458 



THE FUNGI WHICH CAUSE PLANT DISEASE 



C. parasitica Wil.^"^ 



Growing in dense clusters; pileus 6-8 cm., convex or umbonate, 



usually minutely scaly, mottled 

 buff to yellow-brown in color; 

 gills paler, becoming mottled, 

 at first noticeably decurrent; 

 stipe 10-16 cm. high, up to 

 1 cm. thick, solid, usually 

 curved, darker than the pileus; 

 black rhizomorphs present. 



It differs from Armillaria 

 mellea in having no annulus, 

 and in growing in denser clus- 

 ters. 



The fungus causes a root- 

 rot very similar to that caused 

 by Armillaria mellea. There 

 are present typical subcortical 

 strands, mostly between the 

 cortex and cambium and some- 

 subterranean black rhizomorphs adhering 



Fig. 320. — Rhizomorphs of A. mellea 

 After Freeman. 



times characteristic 



close to the cortex of the roots. 



Fungous branches enter the wood chiefly through the medullary 

 rays and there is later rapid vertical growth through the vessels 

 and tracheids. The cell contents are destroyed, the hj^jhse often 

 forming loops around the nucleus. The sporophores occur in 

 groups at the base of the tree after the disease is well developed. 

 An extensive bibliography is given by Wilcox. ^"^ 



Collybia Fries (p. 450) 



Pileus thin, fleshy, margin at first incurved; stipe cartilaginous. 



About two hundred seventy-five species. Fig. 329. 



C. velutipes Curt. 



Cap 2-8 cm. wide, yellow-brown or reddish bro\\Ti, rarely paler 

 except toward the margin, smooth, very sticky when moist, con- 

 vex to plane or somewhat recurved, often excentric or irregular 

 through pressure. 



