346 MODIFIED CIECUMNUTATION. Chap. VU 



side and afterwards bending to the same side, seemed to us so 

 remarkable, that we endeavoured to discover the cause. We 

 imagined that at the commencement of the movement it might 

 be determined by one of the two halves of the leaflet being 

 a little heavier than the other. Therefore bits of wood were 

 gummed on one side of several leaflets, but this produced no 

 effect; and they continued to twist in the same direction as 



Fi?. 140. 



yielUotaa officinalis : A, leaf during the daytime. B, another leaf asleep. 

 C, a leaf asleep as viewed from vertically above ; but in this case the 

 terminal leaflet did not happen to be in such close contact with the 

 lateral one, as is usual. 



they had previously done. In order to discover whether the 

 same leaflet twisted permanently in the same direction, black 

 threads were tied to 20 leaves, the terminal leaflets of which 

 twisted so that their upper surfaces faced west, and 14 white 

 threads to leaflets which twisted to the east. These were ob- 

 served occasionally during 14 days, and they all continued, with 

 a single exception, to twist and bend in the same direction; for 



