Question

what happens when a Pollen Grain falls on stigma?

Answer 1

pollen tube develops and the pollen grain goes through the pollen tube and reaches ovary where it gets fertlised with the ova

Answer 2

When pollen grains fall on stigma of a flower, then a pollen tube is formed which carries the tube and generative nucleus through the stigma to the ovule. On reaching the ovule, the two polar nuclei unite to form secondary nucleus and then the sperm nucleus from the pollen tube unites with it to form endosperm cell.The other sperm nucleus enters egg cell through the assistance of synergids which then degenerate, and unites with its nucleus.This is calld double fertilisation triple fusion.