Germinating lily pollen. Colored scanning electron micrograph (SEM) of lily (Lilium sp.) pollen grains that have sprouted pollen tubes. 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 fertilizes the ovum (egg cell).