Pollen grains of 5 specimens of the heterostylousW. viscosissimawere studied by light- and scanning electron microscopy. A striking pollen dimorphism correlated with a marked dimorphism of the reproductive floral organs was observed. Besides common size and shape differences the pollen grains of long- and brevistylous forms differ markedly in the number of apertures, in the relative length of the ectoapertures and in the nexine thickenings, as well as showing differences in the supratectal sexine elements and in the fine details of the tectum. The taxonomic significance of these differences in pollen characters is discussed.