Pollen Grain Dispersal:-

• In over 60% of angiosperms, pollen grains are shed at the 2-celled stage.
• In others, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed (3-celled stage).
• Once they are shed, pollen grains have to land on the stigma before they lose viability.
• The period for which pollen grains remain viable is variable and depends on the prevailing temperature and humidity.