FEEDS AND FEEDING. 



PART I. 

 PLANT GROWTH AND ANIMAL NUTRITION. 



CHAPTEE I. 



W IT GROWS A 

 FOOD FOR ANIMALS. 



I. Plant Grmcth. 



1. Concerning plant cells. Since plants and their products in 

 some form, directly or indirectly, constitute the food of animals, 

 it is proper in these studies that we briefly examine how the plant 

 grows and elaborates this food. 



The unit of plant growth is the cell. If we study a grain of 

 corn or a corn stalk we find it made up of cells variously modified, 

 the whole group together taking on the form of the object under 

 consideration. In their primary condition all cells are closed 

 sacs, and contain the juices and other substances incident to plant 

 growth. The walls of the plant cells are composed of a woody 

 substance called cellulose. These walls may be thin and tender to 

 the teeth of the animal, as in the young plants of the fields, or 

 thick, woody and tough, as in the stems of the forest trees. Before 

 studying more intimately the plant cell, its contents, and what 

 occurs within it, let us consider the substances essential to plant 

 growth. 



2. Elements essential to plant life. The elementary substances 

 required for plant life are carbon, hydrogen, oxygen, nitrogen, 



