446 



FUNGOUS DISEASES OF PLANTS 



and it is very probable that some of the damping-off which has 

 been ascribed to Pythium could be properly referred to damage by 

 this fungus. It is not possible at the present time to say definitely 

 that such damping-off diseases as those of cotton, lettuce, etc., are 

 produced by the same species or race of Rhizoctonia as that which 



is found upon the potato, but 

 there is reason to believe that 

 the differences which occur 

 between the various forms of 

 the parasite upon a large num- 

 ber of hosts are only such as 

 might be considered varietal or 

 racial, and in some instances 

 we have unquestionably to do 

 with physiological forms. It is 

 certain, however, that Rhizoc- 

 tonia Medicaginis De C. of 

 Europe is a fungus very differ- 

 ent from the common potato 

 fungus of Europe and America 

 and also from the common 

 species producing damping-off 

 of seedlings, rot of beets, etc., 

 in this country. Moreover, a 

 form which has been described 

 (Duggar and Stewart) on rhu- 

 barb is likewise a very different 

 organism. It would not, how- 

 ever, be surprising to find that 

 a very large number of the 

 other forms which have been 

 discussed by various authors may be ascribed to one and the same 

 species, the perfect stage of which would now appear to be Corti- 

 cium vagum B. & C. var. Solani Burt. 



Effects upon the hosts. The fungus is perhaps most disastrous 

 as a damping-off disease. The progress of the disease upon seed- 

 lings resembles very closely that of Pythium, and it is affected by 

 similar conditions. The plants that have thus far seemed to be 



FIG. 218. RHIZOCTONIA ON RADISH 

 (Photograph by H. H. Whetzel) 



