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 
Cnothera 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 Cnothera. 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 Cénotheras 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 
