THE POWER OF SUNLIGHT 101 



kind of pent-house style, sloping gently outwards, one 

 above another, so that rain, pouring on them, is guided 

 away from the trunk. 



A reason for this may be conjectured. Do you 

 remember that it is the soft tips of the roots, where they 

 are clothed with hairs, that suck in moisture from the 

 soil? But in a tree, with its widely spreading roots, 

 those tips are far away from the trunk, often many 

 yards distant. Rain, falling close to the trunk, is not 

 needed; while at the root -tips it is much needed. So 

 when the sloping leaves throw it outwards, it falls 

 where it is wanted. 



At times we may see leaves doing the opposite. If 

 on a rainy evening, after a dry day, you pass a patch 

 of potato-plants, some of the leaves may be tilted up, 

 standing on end and twisted as one might twist a piece 

 of paper, to form a channel for water. Thus again 

 they guide the falling drops to the roots, which in a 

 small plant are not far from the stem. 



However, this curling of the leaves may arise from 

 another cause. Many leaves, which all day long have 

 turned their upper surfaces broadside to the sun, will 

 droop and curl at the coming of night. 



For at night heat pours quickly away from the ground, 

 and from all upturned surfaces ; and the leaves in that 

 position might suffer from cold. So, perhaps, it is 

 mainly on this account that they no longer face up- 

 wards. Such drooping and turning away has been 

 called " the Sleep of Leaves." 



It is not real sleep with them, as with us. It is 

 simply a movement, placing the leaves often also the 

 flowers so that they may keep a little of their warmth 



