14 A STUDY IN CEREAL RUSTS 



In the second trial plants were again exposed to ether and chloro- 

 form, but the time was increased from 15 to 20 minutes. An attempt 

 was made to insure conditions for successful infection. It was ob- 

 served that a film of moisture formed on the leaves at night and the 

 temperature was moderate, insuring successful infection if that was 

 ordinarily possible. 



Of the 20 leaves exposed to ether, 11 became very distinctly 

 flecked, but there were no evidences whatever of successful pustule 

 formation. In the chloroform series one leaf out of 20 produced a 

 small pustule and 8 became clearly flecked. -There were 20 check 

 leaves, and, of these, 4 became flecked. The flecking was, however, 

 rather indistinct. 



Out of a total of 193 inoculations only 3 resulted in pustule-for- 

 mation, and these only after exposure to chloroform. Of the remain- 

 der, 31 were flecked, but this flecking was not always sharp on the 

 control plants. In the other cases, however, it was distinct. The spots 

 were always less than one millimeter in diameter, and usually much 

 smaller. It appeared that this small area of the leaf had been killed, 

 thus preventing the further spread of the mycelium and precluding 

 the possibility of pustule formation. In no case was there any indica- 

 tion whatever that large areas of the leaf were involved, as was the 

 case when rye was inoculated with the rust from barley. In this con- 

 nection it may be mentioned that Freeman and Johnson (1911, p. 19) 

 were able to get 7 successful infections out of a total of 35, but the 

 pustules were always very small. It may be that the difference is due 

 to the use of various strains of the rust. The fact that there are strains 

 of the same biologic form seems to be quite definitely indicated. In 

 any case this seems to furnish an example of rather extreme incom- 

 patibility between host and parasite. In some cases it would seem that 

 the infection threads of the fungus are checked almost immediately ; 

 or that they may gain a temporary foothold, only to kill the cells upon 

 which they depend for nourishment and then develop but little further. 



INOCULATIONS ON WHEAT 



There is no question but that the stem rust from barley, in this 

 country, usually passes to wheat with practically the same degree of 

 readiness with which it passes to barley. In the trials made with this 

 form this appeared to be the case whether susceptible or resistant forms 

 of wheat were used. Inoculations on Arnautka, Khapli, and emmer 

 show that the barley rust is quite as capable as is the wheat rust of 

 attacking these varieties. 



Pritchard (1911-1, pp. 181, 182) cites evidence tending to show 

 that the forms on wheat and barley in North Dakota are distinct. This 

 is not the case, however, with the strains used in the experiments in 

 Minnesota. 



