he
traces considerable analogy, not to say identity
of form, between animal and vegetable fibre,
and especially in one peculiar portion : the fol-
lowing extract will be found interesting. " It
is known that vegetable tissue presents, in some
parts, a feature which has heretofore seemed
wanting, or nearly so, in that of animals, — the
spiral form. I venture to believe that some
appearances met with in my investigations, may
go far towards supplying this deficiency." Dr.
Barry has given plates of these appearances as
they are found " in the nervous tissue, in muscle»
in minute blood-vessels, and in the crystalline
lens."

82. The power of vitality, so wonderfully
conspicuous in the vegetable kingdom, which
enables a seed to retain its vegetating power
though dormant for many years, has a remark-
able analogy with the revivification of some of
the animalcules. " The Rotifer redivivus, or

' • " On Fibre."

WITH ANIMAL PHYSIOLOGY. 119

wheel animalcule, can live only in water, and is
commonly found in that which has remained
stagnant for some time in the gutters of houses.
But it may be deprived of this fluid, and re-
duced to perfect dryness, so that all the func-
tions of life shall be completely suspended, yet
without the destruction of the vital principle ;
for this atom of dust, after remaining for years
in a dry state, may be revived in a few minutes
by being again supplied with water." * Other
animalcules exhibit the same phenomenon ; and
the analogy is still further carried on by the
fact well known to gardeners, that seeds which
have been long kept, will vegetate more surely
if soaked for some time in water before they are
planted.

Every discovery in whatever science, seems
more and more clearly to point to simplicity of
Design and Unity of purpose in nature : —
Where the same course and method will accom-
plish a similar end, a different one seems never
to be adopted. All the researches of modern
physical science, though they may place new
objects and new substances within our view,
tend to lessen, not enlarge the list of elemen-

* Roget, Anim. and Veget. Pbys. vol i. p. 62.

120 VEGETABLE PHYSIOLOGY.

tary bodies; — and all investigations into the
organized parts of creation teach us to refer
more and more to a few simple principles, mo-
dified, indeed, by the nature and requirements
of each species, but all pointing to the same
law, which appears to prevail throughout the
Universe, that nothing shall be unnecessarily
complicated.

>GYSGYDGYD

i *A7^* i/tht c^tfU

CONCLUSION.

THE great Linnaeus, to whom the whole
race of naturalists must ever feel largely
indebted, was the first who struck out a method
that has permanently continued, for the classifi-
cation of plants. This system (of which the
great outlines or classes are given in a tabular
view in the Appendix (A),) is grounded on the
arrangements of the reproductive organs, and
although it is in a great measure artificial, yet
nevertheless it is so practically useful, that it
has hitherto maintained its ground, and may
probably continue to do so in great measure,
although there are serious objections to it ;
chiefly because, being artificial, it does not lead
a student to the knowledge of the properties,
&c. of plants, but only enables him to iden-
tify and arrange them. A sense of the insuffi-
ciency of this method has led modern systema-
tists to form a classification, called the Natural
System, because founded on the natural affini-
ties, characters, and habits of plants, which is

122 CONCLUSION.

much better calculated to afford a real insight
into the Vegetable Kingdom. It would be im-
practicable within the limits of a work like the
present, to give any detailed account of either
system, especially of the natural arrangement,
whose characters, not being arbitrary, require
in order to be understood at all, a fulness of
description inconsistent with brevity. Neither
would such an account of botanical systems
come within the twofold object of this little
treatise, whose aim is to give the reader such
an acquaintance with the wonderful structure
of a large part of the world around him, as may
enhance his pleasure in contemplating it; and
still more to draw his attention to that unity of
purpose, palpable in the whole provision for the
sustenance and comfort of all his fellow inhabi-
tants on our earth. If this work and its prede-
cessor on Organic Chemistry, have been read
attentively, it will have been seen that water,
the soil of the earth, and the action of the air,
furnish the materials from which plants obtain
their nourishment ; that without their interven-
tion, the whole inferior animal race would have
been destitute of food ; and that man not only
obtains a large portion of his sustenance imme-
diately from them, but that they serve to elabo-

