The process of formation of the megaspore from the megaspore mother cell is called megasporogenesis. Ovules generally differentiate a single- megaspore mother cell in the micropylar region of the nucellus. This mother cell undergoes meiosis and as a result, forms a linear tetrad of 4 mesaspores. Usually one of the four megaspores towards the micropylar end is functional, while the other three degenerate. Only the functional megaspore develops into the female gametophyte (embryo sac). The nucleus of the functional megaspore divides mitotically to form two nuclei, which move to opposite poles, forming 2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4 nuclei and the later 8-nucleate stage of the embryo sac.