14 PRINCIPLES OF FEEDING FARM ANIMALS 
The starch of many plants can be identified by their characteris- 
tic microscopic structure, but from the feeder’s point of view there is 
no difference in the value of starch from different sources. 
The average percentages of starch found in some plants are as 
follows: 
Rice, 79; corn, 71; wheat, 69; rye, 67; barley, 65; potatoes, 68 ; 
oats, 53; beans and peas, 39. Starch is found only in small 
amounts in coarse feeds or in stems and leaves of plants. 
When subjected to ultimate chemical analysis, the percentage 
composition of starch is shown to be as follows: 
44.4 per cent carbon, 
6.2 per cent hydrogen, 
49.4 per cent oxygen. 
Sugar is found in many farm crops during the immature stage 
of the plant, but it is as a rule changed back to starch in the mature 
plant. There are a number of different sugars found in plant 
materials, classified as mono-, di,- or poly-saccharides. 
‘The following statement shows the more important sugars in 
each of these classes: 
a. Mono-saccharides.—Dextrose (or glucose), levulose (or fructose), 
and galactose. They occur in unripe plants and in fruits. Like other 
carbohydrates, they are composed of carbon, oxygen, and hydrogen, with 
six atoms of carbon in the molecule; hence are also called hexoses. 
b. Di-saccharides.—Sucrose (cane-sugar), maltose (malt-sugar), and 
lactose (milk-sugar). These contain twelve atoms of carbon in the mole- 
cule, combined with a corresponding number of atoms of oxyg:n and hydro- 
gen (p. 13). Sucrose is found in large quantities in sugar beets and sugar 
cane; when ripe both of these plants contain 12 to 18 per cent of this sugar, 
according to the character of the seed used, method of cultivation, season, 
soil, etc. These crops are the two great sugar plants of the world, all other 
sources of sugar, like sugar maple, sorghum, etc., being of minor importance. 
c. Poly-saccharides or amyloses, containing a multiple of six carbon 
atoms in the molecule. To these belong starch, dextrine, cellulose, and 
glycogen. The substances in both this and the preceding group are readily 
changed into mono-saccharides (glucose) through hydrolysis (boiling with 
dilute acids), or through the action of ferments, as already stated under 
starch. 
The pentosans and pentoses stand close to starch and sugar, 
tespectively, being the corresponding compounds with only five 
atoms of carbon in the molecule. The pentosans are readily changed 
to pentoses on boiling with acids. They have an important nutri- 
tive value, almost equal to that of starch, and well merit the atten- 
tion which they have received from chemists during late years. The 
