The sac-like part inside the nucellus is called embryo sac. It contains embryos, protuberance cells and secondary nuclei.
(i) Embryos : The three cells near the oviduct of the embryo are collectively called the embryos. Among them, the large cell in the middle is called ovule and the smaller cells on both sides are called companion cells.
(ii) Antipodal cells: The three cells on the ovule side of the embryo are collectively called Antipodal cells.
(iii) Secondary Nucleus: Two nuclei from the two poles come to the center of the embryo and fuse to form the secondary nucleus.