Describe the development of male gametophyte from microspore. Draw a neat labelled diagram of male gametophyte.

Answer: The microspore (pollen grain) is the first cell of the male gametophyte. Its development is precocious, i.e. it begins inside the microsporangium.

1. The uninucleate microspore enlarges and its nucleus divides mitotically (unequally) to form a large, irregular vegetative (tube) cell and a small, lens-shaped generative cell. Pollen grains are usually shed at this 2-celled stage.
2. After pollination on a compatible stigma, the pollen grain absorbs moisture and the intine grows out through a germ pore as the pollen tube. The tube nucleus moves to the tip of the tube.
3. The generative cell enters the tube and divides mitotically to form two male gametes (in some plants this happens before shedding, giving 3-celled pollen).
4. The pollen tube with its tube nucleus and two male gametes is the mature male gametophyte, which carries the gametes to the embryo sac.

[Diagram to be drawn: a germinating pollen grain showing the exine with germ pores, intine, the pollen tube growing out of a germ pore, the tube (vegetative) nucleus near the tip of the tube and two male gametes behind it.]