AND AMERICAN RURAL SPORTS. 
221 
sap, elaborated and sent downwards by the leaves under 
the state of proper juice, is absorbed laterally by means of 
the radiating vessels, or gilver grain, and is gradually depo- 
sited in the originally empty vessels of the wood ; that the 
compactness and weight of wood depend upon these juices 
so deposited, and not upon any constitutional difference in 
the wood itself; and that in certain trees, which are re- 
markably light, as the poplar, no deposit, or scarcely any, 
takes place. 
The bark also undergoes material changes in the course 
of time. The first branches which are produced are green, 
like the leaves; their colour being occasioned by the trans- 
parency of the epidermis, which allows the cellular tissue, 
or the parenchyma, to show through. By slow degrees the 
epidermis thickens, and assumes a deeper colour, under 
which appearance it is seen in the winter season. If it is 
raised up, the green colour of the parenchyma is still mani- 
fest enough beneath it. The epidermis necessarily gives 
way gradually to the growth of the tree, and splitting in 
various directions is replaced by another; and by slow 
degrees new layers are formed, and burst in various direc- 
tions. According to the nature of the plant the epidermis 
also takes a variety of forms, sometimes forming the mis- 
shapen knotty crust which is usually called bark, sometimes 
peeling off in thin layers, and occasionally falling from the 
parent tree in hard flakes. 
It is probable that the bark performs the same functions 
as the leaves, in the early state of the buds, and occasionally 
in all states. Otherwise it would not be easy to account for 
the growth of cacti, euphorbias, some apocineous plants, &c. 
which are all destitute of leaves. In fine, the bark may be 
compared to a universal leaf, with one surface only. 
We have seen what ingenious methods nature adopts to 
screen the buds from the rigour of winter; but in countries 
where there is no winter no defence is requisite. These 
protecting scales diminish, therefore, by degrees, as we ap- 
proach the equator. In the trees which cover countries in 
such a latitude, the buds break forth at once into leaves and 
branches, without regarding the order of seasons. By this 
circumstance the apparent difference between trees and 
herbs is removed. 
In like manner, insensible gradations unite the herbs 
which creep or trail along the ground, and those which 
carry their heads aloft in the air: the perennial and the 
annual vegetable. Some exist for two years. The stems of 
others perish every year, but their roots survive. Some 
under shrubs scarcely elevate themselves from the soil, yet 
their slender stems are formed of a firm and woody sub- 
stance. Next come the shrubs whose branched and entangled 
stems from bushes. Lastly are perfected the trees, which, 
from possessing a stem scarcely loftier than the stature of a 
3 K 
man, finally dilate themselves till they become the giants of 
the forest. 
We have assigned, as the cause of increase in the bulk of 
trees, the communication which is established in their system 
between the leaves and roots. The reciprocity of disposition 
of these two organs is so strong, that if a bit of a branch of 
any tree which is robust enough to bear the operation, be 
placed in the earth, it immediately makes good the loss it 
has sustained by being dissevered. It presently produces 
fresh roots, and a new plant is formed. The advantage 
which is taken of this peculiarity of plants, to propagate 
them by cuttings or layers, is well known. But this is not 
all ; a bud separated from its parent, and inserted between 
the bark and the wood of another tree, soon establishes the 
requisite communication between itself and the earth, and 
renders the tree which bears it similar in nature to the kind 
artificially inserted. Hence the origin of budding and graft- 
ing in horticulture. 
From these observations it has become evident that the 
life of a plant is a succession of several lives ; and that the 
greater proportion of its parts consists of an intermediate 
system, which only serves to maintain a communication 
between the extreme points of the vegetable. If a tree is 
destroyed by the ravages of time, its death can be only occa- 
sioned by the destruction of the intermediate portions of its 
fabric, by which the channel of continuous communication is 
effectually interrupted. After such interruption has taken 
place, the still surviving portions of the tree are capable of 
furnishing layers or cuttings, which will renew the opera- 
tion of vegetation with unabated vigour. 
The resources of nature are far from being exhausted by 
these apparent buds ; there exists throughout the vegetable 
system a creative and expansive power, which, according to 
circumstances, is able to operate in the development of new 
buds, where none had been visible before. In fact, there is 
always an abundance of rudimentary buds dispersed among 
the substance of a tree, which are only called into action 
when the ordinary resources of nature begin to fail. They 
are frequently excited very long after the period which had 
been originally assigned for their appearance; and even in 
places where no traces of them could have been expected 
to exist. Thus in all vegetables there appears to be as 
obvious a line of demarcation in the system, at that point 
which is called the collar, whence the first ascending fibres 
direct their course upwards, and the descending downwards. 
Buds are only produced by the former, and form no part of 
the economy of the latter. Yet it not unfrequently happens, 
that roots exposed in a proper degree to the influence of the 
air will form buds, and throw up shoots, in the same way as 
the branches. Even the leaves have, in a few cases, a simi- 
lar power of producing buds, and consequently young plants. 
