explain in detail the following terms

After reaching the right stigma the pollen grain begins to germinate. The intine comes out in the form of  the pollen tube which then enters the ovule through the micropyle. The vegetative nucleus degenerates. The tip of the pollen tube gets dissolved and the male gametes are released into the embryo sac. One male gamete fuses with the egg cell and forms the zygote. This process is called syngamy. The other male gamete moves towards the centre and fuses with the secondary nucleus. This is called triple fusion. Triple fusion results in the formation of triploid primary endosperm nucleus. The syngamy and triple fusion together are called double fertilization