VARIOUS AGENCIES ON DEATH-RESPONSE 1 77 



care being taken that these should not be strong enough 

 to kill the plant. I have carried out experiments on this 

 subject with two different classes of specimens : first, with 

 anisotropic pulvinated organs, like that of Mimosa, where the 

 death-spasm is shown by lateral movement ; and secondly, 

 with radial organs, like the style of Datura, where the death- 

 point is determined by thermo-mechanical inversion. In 

 experimenting on Mimosa, I took a batch of young leaves of 

 the same age, whose death-point was found to be at, or close 

 upon, 59 C. After fatigue caused by moderate stimulation, 

 however, the death-point was found to be at 56 C, that is to 

 say, it had been lowered by 3 . 



Working with Datura pistil, the death-point of which was 

 never normally lower than 6o° C, it was found when fatigued 

 to be at 41 ° C. The lowering in this case was therefore 

 about 1 9 . It will thus be seen that fatigue does lower the 

 death-point of a plant, the degree to which it does so 

 depending on the extent of the fatigue. In the course of the 

 present chapter, I shall be able to demonstrate once more the 

 lowering of the death-point through fatigue, by means of an 

 altogether different mode of investigation. 



Effect of chemical reagents. — Similarly I find that 

 death-response is modified by the action of various chemical 

 reagents. We have seen how characteristic is the thermo- 

 mechanical curve of each plant, under definite conditions 

 We found, for example, that two styles of two different flowers 

 on the same plant, having had the same previous history, gave 

 curves which were practically identical. Specimens thus re- 

 sembling each other are not difficult to obtain in spring, when 

 there is no sudden variation of weather conditions, or from 

 plants grown under glass, in an unchanging environment. The 

 characteristics of the thermo-mechanical curve being so con- 

 stant, the effect of a given agent will then be indicated by 

 certain variations from the normal. Thus, on taking a 

 thermo-mechanical curve — the specimen used being the style 

 of Datura, subjected to the action of a 2*5 solution of copper 

 sulphate — I found that the form of the curve was much 



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