434 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
fect methods, found the increase in carbon and in the elements of water to be almost 
identically in the proportion in which these are known to exist in the so-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 views, 
that they were derived from the soil, and were not the result of a creative power exer- 
cised 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 are fed upon them. 
Besides carbon, hydrogen, oxygen, and the more peculiarly mineral constituents, plants 
had already been shown to contain nitrogen. PRIESTLEY and IncENHOUSZ thought they 
had observed that plants absorbed the free nitrogen of the confined atmospheres in which 
they were placed in their experiments. SENNEBIER and WOODHOUSE arrived at an oppo- 
site conclusion. Dr Savssurg, 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, Dr Saussure. 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 view, 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 Dr SaussurE—however sagacious his conclusions—were less satisfactory 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, Boussineavtr took up the subject of the sources of the Nitrogen of plants, 
where Dr Saussure had left it more than thirty years before. To the investigations 
