318 NOTHERA AND THE MUTATION THEORY 



report of experiments on the crossing over value for 

 some of the factors in this chromosome. 



The interpretation just given will account for a 

 large proportion of the results reported by deVries 

 and others; but there still remain certain curious 

 facts that do not fall into line. There are some 

 other unusual factors that have not yet been taken 

 into account. Nevertheless, it is evident that 

 Oenothera will not long remain as the one out- 

 standing case that cannot be brought into line with 

 other genetic phenomena. 



It is evident from what has been said that 

 (Enothera is not a favorable object for the study of 

 the manner and frequency of occurrence of new 

 mutations in the germ plasm. We require for such 

 a study an organism the normal genetic behavior of 

 which is thoroughly understood, and one that is 

 not normally heterozygous for an unknown number 

 of little understood genes. Yet it was deVries' 

 experiments with CEnothera that first drew attention 

 to mutation, and the whole history of the mutation 

 theory is bound up with (Enothera. These facts 

 have led certain authors to attack the mutation 

 theory and to proclaim its downfall. Lotsy, for 

 example, maintains that mutations do not occur 

 and that all evolution is due to hybridization and 

 recombination. The (Enotheras do furnish con- 

 clusive evidence that new types may appear suddenly 

 and without the occurrence of intermediates. It 

 was this phenomenon that deVries originally termed 

 mutation. Nowadays we use the term mutation 



