1 62 Journal of Agricultural Research voi. iv.No. 2 



before it had been tested upon the radish and thereafter could not be 

 secured again. The morphological studies, however, prove that the 

 American fungus with which we have been working is not A. laevis, but 

 a hitherto undescribed organism. Morphological, physiological, and 

 cytological studies will be presented in another paper. 



In the work with sugar-beet seedlings five strains of the organism were 

 employed which were obtained from the following sources : 



Seedling sugar beets grown at Madison, Wis., 2; at Kenosha, Wis., i; 

 in soil originally infected by radishes showing black-root, 2. 



The disease which it produces on the sugar beet is very similar to that 

 caused by Pythium deharyanum. The fungus is even more aggressive as 

 a parasite than Pythium (Pi. XXIV, fig. i). When the inoculations were 

 made at the time of seeding, it was unusual for plants to appear above- 

 ground. The evidence obtained all goes to show that a seedling once 

 attacked never recovers. 



A disease of the side roots of growing beets was encountered during the 

 course of the studies in soils which had been inoculated with artificial 

 cultures of the fungus several months earlier. A photograph of a speci- 

 men is reproduced in Plate XXIII, figure 2. The fungus was readily iso- 

 lated from diseased side roots of this beet and there appears to be no 

 reason to doubt its causal relation to the trouble. Peters (33, p. 244) 

 has quoted a similar disease of European beets caused by Aphanomyces. 



Comparatively little is known regarding the range of distribution of 

 the fungus. What appears to be the black-root of radish has been 

 observed in the District of Columbia, Maryland, Virginia, Long Island, 

 Illinois, and at several points in Wisconsin, and there is reason to believe 

 that other workers have found it in various places, although no records 

 of such observations have been published. The disease produced by this 

 fungus is so similar to that reported by Barrett (4) that they are not 

 readily distinguishable, and it may be that either of these organisms is 

 responsible for the disease in any of the stations mentioned. The author 

 does not consider that his results should be construed to throw doubt 

 upon the accuracy of Barrett's obser^^ations, merely wishing to record 

 a radish disease that is indistinguishable in external appearance from 

 that produced by Aphanomyces laevis, but which is due to this hitherto 

 undescribed parasite. 



The fungus is readily isolated from beet seedlings by the method al- 

 ready described for Pythium deharyanum,. In this case, however, the 

 subcultures should be made to string-bean agar, upon which the organ- 

 ism produces a luxuriant growth. Sterilized beet seedlings in water in 

 test tubes make an excellent medium for the cultivation of this fungus. 

 The limit of vitality in culture has not been determined, but transfers 

 made to string-bean agar on July 2 from beet-seedling water cultures 

 made on February 12 developed a heavy growth overnight, showing 

 not the least loss of vitalitv. 



