8. F. Armstrong 63 



(e) The parent wheats. 



The varieties of wheat chosen for the main experiment were Wil- 

 hehnina and American Chib. It is of interest to note that these varieties 

 differ in several important respects, e.g. : 



W ilhdmina American Cliih 



Beardless ear Bearded ear 



Medium-lax ear Dense ear 



White chaff Red chaff 



Medium-short straw Long straw 



Starchy grain Fhnty grain. 



Under equal conditions American Club also matures earUer than Wil- 

 helmina. The main point in this connection, however, is that under 

 normal conditions American Club is immune to Yellow Rust, whilst 

 the other variety is moderately susceptible. 



Both varieties are susceiDtible to the Brown Rust (P. iriticina, Erikss.), 

 but, fortunately, this species did not interfere with the observations on 

 Yellow Rust. Brown Rust does not usually make its appearance in the 

 uredo stage in the Cambridge district before the middle of June. Again, 

 so long as the host remains green there is no difficulty in distinguishing 

 the one rust from the other. Occasionally, when the fohage of a plant is 

 beginning to shrivel up, some doubt may occur; but such cases are rare. 



In June 1916, the cross (No. 120) Wilhelmina ? American Club ^ was 

 made. About 20 grains were obtained, and these were planted in the 

 breeding cage on September 30th. 



Section II. THP] EXPERIMENTAL RESULTS. 1917—1020. 



(1) The F-^ plants, 1917. 



The F^ plants had ample space and grew vigorously during 1917, 

 a season that was remarkable for the comparative mildness of the rust 

 attack in the Cambridge district. 



Hot weather was general from May until the end of July, and the 

 rainfall was moderate except during July, which was a very wet month 

 (see Table I). The F-^ plants had a moderate attack of Yellow Rust, and 

 were harvested about the middle of August. 



A portion of the grain from these plants was sown on November 9th 

 in rows numbered 1 to 42. In the following year on February 26th a 

 further sowing was made in rows numbered 43 to 82. The object in 

 making two sowings was partly to lengthen the period during which 