CONCLUSION. 123

rate such matter from the inorganic substances
around them, as is then, and not till then, ca-
pable of affording him the sort of food he needs,
whether derived directly from the plants them-
selves, or furnished by them indirectly through
the animals they support, and on whom he de-
pends for nutriment. Who can look on the
principal constituents of plants, i. e. carbon,
oxygen, hydrogen, and nitrogen, and contem-
plate their gradual transformation into vegetable
albumen, and vegetable caseine,* or on any of
the elementary forms of the nitrogenized com-
pounds, so absolutely essential, directly or indi-
rectly, to animal life, without feeling that no-
thing stands alone in this world, but that " the
chain holds on, and where it ends, unknown."
And even should it also occur to the mind, that
the same process ceases not with us, but that
these human bodies, thus marvellously made
and nourished, are, even the organs by which
the high functions of the brain are performed,
material and perishable, and that " we feed our-
selves to feed the worms," and, being dust, re-
turn literally to that dust again ; let us not
pause on the threshold of the argument, where

* " Introduction to Organic Chemistry," p. 33.

124 CONCLUSION.

despondency might await us, but go boldly on
through the portal, and calmly consider what
deduction we may draw, by the simple light of
reason, from this undeniable truth. We see
that every thing around us here, when it has
accomplished the end of its being, is not anni-
hilated, but only transformed into some other
state, in which it still continues to work out the
will of Him who created it : every material
thing perfectly fulfils its destined purpose ; but
Man has that within which assures him that
here he neither is nor does all that the soul
could be and perform, were it disencumbered of
the body in its present grosser state. Has he
not then the strongest reason to confide in Him
who gave that body for good purposes here,
that He will at its dissolution, still make it sub-
servient to his wise intentions, and after he se-
parates it from its present union with the soul,
will assuredly place his rational creature in a
condition to be and to do all for which that
creature was made ? Man would then no longer
be the exception to the rest of sentient beings ;
their wishes and desires are so arranged, that
the means of their gratification are within their
reach on earth ; we, on the contrary, feel aspi-
rations which never can be fully gratified here,

CONCLUSION. 125

and whose very existence foreshows a time when
they will have their fruition. The moral con.
sequence we may draw from this is almost too
obvious to require notice. If we look forward
to a state in which the body shall be so changed
that its present enjoyments can exist no more,
while those of the soul shall last for ever, how
important is it that the Will, which triumphs
over every thing that is material in us, should
be so regulated, that when that state arrives, it
may not long for those earthly pleasures which
are gone to return no more, but may have al-
ready anticipated in hope the reality it shall
then experience. The wise of old, though but
dimly perceiving what is assured to us under
the pledge and seal of God himself, could yet
draw the right inference from those dim per-
ceptions. When in the varied phases of the
butterfly's frail life they saw prefigured their
own future destiny, they could urge their dis-
ciples to purify the soul, and fit it for compa-
nionship with eternal Love. In the grain of
wheat apparently perishing in the earth, but
springing up in due season in a form " the same,
and yet another," the Apostle found a similar
correspondence with our lot : all can see the
appropriateness and beauty of the comparison,

126 CONCLUSION.

may all likewise take to heart the Apostle's ar-
gument, and having this hope may they con-
tinue " steadfast and immoveable " in all that is
good, knowing beyond all doubt or cavil, that
their labour shall not be in vain.

GYD GYD GYD CYD GYS GYD GYD

4/CT^ ^v^ •/CP^ t/v^t 4AP* *^r>* i/u^rf
**uv* '\jv'» %^** *W* "yCW" *\£y* **&*"* %0^* %^"

> GAD CAT* GAD c3CD G3Cr> CIXD QAD CAD GAD

APPENDIX A.

r I ^HE subject of local circulations has been
JL so clearly handled by Professor Henslow,
and is in itself so important a physiological fact,
that no apology is necessary for transferring his
account of the matter to these pages, which is
here done in a somewhat abridged form.

" In the ascent, descent, and general transfu-
sion of the sap, we can trace the operation of
physical causes modifying and controlling to a
considerable extent, if, indeed, they do not origi-
nate and entirely regulate those 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 or tubes, and
rendered apparent by the presence of minute
globules of vegetable matter floating in it. The
original discovery of this phenomenon was made
about a century ago by Corti, who first observed
it in the Caulinia fmgilis, a maritime plant
found on the shores of Italy. His observations

128 APPENDIX A.

appear to have been generally neglected until
lately, when the re-discovery of the phenome-
non in other plants, has excited the attention of
botanists .... We shall explain the phenome-
non 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."

