FIXING GOOD TRAITS 25 



developing a new race is largely dependent upon 

 the extent to which he has been able to induce 

 the plants with which he experiments to vary. 



So now, when he attempts to restore fixity to 

 something that he has purposely made unstable, 

 he is at once confronted with the danger of 

 undoing much that he has accomplished. The 

 measure of success that he can hope to attain 

 will depend very largely upon the particular 

 kind of unit characters that he has combined in 

 the product that he now wishes to make stable. 



We have seen that, as between the opposing 

 members of any pair of unit characters, it is 

 usually discovered that one has prepotency or 

 dominancy over the other. When blackberries 

 of normal color, for example, are crossed with 

 the white blackberry, the progeny are all black, 

 because this color is the dominant member, and 

 white the recessive or negative member of the 

 pair of unit characters. But we saw also that 

 the recessive trait will reappear in the succeed- 

 ing generation, and that when it does reappear, 

 it will, within certain limits, thereafter breed true. 



So, when in the second generation we again 

 produce a white blackberry, we have a type 

 which is fixed as regards the particular character 

 of whiteness. In other words, our white black- 

 berry, even though both its parents, and one 



