No. 531] GENOTYPE CONCEPTION OF HEREDITY 



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same pure line if the genealogy was but sure. The 

 guarantee of the descendence is thus a main point in the 

 principle of pure lines. Identity of genotypical nature 

 is not at all a proof for identical genealogy: the wide- 

 spread confusion of "resemblance" with "genealogical 

 relation" is the root of much evil— of which the statis- 

 tics of biometricians have given us some instances. 



The isolation of pure lines from plant-populations has 

 been the instrument for gaining the conviction that se- 

 lection is not able to shift the nature of genotypes. 

 The well-known displacement of the "type" of a popu- 

 lation by selection — this displacement proceeding from 

 generation to generation in the direction indicated by 

 the selection — is due to the existence a priori of geno- 

 typical differences in such populations (see the dia- 

 gram). By selection a relatively great number of those 

 organisms, whose genotypical constitution is favorable 

 for the realization of the desired degrees of any char- 

 acter, will be saved for reproduction; hence the result 

 of the selection ! 



Within pure lines — if no mutation or other disturb- 

 ances have been at work — or within a population in 

 which there is no genotypical difference as to the char- 

 acter in question, selection will have no hereditary influ- 

 ence. This result has in recent years also been reached 

 by several other experimenters in genetics. Here I also 

 may recall the brilliant experiments of H. S. Jennings 

 with Paramoecium, experiments which have been carried 

 out quite independently of my own researches and which 

 have been of great importance for the propagation 

 and support of the genotype-conception. The bearing 



