CARBON CYCLE 187 



produce starch and oxygen. This oxygen is thrown off by the plant 

 into the atmosphere for respiration and oxidation. 



Digestion in Plants. Since starch is manufactured in plants it 

 must be changed into sugar by the process of digestion, just as the 

 starch is changed into sugar in the human body. After the starch 

 has been digested, that is, changed into sugar, it is dissolved 

 and distributed throughout all the growing parts of the plants. 



For every six parts of carbon dioxide (6CO2), five parts of water 

 unite with it, making in all 



6C, 

 10H, 

 170. 



Now, starch has 6C, 10H, and 5O. Formula C 6 Hio0 5 . It will be 

 readily seen that starch requires the 6C and the 10H, but only 5 

 of the 17O to make the compound. There will then be 12O left 

 which the plant sends back to the atmosphere as a by-product for 

 man and animal to use. 



The manufacture of starch is expressed by the chemist in the 

 formula 6CO 2 + 5H 2 O changes to CoHioO5 + 6O 2 (120). 



When the plant digests the starch, the formula 



C 6 HioO 5 + H 2 O changes to C r ,Hi 2 O 6 



Starch. Sugar. 



tells us a little more water is added to form sugar. 



Amount of Carbon Required for Growing Plants. - Without some 

 consideration one hardly realizes the magnitude of the process, and 

 the amount of carbon required for growing plants, when compared 

 with the relatively small proportion of carbon in the atmosphere. It 

 has been estimated that to every 10,000 quarts of air there are only 

 4 or 5 grams of carbon dioxide, which means about 2 grams of carbon. 

 About one-half the weight of a plant in a dry state consists of carbon, 

 and a single tree which has a dry weight of about 5 tons will have 

 absorbed from the atkio^pffere about 2| tons of carbon. If 10,000 

 quarts of air contain only 2 grams of carbon and a single tree requires 

 2\ million grams (2| tons), there must necessarily have been a large 

 amount of air deprived of carbon by one plant. 



