Principles of Heredity 205 



distinguish the results of breeding first crosses together 

 into four classes : two pure forms, one or more blend or 

 mosaic forms, and " mule " forms. Such a study could as 

 yet only be attempted in simplest cases : for where we are 

 concerned with a compound allelomorph capable of resolu- 

 tion, the combinations of the integral components become 

 so numerous as to make this finer classification practically 

 inapplicable. 



But in many cases perhaps a majority though by 

 Mendel's statistical method we can perceive the fluctuations 

 in the numbers of the several products of fertilisation, we 

 shall not know whether abnormalities in the distribution of 

 those products are due to a decline in dominance, or to 

 actual impurity of the gametes. We shall have further to 

 consider, as affecting the arithmetical results, the possibility 

 of departure from the rule that each kind of gamete is 

 produced in equal numbers* ; also that there may be 

 the familiar difficulties in regard to possible selection and 

 assortative matings among the gametes. 



I have now shown how the mosaic and blend-forms are 

 to be regarded in the light of the Mendelian principle. 

 What has Professor Weldon to say in reference to them ? 

 His suggestion is definite enough that a study of ancestry 

 will explain the facts : how, we are not told. 



In speaking of the need of study of the characters of 

 the race he is much nearer the mark, but when he adds 

 'that is their ancestry," he goes wide again. When 

 Telephone does not truly divide the antagonistic characters 

 among its germ-cells this fact is in nowise simply traceable 

 to its having originated in a cross a history it shares with 

 almost all the peas in the market but to its own peculiar 



'' In dealing with cases of decomposition or resolution of compound 

 characters this consideration is of highest importance. 



