HOW PLANTS FEED 45 



The leaves take from the air carbon and oxygen. 



The roots take from the soil, water (oxygen and hydro- 

 gen), potassium (potash), phosphorus (phosphates), ni- 

 trogen (nitrates), iron, sulphur, calcium and magnesium, 

 as essential elements of plant growth. While manganese 

 is present in small quantities in nearly all plants, it is not 

 an essential element, nor are sodium, silicon, aluminum, 

 boron, fluorine, barium, lithium, and chlorine. 



Composition of plants. When all sorts of plants are 

 mixed together and dried (all moisture driven off by 

 heat), the following proportion of elements results: 



Element Per cent. Where the plant got it 



Carbon 45.0 Air 



Oxygen 42.0 Air and water 



Hydrogen 6.5 Water 



Nitrogen 1.5 Soil, air and bacteria 



Ash or mineral compounds 5.0 Soil 



Total 100. o 



From this it will be seen that the greater part of all 

 plant food comes from the air and water only a small 

 quantity from the soil. 



Carbon is secured by the leaves. If you partly burn 

 a match, you observe it has become black. You now see 

 carbon this black substance. Every part of a plant con- 

 tains carbon. Do you wonder now why this element is 

 so important? And do you know that all carbon in plants 

 comes from the air? The leaves of the plants gather it, 

 not a particle is taken by the roots. Here is a great ser- 

 vice that leaves perform : they use the carbon of the air 

 for making starch and sugar. Without leaves or without 

 carbon, we would have no starch or sugar in the world 

 in any form. We have two interesting things about this 



