19 16 ] PARASITIC RHIZOCTONIAS IN AMERICA 285 



Under R. Solani Kiihn (Corticium vagum B. & C.), the form com- 

 monly found in this country and to a less extent in Europe, and the 

 name generally used by American authors, Duggar gives the following 

 synonymy : 



BMzoctonia Betce Eidam [non Kiihn] (1887) 

 Ehizoctonia Napcsce West. (1846) 

 Ehizoctonia Rapce West. (1852) 

 Hypochnus Solani Prill. & Del. (1891) 



Duggar states further that with the evidence at hand a number of 

 species of Rhizoctonia described from Europe may be excluded from 

 the genus, while several species are doubtful. He adds that in all 

 probability the six species described from America, listed in Saccardo, 

 may also be excluded, altho a more critical study of material is needed. 

 Many attempts have been made to connect the sterile fungus Rhi- 

 zoctonia with a perfect stage. Fuckel 43 in 1869 stated that the ascomy- 

 cete ByssotJiesium circinans Fkl. (LeptospJiceria circinans Sacc.) was 

 the perfect form. However, beyond the association of these two forms 

 on decaying stems of Medicago sativa, there were no signs of their con- 

 nection. The same observation was also recorded by Prunet, 90 but again 

 with no more conclusive proof than the presence of the two forms on 

 the same plant. Massee 66 considered Rhizoctonia as representing the 

 vegetative condition of Rosellinia, because of the fact that the struc- 

 ture and color of the mycelium and the general habit of Rhizoctonia 

 resembles that of the Rosellinia quercina Hartig and other destructive 

 parasites belonging to that genus. He had no further evidence, how- 

 ever, to support this supposition. 



During the summer of 1913, Cook, 20 while examining tubers af- 

 fected with Rhizoctonia, found a sclerotium that contained a mass of 

 well-developed asci bearing spores. The mycelium of the sclerotium 

 was characteristic of Rhizoctonia and the asci appeared to arise di- 

 rectly from it ; this point, however, could not be determined with any 

 degree of certainty. 



In 1891 Prillieux and Delacroix 89 described a basidiomycete, Hy- 

 pochnus Solani, and altho at the time they did not associate it with 

 Rhizoctonia, it has been accepted by a number of European writers in 

 recent years as the perfect stage of R. Solani. 



In 1897 Frank 41 reported Rhizoctonia violacea as attacking grape- 

 vines, and since a Thelephora was found associated with it, he pro- 

 posed the name Thelephora Rhizoctonia?. 



In 1903 Rolfs, 93 working with the Rhizoctonia disease of potatoes 

 in Colorado, found constantly associated with this fungus a basidiomy- 

 cete which Dr. E. A. Burt identified as Corticium vagum B. & C., var. 

 Solani. He was able to trace the connection between the two forms, 

 and completed his evidence when he obtained cultures of Rhizoctonia 

 from single spores of the Corticium stage. 



