DISEASES OF BOOTS, ETC. 41 



cambium, and the sapwood. As long as connecting 

 parts of these remain intact, the tree will not die, 

 though it may be greatly weakened. With the progress 

 of the fungus, however, the remaining sound sapwood 

 can no longer supply the crown and foliage with water. 

 The weakened foliage stops respiration and assimila- 

 tion; bark and cambium are not sufficiently nourished, 

 and the root system is starved. The final result is 

 death of the tree. The fungi of this group are not, as 

 a rule, confined to trees of any particular age. 



Root diseases can not well be separated from diseases 

 of the stem, since the fungi which cause them, after 

 living for a while off the roots, may, except in very 

 resinous trees, invade the trunk. Root diseases of forest 

 trees, which, with few exceptions, are at present not 

 very important in District 5, are caused by fungi with 

 porous or gill-bearing fruiting bodies, which grow on 

 the roots and on the collar of the tree. Where they do 

 appear, however, they are extremely injurious. Thej 7 

 spread not only by dissemination of spores, but also 

 from infected roots to sound ones of neighboring trees. 



Cj O 



White mycelium found at the collar of a living or 

 recently killed tree, between the bark and wood or 

 between the bark scales, usually indicates the presence 

 of a fungus of this class. Not always does the fungus 

 enter the heartwood. In the pines resin prevents the 

 mycelium from entering the wood of the trunk. In 

 spruce and fir, however, the trunk is invaded and de- 

 stroyed. Resin flow on the lower part of the trunk 

 often indicates diseases of this kind. 



