The Conduction of Excitation in Mimosa pudica
Recueil des travaux botaniques néerlandais , Volume 32 - Issue 1 p. 51- 91
A. When Mimosa pudica is stimulated without being wounded, for example by applying a drop of water at less than 10° C., the excitation is conducted by the action of living cells and accompanied by potential changes, referred to as action currents. The action of the cells can be propagated through the stem, the petioles, the pinnae and the pulvini. In most plants it is stopped at several places, for example at the transition from pinna to secondary pulvinus. The rate at which it is conducted depends upon the temperature. It does not pass through a killed part of the petiole nor through a zone which is cooled to approximately 5° C. The conduction by action of cells naturally depends upon the condition of these cells. The action is best conducted in damp air in a young shoot. The conduction by living cells may be identified with Ball’s ’’rapid conduction” in the stem and with Umrath’s ’’slow conduction” in the leaf. Most of Bose’s work is related to it. He observed the action current and found most of the above mentioned properties of this kind of conduction. B. When a plant is stimulated 'by wounding, for example by burning a leaflet, the excitation can be conducted by the action of cells as well as by' the transport of a stimulating substance, which Ricca has demonstrated to be set free at the wound. The cells which propagate the excitation by their action, are stimulated by this substance. By means of the substance the excitation can be conducted through a killed zone and through such parts of the plant, as do not propagate it by the action of cells. The presence of the substance is indicated by a change of potential, referred to as ’’the variation”. The substance is sucked in from the wound by the negative pressure in the vessels, and is transported by the transpiration stream. By changing the pressure from negative to positive it can be prevented to ’be sucked In. C. When a plant is stimulated by cutting a pinna, the excitation can be conducted by the action of cells, by the transport of the stimulating substance, and also by a third, very fast mechanism of conduction by which only the main pulvinus is affected. It is not accompanied by potential changes. It was observed in young leaves, especially in damp air. It passes a cooled zone of the petiole but was never found to be conducted through a killed part. It may be comparable to Snow’s ’’high-speed conduction” in the stem, and to Umrath’s ’’fast conduction” in the leaf. The probability of a relation between Haberlandt’s ’’Schlauchzellen” and this fast conduction has been discussed. No mechanism of conduction should be referred to as ’’normal conduction”. 1 he author wishes to take this opportunity to thank Prof. F. A. F. C. Went, at whose suggestion this work was commenced, and I rof. V. J. Koningsberger, the present Director of the Institute, lor their valuable aid and criticism.
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