1.] PANMIXIA. 29 



of very large tubers, so heavy a crop that the plant has 

 been obliged to spare some of its energy from the pro- 

 duction of pollen and berries for the purpose of main- 

 taining the subterranean product. It is evident that 

 this high state of amelioration can be maintained only by 

 means of high cultivation. The moment there is a let- 

 down in the factors which have bred and maintained the 

 plant, there is a tendency towards a breaking up and 

 disappearance of the high-bred type. This is an illus- 

 tration of the phenomenon of panmixia, as outlined by 

 Weismann, except that the force which has ceased to act 

 is human selection rather than natural selection. "This 

 suspension of the preserving influence of natural selec- 

 tion," Weismann writes, "maybe termed Panmixia." 

 In his opinion, "the greater number of those variations 

 which are usually attributed to the direct influence of 

 external conditions of life are to be attributed to pan- 

 mixia. For example, the great variability of most 

 domesticated animals and plants essentially depends 

 upon this principle." In other words, certain differences 

 are preserved through the agency of natural selection, 

 and certain differences are lost; if the organism is re- 

 moved from this restraining and directing agency, all 

 variations have the chance of asserting themselves. 

 "All individuals can reproduce themselves," Weismann 

 explains, " and thus stamp their characters upon the 

 species, and not only those which are in all respects, or 

 in respect to some single organ, the fittest." I am con- 

 vinced that this term expresses a very important truth, 

 and one which, as Wiesmann says, is particularly ap- 

 parent in domestic animals and plants; but panmixia 

 does not express an original force. If new differences 

 arise in consequence of the cessation of the directive 



