148 THE AMERICAN NATURALIST [Vol. XLV 



lehre ' ' a rather full discussion is to be found. I may only 

 point out here that many cases of presumed correlation 

 may simply be cases of two or more characters (reac- 

 tions) due to the presence — or even absence — of one 

 single gene. The phenotvpically distinct and even di- 

 versely localized "characters" convey easily the impres- 

 sion that they are reactions of different genes. 



The highly interesting experiences of Correns, Don- 

 caster, Morgan, Spillman and others as to the sex-de- 

 termining factors, are in some way connected with 

 researches of correlation and "coupling" of genes. The 

 discussion of the ingenious Bateson-Punnett scheme for 

 Abraxas and Morgan's suggestive schemes as to Droso- 

 phila may favor the idea of what may be called "rami- 

 fied" genes. Castle has in his splendid researches as to 

 color-factors in rabbits, etc., initiated a systematic de- 

 scription of the (partially) analyzed genotypes, some- 

 what resembling the formulas of organic "structural 

 chemistry." If we suggest an analogy between the 

 radicals of chemistry and the genes, the (partial) geno- 

 type-formulas in Castle's manner may be able to demon- 

 strate ramifications of the genes inserted upon the main 

 group of the genotype-constituents. Pausing a moment 

 on this metaphor, it may be suggested that the "branch." 

 or "branches" of a ramified gene may be more difficult 

 to separate from its "trunk" than the whole gene from 

 the totality of the genotype. I shall here only ask if such 

 views may be of any use as working hypotheses. Their 

 bearing as to the realization of mutations is obvious,— 

 but the purely speculative nature of these suggestions 

 can not as yet warrant a longer discussion here. 



It should always be borne in mind that the Mendelian 

 analysis is purely relative. Baur and Shull and even 

 several others have emphasized this fact when discussing 

 the segregations in their experiments, and Shull has 

 clearly pointed out that it may be quite impossible to in- 

 dicate whether a particular reaction (character) is due 

 to something positive or to the lack of a factor in the 

 genotypical constitution. All that can as yet be deter- 



