ON THE IRRITABILITY OF YE&ETABLES, %Q [ 



It* 



Of the Irritability of Vegetables. By Mr. Robert Lyall, 

 Surgeon. Read at the Literary and Philosophical Society 

 at Manchester, Oct. the 6th, I8O9. Communicated by the 

 Author. 



T 



HE irritability of some plants has attracted much atten- Irritability cf 



vegetables 

 questioned. 



tion from physiologists. Some of the most eminent men ve 



have without hesitation allowed, that vegetables possess the 

 faculty of irritability; while others most strenuously have 

 endeavoured to disprove, tnat any such principle exists in 

 the vegetable kingdom. As soon as the mimosa sensitiva 

 was discovered, without doubt the motion of its leaves when 

 irritated by a stimulus were observed, but at what time the 

 cause of this motion got the title of irritability is perhaps 

 not so certain. Haller was probably among the earliest, who 

 ascribed the motions of some plants to an irritable princi- 

 ple. After speaking of the comparative irritability of the 

 heart, muscles, and intestines, with that of the ligaments, 

 tendons, &c, he proceeds thus : 



" That this irritability exists abundantly throughout the Halter's ac* 

 " animal fibres, appears evidently from the example, which count ° 

 " we have in the polypi and other insects, which have nei- 

 ** ther brain nor nerves, but are notwithstanding extremely 

 " impatient of all stimulus; and lastly we may take into 

 V consideration the analogy of some plants, the flowers and 

 ** leaves of which either expand- or contract by various de- 

 *' g r ees of heat and cold, and some even with a degree of 

 " celerity not inferior to that of animals. This force is a 

 " different and new principle from all other properties of 

 " bodies hitherto known. We cannot account for it either 

 ft by gravity, attraction, or elasticity but by something 

 " which exists in the soft fibres, and which vanishes by dry- 

 f* ing*." Haller afterward in his Elements of Physiology 

 remarks, " It is evident, that there abounds, not only in the 

 ** animal but equally in the vegetable kingdom, a contrac- 



* PrirBS Lines Phys. p. 152. Ed. 1758. 



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