The Morphology and Permeability of Isolated Cuticular Membranes of Hoya carnosa R. Br. (Asclepiadaceae)

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Abstract
This investigation is in part an extension of previous leaf cuticle observations made on 52 other taxa among 34 families. Dewaxed, chemically isolated, adaxial and abaxial cuticular membranes and transverse leaf sections of the wax-flower plant (Hoya carnosa R. Br.) were examined using ordinary staining techniques and light-microscopy methods. Evidence is presented for the existence of ubiquitous, discrete, naturally occurring cuticular pores, concomitant with anticlinally oriented trans-cuticular canals, distributed randomly throughout the cuticular matrix. The surface of the adaxial cuticular membrane contains approx. 6540 unclustered pores per mm2, the abaxial approx. 4680 pores per mm2. Pore and canal diameters range between 0.5 and 0.75 μm. The canals are often arcuate and their lengths are directly related to cuticle thickness. No correlations were found between cuticle thickness and either pore numbers or pore and canal diameters. Based upon experiments with various pH indicators, solutions, and stains, the dewaxed, dry cuticular membrane of H. carnosa appears to be both distinctly hydrophilic and selectively permeable through a myriad of microscopically visible pores and canals permeating its matrix. A de novo interpretation of gross cuticle morphology based solely upon light microscopy observations is presented by semi-diagrammatic illustrations.