LECTURES 



ON AGRICULTURAL CHEMISTRY. 



BY PROFESSOR SAMUEL W. JOHNSON, OP TALE COLLEGE, CONNECTICUT. 



LECTURE I. 



THE COMPOSITION AND STRUCTURE OP THE PLANT. 



The objects of agriculture are the production of certain plants and 

 certain animals which are employed to feed and clothe the human 

 race. The first object in all cases is the production of plants. 



Nature has made the most extensive provision for the spontaneous 

 growth of an immense variety of vegetation; but, except in rare cases, 

 man is obliged to employ art to provide himself with the kinds and 

 quantities of vegetable produce which his necessities or luxuries 

 demand. In this defect, or rather neglect of nature, agriculture has 

 its origin. 



The art of agriculture consists in certain practices and operations 

 which have grown out of an observation and imitation of the best 

 efforts of nature, or have been hit upon accidentally. 



We distinguish here between a,gri-culfacre, or the culture (improve- 

 ment) of the field, and farming, which may be anything but the imita- 

 tion of nature, which often is the grossest violation of her plain 

 precepts. 



The science of agriculture is the rational theory and exposition of 

 the successful art. 



Nothing is more evident than that agricultural art impedes its own 

 growth by holding aloof from science. In many respects the Egyptians, 

 the Romans, and the Chinese, had, centuries ago, as perfect an agri- 

 cultural practice as we now possess; but this fact so demonstrates the 

 extreme slowness with which an empirical art progresses, that incal- 

 culable advantage must be anticipated from yoking it with the rapidly- 

 developing sciences. In fact, the history of the last fifty years has 

 proved the benefits of this union; and no farmer who by the help of 

 science has mastered but one of the old difficulties of his art that for 

 all time have been tormenting the thoughtful with doubt and misleading 

 everyone into a wasteful expenditure of labor or material,would willingly 

 return to the days of pure empiricism. On the other hand, those who at- 

 tempt to unfold the laws of production from considerations founded mere- 

 ly in the pure sciences, without regard to, or knowledge of, the truths 

 of practice, are sure to go astray and bring discredit on their efforts. 



Agriculture, i. e. field culture, not husbandry or farm management 

 in the widest sense, is a natural science, and is based principally upon 

 physics, chemistry, and physiology. 



By physics (natural philosophy) is meant the science of matter con- 

 sidered in relation to those forces which act anion"; masses, or among 



