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On the Sources of the Nitrogen of Vegetation. 



agriculture, both ancient and modern, fails to afford evidence of com- 

 pensation -snch as is now sought for. Indeed we would say, as we 

 have done before, that — " The history of agriculture throughout the 

 world, so far as it is known, clearly shows that a fertile soil is one 

 which has accumulated within it the residue of ages of previous 

 vegetation, and that it becomes infertile as this residue is exhausted." 

 \ In conclusion, we would call attention to the fact, that in the 

 Rothamsted soil and subsoil, down to the depth at which the action of 

 roots has been proved, there exists a store of about 20,000 lbs. per 

 acre of already combined nitrogen. It is true that many soils will 

 contain much less, but many much more. There is then obviously 

 still a wide field for inquiry as to whether or not, or in what way, the 

 very large store of already existing combined nitrogen may become 

 available to growing vegetation. We have indicated some of the lines 

 of investigation which we are ourselves following up ; and we would 

 submit that, whether or not the lower organisms may be proved to 

 have the power of bringing free nitrogen into combination, it would 

 at any rate be not inconsistent with well-established facts, were it 

 found that the lower serve the higher by bringing into an available 

 condition the large stores of combined nitrogen already existing, but 

 in a comparatively inert state, in our soils and subsoils. 



