Triple fusion – The process of fusion of the male gamete with the two polar nuclei inside the central cell located in the embryo-sac to form primary endospermic nucleus (PEN) is called triple fusion. The process takes place inside the embryo-sac.

This process takes place in the following steps –

• When the pollen grains fall on the stigma of a flower, they germinate and give rise to the pollen tube.

• The pollen tube passes through style and enters the embryo-sac from the micopylar end.

• One of the male gamete fuses with egg cell to form zygote (syngamy)

• The second male gamete fuses with the two polar nuclei present in the central cell and form triploid primary endosperm nucleus.

• This process involves the fusion of three haploid nuclei hence is known as triple fusion.

One male gamete nucleus and two polar nuclei are involved in this process.