; NATURE STUDIES. 



derives all its energy or motive-power from tlie sun. 

 The green leaf is the organ upon which the rays act. 

 In its cells the waves of light propagated from the 

 sun fall upon the carbonic acid which the leaves drink 

 in from the air, and by their disintegrating power, 

 liberate the oxygen while setting free the carbon, to 

 form the fuel and food-stuff of the plant. Side by 

 side with this operation the plant performs another, 

 by building up the carbon thus obtained into new 

 combinations with the hydrogen obtained from its 

 watery sap. From these two elements the chief con- 

 stituents of the vegetable tissues are made up. Now 

 the fact that they have been freed from the oxygen 

 with which they are generally combined gives them 

 energy, as the physicists call it, and, when they re- 

 combine with oxygen, this energy is again given out 

 as^eat, or motion. In burning a piece of wood or a 

 lump of coal, we are simply causing the oxygen to 

 re-combine with these energetic vegetable substances, 

 and the result is that we get once more the carbonic 

 acid and water with which we started. But we all 

 know that such burning yields not only heat, but also 

 visible motion. This motion is clearly seen even in 

 the draught of an ordinary chimney, and may be 

 much more distinctly recognised in such a machine as 

 the steam-engine. 



At first sight, all this seems to have very little con- 

 nexion with hyacinth bulbs. Yet, if we look a little 

 deeper into the question, we shall see that a bulb and 

 an engine have really a great many points in common. 



