Chap. IT.] 
COURSE OF THE SAI\ 
51 
proper juices ” and “ peculiar acids ” of all the 
various woods, bark, leaves, flowers, scents, 
fruits, seeds, &c. of that most exquisite kingdom, 
—but we are even ignorant in what part of the 
plant the elaboration takes place, or from what 
part of the plant the new growth is deposited. 
After the ascent of the sap, it is supposed to 
be elaborated in the leaf. It passes from the 
wood into the woody fibrous, or stalky, parts of 
the leaf; thence into their spongy, porous 
(parenchymatous) parts; and thence backwards 
into the green inner bark of the shoot, which is 
called “ the herbaceous envelope.” So that the 
leaves and buds may be considered as the con¬ 
duits, connecting the upward with the downward 
current of the sap. In descending through the 
bark, the elaborated sap is supposed to deposit 
the annual ring of new wood (alburnum), and 
the annual ring of new bark (the new cortical 
layer), (both at once ? or which first ?), round 
the branches, stem, and roots, and also to furnish 
the new growth of the roots in length. 
Whether any chemical change or elaboration 
of the sap really does take place in the leaf, 
greater than in any other part of the tree, I 
shall not question; but I think that possibly one 
chief duty of the leaf is to give off the supernu- 
Sap supposed to 
be elaborated in 
the leaf. 
Growth on 
girthing sup¬ 
posed to be de¬ 
posited from 
this elaborated 
sap in return¬ 
ing down the 
bark. 
First office of 
the leaf, transpi¬ 
ration and ex¬ 
cretion. 
