660 THE FUNGI WHICH CAUSE PLANT DISEASE 



branous, persistent, inseparable; formed among and connected by 

 the mycelial threads. 



There are about a dozen so-called species, some of them very 

 important plant pathogens. See pp. 407, 408. 



R. betae Kiihn and R. solani Kuhn=Corticium vagum solani, 

 as does also part of what has been referred to as R. violaceaj. 



R. medicaginis D. C. (Tul.);" (see also«'^' ««-«0- 



Hyphse subtomentose, on the cambium of the host, forming a 

 membrane or fasciculate strands, covering the host in time with a 

 violet coating; sclerotia reddish-violet. 



On alfalfa in Europe and America.*" 



Duggar who has studied this form and the form allied to Corti- 

 cium (pp. 407, 408) regards the two as distinct though Giissow *^° 

 who has also studied both pronounces them the same. Duggar says, 

 " The fungus appears upon the root as a close weft of violet-colored 

 hjrphae composed of cells more or less uniform in diameter. Mor- 

 phologically it bears no resemblance to the sterile stage of Cor- 

 ticium." This form is found on alfalfa, asparagus, beet, and pos- 

 sibly other plants. 



Leptosphaeria has been reported as its ascigerous stage though 

 the evidence of such connection is not conclusive. 



R. crocorum D. C. is a form which kills the corms of saffron. 



R. strobi Scholz is the name given to a form described as seriously 

 injuring yovmg pine trees in Austria.**^ 



R. subepigea Ber. is destructive on the roots of coffee.*^* 



A Rhizoctonia of undetermined species has been found on buck- 

 wheat in the United States.*''^ 



Sclerotium Tode (p. 659) 



Sclerotia roundish or irregular in form, cartilaginous-fleshy, not 

 connected by mycelial threads; cortex thin, membranous, in- 

 separable. 



Over 200 species have been described. 



S. rolfsii Sacc."' «5. 438 



Sclerotia small, brown, about the size of a mustard seed. 



This sterile fimgus possesses a very aggressive mycelium which 

 under favorable conditions of moisture grows on almost anything 

 living or dead, producing a dense white cotton-like mass of threads. 



