10 The Problems 



dominants were examined and sown it was found that 

 the dominants were not all alike, but consisted of two 

 classes, (1) those which gave rise to pure dominants, and 

 (2) others which gave a mixed offspring, composed partly 

 of recessives, partly of dominants. Here also it was found 

 that the average numerical proportions were constant, those 

 with pure dominant offspring being to those with mixed 

 offspring as one to two. Hence it is seen that the 75 per 

 cent, dominants are not really of similar constitution, but 

 consist of twenty-five which are pure dominants and fifty 

 which are really cross-breds, though, like the cross- breds 

 raised by crossing the two original varieties, they only 

 exhibit the dominant character. 



To resume, then, it was found that by self-fertilising 

 the original cross-breds the same proportion was always 

 approached, namely 



25 dominants, 50 cross-breds, 25 recessives, 



or \D : 2DR : IR. 



Like the pure recessives, the pure dominants are 

 thenceforth pure, and only give rise to dominants in all 

 succeeding generations studied. 



On the contrary the fifty cross-breds, as stated above, 

 have mixed offspring. But these offspring, again, in their 

 numerical proportions, follow the same law, namely, that 

 there are three dominants to one recessive. The recessives 

 are pure like those of the last generation, but the dominants 

 can, by further self-fertilisation, and examination or culti- 

 vation of the seeds produced, be again shown to be made 

 up of pure dominants and cross-breds in the same proportion 

 of one dominant to two cross-breds. 



The process of breaking up into the parent forms is 

 thus continued in each successive generation, the same 



