Diseases of the Sugar Beet. 343 



the fungus. Acidulated bean pods, or bean stems, as mentioned 

 by Professor Geo. F. Atkinson, in his study of the sterile damp- 

 ing off fungus,* are excellent for this purpose. The fungus pre- 

 fers an acid substance, while the ordinary bacteria of decay are 

 shut out by such acidity. One drop of 50 per cent lactic acid to 

 each test tube with the usual amount of medium is sufficient for 

 best results. 



If the beets are much rotted, one may find, even in the field, 

 that the surface of roots in moist conditions is covered with 

 a short, tuft-like growth of the fungus. I have not found that 

 the blackened, crust-like, or more or less rounded, compact 

 masses of the mycelium, called sclerotia, ever occur on beets in 

 the field. 



In this connection it may be well to state that all necessary 

 cultures were made both from affected parts, and from the adja- 

 cent white meat of the beet, to determine the part that bacteria 

 or other fungi might play in the etiology of the disease ; but no 

 other parasitic organism was found. As Pammel has stated, 

 bacteria are probably much concerned in the final rotting of the 

 beet. 



c. The Cause of the Beet Root-Rot. 



The constant association of the brown fungus Rhizoctonia with 

 the cracking and rotting of beets in the field was not taken as final 

 evidence that this fungus caused the trouble, and although late 

 in the season, a few experiments were undertaken to determine 

 the degree of parasitism of the fungus, and the conditions un- 

 der which it acted. 



Experiment i. In a short row of twenty-four half-grown 

 beets eight were inoculated on Aug. 13. The inoculations were 

 made by placing among the crown leaves fresh pieces of beet on 

 which this fungus alone had been growing for a short time. The 

 whole row^ was mulched with straw. The weather was wet for a 

 few days onl^^, but afterwards quite dry. On Sept. 2 eighteen 

 beets in this row were affected by the rot. 



Experiment 2. Six beets or clusters of beets were inoculated 

 as in experiment i , but over each inoculated area was placed a 



* Bulletin 94, Cornell Univ. Agl. Exp. Station, 1895. 



