Formation of embryo sac and production of egg of female gamete:
Embryo sac: the female gametophyte of a seed plant consisting of a thin-walled sac within the nucellus that contains the egg nucleus and other nuclei which give grow to endosperm on fertilization. In plants the flowers use meiosis to produce haploid generations which generate gametes all the way through mitosis. The female haploid is called the ovule and is produced by the ovary of the flower. When mature the haploid ovule produces the female gametes which are prepared for fertilization.
(i) At first the nucleus of a female spore (n) divides to form two nuclei through mitosis and each of these two nuclei moves to each pole.
(ii) The nucleus of each pole divides twice mitotically forming eight nuclei in total
(iii) Each nucleus is surrounded by cytoplasm and therefore they are the also called individual cells.
(iv) At this condition, the orientation of eight nuclei including the female spore (n) is called an embryo sac.
(v) One end of the embryo sac remains towards the micropyle and the other end towards the chalaza.
(vi) The number of 9 ses or spore nuclei entering into the formation of embryo sac Thus embryo sac may be monosporic, bisporic or tetrasporic tyr
(vii) The total number of nuclear divisions occurring during megasporogenesis and development of female gametophyte.
(viii) At this time, two nuclei, one from each pole moves to the middle of the embryo sac and they fuse together to fom\rm a definitive nucleus (2n).
(ix) Three nuclei towards the micropyler end are Called egg apparatus of which large nucleus at the middle is called egg or ovum or oospore (n) and two other nuclei are called synergid.
(x) Three nuclei towards the chalazal end are called Antipodal cells.