BARK OF TREES. 



345 



one part half round or more, the remaining bark in the circle forms a 

 much thicker layer than it would otherwise have done, thicker than 

 anywhere else on the same trunk or branch of the tree ; it is perhaps 

 equal in amount to a whole circle of the ordinary layer of the same 

 trunk or branch. The stimulus of growth is increased by a real 

 weakness being produced. 



Upon the same principle, when a tree or branch is barked all round, 

 the cut-edge nearest to the extremity of the tree or branch, close to the 

 barked part (fig. 2, b), grows faster or thicker than any other part of 

 the same tree or branch (c). But this iu creased growth close to the 

 barked part, is, I believe, only in those trees which live at the barked 

 part (a) ; but in those (as the Laburnum), which only live that season 

 in which they are barked, the growth of the part beyond where the bark 

 is taken off is less near to the part than it is further on. 



Fig. 1. 



Fig. 



An apple-tree barked spirally about once and a half round (fig. 1), 

 threw out many branches below the barked part, but near it (as at a), also 

 in the spiral between the spiral turns of the barked part (b). This is upon 

 the same principle; for the unbarked part has no sensation of the 

 part above, therefore it sends out shoots. 



Pear-trees, when barked, often throw out a new bark from the 

 wood in different parts of the barked part. The same thing takes place 



