Pollen of the Butomaceae and Alismataceae

When the microspores of B. umbellatus are released from the tetrad the developing wall consists only of muri and pilae (bacula). A basal layer is subsequently formed on unitmembrane-like strands. The latter appear to be formed de novo in association with the microspore cell membrane. As a basal layer develops an outer consolidated and an inner stranded layer are differentiated. These are considered ontogenetically equivalent and no terminological distinction appears justified. The basal layer and sexine are not differentiated by basic fuchsin or electron stains. Thus, the stranded (or nonhomogeneous) and amorphous-granular (or homogeneous) types of exine fine structure are histochemically indistinguishable in this species. Concomitant cytoplasmic activity, particularly in the peripheral region of the cell, may be related to substrate or enzyme synthesis, transport, and deposition. Several “unusual” vesicle types are tentatively related to other phases of morphogenetic activity in the protoplast.