for crops. The treeless prairie and the muck swamps have black 

 soils, and are very productive when properly drained. Try to find 

 o\it what kind of trees grew on some of the fields about you, and 

 notice whether some of these fields produce better crops than others. 



PURPOSES OF THE SOIL. 



The purpose of the soil is twofold— to furnish a physical support 

 for plants and to furnish some of the material of which plants are 

 made, or as they are often called, some of the plant foods. For the 

 first purpose almost any kind of soil that is well drained and will per- 

 mit the roots to readily pass through it will suffice. But the plants 

 can only get food from soils which contain these foods in sufficient 

 quantity and in such forms that the plants can take up the foods 

 from the soil and use them to build up its own tissues. 



SOURCES OF PLANT FOOD. 



Ordinary plants are composed of thirteen simple substances. These 

 the living piant uses to build up a considerable number of complex 

 substances, such as starch, sugar, oil and gluten. All plants contain 

 some mineral matter which remains as ash when the plants are 

 burned. These simple substances are taken from the s<jil and from 

 the air. 



QUANTITY OF PLANT FOOD REQUIRED. 



Different plants require different amounts of the simple substances 

 that serve as their food. Water and the carbonic acid of the air 

 furnish the material for the greater part of the plant. But if the 

 other things are less in amoimt they are not less in value, and unless 

 the plant can get all the things that it needs it cannot use to advan- 

 tage those that may be present in abundance. To obtain some idea 

 of the relative amounts of the different substances that go to make up 

 plants we may take as an example an ordinary bundle of wheat just as 

 it comes from the self-binder. It weighs about ten pounds, and 

 nearly nine and one-half pounds of the material are taken from water 

 and the carbonic acid of the air. A large part of the farmer's labor 

 is devoted to operations for supplying the ingredients that make up 

 the other half pound. This half poimd contains ten simple substances 

 and no tyo substances are present in equal amounts. The cut shows 

 the amounts of these different substances contained in the bundle of 



