1986. Anatomy of the Sirelirzia reginae flower (Strelitziaceae). -Nord. J. Bot. 6 : 307-320. Copenhagen. ISSN Ol(37-055X.The Strelitzia reginae Ait. flower has many remarkable structural spezializations, the histology and cytology of which we have investigated. The chromoplasts of the sepals are conspicuously elongated and enclose numerous carotenoid tubules parallel to the long axis of the plastid. The petals have roundedpearshaped leucoplasts with a rhomboid protein crystal and aggregated plastoglobules. The blue colour is confined to the epidermal cells, which contain vacuoles with anthocyanin. Prominent papillar processes from the petal epidermis give rise to brilliance through refraction. Various reinforcements occur within the flower parts. The perianth leaves have permeating fibre ribs and thickened epidermal walls. The stigma and the free part of the style consist mainly of fibre cells (with protoplasm). The base of the style and the ovary are enclosed in the receptacle, the epidermal and hypodermal cells of which have thickened walls. -The ground tissue of the basal part of the receptacle appears aerenchymatous. There are also idioblasts containing raphides, druses, and tannin. The secretory cells of the stigma are long unicellular hairs outwards and columnar cells towards the canal between the three lobes. The stylar canal splits up into three individual arms, each leading to a locule. The epithelial cells are typical transfer cells. A composite secretion is deposited outside these cells. -The nectaries constitute three pockets between the carpels. Their secretory surface is greatly increased by folding of the epithelium and the presence of transfer cells.

Nectary trichomes of Abutilon striatum var. thompsonii arise by sequential periclinal divisions of outpushings from epidermal cells so producing trichomes that, when mature, are about 12 cells long. All epidermal cells within the nectary undergo this transformation. Later, anticlinal divisions lead to a multiseriate lower part of the trichome. The original epidermal cell becomes the basal cell which increases substantially in volume during development, thus leading to lateral separation of the trichomes. Above the basal cell is the stalk cell which develops an apoplastic barrier in its anticlinal (outer) wall. Secretion ultimately takes place from a capitate tip cell. An initially very thin cuticular layer, which overlies the whole trichome, eventually becomes as thick as the cell wall itself (approx. 0.4 μm). The pre‐secretory hairs contain numerous small, condensed mitochondria; poorly differentiated plastids; dictyosomes with coated vesicles; small vacuoles; and a large amount of smooth endoplasmic reticulum (“secretory reticulum”) which contrasts with the rough endoplasmic reticulum seen during earlier developmental stages. As secretion proceeds, vacuolation becomes more extensive. Plasmodesmata are present between all the cells of the trichome and diminish in frequency from about 12.0 μm‐2 in the stalk cell to about 4.0 μm‐2 in the apical cells. This variation in plasmodesmatal frequency along the trichome is seen at all stages of development. The ultrastructural evidence would be consistent with the hypothesis that the pre‐nectar flows through the plasmodesmata from cell to cell, is loaded into a “secretory compartment”, and is then unloaded into the apoplast from all cells of the trichome distal to the stalk cell.

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