396 THE POPULAR SCIENCE MONTHLY. 



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 ni- 

 trogenous constituents of plants are taken up by their roots from the 

 soil, which is almost, if not quite, the exclusive source of these ele- 

 ments of plant-growth, while all of the carbon is elaborated by the 

 leaves from the supplies in the atmosphere. The mineral and nitroge- 

 nous 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 at- 

 mospheric food of plants. By this constant circulation in their appro- 

 priate 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 exj^eri- 

 ments 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 en- 

 deavor to trace the laws which underlie the phenomena under inves- 

 tigation, results of permanent value have been secured ; and the prac- 

 tical 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- 



