Structure of embryo sac

There are three main parts of the embryo. These are-

1. Egg apparatus: The three cells near the oviduct of the embryo are collectively called the egg apparatus. Among them, the large cell in the middle is called ovule and the smaller cells on both sides are called companion cells.
2. Antipodal cell: The three cells on the ovule side of the embryo are collectively called antipodal cells.
3. Secondary nucleus: Two nuclei come from the two poles in the middle of the embryo. The two nuclei then fuse to form a secondary nucleus.