In the flower ovary there are megasporangia enclosed by a tegument having a small opening, the micropyle. Within the megasporangium there is a megasporocyte, or megaspore mother cell, that undergoes meiosis forming four megaspores of which three regress and only one is functional. The functional megaspore undergoes (three) mitosis generating eight cells that as a whole form the embryonic sac.   _{Your Comment}