24 



THE FUNGI WHICH CAUSE PLANT DISEASE 



hypodermic injection produced only limited lesions but similar 

 inoculations with a mixed culture of Ps. avenae and Bacillus avense 

 produced typical disease. Manns, moreover, noticed that the 

 virulence of the Pseudomonas decreased when kept in culture free 

 from the Bacillus, also that in the disease as it occurs in nature 

 these two organisms are associated. His conclusion is that the 

 Pseudomonas is the active parasite and that the Bacillus is an 

 important, perhaps a necessary symbiont. 



3 1 2 



Fig. 11. — Showing effect of inoculation of Ps. campestris into cabbage plants. Nos. 

 1 and 2, six weeks after inoculation. No. 3, check plant uninoculated. After 

 Russell. 



Infection in nature is chiefly stomatal by spattering rain. 

 Soaking of seed in suspensions of bacteria did not produce the 

 disease. Inoculations on wheat failed, though from one variety 

 of blighted wheat, Extra Square Head, the tjT)ical organism was 

 isolated. Inoculations on corn made during wet weather produced 

 lesions which spread rapidly and the organism was re-isolated. 

 Barley is said by Manns to be susceptible and what he believes to 

 be the same disease occurs on blue grass and timothy. 



Ps. campestris (Pam.) E. F. Sm. (Group number 211.333151.) 

 A rod-shaped, motile, organism generally 0.7 to 3.0 x 0.4 to 0.5 ix; 

 color dull waxy-yellow to canary-yellow, occasionally brighter or 

 more pale. One polar flagellum; no spores known. Aerobic but 



