4 SOUTH AFRICAX FLOJVFIUXG PLAXTS. 



The leaf eoiisists of the stalk, or Petiole, and the 

 ]U(((1c, which has three Lectffef,^. Such make a 

 eowjhiiind leaf (Fig. 1). 



Simple leaves have only one blade. 



Their l)ehaviour at suuset should be watched, for 

 while they are spread out horizontally by day (I.) the 

 three leaflets drop down at night (II.), so that they hang, 

 back to back, against the stalk. ]\Iany plants with 

 compound leaves fold their leaflets up. This is called 

 the " sleeping of leaves." Its object is to avoid injury 

 from chill, as the blades, being heated by day, part 

 with the heat at night more quickly and to a greater 

 extent if the blades be horizontal than when they stand 

 erect or hang downwards. 



In England, as the weatliei- is often cold when the 

 trees open their buds, the expanding leaves are always 

 either pressed together, or one half of a blade is 

 folded upon the other half, like a sheet of note-paper. 

 The leaves then place themselves for a time in a 

 vertical position, by the stalk curling downwards or 

 upwards. For it appears that the Kpper surfaces must 

 be particularly protected, as well as the whole leaf, by 

 being placed erect or pendulous. 



In tropical countries, where very intense heat 

 occurs, leaves behave very much in the same way in 

 order to avoid the excessive heat, just as they do to 

 avoid a chill from great cold in England. 



When the dry season comes on, the underground 



