Page:Researches on Irritability of Plants.djvu/130

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The electric response of galvanometric negativity is characteristic of the living condition of the vegetable tissue. Dead plants do not exhibit this characteristic electric-response.

When a plant is subjected for a time to a temperature of 60° C. its electric response disappears, such abolition being indicative of the death of the plant.

A leaf of Mimosa subjected to abrupt variation of temperature—either sudden cooling or sudden warming—exhibits excitatory reaction. But if the temperature be gradually raised, there is a progressive erectile movement of the leaf; gradual cooling induces a depression of the leaf.

When the leaf of Mimosa is continuously raised in temperature, then at a critical point the erectile expansive movement is suddenly converted into one of spasmodic contraction. This inversion takes place under standard conditions at or about 60° C. After this the response of the plant is permanently abolished.

Various other plants, sensitive and ordinary, exhibit this characteristic death-spasm at or about 60° C.

In taking an electric record it is found that an electric-spasm also takes place at the critical temperature, which is very near 60° C.

The death-point of the plant is lowered under physiolological depression. Thus under fatigue induced by tetanising electric-shocks, the death-point was lowered from the normal 60° C. to 37° C.

Poisonous reagents also lower the death-point. In a particular case poisonous solution of copper sulphate lowered the death-point by 18° C.