The process of fertilization observed in angiosperm is called double fertilization. It is a combination of syngamy and triple fusion. Events during fertilization are elucidated. As the pollen grain falls on the stigma of the flower, it germinates and forms a pollen tube. The pollen tube is guided by the secretions of the ovule. Pollen enters the micropylar region of the ovule. The embryo sac inside an ovule consists of antipodals, synergids, egg cells, a central cell with two polar nuclei. Pollen tube releases two male gametes into synergids cytoplasm. Only the male gametes fuse with the nucleus of the egg cells by the process of syngamy to form a diploid zygote (2n). The other male gamete fuses with the central cell and forms the primary endoplasm nucleus (PEN). This function is called triple fusion. Hence, endoplasm is triploid in nature.