RUST-RESISTANCE 155 



most afflicted plants one could well imagine were 

 numbers of individuals with healthy green foliage. 

 Their leaves and stems were dusted over with the 

 loose spores shed from neighbouring plants, but in 

 spite of every chance of becoming infected they 

 remained without a single rust pustule until the 

 crop was ready for harvest. Although one sees 

 similar cases yearly the novelty of it still remains, 

 and I often wonder at the almost Eastern com- 

 posure with which a number of our distinguished 

 visitors from the London Conference of Genetics 

 examined these plots plant by plant. 



On determining the numbers of rusty and 

 healthy plants they were found to be present in 

 the proportion of approximately three of the 

 former to one of the latter class (1609 to 523). 

 The approximation was sufficiently close to indicate 

 that rust resistance was, in Mendelian language, 

 a recessive character and that consequently these 

 resistant plants would breed true to this feature 

 in the next and in succeeding generations. An 

 extensive series of trials proved that this was the 

 case. Several hundred cultures were raised from 

 resistant and susceptible individuals with the 

 result that the former class yielded resistant 

 plants only, whilst the latter either bred true to 

 extreme susceptibility or produced a susceptible 

 and resistant offspring, again in the proportion of 

 three to one. At this stage then we had the first 

 proof that the plant breeder if given a suitable 



