Nectar secretion in a dry habitat: structure of the nectary in two endangered Mexican species of Barkeria (Orchidaceae)

Barkeria scandens and B. whartoniana are endangered, endemic taxa from Mexico. They are epiphytes adapted to dry habitats. Since these plants are xerophytic, their flowers were investigated for structural adaptations to nectar secretion. The flowers of both species are structurally similar, and contrary to most claims for the genus, have functional floral nectaries comprising a nectary chamber and a narrow tubular cuniculus. Nectar is present in both these structures, and contains sugars and lipid-like compounds. The nectary tissue is composed of a single-layered epidermis overlying 1–2 layers of subepidermal secretory parenchyma. The outer tangential wall of the epidermal cells is thick and multi-layered, whereas the cuticle, which often shows blistering, is lamellate and possesses micro-channels. Lipid-like material occurs both between the microfibrils of the cell wall and in the micro-channels. Robust secretory tissue, thick cell walls, and lipid-like nectar components limit nectar evaporation. Moreover, the rigidity of the nectary potentially makes it possible for red-flowered B. scandens to switch from entomophily to ornithophily.

A new species of Combretum sect. Ciliatipetala (Combretaceae) from South Africa

Combretum eugeneanum, a new species from northeastern KwaZulu-Natal, South Africa and confined to the Maputaland Centre of Plant Endemism, is described, illustrated, mapped, and compared with southern African members of the genus with which it may be confused. In a narrowly defined genus Combretum, the new species belongs to Combretum sect. Ciliatipetala. In herbaria, it has usually been confused with close relatives C. apiculatum and C. edwardsii, as well as several other more distantly related members of the genus, in particular C. woodii. The new species is also closely related to the recently described C. stylesii. It is readily distinguished as an essentially glabrous woody climber or scrambling shrub needing other vegetation for support, leaf apices rarely apiculate, tertiary veins raised on the adaxial leaf surface, inflorescences few-flowered and subcapitate, upper hypanthium cupuliform, flowers with orange-red centres (discs) and peltate scales comprised of essentially eight radial cells, most of which are subdivided by at least one tangential wall, the resulting outer and inner cell(s) often with at least one additional radial wall. Combretum eugeneanum grows in Sand Forest and associated sandy bushveld, and its range and habitat does not overlap with that of C. edwardsii or C. stylesii, both of which are also very often lianas.

Gas Carry-Under in Gas-Liquid Cylindrical Cyclone Separator: A Mechanistic Model

Gas Carry-Under (GCU) is one of the two undesirable phenomena that occur in the GLCC©,1 (Gas-Liquid Cylindrical Cyclone) separators when it operates even within the Operational Envelope (OPEN). Earlier studies have shown that maintaining a liquid level below the inlet of the GLCC under control configuration affects the GCU in GLCC. It has been identified that the tangential wall jet is the cause of gas entrainment within the GLCC and has been understood to change with liquid level maintained at the inlet. Also, it has been theorized that effective formation of the vortex formed in the lower part of the GLCC, or a stable gas core enhances the separation of gas entrained in the liquid. At present, there is no mechanistic model which captures these complex physical phenomena in the GLCC. This paper presents a newly developed mechanistic model which can predict the GCU for different flow conditions, fluid properties, and various liquid levels. The proposed model captures the various physical phenomena namely: saturated flow at the inlet, tangential wall jet phenomena, gas entrainment and vortex flow that results in separation of gas. The developed model has been compared with the extensive experimental data and is said to be in good agreement.

The structure of elaiophores in Oncidium cheirophorum Rchb.f. and Ornithocephalus kruegeri Rchb.f. (Orchidaceae)

The shining appearance of the flowers of <i>Oncidium cheirophorum</i> and <i>Ornithocephalus kruegeri</i> results from the presence of lipids on the flower surface. The lipids are produced by elaiophores - secretory structures situated symmetrically at the base of the labellum or upon the callus. In <i>O. cheirophorum</i>, the elaiophores are epithelial type. They consist of one layer of cuboidal secretory cells and subsecretory parenchyma. The thick cuticle covering the outer, tangential wall of epithelial cells becomes distended and wrinkled as secreted oil accumulates beneath its surface. Oil secretion begins at the bud stage and lasts till the end of anthesis, that is 22 days, on average. Pollination does not influence oil production. In <i>O. kruegeri</i>, trichomatous elaiophores are situated on the central part of the callus. Unicellular trichomes project from the epidermis cells. Their outer walls are covered by a thin cuticle. In the dense cytoplasm of the trichomes, small plastids with few starch grains occur, whereas subsecretory parenchyma cells contain amyloplasts with large starch grains and raphides. The oil is already produced at the bud stage, about one week before flower opening, and lasts till the end of anthesis.

A comparative study of mycorrhizas in several genera of Pyroleae (Ericaceae) from western Canada

Genera in the tribe Pyroleae (subfamily Monotropoideae, family Ericaceae) occur as understory plants in northern temperate zones where some form major components of ecosystems. Most have been poorly studied in terms of their association with symbiotic fungi. In this study, colonization patterns of mycorrhizal roots of five members of the Pyroleae ( Pyrola asarifolia Michx., Pyrola chlorantha Sw., Orthilia secunda (L.) House, Chimaphila umbellata (L.) W. Bart., Moneses uniflora (L.) Gray) were explored. Root samples were processed for light, fluorescence, and laser scanning confocal, scanning electron, and transmission electron microscopy, as well as for immunocytochemistry. Roots of all species had enlarged epidermal cells containing hyphal complexes, Hartig nets confined to the epidermis, and mantles. Epidermal cells were penetrated by hyphae originating from the Hartig net at more than one site either along the inner tangential wall or radial walls. The outer tangential wall of epidermal cells of all species, except M. uniflora, was thicker than radial and inner tangential walls and consisted of two layers, the outer containing nonesterified pectins that were labeled with JIM 5 antibodies. Radial walls and inner tangential walls did not label, but cortical cell walls did. Intracellular hyphal complexes developed initially around centrally positioned, enlarged epidermal cell nuclei and, through branching, occupied most of the cell volume. Senescence and degradation of the complexes followed. The fungal species in these symbiotic associations may be important functionally in nutrient exchange, as well as in contributing to broader linkages with other hosts in these plant communities.

A survey of the presence and morphology of orbicules in European allergenic angiosperms. Background information for allergen research

Allergenic activity in the atmospheric aerosol of small particles in the size range of a few micrometres or less may play an important role in causing allergic reactions in the lower regions of the lungs, often seen in pollinosis. Orbicules (= Ubisch bodies) are small, mostly spherical granules of sporopollenin, which can occur on the radial and innermost tangential wall of secretory tapetum cells. In instances where orbicules of allergenic species are dispersed into the atmosphere, they may act as effective vectors of allergens. We investigated the presence and morphology of orbicules in 15 allergenic species using scanning electron microscopy. Orbicules were present in all species investigated of the families Betulaceae, Chenopodiaceae, Fagaceae, Poaceae, Polygonaceae, and Urticaceae. In the species of the Asteraceae and Oleaceae studied, orbicules were lacking. Almost all orbicules observed were spiny. Their mean diameters range from 0.342 to 1.130 μm. Orbicules can be part of the fraction of small particles in the size range of a few micrometres or less, emitted from the anthers. Our results clearly indicate that a thorough investigation of the sites of allergens across the whole anther is required to reveal whether or not these orbicules possess allergens.Key words: allergenic plants, allergen research, morphology, orbicules.