Anatomic and Ultrastructural Study of the Septal Nectary in SomeTillandsia(Bromeliaceae) Species

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Abstract
The anatomy of the septal nectary and the ultrastructural features of the secretory mechanism of several species of Tillandsia are examined. The results are discussed with special reference to the particular ecology of this epiphitic genus. Although the basic anatomy of the secretory epithelium and of the underlying tissue in the nectary shows no outstanding differences from what reported by previous authors as regards other Bromeliaceae, a new fact is worth mentioning: nectariferous tissue is found also in the receptacle although the ovary of Tillandsia is tipically hy- pogynous. The ultrastructural morphology of the epithelium in flower buds near the anthesis and in open flowers in two successive moments of the anthesis indicates that the epithelial cells play an active role in nectar secretion, and that sugars are discharged to the outside mainly by means of a granulocrine process. The post-secretory stage is cytologically characterized by a consistent vacuolization of the cytoplasm and by the thickening of the wall. Therefore the ultrastructure of the septal nectary of Tillandsia shows no significant differences from the Bromeliaceae investigated by other authors. There is, however, a particular aspect in Tillandsia worth underlining, that is the mechanism by which the occlusion of the nectariferous slits is attained once the epithelium has become inactive. This mechanism does not only involve the approaching of the epithelium tangential cell walls, which at this stage are considerably thick, but it is due mainly to the production of a cementing substance made of acid polysaccharides.