CHAPTER II 

 HOW PLANTS GROW 



ONLY a very general statement will be made here, outlining the 

 important features of plant growth. The student is referred to books 

 on botany or plant physiology for detailed information on plant 

 growth, and text-books on soils, for information regarding the rela- 

 tion of soil to plants. 



The Parts of a Plant. A typical plant may be divided into 

 three parts as follows: (1) The root system; (2) the vegetative 

 part, consisting of stem, branches, and leaves ; and (3) reproductive 

 part, consisting of flowers, fruits, and seeds. 



The general functions of the roots are to absorb water and 

 plant food from the soil, to feed the plant. The stem and leaves 

 have three general functions, namely : ( 1 ) To take up the solution 

 absorbed by roots and evaporate the water, leaving the minerals in 

 the plant for food; (2) to take in air and extract therefrom carbon 

 for the plant, and (3) to manufacture the elements taken in from 

 soil and air into material for growth of the plant. The reproductive 

 organs perpetuate the plant, producing the seeds or fruits. A large 

 share of the materials manufactured by the leaves is stored in the 

 seeds. In the cereals, the seeds are the most valuable part of the 

 plant. 



Elements Required for Growth. When a chemist analyzes a 

 plant, he finds that it is composed of thirteen elements. Ten oi 

 these elements are taken from the soil as follows : 



1. Nitrogen 4. Potassium 7. Iron 10. Silicon 



2. Sulfur 5. Calcium 8. Chlorine 



3. Phosphorus 6. Magnesium 9. Sodium 



Only the first seven of the above soil elements are considered 

 essential, but the last three, chlorine, sodium, and silicon, are always 

 present. 



From the air comes : 



11. Carbon 12. Oxygen 



5 



