The plant embryo, ovule, accessory nucleus, accessory cell and secondary nucleus together are called strigametophyte.
The female flower of the plant contains sporogenous cells inside the ovary. The sporogenous cell divides or develops directly into the female mother cell. The female mother cell is diploid and divides by meiosis to produce four haploid macrospores or gametes. Spore is the first cell of female gametophyte. Of the four spermatozoa, the top three are destroyed and the bottom remain viable. The nucleus of the viable zygote enlarges and divides into two nuclei in the process of mitosis. The nucleus is located at the two poles of the cell. Each nucleus is surrounded by little cytoplasm and a thin wall. At this time, the female cell turns into a sac-like organ with two poles. Nuclei of both poles divide twice in succession to form eight nuclei of four each. In this condition, one nucleus from both poles moves to the center of the cell and fuses. It is called fusion nucleus or secondary nucleus. The three upper nuclei together are called the egg apparatus. The middle of the oviduct is large
The nucleus is called the ovum and the smaller nuclei on either side are called companion nuclei or synergids. The bottom three nuclei are called antipodal cells.