BO Observations upon the Motion of 



Dr. Dutrochet viewed these phenomena in some respects 

 more justly. He remarked, in addition to what Lindsay had 

 observed, that if, instead of the upper and under surface, the 

 lateral part of the intumescence be removed, the petiole be- 

 comes not raised or deflected, but inclined towards the side 

 on which it is injured {Fig. 5) ; and that if longitudinal slices 

 of the upper, or under, or lateral portions of the intumescence 

 are immersed in water, these separate slices immediately 

 become incurvated, that edge being concave which looks to- 

 wards the axis of the intumescence. From these facts Dutro- 

 chet inferred that the texture of the intumescence possesses 

 some modification of irritability; that, when excited, each 

 length of the intumescence (to use a very imperfect expression) 

 forcibly assumes an incurvated figure, like a curved spring 

 returning from a state of temporary extension ; that the petiole 

 is raised, when the action of the lower part of the intumescence 

 predominates ; is depressed, when the upper portion acts with 

 increased energy. 



Mr. Burnett and myself had arrived at very similar conclu- 

 sions respecting the agency of the intumescence, before we 

 became acquainted with the inquiries of Lindsay and Dutrochet. 



In Dutrochet's able researches, a more exact analysis, how- 

 ever, was obtained of the functions of this part. He discovered 

 that the cortex of the intumescence is the seat of its irritability: 

 for upon wholly removing the bark, so as to expose the ligneous 

 substance, the petiole was found to have been rendered motion- 

 less. Nevertheless, the intumescence, thus mutilated, remains 

 capable of transmitting an impression made upon its leaflets to 

 the leaves adjoining, Dutrochet further ascertained, that the 

 ligneous substance alone is fitted to convey the peculiar stimu- 

 lus, which spreads, from a point of the plant that has been 

 irritated, to the adjoining leaves. 



The experiments already mentioned appear to explain the 

 mode in which the elevation and depression of the petiole, and 

 the divergence and approximation of the subpetioles are pro- 

 duced. It is probable that the contrivance for folding and 

 expanding the subleaflets is of a similar nature. Mr. Burnett 

 and myself conjectured that each subleaflet is raised by the 

 under part of the intumescence that exists at its base, and de«» 



