12 NATURE OF CARBOHYDRATES 



and so makes life possible upon the earth but that all animal 

 life is absolutely dependent, either directly or indirectly, for food 

 upon the products built up by the chlorenchyma. Let us see 

 how these foods are formed. Various substances are absorbed 

 by the roots, and the vascular bundles, which extend throughout 

 the plant body, transfer them to the chlorenchyma. This ab- 

 sorbed material is in large part water, but various mineral sub- 

 stances are dissolved in it. Various gases, as carbon dioxide, 

 also find their way through the stoma to the chlorenchyma. All 

 of these absorbed substances are composed of elements. Thus 

 water consists of two elements, hydrogen and oxygen, in the pro- 

 portion of two parts of hydrogen to one part oxygen. This compo- 

 sition is indicated by the abbreviation, H 2 O. So the gas, carbon 

 dioxide, contains one part of carbon and two parts of oxygen, indi- 

 cated thus CO 2 . Chloroplasts have the power under suitable con- 

 ditions of decomposing or tearing apart these compounds. They 

 are able with a suitable light and temperature to separate CO 2 into 

 the elements carbon and oxygen and H 2 O into hydrogen anfl 

 oxygen. Furthermore they can reunite these elements into new 

 compounds that are quite different from the original ones. In 

 this way CO 2 and H 2 O are decomposed and the elements re- 

 united into complex compounds or foods consisting of carbon, 

 hydrogen and oxygen. Such complex foods as cane sugar, con- 

 sisting of twelve parts of carbon, twenty-two of hydrogen, and 

 eleven of oxygen are formed in this way. This very common 

 food is expressed by the formula C^H^O^. So also other foods 

 are formed, as grape sugar C 6 H 12 O 6 and starch usually indicated 

 as C 6 H 10 O 5 . The cellulose walls of the parenchyma cells have 

 the same composition as starch. It will be seen that all these 

 foods have carbon united to hydrogen and oxygen in- the same 

 proportion as it exists in water. Cane sugar has carbon united 

 to eleven times H 2 O, and starch five times H 2 O. It was sup- 

 posed that these substances were a combination of carbon and 

 H 2 O. For this reason they were called carbohydrates. This 

 name is still applied to these foods although it is known that the 

 base is not H 2 O but the hydroxyl OH. The actual changes that 

 are effected in the formation of these various carbohvdrates is 



