WOOD. 191 



The WOOD is at once the support of all the deciduous organs 

 of respiration, digestion, and fertilisation ; the reservoir of 

 the secretions peculiar to individual species ; and also the 

 magazine from which newly forming parts derive their 

 sustenance, until they can establish a communication with 

 the soil. 



Regarding the precise manner in whicli it is created, there 

 has been great diversity of opinion. Linnaeus thought it was 

 produced by the pith ; Grew, that the liber and wood were 

 deposited at the same time in a single mass which afterwards 

 divided in two, the one half adhering to the centre, the other 

 to the circumference. Malpighi conceived that the wood of 

 one year was produced by an alteration of the liber of the 

 previous season. Duhamel believed that it was deposited by 

 the secretion existing in Exogens between the bark and wood, 

 and called cambium : he was of opinion that this cambium 

 was formed in the bark, and became converted into both 

 cellular and woody tissue ; and he demonstrated the fallacy 

 of those theories according to which new wood is produced 

 by the wood of a preceding year. He removed a portion of 

 bark from a Plum tree ; he replaced this with a similar por- 

 tion of a Peach tree, having a bud upon it. In a short time 

 a union took place between the two. After waiting a suffi- 

 cient time to allow for the formation of new wood, he ex- 

 amined the point of junction, and found that a thin layer of 

 wood had been formed by the Peach bud, but none by the 

 wood of the Plum, to which it had been tightly applied. 

 Hence he concluded that alburnum derives its origin from 

 the bark, and not from the wood. Many similar experiments 

 were instituted with the same object in view, and they were 

 followed by similar results. Among others, a plate of silver 

 was inserted between the bark and the wood of a tree, at the 

 beginning of the growing season. It was said, that, if new 

 wood were formed by old wood, it would be subsequently 

 found pushed outwards, and continuing to occupy the same 

 situation ; but that, if new wood were deposited by the bark, 

 the silver plate would in time be found buried beneath new 

 layers of wood. In course of time the plate was examined, 

 and was found inclosed in wood. 



