After this, the pollen tube enters between one of the synergids and releases 2 male gametes there. Out of these 2 male gametes, one gamete fuses with nucleus of the egg cell and forms zygote (syngamy). The other male gametes fuses with 2 polar nuclei in the centre form a triploid primary endosperm nucleus. Since this process involves the fusion of 3 haploid nuclei, it is known as triple fusion. It results in the formation of endosperm.