HIS THEORY OF HEREDITY in 



parents. Intermediate conditions do not occur. 

 That one of the two parental qualities that alone 

 appears in the mongrels is called dominant ; the 

 other recessive. Second, in the formation of the 

 pollen or egg-cell the two antagonistic peculiar- 

 ities are segregated ; so that each ripe germ-cell 

 carries either one or the other of these peculiar- 

 ities, but not both. It is a result of the second law 

 that in the second generation of mongrels each of 

 the two qualities of their grandparents shall crop 

 out on distinct individuals, and that the recessive 

 quality shall appear in twenty-five per cent, of the 

 individuals, the remaining seventy-five per cent, 

 having the dominant quality. Such recessive in- 

 dividuals, crossed inter se^ should never produce 

 anything but recessive offspring." 



We have already seen that it is one of Mendel's 

 claims to distinction that he introduced to biolo- 

 gists the idea of unit characters, which can be 

 inherited independently of one another, but his 

 work leads to further reaching considerations than 

 this. In a previous article it was shown that de Vries 

 and others claim that by transmutation alone can 

 different species have arisen. In other words they 

 claim that development is not Continuous, . as 

 Darwin believed, but Discontinuous, just as the 

 face of nature presents us with discontinuous 

 species. Now Mendel's observations show us that 

 there is Discontinuity in Inheritance as well as in 

 Variation. It was once asserted that a mutation 

 was in danger of being swamped by inbreeding with 

 the normal form, but Mendel has shown that this ) 



