424 DISEASES OF ECONOMIC PLANTS 



larly scattered appear. The sporophores vary from 2.5-30 

 cm., averaging 10-15 cm., are bracket-shaped and lobed. 

 The young lobes are bright red to pale yellow, old ones 

 dark red-brown. The lower surface is pale and smooth; 

 watery when bruised. 



Canker (Nummularia and Nectria cinnaharina (Tode) 

 Fr.). — The cankers caused by these fungi occur either upon 

 branches or roots and may be found upon nearly all species 

 of deciduous trees of which they are wound parasites. The 

 spores are borne on soft, l^right red knobs, or in another 

 form in pear-shaped perithecia. Infective material should 

 be burned. 



ROOT ROTS 



Fungi similar to these already considered may also at- 

 tack the roots of trees and thus cause death without any 

 previous rotting of the trunk wood. Prominent among 

 such diseases are the following : — 



Armillariose (Armillaria mellea Vahl). — The fungus 

 usually enters the root through wounds, and grows in 

 the cambium, through which it spreads until it encircles 

 the tree. As its growth proceeds the layers adjacent to the 

 cambium become dry, and the top of the tree is killed by 

 stoppage of its water supply. A characteristic accompani- 

 ment is the profuse development of string-like, hard, black 

 mycelial strands which permeate the soil near the base of 

 the affected tree. From the mycelium around the base 

 of the tree rise the numerous white-gilled, honey-colored 

 sporophores, their viscid tops flecked with white ; the stems 

 swollen and with a ring (annulus). 



This disease may spread for long distances through the 



