Fig. 42. The telegraph plant (Desmodium gyrans). Each leaf is made up of three 

 leaflets, a large terminal one, and a pair of small lateral ones. In the lowest figure 

 the large leaflets are spread out in their day position ; in the central figure they are 

 turned sharply downward in their night position. The name of the plant refers to 

 the peculiar and constant motion of the pair of lateral leaflets, each one of which 

 describes a curve with a jerking moiion, like the second-hand of a watch, as 

 indicated in the uppermost figure. 



