A pollen grain in angiosperm at the time of dehiscence from an anther could be 2-celled or 3-celled. Explain. How are the cells placed within the pollen grain when shed at a 2-celled stage?

In more than 60 per cent of angiosperms, the pollen grains are shed in 2-celled stage containing vegetative cell and generative cell. In remaining plants, before the pollen grains are shed, the generative cell undergoes asymmetric mitotic division and forms two male gametes leading to the formation of 3-celled stage.

The vegetative cell is bigger, has abundant food reserve and a large irregularly shaped nucleus. The generative cell is small and floats in the cytoplasm of the vegetative cell.