SELECTION. 189 



best adapted to the conditions into which a mixture of several 

 of them happen to live for a number of generations, will tend 

 to survive, provided their numerical proportion to the total 

 number is sufficiently large to counteract the tendency of a 

 minority to disappear automatically. In these organisms new 

 species, well adapted to life and to reproduction of their kind 

 have a far lesser tendency to disappear; there is no multitude 

 of individuals of one common type to mate with any surviving 

 individual of the new type, and to compete with mates of its 

 own type. The result is, that whereas the reduction of varia- 

 bility within each species, within the descendants of one 

 individual in these autogamous organisms is extremely rapid, 

 as compared to the purification of the type in an allogamous 

 species, we actually find that the groups of individuals, which 

 are generally reckoned as species in these autogamous organ- 

 isms, are very polymorph compared to species of allogamous 

 organisms. The explanation of the apparent paradox is simply 

 that such species of plants as Triticum vulgare, Draba verna, 

 are compound species, aggregations of numerous species each 

 practically without potential variability, in a mixture. These 

 are the "petites especes" of Jordan, the "pure lines" of Jo- 

 hannsen. 



The discovery that in a good many cases of polymorphy in 

 plants, apparent species in reality consist of a great many 

 small species of a high degree of purity, was one of great im- 

 portance for an insight in evolution. But it is remarkable to 

 observe here once more, the tendency of certain naturalists to 

 over-estimate the importance of a new discovery. 



The director of the Svalof seed-firm, Nilsson, and Prof, de 

 Vries postulated the origin by spontaneous variation, muta- 

 tion, of these pure lines in wheat, barley and oats, and in the 

 existence of so many pure strains in these cereals they saw 

 proof for the idea, that in "mutation-periods" great numbers of 

 new species originate spontaneously from one common parent- 

 species. 



Other authors have generalized the "pure-line-conception" 



