MENDELISM 27 



D x R 



(susceptible) (immune) 



D[R] (all affected) 



I 



DD D[R] D[R] RR 



i. e. one quarter would be insusceptible. But this does not 

 complete Biffen's results, for this large-eared grain was 

 found dominant, as regards size, to the small-eared grain. 

 So we have two dominant characters, viz. Susceptibility to 

 Rust and Large size, contrasted with the two characters 

 Immunity and Small she — a case of di-hybridism com- 

 parable to the tall coloured peas and the dwarf whites, and 

 we can construct the Fij generation thus — 



LR x SI 



LR 



9 LR 3 SR 3 LI i SI 1 



letting L = Large, R = Susceptibility to Rust, S = Small, and 

 I = Immunity. 



According to this there should be, in this Fij generation, 

 about 3 large immune plants out of every 16 ; and these, 

 being immune, will breed true. So that Biffen has 

 transferred the immunity of the foreign wheat to what in 

 other respects closely resembles the British variety. Last 

 year there were several acres of this immune wheat growing 

 on the experimental farm at Cambridge. Surely this is 

 likely, from an economic and commercial point of view, to 

 prove one of the most important experiments ever performed. 

 He has also informed me that last year this corn yielded 

 about io bushels per acre more than the ordinary British 

 wheat. 



1 This is what would almost certainly occur if these were only the factors 

 named, but, as a matter of fact, the result was much more complicated. 



