THE FUNGI WHICH CAUSE PLAXT DISEASE 



427 



P. pergamenus Fr." 



Pileus exceedingly variable, sessile or affixed by a short tubercle, 

 dimidiate to flabelliform, broadly or narrowly attacfied, 2-5 x 2-6 

 X 0.1-0.3 cm.; surface finely villose-tomentose, smooth, white 



or slightly yellowish, 



marked with a few nar- 

 row indistinct laterice- 

 ous or bay zones; mar- 

 gin thin, sterile, entire to 

 lobed; context very thin, 

 white, fibrous; tubes 1- 

 3 mm. long, white to chs- 

 colored within, mouths 

 angular, somewhat irreg- 

 ular, 3-4 to a mm., 

 usually becoming irpici- 

 form at an early stage, 

 edges acute, dentate, be- 

 coming lacerate, white to 

 yellowish or imibrinous : 

 spores smooth, hyaline. 



It causes a sap wood rot of practically all species of deciduous 

 trees, often on dead trees, less frequently on living trees which 

 have been severely injured. In general the rotten wood resembles 

 that produced by P. versicolor; microscopically it is seen that 

 the fungus attacks chiefly the lignin. 



P. hirsutus Fr. 



Pileus confluent-effused, more or less imbricate, sessile, dimi- 

 diate, applanate, corky-leathery, rather thick, flexible or rigid, 

 3-5 X 5-8 X 0.3-0.8 cm.; surface conspicuously hirsute, isabelline to 

 cinereous, concentrically furrowed and zoned; margin at length 

 thin, often fuliginous, sterile, finely strigose-tomentose, entire or 

 undulate: context white, thin, fibrous, spongy above, 1-4 mm. 

 thick; tubes white, 1-2 mm. long, mouths circular to angular, 

 4 to a mm., quite regular, edges thin, firm, tough, entire, white 

 to yellowish or umbrinous; spores smooth, hyaline, cylindrical, 

 slightly curved, 2.5-3 /i. 



It is a wound parasite of the Mountain Ash.^^ 



Fig. 306.- 



-Polystictus pergamenus. 

 Clements. 



After 



