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 ayellowish ring. It grows very copiously on steamed potato, stand- 
ing in water; the yellowslime soon fills the fluid (Vide C. f. B., 2 Abt., m1 Bd., Tafel vt, 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). 
Fig. 121.7 
Fig. 123.§ 
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 torodays. 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. 
{Fic. 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. 
tFic. 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 0. a. 
§Fic. 123.—Contact preparation of Bacterium campestre from a gelatin-plate culture. Organism isolated from 
kohlrabi and stained with fuchsin. x 2600. After Hecke. 
\|Fic. 124.—Bacterium campestre: Cover-glass smear preparation from a cabbage-stem, stained with carbol 
fuchsin. Photomicrograph x 2000. ; 
