122 LUTHER BURBANK 



who has not been confronted by them in actual 

 practice. 



If I have been able to overcome them 

 in a relatively brief number of years, it is 

 because I have worked persistently, selected 

 with discrimination, and invoked the aid of 

 the bees in making experiments on a large 

 scale. 



The modern student of heredity, in dealing 

 with cases such as this, is able to give a somewhat 

 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 con- 

 sider 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. 



