200 



PLANT RELATIONS. 



the power of independent motion, or the whole leaf may 

 move. If there is danger from exposure to drouth, some 

 of the leaflets will be observed to fold together ; in case 



Fig. 172. A heath plant (Erica), showing low, hushy growth and small leaves. 



the danger is prolonged, more leaflets will fold together ; 

 and if the danger j)ersists, the surface of exposure will be 

 still further reduced, until the whole plant may have its 

 leaves completely folded up. In this way the amount of 



