322 



BACTERIA IN RELATION TO PLANT DISEASES. 



In gelatin-stab-cultures liquefaction begins at the surface and passes to the walls of the 

 tube and thence horizontally downward more and more slowly, the depths of the gelatin, 

 even along the track of the needle, remaining solid for a long time (fig. 1 29) . The liquefied 

 gelatin may be cloudy at first as in the middle tube but is finally clear unless shaken. The 

 writer observed some differences in the rate of liquefaction, these depending on the kind 

 of gelatin medium used. Occasionally in unfavorable gelatins there was no liquefaction. 

 On peptonized beef-broth-gelatin feebly acid to litmus, growth was feeble. In the same 

 gelatin rendered more alkaline (feebly alkaline to litmus) growth was better. In stab- 

 cultures in the latter, liquefaction began in 24 hours and was completed (10 cc.) in 15 days 

 at 17° to 19° C. A much longer time than this is often required for complete liquefaction — ■ 

 two months or more. In the writer's experiments o gelatin was liquefied more rapidly 

 than -|-2o or —20 gelatin. According to Harding liquefaction begins in 3 to 18 days. 



In streak-cultures on Ivoeffler's blood-serum at the end of 20 days at about 23° C. there 

 was an abundant dull yellow growth, and a slow liquefaction. All the upper part of the 

 slant was fluid or transparent. Only the extreme base of the serum under the V had retained 

 its original opaque-white color. The fluid serum was pale brownish by reflected light, and 

 the stain and transparency passed down into the solid part. In comparison with a streak 



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's ^ 



<i, 



» Koomm 



Fig. 125.* 



3 c' / 



-I * « 



/ 



Fig. 126.t 



. 'Aoo mm 



Fig. I27.t 



of Bad. phaseoli of the same age Bad. campestre showed more liquefaction and stain, but 

 not more growth : By reflected light the contrast in color of the serum, white vs. brownish, 

 was decided (tests of May, 1 909) . Subsequently this contrast became less. 



It is an organism rather sensitive to acids, even those derived from plants. Complete 

 data (quantitive) are not available. Further experiments should be made. According to 

 Harding the vitality of the organism is lessened by long cultivation, i. e., it liquefies gelatin 

 more slowly and is less resistant to heat and to desiccation. It destroys the middle lamella 

 of cell -walls and possibly (?) on prolonged action the cellulose of crucifers, but not lignified 

 tissues. It has no solvent action on Swedish filter-paper. It produces indol slowly in 

 sugar-free peptonized beef -bouillon or peptonized Uschinsky's solution; it does not reduce 

 potassium nitrate to nitrite when grown in peptonized bouillon or with cane-sugar in 

 Fischer's solution. The organism had no characteristic odor, except (Harding) the strong 

 odor of crucifers when grown on these substrata and in bouillon an odor of sweet corn. 



*FiG. 12s.— Bacterium campestre from a potato culture kept 4 months in ice-box at 12° C. Fluid at bottom of 

 culture was filled solid with bacteria, but the growth was still a fresh yellow color. Drawn unstained from a hanging 

 drop with 2 mm. objective, 1.30 n. a., and 12 compensating ocular, Mar. 8, 1905. 



fFiG. 126. — Bacterium campestre, drawn unstained from a hanging drop Mar. 9, 1905, after 48 hours in beef 

 bouillon at 30°C. The organism was actively motile and short; termo-like paired rods were the common form. No 

 long rods were observed. Bouillon was thinly clouded. It was made from a typical culture on potato, i.e., that which 

 furnished material for fig. 125. 



JPiG. 127. — Bacterium campestre, from a very old potato culture (brownish yellow slime stirred up in water) 

 made Mar. 8, 1905, from a culture inoculated Oct. 4, 1904, and kept in a refrigerator a long time at 12° C. A larger 

 proportion of the rods were vacuolate than are here shown. 



