Furthi:r RrsHARCHiiS in Disi-ases of Plants 537 



of the crown i;all bacterium and its by-products to establish within 

 a range of probabihty wliat takes place within a cell, as a result 

 of a changed metabolism, when a hyperplasia develops. Since 

 these years. Smith has been accredited '" with suggesting, if not 

 establishing, that " the living cells of the host react to some sub- 

 stance generated by the bacteria, and that the bacteria need not 

 be in direct contact with the cells which have been stimulated 

 to divide." 



Cell respiration, disturbed by want or imperfect functioning 

 of the aerating organs of the plant, was believed to be one of 

 the causes " at tlie bottom of tumor formation " — an oxygen 

 hunger within the cell set up by " limited intake of air," re- 

 duced aerating water, etc.*° Professor Albert Joyce Riker of the 

 University of Wisconsin, and co-workers, more recently have cor- 

 related several individual factors suggested yet today to account, 

 by their lack of balance for changes in plants from normal into 

 pathological growth. These include " " oxygen hunger,' changes 

 in osmotic pressure, rearranged amounts of growth substances and 

 vitamins, ' irritating ' substances, and altered amounts of food 

 materials." ^' In another study, " Inhibition of Respiration in Plant 

 Tissues by Callus Stimulating Substances and Related Chemicals," ■*- 

 Dr. Riker et al. accredit Smith in 1917 with opening " the field of 

 chemical induction of gall formation by using materials found 

 in cultures of crown gall bacteria. . . . These bacteria were 

 grown in beef-extract peptone broth, and various compounds were 

 recovered and tested for their ability to induce galls. Many other 

 investigators continued this work and reported numerous com- 

 pounds of various kinds which were active in gall production." *^ 

 Mitchell et al. found that the best chemicals for inducing chemical 

 galls actively induce " oxygen hunger." Several amino acids which 

 inhibit growth are now known.** Further evidence has been 



^^ E. J. Kraus, Nellie A. Brown, and K. C. Hamner, Histological reactions of bean 

 plants to indoleacetic acid, Botanical Gazette 98(2): 4l4, Dec. 1936. 



^ Production of tumors in the absence of parasites, op. cit., 5 f. 



" A. J. Riker, E. Spoerl, and Alice E. Gutsche, Some comparisons of bacterial 

 plant galls and of their causal agents. Botanical Review 12(2): 57-82 at p. 66, Feb. 

 1946. 



*']. E. Mitchell, R. H. Burris, and Riker, Amer. Jour. Botany 36(4): 368-378 at 

 p. 368, Apr. 1949. 



*^ Riker and T. O. Berge in 1935 reviewed this subject, Atypical and pathological 

 multiplication of cells approached through studies on crown gall, Amer. Jour. Cancer 

 25: 310-357. 



** Riker and A. E. Gutsche, The growth of sunflower tissue in vitro on synthetic 



