34 THE STORY OF THE PLANTS. 



a blade, as in the oak or the beech ; though some- 

 times the stalk is suppressed, as in grass and the 

 teasel. Almost always, however, the leaf is green : 

 it is broad and flat, with a large expanded surface, 

 and this surface is spread out horizontally, so as 

 to catch as much as possible of the sunlight that 

 falls upon it. Its business is to swallow carbonic 

 acid from the air, and digest and assimilate it un- 

 der the influence of sunlight. And as different 

 situations require different treatment, various 

 plants have leaves of very different shapes, each 

 adapted to the habits and manners of the particu- 

 lar kind that produces them. The difference has 

 been brought about by Natural Selection. 



^/z(3;/ does the leaf eat ? Carbonic acid. There 

 is a small quantity of this gas always floating about 

 dispersed in the air, and plants fight with one an- 

 other to get as much as possible of it. Most peo- 

 ple imagine plants grow out of the soil. This is 

 quite a mistake. The portion of its solid material 

 which a plant gets out of the soil (though abso- 

 lutely necessary to it) is hardly worth taking into 

 consideration, numerically speaking; by far the 

 larger part of its substance comes directly out of 

 the air as carbon, or out of the water as hydrogen 

 and oxygen. You can easily see that this is so if 

 you dry a small bush thoroughly, leaves and all, 

 and then burn it. What becomes of it in such 

 circumstances ? You will find that the greater 

 part of it disappears, or goes off into the atmos- 

 phere ; the carbon, uniting with oxygen, goes off 

 in the form of carbonic acid, while the hydrogen, 

 uniting with oxygen, goes off in the form of steam 

 or vapour of water. What is there left ? A very 

 small quantity of solid matter, which we know as 

 ash. Well, that ash, which returns to the soil in 



