232 



DESMODIUM. 



[CH. VIII 



graphically represented in the Power 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, 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 gyrans. 



The leaf of Desmodium gyrans 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 1 is about 22 C., and may 

 be remarkably stimulated by a higher 

 temperature, thus at 40 C. the circles 

 are made at the rate of about two in 

 three minutes. The movements may 

 be observed on cut leaves under water, 

 thus the temperature can easily be 

 controlled. 



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

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



FIG. 44. Exp. 202. 



From the Power of 



Movement. 



