The integuments of the ovule encloses a tissue called nucellus except at an opening, micropyle. Within the nucellus a cell, namely, megaspore mother cell forms four haploid megaspores via meiosis forming a linear tetrad. Only one of the four remains functional which later develops into embryo sac or female gametophyte. This, daughter cell of the tetrad is referred to as functional megaspore. Functional megaspore can either be atmicropylar end or chalazal end depending upon the species of the plant.