igo Journal of Agricultural Research voi. xviii, no. 4 



noted that considerable variation may occur among colonies on the same 

 plate. 



Just what the significance of these variations may be is rather difficult 

 to state without more thorough study of this part of the cultural work. 

 We have found, however, that both types of the organism are pathogenic 

 on soybean leaves and are able to produce typical lesions. Further- 

 more, there have been no marked differences in morphology or in cul- 

 tural behavior. It seems, therefore, the justifiable disposition of the 

 matter, at least for the present, to consider that we are dealing with 

 forms of a slightly variable species. Since these forms agree in the 

 characters ordinarily included in descriptions of bacterial species as well 

 as in pathogenicity and host reactions, it does not seem wise nor helpful 

 to segregate them formally by technical description or varietal name. 

 Should subsequent investigations indicate more adequate bases or need 

 for this segregation it may then be made. 



INOCULATION EXPERIMENTS 



During the years 1916 to 191 8, the bacterial leaf spot has been repro- 

 duced many times and in typical form under greenhouse and field condi- 

 tions by artificial inoculation (PI. 16, 17). From lesions produced in 

 this way, the original type organism has been repeatedly recovered. 

 In the early work the tissues were wounded at the time of inoculation, 

 but it was soon found that simply spraying water suspensions of the 

 blight organism upon uninjured leaves was sufficient to produce infection, 

 not only when the tissue was very young and tender but also when the 

 leaves had more nearly approached maturity. It has been found advis- 

 able, however, in most cases, since soybean leaves are very hairy and 

 therefore prevent liquid from spreading readily upon them, to rub the 

 inoculated leaves gently between thumb and finger in order to insure 

 contact between the inoculum and the leaf surface. 



In making greenhouse inoculations the following method was usually 

 employed : Soybeans were sown in 8-inch pots in sterile soil, and when a 

 few leaves had developed they were inoculated with an atomizer spray 

 of a water suspension of the organism. The plants were then allowed to 

 remain in a damp chamber for from 48 to 72 hours, after which they 

 were removed to a greenhouse bench. 



In making inoculations in the field, practically the same method was 

 employed. Plants perfectly free from the disease were selected, the 

 leaves inoculated with atomizer spray and then covered w4th glasine 

 paper bags which were removed after two or three days. In field work 

 the younger leaves of almost mature plants were most often used in the 

 inoculation tests. 



Control plants were always sprayed with sterile water and otherwise 

 treated in the same manner as inoculated plants. Both inside and out 



