VOLUME LIX NUMBER 2 
gS ug 
BOTANICAL G;AZETTE 
FEBRUARY 10915 
ADDITIONAL EVIDENCE OF MUTATION IN 
OENOTHERA! 
HARLEY HARRIS BARTLETT 
(WITH SEVENTEEN FIGURES) 
Introduction 
Much of the advance which has been made in genetics and 
practical breeding during the last decade has been a direct result 
of the promulgation by Dr Vries of the theory of the origin of 
species and varieties by mutation. That recessive Mendelian 
variations originate singly by mutation has been shown by several 
investigators, notably by Morcan, who has observed the origin of 
more than 150 such variations in his cultures of Drosophila. Many 
opponents of the mutation theory deny, however, that progressive 
mutations ever occur in homozygous strains, or that true species, 
differing from the parent in several independent characters, have 
ever been observed to originate at a single step by mutation. 
Davis,? for example, is in accord with the mutationists in regarding 
Oenothera gigas as a marked progressive mutation of specific rank, 
but he denies that Oenothera Lamarckiana, the parent form of O. 
gigas, is homozygous. The facts (x) that O. Lamarckiana is not 
known as a native component of any flora, (2) that its known history 
has been that of a cultivated plant or an escape from cultivation, 
* Published by permission of the Secretary of Agriculture. 
* Davis, B. M., Cytological studies on Oenothera. III. A comparison of the 
reduction divisions of Oenothera Lamarckiana and O. gigas. Ann. Botany 25:941-974. 
is i: _ Denethere gigas isa progressive: mutant, its pecumecties being clearly asso- 
ts chromosome 
number” (0. cit, Dp. 974). 
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