The process in which the eight-nucleate single celled female gametophyte develops into the seven-celled female gametophyte. This mature structure contains two synergid cells and an egg cell at the micropylar end, and three antipodal cells at the other end. A binucleate endosperm mother cell is formed at the center. An example of this process is found in Arabidopsis thaliana.
cellularization of the embryo sac