1915] 



DUGCAR RHIZOCTONIA CROCORUM AND R. SOLAN I 425 



Rhizoctonia differing notably from the violet organism, and 

 to this potato fungus he gave the name R. Solani. The life 

 history of the fungus and the symptoms of the disease induced 

 were very imperfectly known at the time, so that the descrip- 

 tion could not be complete. As a result, those who subse- 

 quently discussed the genus Rhizoctonia have sometimes 

 recognized R. Solani, while others have referred the organism 

 to R. Crocorum (R. violacea), and still others have assumed 

 that R. Solani Kiihn was also the cause of another disease of 

 beets and of carrots mentioned by Kulm without identifying 

 the causal organisms. After a study of certain diseases in 

 America induced by Rhizoctonia, I was keenly aware of this 

 confusion, so when opportunity presented itself in the winter 

 of 1899-1900 I conferred with Professor Kiihn regarding 

 those diseases, and also endeavored to obtain satisfactory 

 specimens of the fungi. There has been no earlier oppor- 

 tunity to utilize the information obtained in connection with 

 a general discussion of the genus. 



Kiihn laid special stress upon a scab ("Schorf oder Grind," 



later termed "Pockenkrankheit") of potatoes, sometimes 



followed by deeper seated injuries and decomposition ("als 



J\^ Raude und Kratze bezeichnet"). The symptoms are clearly 



w those that we now know as one type (cf. McAlpine, '12) of 



^ the potato diseases ascribed to R. Solani Kiihn (Corticium 



vagum B. & C). It has been noted that the fungus was not 

 so well described as might be wished, and the spores men- 

 tioned were evidently those of contaminating organisms, or 

 else the oval cells of the tufted stage of the fungus ; but when 

 we use in connection with this general description Kiihn 's 

 comparison of this plant with the violet fungus (Kiihn, '58, 

 p. 248) it is convincing that the fungus on the potato which 

 he had under consideration was not Rhizoctonia Crocorum. 



The sclerotia were also inadequately described and figured. 

 With reference to that point, however, Professor Kiihn stated 

 that while a common form of the fungus on the tubers con- 

 sisted of irregular superficial sclerotia, this form did not lead 

 to serious consequences and therefore received less attention 

 from him. Material of this superficial sclerotial stage was 





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