Explain double fertilisation angiosperms

Explanation

At the end of pollination pollen is transferred to stigma of female pistil fertilisation followed by pollination

(a) Fertilised embryo sac showing zygote and Primary Endosperm Nucleus (PEN), (b) Stages in embryo development in a dicot [show in reduced size as compared to (a)]
Pollen deposition on the stigma, pollen tube develops. Pollen tube develops into style and enter into ovary and reaches to ovule. At this time two male gametes are included in Lumen of pollen tube.
After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid. One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngampy. This results in the formation of a diploid cell zygote. The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus. As this involves the fusion of three haploid nuclei it is termed as triple fusion. Since two types of fusions, syngam and triple fusion take place in an embryosac the phenomenon is termed as double fertilisation an event unique to flowering plants. The central cell after triple fusion becomes the Primary Endosperm Cell (PEC) and develops into the endosperm while the zygote develops into an embryo