For the formation of embryo sac, the megaspore mother cell undergoes

For the formation of embryo sac, the megaspore mother cell undergoes one meiotic and three mitotic divisions.
The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac.