i6 



Nature-Study Agriculture 



What air 

 does for 

 plants 



The gases 



arbon dioxid gas 

 from the air 



the air 



into the plant and up to the leaves, but the two ele- 

 ments, hydrogen and oxygen, of which water is com- 

 posed, are necessary 

 in building up the 

 woody fiber and other 

 materials of which the 

 plant is made. (Exp. 

 4.) Consequently, 

 water may be consid- 

 ered a food material 



food. 



People seldom stop 

 to think of what use 

 the air may be to 

 crops. Yet since less 

 than half of the plant 

 stands embedded in 

 soil, and since the 

 upper portion is con- 

 tinually bathed in air, 

 it is only reasonable 

 to suppose that air is 

 of some service. In 



FIG. 13. Diagram to show how a plant . . 



supplies its needs from soil and air through One respect it IS more 



roots and leaves. The arrows indicate the irnnortant than Soil 

 course of the sap within the plant. 



It supplies the plant 

 with far more nourishment than the soil does. 



Air is a mixture of several gases. The three most 

 important gases in dry air are oxygen, nitrogen, and 

 carbon dioxid. About one fifth of dry air is oxygen. 



