Herbarium pollen from four Acanthaceae species with caveate exines was rehydrated using a solution of tannic acid and glutaraldehyde (TAG), followed by fixation with osmium tetroxide. The results demonstrate the presence of lipoidal material contained in the caveae and columellar interstices. The nature, synthesis and possible function of this material are discussed. Aspects of endexine ultrastructure and deposition are also discussed.