Super Optimal and Thermal Death Temperatures of the Cotton Plant as Affected by Variations in Relative Humidity

Abstract

In 1863 Sachs reported the results of an attempt to determine the effects of high temperatures on the sensitivity of Mimosa pudica. Transitory insensitivity, he found, was caused by an exposure of one hour to a temperature of 400 C., and at 450 C. for a half hour and 490 C. for a very brief time the same effect was produced. When permanent insensitivity was attained, at higher temperatures, death invariably followed. Sachs also reported ('64) on the effects of high temperatures on tobacco, pumpkin, corn, nasturtium, and rape, exposed for various periods of time. All the plants were able to withstand temperatures of 49-51? C., but none survived 510 C. for more than 10 minutes without injury. The power of resistance to high temperatures was found to vary at different ages. Developing leaves, stems, and roots were more easily killed than older ones. Ewart ('03) noted a decrease in the rate of protoplasmic streaming in Elodea, Tradescantia, Chara, Spirogyra, root hairs, pollen tubes, etc., depending upon the height of the temperature above the optimum and upon the length of exposure. Pfeffer ('03) made the generalization that all turgid plants ultimately die when the temperature reaches from 1? to 20 C. above the maximum where the plant will grow indefinitely, although growth may continue for a time, and that at temperatures of 100 C. above this maximum all flowering plants seem to be rapidly killed. He noted that plants, which at first