120 



MOVEMENT 



clover, the acacia and many other plants adopt different 

 positions during the day and during the night. They show 

 that rhythm which exists throughout all living creatures. 

 The sensitive plant, Mimosa pudica, is, as its name implies, 



Fig. 40. A Laurel twig, A in the frozen, and B in the thawed condition. 



From Darwin and Acton. 



uncommonl}^ sensitive. At the base of the leaf-stalk and at 

 the base of the secondary leaf-stalks, there are swellings. 

 These are comjDosed of turgid cells, and any stimulus such as 

 touch, changes of light, temperature, or chemical stimulus 

 will act on those swellings: the leaf-stalks droop, the leaflets 



