In the majority of angiosperms the pollen grain matures at the two-celled stage, enclosing a vegetative cell and a generative cell. In some plants, pollen maturation occurs at the three-celled stage, when the generative cell divides to produce two sperm cells. Irrespective of the number of cells they enclose, mature pollen grains are released by the dehiscence of the anther and are passively carried to the receptive surface of the stigma of another flower in the act of pollination. This is the beginning of a cascade of events that ensure double fertilization in the embryo sac. This chapter will consider how the pollen grain makes its way through the stigma and style toward the ovary and ovule. Although our knowledge of the intimate details of individual events in the odyssey of the pollen grain is far from complete, there is a considerable body of descriptive information relating to these events.

The environment of the stigma and style where the events subsequent to pollination take place is so overwhelmingly complex that it almost defies analysis. Fortunately, recent advances in biochemical and cell biological methods have gone in tandem with exploitation by the electron microscope, with the result that a detailed account of the structure of most of the participating cells in the stigma and style has become available.