Germinating pollen. Coloured scanning electron micrograph (SEM) of pollen grains from the back of spider that have sprouted pollen tubes (green). Pollen contains the male sex cells of a plant. Pollen tubes are produced when a pollen grain lands on the pistil (female part) of a flower. The tube burrows down into the pistil to reach the ovaries, where it fertilises the ovum (egg cell). Magnification: x200 when printed at 10 centimetres wide.