Page:Researches on Irritability of Plants.djvu/121

 

CHAPTER VIII

DEATH-SPASM IN PLANTS

Criterion of the death of plant—Abolition of electric response at death—Mechanical spasm of death—Water-bath for uniform rise of temperature—Excitatory effect of sudden cooling or heating—Erection of leaf with rising, and depression of leaf with falling, temperature—Thermo-mechanical inversion at the death-point—Necessity for specification of rate of rise of temperature—Death-record of Mimosa—Abolition of response after death-spasm—Constancy of death-point exhibited by different specimens—Death-records of Desmodium gyrans and Vicia Fava—Death-spasm in ordinary plants—The electric-spasm of death—Lowering of death-point by fatigue and by poisonous solution.

A plant may be killed by subjecting it to a certain maximum temperature. The exact moment at which death is initiated is difficult to determine, since there has been found no certain and immediate criterion of death. One method by which the occurrence of death may be determined is by the abolition of that electric response which is characteristic of the living condition. A plant as long as it is alive gives in answer to a stimulus an electric response of galvanometric negativity. On the occurrence of death this particular response disappears. I find that the electric response is abolished when the plant has been subjected for a time to a temperature of about 60° C.

If the plant is subjected to a gradual rise of temperature, there would arrive a time when the death-change will begin to occur. In the animal an early symptom of death is the setting in of rigor mortis. We shall find that in plants also a death-spasm, analogous to the death-throe of the animal, occurs at a critical moment.

In order to obtain an automatic record which would

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