A STUDY OF FOODS 



49 



of the water brought up from the roots. Plants, therefore, 

 in manufacturing food materials that are useful to animals, 

 take the waste carbon dioxid and water that are thrown off 

 from animal bodies, and give in exchange free oxygen, which 

 is essential for animal life. Hence, without plants animal 

 life would soon cease to exist. 



FIG. 15. The Potato Plant, showing Potato (shaded dark) from which 

 Plant has grown ; also the New Growth of Stems, Leaves, and Potatoes. 



Storage of Starch and Sugar. We shall see later that in 

 the human body starch can easily be changed to sugar. In 

 plants, too, a similar process is carried on, and sugar can 

 also be changed to starch. Some of these carbohydrates, as 

 soon as they are made, are used by the plant for the pro- 



6 parts carbon dioxid + 5 parts water give 1 part starch + 12 parts oxygen. 

 Or 6 C0 2 (= C 6 Oi 2 ) + 5 H 2 O (= H 10 O 5 ) give 1 C 6 Hi 5 + 12 O. 



This means that for every six parts of carbon dioxid, five parts 

 of water are needed. During this process a large amount of oxygen 

 (equivalent to all the oxygen in the carbon dioxid) is given back to 

 the air. 



