COMilUNICATlONS. 303 



discovery of the /)?"mcjj9?e5 which control the successful applica- 

 tion of these practices in the management of farms. 



Rational modern agriculture recognizes as the foundation of a 

 successful farming the necessity of a strict restitution to the soil, 

 in an available form, of those substances which the crops have 

 abstracted, and it promises to that class of farmers who strive to 

 comply with that requirement in the most economical way, the 

 best chances of a continued financial success. 



From a similar stand-point the earlier practice of using the 

 above-named mineral substances and others in the farm manage- 

 ment has to be judged as compared with their application at the 

 present time. 



As long as the composition of the air and the water was but 

 little understood, and that of the soil practically unknown, no 

 correct idea could be formed concerning their mutual relations, 

 and still less regarding their connection with the life and the 

 growth of plants. 



For this reason, the first successful attempts to study the rela- 

 tions of the vegetable kingdom to these three agencies date only 

 back to the close of the past century. They are largely the re- 

 sults of the labors of Lavoisier and Priestley. Foremost among 

 the scientists who, at the beginning of the present century, devoted 

 some attention to the chemical physiology of plants and the 

 application of chemistry to agriculture, are De Saussure and Sir 

 Ilumphry Davy. The former was the first who called attention 

 to the variations of mineral constituents in plants, and pointed out 

 some of their relations to the soil and the growth of plants, whilst 

 the latter recognized already the atmospheric source of nitrogea 

 for plant growth. The works of these illustrious investigators 

 remained comparatively unknown to agriculturists until Liebig, 

 in 1840, called the general attention to their excellence and im- 

 portance. Although more exact analyses of the ashes of plants 

 had been accumulating and some interesting features of the results 

 had been pointed out, — as, for instance, the limited number and 

 constant occurrence of the same mineral elements, as well as their 

 varying proportions in the case of different plants, — no material 

 change of opinion regarding their possible more intrinsic relations 



