THE WONDERS OF VEGETATION. 253 



main body could not fall asleep till all the members 

 have been overcome. 



If a little drop of water is delicately put upon the 

 leaflet, De Candolle was not able to perceive any 

 movement ; but if a drop of sulphuric acid was sub- 

 stituted for water, the leaflets shrunk instantaneously, 

 and drooped. The irritation is not merely local ; as 

 we have said, it communicates itself from one part 

 to another. The power of contraction resides in the 

 tiny round cushions placed at the points of junction, 

 which form a kind of knee-joint spring, or hinge, 

 and allows the stem to bend and lie down. 



Certain experiments would seem to prove that 

 these delicate plants can, to a certain extent, accustom 

 themselves to a measure of excitement. Desfontaine 

 observed this in carrying one of them in a cart. At 

 the first movement of the cart it closed its leaflets, 

 and all its leaves shrunk. But by degrees, as the 

 cart rolled on, the plant seemed to accustom itself to 

 its new condition ; its leaves rose once more, and its 

 leaflets unfolded. If the cart started again, after hav- 

 ing stopped awhile, the delicate plant felt the influ- 

 ence, as at first; but after some time it seemed to 

 recover once more from its fright, and showed again 

 all its beauty to the day. It is now, however, con- 

 sidered more probable that the sensitive plant loses its 

 strange sensitiveness from the continual irritation. 

 The power of closing its leaflets is for a time de- 

 stroyed by the repeated application of the external, 

 mechanical agent, and restored again only after the 

 plant has enjoyed some rest. 



