RELATION OF CROWN-GALL TO LEGUME INOCULATION. 5 



a whitish, semitranskicent, wet, shining colony. The crown-gall 

 organism frequently absorbs the stain very freely and produces an 

 intense red colony; even when not strongly colored the colonies are 

 usually tinged with red, at least at the center. The clear whitish, 

 shining colonies should be inoculated into Dunham's solution contain- 

 ing -2 per cent of nitrate and into a special synthetic broth.^ After 

 incubation for 10 days at 25° C, or 2 days at 37° C, the crown-gall 

 organism from alfalfa produces sufficient nitrite to give an intense 

 nitrite reaction with Griess's solution; the nodule organism produces 

 no such reaction. In the synthetic broth the nodule organism reduces 

 the nitrate sufficiently to give an appreciable nitrite reaction, and the 

 alfalfa crown-gall organism does not. 



CROWN-GALL INFECTION THROUGH LEGUMINOUS CROPS. 



The fact that must be emphasized especially in connection with 

 farm practice is that the excrescences, or tumors, formed on certain 

 legumes by the crown-gall organism have occasionally been confused 

 with the desirable nitrogen-fixing nodules. It is obvious, therefore, 

 that in all orchard or sugar-beet regions the possible danger of crown- 

 gall infection through leguminous crops must be considered. The use 

 of soil for inoculating alfalfa or clover, if selected at random, may be 

 a serious menace. In the few years that this matter has been under 

 observation many records of the shipping of alfalfa soil infected 

 with crown-gall under the designation of inoculated alfalfa soil have 

 been obtained. 



It is not impossible that cultures prepared by bacteriologists un- 

 familiar with the slight, though characteristic, physiological differ- 

 ences between the nodule organism and the crown-gall organism might 

 serve as a means of infecting a clean field planted with culture-treated 

 seed. As it is the custom of the bacteriologists of the agricultural 

 experiment stations, and also of the bacteriologists connected with 

 commercial firms, to isolate cultures only from well-grown normal 

 nodules, it is not probable that this second possible source of crown- 

 gall infection is important. 



Whether a leguminous crop infected with crown-gall constitutes 

 an unusually serious menace to succeeding crops of sugar beets or 

 to orchards has not yet been determined. The three leguminous 

 crops, alfalfa, crimson clover, and alsike clover, seem to serve as 

 very favorable hosts for Bacteiium tumefaciens^ and the organism 

 isolated from these legimies appears to be at least as viable as when 

 isolated from its other hosts. It is well known that most leguminous 



1 Wator, 1.000 cubic centimotcrs ; sugar, 10 Rrams ; potassium phospliate (monobasic), 

 1 gram ; maRnesium sulphate, 0.2 gram, and 0.2 per cent of potassium nitrate. 

 [Cir. 76] 



