CHAPTER VI 



EXPERIMENTAL HYBRIDIZING 



WITHIN the limits of the Linnsean species it has been found 

 that varieties, or races, or breeds, are generally perfectly fertile 

 when crossed, and in recent years these fertile crosses have 

 been much studied. In some cases it has been found that a 

 character that is different in two parents blends in the offspring, 

 and may or may not separate again; in other cases, however, 

 a character that differs in the parents does not blend, and all the 

 offspring of the first generation are like one of the parents. The 

 inheritance is alternate. If hybrids of this kind are bred to 

 each other, the original character of one of the grandparents 

 may reappear in some of the offspring, the contrasting char- 

 acter of the other grandparent in others. These cases follow 

 what is known as Mendel's law. 



It is sometimes stated that Mendel's law applies only to 

 crosses between varieties, and this is true for many cases ; but 

 characters that are entirely new to the race may also follow 

 Mendel's law ; and if the appearance of one new character suf- 

 fices to characterize a new form as an elementary species, we 

 must conclude that the characters of some elementary species 

 also follow Mendel's law of alternate inheritance. 



Mendel's Law 



In 1865 Mendel published the results of an elaborate series 

 of experiments that he had made with varieties of peas. It is 

 strange that so important a discovery should have been entirely 

 neglected for thirty-five years, especially since the question of 



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