HOW PLANTS BEGAN TO BE. 15 



only things that know ho7v to manufacture living vui- 

 terial. 



Roughly speaking, plants are the producers 

 and animals the consumers. Plants are like the 

 pine-tree that makes the wood ; animals are like 

 the fire that burns it up and reduces it to its pre- 

 vious unorganised condition. 



It is a little difficult really to understand the 

 true relation of plants and animals without some 

 small mental effort; yet the point is so important, 

 and will help us so much in our after inquiries, 

 that I will venture upon asking you to make that 

 effort, here at the very outset. 



If you take a piece of wood or coal, you have 

 in it a quantity of hydrogen and carbon, almost 

 unmixed with oxygen, or at least combined with 

 far less oxygen than they are capable of uniting 

 with. Now put a light to the wood or coal, and 

 what happens ? They catch fire, as we say, and 

 burn till they are consumed. And what is the 

 meaning of this burning ? Why, the carbon and 

 hydrogen are rushing together with oxygen — 

 taking up all the oxygen they can unite with, and 

 forming with it carbonic acid and water. The 

 carbon joins the oxygen in a very close embrace, 

 and becomes carbonic acid gas, which goes up the 

 chimney and mixes with the atmosphere; the 

 hydrogen joins the oxygen in an equally intimate 

 union, and similarly goes off into the air in the 

 form of steam or watery vapour. Burning, in 

 fact, is nothing more than the union of the carbon 

 and hydrogen in wood or coal with the oxygen of 

 the atmosphere. But observe that, as the carbon 

 and hydrogen burn, they give off light and heat. 

 This light and heat they held stored up before in 

 their separate form ; it was, so to speak, dormant 



