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 ((Enothera Lamarckiana). 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- 
