THIS paper may be considered as a continuation of one read in the Chemical Section, at the meeting of the American Association for the Advancement of Science held at Montreal, in August, 1882, entitled-" Determinations of Nitrogen in the Soils of some of the Experimental Fields at Rothamsted, and the Bearing of the Results on the Question of the Sources of the Nitrogen of our Crops,"-and in order adequately to bring out the bearings of the new results, embodied in the present communication, it is desirable, first to summarise the main results and conclusions of the previous one. The question of the sources of the nitrogen of our crops is one respecting which very conflicting views are still entertained ; and it may a t once be admitted that so long as the facts of agricultural production alone are studied, without knowledge of, or referewe to, the shanges in the stock of nitrogen in the soil, it would seem not unreasonable to assume that a large proportion of the nitrogen, at any rate of some crops, must be derived, in some way or other, from the atmosphere. Yield of Nitrogen p e y Acre in Diferent Crops. Obviously, it is a point of first importance to determine what really is the annual yield of nitrogen in different crops over a given area, excluding, as far as possible, the amounts due to unknown supplies by manure; thus, as far as practicable, limiting the source t o the stores of the soil itself, and to the atmosphere. The Rothamsted field experiments, in which different crops have been grown for very many years in succession on the same land, both without nitrogenous manure, and wit,h known quantities of such manure, afford valuable data of the kind required ; and, in our former paper, the results were discussed in some detail. It must suffice here to summarise them very briefly. The average yield of nit.rogen per acre per annum was, in wheat, 32 years without manure 20.7 lbs., and 24 years with a complex f Read before the Chemical Section, at the Montreal Meeting of the British Aasociation for the Advancement of Science, September 2, 1884.