106 RESEARCHES ON IRRITABILITY OF PLANTS 



the influences of other agencies, such as fatigue or poisonous 

 drugs, in the displacement of the death-point. 



I have already given a record which showed the death- 

 point of the leaf of bean plant to be 6o° C. under normal 

 conditions. Emplo3'ing a similar specimen, fatigue was 

 induced in it by means of tetanising electric-shocks ; the 

 death record was then taken in the usual manner. It 



Fig. 62. — Lowering of death- 

 point under fatigue; death- 

 spasm took place at 37 C. 



Fig. 63. — Effect of poison 

 in lowering the death-point. 



will be seen (fig. 62) that in this particular case, on account 

 of fatigue, the death-point was lowered from the normal 

 6o° C. to 37 C, that is to say, by as much as 23 C. The 

 lowering of the death-point, I find, is determined by the 

 extent of fatigue. 



In order to discover the effect of poisonous solutions on 

 the death-point, I subjected a specimen of the bean leaf 

 to dilute copper-sulphate solution and took its thermo- 

 mechanical record (fig. 63). The effect of the poisonous 

 agent is clearly demonstrated by an appropriate lowering of 

 the death-point, in this case from the normal 6o° C. to 

 42 C, or by 18 C. 



