Inside the uterus, the nucleus of the zygote divides into two nuclei. The nucleus is located at the two poles of the cell. Nuclei of both poles divide twice in succession to form eight nuclei of four each. One nucleus from each pole moves to the center of the cell and fuses to form the secondary nucleus. Among the three upper nuclei, the large nucleus in the middle is the ovum.
Fertilization of sperm and egg occurs in the follicle. After fertilization, the ovum is stimulated. Ovarian changes occur. The ovule changes into a seed. The watery part of the ovule is reduced and the soft part dries up to form a hard seed. Ovule develops into spore, ovule into spore, ovule into ovule, ovule into spore and secondary nucleus into seed.