No. 534] 



THE PURE LIXE THEORY 



861 



Such a run of results as this can hardly be due to 

 chance. 31 They indicate rather the presence of some as 

 yet undetermined physiological factor. 32 



Candidly viewed and considered in comparison with 

 other biometric work on the inheritance of fertility and 

 fecundity. T think those experiments can not be held to be 

 strongly opposed to the theory of the effectiveness of se- 

 lection in general. However this may be, they certainly 

 afford no substantiation for 'Johannsen's genotype 

 theory of heredity. 



IV. Summary and Conclusions 

 By the genotype theory of Johannsen one understands 

 the following propositions : 



An apparently uniform population or phaenotype is 

 generally not homogeneous, but is composed of a large 

 number of differentiated types, which are to be desig- 

 nated—within limitations to be laid down immediately— 

 as genotypes. 



Externally, the genotype can not be distinguished 

 from the phaenotype. Both may have normal variation 

 curves, but while that of the phaenotype may by proper 

 selection be broken up into constituent genotypes, the 

 variation curve of the genotype can not be modified by 

 selection. In short, the genotype is from the standpoint 

 of heredity a rigid unit. All individuals belonging to 

 the same genotype have the same potencies as parents. 

 Only discontinuous segregations or transformations — 

 mutations— may modify them. 



31 The argument that this observed decrease as the result of selection to 

 increase egg production is due to chance must rest chiefly on one or both of 



