Light penetration via leaf windows does not increase photosynthesis in three species of desert succulents

Epidermal windows on leaves may increase the surface area available for lig ht absorption by allowing the transmission of light through the internal su cculent, water-storage hydrenchyma and illuminating the chlorenchyma tissue from the inside of the leaf. This would appear to be advantageous by incre asing photosynthetic rates in these CAM plants, especially for taxa that gr ow partially underground in their native habitats. This hypothetical benefi t of windows, however, has rarely been experimentally investigated. Thus, n et CO2 exchange was measured on plants of Haworthia truncata, Lithops oliva cea (both with a below-ground growth habit), and Peperomia graveolens (with an aboveground growth habit) with their windows covered by reflective tape , and the results were compared with plants having unobstructed windows. De spite past assumptions about the function of leaf windows in these succulen ts, net CO2 exchange and nocturnal accumulations of malic acid were not sig nificantly greater in plants with unobstructed windows.