10 THE PRINCIPLES OP AGRICULTURE 



upon trade, and profoundly influenced by every 

 commercial and economic condition, its suc- 

 cessful prosecution nevertheless depends npou 

 an intimate and even expert knowledge of 

 many natural sciences. Aside from all this, 

 the farmer has to deal with great numbers of 

 objects or facts: thousands of species of plants 

 are cultivated, and many of these species have 

 hundreds and thousands of varieties ; many 

 species of animals are domesticated, and each 

 species has distinct breeds. Each of these sep- 

 arate facts demands specific treatment. More- 

 over, the conditions under which the farmer 

 works are ever changing : his innumerable prob- 

 lems are endlessly varied and complicated by 

 climate, seasons, vagaries of weather, attacks of 

 pests and diseases, fluctuations in labor supply, 

 and many other unpredictable factors. 



3. Its Field of Production 



22. In the production of its wealth, agricul- 

 ture operates in three great fields, — with the 

 soil, the plant, and the animal. Although aided 

 at every point by knowledge of other subjects, 

 its final success rests upon these bases; and 

 these are the fields, therefore, to which a text- 

 book may give most profitable attention. 



