CHILDREN'S GARDENS 157 



more, with, perhaps, something about the bacterial life 

 constantly at work building and tearing down, and the 

 chemical changes. 



A fertile soil is composed of: . 



Fine ground rock. 



Humus. 



Air. 



Water. 



The rock of the soil contains elements needed for 

 plant food, and these must be dissolved in water and 

 carried to the feeding roots of the plants. 



These elements are: 



Nitrogen Chlorine 



Potassium Sulphur 



Phosphorus Silicon 



Calcium Aluminum 



Sodium Carbon 



Iron Hydrogen 



Magnesium Oxygen 



Humus of the soil is the decaying organic mat- 

 ter of dead animals and vegetables, mixed thoroughly 

 with the few inches of top soil, making it darker col- 

 ored. It is in the spaces between the particles of 

 rock, and acts like tiny sponges in holding water. It 

 fills up the too large spaces of a sandy soil, and sepa- 

 rates the too close particles of a fine clay soil. It 



