352 Mr, Knight’s Experiments on 
found in the plant. It appears to be then brought back again, 
through the vessels of the leaf stalk, to the bark, and by that 
to be conveyed to every part of the tree, to add new matter, 
and to compose its various organs for the succeeding season. 
When I have intentionally shaded the leaves, I have found 
that the quantity of alburnum deposited has been extremely 
small. 
In speaking of the circulation within the apple and pear, I 
wish to express myself with much less decision, as I have not 
seen the effects of taking up any of those vessels into which the 
coloured infusions did not enter. The internal organization of 
the leaf, and of the wood, of those trees which have a central 
medulla, seems to admit but of little variation, and (as far as I 
have had opportunities to examine) of no essential difference ; 
whilst that of different fruits is extremely various. The external 
vascular parts of the apple and pear, abstracted from those 
which seem to carry nourishment to the seeds, appear to me to 
resemble, in some respects, those of the leaf ; and, relative to 
the offspring, I suspect that they perform a somewhat similar 
office. 
I do not know how much you will have found in the pre- 
ceding narrative, that is new and interesting to you, for I am 
not very deeply read in the experiments which naturalists have 
made on plants. In the authors I have looked into, I have 
seen many contradictory experiments related, and many con- 
clusions drawn from a small number of facts; and I have found 
much that does not well agree with the things that have come 
under my own observation. I will therefore venture to indulge 
the hope, that you will have found enough that is new, to 
i 
