SEXSITIVE PLANTS. 221 



their peculiar properties, while others, again, will 

 scarcely show any signs of feeling, though ever so 

 roughly treated. They are all more or less armed 

 with sharp prickles, which may partly answer the 

 purpose of guarding their delicate frames from 

 some of the numerous shocks they would otherwise 

 receive."^ 



One of the best known " sensitive plants " is the 

 one usually called the " sensitive plant " — that is, the 

 Mimosa pudica of botanists, a plant of which stands 

 on the tabic before us as we write. In this the 

 leaves are bipinnate, then quadripinnate. There is 

 a pair of pinnae at the end of a long peduncle ; with 

 maturity two others are developed. These pinnre con- 

 sist each of about eight to twelve pairs of opposite 

 leaflets, the two pinnae standing almost at right 

 angles to each other. At a slight touch all the 

 leaflets rise and close the upper surfaces together, at 

 the same time the two pinna; approach each other so 

 as to be nearly parallel, instead of at right angles as 

 before. In this manner the leaves which have been 

 touched respond, and remain closed for some time ; 

 but at length they recover gradually from the shock, 

 and return again to their previously expanded position. 

 The experiment may be repeated with similar results ; 

 but if repeated again and again the movements 



1 Wallace, " Travels on the Amazon," p. 1 1. 



