191 s] BARTLETT— MUTATION IN OENOTHERA 83 



Heribert-Nilsson* 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 0. Lamarckiana 

 would discredit, if not invaUdate, 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 0. biennis by mutation, once in a pure line of 



' Hekibert-Nilsson, 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., Mntations in Oenothera biennis 1,? Amer. Nat. 47:116-121. 1913. 



* De Vries, H., Die Mutationen in der Erblichkeitslehre. pp. 28-30. 1912. 



, Gruppenweise Artbildung. pp. 299-306. 1912. 



' Stomps, Theo. J., Mutation bei Oenothera biennis L. Biol. Centralbl. 32:521- 

 S3S- 1912- 



