be the ruling elements in the feeding experiments. Is this apparent contrast in the materials required as leading factors in the economy of plants and animals a mere coincidence arising from the methods of investigation, or does it represent one of the correlations of organic life concerned in the conservation of energy? The mineral and nitrogenous constituents of plants are taken up by their roots from the soil, which is almost, if not quite, the exclusive source of these elements of plant-growth, while all of the carbon is elaborated by the leaves from the supplies in the atmosphere. The mineral and nitrogenous constituents of the food of animals, on the other hand, are all discharged from the system, after performing their functions, in the liquid and solid excretions, and thus find their way to the soil, where they can be appropriated as plant-food; while a large proportion of the carbo-hydrates are exhaled in respiration as carbonic acid, the atmospheric food of plants. By this constant circulation in their appropriate channels the conservation of the nutrient elements, of both plants and animals, is fully maintained.
The legitimate objects of agricultural experiments are too often overlooked, and it is certainly a satisfaction, in a review of experiments that have been systematically prosecuted for so many years, on such an extended scale, to find that they have been fully appreciated throughout the entire work. In one of the first reports of experiments at Rothamsted, on turnip-culture, published in 1847, it is said, "The object of the experiments has not been the production of immense crops, but to trace, as far as we were able, the real conditions of growth required by the turnip, and to distinguish these from those of the crops to which it is, to a great extent, subservient." In this endeavor to trace the laws which underlie the phenomena under investigation, results of permanent value have been secured; and the practical benefits, measured in pecuniary values, which have been derived from them are of greater importance from the fact that they are not merely empirical and detached facts that are true only under certain conditions, but have a foundation in principles of general application. Too often experiments are made in which the practical or pecuniary ends are the direct and immediate objects of inquiry, but such efforts, in the main, must result in disappointment, so far as any permanent interest is concerned, from the failure to trace the results obtained to their appropriate causes.
The work so well begun at Rothamsted is now carried on with undiminished energy, with a prospect of still more important results in the future. Dr. Lawes is now expending in his experiments more than 815,000 annually. A new building will be erected next year to relieve the laboratory from its accumulated stores of samples, that have a definite history and form the materials for future investigations. From five to nine hundred samples of the ash of experimental crops are collected each year, and with each sample of ash there is a dupli-
