The elucidation of the ultrastructural cytochemistry, coupled with chemical stabilizing procedures during fixation and embedding, make a significant contribution to the understanding of pollen-exine ontogenesis. A combination of the Con-A agglutination and lanthanum precipitation methods proved particular advantageous during the intine formation stage. By using immunogold techniques, it is possible to demonstrate that only the mature exine of the atmospheric pollen grains reacted positively after sectioning, not the intine. An important difference appears when immature pollen grains are treated under the same conditions: in this case, both the microsporal cytoplasm of the future pollen grain and the immature exine react, but not the intine.