92 



if a dead branch is left till it becomes 

 rotten where it joins the stem, as there is 

 no firm sm^ace for the deposit of new 

 w^ood, a hole remains in the stem of the 

 tree. In this the water, running down 

 the stem, lodges, and satm^ates the parts. 

 This, with the action of the oxygen of 

 the air, continues the process of decay, 

 which is communicated by contact to the 

 heart wood of the tree. This is the fruit- 

 ful source of destruction to our timber 

 trees, to the life of which, otherwise, 

 there is apparently no necessary limit. 

 Very little care may avoid this chief cause 

 of decay. 



What is called snag pruning may be 

 defended so far as this,— that if the snags 

 are left sufficiently long to remain alive, a 

 cross grain only is continued in the in- 

 creasing stem, and the diameter of this 

 cross grain does not increase so much 

 each year as if the head of the branch 

 existed, but, owing to the overshadowing 



