146 DISEASES OF THE SWEET PEA 



leaves, however, the disease appears as 

 small circular spots, which gradually coal- 

 esce and eventually involve the entire leaf, 

 which when killed presents a dark brown- 

 ish appearance. 



Pathogenicity. The pathogenicity of 

 the causative organism may be proven by 

 diluting a pure culture of the organism in 

 sterile water and by spraying it on the 

 healthy plants with an atomizer. This is 

 done in the evening when the temperature 

 is cooler and there is less chance for evapo- 

 ration of the infectious liquid which is ap- 

 plied. The disease makes its appearance 

 from seven to ten days after artificial in- 

 fection and the symptoms are similar to 

 those produced in nature. The organism 

 may be re-isolated from the artificially in- 

 fected plants and the disease induced again 

 at will on healthy plants, in each case the 

 uninfected check plants remaining healthy. 



