1915] 



DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 423 



and the following spring were planted to several varieties 

 of carrots, to beets, mangolds, red clover, and alfalfa. At 

 the time of harvest, the carrots were all more or less severely- 

 affected, while the sugar beets and alfalfa showed very light 

 attacks, and the clover none at all. Continuing the work 

 in subsequent seasons he obtained evidence in one case — that 

 of the sugar beet — pointing to an increased virulence of the 

 fungus with adjustment to that host. On the contrary, in 

 the second year the alfalfa exhibited greater resistance, thus 

 rendering a decision as to the existence of physiological races 

 hazardous. He also reported, that on placing diseased soil 

 and diseased carrots in a box in which various weeds were 

 permitted to grow, the fungus appeared on eight species of 

 weeds (representing several families), apparently a consider- 

 able proportion of those present. This also would seem to 

 discourage the idea of marked host specialization. 



Attempts to cultivate the violet fungus on artificial media 



have been made by several investigators without success. 



While in Leipzig, 1900, I obtained particularly good material 

 on alfalfa from Bavaria. Dilution cultures were attempted 

 both on various kinds of agar and on gelatin, but no growth of 

 the fungus was secured in any case. Further trials were 

 made with material from France in 1902, and again upon re- 

 ceiving comparatively fresh material from Kansas in 1911. 

 Bailey ('15) reports an endeavor to cultivate the organism 

 in Oregon, also without success. It is quite possible that 



special conditions are essential to its growth in artificial cul- 

 ture, but we should not assume that it is incapable of growth 

 in this way. It would appear that the presence of contami- 

 nating organisms is not the sole cause of the difficulty, since 

 isolated hyphae in the dilution cultures remain free from the 

 growth of contaminating organisms, and yet themselves fail 

 to develop a colony of growth. It will be recalled that At- 

 kinson 1 found difficulty, but ultimate success, in growing 

 Ozonium omnivorum (Lk.) Shear, the cause of the south- 

 western root rot of cotton. The writer also found that this 

 organism is not readily cultured, but obtained a satisfactory 



iBot. Gaz. 18: 16-19. 1893. 



