64 ELEMENTS OF AGRICULTURE 



by the sap. Oxygen is also taken up by the roots of 

 plants, and nitrogen compounds dissolved in water also 

 enter the plant through its roots. 



65. Compounds are Manufactured in the Leaves. — 

 Through their leaves plants draw from the air supplies 

 of carbon dioxide; through their roots they pump water 

 and the salts it contains in solution; and from these 

 compounds are made many substances that go to build 

 up plants. Chief among these is starch, a substance 

 with which every child is familiar, as it makes up a lary<j 

 part of many foods; wheat flour, corn meal, rice, and 

 potatoes are mostly starch, every grain of which is 

 manufactured in the leaves of the plant which grows 

 them. The so-called starch factories of the world never 

 make an ounce of starch. All they can do is to separate 

 from the other substances with which it is mixed the 

 starch that is actually made in the leaves of plants, 

 and afterwards concentrated in the seed, root, or stem. 

 The real starch factories are the green leaves of plants. 

 Starch is made up of carbon, hydrogen, and oxygen — 6 

 parts of carbon, 10 parts of hydrogen, and 5 parts of 

 oxygen, or, as the chemist writes i^CeHioOs. Carbon 

 dioxide the chemist writes CO 2, two parts of oxygen to 

 one of carbon; and water he writes HO2, two parts of 

 hydrogen to one of oxygen. It is evident that these two 

 compounds contain all the elements necessary to form 

 starch, and it is from them that the plant manufactures 

 it. But how? We may mix water and carbon dioxide 

 in varying proportions and under all sorts of conditions, 

 but no starch results; we may mix six parts of carbon, 

 ten parts of hydrogen, and five parts of oxygen, and 



