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 abd 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 

 3K 



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. 



