Pollen of Lewisia. Coloured scanning electron micrograph (SEM). Lewisia are primarily alpine or rock garden plants but they grow well in crevices or planting holes in retaining walls. Pollen grains are the male sex cells of a flowering plant. Their characteristic surface is used by botanists to recognise and classify plants. Pollen in plants is used for transferring male genetic material from the anther of a single flower to the stigma of another in cross-pollination. In a case of self-pollination, this process takes place from the anther of a flower to the stigma of the same flower. Magnification: x200 when printed at 10 centimetres wide.