EXPERIMENTAL EVOLUTION 



535 



Another mutant of (E. Lamarckiana was called by 

 de Vries (Enothera gigas (Fig. 402). The cell-nuclei of 

 this mutant have twice as many chromosomes as the 

 parent form. 



Fig. 401. — Lamarck's evening-primrose {(Enolhcra Lanidrckiana). A 

 mutating species. (After de Vries.) 



456. The Test of a Mutation.— The deciding test as to 

 whether a given new form, arising without crossing from 

 a form that has bred true for at least two generations, is 

 really a mutant or merely a fluctuating variant, is to see 

 if it breeds true to seed for the new character or characters. 

 If it does it is a mutant; otherwise it is not. It is clear, 

 therefore, that the only way the problem can be followed 

 out is by experiment — hence the term experimental evolu- 



