Double fertilization is a process unique to flowering plants (angiosperms) where one male gamete fuses with the egg cell to form a diploid zygote, while the other male gamete fuses with two polar nuclei to form a triploid primary endosperm nucleus (PEN) /32%3A_Plant_Reproductive_Development_and_Structure/32.07%3A_Pollination_and_Fertilization_-Double_Fertilization_in_Plants). The process involves the fusion of one female gametophyte with two male gametes, resulting in the formation of two structures, namely, zygote and endosperm, hence the name “double fertilization” . The significance of double fertilization is that it gives rise to an endosperm that provides nourishment to the developing embryo, increases the viability of the seeds of angiosperms, and utilizes both the male gametes produced by the pollen grains. The process of double fertilization starts with the deposition of pollen on the stigma, which must germinate and grow through the style to reach the ovule. The microspores, or the pollen, contain two sperm cells. The pollen tube is guided by the chemicals secreted by the synergids present in the embryo sac, and it enters the ovule sac through the micropyle. Of the two sperm cells, one sperm fertilizes the egg cell, forming a diploid zygote, while the other sperm fuses with the two polar nuclei, forming a triploid cell that develops into the endosperm/32%3A_Plant_Reproductive_Development_and_Structure/32.07%3A_Pollination_and_Fertilization-_Double_Fertilization_in_Plants).