DISEASES. 227 



either upon the one-year shoot or upon the stem, after 

 the parenchyma or cork bark is fully formed. The 

 blister is not confined to any one particular part of 

 the tree, but is found sometimes only a few inches 

 above ground, and at other times near the top, and 

 alike upon the stem as upon the branches, but, as already 

 stated, probably never on the one-year shoot, which is 

 completely protected by the epidermis. The whole 

 bark of the young larch tree, like the skin of the 

 little child, is extremely tender and susceptible of 

 injury either from cold, wet, frost, or dull weather. 

 The bark of the young tree bears the same comparison 

 to that of the old, as the skin of the child's hand does 

 to that of the blacksmith's; and the analogy extends 

 further than may at first appear, for as the paren- 

 chyma and epidermis are considered the excretions of 

 the alburnum or sapwood, so the horny skin of the 

 hand is the secretion of the blood. The hard hand is 

 no less serviceable to the man who handles rough and 

 hea%y tools than the corky bark is to the tree in pro- 

 tecting it from a hundred evils. 



The bark of exogenous trees and shrubs in this 

 country consists of three distinct parts: — ist, the 

 liber, inner bark (endophloeum) ; 2nd, the parenchyma, 

 middle layer of bark (mesophloeum) ; 3rd, the epi- 

 dermis, outer bark (epiphlaum). The bark under- 

 goes wonderful changes in different species of trees, 

 and even in the same species at different stages 

 of growth, and in the latter respect none more so 

 than the larch, for in the young shoot it is one thing, 



