Meaning of Plant Building.
—Before the single simple elements were taken into the plant, they were of little value. The animal could not use them for food, they could not be burned to furnish heat, and they stored up no energy to carry on any of the world’s work. What a change the plant makes of them! So used, they become the source of the animal food, and, as food, they contain five principal groups with which the animal is nourished. These five groups are the air, water, the protein compounds, the nitrogen free compounds, such as starch, crude fiber, sugar and gums, and the fat or ether extract, as it is called.