Cytochemistry and transmission electron microscopy reveal that the mature megaspores of Azolla filiculoides contain protein bodies, lipid globules, polysaccharide vacuoles and amylo-plasts whereas the microspores are packed with saturated lipid. The megaspore indusium is lignified but the flotation apparatus, capture mechanism, massulae and glochidia are heavily impregnated with sporopollenin. Ultrastructurally the walls of the massular pseudocells are closely similar to those of the flotation collar, from which filaments, identical to those in fossil taxa, extend. The microspore glochidia usually become attached to this region of the megaspore and the capture mechanism around the latter's blunt end is a misnomer. New details of distinctive internal surfaces of the sporocarps are demonstrated from fractured resin embedded specimens, a technique which may permit more accurate diagnosis of fragmentary fossil remains. The unsculptured exine around the megaspore is overlain by a two layered perine. The inner stratum, or endoperine, has a granular texture and expands to make up the bulk of the notation collar and the excrescences (tubercles) of the capture mechanism, whereas the outer, or exoperine forms a thick continuous layer between the tubercles and an anastomosing network above them. Since the filaments around the flotation apparatus have a similar homogeneous texture these are also assigned to the exoperine.