68 FARM AND SCHOOL PROBLEMS. 



3. To carry soluble plant food from the roots to the different parts 

 above ground. 



4. To serve as a storehouse for foods and various other commercial 

 products. 



Leaves. 



Leaves are the organs of plants that grow on the stems and 

 branches. There are but a very few varieties of plants that can 

 grow without leaves. 



Facts About Leaves. 



1 . Deciduous leaves are those that live but one season. 



2. Evergreen leaves are those that live more than one year. 



3. The color of living leaves is generally green. 



4. They form a very important part of food products. (See 

 alfalfa.) 



5. Leaves and flowers are the most beautiful and interesting parts 

 of plants. 



6. The changing color of the leaves in the fall of the year is one 

 of the most delightful scenes in the phenomena of nature. 



Functions of Leaves. 



1. The leaves are the "lungs" of the plant. 



2. Their extensive surface exposes the sap of the plant to the air 

 and light. 



3. Leaves give off oxygen and absorb carbon dioxide (carbonic 

 acid gas). 



4. The stomata are the organs of transpiration. 



Some of the most brilliant investigations of science have 

 been made in determining the relations of leaves to the earth's 

 supply of organic matter. The leaf-green or chlorophyll contained 

 in the leaf, is the strongest link that binds organic matter to the 

 sun, which is the source of available energy upon the earth. The 

 important work of chlorophyll is the absorption of light, or the 

 taking over of energy, thus the green plant is our foremost con- 

 servator of energy. It is therefore one of the most interesting 

 parts of agriculture to study the green plant, which is the noise- 

 less machine or part of the great laboratory of nature engaged 

 in manufacturing organic material upon which life depends.* 



*For a list of books relating to Agronomy and Plant Physiology 

 see references at end of this chapter. 



