. Carnegie Institution of Washington publication. 198 BACTERIA IN RELATION TO PLANT DISEASES. organism reduces potassium nitrate to nitrite in bouillon; does not produce indol in peptone-water; and does not stain by Gram's method, i. c, is only slightly blue after washing (diaphragm wide open). Cultures were easily obtained from a bouillon-culture after exposing it for 20 minutes to minus77°C.,but quantitative experiments with liquid air show that a large proportion of the rods are killed by a single freezing (pi. 32). The minimum temperature for growth is about io°C; optimum temperature 350 t
. Carnegie Institution of Washington publication. 198 BACTERIA IN RELATION TO PLANT DISEASES. organism reduces potassium nitrate to nitrite in bouillon; does not produce indol in peptone-water; and does not stain by Gram's method, i. c, is only slightly blue after washing (diaphragm wide open). Cultures were easily obtained from a bouillon-culture after exposing it for 20 minutes to minus77°C.,but quantitative experiments with liquid air show that a large proportion of the rods are killed by a single freezing (pi. 32). The minimum temperature for growth is about io°C; optimum temperature 350 to 370 C. (?); maximum temperature not determined (about 410 C.*); the thermal death-point (South Carolina organism, 1896) is above 510 C. and below 530 C, being probably about 520 C. In 1904 all 10-minute exposures of the Dis- trict of Columbia organism at 520 C. remained sterile but not those at 510 C. The organism grew readily and for a long time in the thermostat at 370 C, i. e., in peptonized beef-bouillon held at 370 C. the South Carolina organism was alive in one test after 3 weeks' exposure, and in another after 7 weeks' exposure. At 380 to 400 C. the District of Columbia organism. Fig. clouded + 15 peptonized beef-bouillon in 48 hours and grew well, but not so freely as at room temperature. After 10 days' exposure in the thermostat at this temperature, streaks to slant agar gave only a discrete growth (separate colonies), indicating that the cloudy bouillon was then only thinly occupied by living bacteria. It also lives for a considerable time in peptone-water and in bouillon at 200 to 250 C. This bacterium does not live for many weeks ?Exposed in Feb. 1904 in the thermostat at ; C. the Virginia organism clouded peptonized beef-bouillon of the following reactions: + 25, +15, o, and refused to cloud —20 bouillon, Dunham's solution, or Uschinsky's solution. The experiment was twice repeated with the same results. fFiG. 109.—(a) Bacterium solanacearum
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