Studies in Stomatal Behaviour

Abstract

It has been reported in the literature that onion leaf stomata tend to close at noon (Loftfield, 1921) and that the minimum carbon dioxide concentration (Г) in onion leaf tissue rises from 0.012 per cent to 0.024 per cent. When the leaf temperature increases from 30°C. to 35°C (light intensity 900.f.c.) (Heath and Orchard, 1957). Experiments were therefore carried out of test the hypothesis that raising the left temperature above about 30°C. causes stomatal closing movements in onion leaves (e.g. mid-day closure) by increasing the carbon dioxide concentration in the leaf tissue. This hypothesis has been supported by the results of these experiments. Another and diametrically opposed effect of temperature on stomatal movements in onion leaves has, however, been discovered, Namely that, provided the final width of stomatal pores.