BLACK ROT OF CRUCIFEROUS PLANTS. 



323 



vSo far as known it is strictly aerobic, i. e.,it does not produce gas or grow in the closed end 

 of fermentation-tubes in peptone-water or peptonized beef-bouillon with any of the follow- 

 ing carbon compounds: grape-sugar, fruit-sugar, cane-sugar, galactose, milk-sugar, maltose, 

 dextrin, mannit, glycerin ; neither will it grow in the closed end in potato-broth, cabbage- 

 broth, or cauliflower-broth; nor with nitrates (Harding). If any acids are produced, the pres- 



ence of air is required and theyare readily obscured by the production of alkali (ammonia). 

 It is not conspicuous as a reducer of litmus. Its reducing powers are variable. Occasionally 

 some hydrogen sulphide is formed. In cabbage-broth containing litmus the organism 



*Fig. 128. Petri-dish cultures of Bacterium campestre, showing character of colonies and effect of crowding on 

 size. Cultures 8 days old at room temperature. Figs. 1 and 2 contain crystals due to growth of organism in +15 agar. 

 Small dots are buried colonies; medium-sized faint colonies, as in the center of 2, are thin expansions of the same 

 organism between agar and bottom of dish. These poured-plates were made directly from blackened vascular ring 

 of a young shoot of collard shown in fig. 105 (at the point marked x). Natural size. 



