218 PROCESS OF DEVELOPEMENT. CHAP. IV. 



regarded as being merely an extravasated mucilage, 

 which was somehow or other converted into wood 

 Du Ham- and hark : but Du Hamel regarded it as being 

 already an organized substance, consisting of both 

 cellular and tubular tissue, which he designated by 

 the appellation of the Cambium) or Proper Juice. 

 This opinion seems to have been entertained also by 

 Grew, though it does not appear to rest on any very 

 convincing evidence ; the fact, however, of its exu- 

 dation was evident, though it was not yet ascertained 

 whether it exuded from the wood or from bark of 

 the former year ; and whether the new layer, when 

 formed, separated into two, as Grew had conjectured. 

 This inquiry was undertaken by Du Hamel,* whose 

 experiments on the subject are indeed most lumi- 

 nous, and are, though seldom quoted, an anticipation 

 of almost every thing that has been done by the 

 most distinguished of our modern phytologists. 

 Who as- 1 order to ascertain whether the new layer of 

 thathYs wo d is formed from the former layer of wood or of 

 formed bark, his first experiment was that of a graft par 

 Fecusson ;-f- which is done by means of detaching a 

 portion of bark from the trunk of a tree and supply- 

 ing its place exactly by means of a portion of bark 

 detached from the trunk of another tree, that shall 

 contain a bud. In this way he grafted the Peach on 

 the Prune tree, because the appearance of the wood 

 which they respectively form is so very different that 

 it could easily be ascertained whether the new layer 



* Phys. dcs Arb. liv. iv. chap. ii. f Ibid. chap. 4. 



