With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
The female gametophyte or the embryo sac results from three successive mitotic divisions. First mitotic division- The megaspore forms two nuclei. One moves towards the micropylar end while the other shifts towards the chalazal end. Second mitotic division- At each end, each nucleus divides to form four nuclei each. Therefore, there are now 8 nuclei in total, 4 at each end. Third mitotic division-At the chalazal end, three out of the four nuclei differentiate to form antipodal cells (one nucleus remains). At the micropylar end, three out of the four nuclei differentiate into two synergids and one egg cell (one nucleus remains). This is called the egg apparatus. The two remaining nuclei come to the centre and form the polar nuclei in a large central cell. Thus, the embryo sac in the end contains 8 nuclei, but 7 cells.
