1. Embryo sac develops inside the nucellus of ovule from megaspore.
2. Megaspore mother cell is diploid structure which undergoes meiosis
3. After meiosis, tetrad of haploid cells are produced.
4. The upper three megaspores degenerate and the lower one of the tetrad is functional.
5. The entire embryo sac is developed by elongation and then three mitotic divisions of this single megaspore take place hence the development is described as monosporic.