double fertilisation is a unique events to angiosperms . Explain the event and its possible significance 

Double fertilisation means two fertilisation processes. One is the syngamy of one male gamete and the female egg. And second is the fusion of another male gamete with the two polar nuclei which results in the formation of Primary Endosperm Nucleus. The significance of this process is that the PEN divides and forms the endosperm which nourishes the developing zygote or embryo.