INHERITANCE OF FECUNDITY 261 



indicate excessive complication. To speak in mathematical terms, 

 by way of illustration merely, it may fairly be said, that the for- 

 mula here used to 'fit' the data, has essentially the character of 

 a true graduation formula, rather than that of an interpolation 

 formula. The number of constants (here factors) in the formula 

 is certainly much less than the number of ordinates to be gradu- 

 ated. 



There is no assumption made in the present Mendelian interpre- 

 tation which has not been fully demonstrated by experimental 

 work to hold in other cases. That the expression of a character 

 may be caused by the coincident presence of two (or more) sepa- 

 rate factors, either of which alone is unable to bring it about, has 

 been shown for both plants^^ and animals by a whole series of 

 studies in this field of biology during the last decade. To find 

 examples one has only to turn to the standard hand-books sum- 

 marizing Mendelian work, as for example those of Bateson and 

 Baur. Again sex-linkage or correlation of characters in inher- 

 itance has been conclusively demonstrated for several characters 

 in fowls by the careful and thorough experiments of a number of 

 independent investigators. Finally it is to be noted that Bate- 

 son and Punnett (4) have recently shown that the inheritance of 

 the peculiar pigmentation characteristic of the silky fowl follows 

 a scheme which in its essentials is very similar to that here worked 

 out for fecundit}''. 



The selection problem ' 



The results of the present investigation have an interesting and 

 significant bearing on the earlier selection experiments on fecun- 

 dity at this Station. It is now quite plain that continued selec- 

 tion of highly fecund females alone could not even be expected 

 to produce a definite and steady increase in average flock produc- 

 tion. The gametic constitution of the male (in respect especially 

 to the Lo factor) plays so important a part in determining the 

 fecundity of the daughters that any scheme of selection which 



18 Particularly important here are the brilliant researches of Nilsson-Ehle 

 (24, 25) on cereals, and of Baur (2) on Antirrhinum. 



