278 LEAVES 
as cane sugar but differing in arrangement of atoms, occurs in 
germinating seeds, and is especially abundant in germinating 
Barley. It is formed when starch is broken into its components. 
Maltose, when broken into its constituents, gives rise to two 
molecules of glucose. 
The starches are the most abundant storage forms of food into 
which the photosynthetic sugar is converted. They occur in all 
parts of the plant, but are especially abundant in seeds, tubers, 
and fleshy roots, where they are extensively used by man for food. 
The food value of Corn, Wheat, Rice, and other Cereals, and of 
Potatoes depends mainly upon the starch which they contain. 
The starches, unlike the sugars, are in- 
soluble and occur in the form of definitely 
shaped bodies, known as starch grains, 
which vary much in shape, size, and mark- 
ings in different plants. (Fig. 249.) The 
size, shape, and markings of the starch 
grains are so characteristic of many plants 
that by a study of the starch grains in a 
mixture of ground vegetable products, the 
constituents can often be determined and 
the adulterants thereby detected. 
Hes 4G =") Slarah Starch and cellulose have the same for- 
grain of Irish Potato; mula (CeHOs)n but they differ in the num- 
b, starch grain of Wheat; ber of combinations, CsHi0s, contained in 
¢, starch grain of Corn. their molecules. Their exact difference in 
structure is not known, for the number of combinations, CgH00s, 
contained in a molecule of either starch or cellulose has not been 
determined. They differ in physical properties as well as chemi- 
cally. The starches are readily converted back into sugar, in 
which form they are used by the plant. The starches are broken 
into simpler compounds by a group of enzymes, and the prod- 
ucts formed are dextrin, maltose, and glucose according to the 
extent to which the starch molecules are broken up. 
The hemi-celluloses are quite prominent in some seeds, and 
occur in many other places in the plant. They are much like 
ordinary cellulose, but, being easily converted into sugar, they 
are available sources of food and on this account are often called 
reserve celluloses. They are usually very hard substances and 
are deposited as extra layers on the cell walls. The hardness of 
