In angiosperms, the nutrient-storing tissue that nourishes a developing embryo is called the endosperm. The endosperm is a triploid tissue that is formed as a result of the double fertilization process in angiosperms. During double fertilization, one sperm fertilizes the egg to form the zygote, while the other sperm fuses with two polar nuclei to form the triploid endosperm. The endosperm serves as a nutrient source for the developing embryo, providing it with the energy and nutrients it needs to grow and develop until it can photosynthesize on its own. The endosperm can also serve as a nutrient source for the developing seedling after germination.