WILT-DISEASES OF TOBACCO. 



233 



Fig. 124.* 



much rim. Most of the tubes were still somewhat cloudy and all became very turbid on shaking. 

 Four of the six cultures from as many colonies produced crystals in the bouillon ; two did not. 



Milk. Like Bacterium solanacearum, except that a brown rim formed on old cultures. No acid 

 was formed, and there was no coagulation of the casein; the fluid became more and more alkaline, 

 and after some weeks was translucent and pale brownish. (See 

 pi. 41, fig. 3.) The milk was browner by transmitted light and 

 so clear that print could be read behind it and that a penholder 

 could be seen very readily behind two tubes when one was placed 

 back of the other ; the brown bacterial rim was not visible until 

 toward the close of the experiment, it having increased very 

 noticeably during the last 2 weeks ; the black rim has not been ob- 

 served in milk cultures of the tomato and potato organism. 



Litmus milk. Like Bacterium solanacearum (pi. 41, fig. 6), 

 except that I have not seen any crystals such as shown in fig. 1 24. 



Colin' s solution. No growth. Numerous tests. 



Reduction of nitrate to nitrite.- Copious in bouillon. 



Thermal death-point. This is above 48 C. and below 52 C. 



Minimum temperature. This is above 8 C. No growth was 

 obtained at 8.2 C. in 6 tubes of +15 peptonized beef-bouillon 

 exposed for 5 weeks. These were inoculated from as many colo- 

 nies. Four out of 6 similar tubes finally clouded at 8.7 C. 



Gas. None from any medium. 



Aerobism. Strictly aerobic so far as can be determined from general appearance of buried colo- 

 nies, failure to grow in hydrogen, and behavior of stabs in agar and gelatin. 



ETIOLOGY. 

 EXPERIMENTS OF 1907. 



On July 29, 1907, three young tobacco plants about 4 to 6 inches high, Nos. 595-597, 

 were inoculated directly with Bacterium solanacearum from the browned bundles of tomato 



stems from Lanham, Maryland. The stems were squeezed 

 until the juice came out, and this and bits of the browned 

 bundles themselves were pricked into the stems and peti- 

 oles of the tobacco plants. 



Result. The leaves finally wilted and the stems were 

 full of bacteria [some vessels probably]; then the plants 

 recovered. (Notes made by Miss McCulloch.) 



EXPERIMENTS OF 1908. 



On July 9, 1908, a dozen large wilted tobacco plants 

 were received from Creedmoor, North Carolina, affected 

 by the vascular bacterial disease (Granville wilt) . These 

 were buried in good soil in rows about 1 5 inches apart in 

 the old rose house. 



On July 22,1 received a much larger number of wilted 

 tobacco plants (Granville bacterial disease) from the same 

 locality and buried them in rows in the same way in the 

 same house. 



After the receipt and burial of the second lot of 

 tobacco, I planted tomato plants (large size) between 

 the rows of tobacco laid down on July 9 ; and large plants 



These plant- 



Fig. I25.t 

 of Datura stramonium between the rows of the more recently buried tobacco. 



*Fic. 124. A crystal complex from a shining small mass on the inside of a test-tube above the fluid, in an old 

 litmus-milk culture of North Carolina tobacco-wilt organism: Colony A, from poured plate IV, made direct from a 

 tobacco plant received from Creedmoor. Tube inoculated June 19. Drawn free-hand Nov. 13 (Zciss 8 mm. apochro- 

 matic objective. No. 12 compensating ocular) and then reduced somewhat, Xso (?). Contamination (?). 



fFlG. 125. Stem of Datura stramonium showing gray bacterial ooze from the vascular system. The plant stood 

 in a bed where tobacco plants affected by the Granville (North Carolina) tobacco wilt had been buried and the infection 

 took place through roots broken at the time of transplanting. (For appearance of the whole plant at this time see pi. 

 43). It grew in the bed, healthy to all appearances, for about 5 weeks and then suddenly wilted. Photographed 

 Aug. 29. 1908. Xz. 



