The movement of water in plants

Abstract

Sections 2 and 3 of this thesis describe respectively the construction and testing of a 50 channel automatic Peltier psychrometer which records on a printed paper roll. It was shown that with the Peltier type of psychrometer errors caused either by a sample geometry other than that used during the calibration, or by the diffusive resistance of the sample can be eliminated by reducing the Peltier cooling time, and the reading time below a critical value. There was reasonable agreement between the theoretically and the practically determined estimates of the critical cooling time. When short cooling times are used however contamination of the thermocouple junction by osmotica is liable to cause a more serious error than when longer times are used. The size of these errors was not sufficient to account for the finding of other workers that leaf water potential measurements are almost constant over large range of transpiration rates. Equipment for the simultaneous measurement of water uptake, transpiration and plant turgidity of plants growing in nutrient solution was constructed (section 4) and used (section 3) to examine the movement of water through bean plants exhibiting cyclic variations in transpiration. The hypothesis that such variations in transpiration were caused by a delay in the response of the stomata to a change in the leaf water potential was examined with the aid of a simple mathematical model. The behaviour of the model was similar to that of the plants. The implications of the differences between the two are discussed.