Scanning electron micrograph of a pollen grain of Cats Ear Hypochoeris radicata. The grain is about 30 micrometres across. Its outer wall (exine) consists of sharp spines on top of thickened ridges, which are finely perforated. Between the ridges 3 germinal pores are visible, each capped with an operculum (lid). When the pollen grain, containing the male gametes, lands on the stigma of the flower, it germinates. A pollen tube grows out from one of the pores, down through the stigma, to the ovary. The male nuclei pass down the tube, fertilize the ovules & a seed is formed. Magnification: x5500 (at 10x8 size).