28 OF THE WOOD. 



Dr. Thomas Hope, the present Chemical Professor at 

 Edinburgh. 



Du Hamel engrafted a portion of the bark of a 

 Peach-tree upon a Plum. After some time he found a 

 layer of new wood under the engrafted bark, white 

 like that of the Peach, and evidently different from the 

 red wood of the Plum. Moreover, in this and other 

 experiments made with the same intention, he found 

 the layers of new wood always connected with the bark, 

 and not united to the old wood. See his Physique 

 des Arbres, vol. 2.29, &c. It deserves also to be men- 

 tioned, that by performing this experiment of engraft- 

 ing a portion of bark at different periods through the 

 spring and summer, the same accurate observer found 

 a great difference in the thickness of the layer of new 

 wood produced under it, which was always less in pro- 

 portion as the operation was performed later in the 

 season. 



That the bark or liber produces wood seems there- 

 fore proved beyond dispute, but some experiments per- 

 suaded Du Hamel that in certain circumstances the 

 wood was capable of producing a new bark. This 

 never happened in ^.ny case but when the whole trunk 

 of a tree was stripped of its bark. A Cherry-tree 

 treated in this manner exuded from the whole surface 

 of its wood in little points a gelatinous matter, which 

 gradually extended over the whole and became a new 

 bark, under which a layer of new wood was speedily 

 formed. Hence Mirbel concludes, vol. 1. 176, that 



