Heredity 



159 



recessives, one-fourth that are constant dominants, and 

 one-half that are dominants to all appearances, but which 

 in the next generation break up again into dominants 

 and recessives. This one-half part that breaks up into 

 the two characters are the true hybrids; but they are 

 hybrids only in the sense that they hold each of the two 

 parental characteristics roundness and angularity in 

 their purity and not as blends or intermediates ; and these 

 two characteristics reappear in all succeeding generations 

 in a definite mathematical ratio. Proportionally, these 

 facts may be expressed as follows : 



1900. 



Iseed 



1901. 



8R 



16 R 



It will be seen that two-thirds of the dominants break 

 up the following year into one-fourth constant dominants, 

 one-fourth recessives, and one-half that again break up, 

 the half that break up being the hybrids. This formula 

 for the hybrids is Mendel's law. In words, it may be 

 expressed as follows : Differentiating characters in plants 

 reappear in their purity and in mathematical regularity 



