IRRITABILITY AND MOVEMENT IN PLANTS. 225 



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.* 



By D. T. 1L4CD0UGAL. 



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 be- 

 comes a question of very great interest. The more apparent 

 movements of plants have long been matters of common ob- 

 servation, 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 Linnaeus, 

 "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 Linnaeus between the two groups was the 

 denial of ideal perception to plants. Erasmus Darwin, in his 

 Zoonomia (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,f in which he attrib- 

 utes to plants irritability, a form of instinct (to account for 



* Abstract of two lectures given before The Fortnightly Scientific Club of the Uni- 

 versity of Minnesota, October 20, 1894, and January 19, 1895. 



\ An Essay on the Probability of Sensation in Vegetables, with Additional Observations 

 on Instinct, Sensation, Irritability, etc. London, 1811. By James Perchard Tupper, Mem- 

 ber of the Royal College of Surgeons and Fellow of the Linnaean Society- 



VOL. XL VII. 19 



