OENOTHERA GIGAS NANELLA, A MENDELIAN 



MUTANT. 



In a recent book Gates has studied the significance of the experi- 

 ments made with species of Oenothera as proofs for the general theory 

 of mutation and has given an exhaustive and critical review of 

 the facts in this rapidly increasing field of research 1 ). He has laid 

 special stress upon the results of crosses, which show the great 

 diversity of these phenomena when studied in some wild plants, as 

 contrasted with the now prevailing doctrine of Mendelism; for 

 among the mutants of Oenothera instances of Mendelism are rare. 

 The first known example is that afforded by 0. brevistylis, which 

 follows the law of Mendel as a recessive in all its crosses with the 

 parent species, with other mutants, and with other species of the 

 same group 2 ). But, unfortunately, the production of this form by 

 means of mutation from 0. Lamar ckiana is so rare that it has not, 

 as yet, been repeated under experimental control. Another instance 

 is 0. rubricalyx, discovered and studied by Gates (op. cit., p. 103), 

 which behaves as a dominant in its crosses with 0. Lamarckiana. 



In this article I hope to show that the dwarf character, which in 

 so many instances complies with the formulae of Mendel, but which 

 behaves in a different way in crosses of the derivatives of 0. La- 

 marckiana, may, at least in one instance in this group, follow that 

 law as exactly as in any other pure Mendelian case. This instance, 

 therefore, affords a means for the experimental study of the origin 

 of such a form by mutation. The main result of this study is the 

 proof of the occurrence of mutant Mendelian hybrids besides the 

 pure dwarfs. 



In my book on the mutation theory I have pointed out that the 

 origin of 0. brevistylis from 0. Lamarckiana may have been induced 

 by the mutation of a single sexual cell. If this combined in fertili- 

 zation with a normal gamete, a hybrid would be produced which 

 would not be distinct from the parent species in its external features. 

 This hybrid would then, in its self-fertilized seeds, follow the law of 



i) Gates, R. R., The mutation factor in evolution. London, 19 15. 

 2) Die Mutations-Theorie. 1:223; 2:151 — 179, 429. 



