350 LUTHER BURBANK 



is a second pigment involved. The "Crystal 

 White" berry, it will be recalled, was not white 

 but brownish in color. There were thus trans- 

 missible two pairs of unit characters involved as 

 regards the matter of color, namely ( 1 ) black ver- 

 sus white, and (2) yellow or brown versus white. 



The black factor or determiner dominated 

 absolutely in the first generation; but in the 

 second generation a certain number of germ cells 

 were paired in such a way as to eliminate the 

 black but retain the yellow factor. 



It required a third mixture of the germ-cell 

 factors to produce a union in which neither black 

 nor yellow factors appeared, the offspring of this 

 union being of course the pure white blackberry. 



The presence of the yellow factor accounts for 

 the further fact, to which reference should be 

 made, that there were various intermediate types 

 of berries, neither black nor white, which ap- 

 peared in successive generations but which are 

 eliminated by selection as they did not fall in 

 with our plan of development of a white race. 



The explanation just given makes it clear 

 that, once a union of germ-cell factors having 

 only the white element was effected, the black 

 and the yellow factors being entirely eliminated 

 from that particular individual, the germ cells 

 arising from that individual would necessarily 



