SUMMARY (1) Observations were made of the stomatal behaviour of tea growing in Malawi. Measurements of stomatal conductance made with an automatic diffusion porometer were consistent with measurements of stomatal aperture made with silicone rubber impressions. (2) Except for the 2- to 3-month annual dry season, stomatal conductance was principally determined by incident irradiahce; it was independent of shoot water potential, vapour pressure deficit and the rate of photosynthesis. Within the dry season, conductance remained unaffected by shoot water potential and vapour pressure deficit but became more closely related to the rate of photosynthesis. (3,) It is suggested that a factor, associated with climatic change at the beginning and end of the dry season, alters the sensitivity of the stomata towards one or other of the two principle mechanisms by which they respond to light. (4) Two anomalous forms of stomatal behaviour were observed: a transient opening in the middle of the day and a temporary closure in the middle of the morning. (5) The different diurnal patterns in the wet and dry seasons, and the anomalous stomatal movements, illustrate the diversity of stomatal response which can occur in a woody perennial species.
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G. R. Squire (1978) studied this question.