COURSE OF THE SAP. 



PT. n. 



Sap sup- 

 posed to be 

 elaborated 

 in the leaf. 



Growth in 



girthing 



supposed 



to be 



deposited 



from this 



elaborated 



gap in 



returning 



doAvn the 



bark. 



First office 

 of the leaf, 

 transpira- 

 tion and 

 excretion. 



or from what part of the plant the new growth is 

 deposited. 



After the ascent of the sap, it is siqjposed 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 the 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 

 lensfth. 



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 

 olf the supernumerary watery parts necessary to take 

 up from the soil and conduct to their destination the 

 carbonic acid, ammonia, and inorganic matters requisite 

 for vegetable life, and that it exhales the unnecessary 

 gases, &c., after the decomposition of the constituents 

 absorbed from the soil. And is not the great accumu- 

 lation of ash, or incombustible or inorganic matter, 

 found in the leaf, as compared with that found in the 



