$\text{Trace the development of megaspore mother cell up to the formation of a mature embryo-sac in a flowering plant. }$

The process of formation of megaspores from megaspore mother cells is called megasporogenesis. Ovules generally differentiate a single megaspore mother cell [MME] in the micropylar region of the nucellus. The megaspore mother cell undergoes meiosis resulting in the formation of four megaspores. In the majority of flowering plants, one of the megaspores is functional while the other three degenerate.

Only the functional megaspore develops in female gametophyte (embryo sac). This method of embryo sac formation from a single megaspore is termed monosporic development. The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles forming two nucleate embryo sacs. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. After the 8-nucleate stage, cell walls are laid down leading to the organization of the typical female gametophyte or Egg embryo sac. Six of the eight nuclei are surrounded by cell walls and organized into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell. Three cells are grouped together at the micropylar end and constitute egg apparatus. It consists of two synergids and one egg cell. Three cells at the chalazal end are called antipodals, Thus, a typical angiosperm embryo sac at maturity, though eight nucleate is seven celled.