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 

 minus77C.,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 

 ioC; optimum temperature 35 to 37 C. (?); maximum temperature not determined 

 (about 41 C.*); the thermal death-point (South Carolina organism, 1896) is above 51 C. 

 and below 53 C, being probably about 52 C. In 1904 all 10-minute exposures of the Dis- 

 trict of Columbia organism at 52 C. remained sterile but not those at 51 C. The organism 

 grew readily and for a long time in the thermostat at 37 C, i. e., in peptonized beef-bouillon 

 held at 37 C. the South Carolina organism was alive in one test after 3 weeks' exposure, and 

 in another after 7 weeks' exposure. At 38 to 40 C. the District of Columbia organism 



Fig. I09.f 



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 20 to 25 C. This bacterium does not live for many weeks 



Exposed in Feb. 1904 in the thermostat at 39.4" 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 (District of Columbia strain). From a slide (2a) of August 9, 1904. 

 Flagella stained by Lowit's method. (B)Bacl. solanacearum (D. C. strain) showing flagella stained by van Ermengem's 

 silver nitrate method. Slide of August 12, 1904. (c) Freehand sketches of flagella from three slides of Bad. solana- 

 cearum, stained in 1896 by van Ermengem's silver nitrate method. Slides X, XX, and XXX (South Carolina organ- 

 ism, No. XXX taken from inoculated Physalis No. 57, the others from cultures). The numbers correspond to the fol- 

 lowing vernier readings on Zeiss photomicrographic stand 32532 used by the writer: (1) 12.8X5.35; ( 2 ) 12.2X6.8+; 



14.4X7-3; (4) 20.1 X7-3! (5) 20+X7-2; (6) 18.5X7-15; (7) 13-6X5-6; (8) 20X5; (9) 19-3X6.75; (10) 18X44; (") 

 17.3X0.9; (12) 15.4X6.6; (13) 16.1X6.9; (14) 15.6X575; (15) 13-8X5-6 artefact (?); (16) 16.35X11.35; (17 and 18) 

 14.17 X6.35. Numerous flagellate rods are visible on slide XXX at 14.17 X6.35 and all seem to be one-flagellate, but it 

 requires a high power and a bright light to make them out as all are feebly stained: One might also add. keen eyesight 

 1 I 1 " paration of Bad. solanacearum (D. C. strain) stained August 12, 191)4, by van Ermengem's method 

 from a young agar culture. Flagella wanting or not visible. This organism was extremely pathogenic at first (see 

 pis. 30, 3 1 . and vol. 1, pi, 26), but afterwards lost much of its virulence. The bacteria are thicker than when stained 

 without mordanting. 



