rots] BARTLETT—MUTATION IN OENOTHERA ee 
HERIBERT-Nitsson® has made the first serious effort to explain 
the variations of Oenothera Lamarckiana on a strictly Mendelian 
basis. He does not hold with Davis that this species is necessarily 
of hybrid origin, but rather that it is a collective species, embracing 
a number of different strains which constantly cross among them- 
selves. Consequently he assumes that the mutation phenomena 
do not exemplify progressive and regressive species formation, 
but merely the synthesis of new combinations from factors already 
existing within the species. 
Although it is by no means true, as some critics seem to imply, 
that the mutation theory must stand or fall on the evidence derived 
from Oenothera, it must nevertheless be admitted that failure to 
find a parallel among other more fortunately chosen species of this 
genus to the mutation phenomena shown by O. Lamarckiana 
would discredit, if not invalidate, much of the direct evidence of 
mutation which has been so laboriously won by DE Vries. Davis? 
has said that “it is evident that the adherents of the mutation 
theory are sensitive to the doubts freely expressed concerning the 
status of Oenothera Lamarckiana, the behavior of which in throwing 
off marked variants is cited as the most important evidence for 
the origin of species by mutations... . . Consequently, muta- 
tionists are likely to bring forward as rapidly as possible any evi- 
dence that may seem to indicate the appearance of clear inheritable 
Variations of a marked character in forms of pure germinal con- 
stitution, i.e., in homozygous material.” 
It is the object of this paper to present additional evidence of 
mutation in Oenothera, derived from one of the small-flowered, 
self-pollinating wild American types. Before proceeding farther, 
however, it should be stated that a considerable body of similar 
evidence has already been obtained. 
De Vries* and Stomps? have twice observed the origin of a 
dwarf variety of O. biennis by mutation, once in a pure line of 
* HertBert-Nitsson, N., Die Variabilitat der Oenothera Lamarckiana und das 
Problem der Mutation. Zeitsch. Ind. Abst. u. Vererb. 8:89-231- 1912 
————, Oenothera Problemet. Svensk. Bot. Tidskr. 7‘: pp. 16. 1913. 
: Davis, B. M., Mutations in Oenothera biennis L?. Amer. Nat. 47:116-121. 1913. 
* DE Vrirs, H., Die Mu Soe ree in der Sh eee pp. 28-30. 1912. 
Ragaaurie , Gruppenweise Artbildung. pp. 299-3 
O12 
a 9 Stowers, THEO. J., Mutation i. Ocnothera Sines - Biol. Centralbl. 32:521- 
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