EXPERIMENTAL EVOLUTION 



117 



Since that time, both the new forms have more or less 

 spread over the field" {de Vries). 



Another mutant of 0. Lamarckiana was called by 

 de Vries (Enothera gigas (Fig. 62). The cells of this 

 mutant have twice as many chromosomes as the parent 

 form. 



Fro. 62. — Giant evening-primrose (Enothera gigas, a mutant from 

 (Enotheta Lamarckiana, originated in 1895. Cf. Fig. 61. (After de 

 Vries.) 



92. 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. 



