Humphrey Davy ' was the first savant to consider the mineral con- 

 stituents essential for the development of plants. He says: "The 

 chemistry of the simpler manures (the manures which act in very small 

 quantities, such as gypsum, alkalies, and various saline substances), 

 has hitherto been exceedingly obscure. It has been generally supposed 

 that these materials act in the vegetable economy in the same manner 

 as condiments or stimulants in the animal economy, and that they 

 render the common food more nutritive. It seems, however, a much 

 more probable idea that they are actually a part of the true food of 

 plants, and that they supply that kind of matter to the vegetable fiber 

 which is analogous to the bony matter in animal structures." Davy 

 mentions among other things the beneficial action of gypsum, bone 

 dust, and slaked lime. Indeed, the favorable effects of wood ash, bone 

 dust, and liming upon vegetation have been known since olden times. 

 Furthermore, mills for grinding bones existed early in this century in 

 France and England, and enterprising men went so far as to dig up 

 battlefields in Europe and unearth thousands of tons of bones for agri- 

 cultural purposes. 



SprengeP was the second one to express an opinion on this sub- 

 ject. He says: " We can accept it as an indisputable fact that mineral 

 matters found in plants also are real nutrients for them, and that it is 

 not their action upon the humus which makes them important, since 

 gypsum, potassium sulpliate, and calcium phosphate do not at all act 

 upon the humus.''-' 



In quite a diflerent sense Berzelius argued the same year that the 

 action of lime is simply that of a stimulant for the plant and a solvent 

 for the humus, while lime and alkali promote the rotting of organic 

 materials, as manure. 



After Sprengel followed Liebig (1840), whose theories received sub- 

 stantial support in the important researches of Wiegmann and Polstorf 

 (1842). However, great as was Liebig's merit in overthrowiiig the 

 dominant theory of the nourishing qualities of organic matter, called 

 humus, in the soil, and in showing the absolute necessity of mineral 

 salts in plants, the fact can not be denied that he made various errors, 

 especially in his earlier years. For instance, he at one time believed 

 that mineral bases serve merely to neutralize the organic acids in the 

 plant and that they could replace each other, and further, that alkaloids 

 in plants could play the part of mineral bases. He ascribed certain 



' Elements of Agricultural Chemistry, Loudon, 1814. 



^Theorie der Dlinguug, 1839. 



''As a significant fact it may be mentioned that the Prussian Academy of Sciences, 

 in the year 1800 oftered a prize for an investigation to decide whether the mineral 

 matters found in plants are taken up from the soil or whether they are produced in 

 the plants themselves hy vital power. This question was treated hy Schrader, whose 

 decision was in favor of the latter opinion. How much farther advanced was 

 Sanssure, who, in 1804, declared that the mineral matter of humus contribute in a 

 certain degree to its fertility, since the same are found in the ashes of the plants 

 (Recherches sur la vegetation;. 



