100 MASSACHUSETTS HORTICULTURAL SOCIETY 



experiments tending to show a wide range of natural cross-inocula- 

 bility. 



Life History. It is probable that the bacteria causing crown-gall 

 must enter the plant through wounds. The development of certain 

 cells in the host plant is stimulated resulting in the formation of 

 large galls. The size of the tumors, other things being equal, 

 depends on how rapidly the plants are growing. The galled tissue 

 is often of a soft fleshy nature and is much subject to decay. Tumor 

 strands develop into the normal tissue as roots of the tumor, in the 

 substance of which secondary tumors arise. These secondary 

 tumors rupture their way to the surface. 



The bacterium is a soil organism, probably being able to live in 

 the soil for years without losing its virulence. Its entrance into 

 the host is favored by careless grafting and by the presence of 

 borers, nematodes, and the like. 



Control. Since B. tumefaciens is a soil organism, growers should 

 plan to keep their soil free from it by planting only healthy stock. 

 All plants should be carefully inspected for galls before they are 

 set in the benches. It is advisable to burn all cuttings showing 

 galls. Do not plant healthy plants in soil in which diseased plants 

 have grown. Infested soil should be sterilized by steam or re- 

 placed by soil in which no diseased plants have grown. When 

 infested soil is removed from the greenhouse the benches should 

 be thoroughly disinfected. The removal of galls from plants is 

 of doubtful value. Once a plant is affected no treatment will 

 cure it. 



Bibliography. 



1. Laubert, R., and Schwarz, M. Rosenkrankheiten und 



Rosenfeinde, pp. I-VI + 59. 1910. 



2. Scribner, F. L. Black spot of rose leaves. U. S. Dept. Agr. 



Report 1887:366-369. 1888. 



3. Maynard, S. T. Rose leaf bUght (Actinonema rosse). Mass. 



Agr. Exp. Sta. Bui. 4: 10. 1889. 



4. Humphrey, J. E. The black spot of rose leaves. Mass Agr. 



Exp. Sta. Bui. 6: 13-15. 1889. 



5. Wolf. F. A. The perfect stage of iVctinonema rosfe. Bot. 



Gaz. 54: 218-234. 1912. 



