Functions:
i. Pollen grains are generally spherical with a prominent two-layered wall. The hard outer layer is called exine made up of sporopollenin, which is a resistant organic material.
ii. Exine can withstand high temperature, strong acids and alkali, thus provide protection.
iii. It has prominent aperture called germ pore, through which pollen tube comes out.
iv. Vegetative cell has abundant food reserve.
v. Generative cell divides mitotically giving rise to two male gametes, before pollen grains are shed (3-celled stage).
