194 J. H. Gilbert— Points in connection with Vegetation. 



there is little doubt that they can be overcome, at any rate so 

 far as the nitrogen existing as nitric acid is concerned ; and by 

 the kindness of Dr. Frankland, Mr. Warington is at the present 

 time gaining experience in the use of those methods, in the lab- 

 oratory of the College of Chemistry, before entering upon this 

 special investigation at Bothamsted. 



But even supposing we arrive at a satisfactory solution <>f 

 the, at present, unsettled points in regard to the sources of the 

 nitrogen yielded in agricultural production, when, as in the 

 experiments to which attention has been directed, we have a 

 soil to work upon which already contains accumulations of com- 

 bined nitrogen amounting to several thousands of pounds per 

 acre within the range of the roots of our crops, further questions 

 in regard to the nitrogen may still be left open, namely —to 

 what actions a large proportion of the existing combined nitro- 

 gen may be attributed: and what in particular is the exact 

 source of the accumulations of it in our soils and subsoils ? And 

 here it may be observed, in passing, that determinations made 

 at Bothamsted have shown approximately the same percentage 

 of nitrogen in the Oxford-clay obtained in the recent Sub- Weal- 

 den exploration boring at a depth of 500 and 600 feet, and in 

 the subsoil at Bothamsted, taken a depth of about 4 feet only 



It is not within the scope of the present discourse to discuffl 

 fully what is known of the actual or possible sources of the 

 already existing combined nitrogen, the special object ol the 

 enquiry being, as intimated at the commencement, to brine' to 

 view the facts relating to the yield of nitrogen in agr 

 production, which the extended period of the investigations of 

 Mr. Lawes and myself have enabled us to establish, and to point 

 out the relation of this to the various known or supposed sources 

 of present periodic supplies, so as to indicate what [joints seem 

 the most urgently to demand further investigation. In the 

 papers already referred to, we have more fully considered wnat 

 ■was known of the various actual or possible sources of the 

 combined nitrogen which we know to exist, and to circulate, 

 in land and water, in animal and vegetable life, and in the at- 

 mosphere, and we have pointed out how little was established 

 of either the actual or the relative importance, in a qnuid<t<iike 

 sense, of the various actions by which it is admitted that free 

 nitrogen may in nature be brought into combination. I may, 

 however, observe that M. Boussingault and M. Schlosing have 

 tions to the discussion 

 of this subject. (Compt. Rend., t. lxxvi, lxxx, lxxxi, and 

 Ixxxii). 



But whatever may be the origin of the existing combined ni- 

 trogen, or whether or not the agencies of its formation are more 

 or less active now than during the earlier history of the earth 



