8. F. Armstrong f>5 



mixed stock of "Jap." On May 12th, 1920, out of 57 plants in culture 

 3/16/29, 41 were attacked by Yellow Rust; on the same date the 66 plants 

 in culture 1/4/10 were free from infection. Culture 3/16/29 was about 

 7 days earlier than the other, and all the plants in it were rusted by 

 June. Only a few slight traces of attack and some " flecked" plants 

 were found on culture 1/4/10 before harvesting. 



The original intention in growing these cultures was merely to see 

 whether the extracted types bred true to resistance and siisceptibihty 

 respectively, but, at harvest-time, they seemed to offer very favourable 

 material on which to determine the loss directly due to Yellow Rust. 

 In the first place, their identical — or almost identical — morphological 

 features appeared to afford safe ground as a basis for such a comparison. 

 Again each culture had remained free from attack by Brown Rust or 

 other fungi up to the time the plants were pulled — July 23rd — so that the 

 difference in yield was chiefly, if not entirely, due to the presence or 

 absence of Yellow Rust. Further, each plot was sown on the same day. 

 grown under identical conditions side by side, and no loss of grain had 

 occurred at harvest-time. In one respect only there was a sUght cUiTerence 

 between the cultures, viz. in the number of plants per row, this being 

 due to the rather poorer germination of the grain in the susceptible 

 cultures. The results were as follows: 



It will be seen that the weight of ears in the "mixed" culture was 

 reduced by 18 per cent, per plant, and by nearly 50 per cent, per plant 

 on culture 3/16/29. The reduction per unit area was still greater in each 

 case. Had the grain been threshed out and weighed separately, it is 

 certain that the differences would have been still more striking, but this 

 unfortunately was not done. 



These figures indicate that a variety of wheat having on the average 

 a moderate degree of susceptibihty (comparable with, say, Square Head's 

 Master) may give a yield at lea.st 25 per cent, below that obtainable 

 from almost precisely the same form when rendered rust-resistant. 



