24 



A STUDY IN CEREAL RUSTS 



It will be noticed that the percentages of infection are practically 

 the same as are those developed from uredospore inoculation. This 

 is true also of the character of the infection. 



On the rye plants, for instance, there was the same characteristic 

 spotting and the same small, abortive pustules. The pustules on rye 

 were all very small and there was no observable increase in virulence. 

 The same .thing is true of einkorn. On oats but one rather doubtful 

 pustule developed, indicating that the aecidial stage in no way broke 

 down the barriers in this case. 



EXPERIMENTS IN 1913 



Iii the fall of 1912 the barberry bushes in the rust plat were sur- 

 rounded with badly rusted wheat straw, the rust being in the teleuto- 

 spore stage. In the spring of 1913 the aecidiospores were used in 

 inoculating the four common cereals and einkorn. The results were 

 surprising since it was supposed that the aecidia had been developed 

 from the wheat-rust teleutospore sporidia. The results of the various 

 trials are given below : 



RESULTS OF INOCULATIONS OF CEREALS WITH AECIDIOSPORES FROM FIELD BARBERRIES 



It will readily be seen that there would naturally be much doubt 

 as to the origin of these aecidia from wheat-rust teleutospore sporidia. 

 These aecidiospores were being used in spraying wheats in the rust 

 nursery for the purpose of developing a rust epidemic. The results 

 were very discouraging. There was a great deal of Agropyron repens, 

 badly affected with the teleutospore stage of Puccinia graminis, near 

 the barberry bushes. Experiments were therefore started to determine 

 whether or not the aecidia on barberries might not have been devel- 

 oped from this source rather than from the wheat-rust material. This 

 view seemed all the more reasonable when it was observed that the 

 Agropyron repens was very severely affected with the uredospore 

 stage of rust, while the wheat, although it had been thoroughly and 

 persistently sprayed with water containing the aecidiospores, had only 

 a few scattered pustules of rust. 



