Twin Hybrids of Oenothera Hookeri

The researches of MORGAN on lethal factors, of BARTLETT on mass mutation, and of RENNER on empty seeds, have led me of late to the conception that lethal factors and hybrid mutants play a large part in the splitting phenomena which accompany the normal mutations of so many species of Oenothera. The question, which part of those phenomena may be explained by this view, has to be faced. The crosses of Oenothera Hookeri with the mutating species behave in so many respects difierently from the remainder of the cases that they seem to afford suitable material for this study. Oe. Hookeri X Oe. bienrtis produces a splitting in the second generation that does not follow the rules of MENDEL and Oe. Hookeri X Oe. Lamrckiana produces twins of the type of laeta and zielutina, but without their ordinary constancy, the laeta splitting in every generation into the same two types. The discovery of mass mutation in Oe. grandiflora and of its relation to the production of twin hybrids by this species affords the clearest instance for this new conception and for this reason I shall describe in the first place the results of my crosses of this species with Oe. Hookeri.