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extent in their trunks. Tliis disease, by preventing the circulation, impairs the fibres and 

 renders the timber obtained from such trees unfit for use, except for temporary purposes. 



Another disease, if I may so term it, is prematurity ; it is indicated by the death of the 

 lops and topmost branches of trees. Whole forests sometimes present this appearance. It 

 arises from a rock-bound or shallow soil, which does not furnish the necessary nutritive 

 substances. Trees so affected do not grow large, nor are they rendered unfit for some uses in 

 rural economy ; the chief loss arises from the perishing portions, which can seldom be applied 

 to advantage even for fuel. 



This diagnosis was well understood by the early settlers of some districts of our country, 

 as is manifested by the ui- reclaimed lands of this character which are frequently to be met with. 



Trees from old age present the same aspect not unfrequently as those just described. 

 In such cases the duramen or heart, as it is generally named, will have partially lost its 

 strength, toughness and elasticity ; they are only fit for the most common uses. 



They are also sometimes aflfected by frosts and tempestuous winds, which render them 

 cuppy near their centres, or, in other words, separate the woody fibres of a few years' accretion 

 into annular and not unfrequently into broomy divisions. This disease does not generally 

 aifect the wood far up the trunk of trees, and is, therefore, remedial by lopping off. 



There are other diseases to which trees are liable, such as maims, rind galls and excres- 

 cences, but I will pass over these to the decay, or to the more important ones to which timber 

 is subject, and then notice some of the preventatives which chemical science has revealed. 



If trees, when felled, be suffered to remain for a season on the ground, the temperature 

 being favorable, a partial decomposition of the caseous and soluble portions of the woody fibres 

 follows and sometimes very speedily, particularly in the alburnum ; but as this should never 

 be employed in building, except for the most temporary purposes, unless chemically prepared 

 it would scarcely be necessary to refer to diis exterior change, were it not in its progressive 

 state a certain criterion by which to judge of the condition of the more perfect wood. 



But the constituents of diflerent genera and species differ in substances and proportions 

 so materially as greatly to modify these changes, retarding or accelerating them according 

 to the organism acted on. 



, Thus, some species of the pine may lay so exposed for a succession of years without 

 sustaining any injury — except in their sappy coverings ; while the oak and most other hard 

 v/ood trees similarly exposed soon exhibit signs of deterioration and decay. 



