1923] 



JENNISON — POTATO BLACKLEG 19 



Physiology : Prompt coagulation of milk, extrusion of whey in 3 

 days, a few gas bubbles visible ; litmus milk acid. Strong growth in 

 Uschinsky's solution. In fermentation tubes gas was produced in 

 bouillon containing mannite and lactose; growth in closed arm, with 

 production of acid in each of the following: dextrose, saccharose, 

 lactose, maltose, glycerin, mannite, and levulose. Nitrates in nitrate 

 broth were reduced, nitrites present, indol production moderate to 

 feeble; vitality on culture media long; thermal death point 54° C, 

 optimum temperature for growth 25-28° C, growth slight at 37° C; 

 maximum temperature for growth 37.5 °C, minimum temperature for 

 growth about 0° C. Pathogenicity proven to following vegetables: po- 

 tato, tomato, Jerusalem artichoke, and others; also to living plants of 

 potato, tomato, common red pepper, and slightly in cucumber and 

 physalis. Index No. 5312-32120-1212. 



Bacillus melanogenes Pethybridge and Murphy. — The account 

 presented below is summarized from Pethybridge and Murphy's 

 fll) original diagnosis: 



Morphology : Vegetative cells 0.7-0.9 p x 1.3-1.8 jj, found most fre- 

 quently in pairs. Flagella peritrichic (fewer than in B. solanisaprus 

 Harrison). No endospores. Gram's stain negative. 



Cultural features: Nutrient broth clouded, more or less sedi- 

 ment, fluid turbid, no pellicle. Organism did not form a distinct ring 

 on surface of potato juice. Gelatin colonies round. Growth best at 

 top in gelatin tubes, some growth along needle track Gelatin liquefied. 

 On potato plugs growth abundant, and chromogenesis yellowish. 



Physiology : Facultative anaerobe. Milk acid curd, curd not very 

 compact. No indol produced, nitrates reduced to nitrites with for- 

 mation of gas. Diastatic action on starch. Acid and gas in fermenta- 

 tion tubes, in broth plus glucose, lactose, and saccharose. No acid 

 from glycerin. Pathogenic to potato. 



They comment upon the marked resemblance of their organism to 

 B. phytophthorus Appel and state that they were tempted to regard 

 it as a variety of the latter. Index No. 5312-3211 1-1111. 



After comparing the contributions of these earlier investiga- 

 tors, and in the light of the observations which I had previously 

 made, I planned a thoroughgoing study of the relationship of 

 the blackleg pathogen. To this end it was thought best to make 

 careful comparative studies of a number of strains, including 

 if possible the 4 species described above. 



Source and history of the cultures used. — Some difficulty was 

 experienced in obtaining authentic and viable subcultures of 

 the organisms described by van Hall, Appel, Harrison, and Pethy- 

 bridge and Murphy. Cultures of these organisms, however, were 



