Page:Life Movements in Plants.djvu/208

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LIFE MOVEMENTS IN PLANTS

In some plants the optimum is reached at about 28°C, and the rate remains constant for the next 10 degrees or more.


Fig. 64.
Fig. 65.

Fig. 64.—Record of effect of fall of temperature from 30°C to arrest of growth at 22°C.

Fig. 65.—Effect of rise of temperature from 53°C to 60°C. A sudden contraction, indicative of death-spasm, takes place at 60°C.

Temperature maximum: Experiment 60.—For the determination of the maximum, the temperature was raised much higher. At 55°C. growth was found to be greatly retarded with practical arrest at 58°C. At 60°C there occurred a sudden spasmodic contraction (Fig. 65), which I have shown elsewhere to be the spasm of death. This mechanical spasm at 60°C is also strikingly shown by various pulvinated organs. An electric spasm of galvanometric negativity, and a sudden diminution of electrical resistance also take place at the critical temperature of 60°C.[1]

I have described the immediate effect at the critical point. Long maintenance at a temperature few degrees

  1. ↑ Bose — "Plant Response," p. 168; "Comparative Electro-Physiology," p. 202, p. 546.
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