The Bactekial Diseases of the Bean 



41 



various bacteria described in this memoir. The peculiarity, however, 

 which sets it apart from the leaf spots of the other diseases, is a chlorotic 

 area, or zone, about the dead part. This zone is very pale green, and 

 varies in width from a half inch to an inch. The zone naturally changes 

 with the size of the necrotic area, but a very small spot may show a sur- 

 prisingly large zone (figure 6). A leaf spot of this type is a fairly good 

 diagnostic symptom, but probably is not infallible. The halo spot is 

 found, as a rule, during cool weather, and later in the season, during the 

 hot weather, it gives place to another type of lesion. The lesions of this 

 latter type are numerous on the leaf, and are small and angular (figure 7). 



Figure 7. a type of leaf spot often produced by phytomonas medicaginis var. 



phaseolioola 



