CHEMICAL FERTILIZERS. 123 



las, which only require enough of the fertilizers to compensate for 

 what wc remove more than the natural 3'ield. 



What is New in this System. — Reference has already been 

 made to the experiments of the two learned professors, at Munich, 

 given by Liebig in his " Natural Laws of Husbandry." They 

 used the same three elements, nitrogen, potash, and phosphoric 

 acid, which Prof. Stockbridge uses. They cultivated their plants in 

 pots filled with soil of the same kind, carefully prepared ; and ap- 

 plied the elements in different proportions and quantities. I can 

 only refer to the volume itself for the exceedingly interesting 

 account and discussion of these experiments. I am not able to 

 see that they do not include the whole ground covered by Prof. 

 Stockbridge in his experiments, and they show that the three ele- 

 ments used by him as the essentials of plant food, were at that 

 time familiarly known as such, and as the most essential. 



In 1866 a translation was published in Boston, of a little book 

 entitled " High Farming without Manure ; six lectures on Agri- 

 culture, delivered at the experimental farm at Vincennes " (in 

 France), by M. George Ville, Professor of Vegetable Phj-siology 

 at the Museum of Natural History, Paris. In the college report 

 of 1875, Prof. Stockbridge speaks of this author and his experi- 

 ments, and says that it seemed proper to test the matter and as- 

 certain whether it was necessarj^ to supply the same elements in 

 this country that were found to be necessary in France. So far as 

 appears, he pursued the same system of experiments, with pots in 

 a plant house, to ascertain what elements were necessary to add to 

 the natural soils of that region to render them productive of given 

 crops. His conclusions I have already given you, that only three 

 elements, — nitrogen, potash, and phosphoric acid — need be sup- 

 plied, nature furnishing the rest. 



M. Ville, at the opening of his last lecture says: "All that I 

 have stated to you previously ma}' be summed up in the two fol- 

 lowing propositions : 



1st. There exist four regulating agents par excellence, in the pro- 

 duction of vegetables: nitrogenous matter, phosphate of lime, 

 potassa, and lime. 



2d. To preserve to the earth its fertility, we must supply it 

 periodically with these four substances in quantities equal to those 

 removed by the crops. 



You will observe that M. Ville supplies precisely the same three 



