THE SUBGLANDULAR TISSUE OF HIBISCUS-ROSA-SINENSIS NECTARIES

The nectary of Hibiscus rosa-sinensis is subtended by subglandular par enchymatous tissue extending from the bases of the nectary hairs to th e depth of about 30 cells. Several of these cells contain large crysta ls. The subglandular tissue shows a well developed vascularization. In principal two cell types were found. When Sudan Black B or the select ive osmium impregnation method were applied, many cells, especially th ose around the parenchymatous tissue and under the vascular bundles, w ere stained brown to black. They can be distinguished from neighboring cells by their large size and intense absorption of stains or high el ectron density. They deposit in their large vacuoles osmiophilic subst ances, presumably oil and have been named oil cells. Groups of oil dro plets, in contact with the nucleus, were also present in the parenchym atous and oil cells. Tissue fixation in glutaraldehyde and osmium tetr oxide vapors revealed granular electron dense remnants within oil cell s. Another cell type, the mucilage cells, was found in the subglandula r tissue. These cells became evident after the application of histoche mical methods for polysaccharides. Autoradiographical study showed tha t, externally applied labelled glucose incorporated into the mucilage and cell walls. Mucilage plays an important role in the regulation of water economy, which is decisive in nectar secretion. The oil cells ma inly protect the sugar containing tissues (phloem, parenchyma) against herbivores.