On the Action of detached Leaves of Plants. 345 



instantaneous as the spark itself ; but the effect of the same two 

 elements, brought into action by the electric columns, may ba 

 continued at pleasure for months, or even years. 



Now, as all the operations of Nature are produced by general 

 laws, it is very probable, that all the phsenomena of electricity, 

 chemistry, meteorology, and the living functions of animals and 

 \ egetables, are the effects of these two elements. 



This hypothesis (like many others) is easily formed, but the 

 iuvestigatiou of a theory is a work of greater labour ; and may 

 perhaps, in this instance, require the assistance of some instru- 

 ment not yet invented ; for nothing tends so much to enlarge 

 the native intellectual powers of man as improvements in the 

 arts. 



Lynn, Nov. 13, 1816. EZKKIHL WaLKER. 



[To be continued.] 



LXIX. On the Action of detached Leaves of Plants. By 

 T. A. Knight, Esq. F.R.S. In a Letter uddre<!sed to the 

 Right Hon. Sir Joseph Banks, Bart. G.C.B. P.R.S.* 



Dear Sir, — Oince I had last the honour to address a com- 

 munication to you, with a request that you would lay it before 

 the Royal Society, I have repeated great part of the experiments 

 which "formed the sulyects of my former letters, with such ad- 

 ditions and variations, as might probably lead to the detection 

 of any erroneous conclusions vvliich I might have drav/n : but I 

 have not been able to detect any errors, nor to add any thing 

 very important to my former observations. I have, however, 

 been able to ascertain a few new facts, which 1 think too in- 

 teresting to be lost. 



I endeavoured, in my former communications, to adduce 

 evidence, that the matter, which becomes vitally united to trees, 

 previously passes through their leaves; and I shall now proceed 

 to state some facts, which, I trust, will prove that a fluid pos- 

 sessing tlie power which I have attributed to the true sap, ac- 

 tually descends through the leaf-stalks. 



A slender knife was passed through some leaf-stalks of the 

 vine, about two-thirds of ati inch distant from their junction to 

 the branch: and down to that point, the leaf-stalks were divided 

 longitudinally, and a transverse section, about half an inch long, 

 was made through the bark opposite the middle of the leaf-stalk. 

 A similar transverse section through the bark, was made some- 

 what less than an inch distant below; and these sections were 



* 1 rom the T.aiisactioiis of the Ro^al Society for 1816^ part ii. ^ 



united 



