58 Dr Seller on the Nutrition of Plants. 



years of permanent pasture. Nor does the aspect of the 

 earth's surface at present give any sensible indications of its 

 having already lost half of the original store of material des- 

 tined for the maintenance of plants and animals. 



But to enter at present on the changes of particular parts 

 of the soil w^ould lead me too much into matters of detail, 

 while the general argument with which I am engaged is but 

 half concluded. 



Hitherto I have supposed the hypothesis to assume (what 

 some physiologists still maintain) that there is no decompo- 

 sition of the carbonic acid of the air by the green parts of 

 vegetables, or, at least, that there is no compensation by the 

 vegetable kingdom for the carbon of organic compounds de- 

 stroyed by the animal kingdom, and other sources of waste 

 in nature. But this is not the form in which the hypothesis 

 is most genei'ally maintained at present — ^the evidence of the 

 appropriation of carbon by plants from the inorganic carbonic 

 acid of the atmosphere is so conclusive, that the opposition 

 to this belief may be regarded as already making its expiring 

 effort. And here it should be remarked, that tlie acknow- 

 ledgement of a great part of the constituent carbon of plants 

 being drawn from an inorganic compound in the atmosphere, 

 is a plain admission of an analogy which goes far to make it 

 probable that all the food of plants is inorganic. 



But does this limitation better the hypothesis of the food 

 which the soil aflbi-ds being oi'ganic matter. Carbon is not 

 the only constituent of plants : wherever the vegetable tissue 

 contains carbon, it contains hydrogen also, infixed proportions, 

 along with oxygen, and even nitrogen. Now, it cannot avail 

 to assume that the exhaustion of the carbon of the soil is 

 postponed by a large proportion of the carbon of plants being 

 derived from inorganic matter in the atmosphere, while the 

 remaining portion, along with their hydrogen, &c., is drawn 

 from organic matter in the soil. For the fixed constitution 

 of the vegetable tissues must be preserved as respects all 

 their component elements. A plant cannot fix carbon in its 

 substance without obtaining from some source the due rela- 

 tive proportion of hydrogen and its other elements. If this 

 hydrogen be supposed to be obtained from the organic matter 



