380 CONSERVATIVE ORGANS. [LECT. VII. 



evolved, before we can accord with his position; for 

 it is during that period only that the pith is es- 

 sential in trees and shrubs. But although its 

 functions cease, yet the pith still remains a part of 

 the trunk of the oldest trees, as long as these re- 

 main sound. Some authors, among whom we find 

 Willdenow *, Mr. Keithf , and Sir J. E. Smith +, 

 assert that it disappears altogether, obliterated 

 " by the increasing solidity of the wood." Darwin $ 

 supposes that it is either absorbed or imbued with 

 ligneous matter, so as not to be distinguishable 

 from wood; an opinion which Mr. Knight com- 

 bats, affirming that its place " is never filled with 

 " wood || ;" while others contend that it never va- 

 ries, being the same in the old trunk as in the 

 young branch. Let us examine in what these 

 opinions are correct. 



In stems, the wood of which is of a close 

 texture, and the divergent layers very thin, no 

 obliteration of the pith can take place, nor even 

 any compression of it occur, after the case of 

 wood which encloses it is perfected ; and, on 

 close examination, it can readily be detected in 

 the oldest sound stems of this description ; but, 



* Principles of Bot. trans, p. 251. 

 f Syst. of phys. Bot. vol. ii. p. 213. 

 J Introd. to phys. and syst. Bot. p. 39. 

 Phytologia, xviii. 2, 13. 

 I] Phil. Trans. 1803. 



