FEEDS AND FEEDING. 



Part I. 

 PLANT GROWTH AND ANIMAL NUTRITION. 



CHAPTER I. 



THE PLANT; HOW IT GROWS AND ELABORATES FOOD FOR 

 ANIMALS. 



I. Plant Growth, 



Aside from air, water, and salt, plants either directly or indi- 

 rectly supply all food for animals ; it is therefore proper in begin- 

 ning these studies to briefly consider how plants grow and elaborate 

 this food. 



1. The food of plants. — Of the 80 or more elements known to the 

 chemist, only 13 are essential to plants, viz. : carbon, hydrogen, oxy- 

 gen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium, 

 iron, sodium, silicon, and chlorin. Iodine and manganese are pres- 

 ent in some plants, and while not regarded as vitally necessary 

 may be more or less useful. With the limited exceptions noted fur- 

 ther on, plants cannot make use of the elements, as such, for food, 

 but are nourished and supported by chemical combinations of the 

 elements. 



Water is the largest single component of the plant, that not held 

 in chemical combination constituting from 75 to 90 per et. of its 

 fresh weight. The plant obtains practically all its water from the 

 soil thru its roots, only a small amount being taken from the air by 

 the leaves. Soil water, absorbed by the roots, enters the cells of 

 which the plant is composed and passes onward and upward thru 

 the stem, moved by capillarity and sap currents, eventually reach- 

 ing every portion of the structure, being especially abundant in the 

 leaves and growing parts. Thruout its existence the plant takes 



