Fully developed mature pollen grain in angiosperm is a 3 celled structure and is the mature male gametophyte. In the gametophyte, cytoplasm and tube cell nucleus are found at the terminal position and the two male gametes are positioned at the back side of the tube nucleus. Majority of the angiospermic plants releases their pollen grain in 2-celled stage which develops to 3-celled on reaching the stigma. Around 40% of angiosperms, pollen grain is released at 3-celled stage.