2 26 THE LARCH. 



from blister, at least in that part of the stem, is past. 

 It is remarked that trees in their young state are much 

 more tender than they are when old and the bark has 

 become corky. We have only to look at the branch of 

 an old or advanced tree and examine its bark, to see 

 wherein the difference of results arises. The cuticle of 

 the shoots of the young tree almost entirely disappears 

 after the third year's growth, whereas on the branches 

 of old or middle-aged trees it is comparatively whole 

 at five, six, or seven years ; and while the cuticle is 

 comparatively whole, the parenchyma is increasing at 

 a rate far beyond that at which it grows on the stem 

 of the young tree. The parenchyma is thus as thick 

 and corky on the branch at three years old as it is 

 upon the stem or branch of the young tree at six or 

 seven years. This, I think, sufficiently explains the 

 difference of hardiness between young trees and that 

 of older ones. I am not aware of ever having seen 

 one year's shoots, whether vertical or horizontal, in- 

 jured by frost after the wood had been fairly matured 

 and ripened. As the spring however advances, and 

 the force of the sap expands the liber, the epidermis 

 of the young shoots is ruptured and opened, leaving 

 the thin and tender green bark entirely exposed 

 to the elements, whether frost, rain, or cold. It is 

 therefore between the periods of the expanding or 

 breaking of the epidermis and that of the forming 

 of the parenchyma, or corky part of the bark, that 

 the greatest danger to young larch plantations takes 

 place. The much-deplored blister rarely if ever occurs 



