Stomatal responses to changes in vapour pressure difference between leaf and air

We observed that stomata of Gossypium hirsutum, Glycine max and Xanthium strumarium respond to a change in vapour pressure difference between leaf and air at ambient partial pressures of CO2 and below the CO2 compensation point. Our report is at variance with a recent report (J. A. Bunce 1997, Plant, Cell and Environment 20, pp. 131–135) that stomatal sensitivity of leaves to a change in vapour pressure difference between leaf and air was eliminated when gas exchange measurements were made at near‐zero carbon dioxide partial pressures (0–5 Pa).