Sexual Reproduction in Flowering Plants — BIOLOGY STD 12 Science — Question

After entry of pollen tube into embryo sac of ovule, two male gametes are discharged. Of these, one male gamete that approaches the egg cell, fuses with it forming diploid zygote (2n) and this process is called syngamy. The other male gamete that approaches the secondary nucleus, fuses to form primary endosperm nucleus (3n) and this process as triple fusion.
Because fussion occurs twice hence this process is said to be double fertilization. It is the characteristic of Angiosperms.