RESISTANCE OF VARIETIES OF TIMOTHY. 



15 



When the timotliy was about 2 inches liigh, it was thinned to 10 

 plants or less in a ])ot and the first leaf of each plant was inoculated 

 by placing on it, by means of a flattened inoculating needle, a small 

 quantity of fresh nredospores. The pots were placed in a moist 

 chamber for 48 hours, as described on page 8 of this paper, and 

 were then removed and allowed to stand for 17 to 21 days, when 

 final notes were taken. The ])ercentage of noninfection from uredo- 

 sporo inoculations of timothy selections and the rust-resistance 

 percentages of tliese selections in the field during 1908 and 1909 

 are shown in Table III. 



Table III. — The percentage of noninfection from uredospore inoculations of timothy 

 selections and the rust-resistance percentages of these selections in the field during 1908 

 and 1909. 



1 Discarded. 



The percentages of inoculated leaves which did not develop rust do 

 not correspond with the rust-resistance figures obtained in the field. 

 This is accounted for by the fact that even the most rust-resistant 

 varieties of both grasses and cereals will develop rust to some extent 

 when carefully inoculated in the greenhouse with the rust most com- 

 mon on the respective hosts. It is always noticeable, however, that 

 although every moculated leaf of a rust-resistant strain may be 

 affected, the rust infection is much less severe on them than on sus- 

 ceptible varieties. Therefore in making observations on rust resist- 

 ance not only the percentage of leaves developing rust pustules but 

 also the severity of the infection must be considered. Although such 

 observations are not noted in Table III it was found that, in so far iis 



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