Imjirovemcnt of Forest Plantations. 243 
tiire's own immediate electrical agents, and that all hydro-carbonous 
combinations, are, in fact, but infinitely varied modifications of the 
elements of water ; that otmospheric air also, is one of these modifica- 
tions : — but this is to view primary causes, to look into the first principles 
of created things. 
"If we are to investigate the immediate agents concerned in the work 
of vegetable nutrition, I should say that the tree being; a hydro-carbonous 
body, requires for its support, that the supply of food to its root be of 
such a nature as may afl:ord the readiest means of assmiilation. Now, 
vegetable and animal substances, when subjected to fermentation, fur- 
nish solid, fluid, and gaseous matters, contaming all the elements of the 
vegetable structure, which elements, when blended with the earths, are 
distributed to the roots, and are taken up by their vascular system. Ma- 
nures therefore, must be of essential utility in promoting the vigour and 
growth of trees. 
"If we enquire into the causes that promote vegetable growth I should 
say that, I cannot but think — nay, firmly believe, every pointed termina- 
tion of the leaves, twigs, buds, every bristle and prickle, to be an efficient 
agent in inducing atmospheric decompositions. At page 98 of your 
Letter to Sir W. Scott, you have introduced the foUov/ing most philoso- 
phic quotations, which bears upon my theory : ' If you deprive a tree 
of its leaves or mouths, the roots are unable to obtain that wh ch enables 
them to perform their functions. Nature is true to herself. The single 
tree sends out its branches to catch and inhale every tiling conducive to 
its productive powers. Where teees are thickly planted, nature directs 
them upwards to obtain that which their situation prevents them from 
getting in a lower medium; consequently you observe the lower boughs 
are thin and weak within, and fall oif, whilst, in a young healthy tree, 
the topmost shoots exhibit vigour, and will make more wood upward in 
a given time than trees that stand singly; and hence the great length 
that trees attain in woods.' 
"The agency of light induces the ascent of the sap in the spring, at 
the moment that it propels downward the descendmg laborated juices: 
thus, from the moment of the first germination of the seed, the descend- 
ing and ascending fluids are co-existent; and the solar light in its pas- 
sage through the vegetable vessels, operates by induction, and attracts 
those fluids which have been prepared in the soil by electro-chemical 
agency, in the immediate neighbourhood of the rootlets of plants, and 
brings them into the sap- vessels, whence they are distributed into appro- 
priate cells, wherein they are further laborated by the agency of that 
lateral attraction, which I think is the real basis on which rests tiie the- 
ory of Endosmose, of Dutrochet. 
"What I have said, leads to a two-fold deduction. The first is, that 
every twig, having a vital function to perform, is of vital consequence 
