22 A STUDY IN CEREAL RUSTS 



Attempts to transfer directly from wheat were unsuccessful. Not 

 a large numbe/ were made, but of the 46 attempts no leaves produced 

 pustules and only 2 of them developed flecks. The flecks were very 

 small and not very distinct. In this connection it may be mentioned 

 that when oat leaves were inoculated with aecidiospores derived from 

 wheat teleutospores one leaf out of 56 developed pustules. This ap- 

 pears to indicate that direct transfer can be made. The success of the 

 inoculation was probably not due to the fact that the rust had passed 

 through the barberry stage. This seems especially true since the 

 other cereals behaved in the same way toward the aecidiospores as 

 they did toward the corresponding uredospores. 



Inoculation after exposure to ether- 

 Only 30 leaves were inoculated after having been in ether fumes 

 for from 3 to 5 minutes. No pustules were developed, but 10 of the 

 leaves were flecked. There was a perceptible difference between the 

 check plants and those of this series, although it cannot be said that 

 the results were very striking. 



INOCULATIONS ON OATS AND RYE AFTER THE USE OF BARLEY AS A 



BRIDGING FORM 



The work done on bridging species has already been mentioned. 

 Since it is almost impossible to infect oats directly with wheat aecidio- 

 spores or uredospores, attempt was made to transfer aecidiospores de- 

 veloped from wheat teleutospores first to barley and then to infect 

 oats with the resulting uredospores. The attempt was made with 

 fourth- and fifth-generation uredospores from barley, these uredo- 

 spores having been derived from wheat-rust aecidiospores. Successful 

 infection took place in one out of 39 attempts, 4 leaves being distinctly 

 flecked. 



The rye plants are possibly slightly more severely attacked if the 

 rust is transferred first to barley, 16 out of 19 of the plants inoculated 

 becoming infected. 



SUMMARY OF EXPERIMENTS WITH PUCCINIA GRAMINIS TRITICI 

 Wheat rust to: 



Barley fg- 



Rye -g^; 20 flecked 



Rye after exposure to ether -$; 43 flecked 



Rye after barberry and 4 generations on barley -J-| 



Oats, uredospores T -g-; 2 flecked 



Oats, aecidiospores -^ 



Oats after exposure to ether --$ ; 10 flecked 



Oats after barberry and 4 generations on barley -^ ; 4 flecked 



