LUTHER BURBANK 



tangible illustration of the difficulties involved 

 with the aid of simple mathematics. He does this 

 on the basis of the Mendelian interpretation of 

 the method of transmission of unit characters of 

 which we have learned something in an earlier 

 chapter. 



THE COMPLICATIONS ILLUSTRATED 



It will be recalled that we had occasion to 

 consider such opposing traits as blackness and 

 whiteness in our white blackberry, large size and 

 dwarf size in the case of our walnut trees, stone 

 fruit versus stoneless fruit in cases of our plums, 

 and perfume versus lack of perfume in cases of 

 the calla, as pairs of unit characters that are 

 mutually exclusive in case of any individual, but 

 which both tend to recur in the second generation 

 of hybrid offspring. 



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

 tion 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 



[218] 



