Nettle stinging hair. Polarised light micrograph of a stinging hair from a Roman nettle (Urtica pilulifera). This tapering needle-shaped cell consists of a round basal part embedded in a multi-cellular pedestal (turquoise-green). The stinging cell itself has a central vacuole that is blue at the base and red at the tip. The cell wall (yellow) is thick and glass-like (silicified), especially at the red end. The tip itself ends in a spherical seal. Magnification: x230 when printed at 10 centimetres high.