142 FIRST PRINCIPLES OF AGRICULTURE. 



is usually white in color, and is odorless and tasteless. 

 Manufactured flax and cotton, and unsized paper derived 

 from them, are good examples of nearly pure cellulose. 

 It is not readily soluble, and is capable of only partial 

 digestion. It is identical with starch in chemical com- 

 position, and may be converted first into dextrine, then 

 into grape sugar, by suitable treatment with acids or 

 alkalies. 



Starch is a very abundant substance ; it is found in all 

 plants, and in nearly all parts of them. The cereal 

 grains, and the dry matter of root and tuber crops, are 

 especially rich in this substance; and because of its 

 abundance and ease of digestion it is one of the most 

 important of the non-nitrogenous substances. It is readily 

 converted into dextrine and grape sugar by treatment 

 with acids; in fact, the grape sugar or glucose of com- 

 merce is largely derived from the starch of corn. 



Sugars are of four kinds, — cane, milk, grape, and fruit 

 sugar : these differ but little in composition ; all resem- 

 ble each other in their properties. Cane sugar is derived 

 from sugar-cane and sugar-beet, and milk sugar from 

 the milk of the cow, while grape and fruit sugars usu- 

 ally occur together in the juices of plants, sweet fruits, 

 and in honey. These are all readily soluble in water, 

 and easily digested ; and, although occurring in small 

 quantities in ordinary feeds, they are very important, 

 because formed in large quantities from other carbo- 

 hydrates in digestion. 



The gums exist in small amounts in plants used for 

 animal food, and are relatively unimportant food com- 

 pounds. 



