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Summary

The parietal tapetal cells in the olive can, through their greater ribosome density, be distinguished from the pollen mother cells by about the leptotene stage. The organelles of these two cell types remain similar up to the tetrad stage. At this stage the tapetal and microspore cytoplasm are separated by four walls; the tapetal cell wall, the pollen mother cell wall, the tetrad callosic wall and the primexine. Microtubules are prominent against the radial walls of the tapetal cells. The cytoplasm of the tapetal cells is orientated around a central vacuole in a form suggesting cyclosis. Cytoplasmic vesicles generated from various sources within the tapetal cytoplasm appear to migrate towards the plasmalemma adjacent to the loculus or adjacent to the intercellular spaces. These vesicles, which are of at least three different types, fuse with the plasmalemma, apparently to discharge their contents.

The points of contact between the plasmalemma of the tapetal cells and the exine sculptures leave a transitory layer, the ‘tapetal printing’, on the pollen surface. Fibrillar material, probably protein, accumulates in the tapetal intercellular spaces and eventually comes to rest on the pollen poral surfaces. Granular electron dense bodies also accumulate in the tapetal intercellular spaces and finally come to lie between the pollen bacula. Orbicules are also produced by the tapetal cells and, at maturity, cluster around the degenerate lipoidal mass which is the final state of the tapetal cells.