Trace the development of megasporocytes into the mature ovule
(i) A single Megaspore mother cell is differentiated in the micropylar region of the nucleus of an ovule & undergoes meiosis & forms a cluster of haploid cells called megaspore tetrad. Of these, soon three degenerates & only one megaspore becomes functional (ii) Functional megaspore enlarges to form embryo sac. Its nucleus undergoes mitotic division & two nuclei move to opposite poles forming a 2-nucleate embryo sac. (iii) Two successive mitotic divisions in each of these two nuclei result in information of 8- nucleate embryo sac. (iv) Three cells are grouped together at the micropylar end to form egg apparatus. consisting of two synergids & a female egg cell. (v) Three cells are grouped together at the chalazal end, they are called antipodal cells. (vi) The remaining two nuclei are called Polar nuclei, they move to the center of the embryo sac & fuse to form the secondary nucleus. Thus a typical angiosperm embryo sac is 8-nucleate 7-celled.
