RESERVE FOODS 277 
and its compounds serve as fuel, either in the form of wood, peat, 
or coal. Man converts cellulose into celluloid, artificial silks, 
artificial rubber, 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 CsH.».O¢, 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, 
but 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 CyH20n, contains a molecule of glucose and one of 
fructose with a molecule of water dropped in making the com- 
bination. The formation of cane sugar is represented by the 
equation CeHi20¢ + CeHi2Os a H,O = CoH 2041. 
Another sugar, known as Maltose and having the same formula 
