Abstract
Seedlings of Dipterocarpus zeylanicus Thw.. D. hispidusThw .. Mesua ferrea L..and AI nagassarium (81.11'11I. f) Kosterm .. were grown under light treatments.three ofwhich simulated the radiation experienced by the forest understorey andforest edge, two ofwhich simulated the centres of canopy openings of 200 and./00 Ill::. and a control simulated full sunlight. For each light treatment the soilII'as either regularly watered to field capacity or kept at --30% of field capacity.After two years measurements were made of stomatal frequency; of thethicknesses of the leaf-blades and of the upper epidermal, palisade mesophyll,and lower epidermal cell layers; and of cell dimensions. Significant differenceswere found between species and treatments. In general the measured dimensionsincreased with increase in light and decrease in soil moisture. Mesua ferrea hadthe thickest leaf blades followed by M. nagassarium, D. zeylanicus and D.hispidus, while D. zeylanicus had thicker epidermal and palisade mesophyll thanAI ferrca; taken together, these findings suggest that M. ferrea has a muchthicker mesophyll than the other species. In certain treatments, the twoDipterocarpus species had double rows of cells within both the palisademesophyll and the lower epidermal layers; the frequency of this phenomenonincreased with increasing light. It was not observed in Mesua, The greatestdensities of stomata were found in D. hispidus, followed by M. ferrea, M.nagassarium, and D. zeylanicus. Differences in shade and drought tolerancebetween species are discussed.
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