Studies in Stomatal Behaviour

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Abstract
Experiments are described in which the responses of wheat stomata to carbon dioxide concentration (0·00, 0·01, 0·02, 0·03 per cent.), light intensity (275, 625, 975 f.c.), and rate of air flow (2, 5, 12·5 l./hr.) were studied. Reduction of carbon dioxide concentration from 0·03 to 0·01 per cent. resulted in marked stomatal opening; further reduction to 0·00 per cent, was accompanied by a slight but not significant closure. These effects were found at all light intensities and rates of flow, except at 975 f.c. with 2 l./hr. air flow, where no effect of carbon dioxide concentration was detected. This last is attributed to excessive depletion of the carbon dioxide supply by assimilation. The apparent lower limit of 0·01 per cent, carbon dioxide causing maximal stomatal opening is discussed in relation to recent assimilation experiments. Increase of light intensity caused considerable stomatal opening, this effect being as great with air of 0·00 and 0·01 per cent. as with higher concentrations of carbon dioxide. This suggests an effect of light on stomatal movement other than that exerted indirectly through photosynthesis by the mesophyl cells. Increased rate of flow of dry air caused closure of the stomata; this was shown to be a drying effect and was absent when moist air was used.

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