Pollen wall characters with emphasis upon applicability

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Abstract
The message for exine pattern resides ultimately in the genome, yet the information for the initial form exists in the cytoplasm or with the plasma membrane and its glycocalyx. Subsequent wall development is likely to be the result of an interplay between the genome, the cytoplasm, and the intralocular environment. The exine consists of units derived from the plasma membrane glycocalyx and enveloped in the exinous polymer sporopollenin. Growth of the exine in accomodation to cell surface expansion is modeled as involving a doubling in diameter of the units, separation of components, and incorportation of new units within the nexine but not the tectum. If the tectum is thick and does not become disjunct, its restraint upon cellular expansion may result in the crushing of bacules. Both the final shape and ornamentation of the exine may be influenced by cytological processes like oncoid plugs that limit the effect of protoplast expansion to nonapertural regions or globules in the exine arcade that can cause distention of the tectum and rupturing of bacules. Subunits of exinous units can be seen in distinctive patterns at the outer surface of the exine, in the arcade of the exine, and prior to intine formation at the inner surface of the nexine.