BIOLOGIC FORMS 17 



was stripped from others and the inoculations then made. The results 

 were not different from those obtained on check plants. Only one 

 pustule developed on one leaf out of a total of 28. Six of the remain- 

 ing leaves were flecked, but the flecks remained small. In no case did 

 the virulence of infection equal that on plants grown in highly fertilized 

 soil. 



The stem rust of oats, then, can be transferred directly to rye. 

 This was accomplished most easily when the plants were grown in 

 heavily manured soil. Exposing them to various anesthetics before 

 inoculation seems to increase the virulence of infection slightly, while 

 leaf injury had no apparent effect. In the various trials, under differ- 

 ent conditions, 27 out of 236 leaves developed pustules and 73 were 

 flecked. Under conditions which might exist in the field 12 out of 73 

 leaves produced pustules and 22 were flecked. 



INOCULATIONS ON WHEAT 



The stem rust of oats can be transferred to wheat only with great 

 difficulty. Carleton (1899, p. 60) did not succeed in obtaining infec- 

 tion in his experiments. Freeman and Johnson (1911, p. 22) made 

 100 inoculations but none was successful. They report, however, that 

 Derr was able to make transfers. 



Inoculations under ordinary conditions 



The fact that the oat rust is transferred with great difficulty to 

 wheat became apparent very soon. Out of 108 inoculations only one 

 was entirely successful, although 5 leaves became slightly flecked. 

 Very evidently the infection threads, after having grown among the 

 tissues of the leaf, must have died, since only very minute flecks de- 

 veloped, and these in only a few cases. 



Effect of anesthetics 



Plants were inoculated after exposure to ether and chloroform 

 for periods of from 1 to 15 minutes. The best results were obtained 

 after exposure to ether for 5 minutes. In this case 3 leaves out of 50 

 developed pustules while all the other leaves were flecked. These 

 pustules and flecks appeared 10 days after inoculation, this being 

 slightly longer than a normal incubation period. None of the check 

 plants showed any distinct signs of successful infection, while the 

 flecks on the plants which had been exposed to ether were very con- 

 spicuous, forming a sharp contrast with the check plants. These 

 flecks were scattered all along the line of inoculation and had the 

 appearance of young, unruptured pustules. 



This series offered the best evidence that anesthetics may have 

 some influence in rendering a plant more susceptible to a rust than it 

 would otherwise be. In subsequent trials, exposing the plants for a 



