Chav. Vll. SLEEP OF LEAVES. 391 



leuves rise so much at night that they may almost be said to 

 sleep. 



Strepkium floribundum' (Grnminese) — The oval leaves are 

 provided with a pulvinus, and are extended horizontally or 

 declined a little beneath the horizun during the day. Those 

 on the upright culms simply rise up vertically at night, so 

 lbs.t their tips are directed towards the zenith. (Fig. IfrL) 



Fig. 164-. 



Strephium fioribundum : culms with leaves during the iny, and wheQ aslfe|.' 

 at night. Figures reduced. 



Horizontally extended leaves arising from much inclined or 

 almost horizontal culms, move at night so that their tips 

 point towards the apex of the culm, with one lateral maraiii 

 directed towards the zenith; and in order to assume this 

 position the leaves have to twist on their own axes through an 

 angle of nearly 90°. Thus the surface of the blade always stands 

 vertically, whatever may be the position of the midrib or of the 

 leaf as a whole. 



The circumnutation of a young leaf (2 • 3 inches in length) was 

 traced during 48 h. (Fig. 165). The movement was remarkably 

 simple; the leaf descended from before 6.40 a.m. until 2 or 

 2.50 P.M., and then rose so as to stand vertically at about 6 p.m., 

 descending again late in the night or in the very early morning. 



* A. Brongiiiart first observed la Soc. Bot. de France,* torn, vii 

 that the leaves of this plan t and X860, p. 470. 

 of Miirsilua sleep : see ' Bull, de 



26 



