190 FIXATION OR ASSIMILATION OF NITROGEN 



atmosphere as the source from which leguminous plants 

 draw their store of nitrogen. Since the amount present 

 in the form of ammonia and oxides of nitrogen was 

 found to be very small and quite insufficient to account 

 for the quantity collected by leguminous crops, chemists 

 and physiologists were driven to consider the free 

 nitrogen of the air as a possible nutrient substance, 

 although on a priori grounds it appeared unlikely that 

 plants could assimilate and bring into chemical com- 

 bination an element of such inert and indifferent nature. 



The careful investigations of Leibig and Boussingault 

 in the first half of last century appeared to support 

 the view that plants could not utilize free nitrogen ; 

 but between 1850 and 1857 Georges Ville in France 

 carried out some experiments with leguminous plants 

 grown in natural soil in closed glass cases, to which only 

 air which had been carefully deprived of any combined 

 nitrogen had access, and found that they grew luxuriantly 

 under these conditions and contained more nitrogen 

 than was originally present in the soil and seed used. 

 He concluded that the plants were able to assimilate 

 free nitrogen, and although it was suggested that small 

 amounts of ammonia had been inadvertently supplied to 

 the plants in the distilled water used for watering them, 

 Ville convinced himself by repeated experiments that 

 his conclusion was correct. 



Later, Lawes and Gilbert in England carried out 

 experiments upon peas, vetches, and lupins, growing 

 them in carefully sterilized sand, to which were added 

 phosphates, potash, and other necessary mineral food- 

 constituents, but no combined nitrogen : air, however, 

 with its free nitrogen was admitted to the cultures. In 

 all cases their results were negative ; the plants under 



