Page:Researches on Irritability of Plants.djvu/119

dioxide, on the other hand, is extremely poisonous. Introduction of this gas was attended by an immediate excitatory fall, which was repeated twice. After this the plant became perfectly insensitive (fig. 55); the gas had in reality killed it.

Sulphur Dioxide

Equally fatal is the effect of sulphur dioxide. Introduction of the gas was attended by an immediate excitatory

Fig. 55.—Toxic effect of nitrogen dioxide: application of gas at X induced excitation, followed by loss of excitability and death of plant.

Fig. 56.—Abolition of excitability and death of plant by the action of sulphur dioxide.

fall of the leaf, after which it became quite insensitive (fig. 56). Restoration of fresh air did not revive the plant, which succumbed completely to the toxic action of the gas.

Summary

There is in general a temporary depression of excitability in Mimosa under sudden diminution of intensity of light.

Absorption of water induces a depression or abolition