6 Effective Farming 



in others, the fiber on the seeds or in the stem, as cotton and 

 hemp ; in others, the seed itself, as beans and peas ; in others, 

 the entire herbage above ground, as alfalfa, timothy, June- 

 grass. In other cases, the product is a manufactured com- 

 modity, as sugar. The study of plants is fundamental to the 

 study of crops. One does not understand nature until one 

 knows something about plants. The earth is covered with 

 vegetation ; the vacant lot soon becomes covered with weeds. 

 All the plants, of so many thousand kinds, take nourishment 

 from the soil and the air. They live and grow and multiply 

 their kind. We could not live on the earth were it not so. 

 The processes in plant life are therefore very important for us 

 to know before we proceed. 



5. Elements and compounds. Before taking up the study 

 of plants, it will be well to recall a few principles of physics and 

 chemistry. All substances in nature are subject to changes in 

 form and composition. When a piece of iron is broken or 

 crushed the form is changed, but each particle has the same 

 composition as before. This change is physical. If the piece 

 of iron is left out of doors, rust forms on its surface. This is 

 a different substance from iron ; it is composed of iron and 

 oxygen, the oxygen coming from the air. Such a change in 

 composition is chemical. The simplest form in which matter 

 can exist is as an element ; the chemical union of two or more 

 elements forms a compound. In nature there are only about 

 eighty different elements, but there are many compounds. 

 When compounds or elements mix physically and do not unite 

 chemically, a mechanical mixture is formed. The air is an 

 example of this, as it is made up of oxygen, nitrogen, carbon 

 dioxide, and some other gases, but they are not united 

 chemically. 



6. Classes of compounds in plants. Analyses of plants 

 show many different compounds, but these can be grouped into 

 five classes known as : water, ash, carbohydrates, fat, and 

 protein. 



