Embriologia de <I>Picramnia glazioviana</I> Engl. (Simaroubaceae)

Resumen

This work describes the embryological development of Picramnia glazioviana Engl. (Simaroubaceae - Picramnioideae) and includes Megasporogenesis, Microsporogenes, endospermogenesis, and descriptions of the structure and development of the Megasporangium and Microsporagium. P. glazioviana has a multicellular archesporium, although only one cell generally develops further. The megaspore mother cell undergoes one division, producing a dyad where the chalazal megaspore enlarges and gives rise to a bi-nucleate embryosac with a conspicuous central vacuole. Two subsequent divisions give rise to the four-nucleate and eight-nucleate gametophytes. Developmente of the embryosac thus conforms to the allium type. The divisions of the endosperm nucleus are not followed by the cell wall formation, and hence its development is nuclear. The bitegmic crassinucellate ovule is epitropous, and the micropyle formed by both the inner and outer integuments is in straight line. The anther has four microsporangia and shows a Dicotyledonous type of wall formation. With fibrous thickenings in the endothecium. The behavior of the tapetum conforms to that of the secretory type. Cytokinesis is simultaneous and leads to the formation of tetrahedral tetrads. The Pollen grains are small with striate exine. P. glazioviana shows an apomitic. Reproductive strategy of the agamospermic and diplosporic types and at least in the examined population is obligatory.