Furthi:r Ri:sEARCHFS IN DisiiASFS OF Plants •j6') 



and Dr. S. B. Locke explained the association of several hormone 

 cfl'ects with crown i^all infection and, in the course of their dis- 

 cussion, cited another study *'" by Riker and T. O. Berge to the 

 effect that, " following Smith,"' they have listed " numerous other 

 chemical agents capable of stimulating cell division locally." A 

 conclusion reached was: " The great diversity of materials reported 

 to cause stimulation suggests that irritation or injury induced by 

 them, which is apparently a common characteristic, is more impor- 

 tant than the nature of the substance." This would seem to add 

 credence to Smith's earlier beliefs about irritants and injuries as 

 causal factors in tlie processes of gall formation. 



Smith's studies of the processes of tumor formation included 

 examining the nature, amount, and the continuity of chemical- 

 physical stimuli required to induce structural modification and 

 tissue reactions of variously aged plants under differing environ- 

 mental conditions. After publishing his paper, " Appositional 

 Growth in Crown-Gall Tumors and in Cancers," he wrote Brierley, 



My last paper I think throws considerable light on the early develop- 

 ment of the tumor and ought to be of more than a little interest to cancer 

 research workers. I am planning another paper on what goes on inside the 

 cell, a subject which so far I have not published much upon. I would like 

 very much also to see the tumor develop under the microscope from single 

 cells, and I believe that I can bring it about with enough patience. This 

 I am hoping to try the coming year. 



His diary reveals that on August 30, 1922, he began new experi- 

 ments to demonstrate bacteria in the cells. Nothing in his diary 

 or letters discloses that he had read in Phytopathology ^°' a pre- 

 liminary announcement that year that Dr. Riker, from " evidence 

 secured from microscopic study of the tissues at different stages 

 of gall formation and from the development of the original and 

 secondary galls," w^as securing evidence on the location of the 

 bacteria in crown gall. Dr. Riker reported their location to be 

 intercellular, rather than intracellular, as Dr. Smith had said they 

 must be. According to the new pronouncements, Bacterium tume- 

 faciens lives in the gall tissue of the host plant " between the 

 cells," rather than within the cells, " Its intercellular position and 



^'" Atypical and pathological multiplication of cells approached through studies 

 on crown gall, Amer. Jour. Cancer 25: 310-357, 1935. 



"^Studies of crown gall, Phytopath., 12(1): 55, Jan. 1922. 



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