196 



BACTERIA IN RELATION TO PLANT DISEASES. 



end of a week (temperature 28 C.). 

 days later they were brownish and the 

 after the first i o days. On steamed 

 potato this organism was white at 

 first, then a dirty yellowish-white, 

 and finally brown or even nearly 

 black. 



The poorest agar-streaks, with 

 perhaps one exception, were on al- 

 kaline agar containing 6 per cent 

 glycerin. In agar-stabs the growth 

 was best on the surface and in the 

 upper part of the needle-track. 



No gas-bubbles or acid reac- 

 tions were observed as the result of 

 cultivation in any of the ordinary 

 culture-media, but in each case 

 there was a gradually increasing 

 alkalinity. Grown in fermenta- 

 tion-tubes in 2 per cent alkaline 

 peptone-water with addition of 

 grape-sugar, fruit-sugar, cane- 

 sugar, milk-sugar, galactose, mal- 

 tose, or dextrine, there was no gas 

 production, no detected acid de- 

 velopment, and no clouding of the 



These were circular, white, and wet-shining, and 9 

 agar was also browned. They did not enlarge greatly 



Fig. I06.f 

 have been tried and in all of them it requires free oxygen for respiration. 



Fig. 105.* 



closed end of the tubes. The same result 

 was obtained with the juice of potato 

 tubers diluted with water and sterilized 

 in fermentation-tubes (1909 organism from 

 tobacco) . Culture-fluids containing grape- 

 sugar, fruit-sugar, and cane-sugar browned 

 decidedly after some weeks. In 1904, 

 using the District of Columbia organism, 

 clouding was heaviest with cane-sugar. 

 All of the writer's numerous experiments 

 go to show that Bacterium solanacearum 

 is a strict aerobe (the fermentation-tube 

 experiments were repeated with the same 

 results in 1904). If it is ever capable of 

 growing in the absence of air we do not 

 know on what media or under what cir- 

 cumstances. All of the common media 



*FiG. 105. Border of a small cavity in the vascular region of a potato tuber attacked by Bacterium solanacearum 

 showing 7 uncorroded starch-grains lying in one cell embedded in a mass of bacteria. Slide 156(3. Vernier readings 

 on Zeiss photomicrographic stand, 12.5 X8.i. Plant No. 14, 1896, inoculated on the stem June 15. Drawn by polar- 

 ized light. The dark patches are masses of bacteria. 



fFic. 106. Detail from fig. 83 at x, showing uncorroded starch-grains embedded in a cell occupied by Bacterium 

 solanacearum. The dotted parts of the starch-grains are the only ones stained by the carbol-fuchsin. Light and dark 

 rings can not be made out in these grains, but they polarize the same as grains in the middle of the tuber, remote from 

 the bacteria. Drawn with 2 mm. 1.30 n. a. Zeiss apochromatic objective, 12 compensating ocular and Abbe camera. 

 Slide 349(15- 



