Oct. 28, 1918 Plasticity of Biologic Forms of Puccinia graminis 233 



The original rust was mixed here (diagram 4) also, and only after six 

 successive sets of inoculations had been made were the tritici and secalis 

 forms finally separated. Neither barley nor Agropyron tenerum acted as 

 bridging hosts for the tritici form. The secalis form likewise remained 

 fixed and did not acquire the ability to attack wheat after growing on 

 either barley or Agropyron tenerum. 



Diagram 5 (condensed). — Results of inoculations made with Puccinia graminis secalis 



from Hystrix patula. 



Puccinia graminis secalis 

 from Hystrix patula, St. 

 Paul, Minn., Septem- 

 ber 2, 1915. 



R2— B4— (W:^)— Rr- (W- ) / . 



/ o\ At9— IWx-) 



—Br- [W - j — An— Bi-Ev3- ^ ^^Z 



At4— B22— 



V 104/ 



Ar= A gropyron repens. 

 AX= Agropyron tenerum. 



At4— Hj 



September 17, 1917. 

 H j= Hordeum jubatum. 

 Ev= Elymus virginicus. 



^^(^75) 



The strain of P. graminis secalis from Hystrix patula was somewhat 

 different from normal secalis strains (diagram 5). It was not as virulent 

 on barley and rye, and the spores were somewhat smaller. Attempts 

 were made to induce the rust to attack wheat by growing it on barley, 

 Elymus virginicus, Agropyron tenerum,, and Hordeum, jubatum. None, 

 however, acted as a bridge. The rust was kept for over two years, 

 during which 18 sets of inoculations were made on wheat; but none of 

 the 305 inoculated leaves became infected, except in one case, which was 

 quite evidently an accidental infection with P. graminis tritici. How- 

 ever, the rust did not act normally and may have been a different biologic 

 form. Some of the results were difficult to explain, and more work will 

 probably be done with it. 



