ON THE SMALL GRAINS 



in that there was a race of wheat known to be 

 immune to the yellow rust which had not hitherto 

 been thought of as solving the rust problem be- 

 cause it bore grain of very poor quality. 



To Professor Biffen, armed with his new knowl- 

 edge, it appeared that it should be possible to com- 

 bine this immune wheat of poor quality with sus- 

 ceptible races of wheat bearing a good grain in 

 such a way as to secure a new race that would 

 present the good qualities of each parent and 

 eliminate the bad qualities. 



So he crossed a race of wheat that bore a grain 

 susceptible to rust with the immune variety that 

 bore the grain of poor quality, and developed a 

 generation of crossbreds all of which were quite 

 as he had expected susceptible to the attacks of 

 the rust. 



To the untrained plant experimenter it would 

 have appeared that this experiment should be car- 

 ried no further. Progress was apparently being 

 made in the wrong direction; for whereas half the 

 parents were immune to rust, all of the children 

 were susceptible. 



But Professor Biffen knew, as we have already 

 seen, that susceptibility and immunity constituted 

 a Mendelian pair of hereditary factors. So he 

 knew that in the next generation one fourth of the 

 hybrid plants would be immune to rust. And this 



[69] 



