Responses of stomata to environmental factors-experiments with isolated epidermal strips of Polypodium vulgare : I. Temperature and Humidity.

Stomatal responses in isolated epidermis strips of the fern Polypodium vulgare to humidity and temperature were investigated. Movements were observed under a microscope, the epidermis being mounted in a climatized chamber above a water table, the gap between tissue and water being similar to that between epidermis and mesophyll in the intact leaf. Stomatal aperture increases as the water vapor deficit is decreased. The relationship is approximately linear until full aperture is reached. The speed of stomatal movement depends on the magnitude of the change in saturation deficit. Temperature also exerts a strong influence on stomatal aperture. Low temperature causes closure. Maximal opening occurs between about 20° C and 28° C. Higher temperature leads to a slight reduction in aperture. The temperature range corresponding to maximum apertures depends on the temperature that prevailed during cultivation of the plants. The data are used to construct three-dimensional graphs showing stomatal behavior under the simultaneous influence of temperature and humidity for plants of different precultivation. The possible mechanisms that lead to the observed stomatal reactions are discussed.