The process found in most flowering plants where two male gametes enter the embryo sac and both participate in fertilization. One male gamete fuses with the female gamete or egg nucleus to form a *zygote
, which develops into the embryo. The other male gamete fuses with either the *polar nuclei
or the *definitive nucleus
to form a triploid primary endosperm nucleus, which will give rise to the endosperm. A form of double fertilization is also seen in some species of the gymnosperm genus Ephedra, in which one male gamete fuses with the egg cell and the other fuses with the ventral canal cell. However the product of the second fertilization does not undergo further development.