THE WHITE BLACKBERRY 347 



after generation the white factors continue to be 

 produced in the germ cells, but the union with a 

 germ cell containing the black factor obscures the 

 result just as in the case of the first cross, because 

 the factor of blackness continues to be dominant. 



But, however long delayed, when a cell con- 

 taining the white factor or determiner does mate 

 with a similar cell, the offspring is white and — in 

 the older terminology — reversion or "atavism" is 

 manifested. 



A very simple and tangible illustration of the 

 phenomena in question is furnished by the ex- 

 periments in animal breeding made by Professor 

 William E. Castle of Harvard. These experi- 

 ments furnish a peculiarly appropriate illustra- 

 tion in the present connection because it chances 

 that the animals experimented with are compa- 

 rable to our blackberries in that they are respec- 

 tively black and white in color. 



The animals used in the experiment are guinea 

 pigs. 



An Illustration from the Animal World 



Professor Castle shows that if a black guinea 

 pig of a pure strain is mated with a white guinea 

 pig of a pure strain, all the offspring of the first 

 generation will be black; and it is therefore said 

 that blackness is preponent or dominant, and 



