In angiosperms , the embryo sac represents the female gametophyte that derived from the megaspore mother cell through meiosis, that is why it is haploid. In angiosperms that double fertilization that includes syngamy and triple fusion causes the developement of diploid zygote and triploid endosperm. During fertilization, one of the two male gamete nuclei fuses with the egg nucleus to form the diploid zygote that later develops into the embryo while the other male gamete nuclei fuses with two secondary nuclei to form triploid endosperm nucleus that develops into the endosperm .
