BLACK ROT OF CRUCIFEROUS PLANTS. 



321 



It prefers neutral or alkaline media, and its growth is inhibited or retarded by acids (strong 

 litmus reaction). No true pellicle is formed on neutral peptonized beef-bouillon (Harding) 

 but after a time there is a yellowish ring. It grows very copiously on steamed potato, stand- 

 ing in water; the yellow slime soon fills the fluid (Vide C. f. B., 2 Abt., in Bd.,Tafel vi, fig. 4), 

 converting it into a solid alkaline mass which turns brownish with age. It destroys potato- 

 starch so that it will not react with iodine. The conversion of the potato-starch, when 

 potato-cylinders are used as the culture-medium, is never quite completed. There always 

 remain some scattering starch-grains or groups of grains which react purple with iodine, 

 although on first mashing in the iodine water, which should be abundant,* all appear to 

 have been converted. The conversion is so nearly complete, however, that one might 

 probably safely estimate it at 99 + per cent, not only for this organism but also for several 

 similar yellow species, e. g., Bacterium phaseoli (plate 17, fig. 3). The action was always 

 well marked and often practically complete after two weeks (Harding). Potato cultures 

 are of a butyrous consistency and give off an odor of ammonia (Harding). 



,c 





e* 



Fig. 1224 



I 1 



* 



Fig. 12) _t 



Fig. I23.i 



Fig. 124 



The organism blues litmus milk and throws down the casein slowly by means of a lab 

 ferment. The milk is not coagulated into a stiff mass but remains fluid for a long time, the 

 small amount of clear whey slowly increasing over a mobile, bulky precipitate, which 

 gradually becomes compacted. At no time is any acid developed in litmus milk. Harding 

 also observed the slowly increasing layer of whey on top of the culture in milk and says that 

 the casein is gradually digested, the liquid then assuming a yellowish tint. His time limit 

 for beginning of the extrusion of whey is 3 to 10 days. Tyrosin crystals have been observed. 

 It inverts cane-sugar (?). It liquefies gelatin and Loeffler's blood serum, both slowly. 



*Ammonia bleaches alcohol iodine and if only a little of the latter is added there may be enough ammonia in the 

 culture to interfere with the test, if the particular organism on trial produces this alkali abundantly. 



fFic. 121. Bacterium campestre, from a cover-glass preparation stained with Fischer's modification of Loeffler's 

 flagella stain. Feb. 27, 1897. Cover made from an agar culture 8 days old which contained many actively motile 

 rods (tube 4, Feb. 18, descended from a colony isolated from a turnip). Drawn directly from the slide, x 1000. 



JFig. 122. Bacterium campestre: Cover-glass preparation direct from stem of charlock (Brassica sinapistrum) 

 Racine, Wisconsin, Aug. 30, 1897. Drawn with a Zeiss 12 ocular and 2 mm. apochromatic oil immersion objective 

 1.30 n. a. 



Fig. 123. Contact preparation of Bacterium campestre horn a gelatin-plate culture. Organism isolated from 

 kohlrabi and stained with fuchsin. x 2600. After Hecke. 



]|Fig. 124. Bacterium campestre: Cover-glass smear preparation from a cabbage-stem, stained with carbol 

 fuchsin. Photomicrograph x 2000. 



