Leaf windows are multi-celled, translucent portions of epidermis, lacking chlorophyll, found on some species in the Asteraceae, Liliaceae, Mesembryanthemaceae, and Piperaceae families. A proposed theory regarding this morphological characteristic is that the window may increase the surface area available for light interception by transmitting light through the succulent, water-storage parenchyma and illuminating the chlorenchyma tissue from the inside of the leaf. This would appear advantageous by increasing photosynthetic rates in these CAM plants, especially for window plants that are partially subterranean in their growth habits. In order to test this theory, gas exchange was measured on five species of window plants with their windows covered by reflective tape or with windows unobstructed. Three species with subterranean growth habits (Haworthia truncata, Lithops olivaceae and Ophthalmophyllum longum) and two species with above ground growth habits (Peperomia graveolens and Senecio rowleyanus) were included for net CO2 gas exchange. The internal micro-light environment was also measured using a fiber optic probe. All species showed Crassulacean acid metabolism. Results showed no significant increase in CAM due to the additional light provided by the windows. Alternative hypotheses concerning the possible function of these putative windows will be presented.

Key words: CAM, Crassulacean acid metabolism, leaf windows