26 LUTHER BURBANK 



grandparent, were black, may be considered a 

 berry of pure white strain. From the moment 

 of its appearance it is a fixed type as to color. 



But, unfortunately, it is not sufficient that the 

 white blackberry should breed true as regards 

 the quality of whiteness alone. There are other 

 qualities of size and flavor and many others that 

 are equally essential. And these, it would 

 appear, include sundry other pairs of unit char- 

 acters sweetness versus sourness, large size 

 versus small size, profuse bearing versus scant 

 bearing, and the like that are represented in 

 our berry by mixed factors. 



In the Mendelian view, it will be recalled, 

 there are always two factors representing any 

 pair of unit characters. 



In the case of our white blackberry, in the 

 Mendelian view, both factors for the unit char- 

 acter blackness-versus-whiteness are of the white 

 order; or in the technical phrase, the berry is 

 "homozygous" for that pair of factors. 



But as regards, let us say, the factor for the 

 unit character bigness-versus-smallness the case 

 is different; for this character may chance to be 

 represented by one factor of each type. In other 

 words, resorting again to the technical language, 

 the berry may be "heterozygous" as regards that 

 character. 



