Page:Researches on Irritability of Plants.djvu/114

Rh in the growing amplitude of successive responses till a limit was reached.

The effect of undiluted carbonic-acid gas is a depression of excitability. This is seen in the present record (fig. 47), where on the application of this gas the amplitudes of successive responses are seen to undergo a decline. Another noticeable fact is the incompleteness of recovery after each

excitation. The plant-chamber was next refilled with fresh air, and we observe the restoration of normal excitability.

The immediate effect of dilute vapour of alcohol is sometimes a transient enhancement of excitability. But continued action of the vapour induces a depression. In the accompanying record (fig. 48) there was little immediate effect; but after an application of 15 minutes there was induced a depression of response; another effect also