Pollen tetrads of R. japonicum, R. schlippenbachii, R. tsusiophyllum and M. pentandra were examined also with transmission electron microscopy. In all the genera studied, 3-colporate, oblate to suboblate pollen grains are arranged in tetrahedral tetrads. The apocolpial pollen wall is composed of the exine - well developed tectum, columellae, foot layer and endexine, and the intine