216 THE FACTORIAL HYPOTHESIS 



and that, in consequence, many factor differences 

 may occur which will, in turn, cause the character 

 differences in question. Secondly, Bateson argues 

 that we should expect these irregularities to occur in 

 the segregation of character-factors during germ-cell 

 formation, because we find irregularities in the seg- 

 regation of factors during development. Appar- 

 ently Bateson holds the view that differentiation 

 of characters is the result of sorting out of factors 

 in the somatic divisions; in other words, he adopts 

 Weismann's theory of embryonic development. Lo- 

 calization of factors is inferred from localization of 

 characters. Hence his employment of the idea 

 chiefly when patterns are involved. The conclusion 

 to which most modern students of experimental 

 embryology have arrived, a conclusion based on a 

 considerable body of evidence, is that differentiation 

 is not a consequence of sorting out of the hereditary 

 (genetic) materials. This conclusion is not con- 

 sidered or else is ignored by Bateson in this argument. 

 5. The confusion of character with factor is nowhere 

 more apparent than in the well-known presence and 

 absence hypothesis, and since this hypothesis has 

 been so widely employed in Mendelian literature it 

 calls for somewhat more extended analysis. The 

 hypothesis was first proposed to explain the inherit- 

 ance of combs in poultry (Fig. 64). Rose comb by 

 single comb gives in F 2 three rose to one single; pea 

 comb to single gives in F 2 three pea to one single. 

 When rose is bred to pea a new type of comb, called 

 walnut, appears, and in F 2 there are nine walnut: 



