Fertilization in plants occurs when haploid gametes meet to create a diploid zygote, which develops into an embryo. The female reproductive organ of angiosperms is the pistil, located in the middle of the flower and the male gametophyte is the pollen grain. A major distinguishing feature of angiosperms is the practice of double fertilization. An angiosperm ovule contains an egg cell and a diploid fusion nucleus, which is created through the joining of two polar nuclei within the ovule. The triploid nucleus turns into an endosperm, which nourishes the developing embryo.