(i) Megaspore is the first cell of the female gametophyte.
(ii) The megaspore increases in size and its nucleus divides mitotically into two nuclei which move apart to opposite poles. Thus, a 2-nucleate embryo sac is formed.
(iii) The two daughter nuclei undergo another mitotic division giving rise to the 4-nucleate stage.
(iv) The third mitotic division, which gives 8-nucleate embryo sac comprises of a micropylar and a chalazal end with four nuclei at each end.
(v) One nuclei from each end proceeds towards the centre of the embryo sac and are called the polar nuclei.
(vi) The three nuclei remaining at the micropylar region form the egg apparatus, without any cellular wall.
(vii) In the egg apparatus, the middle cell is the largest and is called oosphere/egg/ovum, while other two naked cells adjoining the egg cell are called synergids.
(viii) The three remaining nuclei at the chalazal end are surrounded by cytoplasm and cellular wall. These are called antipodal cells.
