What is triple fusion ? Where and how does it take place ? Name nuclei involved in triple fusion.

Explanation

Triple fusion. In the embryo sac both trhe male gametes are released. One of these nuclei fuses with the egg nucleus resulting in the formation of diploid zygote. The process is called syngamy or true fertilization.
The other male gamete fuses with two polar nuclei (secondary nucleus) and results in the formations of a triploid Primary Endosperm Nucleus (PEN). Since, the process involves fusion of three haploid nuclei (two polar nuclei and one male gamete), it is known as Triple fusion.
The fusion product is Primary Endosperm Cell (PEC) having triploid endosperm nucleus. The PEN divides and ultimately forms multicellular triploid nutritive trissue called as endosperm.