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On the Resistance to Transpiration of the Sites of Evaporation within the Leaf

Graham D. Farquhar and Klaus Raschke
Plant Physiology
Vol. 61, No. 6 (Jun., 1978), pp. 1000-1005
Stable URL: http://www.jstor.org/stable/4265346
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
On the Resistance to Transpiration of the Sites of Evaporation within the Leaf
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Abstract

The rates of transpiration from the upper and lower surfaces of leaves of Gossypium hirsutum, Xanthium strumarium, and Zea mays were compared with the rates at which helium diffused across those leaves. There was no evidence for effects of CO2 concentration or rate of evaporation on the resistance to water loss from the evaporating surface ("resistance of the mesophyll wall to transpiration") and no evidence for any significant wall resistance in turgid tissues. The possible existence of a wall resistance was also tested in leaves of Commelina communis and Tulipa gesneriana whose epidermis could be easily peeled. Only when an epidermis was removed from a leaf, evaporation from the mesophyll tissue declined. We conclude that under conditions relevant to studies of stomatal behavior, the water vapor pressure at the sites of evaporation is equal to the saturation vapor pressure.

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