iiOW PLANTS fcEGAH TO BE. 1? 



when lighted. In both cases the light and heatj 

 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 nlodern 

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

 which constitute coal, and separated^in them the 

 carbon from the oxygen oT caT'bo^mc^acid , and 

 trie* hydrogen from the oxygen of tfe^^ii^" m ,' 

 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 lelTln 



in the leaves 



and wood of the^oak or tEe club-mos.s. 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 611 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 

 ggl^yajiprL 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 anal 

 heat from the sun "to builcf lip l tEe~pTaht as you* 

 can get out of the plant in the end by bum-j 

 ing it. 



Now, let us burn .our piece of wood or coal, 

 and what happens ? Why, particles 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 



