84 Mendiiiun InlKritance tniii Yrlhnr Rust In Wlniif 



therefore relatively three times as numerous on the "exterior" as on 

 the "interior" plants. 



An experiment was planned in order to find out if possible to what 

 relative extent such "circumstances as wide spacing and large amounts 

 of available nitrogen were responsible for the increased severity of attack 

 observed. The varieties included in the test were tlie two parent wheats 

 Wilhelmina and American Club and the following extracted F^ tjrpes 

 descended from these parents: 



GG/'djd, a rust-resistant type, with white chaff and beardless medium- 

 lax ears (a resistant Wilhelmina type). 



82/14/a, a rust-resistant type, witli red chaS and beardless medium- 

 lax ears. 



75/7 /c, a susceptible type, with wliite chaff, and dense bearded ears 

 (a white chaffed susceptible American Club type). 



75/1 1/(^, a dense eared, bearded, susceptible type with red chaff'. 

 (This was practically a susceptible American Club.) 



Four beds, A, B, C, and D, each 4 feet wide, were laid out, and each 

 variety was sown across these in a single row 16 feet long. A space of 

 () inches was allowed between each row, but the grains were sown 2 inches 

 apart on beds A and D, and 12 inches apart on B and C. The grain was 

 sown on November 2'lth, 1919, and a fairly uniform plant was obtained. 



On May 4th, 1920, beds A and B were top-dressed witli nitrate of 

 soda at the rate of 7 cwt. ))er acre. It should be noted that, although 

 beds C and D received no nitrate, the soil was in good condition after 

 the potato crop of the previous year; the comparison to be made was not 

 between starved and overfed plants, but between plants grown under 

 normal and abnormal conditions as regards space and nitrogenous 

 manuring. 



Yellow Rust was first seen on May 7th on one or two plants of 75/11/rf 

 and Wilhelmina (exterior row) in each case on bed A. By May 12th rust 

 attack had become general on all the susceptible varieties, the only 

 difference being that it was of a less pronounced character on Wilhelmina. 

 At that date no sign of attack could be found on any of the resistant 

 varieties although their foliage was literally ])owdered daily with nredo- 

 spores from their susceptible neighbours. 



The condition of the plants on May 21st and June 2nd is shown in 

 Table XII in which the numerator of each fraction indicates the number 

 of plants rusted out of the total surviving plants of each variety on each 

 bed (given as the denominator). 



