248 FREAKS OF PLANT LIFE. 



of each leaf twist through an angle of ninety degrees, 

 so that their blades stand vertically at night, with 

 one lateral edge presented to the zenith. We shall 

 best understand the other and more complicated 

 movements if we imagine ourselves always to hold 

 the leaf with the tip of the terminal leaflet pointed to 

 the north. The leaflets in becoming vertical at night 

 could, of course, twist so that their upper surfaces 

 should face on either side ; but the two lateral leaflets 

 always twist so that this surface tends to face the 

 north, but as they move at the same time towards 

 the terminal leaflet, the upper surface of the one faces 

 about N.N.W., and that of the other N.N.E. The 

 terminal leaflet behaves differently, for it twists to 

 either side, the upper surface facing sometimes east, 

 and sometimes west, but rather more commonly west 

 than east. The terminal leaflet also moves in another 

 and more remarkable manner, for whilst its blade is 

 twisting and becoming vertical, the whole leaflet bends 

 to one side, and invariably to the side towards which 

 the upper surface is directed : so that if this surface 

 faces the west, the \\hole leaflet bends to the west,, 

 until it comes into contact with the upper and 

 vertical surface of the western lateral leaflet. Thus 

 the upper surface of the terminal and of one of the 

 two lateral leaflets is well protected."^ This com- 



1 Darwin, "Movements of Plants," p. 345. 



