Page:Researches on Irritability of Plants.djvu/129

106 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 60° C. under normal conditions. Employing 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

will be seen (fig. 62) that in this particular case, on account of fatigue, the death-point was lowered from the normal 60° 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-mechanioal 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 60° C. to 42° C., or by 18° C.