82 Journal of Agricultural Research voi. xxii. no. 2 



an inactive stage of jelly-end rot or for an after effect of freezing injury, 

 particularly if the disease has made but little headway. The true 

 nature of such obscure cases of the disease may be revealed with cer- 

 tainty only by a series of cultural studies, coupled with experimental 

 work and field observations. 



CAUSAL ORGANISM 



Isolations were made from every tuber of each of the four samples 

 received from the West in 191 7-18. The results were surprising. In 

 no case was Fusariu^n radicicola obtained; only one tuber yielded F. 

 trichothecioides Wollenw. (from Nevada), two yielded Rhizoctonia 

 (from Nevada), two F. oxysporum (from California), and a few gave 

 miscellaneous, apparently saprophytic, fungi. Bacteria, on the other 

 hand, were constantly present in the cultures, even when slightly acidu- 

 lated potato agar was used. Carpenter (2)^ noted the presence of 

 bacteria in jelly-end rot material, but he regarded these organisms as 

 saprophytic, as they probably were. In the writers' cultures, however, 

 the constant prevalence of one type of bacterial colony in the dilution 

 plates was significant and warranted a detailed study of this organism. 

 In the subsequent inoculation experiments with pure cultures it proved 

 to be strongly pathogenic and produced a progressive decay of the 

 tubers as well as a disease of the stems. A study of the cultural and 

 biochemical features of the organism showed them to be fully in accord 

 with the published description of the blackleg bacillus (5). 



MORPHOLOGY 



Short rod with rounded ends, also short chains; 0.5 to 0.9 Xi.c to 

 2.2 ;u, average 0.6 X i-S /x; flagella few, peritrichiate; no endospores and 

 no capsules; stains well in aqueous gentian violet, aqueous methylene 

 blue, aqueous fuchsin, anilin water gentian violet, alkaline methylene 

 blue, and carbol fuchsin. 



CULTURAL FEATURES 



Agar stroke. — Growth moderate, filiform, flat to slightly raised, 

 glistening, smooth, slightly opalescent; white, no odor; consistency slimy 

 to butyrous; one strain distinctly viscid at first, but after a few replat- 

 ings it lost its viscidity. 



Potato. — Growth moderate to abundant; filiform at first then spread- 

 ing, slightly convex changing to flat, glistening, smooth to slightly ru- 

 gose, yellowish white or dirty white; a decided odor of decayed potatoes 

 on the third to fourth day at 22° to 25° C. ; consistency somewhat slimy; 

 medium slightly grayed at first, changing later to either plainly gray, or 

 purplish, or brown, or a combination of these shades. 



' Reference is made by number (italic) to " Literature cited," p. 91-92. 



