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THE AMERICAN NATURALIST [Vol. XL VI 



It can not justly be urged against the conclusions of 

 this study that the Mendelian hypothesis advanced to 

 account for the results is so complicated, and involves 

 the assumption of so many factors or such complex inter- 

 actions and limitations of factors, as to lose all signifi- 

 cance. As a matter of fact the whole Mendelian inter- 

 pretation here set forth is an extremely simple one, 

 involving essentially but two factors. This surely does 

 not indicate excessive complication. To speak in mathe- 

 matical terms, by way of illustration merely, it may 

 fairly be said that the formula here used to "fit" the 

 data has essentially the character of a true graduation 

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

 formula is certainly much less than the number of ordi- 

 nates to be graduated. 



There is no assumption made in the present Mendelian 

 interpretation which has not been fully demonstrated by 

 experimental work to hold in other cases. That the ex- 

 pression of a character may be caused by the coincident 

 presence of two (or more) separate factors, either of 

 which alone is unable to bring it about, has been shown 

 for both plants 11 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 summarizing Mendelian work, as for example those 

 of Bateson and Baur. Again sex-linkage or correlation 

 of characters in inheritance has been conclusively demon- 

 strated for several characters in fowls by the careful and 

 thorough experiments of a number of independent inves- 

 tigators. Finally it is to be noted that Bateson and 

 Punnett 12 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 fecundity. 



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



