Give scientific reasons: Two types of fusions,syngamy and triple fusion,take place in the embryo sac.

(N/A) After entering one of the synergids,the pollen tube releases the two male gametes into the cytoplasm of the synergid.
One of the male gametes moves towards the egg cell and fuses with its nucleus,thus completing the $syngamy$. This results in the formation of a diploid cell,the $zygote$.
The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid $primary$ $endosperm$ $nucleus$ $(PEN)$.
As this involves the fusion of three haploid nuclei,it is termed $triple$ $fusion$.
Since two types of fusions,$syngamy$ and $triple$ $fusion$,take place in an embryo sac,the phenomenon is termed $double$ $fertilisation$.