+ 
BLACK ROT OF CRUCIFEROUS PLANTS. 323 
So far as known it is strictly aerobic, 7. ¢.,it does not produce gas or growin theclosedend 
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 anyacids are produced, the pres- 
3 
Fig. 128.* 
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 
*Fic. 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. 
