CHAPTER XV 



EFFECT OF VARIOUS AGENCIES ON DEATH-RESPONSE : 

 THERMOGRAPHS OF REGIONAL DEATH 



Lowering of death-point by fatigue — Modification of characteristic thernio- 

 mechanical curve by the action of chemical ngQWi^ — Coiiipan'soii'Morograph — 

 Duplication of rigor-point — Death- response a physiological response and not 

 due to coagulation — Death-movement of flowers — Approximate constancy of 

 death-point of florets in a capitulum — Definite interval between death-point 

 and discoloration-point — Translocation of discoloration-point by various 

 agencies — Thermographs of regional death — Thermograph of local fatigue — 

 Thermographic investigation of electrotonic excitation. 



I HAVE shown that the death-contraction is a phenomenon 

 of excitatory response. We might expect from this that 

 various conditions which affect the excitabihty of a plant 

 would also have a modifying influence upon the characteristic 

 thermo-mechanical curve of death- response. One such 

 modification would lie in the translocation of the point of 

 inversion, or, in other words, in the displacement of the 

 death-point. In order to test this inference we might subject 

 the plant to the influence of various agents which modify the 

 physiological condition, and observe the consequent modi- 

 fication of the death-response. We have already seen how 

 the physiological modification induced by age causes dis- 

 placement of the death-point. We have seen, further, how 

 unfavourable seasonal conditions, such as sudden prevalence 

 of cold, will lower the death-point by several degrees. We 

 shall now study the effect of other agencies, such as fatigue, 

 and the action of chemical reagents, in producing displace- 

 ment of the death- point. 



Effect of fatigue. — In the course of these experiments, 

 fatigue was produced by means of tetanising electric shocks, 



