Page:Researches on Irritability of Plants.djvu/74

Rh rapid at the beginning and very slow towards the end. The maximum rate of recovery was ·09 mm. per second in contrast with the maximum rate of contraction of 24 mm. per second. The movement of recovery was about three hundred times slower than the movement of excitatory contraction.

A stronger stimulus, generally speaking, requires a longer period for recovery.

Under the physiological depression induced by winter the responsive reactions are modified. The latent period is prolonged and amplitude of response reduced. The period of recovery may also become protracted.

Different plants exhibit different characteristics of response. Biophytum sensitivum may be taken as a type of quickly reacting plant, while Neptunia oleracea is very sluggish in its reactions. In Biophytum the apex time is reached in a second and the recovery accomplished in 3 minutes. In Neptunia the apex time is reached in 180 seconds, and recovery completed in 60 minutes.

Mechanical response of Mimosa is due to differential contraction of the upper and lower halves of pulvinus.

Erectile responses of Mimosa may be obtained by local stimulation of the upper half of pulvinus.

Distinction of plants into sensitive and ordinary is arbitrary. Under suitable conditions, ordinary plants, so-called, may be made to exhibit motile response.

By means of electric response it may be shown that every plant, and every organ of the plant, is sensitive and responds to stimulation by a definite electric change.

The sensitiveness of Mimosa to electrical stimulus is high and may even exceed that of a human subject.