THE FUNGI WHICH CAUSE PLANT DISEASE 



425 



due to the shrinking of the walls. Fig. 289. Diseased wood is 

 yellowish and of cheesy consistency; brittle when dry. 



P. betulinus (Bui.) Fr.«^' ^^ 



Pileus fleshy to corky, compressed-ungulate, convex above, 



plane below, attached by a short umbo behind, varying to bell- 

 shaped when hanging from horizontal trunks, &-30 x 5-20 x 2-5 

 cm.; surface smoky, covered with a thin, separating pellicle, 

 glabrous, devoid of markings, cracking with age; margin velvety, 

 concolorous, obtuse, projecting nearly a centimeter beyond the 



