THE CROWN GALL: TECHNIC 



439 



B 



FIG. 336. Crown galls on tobacco. A. Teratoma containing perhaps 100 

 leafy shoots. Inoculated July 29, 1916, by needle pricks on the cut end of the 

 stem (middle of an internode) introducing the hop strain of Bacterium tumefaciens 

 from a 48-hour agar culture. Photographed September 1, 1916. % natural size. 



B. Like A but inoculated March 1, 1918 (from hop through sunflower) on a 

 cut internode of the main axis. The white part of the tumor was very smooth, 

 free from chloroplasts and covered by an epidermis, i.e., the malignant part lay 

 deeper. Twelve of 13 inoculated internodes contracted the disease. Photo- 

 graphed May 8, 1918, natural size, nearly. 



