10 ' SOURCES OF THE NITROGEN OF VEGETATION 



tained 257 Ib. per acre down to a depth of 6 feet. As a 

 result of the three years' cropping with barley and clover, and 

 then with clover only, an average amount of 31 9 '5 Ib. of 



TABLE IV. Nitrogen accumulated 'by Clover Crop. 

 Little Hoos Field. 



nitrogen was removed, yet the soil contained, on analysis at 

 the end of the experiment, 2832 Ib. of nitrogen per acre in the 

 top 9 inches, or a gain of 175 Ib. per acre in the three years ; 

 making a total, with the crop removed, of nearly 500 Ib. of 

 nitrogen per acre to be accounted for. 



Experiments like these, coupled with the long experience of 

 practical farmers* of the beneficial effects of the growth of 

 clover and other leguminous plants on the succeeding crops 

 in a rotation, led many men to think that there still might 

 be fixation of nitrogen by leguminous plants, in spite of the 

 apparent exclusion of any such hypothesis by Pugh's experi- 

 ments at Rothamsted. Voelcker, in England, when discussing 

 the power of a clover crop to accumulate nitrogen, expressed 

 the opinion that the atmosphere furnishes nitrogenous food to 

 that plant ; in France it was maintained by Ville ; Berthelot 

 also brought evidence to show that the soil itself, by the aid 

 of microscopic vegetation, assimilated some free nitrogen. 



* Vergil, Georgics I., 73 : 



"Aut ibi flava seres, mutato sidere, farra 



Unde prius laetum siliqua quassante legumen 

 Aut tenuis foetus viciae, tristisque lupini 



Sustuleris fragiles calamos, sylvamque sonantem. 1 ' 



" Or, under a changed star, you will then sow the golden wheat, whence 

 earlier you took away the bean, luxuriant with quivering pod, or the growth of 

 the slender vetch, and the fragile stalks and rustling grove of the bitter 

 lupin." 



