Petal papillae. Coloured scanning electron micrograph (SEM) of papillae on the surface of a wild primrose (Primula vulgaris) petal. Papillae are projections from epidermal cells. They are often swollen and covered in wax to help reduce water loss. The wild primrose is a woodland and hedgerow plant with yellow flowers. Magnification: x1015 when printed 10cm high.