Levine: Studies on Plant Cancers 



9 



obtained by inoculating young geraniums and branches of a 

 rubber tree with a known culture of Bacterium tumefaciens. 

 This supports the contention that the bacteria in the distant parts 

 of the stem bearing a crown gall are of a less virulent strain. 



Summary 



1. Bacterium tumefaciens inoculated into the apical internode 

 of the' branches, into the leaves, or main stem of the rubber tree, 

 Ficus elastica, stimulates the development of a neoplasm in the 

 region of inoculation of a benign or malignant nature. The 

 crown galls so formed, in this plant, are of two kinds, one in 

 which growth is uniform and appears to be a swelling, the other 

 is the characteristic convoluted type indicating a peripheral 

 growth of isolated nodules. 



2. The early stages in the development of the crown gall in 

 Ficus elastica does not interfere with the life of the plant as a 

 whole nor does it interfere with the growth of the inoculated 

 branches. 



3. The crown gall in Ficus elastica after a number of months 

 of active growth becomes hard and dry and finally dies. This is 

 associated with the differentiation of the tissue which converts the 

 gall into a mass of parenchymatous cells and nodules of woody 

 fibers. The central portion of the crown gall which generally 

 lies near the woody cylinder disintegrates. 



4. The invasion of the stem by the new growth does not de- 

 stroy the entire conducting system of the stem, yet that portion 

 of the stem above the gall dies as well as considerable portion of 

 the stem below. 



5. Cultures made from pieces of the crown gall and stem above 

 the gall yield only a schizomycete which in appearance is not 

 unlike Bacterium tumefaciens and which when inoculated into 

 the stem of young geranium and rubber plants produce crown 

 galls in the region of inoculation. 



6. It is possible that the crown gall cells or the crown gall 

 forming organisms are responsible for the progressive necrosis of 

 the stem from the gall upward and downward. The death of the 

 plant due to crown gall is at least suggestive of the death caused 

 by malignant growths in animals. 



