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
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 you 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.