258 



MUTATIONS OF OENOTHERA SUAVEOLENS DESF. 



Oe. (biennis x suaveolens) x Oe. (suaveolens x biennis). — Cross 

 in 1915; 80 specimens were grown in 1916, of which 16 were lutescens, 

 showing that the corresponding mutability of Oe. suaveolens passed 

 unweakened through the double cross. The lutescens flowered in 

 August but of the remaining only 10 have flowered, whereas the 

 others stayed in the condition of rosettes of radical leaves throughout 

 the whole summer. They resembled exactly Oe. biennis, and so did 

 the ten flowering plants in all their marks. 



From these facts we may conclude that Oe. suaveolens is a hetero 

 gamic species in the same sense as Oe. biennis, though perhaps 

 somewhat less completely so. 



The appearance of lutescens in the described crosses seems to point 

 to some kind of mass mutation in the sense proposed by Bartlett 

 (1915), since the figures are always relatively high. But it is com- 

 plicated by the fact, mentioned above, that in the crosses between 

 lutescens and suaveolens the marks of lutescens are handed down 

 through the egg cells and not through the pollen, at least to the first 

 generation of hybrids. Moreover the production of lutescens is not 

 a regular, but rather a rare phenomenon. This is shown by the 

 following review of the experiments: 



Appearance of Oe. lutescens in crosses of Oe. suaveolens with other species. 



Cross 



Percentage of lutescens in 



2nd generation 



A. Pollen of suaveolens 



biennis x suaveolens 



biennis Chicago x suaveolens 



syrticola x suaveolens 



(suaveolens x biennis) x (biennis x suaveo- 

 lens) 



B. Egg cells of suaveolens 



suaveolens x biennis 



suaveolens x syrticola 



suaveolens x biennis Chicago 



(biennis x suaveolens) x (suaveolens x bien 

 nis) 











37 



0*) 



If it were allowed to apply the ideas of Bartlett (1900) concerning 

 mass mutation to our case, we might assume a stray initial mutation 

 of a sexuall cell of Oe. suaveolens into lutescens and its copulation 

 with a normal gamete. This would give a half-mutant, which after 



') .... indicates that the generation has not been cultivated. 

 2) No lutescens from the biennis specimens; the lutescens of the first generation 

 were constant from seed. 



