PARTS OF TREES FIRST IMPAIRED BY A«K. J^P 



disease. I am, therefore, much disposed to attribute the The le»t«« th» 

 drsia/ics aud debility oK old age in trees to an inability to org»"s it«^ 

 produce l<!aves, whicii can elficiently execute their natural 

 office : and to »ome consequent inaperfection in the circu- 

 lating fluid. Jt iii true, that the leaves are annually repro- 

 duced, aad therefore annually new : but there is, 1 eonceive, 

 a very essential difference between the new leaves of an old, 

 and of a young variety: and in support of this opinion, I 

 shall observe, that the external character of the leaf of the 

 Siitne variety at two, and at twenty years old, is very dis- 

 similar; and it therefore appears not improbable, 'hat 

 farther changes will have taken place at the end of two 

 centuries*. 



If these opinions be well founded, and the leaves of trees 

 be analogous to the lungs of animals, is it very improbable, 

 that the natural debility o. old age of trees and of animals 

 may originate from a similar source? — This is a question, Longevity 



upon which I am not by any means prepared to give an l>»^"t--pally a^^ 



• 1 ^ T u r -.11 n u 1 •. 1 feciedbythe 



opinion: but I believe it will very generally be admitted, ^tate of the 



th^it the human subject is best formed for long life, when lungs? 

 the chest is best formed to permit the lungs to move with 

 most freedom. I have also long and attentively observed 

 among our domesticated, animals, that those individuals 

 longest retain their health and strength, and best bear ex- 

 cessive labour and insufficient food, in which the chest is 

 most deep and capacious, proportionately to the length of 

 current the circulating fluid has to run ; and the same 

 remark will, I believe, be generally found applicable to the 

 human species, I am, my dear Sir, 



with great respect, sincerely yours, 

 Downton, Feb, 26, TliO. AND/kNIGHT. 



IgrlO. 



♦ The leaf of a seedling apple or peai-tree, when the plant U very Down on 

 young, is geneially almoFt wholly fr«e trom tlie pubr»cence or down, leaves a symj)- 

 whicli subsequently appears on its under surface ; and which Bonnet and ^^^ of <i<?- 

 Mr. Mirbel have supposed to increase its surface and jjowers. But "^* 

 I feel little disposed to adopt this hypothesis, having observed, that the 

 leaves ef some new varieties of the apple, which have sprung from seeds 

 of the Siberian crab, have both surfaces nearly equally smooth j and rhat 

 these varieties grow faster, and bear heavier crops of ver^ rich fruit, tXvxii 

 an^ others, without being exhausted or injured, 



vr. 



