No. 531] GENOTYPE CONCEPTION OF HEREDITY 133 



all the ' 'genes" in a gamete or in a zygote. When a 

 monohybrid is formed by cross fertilization, the ''geno- 

 type" of this Fi-organism is heterozygotic in one single 

 point and the "genotypes" of the two "genodifferent" 

 gametes in question differ in one single point from each 

 other. 2 



As to the nature of the "genes" it is as yet of no value 

 to propose any hypothesis; but that the notion "gene" 

 covers a reality is evident from Mendelism. The Men- 

 delian workers have the great merit of being prudent in 

 their speculations. In full accordance with this restraint 

 — a quite natural reaction against the morphologieo- 

 phantastical speculations of the Weismann school— it 

 may be emphatically recommended to use the adjectival 

 term " genotypical " instead of the noun "genotype." 

 We do not know a "genotype," but we are able to demon- 

 strate "genotypical" differences or accordances. Used 

 in these derivated ways the term "gene" and "geno- 

 type" will prejudice nothing. The very appropriate 

 German term "Eeaktionsnorm" used by Woltereck is, as 

 may be seen, nearly synonymous with ''genotype," in 

 so far as the "Eeaktionsnorm" is the sum total of the 

 potentialities of the zygotes in question. That these 

 potentialities arc partly separable ("segregating" after 

 hybridization) is adequately expressed by the "geno- 

 type" as composed of "genes." The "Reaktionsnorm" 

 emphasizes the diversity and still the unity in the 

 helmviorof the individual organism; certainly, the partic- 

 ular organism is a whole, and its multiple varying reac- 



the totalitv of all incident factors, mav it be external or 

 internal. Thence the notion "Eeaktionsnorm" is fully 

 compatible with the genotype-conception. 



The genotypes can be examined only by the qualities 

 and reactions of the organisms in question. Supposing 



