Page:Researches on Irritability of Plants.djvu/129

This page has been proofread, but needs to be validated.
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 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


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 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.