262 THE SECOND BOOK OF BOTANY. 



When the surface is touched, the leaf suddenly closes, 

 like a steel-trap, and, if the intruding substance be an 

 insect, it is immediately imprisoned, as shown in the 

 figure. If nothing is caught, the trap soon reopens 

 of itself, but, if there is a victim, it is held with con- 

 siderable force. 



This irritability, or sensitiveness, seen in leaves, 

 is not uncommon, also, in the flower. Spontaneous 

 motions occur in the petals of the sundew, and in 

 the lip of the corolla of several of the Orchis tribe. 

 It occurs in the organs of reproduction, and is then 

 connected with the process of fertilization of the 

 ovule. The stamens of the various species of bar- 

 berry exhibit this irritability to a remarkable degree. 

 If touched with a pin, or other object, at the base of 

 the inside filament, the stamen will spring violently 

 forward from its place within the petal, so as to bring 

 the anther in contact with the stigma. In Fig. 418 



FIG. 4ia 



the first position is shown at #, and the second at I. 

 After a time the stamen slowly resumes its position. 

 It might seem as if this arrangement were designed 



