C 17S 3 
VIII. On the Parts of Trees primarily impaired by Age. In a 
Letter from T. A. Knight, Esq. F.R.S. to the Rt. Hon . Sir 
Joseph Banks, Bart. K.B . P.R.S. 
Read March 22, 1810. 
My dear Sir, 
In the first communication I had the honour to address to 
you, (it was in the year 1795,) I stated the result of many 
experiments on grafted trees, from which I inferred that each 
variety can be propagated with success, during a limited 
period only ; and that the graft, or other detached part of an 
old tree, or old variety, can never form that, which can with 
propriety be called a young tree. 
I have subsequently endeavoured to ascertain which, 
amongst the various organs that compose a tree, first fails to 
execute its office, and thus tends to bring on the incurable 
debility of old age ; and the result of the experiments appears 
sufficiently interesting, to induce me to communicate an ac- 
count of them to you. 
Whatever difference exists between the functions of animal 
and vegetable life, there is a very obvious analogy between 
some of the organs of plants, and those of animals; and it 
does not appear very improbable, that the correspondent 
organ, in each, may first fail to execute its office ; and satis- 
factory evidence of the imperfect action of any particular 
