The Closing Response in Dionaea

The closing response in Dionaea depends upon the intensity rather than upon the number of stimuli, the number of stimuli required varying in the inverse order of their intensity. Response is normally brought about by the compression of certain cells at the bases of the sensitive hairs, but the compression of other cells of the blade also causes closure, and it is probable that the latter cells are equally sensitive with the cells at the bases of the hairs, as is indicated by electrical and thermal stimulation. The closing response follows the application of mechanical, electrical, and thermal stimulation. It also follows a combination of stimuli of two kinds when consecutively applied, the individual stimuli being of an intensity such that either alone would be insufficient. The effect of mechanical stimulation is due to compression of cells, and not to contact with a hard object, continued pressure, or release of pressure. The failure of the leaf to respond to shaking is probably connected with the small inertia of the sensitive hairs, and the slight resistance offered by the air to their passage through it. Water at room temperature causes closure only when it bends a sensitive hair. After one mechanical stimulus there is a short period during which a second mechanical stimulus is ineffective.