Post-pollination development

When the microspores or pollen grains fall on

the stigma of the pistil, post-pollination changes occur. The pollen grain absorb water and nutrients available on the stigmatic surface. The intine of the pollen grain protrudes out through one of the germ pores and a pollen tube is formed. The pollen tube pierces the stigmatic surface and moves down through the style of the pistil. The nucleus of the generative cell divides mitotically to form two male nuclei which become surrounded by a thin cytoplasmic sheath and appear as distinct non-motile male gametes. The nucleus of the generative cell, migrates to pollen tube. Formation of male gametes may also occur prior to formation of pollen tube. This three -celled male gametophyte remains viable for a short time. As the pollen tube elongates, the distal part becomes highly vacuolated and becomes separated from the anterior part containing the three nuclei, by formation of callose plug
Source:USHA