292 Agricultural Chemistry. 



kingdoms of nature. Inorganic matter affords food to plants, and they, on 

 tlie otlier band, yield tlie means of subsistence to animals. Plants find neAV 

 nutritive material only in inorganic substances. Hence one gi-eat end of 

 vegetable life is to generate matter adapted for the nutrition of animals, out of 

 inorganic substances, which are not fitted for that purpose." — p. 12. 



Carbonic acid, ammonia, loater, sulphuric acid, nitric acid, 

 ■phosphoric acid, are inorganic or mineral substances. 



In contrast to those inorganic nutritive matters which plants 

 receive from the atmosphere (carbonic acid, Waaler, ammonia, 

 nitric acid), they require for their formation and the development 

 of their vitality, certain inorganic substances, derived from the 

 soil, which we find in their ashes after they have been burned. 



These constituents of the ashes of plants are nutritive materials 

 and not stimulants. The atmospheric nutritive materials only 

 act when the plants are at the same time supplied with the 

 materials of nutrition derived from the soil. 



When plants require, for their nutrition and development, 

 certain materials of nutrition derived from the soil, which ma- 

 terials were originally constituents of certain minerals, then the 

 nutritive power or the fertility of the soil is proportional to the 

 amount of these materials which it contains ; they are the first 

 conditions essential to the cultivation of plants. The nutritive 

 power of the atmosphere is proportional to the amount of gaseous 

 nutritive matters contained in it. These last belong, by their 

 nature and origin, to the same class as the nutritive matters of 

 the soil : but the nutritive materials of the soil are never gaseous ; 

 and as we are in the habit of regarding air and earth as opposed 

 to each other, I shall employ, in the following considerations, as 

 is uniformly done in science, carbonic acid and ammonia (which 

 are mineral constituents of the atmosphere), or atmospheric 

 matei'ials of nutrition, and the mineral constituents of the soil, 

 or terrestrial materials of nutrition, as contrasted with one 

 another ; which, however, it is self-evident that they are not, if 

 we consider their nature. The carbonic acid in limestone, and 

 the ammonia in sulphate of ammonia, are not gaseous and can 

 never be constituents of the atmosphere in these forms of 

 combination. 



The duration of the fertility of a field or soil is proportional to 

 the quantity or the sum of those conditions of nutritive power 

 which are present in the soil ; that is, of the nutritive constituents 

 of the soil. 



The exhaustion of the soil by cultivation is directly propor- 

 tional to that part of this quantity or sum which the soil has 

 annually yielded to the crop raised on it. 



Since neither the nutritive constituents of the atmosphere alone, 

 nor those of the soil alone, exert any influence whatever on the 