" In the genus Nitella" (a section of the
Chara, and which is to be preferred to the true
Chara, from the superior transparency of its
tubes) " the stems consist of single, jointed
tubes. At the joints of the stem are whorls of
branches, composed also of short tubes, in each
of which the same rotation of the contained fluid
may be seen. If an entire tube occupying the
space between two joints, be placed under the
microscope, its inner surface appears to be stud-
ded with minute green granules, arranged in
lines, which 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,
forming two spiral lines from end to end. The
globules of transparent gelatinous matter dis-
persed 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

APPENDIX A. 129

directions, on contrary sides of the clear spaces
on the minor surface of 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 ligaments still con-
tinues to circulate, even though the extremities
of the tube should be cut away. The motion
here described is precisely similar to what takes
place in the tubes of Corallines, and must un-
questionably be considered as the result of a
vital action." Although the circulation in the
laticiferous vessels is denied by many of the
most distinguished physiologists, yet the subject
is so curious, and so well worthy of farther in-
vestigation that it is deemed advisable to add
the account of it also in Prof. Henslow's words.
" It was in the year 1820, that a distinguished
naturalist, M. Schultes, first announced his dis-
covery of a peculiar movement in the juices of
plants, which more nearly resembles the circula-
tion of the blood in animals than any thing

which had formerly been observed The

liquid, whose movement is described, and which
M. Schultes terms the 'latex,' is sometimes
transparent and colorless, but in many cases
opaque, and either milk-white, yellow, red, orange,
or brown. . . . This liquid is considered to°be
the proper juice of the plant, secreted from the
crude sap in the intercellular passages, and con-

130 APPENDIX A.

sequently analogous to the blood of animals, as
was long since suggested by Grew ; who fur-
ther likened the lymphatic, or crude sap, to their
chyle. It is contained in delicate transparent
membranous tubes, which become cylindrical
when isolated, but when pressed together in

bundles, assume a polygonal shape The

movement of the latex can be witnessed only in
those parts which happen to be very transparent,
and it has not been actually seen in many plants.
TheFicus elastica, Ckelidonium majits, and Alls-
ma plant ayo, are the species upon which most of
the observations hitherto recorded have been
made. Distinct currents are observed traversing
the vital vessels, and passing through the lateral
connecting tubes or branches, into the principal
channels. These currents follow no one deter-
minate course, but are very inconstant in their
direction, some proceeding up, and others down,
some to the right, and others to the left; the
motion occasionally stopping suddenly, and then
recommencing. . . . The effect does not seem
to depend upon a contractile power of the tubes,
because the latex flows chiefly or entirely from
one end of a tube, even when it has an orifice
open at both extremities. The appearance is
especially analogous to the circulation of some
of the lowest tribes of animals, as in the Diplo-
zoon paradoxum, which may be divided into two

APPENDIX A. 131

parts, and the blood will continue to circulate
for three or four hours in each. By a strong
electric shock," the force by which the latex is
propelled, is paralysed, and its motion arrested."
(Henslow's Principles of Botany, p. 207, et
seq.)

B.

ANALYSIS OF THE LINN^LAN CLASSES.

FROM HALF'S " ANALYSIS OF THE BRITISH
FLORA."

( Neither stamens nor pistils Cryptogamia (24.)
\ Stamens and pistils 2.

/'Stamens and pistils in sepa-

I rate flowers 3.

i All or many of the flowers

perfect 4.

^•Barren and fertile flowers on

different plants Dirccia (22.)

j Barren and fertile flowers on

L the same plants Monoecia (21.)

('Some flowers with pistils

Ionly, and a perianth unlike
that of the united or of the

4<^ barren flowers Polygamia (23.)

Flowers with both stamens
and pistils, or with similar
perianths 5.

lOZ APPENDIX B.

/-Stamens situated upon the

5 <r style Gynandria (20.)

^Stamens not on the style.... 6.

/-Flowers compound; (anthers

6 < 5, united) Syrigenesia (19.)

^Flowers not compound 7.

/"Filaments united in one or

7 <{ more sets 8.

^Filaments not united 9.

/'Filaments united in one set Monadelphia (16.)

o j Filaments united in two sets Diadelphia (17.)

I Filaments united in more

I- than two sets Polyadelphia (18.)

C Stamens 16 or more 10.

^ Stamens 15 or fewer 11.

/-Stamens inserted into the re-

j ceptacle Polyandria (13.)

] Stamens inserted into the

k calyx Icosandria (12.)

f Stamens 12 or more Dodecandria (11.)

Stamens 10 Decandria(10.)

Stamens 9 Enneandria (9.)

Stamens 8 Octandria (8.)

Stamens 7 Heptandria (7.)

^.Stamens 6 or fewer 12.

