FIG. 42. The telegraph plant (Desmodium gyrcms). 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 motion, like the second-hand of a watch, as 
indicated in the uppermost figure. 
