IXTktOl^IrCTION. 19 



mother seed, the materials, as well as the mode of its nu- 

 trition, are for the most part completely changed. Hence- 

 forth the tissues of the plant and the cell-contents must 

 "be principally, and may be entirely, built up from purely 

 inorganic or mhieral matters. 



In studying the nutrition of the plant in those stages^ 

 of its growth that are subsequent to the exliaustioii of the 

 cotyledons, it is needful to investigate separately the nu- 

 tritive functions of the Atmosphere and of the Soil, for 

 the important reason that the atmosphere is nearly con- 

 stant in its composition, and is beyond the reach of human 

 influence, while the soil is infinitely Aariable and may be 

 exhausted to the verge of unproductiveness or raised to 

 the extreme of fertility by the arts of the cultivator. 



In regard to the Atmosphere, we have to notice minutely 

 the influence of each of its ingredients, including Water 

 in the gaseous form, upon vegetable production. 



The evidence has been given in " How Crops Grow," which 

 establishes what fixed earthy and saline matters are essential 

 ingredients of plants. The Soil is i)lainly the exclusive 

 source of all those elements of vegetation which cannot as- 

 sume the gaseous condition, and which therefore cannot ex- 

 ist in the atmosphere. The study of tlie soil involves a con- 

 sideration of its origin and of its manner of formation. The 

 productive soil commonly contains atmosjiheric elements, 

 which are important to its fertility; the mode and extent 

 of their incorporation with it are topics of extreme prac* 

 tical importance. We have then to examine the signif- 

 icance of its water, of its ammonia, and esjiecially of its 

 nitrates. These subjects have been recently submitted to 

 extended investigations, and our treatise contains a large 

 amount of infoiTnation pertaining to them, which has never 

 before appeared in any publication in the English tongue. 

 Those characters of the soil that indirectly affect the 

 growth of plants are of the utmost moment to the fann- 

 er. It is through the soil that a supply of solar heat, with' 