/"Stamens 6 13.

12 < Stamens 5 Pentandria (5.)

LStamens 4 or fewer 14.

f Four stamens longer ; (petals

4, rarely wanting) Tetradynamia (15.)

| Stamens equal (petals more

*• orlessthan4) Hexandria (6.)

^Stamens 4 15.

\ Stamens 3 or fewer 16.

11

APPENDIX B. 133

^ C Two stamens longer Didynamia (14.)

( Stamens equal Tetrandria (4.)

/'Stamens 3 Triandria (3.)

16 ^Stamens 2 Diandria (2.)

l-Stamensl Monandria(l.)

The above form is given in preference to a
mere enumeration of the Linnaean Classes as
being more useful and instructive. It will at
once be perceived that if it is wished to know
what class any plant belongs to, we must in the
first instance observe whether it has stamens or
pistils, if it has neither, it is one of the Crypto-
gamia, and our point is ascertained at once. If
it have stamens .and pistils we are referred to
No. 2, and, accordingly, as the stamens and
pistils are, or are not, on the same flower, we
are to turn to No. 3 or 4, and so on till we have
completed our search. Such an analysis is of
great practical utility. The number of each
class in Linnaeus' arrangement, is given at the
end of each in a parenthesis.

C.

AT the end of a chapter on the longevity of
trees, in which M. De Candolle fully shows
his grounds for concluding their ages to be
what he has stated, he gives the following table
of some of the most remarkable in the world.

134 APPENDIX C.

Years.

"Elm 335

Cheirostemon (a Mexican

tree) 400 (about)

Ivy 450

Larch 576

Lime 1147—1076

Cypress 350 (about)

Oriental Plane 720 and more

Granger 630

Cedar of Lebanon SOO(about)

Olive 700 (about)

Oak 1500—1080—810

Yew 1214—1458—2588—2880

Baobab 5150 (in 175?)

Taxodium (of Oaxaca) 4000 to 6000 (about)."

"The Baobab (Adansonia digitata) is the
most celebrated example of extreme longevity
that has yet been observed with precision. It
bears in its native country a name which signi-
fies a thousand years, and contrary to custom,
this name is short of the truth." *

The following notice respecting this species
of tree has been kindly furnished by a friend.
" Adanson's own statement concerning the Bao-
bab, and his reasonings upon it amount to this.
He saw, in one of the two Magdalen Islands,
two Baobabs, bearing European names, some
of which were very distinctly of the date of the

* De Candolle, Physiologic Vegetale, torn. ii. p.
1003.

APPENDIX C. 135

16th and 15th centuries,* and others somewhat
confusedly (' assez confinement') of the 14th ;
years having effaced, or filled up the greater
part of the characters. These were probably
the same trees which Thevet mentions having
seen in those islands, in his voyage to the Ant-
arctic Seas in 1555 (in which, however, no no-
tice is taken either of the size of the trees,
or of inscriptions on them). These characters
were six inches at the utmost in length, and not
so much as two feet in width, being about the
eighth part of the circumference of the trunk,
from which Adanson concluded that they had
not been cut while the trees were young. Neg-
lecting the date of the 14th century, and taking
that of the 15th, which is very distinct, he holds
it to be evident that, if these trees have been
two centuries in gaining six feet in diameter,
they would be at least eight in acquiring twenty-
five feet. But experience teaches that trees
grow rapidly at first, afterwards more slowly,
and finally cease to increase in diameter, when
the tree has attained the size usual to its spe-
cies. Adanson knew from observation, that the

* It seems clear that Adanson in speaking of the 14th,
loth, and 16th centuries, really means the 15th, 16th,
and 17th, inasmuch as he in one place carefully reckons
from the date of the 15th century to the year 1749, as a
period of two centuries.

136 APPENDIX C.

Baobab in its first year, measured from an inch
to an inch and a half in diameter ; that at the
end of ten years it reached a foot in diameter ;
and at the end of twenty, about a foot and a
half. These data, he adds, are insufficient for
any precise determination ; he, therefore, limits
himself to suspecting that the growth of the
Baobab, which is very slow with relation to its
monstrous size (of twenty-five feet diameter)
must continue for several thousand years, and
perhaps ascend to the time of the deluge ; so
that we have good reason to believe that the
Baobab is the most ancient of the living monu-
ments which the terrestrial globe can furnish.
These particulars are given in a 'Description
d'un Arbre d'un nouveau genre, appele Baobab,
observe au Senegal,' published by Adanson in
the Memoires de VAcademie des Sciences, for
1761, where he also states the circumference of
the tree as reaching to sixty-five feet, or even
seventy-seven and a half feet, making its dia-
meter somewhat less than twenty-five feet. In
his ' Voyage au Senegal,' he speaks, p. 54-5,
of having measured two trunks of sixty-five feet
and sixty -three feet circumference ; and again, p.
104, of two others measuring seventy-six and
seventy-seven feet, but it does not appear that
these were the trunks on which the names were
cut.

