Events occurring after the arrival of a dormant pollen grain to the surface of a compatible stigma are diagrammatically presented

Generative cell in plants with bi-cellular pollen divides in pollen tube to produce two sperm cells

After the arrival on the stigmatic surface of the pistil, the dormant pollen grain (phase 1) adheres to a papilla, absorbs water (rehydration) and swells. This brings about the breaking of dormancy, mobilization of food reserves and activation of metabolism in the vegetative cell. The germination of the pollen grain takes place by the emergence of the pollen tube through one of the apertures (phase 2).

The emerging pollen tube first appears as a bulge of the intine protruding through the germination aperture since the polysaccharide tube wall is essentially a continuation of the intine. The nucleus of the vegetative cell and then the sperms, in plants with three-cellular pollen grains, are soon moved into the growing pollen tube by the cytoskeleton. In plants with bi-cellular grains (as shown here), the second division of the microgametophyte resulting in the formation of two sperm cells, occurs in the pollen tube.