A COMPARATIVE STUDY OF GRADUAL AND ABRUPT CHANGES IN ROOT TEMPERATURE ON WATER ABSORPTION

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Abstract
The changes in rate of water absorption under gradual and abrupt changes in root temp. within the range of 25[degree]-5[degree]C was studied by daily measuring the decrease in volume of the culture soln. in which sunflower, tomato and red kidney bean plants were growing. In general, gradual decrease in temp. resulted in a gradual reduction in the absorption rate, and abrupt changes in temp. resulted in a correspondingly abrupt decrease in the absorption rate to a value slightly below the absorption rate of the plants which had been gradually cooled to that same temp. The absorption rate of bean plants showed greater reduction in the temp. range of 10[degree]-17[degree]C than at lower temps. and appeared to follow the trend of reported changes in viscosity of protoplasm, indicating the probability that in this species the change in viscosity of the protoplasm is an important factor in controlling water absorption. The absorption rate of sunflower and tomato plants, however, showed greater reduction at temps. below 10[degree]C than at higher temps. and tended to conform mainly with the reported changes in viscosity of water. None of the plants with root temp. decreased gradually from 25[degree] to 5[degree]C showed signs of wilting. Tomato and sunflower plants wilted severely on the day when the temp. was dropped abruptly from 25[degree] to 5[degree]C and recovered gradually on subsequent days with little or no permanent injury; but bean plants wilted severely and were greatly damaged from desiccation of the foliage when the temperature was dropped abruptly from 25[degree] to 10[degree]C and from 25[degree] to 5[degree]C, and showed very slow recovery of the uninjured portion of the foliage.