Question

Explain events prior to entry of pollen tube into ovule

Answer 1

Pollen tubes are produced by the male gametophytes of seed plants. They act as conduits to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms.

Answer 2

the pollen grain on getting nourished by the sugary secretion of the stigma germinates to give the pollen tube which carries two nuclei
the generative nucleus and tube nucleus
the tube nucleus disappears when the pollen tube reaches the micropyle and the generative nucleus gives two male gametes