270 SENSIBLE MOVEMENTS OF PLANTS. 



body, will produce similar effects. Thus, if electric sparks be 

 communicated to the lower side of the intumescence, or the rays 

 of the sun be concentrated on it with a burning-glass, a similar 

 contraction of its vesicles, and depression of the leaf, will follow. 

 In this, as in the foregoing instance, the leaves return after a 

 time to their usual condition. Several species of the Acacia 

 tribe, growing in warm climates, exhibit corresponding changes 

 in a less degree. The closure of the fly-trap of the Dionaea 

 (. 246.) may be probably explained on similar principles; the 

 part here irritated, is the tissue at the base of the three thorns, 

 on each side of the leaf; one of which must be touched, in order 

 to excite the movement. 



