432 THE FUNGI WHICH CAUSE PLANT DISEASE 



In the holes caused by the fungus in the heart-wood is found 

 a velvety mass of reddish-yellow mycelium, glistening with color- 

 less liquid and holding masses of reddish-brown wood fiber. Long 

 white fibers of cellulose with the lignm removed project into the 

 cavities from the ends. 



Structural change begins soon after the mycelium enters a 

 cell lumen. The primary lamella becomes granular and is dissolved 

 by a lignin-splitting enzjnme, the secondary lamella becomes white 

 and the cells fall apart. 



The mj'celium in newly invaded tissue is nearly hyaline and 

 extends lengthwise. Within the tracheids branches are given off 

 in all directions. 



The sporophore appears after decomposition is considerably 

 advanced. 



F. laracis (Jacq.) Murr.''* 



Pileus firm, at length fragile, ungulate to cylindical, 3-8 x 5-10 

 X 4-20 cm.; surface anoderm, powdery, white or slightly yellow- 

 ish, concentrically sulcate, becoming slightly encrusted, tuberculose 

 and rimose; margin obtuse, concolorous: context soft, tough, at 

 length friable, chalk-white or slightly yellowish, very bitter, 

 vdth the odor of fresh meal, 1-3 cm. thick; tubes evenly strati- 

 fied, concolorous, 5-10 mm. long each season, mouths circular to 

 angular, 3-4 to a mm., edges thin, fragile, white, becoming dis- 

 colored and lacerate, wearing away with age: spores ovoid, smooth, 

 hyaline, 4-5 n; hyphse 5 n; cystidia none. 



A wound parasite of the larch, pine and spruce in Europe and 

 America. 



F. ribis (Schw.) Gill.*'' 



Pileus tough, corky, becoming rigid, conchate, laterally connate, 

 3-5 X 5-10 X 0.7-1.5 cm.; surface rough, velvety, anoderm, in- 

 distinctlj' zoned, ferruginous to umbrinous, becoming glabrous 

 and slightly encrusted with age; margin undulate to lobed, fer- 

 ruginous, furrowed: context punky, fulvous, 3-5 mm. thick; 

 tubes indistinctly stratified, 1-2 mm. long each season, fulvous, 

 mouths circular, 5-6 to a mm., edges rather thin, entire, ferruginous 

 to fulvous, hoary when young: spores globose or subglobose, 

 pale yellowish-brown, smooth, 3-4 x 3 ju; hyphae 2.5 ja; cystidia 

 none. 



