Structure of Pollen:
Pollen itself isn’t the male gamete. Each pollen grain contains vegetative cells, only a single cell in most flowering plants but several in other seed plants, and the generative cells contain two nuclei. A tube nucleus produces the pollen tube and a generative nucleus that divides to form the two sperm cells. The group of cells is surrounded by a cellulose-rich cell wall called the intine and a resistant outer wall composed largely of sporopollenin is called the exine.
The pollen is eventually released when the anther forms openings. These may consist of longitudinal slits, or pores, as in the health family, or by valves, as in the barberry family. In some plants, notably members of Orchidaceae and Asclepiadaceae, the pollen remains in masses called pollinia, which are adapted to attach to particular pollinating agents such as birds or insects. More commonly, mature pollen grains separate and are dispersed by wind or water, pollinating insects, birds, or other pollination vectors.