THE BURBAXK CHERRY 123 



It will be recalled, too, that a specific illus- 

 tration of the formula according to which 

 such recurrence takes place, was found in 

 Professor Castle's experiments in crossing a 

 black guinea pig with a white one; in which 

 case, although all the offspring were black, 

 the quality of whiteness reappeared in one- 

 fourth of the descendants of the second filial 

 generation. 



Now it should be observed that this ratio of 

 one in four is a ratio that has been found to hold 

 good in a very great number of experiments 

 applied to various races of animals and plants, 

 when a cross has been made and a record kept of 

 the results with reference to a single pair of unit 

 characters, such as blackness versus whiteness 

 in the case of the guinea pigs. In such a 

 case, where the offspring of the second filial 

 generation are interbred, it has been clearly 

 demonstrated that, on the average, one- 

 fourth of the offspring of the second filial 

 generation will resemble the paternal grand- 

 parent, and one-fourth the maternal grand- 

 parent; the remaining half being of mixed 

 heredity. 



Stated otherwise, there is an even chance that 

 in any group of four offspring of the second filial 

 generation, one individual will resemble each 



