S. F. Armstrong 79 



versity Seed Farm near Cambridge. The ground, wliich had received 

 a dressing of 10-12 loads of farmyard manure and had been cropped with 

 potatoes in the previous year, was in good condition for wheat growing. 

 Cultures of tlie Fo, F^ and F^ generations of the cross Wilhelmina 

 X American Club were raised, in addition to others. 



During the winter 1919-1920 abnormally mild weather was almost 

 continuous. One interesting feature associated with this mild weather 

 was that freshly formed uredospores of Yellow Rust were found from 

 the first week in October, 1919, onward to the following summer on 

 certain susceptible wheats which had been sown at the end of August, 

 1919. During the spring and summer of 1920 the weather was favourable 

 to the normal growth of the cultures (see Table I). 



Yellow Rust attack was general amongst the field cultures at a very 

 early date, and by the beginning of May in many of the susceptible 

 cultures all the plants were rusted. By the first week in June the attack 

 was at its Jieight. 



(n) Further Fn statiMici nhUiined in 1920. 



In raising the i^., generation (cross No. 120) in 1918, no attempt was 

 made to keep separate the grain of the several F^ plants. In a later 

 cross, however (Brooker's x American Club, cross No. 154), this was done, 

 and several distinct F^ famihes were raised in 1920. Two of these 

 families were examined in the same manner as the F^ of cross No. 1 20 

 had been in 1918 with the following results: 



A population of 198 7^., individuals raised fi'oni a moderately rusted 

 f J plant contained 42 badly rusted plants and fO whicli remained abso- 

 lutely rust-free. On the remaining plants, the rust varied from the 

 merest trace up to a moderate attack. 



The second i^, family consisted of 2-58 individuals and was raised 

 from an F-^ plant which had a shght attack only. It contained 62 badly 

 rusted and 61 perfectly rust-free plants, the remaining 135 indixaduals 

 being attacked to not more than a moderate extent in any case. 



These figures indicate that similar results are obtained whether the 

 analysis be made upon the progeny of separate i^j plants or upon the 

 offspring of several ^''j^'s combined. 



The small F^ crop of the original Wilhelmina x American Club cross 

 grown in 1920 contained 114 plants, and by the end of July it was found 

 that 86 of these were rusted and 28 were rust-free. Of the rusted plants 

 six had a much severer attack than Wilhelmina grown under similar 

 conditions. 