APPENDIX C. 137

" The only certain way of discovering the age
of trees of temperate and northern climates is
by cutting them down, and counting their an-
nual layers, but even this method becomes un-
certain with respect to the trees of tropical
countries, in which the layers are frequently
very indistinct, and in which they are also, in
some instances, repeated several times in the
year.

" With respect to the Baobab, if its age be
doubtful, its size at least has not been exagge-
rated. M. Perottet states in the " Flore de
Senegambie," that Baobabs are frequently to be
found measuring from seventy to ninety feet in
circumference. He promises a memoir on their
mode of growth, but the writer of this is not
aware if he has yet published it.

" The subject of inscriptions in trees, (origi-
nally cut through the bark, and having their
woody portion covered up by successive annual
layers) is a very curious one. It has been the
subject of numerous memoirs, of which a list is
given in the Catalogue of Sir Joseph Banks's
Library."

Although England has no trees whose usual
size can compete with that of the gigantic Bao-
bab above mentioned, some of her yews and
oaks are as worthy of record, and approach
more nearly to it in dimensions, than is perhaps

I3o APPENDIX c.

generally known or remembered. Evelyn, after
mentioning several giants of the forests, both
of his own and of foreign countries, says,

" To these I might add a yew tree in the
churchyard of Crowhurst, in the county of Sur-
rey, which I am told is ten yards in compass ?
but especially that superannuated yew tree now
growing in Braburne churchyard, not far from
Scott's Hall, in Kent ; which being fifty-eight
feet, eleven inches, in the circumference, will
bear near twenty feet diameter, as it was mea-
sured first by myself imperfectly, and then
more exactly for me, by order of the late Right
Honourable Sir George Carteret, Vice Cham-
berlain to his Majesty, and late Treasurer of
the Navy : not to mention the goodly planks,
and other considerable pieces of squared and
clear timber, which I observed to lie about it,
that had been hewed and sawn out of some of
the arms only, torn from it by impetuous winds.
Such another monster, I am informed, is also
to be seen in Sutton churchyard, near Winches-
ter."* In a note, the Editor of the Sylva (Dr.
A. Hunter) gives the following account of a
most remarkable oak, actually rivalling the Bao-
bab in girth, — it is accompanied by an engrav-

» Sylva. Vol. ii. Book 5, Ch. 3, p. 195. Hunter's

APPENDIX C.

139

ing. " My ingenious friend, Mr. Marsham,
informs me that there is now growing in Holt
Forest, near Bentley, a vigorous and healthy
oak, which at five feet from the ground, mea-
sures thirty-three feet, eight inches, in girt;
however, neither this, nor any of the oaks men-
tioned by Mr. Evelyn, bear any proportion to
one growing at Cowthorpe, near Wetherby,
upon an estate belonging to the Right Hon.
Lady Stourton. The annexed plate is taken
from a drawing made upon the spot in the year
1776. The dimensions are almost incredible.
Within three feet of the surface it measures six-
teen yards in circumference, and close by the
ground, twenty-six yards. Its height is about
eighty feet, and its principal limb extends six-
teen yards from the bole. Throughout the
whole tree, the foliage is extremely thin, so that
the anatomy of the ancient branches may be
distinctly seen in the height of summer."*

If we may descend from the lordly oak to s'o
humble a plant as a radish, the reader may per-
haps be amused by the following notice of an
enormous specimen of this vegetable, also men-
tioned by Evelyn, in his " Terra. A Philoso-
phical Discourse of Earth, relating to the Cul-
ture and Improvement of it for Vegetation, and

* Ibid. p. 197.

