kOW PLANTS iSEGAN T6 BE. 1? 



when lighted. In both cases the light and heat, 

 as we shall see more fully hereafter, are derived 

 from the sun, our great storehouse of energy. 

 The sunshine fell upon the leaves of the triddern 

 oak-tree, or of the very antique club-mosses 

 which constitute coal, and separated in them tlie 

 carbon from the oxygen of carbonic acid, and 

 the hydrogen from the oxygen of the water in 

 the sap. In each case the oxygen was turned 

 loose upon the air in its free form, while the 

 carbon and the hydrogen (with a very little 

 oxygen and a few other materials) were left in 

 loose and almost free conditions in the leaves 

 and wood of the oak or the club-moss. But the 

 point to which I wish now specially to direct 

 your attention is this — the sunlight was actually 

 used up for the time being in effecting this 

 separation between the oxygen on the one hand, 

 and the carbon and hydrogen on the other. As 

 long as the plant remained unburnt, the light 

 and heat it received from the sun lay dormant 

 within it, not as actual light and heat, but as 

 separation between the oxygen and the hydrogen 

 or carbon. Coal, indeed, has been well described 

 as ** bottled sunshine." 



More than this ; it took just as much light and 

 heat from the sun to build up the plant as you 

 can get out of the plant in the end by burn- 

 ing it. 



Now, let us burn our mece of wood or coal, 

 and what happens ? Why, p£irticles of oxygen 

 rush together with particles of carbon in the 

 fuel, and form carbonic acid. How much 

 carbonic acid ? Just as much as it took 



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