i ae 
On the Parts of Trees primarily impaired ly Age. 59 
simply in contact. Since then, we took every necessary 
precaution in order that the fly-press and the metallic preces 
should be at the same temperature before making the fly- 
press act. 
It results from what precedes, that the heat which is pro- 
duced by compression in bodies which do not undergo 
any chemical change, is merely owing to the changes of 
dimension which these bodies undergo; and when the di- 
mensions can no longer be diminished, the shock, how- 
ever violent does not cause any heat: solids then become 
similar to liquids, which may undergo violent and repeated 
shocks without any change in temperature: for it appears 
to me to be natural to attribute the small extrication of 
heat which we have been able to observe in the pieces which 
had undergone three operations, either toa small condensa- 
tion which might still be produced in them, or to the effects 
of the elastic particles of the fly-press,’;which had been able 
to re-adjust themselves after the sbock. dly, That the 
communication of the heat takes place much more rapidly 
by a strong compression than by simple contact: from 
which it follows, that in our experiments we bave been able 
to obtain but a small part of the effects of the extrication 
of heat produced by compression; but this part ought to 
be in relation with the total effect. , 
X. On the Parts of Trees primarily impaired by Aze. 
In a Letter from T. A. Knicut, Esq. F.R.S. to the Rt. 
Hon. Sir Joseru Banks, Bart. K.B. P.R.S.* 
My pear Sir, In the first communication I had the ho- 
nour to address to you, (it was in the year 1795,) I stated 
the result of many experiments on grafted trees, trom which 
I inferred that each variety can he 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 iree. 
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 ap- 
pears sufficiently interesting to induce me to communicate 
au account of them to you. 
Whatever difference exists between the functions of ani- 
* From the Philosophical Transactions for 1810, Part IL 
mal 
