on the Mimosa pudica. 63 



The next experiments are concerning tlie organs of motion 

 in the sensitive plant, — as to the kind of motion, it is by what 

 M. Dutrochet terms incurvation, — the meaning of which will easi- 

 ly be understood by the following experiments, which I have re- 

 peated, tending to prove what part of the sensitive plant it is 

 which possesses this power. He states that the moving power 

 of that plant is situated at the basis of the primary petioles, the 

 secondary petioles, and also at the basis of each of the leaflets. 

 This organ of motion then, which he terms a bourrelet, is the 

 little oblong swelling situated at the different places mentioned. 

 To prove that it does possess the powers attributed to it by M. 

 Dutrochet, following him, I removed the whole of the cellular 

 substance of the bourrelet at the base of a primary petiole, leav- 

 ing merely the central bundle of vessels : it was not every leaf 

 which could supportitself after this operation, but afewdid so, and 

 the better after the removal of a portion of the leaf, so as to les- 

 sen its weight ; and it was impossible to excite any motion in the 

 primary petioles of such afterwards, although otherwise the leaf 

 appeared quite healthy, and motion was excited as usual in the 

 other bourrelets. This then proves, that the bourrelet is the or- 

 gan of motion ; and the next question is, How do the flexion 

 and extension of the leaves take place.'' This is solved by the 

 following experiments : — 



I removed the upper half of the bourrelet at the base of one 

 of the primary petioles, with a sharp knife ; immediately after 

 this, the leaf, instead of flexing itself towards the earth, which 

 was always the case with those leaves in which the bourrelet 

 was uncut, after the same extent of agitation which necessarily 

 arises during the performance of the operation, remained for a 

 lime in the same position in which the leaf happened to be 

 when this was performed, but soon began to move gradually 

 upwards, and there it remained stationary while the plant was 

 sufficiently supplied with water ; for this, as M. Dutrochet re- 

 marks, has a great effect on the motion, which is supposed by 

 him to occur, in consequence of an afflux of fluid to the one or 

 other side of the bourrelet, according to circumstances. The 

 application of a drop of water to the cut surface, in general 

 caused a rapid movement of the leaf upwards, and to a greater 

 extent than usual ; and no agitation or stimulus short of such as 



