Virulency of Tilletia carles on Wheat Varieties

IN a letter in NATURE of Feb. 16, 1929, vol. 123, p. 243, I stated that certain wheat varieties thought to be resistant to bunt were susceptible when they were contaminated with the bunt spores that had been produced on those varieties. It was inferred that, in the same way that the plant breeder could select a unit from a population of a variety for resistance to a certain pathogen, so the mycologist might select a pathogen from an analogous population to which the given host was susceptible.