RIKER AND THOMAS 4^7 



The virulent cultures induced large galls, and the attenuated cultures 

 induced small galls covered with many little shoots. Recently Hodgson, 

 Peterson, and Riker (unpublished) found that d-tryptophane inhibited 

 the bacteria more than the attenuated culture. Schurr (unpublished) 

 found by means of microbiological assays that the virulent culture 

 produced more free tryptophane in a synthetic medium than the 

 attenuated culture. Tryptophane can stimulate galls about attenuated 

 bacteria. It is a precursor for other important substances. 



The presence of growth substance in crown gall has been shown by a 

 number of workers. For example, growth-substance responses in plants 

 with galls were described by Locke et al. in 1938 (9). A substance in 

 tomato was found in 1939 by the same workers (11) to behave like 

 indole-3-acetic acid in the presence of strong acid and alkali. In related 

 studies, Riker et al. (18) detected no difference in the amount of growth 

 substances in tomato plants grown at 27° C, where galls developed well, 

 and 31° C, where the galls did not develop. 



Galls were shown (13) to contain more of tyrosinase, oxidase, peroxi- 

 dase, and catalase than normal tissue. The question has appeared whether 

 this excess of oxidizing enzymes had any connection with the lowering 

 of oxidation-reduction potentials (21) by the bacteria and with the 

 reduced oxygen uptake (12) induced by gall-stimulating growth sub- 

 stances. 



Indole-3-acetic acid has been reported by some workers to be the 

 cause of crown gall. The subject is reviewed elsewhere (12). It was pointed 

 out that thus far the technique employed had not been adequate to 

 justify this conclusion. However, the association of such material with 

 embryonic growth, including galls, has been well established. 



Chemical induction of galls. — Various chemicals have been employed 

 to induce galls on different plants. Among these the growth substances 

 are the most prominent. However, many other unrelated chemicals 

 seem to be active (16). We (unpublished) have found that substances 

 such as thiamin, ammonium carbonate, and 1,2,5,6-dibenzanthracene all 

 will induce chemical galls under certain conditions. Thus the formation 

 of galls seems to be a relatively nonspecific reaction. If this should be 

 true, then the cause must involve rather broad biological phenomena. 



The possibility of stimulating growth of galls with chemicals after 

 inoculation with attenuated strains arose from the observation by Locke 

 et al. (9) that virulent bacterial galls a few inches above inocula- 



