In the process of microsporogenesis, four microspores or pollen grains are produced from each pollen mother cell. Pollen is the first cell of pungametophyte. It can be round, oval, oblong or triangular. Each pollen grain is covered by a two-layered coat. The outer one is called exine and the inner one is called intein. Exine is thick, tough, uneven and composed of lignin. Its main chemical component is sporopollenin. In place of the exine are thin pore-like areas. This is called the reproductive pore (renurandhra or germpore). Pollen has 3-4 germpores (but can have up to 20). On the other hand, intein is thin, soft, smooth, elastic and made of cellulose. The cytoplasm of pollen is dense and the nucleus is in the middle of the cell. When the cell cavity is formed in the transformed state, the nucleus moves towards the periphery of the cell. Each pollen grain is 10-200 µm in diameter (according to many, 0.025-0.25 mm).
[If a pollen grain has one pore it is called monocolpate and if it has many pores it is called polycolpate]