Oct. 28, 1918 Plasticity of Biologic Forms of Puccinia graminis 237 



The rust from the Hordeum jubatum in this series (diagram 7) consisted 

 originally of both the tritici and secalis forms. However, they were easily 

 separated and remained fixed after separation. The secalis strain was 

 kept only for a short time, since it proved to be an ordinary strain 

 which failed to attack wheat either when transferred directly from rye 

 or after having been transferred to barley. The tritici strain, however, 

 was kept for some time in the expectation that it might be induced to 

 attack rye more vigorously. Barley was used almost exclusively as a 

 bridging host, but it is perfectly clear that it did not enable the rust 

 to attack rye any more vigorously than the rust taken directly from 

 wheat. Neither did it acquire the power to attack Agropyron repens, 

 Dactylis glomerata, oats, or Phleum pratense any more readily than the 

 rust taken directly from the wheat. It should be remembered that rye 

 and Agropyron repens can often be attacked weakly by the tritici form, 

 while oats and Dactylis glomerata are very rarely attacked, and timothy 

 has so far proved entirely immune. One attempt was made to use 

 Bromus tectorum as a bridging host, but it did not enable the rust to 

 transfer to rye. In fact, no uredinia were developed, only a few strong 

 flecks. 



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