547 



De Luca, Harting, Petzholdt and others, from the results of which 

 diametrically opposite conclusions had been arrived at. Before enter- 

 ing on the discussion of their own experimental evidence, the Authors 

 give a review of these results and inferences ; more especially those of 

 M. Boussirigault who questions, and those of M. Georges Ville who 

 affirms the assimilation of free nitrogen in the process of vegeta- 

 tion. 



The general method of experiment instituted by Boussingault, 

 which has been followed, with more or less modification, in most 

 subsequent researches, was that adopted by the Authors in the pre- 

 sent inquiry ; namely, to set seeds or young plants, the amount of 

 nitrogen in which was estimated by the analysis of carefully chosen 

 similar specimens ; to employ soils and water containing either no 

 combined nitrogen, or only known quantities of it; to allow the 

 access of free air (the plants being protected from rain and dust) 

 of a current of air freed by washing from all combined nitrogen or 

 of a limited quantity of air, too small to be of any avail so far as any 

 compounds of nitrogen contained in it were concerned ; and finally, 

 to determine the amount of combined nitrogen in the plants pro- 

 duced, and in the soil, pot, &c., and so to provide the means of 

 estimating the gain or loss of nitrogen during the course of the ex- 

 periment. 



The plan adopted by the Authors in discussing their own experi- 

 mental results, was 



To consider the conditions to be fulfilled in order to effect the 

 solution of the main question, and to endeavour to eliminate all 

 sources of error in the investigation. 



To examine a number of collateral questions bearing upon the 

 points at issue, and to endeavour so far to solve them, as to reduce 

 the general solution to that of a single question to be answered by 

 the results of a final set of experiments. 



To give the results of the final experiments, and to discuss their 

 bearings upon the question which it is proposed to solve by them. 



Accordingly, the following points are considered : 



1 . The preparation of the soil, or matrix, for the reception of the 

 plants and of the nutriment to be supplied to them. 



2. The preparation of the nutriment, embracing that of mineral 

 constituents, of certain solutions, and of water. 



