248 



Rust in Wheat. 



[JULY, 



These varieties have been tested season by season by growing 

 them in alternate rows with the most susceptible varieties 

 which could be found. They have thus been surrounded by 

 quantities of rust and have had every opportunity of becoming 

 infected. In these open air trials, Einkorn and " Club " have 

 remained perfectly free from disease, whilst Little's Anti- 

 mildew has only shown a few of the characteristic flecks of 

 yellow rust. Further, these varieties have been grown under 

 exceedingly unfavourable conditions in the laboratory, and 

 the spores of yellow rust applied to them without producing 

 more than the slightest symptoms of disease. In some cases 

 small yellow patches appeared on the foliage where the rust 

 spores had been applied, but these patches failed to produce 

 crops of viable spores. For all practical purposes then we 

 may speak of these varieties as immune to the attacks of 

 yellow rust. 



These and also a few others have been crossed with sus- 

 ceptible varieties in order to determine whether this feature 

 of rust resistance is a unit character comparable, for instance, 

 with dwarfness or fairness in the case of the peas already 

 quoted. 



The clearest results are those afforded by a cross between 

 " Club " wheat and Michigan Bronze. This latter variety was 

 chosen as a parent sole]y because of its extraordinary liability 

 to the attacks of yellow rust. Under our experimental con- 

 ditions it is one of the first to show signs of rust, and by the time 

 the ears are pushing through the sheaths the foliage and stems 

 are as a rule so covered with rust pustules that one can hardly 

 distinguish the normal green colouring of the plant. The rust 

 then spreads to the ears, covering the chaff, the beard and the 

 grain moie or less completely. As a rule the attack is so severe 

 that the plants fail to set any grain capable of germination. 

 Michigan Bronze differs from " Club " wheat in producing 

 lax or loosely set ears. Previous experiments had shown that 

 laxness and denseness of the ears were unit characters. If, 

 then, as the result of this crossing, varieties (i) similar to Michigan 

 Bronze in ear shape but immune to the attacks of yellow rust, 

 and (2) similar to " Club " wheat but liable to the attacks of rust, 

 could be obtained, immunity and susceptibility to rust would 

 also be unit characters. 



