C 3>3 3 
XX. On the Origin and Office of the Alburnum of Trees . In a 
Letter from T. A. Knight, Esq . F. R. S. to Sir Joseph Banks, 
Bart . JC. P. P. R . S. 
Read June 30, 1808. 
My Dear Sir, 
In my last communication I endeavoured to prove that the 
bark of trees is not subsequently transmuted into alburnum ; 
and if the statements that I have there given be correct, they 
are, I conceive, decisive on the point for which I contended : 
and if the bark be not converted into alburnum, the experi- 
ments of Duhamel, and subsequent naturalists, and those of 
which I have given an account in former memoirs, afford suf- 
ficient evidence that the bark deposits the alburnous matter. 
If the succulent shoot of a horse chesnut, or other tree, be 
examined, at successive periods in the spring, it will be seen 
that the alburnum is deposited, and its tubes arranged, in 
ridges beneath the cortical vessels ; and the number of these 
ridges, at the base of each leaf, will be found to correspond 
accurately with the number of apertures through which the 
vessels pass from the leaf-stalks into the interior bark, the 
alburnous matter being apparently deposited (as I have en- 
deavoured to prove in former memoirs) by a fluid which 
descends from the leaves, and subsequently secretes through 
the bark.* I shall therefore venture to conclude that it is 
* Phil. Trans. iSoi, p. 336, 
Ss 
MDCCCVIII. 
