section_path: Fertilization
section_name: Fertilization
paragraph_text: Fertilization
  
  Fertilization, also called Synagmy, occurs following pollination, which is the movement of pollen from the stamen to the carpel. It encompasses both plasmogamy, the fusion of the protoplasts, and karyogamy, the fusion of the nuclei. When pollen lands on the stigma of the flower it begins creating a pollen tube which runs down through the style and into the ovary. After penetrating the center-most part of the ovary it enters the egg apparatus and into one synergid. At this point the end of the pollen tube bursts and releases the two sperm cells, one of which makes its way to an egg, while also losing its cell membrane and much of its protoplasm. The sperm's nucleus then fuses with the egg's nucleus, resulting in the formation of a zygote, a diploid (two copies of each chromosome) cell.
  
  Whereas in fertilization only plasmogamy, or the fusion of the whole sex cells, results, in Angiosperms (flowering plants) a process known as double fertilization, which involves both karyogamy and plasmogamy, occurs. In double fertilization the second sperm cell subsequently also enters the synergid and fuses with the two polar nuclei of the central cell. Since all three nuclei are haploid, they result in a large endosperm nucleus which is triploid.