THE FUNGI WHICH CAUSE PLANT DISEASE 407 



arising immediately from the mycelium, smooth or minutely 

 warty; basidia clavate, with foiu- sterigmata; spores small, globose 

 or ellipsoid, with a smooth colorless membrane. 



A genus of some two hundred fifty species, mostly wood inhab- 

 iting. 



One species possesses a mycelium which has long been known 

 in its sterile form as a Rhizoctonia. 



Corticium vagum solani Burt. ^*'^^' '^* 



Hymenophore, white when sporing, poorly developed, of loosely 

 interwoven hyphae; basidia short, cylindric or oblong; spores some- 



■sF- Fig. 294. — C. vagum-solani. 



Fig. 293. — C. vagum solani Rhizoc- basidia, sterigmata and 



tonia stage. After Duggar. spores. After Rolfs. 



what elliptic, often irregular in outline, 9-15 x 6-13 ft. 



Sterile mycelium(=Rhizoctonia solani = Rhizoctonia violacea)" 

 turning yellowish with age, and branching approximately at 

 right angles; often forming sclerotia-like tufts with short, broad 

 cells more or less triangular which function as chlamydospores. 



Brown to black sclerotial structures, a few millimeters in diam- 

 eter, consisting of coarse, broad, short-celled hyphae of peculiar 

 and characteristic branching also occur freely, both in nature and 

 in culture. Fig. 293. These cells seem capable of functioning as 

 chlamydospores. 



The hymenophore consists of a dark network of hyphae which 

 changes to grayish-white when spormg. It frequently entirely 

 surrounds the green stems of the host near the groimd. The tips of 

 the outermost hyphae are sterigmatate. The spores germinate 

 readily, developing into typical Rhizoctonia myceliiun. 



The relation which the various Rhizoctonias which have been 

 described on numerous hosts may bear to the one species under 



