Double fertilisation is found only in angiosperms. In this group of plants, the pollen tube on entering the embryo sac bursts open in one of the two synergids to release the two male gametes. One male gamete fuses with the egg or oosphere to form a diploid zygote or oospore. It is called generative fertilisation. The second male gamete descends down and fuses with the diploid secondary nucleus of the central cell to form a triploid primary endosperm cell. It is known as vegetative fertilisation. Thus, after double fertilisation, a mature angiospermous ovule contains one diploid cell (zygote) and one triploid cell (primary endosperm cell). The haploid cells of the ovule such as antipodals and synergids degenerate after fertilisation.