THE EVOLUTION OF LIVING BEINGS. 79 



maters, the difference between the Linneons, consis- 

 ting of self-fertiUsers, and those consisting of freely 

 intercrossing types, is too apparent to be explained 

 away. 



Now what is the reason of this difference? 



If it is correct that mutation does not exist — and 

 a sentence in NiUson-Ehle's article on : „Gibt es erb- 

 liche Weizenrassen mit mehr oder weniger vollstan- 

 diger Selbstbefruchtung? Ztschr. f. Pflanzenztichtung 

 1915 p 5., gives additional support tot his conten- 

 tion: 



. „In der Nachkommenschaft recessiv-merkmaliger F, individuen 

 „von Weizenbastardirungen kommen nicbt selten vereinzelte Indi- 

 „viduen mit dem dominanten Merkmal vor und ihre Zuriickfuh- 

 „rung auf Vicinismus (crossing with a neighbour of another form) 

 „kann, angesichts der bei diesem Versuch gefundendenen oben 

 „mitgeteilten, Zahlen keineswegs als unbegrundet angesehen wer- 

 „den", 



then the only way by which the number of homozy- 

 gotes can increase in succeeding generations of a freely 

 intercrossing community is: selection. 



So that, if it is correct, that a Linneon is the rest of 

 what arose from a former cross, the fact that 

 Linneons inside of which free inter- 

 crossing occurs, obtain generally 

 a more or less uniform aspect, is 

 definite proof for Darwin's conten- 

 tion that selection, at least intra- 

 linneontic one, in nature, is a fact. 



It must, of course, be argued that selection will occur 

 as well within self-fertilizing Linneons as within Lin- 

 neons inside of which free-intercrossing occurs, but 

 this must then lead to a different effect. 



