NEW DIMORPHIC MUTANTS OF THE OENOTHERAS. 



(WITH FIVE FIGURES.) 



Among the previously described mutants of Oenothera Lamarcki- 

 ana Ser. there is a form which, although fertile with its own pollen, 

 yields a dimorphic progeny. Some of the individuals exactly repeat 

 the stature and characters of their parent, but others return to 

 the type of 0. Lamarckiana. Besides these, new mutants, especially 

 0. oblonga, are relatively numerous. The two main types are 

 produced in varying proportions, according to the individual cul- 

 tures. The typical specimens may be as few as 10 per cent, or as 

 numerous as 80 per cent. In most instances, however, they show 

 a proportion of about 35-40 per cent. Considering the much smaller 

 individual strength of the typical ones, as compared with the 

 atavistic specimens, these figures may be regarded as indicating 

 a splitting, ordinarily, into nearly equal parts. 



This inconstant mutant is 0. scintillans. 1 ) Exactly the same 

 phenomenon of splitting has been observed recently in a number 

 of new types. In the first place, in 0. stenomeres mut. lasiopetala, 

 described by Bartlett. 2 ) In the second place, it has occurred in 

 my own cultures, among the new mutants of 0. Lamarckiana, as 

 well as among those of another American species, described under 

 the preliminary name of 0. biennis Chicago. 3 ) I shall deal with this 

 one under the name 0. saligna, and designate the new inconstant 

 mutants of 0. Lamarckiana as 0. cana, 0. pallescens, 0. Lactuca, 

 and 0. liquida. As far as investigated, they all follow the rule 

 that in every generation they split up into two ordinarily almost 

 equal groups of typical specimens and of atavistic individuals 

 which, in all cases, exactly duplicate the characters of 0. Lamarcki- 

 ana. 4 ) Moreover, they show a relatively high degree of mutability. 



i) The mutation theory, Chicago 1909, Vol. I, p. 377; and Gruppen- 

 weise Artbildung, p. 257, 19 13. 



2) Bartlett, H. H., Mutations of O. stenomeres. Amer. Jour. Bot. 

 2: 100 — 109; see also 2:146, 1915. 



3) Gruppenweise Artbildung, p. 52 fig. 18 and pi. 6, 1913. 



4) In the wild condition such a splitting would evidently cause a race 

 to die out after a few generations, especially since the atavists are very 



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