1. In Cypripedium two cells are formed by the mother cell, a wall not appearing in the second division, even in the rare instances in which the nuclei of both daughter cells divide. Two megaspore nuclei are used in forming the embryo sac, the Lilium type using four, and most angiosperms only one. The two megaspore nuclei in the sac of Cypripedium and the four in that of Lilium may be related to double fertilization. 2. Cypripedium has only four nuclei in the completed embryo sac. The Lilium type and Cypripedium have the fewest divisions from mother cell to egg reported among angiosperms. A comparison with the animal egg shows only one more division from the mother cell to the egg in Lilium and in Cypripedium than in the maturation of the animal egg. 3. So-called double fertilization is probably constant in Cypripedium. The primary endosperm nucleus (triple-fusion nucleus) is formed by the fusion of the polar, one synergid, and one male nucleus. Endosperm of four nuclei was found and the probability of oth...