Page:Popular Science Monthly Volume 47.djvu/235

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225
IRRITABILITY AND MOVEMENT IN PLANTS.

ties are concentration, passivity, calmness, and reserve of force, and upon whom, more than upon man, rest the burdens and responsibilities of the generations, is too sacred to be jostled roughly in the struggle for existence, and that she deserves from man a reverent exemption from some of the duties for which his restless and active nature adapts him?

 

IRRITABILITY AND MOVEMENT IN PLANTS.[1]
By D. T. MACDOUGAL.

WITH the extension of information concerning the scope, purposes, and adaptations of the movements exhibited by plants, the determination of the nature of the specific forms of irritability under which these movements are induced becomes a question of very great interest. The more apparent movements of plants have long been matters of common observation, yet no apprehension as to their real nature existed before the middle of the present century. Previous to that time natural philosophy was chiefly busied in the definition of the "distinctive qualities" of the great groups—plants, animals, and minerals—and perpetuated without serious inquiry the beautiful vagaries of Aristotle as to the possession of a materialistic soul by plants. Both before and after the dictum of Linnæus, "Lapides crescunt, vegetabilia crescunt et vivunt, animalia crescunt, vivunt et sentient" (1735), the literature of natural history is rich in allusions to the possessions of functions by plants corresponding to the senses of animals. The only actual distinction made by Linnæus between the two groups was the denial of ideal perception to plants. Erasmus Darwin, in his Zoönomia (1794), supposes that plants possess voluntary power. He says: "The sleep of animals consists in the suspension of voluntary motion, and as vegetables are subject to sleep there is reason to conclude that the various actions of opening and closing their petals and foliage may be ascribed to a voluntary power; for without the faculty of volition sleep would not have been necessary for them." Probably a fair representation of prevalent thought on this subject at an early part of the present century is made by the admirable treatise of Tupper,[2] in which he attributes to plants irritability, a form of instinct (to account for


  1. Abstract of two lectures given before The Fortnightly Scientific Club of the University of Minnesota, October 20, 1894, and January 19, 1895.
  2. An Essay on the Probability of Sensation in Vegetables, with Additional Observations on Instinct, Sensation, Irritability, etc. London, 1811. By James Perchard Tupper, Member of the Royal College of Surgeons and Fellow of the Linnæan Society.