Embryology of Mimulus Ringens

Abstract

The wall of the microsporangium in Mimulus ringens L. consists of an epidermis, endothecium, middle layer, and glandular tapetum. The tapetal cells become binucleate, and the endothecial cells develop fibrous thickenings in later stages. Division of microspore mother cells is simultaneous, and quadripartition takes place by cleavage. The pollen grains are two-celled at shedding. Development of the female gametophyte in the tenuinucellate hemianatropous ovules conforms to the Polygonum type. Two superposed persistent antipodal cells are organized, the more micropylar cell being larger and binucleate. An endothelium surrounds the central portion of the embryo sac. The endosperm is ab initio cellular. A chalazal haustorium, which consists of four uninucleate cells, becomes conspicuous only after degeneration of the antipodal cells. A micropylar haustorium, made up of two large binucleate cells, also occurs. The haustorial cells do not fuse but degenerate as such. Development of the embryo conforms to the typ...