POLLEN DEVELOPMENT IN CENTROLEPIS-ARISTATA (CENTROLEPIDACEAE)

The pollen grain exine of Centrolepis aristata (R.Br.) Boem. & Schultz . is like a quilt with top and bottom layers tied together at interval s with ring shaped fasteners, each having an open center (''scrobiculi i'', Potonie 1934). Thus the top (tectum) extends down at intervals in the form of ring-shaped extensions providing continuity with the foot layer. In effect there are no columellae (bacules). The ectexine syste m is alveolate and much like the cap region of pollen of Pinus. Prior to the microspore vacuolate period there is no continuous footlayer. C ontents of the alveoli, which includes spherical bodies, are in direct contact with the cell surface. During vacuolate stages a footlayer is formed. At first it's structure includes spherical components. Before the vacuolate period there are no definite scrobiculi. As scrobiculi (and footlayer) develop during the vacuolate stages there is a ''commi ssural line'' (junction plane) across scrobiculi and between the footl ayer and plasma membrane of the cytoplasm. Components of the inner exi ne between the junction plane and plasma membrane are spheroidal to he mispheroidal during the vacuolate stages. After microspore mitosis an intine develops apparently beginning from the aperture region to encom pass the entire pollen wall. From that time there is no evidence of a junction plane either under the footlayer or across scrobiculi. Betwee n footlayer and tectum, within the alveoli, there are spheres. Some sp heres are in contact with the exine or even a part of it but most are without obvious contact with either tectum or footlayer. During the mi crospore vacuolate stages the tapetum degenerates. There is a massive influx of tapetal translocation material and organelles into locules a nd microspores. All microspores are enveloped by tapetal organelles an d materials. The tectum of alveoli contact the cell surface before the re is a footlayer. After formation of the footlayer it was in contact with the tectum. We refer to the zone proximal to the white-line lamel lation of the junction plane in young material as a ''transitory endex ine''.