68 THE POLYPORACEAE OF WISCONSIN. 



Polystictus pergamenus Fries. 



Pileus eoriaceous-membranaeeous, rigid, tomentose, concentrically 

 snlcate, white; pores seriate (pallescent), changing at length into very- 

 thin dentate lamellae. 



This is probacy our commonest Polystictus, occurring on the wood 

 of very many species of deciduous trees and found at all times of the 

 year; even in winter beginning to grow with every warm spell of 

 weather. 



It is quite variable, being resupinate, reflexed, dimidiate or imbri- 

 cated. The color varies from almost snow white to gray; sometimes 

 without zones, and sometimes with variously colored zones or more or 

 less shining bands; soft velvety; tomentose or glabrate. The margin 

 is always acute but may be even or lobed ; it may be of a fuscous color, 

 or violet or whitish. It is usually violet when growing but not always. 



The pores are small, irregular, seriate, produced at length in the 

 form of very thin, dentate, more or less concentric lamellae. Their 

 color varies. It is usually violet when growing but changes to some 

 shade of brown on drying. However, some are never violet, but may 

 be pale tawny or straw-color. 



Old pilei seem to grow from the margin so that one frequently finds 

 specimens concentrically sulcate, with a broad whitish margin while 

 the rest of the pileus is darker gray. 



According to Peck. (22, Kept. 33, p. 36) the synonomy includes 

 P. elongatus Berk., P. pseudopargamenus Thiim., and according to 

 Berkeley and Curtis P. Mendanianus and P. laceratus also belong here. 



I have collected a small form — narrow and long — ^usually growing on 

 birch, which is perhaps Berkeley's P. elongatus. It is almost glabrous 

 from the beginning with delicate concentric shining zones and with ra- 

 diate striations. 



P- pergamenus varies much in size and shape, the resupinate forms 

 often covering the whole underside of a log. My largest dimidiate 

 specimen is about 10 cm. wide, 5 cm. long and from 2 to 4 mm. thick. 

 Of the small variety the largest is about 3 cm. wide, 4 to 5 cm. long 

 and not more than 1 mm. thick. 



The soft white mycelium creeps through the wood and produces very 

 destructive decay. We find it on wood that is comparatively sound as 

 well as on very rotten wood. In nearly all eases the mycelium can be 

 found throughout the infected piece of timber. Von Schrenk has de- 

 scribed the decay in detail. 



Syn. : Coriolus pergamenus (Pries) Pat.; 19, 32, p. 654. 



