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XV. Account of some Experiments on the Ascent 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 May 14, 1801. 
MY DEAR SIR, 
The cause of the ascent of the sap in trees appearing to me 
not to have been satisfactorily accounted for, I have lately turned 
my attention to that subject; and, as some facts have come 
under my observation, which do not appear to have been noticed 
by any author that I have seen, I take the liberty to trouble yoie 
with an account of a few of the experiments that I have made ; 
hoping that some of them may appear new and interesting to 
you. These experiments were made on different kinds of trees ; 
but I shall confine myself to those made on the crab-tree, the 
horse-chesnut, the vine, and the oak; and shall begin with 
those made on the crab-tree. 
Choosing several young trees of this species in my nursery, 
of something more than half an inch diameter, and of equal 
vigour, I made two circular incisions through the bark, round 
one half the number of them, about half an inch distant from 
each other, early in the spring of 1799 ; and I totally removed 
the bark between these incisions, scraping off the external coat 
of the wood. The other half I left in their natural state. 
At the usual season, the sap rose in equal abundance in all ; 
