The embryo sac was classified by P. Maheshwari. He classified them based on the number of megaspore nuclei that are participating in the formation of the embryo sac. They were classified into three types:Monosporic Embryo Sac: It is formed from a single megaspore. This takes place in Polygonum. Bisporic Embryo Sac: In this two megaspore nuclei take part in the development of the embryo sac. This takes place in Allium. Tetrasporic Embryo Sac: In this, all the four megaspore mother cells take part in the development of the embryo sac. This takes place in Adoxa.