Genetical Studies on Oenothera. V. 197 



(4) Reciprocal Crosses between Oenothera mtiricata Linnaeus 

 and O. (figas de Vries. 



This is a cross upon which I have been at work for three years 

 but I have met with serious difficulties in the apparently very common 

 sterility of the Fi hybrids. It is an exceedingly attractive cross to 

 make because the parents differ so widely in the expression of their 

 characters and because gigas having 28 chromosomes and muricata 14 

 the hj'brids should present exceptionally interesting material for cyto- 

 logical study. 



My first cross was a race of muricata from Woods Hole, Massa- 

 chusetts {muricata W) pollinated by gigas, the Fi generation being grown 

 in 1909; the reciprocal of this cross was not made at that time. This 

 culture is described in the first of my "Genetical Studies an Oenothera'' 

 (Davis '10, p. 109). It consisted of 12 plants of which 6 inclined 

 towards the muricata parent and 6 showed a greater resemblance to 

 gigas. Both groups presented their characters as intermediate between 

 the parents and therefore no character of either parent was duplicated 

 in the hybrids. At the time they seemed to me to illustrate the phen- 

 omenon of "twin hybrids" reported by de Vries for numerous crosses 

 between species of the Onagra group and Lamarchiana or one of its 

 derivatives. 



The differences between the two groups (6 + 6) of this cross 

 {muricata W X gigas) were chiefly those of habit and foliage. The 

 6 plants that resembled gigas most strongly had rosettes of broader 

 leaves, conspicuously crinkled, but the leaves were not so broad as those 

 of gigas. At maturity these plants presented a more stock}' gigasAi^Q 

 habit with broader, crinkled leaves, but these leaves also were relatively 

 not so broad as those of gigas. The 6 plants that inclined towards 

 muricata had rosettes of narrower, plane leaves, but these were broader 

 than those of muricata. At maturity the plants were less stocky and 

 had a foliage of narrower leaves although they were both longer and 

 2 — 3 times broader than those of muricata W. In the inflorescence, 

 flowers, and capsules, patroclinous and matroclinous tendencies were less 

 evident, the form and measurements of the structures being intermediate 

 between the parents, except that the flowers in size were below the 

 mean of the parents and therefore closer to muricata although larger 

 than in this species. 



This first cross, muricata W X gigas, has given, I believe, the only 

 hybrids between these species, so far grown, that have proved fertile 



