6 



FEEDS AND FEEDING, ABRIDGED 



tained from the air, ten thousand parts of which contain 3 to 4 parts 

 by volume of carbon dioxid. The air supplies carbon dioxid to the 

 cells of the plant thru the innumerable minute openings on the 

 under surface of the leaves. In producing a 15-ton crop of green 

 corn over 5 tons of carbon dioxid are required, to obtain which the 

 plants must take in over 12,000 tons of air. Yet the suppl}^ of carbon 

 dioxid is never exhausted, for it is being continuously returned to the 

 air thru the breathing out of carbon dioxid by animals and the decay 

 of plant and animal matter. 



Nitrogen abounds in the living, growing parts of plants. Altho 

 about three-fourths of the air is nitrogen gas, plants in general cannot 

 use the free nitrogen of the air, but obtain their supply from nitrogen- 

 containing compounds in the soil, chiefly the nitrates. Bacteria living 



Carbon cf/'oxid 



^^^%-^ 



^ _ ^(ffyo/roi^enondoKyqen) 



m/hera/ mo/^er ^^^^^'^rates 

 Sa/phur Ca/c/'um 

 P/}03p^orus magnesium 

 Potosd/um Iron 



Fig. 2. — ^Where Plants Secure Their Food 



Plants obtain carbon dioxid from the air, and water, mineral matter, and 

 nitrates from the soil. Legumes are able to use indirectly the nitrogen of the 

 air. Plants give off water and free oxygen gas to the air thru their leaves. 



in nodules on the roots of legumes, such as clover, alfalfa, and peas, 

 are able to take nitrogen gas from the air and pass it on in combined 

 form to the host plants. Thus, the legumes are able indirectly, thru 

 the aid of these bacteria, to use the nitrogen of the air as food. 



Oxygen, which is a part of all plant compounds, is obtained largely 

 from water and carbon dioxid, and not from the free oxygen gas of 



