1908.] 



Rust in Wheat. 



249. 



If so, we might loosely describe the results as transferring 

 immunity to Michigan Bronze and susceptibility to the " Club " 

 wheat. 



The crossbred plants proved to be very susceptible to yellow 

 rust, for their foliage and even the ears were as badly attacked 

 as the Michigan Bronze growing alongside. They could be 

 distinguished from the latter by the shape of the ears, which 

 were not so lax, though they were not so dense as those of the 

 " Club " wheat. In spite of the severity of the attack these 

 plants produced a fair crop of grain, the vigour generally 

 associated with hybrids being in their favour. From this over 

 2,000 plants were raised in the open and several hundred 

 in pot cultures for demonstration and experimental work in 

 the laboratory. The plots growing in the open were badly 

 diseased by the end of May (1906). A close inspection of 

 these showed that, there were many plants completely free 

 from the parasite. Even when the dying leaves at the bases 

 of the plants were examined no signs of it could be found. 

 Such plants were kept under almost daily observation until 

 ripening time, and they were found still to retain their capacity 

 to resist the attacks of yellow rust. To anyone who saw the 

 plots it was inconceivable that the plants which remained 

 immune did so owing to lack of opportunity of becoming 

 infected, for the rust- coated leaves of contiguous plants 

 were blowing against them and frequently coating them with 

 powdery masses of spores. In fact, so much rust was present 

 that the surrounding soil was coloured by it. The descendants 

 of the hybrid plants then were of two sorts, one liable to ; and 

 the other immune to, the attacks of yellow rust. Between the 

 beginning of June and the middle of July a statistical examina- 

 tion of the plpts was made with the object of determining the 

 proportions of these two classes. If susceptibility and 

 immunity were a pair of unit characters, then it was known 

 that there should be on the average three of the rust-susceptible 

 plants present to each rust-immune individual. 



The result was that 1,609 of the former and 523 of the latter 

 were found, a close approximation to the expected proportion 

 of three to one. 



Previous experiments made with wheats with similarly 

 shaped ears to those used as parents in this case had shown 