140 APPENDIX C.

the Propagation of Plants, as it was presented
to the Royal Society." — " Peter Hondius tells
us (in his book entitled Dopes inemplte) that by
the sole application of sheep's dung he produced
a raddish root in his garden as big as half a
man's middle, which being hung up for some
time in a butcher's shop, people took for an
hog." The date of this paper is Ap. 29. 1675.
It is a curious mixture of valuable information
with the crude speculations that formed much
of the, so called, science of that day — yet giving
evidence of the value of the new light that had
been already thrown on the path of knowledge
by directing the attention to experimental re-
search, of which it contains a record exhibiting
much patient investigation. It is also an inte-
resting document, being one of the very early
communications to the Royal Society, during
the Presidency of Lord Brouncker. A few fur-
ther extracts from it may be entertaining, and
if they induce us of the 19th century to smile
at the strange notions which such men as Lord
Bacon and John Evelyn could think worthy of
notice, the smile will be any thing rather than
a sneer, and will be quickly followed by a feel-
ing of gratitude to those great men, who, born
in days of comparative ignorance, were never-
theless so far beyond the times in which they
lived, that they could perceive and point out the

APPENDIX C. 141

very course which has obtained for science the
enlarged boundary she now possesses ; and to the
Society which first made the cause of science a
national question, and under whose auspices
England has attained an eminence which all
her sons must ardently pray she may never
lose.

A passage near the commencement of the
" Discourse of Earth," is so characteristic of the
style of writing of the period, that it is worth
extracting. After a modest disclaiming of his
own powers, Evelyn goes on to say, " There
are few here I presume, who know not upon
how innocent and humble a subject I have long
since diverted my thoughts ; and, therefore, I
hope they will not be displeased, or think it un-
worthy of their patience, if from their more
sublime and noble speculations (and which do
often carry them to converse among the brighter
orbs and heavenly bodies) they descend awhile,
and fix their eyes upon the earth, which I make
the present argument of my discourse. I had
once indeed, pitched upon a subject of some-
what of a more brisk and lively nature; for
what is there in nature so sluggish and dull as
earth? What more spiritual and active than
vegetation, and what the earth produces ? But
this, as a province becoming a more steady hand
and penetrating wit than mine to cultivate, (un-

142 APPENDIX C.

less where it transitorily comes in my way to
speak of salts and ferments) I leave to those of
this learned society, who have already given
such admirable essays of what they will be more
able to accomplish upon that useful and curious
theme ; and, therefore, I beg leave that I may
confine myself to my more proper element, the
earth, which though the lowest and most infe-
rior of them all, yet is so subservient and ne-
cessary to vegetation, that without it, there
could hardly be any such thing in nature." He
then gives a long account of different strata of
earths, &c. in which some of the phraseology
sounds strangely to modern ears — for instance,
"marsh-earth," is said to be "the most churl-
ish," and marl, " of a cold, sad nature." The
two following passages are among those which
cannot be read without a smile, "If, upon ex-
cavating a pit, the mould you exhaust do more
than fill it again, Virgil tells us 'tis a good au-
gury ; upon which Laurembergius affirms, that
at Wellemberg, in Germany, where the mould
lies so close, as it does not replenish the foss
out of which it has been dug, the corn which is
sown in that country soon degenerates into rye;
and what is still more remarkable, that the rye
sown in Thuringia (where the earth is less com-
pacted) reverts, after three crops, to be wheat
again."

APPENDIX C. 143

" My Lord Bacon directs to the observation
of the rainbow, where its extremity seems to
rest, as pointing to a more roscid and fertile
mould ; but this, I conceive, may be very falla-
cious, it having two horns, or bases, which are
ever opposite."

Among such strange ideas, which, however,
bear but a very trifling proportion to the bulk
of practical information which was probably new
and valuable to the agriculturist of those days,
there is the dawning of a true knowledge of
Vegetable Physiology. The indispensable im-
portance of water, the probable influence of the
atmosphere, both on the plants themselves, and
on the soil, the strong suspicion at least, " that
plants do more than obscurely respire, and ex-
ercise a kind of peristaltic motion," are among
the indications of an approach to truth, and
when we remember that about this time Grew
was employed on the " Anatomy of Plants," we
may fairly trace back to these days the begin-
ning of the Science, properly so called, which is
the subject of this little book ; nor can better
words be found with which to conclude it, than
those of Evelyn, speaking of the " Groves and
Woods," — " But I cease to expatiate farther on
these wonders, that I may not anticipate the
pleasures with which the serious contemplator
on those stupendous works of Nature (or rather

144 APPENDIX C.

God of Nature) will find himself wrapt and
transported, were his contemplations only ap-
plied to the production of a single tree." *

* Sylva, Book 4, p. 345.

FINIS.

,.,U. .fPUTHERN REGIONAL LIBRARY FACIl

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