What is double fertilisation in flowering plants and why is it called double?

Double fertilisation is a special feature of flowering plants where two fusion events happen inside the embryo sac. When the pollen tube reaches the ovule, it releases two male gametes. The first male gamete fuses with the egg cell. This is called syngamy and forms the diploid zygote, which later grows into the embryo. The second male gamete fuses with the two polar nuclei in the central cell. This is called triple fusion because three nuclei combine, and it forms the triploid primary endosperm nucleus, which develops into the endosperm that nourishes the embryo. Since two separate fusions, syngamy and triple fusion, take place using the two male gametes from a single pollen grain, the whole process is called double fertilisation. It ensures food is made only when an embryo actually forms.