296 



Bulletin 239. 



site and one that requires further observation before definite statements 

 can be made. Having gained entrance to the leaf, the disease graduahy 

 travels down the stem to other leaves and to the pods. Professor Barlow, 

 of the Ontario Agricultural College, has shown that the progress of the 

 disease is comparatively slow. Leaves of beans inoculated with the bac- 

 teria did not show -symptoms of the disease until the third week. The 

 bacteria increase in such numbers that finally they may fill up the sap 

 tubes in the stem, cutting ofi: the water supply and so cause the entire 

 plant to wilt and die. 



The disease in the pods. — Through wounds or by way of the stem 

 the bacteria find their way into the pods which, if young, may shrivel and 

 die. In the larger pods they produce spreading watery spots (Figs. 1 10 and 

 III) wdiich finally become more or less discolored but never sunken and 

 black as in the case of the anthracnose. 



The disease in the seed. — From the pod the disease readily gains 

 entrance to the growing seeds. The pods are not destroyed unless at- 

 tacked when very young, and when ripe they may show considerable dis- 

 coloration or none at all. The bacteria, however, having gained entrance 

 into the seed, as in the case of the anthracnose, remain there dormant 

 throughout the winter. With the germination of the seed 

 in the spring the bacteria also begin to multiply and find 

 their wav to healthv beans and so the infection spreads. 



Fig. 112. — Bac- 

 teria thai- cause 

 the bean blight 

 initch mai^ni- 

 ficd. {After 

 Smith.) 



Treatment of Blight 



Seed treatment.— No method of treating the seed to 

 prevent the blight has yet been proposed and properly 

 tested. Professor Barlow has demonstrated that the bac- 

 teria arc readily killed by exposure for ten minutes to 



...4 



k 



A 



B 



Fig. 1 13. — Bean rust. A. Summer spores on under side of leaf. B. and C. Winter 

 spore. Note the light border around the spots on the upper side of tlte leaf B. 



