Types

• Each pollen grain contains a cell that divides by mitosis to generate two sperm. Once pollen has landed on the stigma, the sperm from the pollen grain can fertilize the egg in an ovule of the flower. Pollination is the process by which the pollen from the anthers is transferred to the stigma (typically the stigma of another flower); fertilization refers to the fusion of the sperm with the egg in the ovule.
  
  

Considerations

• Because flowers are often widely separated, they rely on a variety of means to transfer pollen. Some angiosperms are wind-pollinated, while others use birds and insects to transfer pollen for them. Some plants can even self-pollinate.
  
  

Function

• Once the pollen lands on the stigma, the generative cell inside the pollen divides to yield two sperm and the pollen grain forms a pollen tube, a long tube that extends from the stigma through the style and into the ovary of the flower. The sperm travel down the pollen tube and into the embryo sac inside an ovule, where one of them fertilizes the egg while the other fuses with two polar nuclei in the ovule. The polar nuclei and sperm that combine will form part of the seed that will help to nourish the young progeny plant during its growth.