In angiosperms the endosperm is formed by the fusion of one sperm and two polar nuclei. Therefore, the endosperm is triploid in angiosperms. The endosperms is common nutritive tissue for the developing embryo. The haploid endosperms (gametophytic generation) is found in gymnosperms. It is formed from the outer unused layer of female prothallus. The fertilized egg (fusion of sperm and egg nucleus) is called zygote. It is diploid. It gives rise to embryo following a predetermining mode of development.