IntroductionThe effects of low root temperature on various plant processes have long been known and extensively studied. It is generally recognized that one of its important effects is the reduction in water absorption of the plant; and the nearer the root temperature approaches the freezing point of water, the greater this effect will be manifested. The change in physical state, particularly the increase in viscosity with the decrease in temperature, of both water and protoplasm are undoubtedly two basic factors influencing water absorption at low root temperatures. The reduction in water absorption will affect other plant processes, directly or indirectly, to a greater or smaller degree depending on the extent of water shortage within the plant, and consequently may result in corresponding injury to the plant. Conditions favorable to high transpiration have been reported to bring about wilting and injury to the plant from desiccation when its roots are subjected to low temperature. However, different plant species appear to differ in their capacity to withstand the effects of low root temperature. KRAMER (7) observed that species which grow in the winter and species native to cooler climates are less affected by low soil temperature than warm-weather species. The statement by KRAMER (7), which will be discussed later, that plants cooled slowly wilted less severely than plants cooled rapidly, seems to be the only report in the literature on the comparative effects of rates of lowering root temperature. Under natural conditions, the change in temperature varies not only in respect to the level to which the temperature falls but also in the rate at which it occurs. Information regarding the effects of different rates of temperature decrease seems at the present to be limited, and it was the purpose of this investigation to compare the effect on water absorption of an abrupt decrease in root temperature with a gradual decrease in root temperature.