THE WHITE BLACKBERRY 



mere law of chance the union of these germ cells 

 brought together about one time in four two of the 

 cells having the recessive white factor; such union 

 resulted in a white individual. 



Meantime by the same law of chance the other 

 three matings out of the four brought together in 

 one case two black factors and in two cases a 

 mixture of black and white factors. 



As black is dominant, these individuals having 

 the mixed factors would be individually black 

 (just as those of the first cross were black) ; but 

 their progeny in due course will repeat the 

 formula of their parent by producing one white 

 individual in four. 



It should be explained that the Mendelian, in 

 expressing this formula, usually substitutes for 

 the word "factor," as here employed, the newly 

 devised word "allelomorph," although the less 

 repellent • equivalent "determiner" is gaining in 

 popularity. He calls the body substance of an 

 animal or plant a "zygote," and he describes an 

 individual that contains factors of a single kind, 

 as regards any pair of unit characters (say only 

 for blackness in the case "of our blackberries or 

 Professor Castle's guinea pigs) as a "homozygote" ; 

 contrariwise a body having both types of factors 

 (blackberries or guinea pigs of the second genera- 

 tion, for example) as a "heterozygote." 



[67] 



