The ontogeny and the vascular pattern of the flower of Oenothera biennis L. and some other species of the genus were studied. The “ring” in the vascular system of the flower has been analyzed and appears to be composed of a partly degenerated system of nodal branches. The results affirm the theory that ovary wall and hypanthium are at least partly of axial origin. The petal and the associated epipetalous stamen do not arise from the same primordium. They are not supplied from a common, single vascular strand. Difference in size, shape, and stainability of cells of the inner and of the outer layers of the ovary wall are not related to a carpellar or an axial origin of these layers.