12 PRODUCTIVE FARMING 



guard-cells. The stomates are partly closed in dry weather. 

 This keeps moisture from passing too freely out of the leaves 

 into the air. 



Plants Get Food from Air. Growing plants take much 

 of the substance which produces growth directly from the 

 air. They use the carbon dioxide from the air which is given 

 off to the air by the breathing of animals and by the burning 

 and decay of wood. This plant-food from the air furnishes 

 about ninety-five per cent of the dry weight of plants. It 

 is through the leaves that this form of food is taken. The 



~^^/M?T>r*r!?zr<07!>n^!&&*rrz^tfi3&[$iffi 



FIG. 4. Cross section of leaf. The inner cells contain chlorophyl; those near 

 the under side are loose to allow the free passage of air (A). Many breathing pores 

 are in the under skin. One shows at S. 



breathing pores on the surface of green leaves allow the air 

 to come in contact with the soft cells of the inner tissue 

 (Fig. 4). 



Sunlight aids the plant in changing the carbon dioxide 

 into starch or other organic food. Only those plants which 

 contain the green coloring matter, chlorophyl, are able to 

 use the carbon dioxide from the air and change it in this 

 way. Mushrooms grow in the dark, and have no chlorophyl. 

 Their food is not taken from the air nor from the real soil, 

 but from the partly decomposed matter in the soil. 



EXERCISE. Need of Sunlight. Place a board, box, or 

 other object over the green grass of a lawn and let it remain 

 for several days. Notice that the color is soon gone from 

 the leaves. In time the grass would be killed. Celery is 



