Explain the development of the female gametophyte.
Development of female gametophyte: The functional megaspore is the first cell of the female gametophyte of angiosperms. It enlarges to form the female gametophyte, also called embryo sac. Its nucleus undergoes a mitotic division and the two nuclei move to the opposite poles, forming the 2-nucleate embryo sac. Two successive mitotic divisions in each of these two nuclei result in the formation of an 8-nucleate embryo sac. Cell wall formation starts at the eight-nucleate stage, resulting in the formation of a typical female gametophyte. Three cells are grouped together at the micropylar end to form the egg apparatus, consisting of two synergids and a female gamete/egg cell. Three cells are grouped together at the chalazal end. They are called antipodal cells. The remaining two nuclei are called polar nuclei. They move to the centre of the embryo sac (now called a central cell) and fuse to form a diploid secondary nucleus. Thus, a typical angiosperm embryo sac is 8-nucleate and 7-celled.
