CHAPTER XVII. 



CONSTITUENTS OF PLANTS. 



For the purpose of ordinary agricultural analysis, the various 

 compounds in plants and feeds are divided into six groups, each of 

 which, with the exception of the first (water), is composed of a 

 number of chemical compounds, varying in their nature and rela- 

 tive proportion according to the plant, or portion of plant, under 

 examination. 



These groups are as follows : 



1 i ) Water, which is present in all feeds. 



(2) Ether Extract. This is the material extracted by ether 

 and, in the case of seeds, is composed mostly of fats and oils, but 

 it contains large quantities of substances other than fats in the 

 case of hays, straw, and grass. 



(3) Protein. This includes all the nitrogenous constituents of 

 the plant or feed. 



(4) Crude Fiber. This is the residue left on boiling the 

 material with sulphuric acid and with caustic soda, a purely 

 arbitrary method. It consists of cellulose, lignin, cutin, and 

 other substances. 



(5) Ash. This is the residue left after the material has been 

 burned, and consists of the substances not volatile at the tem- 

 perature of the combustion. It consists chiefly of lime, magnesia, 

 soda, and potash united with phosphoric acid, chlorine, carbon 

 dioxide, sulphur trioxide, silica, and some unburned carbon. 



(6) Nitrogen-Free Extract comprises all the other ingredients 

 of the plants not included in the above groups. In estimating 

 its quantity, the water, protein, ether-extract, crude fiber, and 

 ash, are added together, and the sum subtracted from 100. The 

 difference is the nitrogen-free extract. 



Water. Water is abundantly found in the green and growing 

 portions of the plant, as in leaves, tender shoots, and immature 

 seeds, but chiefly in the sap, in which it transports the materials 

 used in the growth of the plants. The older portions of plants, 

 such as the stems, and old wood, and the mature seeds, contain 



