2 SOUECES OF THE NITROGEN OF VEGETATION 



his Recherches Chimiques sur la Vegetation in 1804, confirmed 

 the above-mentioned discoveries and gave them a coherent 

 shape. He then proceeded to discuss the mineral or ash 

 constituents of plants, made a series of analyses of the ashes 

 of various plants, and pointed out the importance of these 

 substances in the nutrition of the plant. Davy, whose lectures 

 on Agricultural Chemistry to the Board of Agriculture 

 were published in 1813, though he did not advance the 

 subject much by his own investigations, yet did much service 

 in presenting to the agricultural public the science that 

 was then available. He laid more stress than before on 

 the importance of the ash constituents and the use of 

 manures to supply them, but he appears still to have con- 

 sidered that much of the carbonaceous matter of plants 

 was directly derived from the humus of the soil, and that 

 the assimilation of carbon from the atmosphere was of minor 

 importance. 



Boussingault's memorable work began in 1834, and in 1838 

 he published the result of the enquiries he had been making on 

 his farm into the principles underlying the rotation of crops. 

 He analysed both the manures applied and the crops removed 

 from the land, and thus demonstrated statistically that the 

 source of the enormous quantities of carbon removed annually 

 can only be the carbonic acid of the atmospliere, not the soil 

 nor the manures applied. In 1840 appeared Liebig's famous 

 report to the British Association on *' Organic Chemistry in its 

 applications to Agriculture and Physiology." Here, building 

 upon the foundations laid by De Saussure and by Boussingault 

 (for in this direction Liebig was not an original investigator), 

 and illuminating these facts by the light of his own recent 

 discoveries in organic chemistry, Liebig drew out a convincing 

 scheme of the nutrition of the plant. Green plants by the aid 

 of sunlight derive their whole substance from carbonic acid, 

 water, ammonia present in the atmosphere and produced 

 by decaying matter in the soil, and the simple inorganic 

 salts which are afterwards found in the ash when the plant 



