RESERVE I'OODS 277 



and its compounds serve as fuel, either in the form of wood, peat, 

 or coal. Man converts cellulose into celluloid, artificial silks, 

 artificial rubl)er, and powerful explosives, such as gun cotton. 



Reserve Foods. — ■ The photosynthetic sugar, which is not used 

 immediately as food, is stored in seeds, stems, roots, and tem- 

 porarily in leaves for use at some future time. The reserve foods 

 into which the excess of photosynthetic sugar is transformed are 

 of various forms, but are chiefly of three general classes — carbo- 

 hydrates, fats, and proteins. 



The carbohydrates include the sugars, starches, and hemi- 

 celluloses, and are so named because their proportion of hydrogen 

 and oxygen, being the same as in water, suggested that they were 

 compounds of carbon and water. 



Sugars are of various kinds, but only a few occur in considerable 

 quantities in the plant. Grape sugar, fruit sugar, and cane sugar, 

 the most important of the sugars, are commonly present in the 

 sap of plants. Grape sugar, called glucose or dextrose, and fruit 

 sugar, called fructose or levulose, are the simplest of the sugars. 

 They have the same formula C6H12O6, but differ in the arrange- 

 ment of atoms. Both are found in all parts of plants, but usually 

 one is more abundant than the other. In sweet fruits and the 

 nectar of flowers, fruit sugar is usually more abundant than either 

 glucose or cane sugar, while in Sugar Cane, where both occur 

 along with cane sugar, glucose is more abundant than fructose. 

 Much glucose accumulates in the stems of Corn and other Grasses. 

 Both glucose and fructose are produced not only synthetically, 

 l)ut also through the decomposition of some of the more complex 

 carbohydrates. Thus when Cane sugar is boiled with hydro- 

 chloric acid, glucose and fructose in equal amounts are produced. 



Cane sugar, called sucrose or saccharose, is the sugar of most 

 service to man. It is present in the sap of most plants and 

 accumulates in great abundance in Sugar Cane, Sorghum, Beets, 

 and the Sugar Maple. From the stems of Sugar Cane and the 

 roots of Sugar Beets many million tons of cane sugar are extracted 

 each year. A molecule of cane sugar, as represented by the 

 formula C12H22O11, contains a molecule of glucose and one of 

 fructose with a molecule of water dropped in making the com- 

 ])ination. The formation of cane sugar is represented by the 

 equation CeR^O, + CeHioOe - HoO = CioHooO„. 



Another sugar, known as Maltose and having the same formula 



