Describe double fertilization in plants.

In the case of plants, the pollen grain releases two male gametes. One fuses with the egg and forms the zygote. The other male gamete fuses with the two polar nuclei. This fusion is said to be triple fusion. Thus, inside an embryo sac, two fusions, syngamy and triple fusion, take place. This mechanism of two fusions occurring in an embryo sac is called double fertilization.