WILT-DISEASES OF TOBACCO. 

 MORPHOLOGY AND CULTURAL CHARACTERS OF THE PARASITE. 



231 



In tobacco plant No. 6, which was inoculated July 13, 1905, and examined July 20, 

 many of the bundles were found to be swarming with an organism in the form of short rods 

 having rounded ends. These rods were single, or in pairs, or occasionally in fours, end to 

 end. Tumbling movements were observed, but no darting ones. Organism morphologi- 

 cally like Bad. solanacearum. This was the common form of the organism found in all of 

 these plants. Pseudozoogloeae occur in culture media. 



Fig. 120.* 



Fig. 121. f Fig. I22.J 



Agar. Like Bacterium solanacearum (see pi. 23). Colonies on plates of +15 standard nutrient 

 agar at 25 C. to 30 C. do not develop rapidly. They are not visible the first day and often not 



*Fig. 120. Cross-sections of base of petiole of inoculated tobacco plant No. 34, showing blackened vascular 

 bundles. These were occupied by the bacteria. Surface of the petiole and midrib sound. The infection entered the 

 leaf from the stem, which was the inoculated part. Inoculation Sept. 23. Photographed Dec. II, 1905. 



tFic. 121. Portion of midrib of a large tobacco leaf sliced longitudinally to show brown stain due to bacterial 

 occupation of the vascular bundles. The lighter portions of the tissue were green and sound. Photographed Feb. 20, 

 1906. The infection was due to a stem-inoculation made Sept. 23, 1903, with a pure culture of the North Carolina 

 tobacco organism. The left-hand streak is simply a shadow due to a sulcus in the midrib. The stem should have 

 been lighted from the left side. 



tFic. 122. Petri-dish poured-plate from the cavity in stem of inoculated tobacco plant No. 31 (plate 38), show- 

 ing the presence of a white organism producing branching colonies. The broader pale patches are thin colonies growing 

 under the agar. This organism has the same type of colony-growth as Bacillus aroideae. 



