042 



THE AMERICAN NATURALIST 



[Vol. XLVI 



dwarfs) further works against the unit character hypothesis as of 

 practical value in the analysis of a hybrid generation of this character. 

 It should be remembered, however, that there were in this cross no 

 sharply contrasted distinctions of color, anthocyan (stem) coloration 

 proving most unsatisfactory for the purpose of a genetical study. 



These four paragraphs are practically a resume of 

 Davis's genetic facts : I take exception only to some of the 

 implied conclusions. It is quite evident that Dr. Davis 

 believes that many breeding facts are expressed in 

 shorthand by the Mendelian notation. His statements, 

 however, imply a feeling of loss of caste or something of 

 the kind if he makes definite use of Mendelian phraseol- 

 ogy. His F 2 generation was exactly what would be ex- 

 pected when several Mendelian units without dominance 

 segregate and recombine. The advance in size of corolla 

 was predicted by me in 1910 ( Amek. Nat., 44 : p. 81) as 

 a direct consequence of size inheritance. It has since 

 been demonstrated by Tschermak for time of blossom- 

 ing of beans and clearly analyzed by Hayes for number 

 of tobacco leaves. It demands neither modification of 

 old nor the creation of new factors. It occurs when- 

 ever AABB (size factors) is crossed with CCDD, and 

 each factor is allelomorphic to its own absence, to use 

 the ordinary phraseology. 



As to the difficulty of precise analysis into factors, I 

 agree with Dr. Davis, but that there is no advantage in 

 showing that this behavior is described in typical Men- 

 delian terms I can not admit. One holds the same prac- 

 tical advantage here— though the case is complex— that 

 one holds in all Mendelian inheritance. He knows that 

 somatic appearance is not the criterion of breeding ca- 

 pacity, but that it is determined in some way by gametic 

 constitution, although no germ cell architecture is pre- 

 supposed. He knows that recombination of some kind 

 of factors occurs and has some idea of the number of 

 progeny to be grown to obtain the desired combination. 

 In other words, the blend in does not indicate com- 

 plete loss of extremes. 



