THE RELATIONS OF CROWN-GALL TO OTHER 

 OVERGROWTHS IN PLANTS 



ERWIN F. SMITH 

 Bureau of Plant Industry, U. S. Department of Agriculture 



In the time assigned the most I can hope to do is to give the 

 barest outline of the suggested relationships. Some of these are well 

 determined; others are only suspected and are mentioned here as 

 hopeful lines of research rather than as definite conclusions. Indeed, 

 I am quite willing to admit that our work on crown gall has opened up 

 more problems than it has settled, but, one way or another, all of this 

 present uncertainty will make for progress and an eventual better 

 understanding of the whole mechanism of overgrowth. My own 

 belief is that all overgrowths are correlated phenomena, are the 

 response of the organism to essentially similar (but not necessarily 

 identical) stimuli, the visible difference in response when brought 

 about by parasites being due to number and location of the parasites, 

 age and kind of tissues invaded, and volume, direction, and velocity 

 of the stimulus exerted. In other words, in every case, I think the 

 stimulus is primarily a physical stimulus due to changed osmotic 

 pressures rather than a direct chemical stimulus. Overgrowths, 

 therefore, do not always involve the presence of a parasite although 

 as observed in nature parasites are probably responsible for most of 

 them. 



I. Factors governing type of overgrowth in crown gall. 



A. The host reaction depends on the type of tissue infected. 



(i) Vascular vs. parenchymatic. For example, depend- 

 ing on the tissue in which it originates the vessels 

 in a tumor may be numerous or few, the paren- 

 chyma abundant or scanty. 



(2) Nexus of cells stimulated, i. e., unipotent, multi- 

 potent, or totipotent cells. Thus, according to the 

 tissues infected by the crown gall schizomycete, we 

 have it causing either organoid galls or histioid 

 galls. 



(3) Rate of growth. The rate of growth depends on the 



readily available supply of food and water, on the 

 age of the tissues when infected and on the species 



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