72 



THE DESTRUCTIVE AGENTS OF FORESTS. 



the lack of resistance of living trees and the presence of water 

 and other favorable conditions of dead wood, it becomes advan- 

 tageous to consider separately some of the enemies of trees and 

 wood enumerated under a foregoing head. 



Water in Its Relation to Tree Diseases. 



An immense quantity of water passes through every tree 

 during the period of its growth. The water is dravm from the 

 soil through the roots and passes out, or is transpired, from the 

 leaves. In the summer months a large broad-leaved tree will 

 transpire from 500 to 900 pounds, or we may say a barrel, of 

 water daily. Coniferous trees transpire about one-tenth that 

 amount. A small amount of water passes out through the bark 

 and even in the winter months a large tree may lose from 10 

 to 15 pounds of water every day. 



The water requirements of trees vary greatly, and their 

 distribution is affected everywhere by the amount of moisture 

 present in the soil. The water content of the soil that will 

 suit the needs of one tree will be the death of another. The 

 tree that thrives in swampy ground will die if planted upon a 

 dry hill and vice versa. That is to say, either an excessive or 

 a meager supply of water may produce a diseased condition ac- 

 cording to the species of the tree. If the roots of the yellow 

 poplar or the white oak are flooded with water they are unable 

 to get the amount of oxygen they require and will soon show 

 signs of bad health. The same is true to a less extent of 

 many other trees that prefer a jjorous, airy soil. A group of 

 dead oaks or poplars, killed by the comparatively small quan- 

 tity of water which drains from a culvert, may frequently be 

 seen along a forest road. On the other hand, swamp white oaks, 

 sweet gums, and other trees that prefer wet ground will im- 

 mediately show signs of disease when the water is drained from 

 their roots. 



Plant Food Supply in Its Relation to Tree Diseases. 



It is just as impossible for a good crop of trees to grow in a 

 shallow and poor soil as it is for a crop of com or other agricul- 

 tural crop to thrive on the most infertile land. One looks for 



