Page:Researches on Irritability of Plants.djvu/117

94 much reduced immediately after application; the power of recovery was also abolished. Subsequent application of stimulus did not result in any sign of response. Even on blowing off the vapour there was no restoration of excitability for a very considerable period. In the present case the period of total insensibility lasted for six hours, after which the excitability was slowly restored.

The vapour of ammonia is found to cause an abolition of excitability in a very short time. On the introduction of ammonia there is produced an excitatory fall. This may be avoided, however, by introducing this vapour immediately after the excitation induced by the testing stimulus. In the record here given (fig. 53), the first two are the normal responses. Introduction of ammonia is seen to induce an abolition of excitability, three successive stimulations, represented by thick dots, at the usual intervals of 15 minutes proving to be quite ineffective. On blowing off the vapour the excitability is seen to be very gradually restored. If stronger vapour of ammonia be employed, then the loss of excitability lasts for several hours.

The effect of this gas is not merely depressing but extremely toxic. It can be seen from the record that the introduction of this gas caused the period of recovery to be very protracted. The abolition of excitability is evidenced by the fact that successive stimulations at the usual interval