Abstract
The general facts indicating that stimulation is dependent on a temporary increase in the permeability of the surface layer or plasma membrane of the irritable element are as follows:
A. The nature of the motile process in such plants as Mimosa, Dionœa and the Cynareæ, where the movement depends on a sudden loss of turgor. Such a change indicates either (1) a sudden decrease in the concentration of the osmotically active substances within the cell due to chemical action, or (2) a sudden loss of impermeability relatively to the osmotically active substances. The latter explanation is almost certainly the correct one.
B. The identity of the electrical change accompanying stimulation in motile plant cells with that observed in irritable animal tissues (Burdon-Sanderson), indicating a fundamental similarity in the conditions of stimulation in the two classes of organisms.
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