The Effect of an Oxygen-free Atmosphere on Net Photosynthesis and Transpiration of Barley (Hordeum vulgare L.) and Wheat (Triticum aestivum L.) Leaves

Stomata of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) leaves failed to open in the light and close in the dark or respond to changes in the CO₂ concentration of the atmosphere in either light or dark when the leaves were in an O₂-free atmosphere. In contrast, the expected responses to environmental changes were found in atmospheres containing 1.5% O₂. It appears that O₂ is necessary for both opening and closing of wheat and barley stomata.