1. The archesporium of Epipactis consists of a single hypodermal cell, which, without formation of parietals, functions as the megaspore mother cell. 2. In most cases the megaspore mother cell divides to two unequal daughter cells, the chalazal one again dividing to form two megaspores. The innermost megaspore then gives rise to the embryo sac. 3. In other cases four megaspores take part in the formation of the sac, the walls appearing at the first two divisions of the megaspore mother cell being evanescent. At least one of these walls often shows a tendency to persist, which results in a six-nucleate type of sac. The same appearance may also result from irregularities in the orientation of spindles. 4. There is some evidence that the embryo sac may at times be derived from two megaspores. 5. The normal mature embryo sac contains an egg, two synergids, three evanescent antipodal cells, and two polar nuclei which fuse. 6. The usual type of "double fertilization" occurs. 7. The fertilized egg gives rise to ...