The most important and unique characteristic feature of angiosperms is the participation of both male gametes in the act of fertilization. The pollen tube releases the two male gametes into the cytoplasm of one of the synergids, then the penetrated synergid starts degenerating. One male gamete fuses with the egg cell to form a diploid (2n) zygote. This process is called zyngamy or true fertilization. The diploid zygote finally develops into embryo. The second male gamete fuses with the two polar nuclei or secondary nucleus in the central cell to form the triploid primary endosperm nucleus. This process is called triple fusion as three haploid nuclei are involved in the fusion. After triple fusion, the central cell becomes the primary endosperm cell, which gives rise to the endosperm.
