No. 534] 



THE PURE LINE THEORY 



341) 



(lass vide phvsioln-iscli sehr dit'ferierende Heferassen in vermeintlieh 



Proposition 2. — These genotypes are separated gen- 

 erally by differences which are exceedingly minute. 



Notwithstanding the constant flood of new species 

 segregated from the classic Linnean groups, necessita- 

 ting frequent supplements to "Index Kewensis" and 

 other works of its kind, many naturalists could hardly 

 understand the small species discussed by de Vries in 

 his great work. Indeed, many laboratory men hardly 

 perceived the usefulness of recognizing species — per- 

 fectly constant, we were assured — so closely related that 

 one taxonomist could not identify the species of another 

 from his descriptions; species so similar that herbarium 

 material was worthless, and only culture side by side 

 could distinguish them. Yet after a lapse of only ten 

 years we find de Vries criticized for not recognizing 

 even smaller divisions than these! Spillman says: "de 

 Vries overlooks entirely those closely related pure lines, 

 differing frequently only quantitatively, and in a single 

 character. . . . They not only do not differ in all their 

 characters as the (Enothera mutants do, but their norms 

 present a regular series coming under ( L )uetelet's law." 6 



As examples of these minute differences both he and 

 Lang 7 quote the "72 Formen einer Population einer 

 gewissen Heferasse" discussed by Nilsson-Ehle. 8 



Jennings says : 9 



