of Heredity 31 



It has now been shown that the question whether in the 

 cross-bred zygotes in general the characters blend or are 

 mutually exclusive is an entirely subordinate one, and 

 distinctions with regard to the essential nature of heredity 

 based on these circumstances become irrelevant. 



In the case of a population presenting continuous 

 variation in regard to say, stature, it is easy to see how 

 purity of the gametes in respect of any intensities of 

 that character might not in ordinary circumstances be 

 capable of detection. There are doubtless more than 

 two pure gametic forms of this character, but there may 

 quite conceivably be six or eight. When it is remem- 

 bered that each heterozygous combination of any two 

 may have its own appropriate stature, and that such a 

 character is distinctly dependent on external conditions, 

 the mere fact that the observed curves of stature give 

 " chance distributions " is not surprising and may still be 

 compatible with purity of gametes in respect of certain 

 pure types. In peas (P. sativum\ for example, from 

 Mendel's work we know that the tall forms and the ex- 

 treme dwarf forms exhibit gametic purity. I have seen 

 at Messrs Sutton's strong evidence of the same nature 

 in the case of the tall Sweet Pea (Latki/rus odoratus) 

 and the dwarf or procumbent " Cupid " form. 



But in the case of the Sweet Pea we know at least one 

 pure form of definitely intermediate height, and in the 

 case of P. sativum there are many. When the extreme 

 types breed together it will be remembered the heterozygote 

 commonly exceeds the taller in height. In the next 

 generation, since there is, in the case of extremes, so much 

 margin between the types of the two pure forms, the return 

 of the offspring to the three forms of which two are homo- 

 zygous and one heterozygous is clearly perceptible. 



