Exine Ultrastructure of Myrtaceous Pollen

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Abstract
Exine ultrastructure has been determined by transmission electron microscopy analysis of the grains of a number of species of Myrtaceae, chosen to represent some of the diversity of sculpture and structure that can be observed using light microscopy and scanning electron microscopy. The species all show a typical angiosperm exine differentiation consisting of two chemically different layers, an electron-dense ektexine and a less dense endexine divided by a very thin electron-transparent lamella. They all differ, however, from the typical angiosperm architecture by the presence of a somewhat unstructured, granulate infratectal layer and a granular/alveolate endexinous layer around the pores. Species differences relate to the granulate coiumellate organization of the infractectal layer, the extent or density of tectal perforations and the presence and thickness of a foot layer around the grain.