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Journal Article

The Adaptive Significance of Stomatal Occurrence on One or Both Surfaces of Leaves

David F. Parkhurst
Journal of Ecology
Vol. 66, No. 2 (Jul., 1978), pp. 367-383
DOI: 10.2307/2259142
Stable URL: http://www.jstor.org/stable/2259142
Page Count: 17
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The Adaptive Significance of Stomatal Occurrence on One or Both Surfaces of Leaves
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Abstract

(1) The relationship of stomatal occurrence (on one or both sides of leaves to environment was studied by literature search, mathematical modelling and investigation of herbarium specimens. The starting hypothesis, that hypostomatous leaves (with stomata only on the underside) should occur in dry habitats, was contradicted by all three sources. (2) The models, based on mass-transfer physics, produced three major results: (a) mesophyll thickness is the chief variable determining stomatal distribution, with thick leaves tending to be amphistomatous (with pores on both sides); (b) stomatal distribution does not depend much on environmental variables, but the dependence is strongest under conditions of low water stress; (c) within the limits of the models, amphistomatous leaves appeared nearly always to be better adapted than hypostomatous leaves, indicating that the models are not yet complete. (3) Leaf thickness and stomatal distribution were determined from herbarium specimens of the Indiana species of Compositae, Liliaceae, Salicaceae and Scrophulariaceae. These measurements were then compared with a simple habitat rating derived for each species from published habitat descriptions. Hypostomatous leaves occurred least often in xeric habitats, most often in mesic ones, and again less often in hydric habitats. However, the data suggest that this relationship is secondary, with leaf thickness being the intervening variable. (4) Finally, explanations are considered for the predominance of hypostomatous leaves over hyperstomatous ones.

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