the Leaves of the Sensitive Plant, 



81 



pressed by some action of the upper portion of the same intu- 

 mescence. In trying the soundness of this hypothesis, we met 

 with the following evidence in its favour : — 



Mr. Lindsay had observed, that at the moment when the 

 petiole is depressed, the under part of its intumescence assumes 

 a deeper colour. But the under part of the intumescence of 

 the petiole is the portion which is shortened during its depres- 

 sion, and which is overcome on this occasion by the superior 

 force of the upper portion. 



Now it is to be remarked that in the subleafiets the upper 

 part of the little intumescence belonging to each corresponds, 

 in one respect alluded to, with the lower portion of the intu- 

 mescence of the petiole ; it is the portion shortened when the 

 leaf is folded. And we found, upon examination, that it like- 

 wise distinctly changes colour at the moment when the sub- 

 leaflet rises, while the under surface of the intumescence of the 

 subleaflet does not change its hue. 



In pursuing this inquiry, another point of correspondence 

 between the mechanism which depresses the petiole, and that 

 which raises the subleaflets, was stated, which has yet additional 

 interest. 



When the plant is not in its most lively state, the under sur- 

 face of the intumescence of the subleaflet (6, Fig. 2,) and the 

 upper surface of the intumescence of the petiole (a, Fig. 6,) 



Fig. 7. 



/k 



Fiff. 8. 



may be pricked with a needle, without producing action. 

 But if the opposite surfaces, those namely, which change colour 

 and are shortened when the petiole is depressed and the 

 subleaflets folded, are touched with the point of the needle 

 these actions are instantaneously produced. Here the sub- 



JULY — OCT. 1827. G 



