ON THE NUTRITION OF PLANTS. 
193 
He regarded this question as one not merely of high in- 
terest in itself, but as bearing expressly on the solution of 
the problem, whether the food of plants be organic or mine- 
ral. Dr. S. calculates the annual conversion of the carbon 
of organic matter into inorganic carbonic acid at not less 
than 600,000,000 tons ; and infers, on the most favorable 
aspect of the amount of soil over the earth's surface, that 
such an annual loss could not be withstood beyond 6,0C0 
years ; and, on a less exaggerated assumption of its amount . 
probably very near the truth, that the waste would absorb , 
the whole of the existing organic matter of the soil in about 
740 years. 
Dr. S. contends that the truth of these conclusions remains 
unaltered, even if it be conceded that much of the carbon 
of plants is drawn, not from the organic matter of the soil, 
but from the inorganic carbonic acid of the atmosphere, 
unless some inorganic source of their hydrogen and oxygen 
be at the same time admitted. He therefore regards Liebig's 
views of the inorganic nature of the food of plants as support- 
ed, not merely by many special facts — for example, by the in- 
crease of the organic matter of the soil, often observed during 
the growth of plants — but also by the general view of the 
earth's surface just taken, because there is nothing in its as- 
pect to warrant the idea that its means of maintaining the 
organic kingdoms are declining with the rapidity indicated 
in the statements just made. 
He next examined Liebig's views of ammonia. 
1st. As the sole source of the nitrogen of plants, and there- 
by of animals. 
2d. As having its exclusive origin from the interior of the 
earth, and never from the nitrogen of the atmosphere. In 
regard to these statements he made it appear, as there is no 
evidence of ammonia being thrown forth from the bowels 
of the earth at all times, in quantities proportioned to the 
waste of it necessarily sustained at the surface, by decom- 
position into uncombined hydrogen and nitrogen, that Lie- 
