Explain double fertilisation.

The union in flowering plants of two sperm nuclei. One sperm nucleus unites with the egg to form the diploid zygote, from which the embryo develops, and the other unites with two polar nuclei to form the triploid, primary endosperm nucleus.

  the process in which fertilization takes place twice in a flowering plant, first between male gametes and egg & second between male gametes & polar nuclei..is called as double fertilization

 Double fertilization is a characteristic feature of flowering plants. In the process of double fertilization out of the two sperm nucleus, one sperm nucleus fuses with the egg nucleus to form an embryo ( process is called syngamy) and another fuses with polar nuclei to form endosperm ( process is clled triple fusion).