How the Plcmt Grows. 5 



The chemist writes the substances formed from carbonic acid gaa 

 and water in the plant thus: 



Starch ■> 



CeUulosel ^^i^^^oO,, 



Cane sugar OjjHjjO,, 

 Glucose CjjHj^Oi, 

 Let us now consider from the chemist's standpoint how starch 

 may be formed by the plant from carbonic acid and water, and, 

 when once formed, how it may be changed to sugar, glucose or 

 cellulose. 

 This may be shown by the following equations: 



Taken in by the plant. Changed in the plant to — 



Carbonic acid Water Starch Oxygen 



12 (CO,) + 10(H,O) = C,,H,„Oi„ +24 

 Starch by the addition of one part of water becomes cane 

 sugar; thus: 



Starch Water Cane sugar 



Cx2H3„0,„ + H,0 = C,,H,,0„ 

 Cane sugar plus one part of water becomes glucose, thus: 

 Cane sugar Water Glucose 



C,,H,,0„ + H,0 = Ci,H,,Oi, 



In the above we observe that 12 molecules of carbonic acid 

 united with 10 molecules of water form 1 molecule of starch 

 with 24 atoms of oxygen remaining. By the second equation we 

 learn that if one molecule of water is added to the starch molecule, 

 a molecule of cane sugar results. The addition of another mole- 

 cule of water to cane sugar gives glucose. The removal of one 

 molecule of water from cane sugar and two from glucose reduces 

 these substances back to starch, or to cellulose. 



In the above cases the hydrogen and oxygen stand in the same 

 relation to each other as in water, there being two atoms of the 

 former to one of the latter. For this reason, starch, cane sugar, 

 cellulose and similar substances are called carbohydrates. ' 



8. Plant oils. — Another group of building materials found in 

 the plant comes under the term "fats" or "oils." Though they 



1 For information concerning scientific and technical terms the student 

 will consult the Glossary at the end of the voliune. 



