390 chap. xxxiv. the mechanism of the twining stem 



The Critical Fatal Temperature 



As the temperature is raised above the optimum, 

 a very abrupt and striking change occurs at a critical 

 temperature of about 60° C. 



Fig. 219. Death-spasm at fatal temperature of 60°, 

 double optima before reversal. (Thunbergia.) 



Note 



Experiment 210. — The results are graphically repre- 

 sented in the automatic record obtained with Thunbergia, 

 during rise of temperature between 23° and 60° C. 

 (fig. 219). It will be seen that the rate of torsion con- 

 tinuously increased till a diminution of the rate occurred 

 above the first optimum at 32° ; with further rise of tem- 

 perature to about 40°, a second optimum was attained. At 



