OSMOPHORES OF STANHOPEA (ORCHIDACEAE)

Species of the Neotropical orchid genus Stanhopea produce a fragrance comprising terpenoids and aromatics which attracts euglossine bee pollinators. The secretory tissue, called an osmophore, is located in the adaxial region of a sac formed near the proximal portion of the floral lip. This region is easily recognized in Stanhopea oculata and S. wardii because it is papillate. The osmophore in these two species includes all the cells of the papillae and those directly below, that grade into fundamental tissue. Osmophore cells are more densely cytoplasmic than cells in the adjacent tissue. Numerous amyloplasts and mitochondria are seen in these cells from the earliest bud stages we examined through anthesis. Smooth and rough endoplasmic reticulum are abundant, but dictyosomes are uncommon. Mitochondria of osmophore cells appear to be distributed with no apparent pattern during bud stages, although they tend to be aligned near the plasmalemma at anthesis. Osmophore cells are highly vacuolate after anthesis.     

FOLIAR TRICHOMES OF PLEUROTHALLIDINAE (ORCHIDACEAE): FUNCTIONAL SIGNIFICANCE

Foliar surfaces of nine pleurothallid orchids (Cryptophoranthus lepidotus L. O. Wms., Octomeria sp., Pleurothallis pidax Luer, P. poeppigii Lindl., P. revoluta (Ruiz & Pav.) Garay, Restrepiella ophiocephala (Lindl.) Garay & Dunsterv., Restrepia muscifera Rchb. f. ex Lindl., Scaphosepalum rapax Luer, Stelis endresii Rchb. f.), four nonpleurothallid orchids (Cyrtopodium punctatum (L.) Lindl., Encyclia cochleata (L.) Lemee, E. tampensis (Lindl.) Small, Paphiope-dilum hybrid) and five tillandsioid bromeliads (Catopsis nutans (Sw.) Griseb., Tillandsia fas-ciculata Sw., T. streptophylla Scheidw., T. stricta Soland., T. tectorum E. Morr.) were assayed for permeability to Ca, S and P ions. Compared to leaves of the atmospheric bromeliads, those of the orchids proved less permeable to Ca and S. Moisture exchange profiles were determined for two of the bromeliads and three orchids; bromeliad leaves were able to rehydrate completely, orchid leaves only partially. Absorptive capacities of trichomes borne by five taxa were tested by autoradiographic analysis. Unlike bromeliad trichomes, those of the orchids exhibited no capacity to accumulate ³H-leucine. These results and other considerations described here suggest that, unlike tillandsioid bromeliads, neither the pleurothallid nor the nonpleurothallid orchids examined in this survey rely heavily on shoots for mineral and moisture procurement.     

AN UNUSUAL EPICUTICULAR WAX ULTRASTRUCTURE ON LEAVES OF PROSOPIS TAMARUGO (LEGUMINOSAE)

Studies of Prosopis tamarugo Phil. leaflet surfaces by scanning and transmission electron microscopy disclosed an aggregate coating of basic wax structures of various shapes along with large semi-vertical plates. The basic structures, with some degree of variation, were also present on P. velutina Woot. and on several other Prosopis species which had been previously investigated. However, the plates, about 3 μm in size, were observed only on P. tamarugo. The basic wax structures were first observed on very young leaflets, about 6 h after emergence from the apical bud. The plates appeared after 24 to 72 h. Both plates and basic structures were larger on seedlings grown in a low (20–25%) relative humidity as compared to high (70%) humidity. When grown side-by-side in the greenhouse, leaflets of P. tamarugo seedlings were more isolateral in structure than those of P. velutina, suggesting a greater xeromorphic adaptation. The unusual epicuticular configuration described could be a mechanism that enhances the foliar absorption of atmospheric moisture, or at least minimizes cuticular transpiration, thereby aiding survival of this unique tree in its native habitat of northern Chile.     

CARBOHYDRATE PHYSIOLOGY OF ORCHID SEEDLINGS. III. HYDROLYSIS OF MALTOOLIGOSACCHARIDES BY PHALAENOPSIS (ORCHIDACEAE) SEEDLINGS

Germinating seeds and developing seedlings of Phalaenopsis Habsburg and Phalaenopsis Ruth Burton × (Phalaenopsis Abendrot × Phalaenopsis Abendrot) can utilize glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose as carbon sources. Fresh weight decreased significantly with increased polymerization from glucose through maltoheptaose. Seedling survival declined on higher molecular weight sugars reaching levels which were significantly different from those on glucose. Sugar uptake increased moderately with increasing molecular weight of oligomers. The maltooligosaccharides used in these experiments are hydrolyzed by the orchid seedlings and of the sugars which can support good growth glucose, but not maltose accumulate in culture media. As a result, media which supported seedlings contained substantial levels of glucose, the starting sugars, and decreasing amounts of the next shorter oligomers. This suggests enzymatic endwise hydrolysis of these maltooligosaccharides. Similar results were obtained with Phalaenopsis seedlings produced from seeds which were germinated on sugar-free medium and transferred to a solution containing the same oligomers. Sugars in media which did not support seedlings were not hydrolyzed.     

POLLINATION BIOLOGY OF LISTERA CORDATA (ORCHIDACEAE)

Pollination biology of northern California populations of Listera cordata (L.) R. Br. is presented. The flowers are allogamous, self-compatible, and protandrous. At anthesis, access to the stigma is blocked by the flap-like rostellum. When an insect contacts the touch-sensitive trigger hairs of the rostellum, the pollinia are suddenly released and become cemented to the insect's body. One to two days after the pollinia are removed, the rostellum rises and exposes the receptive stigma. Visitors are attracted to the flowers by their foul odor and minute quantities of nectar presented on the surface of the labellum. Pollination efficiency is high with 61–78% of flowers from several localities setting fruit. The most important and abundant pollinators of L. cordata at our study sites are fungus gnats (Sciaridae and Mycetophylidae). Other less frequently encountered pollinators are members of these families: Braconidae, Ichneumonidae, and Tipulidae. At present, there is no compelling evidence that the floral characteristics of L. cordata have evolved as a result of an evolutionary interaction with any specific group of insects. Nor is there any indication that the flowers are sapromyophilous, despite their putrid odor.