Who discovered the pollen tube?

Mesogamy is the process in which:

The pollen tube usually enters the embryo sac through:

At which temperature are pollen grains stored (in $^{\circ} C$)?

How many of the following statements are true about the figure given below?
i. Germination of pollen grain.
ii. Motile male gametes.
iii. Two male gametes and one female gamete.
iv. Pollen grain without exine.
v. Tube nucleus at the tip of pollen tube.

In . . . . . . pollen grains cause allergy.