Oct. 28, 1918 Plasticity of Biologic Forms of Pticcinia graminis 239 



The strain of tritici used for the inoculations represented in diagram 8 

 was originally obtained from Agropyron tenerum at Valley City, N. Dak. 

 It was one of the most vigorous tritici strains which has been obtained, 

 but it was incapable of attacking rye, Agropyron repens, or oats with 

 any degree of success, after having been kept on barley for a number of 

 generations. The rust transferred readily to Bromus tectorum and was 

 transferred from this host again to Bromus tectorum and B. hordeaceus, 

 but it acquired no new power as a result of its sojourn on B. tectorum. 

 Elymus virginicus was used in an attempt to get the rust to transfer to 

 Agropyron repens but without success, only one small uredinium develop- 

 ing on one of the 31 inoculated leaves. Agropyron smithii, which is a 

 congenial host, was inoculated and transfers then made to Agropyron 

 repens in order to further test the taxonomic relationship theory. The 

 results, however, were disappointing. Successive transfers were made to 

 rye with urediniospores from a large uredinium which developed in one 

 set of inoculations, but the rust died after three successive inoculations 

 had been made. 



