14 SOURCES OF THE NITROGEN OF VEGETATION 



when grown under ordinary field conditions, for then they 

 become collectors of atmospheric nitrogen in virtue of the 

 nodule bacteria with which they are associated. 



Without doubt, Hellriegel and Wilfarth's discovery came as 

 somewhat of a disappointment to the Rothamsted investi- 

 gators ; although the statistics they had accumulated form to 

 this day the best demonstration of its truth on a field scale, 

 still they had so long and so rightly upheld the necessity of 

 combined nitrogen to the nutrition of the plant, that to have 

 to concede the point in issue, as far even as the leguminous 

 plants were concerned, could not have been welcome. Indeed, 

 Liebig's idea having thus triumphed in the one special case, 

 his most sweeping generalisation was justified — that it is the 

 function of plants to manufacture the complex nitrogen com- 

 pounds from elementary nitrogen, just as they do the carbon 

 compounds from the carbon dioxide in the atmosphere. These 

 complex nitrogen and carbon compounds are necessary to 

 animals, which derive their vital heat and energy by breaking 

 them down again into the simpler materials used by the 

 plant. In this eternal cycle Liebig had placed nitrogen 

 alongside of carbon, and though the statement may be true 

 only of the particular leguminous plants, it is true, in a 

 general sense, in that these plants (or rather the bacteria 

 with which they are associated) are probably the original 

 sources of the world's stock of combined nitrogen. 



References 

 " Agricultural Chemistry, especially in relation to the Mineral Theory of 



Baron Liebig." J.R.A.S., 12 (1851), 1. R. Mem., Vol. I., No. 5. 

 "On the Sources of the Nitrogen of Vegetation." Phil. Trans., 151 (1861), 



431. B. Mem., Vol. I. (4to), No. 1. 

 "On the Sources of the Nitrogen of Vegetation." Jour. Chem. Soc, 16 



(1863), 100. R Mem., Vol. III., No. 1. 

 "Sketch of the Progress of Agricultural Chemistry." Rep. Brit. Assn. for 



1880. R. Mem., Vol. V., No. 13. 

 " On the Present Position of the Question of the Sources of Nitrogen of Vege- 

 tation." Phil. Trans., 180, B (1889), 1. R. Mem., Vol. I. (4to), No. 2. 

 " Results of Experiments at Rothamsted on the Question of the Fixation 



of Free Nitrogen." Agricultural Students' Gazette, New Series, 5, 



1890-91. R. Mem., Vol. VII., No. 1. 



