2 difference between cross pollination and self pollination

Explanation

The process of formation of microspores from a pollen mother cell is called microsporogenesis. Microspores, as they are formed are arranged in a cluster of four cells the microspore tetrad. As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. When the pollen grain is mature it contains two cells - the vegetative cell and generative cell. The vegetative cell is bigger, has abundant food reserve and a large irregular nucleus. The generative cell is small and floats in the cytoplasm of the vegetative cell. It is spindle shaped with dense cytoplasm and a nucleus. In over 60 per cent of angiosperms pollen is shed at 2 celled stage. In the remaining species generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed (3-celled stage).