Double fertilization is the fusion of two male gametes brought by a pollen tube with two different cells of the same female gametophyte in order to produce two different structures. Double fertilization was discovered independently by Nawaschin and Leon Guingnard. One male gamete fuses with the egg or oosphere to form a diploid zygote or oospore. It is called generative fertilization. The second male gamete fuses with the diploid secondary nucleus of the central cell to form a triploid primary endosperm nucleus. It is called as vegetative fertilization. This primary endosperm nucleus gives rise to a triploid nutritive tissue called endosperm.