The archesporium of Habenaria arises as a single hypodermal cell, which without dividing functions as a megaspore mother cell. The mother cell divides to two daughter cells and each of these to two megaspores. The division of the daughter cell nearest the micropyle is usually delayed. In some cases an embryo sac is probably formed from more than one megaspore; but the condition in the orchids, where there is a gradual reduction of the divisions of the megaspore mother cell without an indication of walls in the embryo sac, indicates that megaspore formation may be omitted and the place of reduction changed to the first division of the nucleus of the embryo sac mother cell. The embryo sac of Habenaria contains eight nuclei: an egg, two synergids, two polar nuclei, and three ephemeral antipodals. The primary endosperm nucleus is formed by the fusion of the polar and second male nuclei, but degenerates without dividing. The absence of endosperm in many orchids offers no support to the view that the endosperm ...