40 



Walter H. Burkholder 



which moves ahead of the bacteria and causes an injury in the still unin- 

 fected part of the plant. At least the pathogene cannot be isolated from 

 the chlorotic tissue beyond the microscopically visible advancing line of 

 bacteria. 



On the leaf 



There are two types of symptoms produced on the leaves of beans 

 by Phyt. medicaginis var. phaseolicola, namely, those due to a systemic 

 infection and those due to a local infection. 



The most striking symptom arises from a local infection, and is the 

 spot to which Miss Hedges has applied the term halo blight. The spot, 

 which varies in size, may become necrotic, dry, and brown, and appear 

 indistinguishable at the center from other necrotic leaf spots due to the 



Figure 6. the " halo 



LEAF SPOT OP THE BEAN CAUSED BY PHYTOMONAS MEDICAGINIS 

 VAR. PHASEOLICOLA 



