PHILOSOPHICAL 
TRANSACTIONS. 
XI. Account of some Experiments on the Descent of the Sap in 
Trees. In a Letter from Thomas Andrew Knight, Esq. to 
the Right Hon. Sir Joseph Banks, Bart. K. B. P . R. S. 
Read April si, 1803. 
MY DEAR SIR, 
In a Memoir which I had the honour to present to you two 
years ago,* I related some experiments on trees, from which I 
inferred, that their sap, having been absorbed by the bark of the 
root, is carried up by the alburnum or white wood, of the root, 
the trunk, and the branches ; that it passes through what are 
there called the central vessels, into the succulent part of the 
annual shoot, the leaf-stalk, and the leaf ; and that it returns to 
the bark, through the returning vessels of the leaf-stalk. The 
principal object of this Paper is, to point out the causes of the 
descent of the sap through the bark, and the consequent for- 
mation of wood. 
These causes appear to be, gravitation, motion communicated 
* See Phil. Trans, for 1801, p. 333. 
O o 
MDCCCIIT. 
