ORIGIN OF MUTANT CHARACTERS 



69 



gate, giving the two kinds of gametes peculiar to Men- 

 delian inheritance. 



De Vries says that such a process represents a step 

 backward in evolution. It is not progressive but degres- 

 sive and produces a ''retrograde variety." This inter- 

 pretation is, as I have said, closely akin to a current 

 interpretation of mutational changes as due to a loss of a 

 gene — in principle the two ideas are the same. 



Fig. 42. 



Oenothera Lamarckiana (to the left), and O. gigas (to the right). 

 (After Castle, from Davis.) 



It is not without interest, therefore, to examine the 

 evidence that led de Vries to develop his mutation hy- 

 pothesis. 



De Vries found near Amsterdam, in a waste field, a 

 colony of evening primroses, Oenothera Lamarckiana 

 (Fig. 42). Amongst them were a few individuals that dif- 

 fered somewhat from the common forms. He brought 

 some of these into his garden and found that they bred 

 true for the most part. He also bred the parent form, or 

 Lamarckiana. It produced, in each generation, a small 

 number of the same new types. In all, about nine such 



