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What is double fertilisation? Why is it called so?
When one male gamete fuses with the egg and the other male gamete fuses with the primary endosperm nucleus inside the embryo sac it is called Double Fertilisation (Discovered by S.G. Nawaschin).
The fusion of two polar nuclei and one male gamete to form the Primary Endosperm Nucleus is known as Triple Fusion (Discovered by S.G. Nawaschin).

    The pollen tube reaches the ovule through the style
    The two haploid male gametes are discharged into the embryo sac
    One male gamete fuses (fertilises) with the egg to form a zygote. This process is called syngamy
    Two polar nuclei from the two poles of the embryo sac reach the centre and fuse to form the Secondary Nucleus(2n)
    The other male gametes fuses with the diploid secondary nucleus in the centre to form the triploid Primary Endosperm Nucleus
    Since two fusions take place inside the embryo sac this process is called Double Fertilisation


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