434 MR. .1. It. I,\\\'i:s, dr. GILBERT, AND DR. PUQB OS 



feci methods, found the increa e in carbon and in the elements of water to be ah 

 identically in the proportion in which these are known to exist in the tc-denomi- 

 nated carbo-hydrates. He further maintained the essentialness of the so-distinguished 

 " mineral " constituents of plants ; and he pointed out, in opposition to previous in 



that they were derived from the soil, and were not the result of a creative power exi r- 



ciscd by the living plant. He also called attention to the probability that the incom- 

 bustible or mineral constituents derived by plants from the soil, were the source of those 

 found in the animals which arc fed upon them. 



Besides carbon, hydrogen, oxygen, and the more peculiarly mineral constituents, plants 

 had already been shown to contain nitrogen. PlUESTLEY and Lngekhou&Z thought they 

 had observed that plants absorbed the free nitrogen of the confined atmospheres in which 

 they were placed in their experiments. Sexxebiee and "Woodhou.se arrived at an oppo- 

 site conclusion. De SAUSSDBEj again, did not find that plants took up appreciable quan- 

 tities of the nitrogen supplied to them in the free and gaseous form. On the other 

 hand, he thought that his experiments indicated rather an evolution of that element at 

 the expense of the substance of the plant, than any assimilation of it from gaseous 

 media. On this point he further concluded that the source of the nitrogen of plants 

 was, more probably, the nitrogenous compounds in the soil, and the small amount of 

 ammonia which he demonstrated to exist in the atmosphere. 



From his results, as a whole, De Saussuee concluded that air and water contributed 

 a much larger proportion of the dry substance of plants, than did the soils in which they 

 grew. In his new, the fertile soil was the one which yielded liberally to the plant nitro- 

 genous compounds and the incombustible or mineral constituents ; whilst he attributed 

 to air and water, at least the main part of the carbon, hydrogen, and oxygen of which 

 the greater portion of the dry substance of the plant was made up. 



Up to the present time, carbonic acid and water are admitted to be the chief sources 

 of the carbon, hydrogen, and oxygen which constitute the great proportion of vegetable 

 produce. Nor is it questioned that ammonia, and especially ammonia provided within 

 the soil, is at least an important source of the nitrogen of such produce. But the experi- 

 ments of De Saussuee — however sagacious his conclusions — were less satisfactorv as to 

 the source of the nitrogen, than as to that of the carbon, hydrogen, and oxygen, of vege- 

 table matter. 



It will not be supposed, from what has just been said, that there remain no questions, 

 of vast scientific as well as of practical interest, to be yet solved, regarding the con- 

 ditions under which our different crops take up their carbon, hydrogen, and oxygen. At 

 the same time, those who devote themselves to the subject of Agricultural Chemistry 

 soon find that the explanation of the chemical phenomena of agricultural production 

 awaits much more for a further elucidation of the sources, and of the modes of assimila- 

 tion, of the nitrogen than of the other, so-called, organic elements of our crops — carbon, 

 hydrogen, and oxygen. 



In 1837, Boussixgault took up the subject of the sources of the Nitrogen of plants, 

 where De Saussuee had left it more than thirty years before. To the investigations 



