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 Biff en, 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 Biff en 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] 



