THE GREENWOOD TREE. 145 



pursed-up lips which have a ridiculously human appear- 

 ance when seen through a simple microscope. When 

 the conditions of air and moisture are favourable, these 

 lips open visible to admit gases ; and then the tiny 

 mouths suck in carbonic acid in abundance from the air 

 around then. A series of pipes conveys the gaseous 

 food thus supplied to the upper surface of the leaf, 

 where the sunlight falls full upon it. Now, the cells of 

 the leaf contain a peculiar green digestive material, 

 which I regret to say has no simpler or more cheerful 

 name than chlorophyll; and where the sunlight plays upon 

 this mysterious chlorophyll, it severs the oxygen from the 

 carbon in the carbonic acid, turns the free gas loose 

 upon the atmosphere once more through the tiny 

 mouths, and retains the severed carbon intact in its own 

 tissues. That is the whole process of feeding in plants : 

 they eat carbonic acid, digest it in their leaves, get rid 

 of the oxygen with which it was formerly combined, and 

 keep the carbon stored up for their own purposes. 



Life as a whole depends entirely upon this property of 

 chlorophyll ; for every atom of organic matter in your 

 body or mine was originally so manufactured by sun- 

 light in the leaves of some plant from, which, directly or 

 indirectly, we derive it. 



To be sure, in order to make up the various substances 

 which compose their tissues to build up their wood, 

 their leaves, their fruits, their blossoms plants require 

 hydrogen, nitrogen, and even small quantities of oxygen 

 as well; but these various materials are sufficiently 

 supplied in the water which is taken up by the roots, 

 and they really contribute very little indeed to the bulk 



