Part I 



PLANT GROWTH AND ANIMAL 

 NUTRITION 



CHAPTER I 

 HOW PLANTS GROW AND BUILD FOOD FOR ANIMALS 



I. Plant Growth 



All food for animals, with the exception of air, water, and salt, is 

 supplied either directly or indirectly by plants. To understand the 

 feeding of live stock, one should therefore know how plants grow and 

 build this food and of what it consists. 



The food of plants. — Both plants and animals are composed of a 

 great many substances or compounds — yet all are made up of a rela- 

 tively small number of chemical elements. Indeed, of the 80 or more 

 elements known to the chemist, only 14 are commonly present in 

 plants. Of these, at least 10 are absolutely necessary for plant growth. 

 These are : carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, po- 

 tassium, calcium, magnesium and iron. Sodium, silicon, chlorine, 

 and manganese are also usually found in plants and may be essential 

 to growth. lodin also is present in some plants. Except in the two 

 instances which will be noted later, plants cannot use for food the un- 

 combined elements, such as metallic iron or carbon in the form of 

 charcoal, but they are nourished by water, carbon dioxid (carbonic 

 acid gas), and mineral salts — all of which are compounds containing 

 the elements in chemical combination. 



Water (composed of hydrogen and oxygen) serves a double pur- 

 pose in plants. Some of the water taken up by the plant roots is used 

 as food, while the rest serves as the carrier of plant food. Only when 

 it is dissolved in water can plant food be taken from the soil by the 

 roots or be carried from one part of the plant to another. A surpris- 

 ing amount of water is needed by plants during growth. For every 

 pound of dry matter which they manufacture, from 200 to 500 lbs. of 

 water is drawn from the soil in humid climates, and as high as 1,800 

 lbs. in arid districts. 



Next to water, carbon dioxid, or carbonic acid gas (composed of car- 

 bon and oxygen), is the great food material of plants. This is ob- 



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