HEREDITY 189 



the dominant character, but also individuals which presented the 

 recessive character. Such a fact also was known in a good many 

 instances. But Mendel discovered that in this generation the numer- 

 ical proportion of dominants to recessives is on an average of cases 

 approximately constant, being in fact as three to one. With very con- 

 siderable regularity these numbers were approached in the case of 

 each of his pairs of characters. 



"There are thus in the first generation raised from the cross- 

 breds seventy-five per cent dominants and twenty-five per cent re- 

 cessives. 



" These plants were again self-fertilized, and the offspring of each 

 plant separately sown. It next appeared that the offspring of the 

 recessive remained pure recessive, and in subsequent generations never 

 produced the dominant again. 



" But when the seeds obtained by self-fertilizing the 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 dom- 

 inants, 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 domi- 

 nant offspring being to those with mixed offspring as one to two. 

 Here it is seen that the seventy-five-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-fertilizing the original 

 cross-breds the same proportion was always approached, namely: 

 25 dominants, 50 cross-breds, 25 recessives, 

 or ID : 2DR : 1R. 



"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 pro- 

 portions, follow the same law, namely, that there are three dominants 

 to one recessive. The recessives are pure like those of the last genera- 

 tion, but the dominants can, by further self-fertilization, and exam- 

 ination or cultivation 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. 



