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THE AMERICAN NATURALIST [Vol. XLVII 



etc. Morgan's trouble lies in the fact that he is attempting to 

 force a letter to represent a character rather than merely one of 

 the factors concerned in the development of that character or to 

 represent the character and one of the factors. As a matter of 

 fact, in the formula PVo, the character eosin is not represented 

 by o but by PV when is absent (with the addition, perhaps, of 

 many factors as yet unknown). Similarly P does not stand for 

 pink but for one of the factors concerned in the production of 

 pink. One of the other factors concerned in the development of 

 pink Morgan has identified and named ; there are probably 

 other factors as yet unidentified. For orange he has identified 

 only a single factor and that is this same 0. No one has shown 

 more clearly than Morgan that a character is not determined by 

 a single factor. Why then should it be thought necessary to 

 designate the first factor identified for any character, say pink, 

 by the initial letter of that word? It is quite likely that P is no 

 more important in the production of pink than is 0. And it is 

 equally probable that is no more concerned in the development 

 of orange than are perhaps a half dozen other factors not yet 

 identified. The logical thing in such cases is to adopt Baur's 

 A-B-C- designations, which fit in readily with current Men- 

 delian usage. True, as Morgan insists, this necessitates the con- 

 stant use of a key. But what system does not ? What is there in 

 Morgan's PVO, or even in his later PVE, to suggest red color? 



It is fortunate that Mendelians "have not always taken the 

 pains to state explicitly that the symbols represent both a factor 

 and a residuum, ' ' for this, it seems to me, is not true. The re- 

 siduum left when any factor is lost is usually not represented 

 except by the few factors that have been identified in it. It is 

 careless without doubt to leave so much to be taken for granted, 

 but it would be cumbersome to have to write for pink 



PvOX % X*K t • • • X n . 

 Perhaps we might use a single X to represent an unknown num- 

 ber of unidentified factors, or perhaps it would be as well to use 

 UR for this unexplored residuum. 



I am inclined to agree fully with Castle that Morgan's sugges- 

 tion for a change in the current Mendelian formula? is "con- 

 fusion worse confounded," but here our agreement stops. I can 

 see that it might be possible to do away with the use of small 

 letters, since on the pre.senfc-;ui(l-aksi>n<r hypothesis they repre- 

 sent nothing but the absence of factors designated by the corre- 

 sponding capital letters. The designations of eye colors in 



