FOLIAGE. 131 



is known as to the exact details of this process ; but, it 

 is certainly the green colouring matter of the leaf which 

 absorbs light and heat from the sun's rays. Carbonic 

 acid gas and water are then made to form sugar by the 

 action of the small living chlorophyll bodies, or chloroplasts. 

 These are very numerous, about 400,000 having been 

 counted in a square millimetre of the leaf of the 

 Castor-oil plant.^ 



The importance of leaves depends on the amount of 

 sunlight-energy which they are capable of intercepting. 

 In countries such as the United Kingdom, the hours of 

 sunshine are by no means excessive. The south coast 

 of England and Ireland, part of East Anglia, and 

 a very small part of Wales and the Isle of Man, 

 are the only districts of Britain which enjoy even 

 the moderate amount of more than 1500 hours of 

 sunshine annually, whereas practically the whole of 

 Germany and even St. Petersburg have at least that 

 number of hours of sunshine. It follows that, in such 

 a country as Britain, every plant must so shape and 

 arrange its leaves that they will lose as little as possible 

 of this scanty allowance of sunshine. Hence we find in 

 most British plants a tendency for the leaves to fit 

 together like the pieces of glass in a mosaic, so that a 



^ The aclual process is probably as follows : 



Carbonic Acid splits into carbon monoxide and oxygen ; water splits 

 into hydrogen and oxygen ; the separation is due to the action of the 

 chlorophyll bodies, or chloroplasts, which utilise the energy absorbed in the 

 chlorophyll. 



6C0., + 6H2O = 6CO + 60 + 6H0 + 60 

 = 6CHoO + 602 

 = CfiHioOg (Sugars) + 6O2 

 It follows that the volume of COg taken in approximately, equals the 

 volume of the oxygen given off. 



Moreover, fires cannot go on burning if oxygen is prevented from reach- 

 ing them, so that when the sugar is destroyed by burning, oxygen must be 

 taken from the atmosphere. It follows that in the original making of sugar, 

 oxygen must have been given back to the atmosphere. 



