HISTORY. The first attempt to bring together in a systematic manner flub teachings of chem istry as applied to agriculture was made by Sir Ilumphry Davy. in a series of lectures before the British Board of Agriculture. early in the Nineteenth Century (Elements of _tyrieultural chemistry, 181-11. Davy regarded the soil as the source of all nourishment of plants, and he anntmneed the general principle that plant food nest be practically dissolved before it can enter the organism of the plant. But while he and his predecessors knew the value of certain ma terials for plant food, they did not know the constituents which gave them this value. Oil. for example. was long supposed to be one of the most valuable fertilizing constituents. and Davy supposed sugar to be also. One of the reasons for this error was undoubtedly the belief that the carbon of plants derived through the roots from the humus—i.e. the partially decom posed organic matter of the soil. The errors of this 'humus theory' were pointed out. about 18-10. by Justus von Liebig, who in his generalizations drew heavily upon the works of Saussure and Boussingault. Liebig showed the carbonic acid of the air to be the source from which plants derive their carbon, and the leaves to he the medium through which this assimilation takes place. He thus laid down a fundamental prin ciple of physiological botany. He established the interdependence of plants and animals with relation to carbonic :mid, which is a vitalizing prineiph• of the one and an excretory product of the other. In place of the 'humus theory' he advanced his famous 'mineral theory.' accord iu which the soil furnishes to plants their ash or mineral constituents; and this led him to suggest the employment of artificial fertiliz ers for keeping up the supply of the mineral con stituents of the soil, and thus maintaining its fertility. Liebig's views, with some modifica tions, form the basis of our present theories; but, on the other hand, we have learned much re garding the true value of humus and its func tions in the soil. See :M.\ NUEES.
In the field of animal nutrition. or the utili zation of plants and their products in animals, agrieultural chemistry has likewise led to the establishment of the underlying principles and the methods of research. The earlier ideas regarding the valuable food constituents of plants were equally as crude as those regarding the fer tilizing constituents. There was a prevalent he lief in a subtle, undefined property of forage plants. upon which their nutritive properties largely depended, and it was a long time before the connection between nutritive value and eli•ndeal composition was traced. Boussingault,
in France, attempted to classify feeding stuffs on the basis of their nitrogenous constituent‘; and Timer, in Germany. compared them with hay, and prepared his tables of 'hay value,.' length Ilenneberg worked out a classification of the nutritive constituents of feeding stuffs, and a method of analysis known as time Wecnde method. llis elassi ficat ion and method have been extensively employed, having served as the basis in most of the investigations sinee. These studies in animal nutrition have led time agricultural chemist into a field of inquiry intimately eon neeted with physiology proper: and in the de velopment of the present theories, as well as in their application in practice. agricultural chem istry has contributed much more than physiology itself, and has usually been the hailer.
Agrieultural chemistry laid the foundation for a science of agriculture, and one of the most iin portant and far-reaching influences of the early agricultural chemists was that Nvliielt led to the establishment of the agricultural experiment station. The teaching of agriculture in agri cultural schools and colleges preceded it in most countries. but the investigation and experimen tation was for the most part in the hands of the agricultural chemists. Their work led them into agricultural experiments of various kinds, as a matter of necessity, and Liebig, Boussin gault. Lawes and Gilbert, and others. laid out experimental fields for carrying on their studies and testing their theories. As the practice of fertilizing the soil became introduced in the Old World, farmers found themselves confronted by a variety of problems relating to their soils and fertilizing materials which they were mumble to answer, and they quite naturally turned for ad vice and guidance to the agricultural chemists who had developed these theories. Thus experi ment stations came to be established, first by agricultural societies of private individuals. and later with Government aid. (See AGRICULTURAL EXPERIMENT STATIONS.) In the United States, the researches and writings of S. W. Johnson I Hour Crops rOlr, 1S69: Hon- Crops Feed, H70). C'. A. Goessmann, E. W. Hilgard. G. C. Caldwell, W. Atwater, and other chemists. prepared the way for the establishment of ex periment stations as State institutions: and out of these has grown a system of stations under Government aid and supervision. embracing every State and Territory in the Union. and providing, incidentally. the most munificent endowment for agri•nItural-chemical research to be found in any country.