M. Dutrochet on the Irritabiltty of the Sensitive Plant. 381 



curvature impressed on these parts in the place where the organ 

 of motion occurs. Thus, in the sensitive plant, it is the bourre- 

 lets alone, that, by curving, produce the folding of the leaves. 

 M. Dutrochet has found, that this curvature is the result of a 

 vital elastic power, which even manifests itself in the thin slices 

 that are taken from these bourrelets. He has given the name of 

 incurvatioft to this phenomenon. Thus the vegetable irritabi- 

 lity consists only in an elastic incurvation, which i^ sometimes 

 Jixed and sometimes oscillator^/. For example, this elastic in- 

 curvation is JiiVed in the tendrils of vegetables, in the valves of 

 the ovarium of the balsamine, &c. ; it is osciUaiory in the vege- 

 tables that are named irritable, — vegetables which present, in 

 their mobile parts, a state of alternating incurvation and straight- 

 ening. 



It has long been known that the sensitive plant presents a 

 phenomenon of sympathic transmission. If one of the leaflets 

 of this plant be slightly burnt with a burning glass, all the leaf- 

 lets belonging to the same stalk will fold themselves one after 

 another. This motion deserves to be carefully examined ; and, 

 in order to determine the part of the stalk by which the trans- 

 mission in question is operated, M. Dutrochet made several very 

 delicate experiments, from which there results, that it is neither 

 produced by the pith nor the bark, but that it takes place ex- 

 clusively by means of the woody part of the central system. 

 Inquiring afterwards what, in this woody part, are the special 

 organs of the transmission in question, he arrives at the conclu- 

 sion of its being effected through the medium of the sap con- 

 tained in the tubes, which he names corpuscidiferous. He has 

 found, that the maximum of velocity of this motion of transmis- 

 sion is fifteen millimetres per second in the petioles of the leaves, 

 and only three millimetres per second in the body of the stalk. 

 The state of the temperature does not appear to have any in- 

 fluence upon its velocity. 



Light exercises a very remarkable influence upon the irrita- 

 bility of the sensitive plant, the observation of which equally 

 belongs to M. Dutrochet. If a sensitive plant be placed in 

 complete darkness, by covering it with an opaque vessel, it 

 will entirely lose its irritability, and that in a variable time, ac- 

 cording to a certain state of depression or elevation of the sur- 



