THE FUNGI WHICH CAUSE PLANT DISEASE 421 



dark brown or black, velvety tomentum, often reduced, variable 

 in length. 



The mycelium causes white rot of nut, ornamental and fruit 

 trees, particularly maple, pear, oak, elm, walnut, linden, willow, 

 ash, birch, chestnut, beech, growing on dead parts of living trees. 

 The hyphse advance most rapidly along the wood vessels and 

 often bear clamp connections. 



A beautiful biological study has been published by BuUer ^' *^ 

 who states that a single sporophore may produce 11,112,500,000 

 spores and that "the number produced by a single fungus from a 

 single tree in the course of a year may, therefore, be some fifty 

 times the population of the globe." 



He showed the following enzymes to be present in the sporo- 

 phore: laccase, tyrosinase, amylase, emulsin, protease, lipase, 

 rennetase, and coagulase. Pectase, maltase, invertase, trehalase 

 and cytase were not found; It is evident, however, that the my- 

 celium in wood produces cytase and possibly hadromase. 



P. hispidus Bui. 



Pileus thick, compact, fleshy to spongy, dimidiate, sometimes 

 imbricate, compressed-imgulate, 7-10 x 10-15 x 3-5 cm. ; surface 

 hirsute, ferruginous to fulvous, azonate, smooth; margin obtuse, 

 velvety; context spongy-corky, somewhat fragile when dry, fer- 

 ruginous to fulvous, blackening with age, 1-1.5 cm. thick; tubes 

 slender, about 1 cm. long, ferruginous within, mouths angular, 

 2-3 to a mm. ferruginous to bay, blackening with age, edges thin, 

 very fragile, lacerate; spores broadly ovoid, smooth, thick-walled, 

 deep-ferruginous, 2-guttulate, 5-6 x 7-8 li. 



It is common on all kinds of deciduous trees, often injuring fruit 

 trees, especially the apple. 



P. giganteus (Pers.) Fr. has been reported as injurious to the 

 oak. 



P. glivus Fr. is a common saprophyte on deciduous trees and in 

 some cases may be parasitic. 



P. dryophilus Berk. 



Pileus thick, uneiqual, unguliform, subimbricate, rigid, 7-8 x 10- 

 14 X 2-3 cm. ; surface hoary-flavous to ferruginous-fulvous, becom- 

 ing scabrous and bay with age; margin thick, usually obtuse, 

 sterile, pallid, entire or undulate: context ferruginous to fulvous, 



