232 



DESMODIUM. 



[CH. VIII 



graphically i-epresented in the Potuer of Movement in 

 Plants, p. 334, fig. 135. The ordinates represent the 

 angle made with the vertical by the leaflet under obser- 

 vation ; a fall in the curve thus represents a drop of the 

 leaflet, 0° representing a vertically dependent position. 

 The dotted line represents temperature, and is to be read 

 in connection with the numbers 76° F....90° F. on the right 

 hand of the diagram. 



(262) Autonomous movements: Desmodium gyrxms. 



The leaf of Desmodium gy7^ans represented in fig. 44 

 consists of one large and a pair of very 

 minute leaflets. It is these which 

 execute the movements for which the 

 plant is celebrated. The point of each 

 leaflet describes a rough sort of circle 

 or ellipse, but the movement being 

 exceedingly jerky and irregular the 

 circular course is not obvious. The 

 movement does not occur unless the 

 temperature^ is about 22^ C, and may 

 be remarkably stimulated b}^ a higher 

 temperature, thus at 40^ C, the circles 

 are made at the rate of about two in 

 three minutes. The experiment may 

 be performed by immersing a leaf in 

 cool water which is gradually heated. 



Fig. 44. Exp. 262. 



From the Power of 



Movement. 



^ This is only true of full-grown plants. Seedlings move at lower 

 temperature : see Power of Movement in Plants, p. 362. 



