Explain the mechanism of double fertilization.

Explanation

Double Fertilisation
After entering one of the synergids, the pollen tube discharges the two male gametes into the cytoplasm of that synergid. One of the male gametes moves towards the female gamete (egg) and fuses with it, this fusion is called syngamy and it results in the formation of azygote.
The second male gamete moves towards the two polar nuclei in the central cell. The two polar nuclei just fuse to form a secondary nucleus and the second male gamete fuses with the secondary nucleus in the central cell, this fusion is called triple fusion and it results in the formation of a triploid primary endosperm nucleus .
Since two fusion, syngamy and triple fusion occur in an ovule, the phenomenon is known as double fertilisation in angiosperms