220 



CHAP. XX. THERMONASTIC MOVEMENT 



the course of the opening and closing movements is, as will 

 presently be shown, not strictly coincident with the daily 

 changes of light and darkness. The movement of the petals 



Fig. 128. The Thermonastic Recorder, 



The specimen of Nymphaea has one of its perianth-leaves, n, attached 

 to the short arm of the lower lever by a thread, t, metallic 

 thermometer attached to the short arm of the upper lever ; 

 c, clockwork for oscillation of the plate. 



of Nymphaea is therefore not essentially dependent on 

 variation of illumination. 



Possible effect of geotropism. — It maybe asked, Does the 

 stimulus of gravity exert any influence on the movement 

 of the opening or closing of the flower ? The petals close 



