436 Journal of Agricultur-al Research voi. x, N0.9 



Many inoculation experiments were made with known strains of P. 

 graminis secalis and P. graminis iritici on Agropyron repens, and the 

 results confirm the conclusions to be drawn from the results given in 

 Table III. The grass is very susceptible to P. graminis secalis, while 

 normal infection with P. graminis tritici is rare. 



It is quite probable that the successful infections on wheat, recorded 

 as No. 3, 4, and 10 (Table III), resulted from chance spores which may 

 have been blown to the Agropyron repens before it was taken from the 

 field. It is very doubtful whether uredinia actually were developed on 

 the grass in the field. The reason for suspecting that they were not is 

 that on the wheat leaves which became infected single uredinia were 

 produced, indicating the probable source of infection as being one or, 

 at most, a very few spores. If the infection had resulted from the 

 spores taken from a uredinium, several uredinia would probably have 

 developed on the wheat. There is evidence that Agropyron repens does 

 not become infected with P. graminis tritici in nature even when oppor- 

 tunities for infection are very favorable. This is shown as a result of 

 inoculations No. 14. The rusted grass plants were growing in a wheat 

 plot which had been thoroughly and frequently sprayed with uredinio 

 spores of P. graminis tritici in suspension in water. The wheat plants 

 were all very heavily rusted, and it was supposed that the quack -grass 

 plants might be infected with P. graminis iritici also, because they had 

 been inoculated in the same way, but it will be seen by reference to 

 Table III that such was not the case. Only P. graminis secalis occurred 

 on the quack-grass plants. 



Agropyron repens is very commonly and very heavily rusted with P. 

 graminis secalis. It is often among the first of the grasses to become 

 rusted in the spring. Severe epidemics may develop before other grasses 

 become even moderately rusted. 



It is quite apparent from Table IV that Agropyron smithii may be 

 affected with both P. graminis tritici and P. graminis secalis. Artificial 

 inoculations show that both can attack the grass about equally well, 

 especially when young seedlings are inoculated. It is interesting to 

 note that in No. 5 nearly every leaf of wheat, rye, and barley became 

 infected. This might very easily at first glance indicate the occurrence 

 of a single biologic form capable of attacking all three of these cereals. 

 The original rust on the grass, however, was unquestionably a mixture of 

 P. graminis tritici and P. graminis secalis. This is shown clearly in 

 diagram i. The rust on rye was transferred to rye or barley 14 succes- 

 sive times during a period of 8 months and wheat was inoculated 8 times, 

 but no uredinia developed on any one of the 107 inoculated leaves. Both 

 rye and barley, on the other hand, were easily infected, showing that the 

 rust originally developed on rye was P. graminis secalis. 



