1915] 



DUGGAR RHIZOCTONIA CROCORUM AND B. SOLANI 447 



7. The organism has not yet proved culturable with the 

 usual laboratory methods. 



8. At the present time there is insufficient evidence to de- 

 termine what the perfect stage of this organism may be. 



Obviously much still remains to be done regarding the 

 physiological, pathological, and taxonomic relationship of the 

 culturable forms which in the vegetative stage may be re- 

 ferred to the form-genus Rhizoctonia. The writer has grown 

 in culture Rhizoctonia from twenty-three different American 

 hosts, most of which are mentioned by Duggar and Stewart 

 ('01). Most of these were grown upon a variety of culture 

 media including prune juice, beet, and potato agar ; also beans, 

 stems and pods, celery, sugar beet and potato cylinders, and 

 corn meal mush. With one exception (the organism from 

 rhubarb) the cultural characteristics have been sufficiently 

 similar, especially after protracted culture in the laboratory, 

 to suggest a single species, with characteristics of the beet 

 and cotton fungus, already sufficiently described (Atkinson, 

 '92, '95; Duggar, '99). Moreover, these cultural studies have 

 confirmed in all cases the conclusions tentatively arrived at 

 from the preliminary microscopic examination of the fungus 

 on the different hosts. Eeasons have already been given to 

 indicate why this species is properly R. Solani. It is recog- 

 nized, however, that much culture and inoculation work is 

 necessary to establish the point that the fungus on the various 

 hosts is the same species, and to determine to what extent 

 physiological forms may occur. 



The following brief summary of conclusions may be pre- 

 sented with regard to Rhizoctonia Solani: 



1. The common American species of Rhizoctonia is R. 

 Solani Kiihn. 



2. This fungus is widely distributed in America and else- 

 where, and would seem to occur on the potato in most regions 

 of the world where this crop is a staple product. 



3. The host plants represent many families of dicot- 

 yledons, Asparagus Sprengeri being the only monocotyle- 

 donous host thus far reported. 



