106 SOILS AND FERTILIZERS 



(£, Fig. 23) the carboy was kept supplied with a 

 liberal amount of carbon dioxide, so that plant growth 

 would not be checked for lack of this material. When 

 experiments were carried on in this way using a fertile 

 soil, the plants reached full maturity, but when a soil 

 free from nitrogen was used, plant growth was soon 

 checked. A general summary of this work is given in 

 the following table : 39 



Nitrogen. 



In seeds. In plant. Loss. 



Gram. Gram. Gram. 



Dwarf beans 0.1001 0.0977 — 0.0024 



Oats 0.0109 0.0097 — 0.0012 



White lupines 0.2710 0.2669 — 0.0041 



Garden cress 0.0013 0.0013 



These experiments show that with a sterilized soil, 

 and all sources of combined atmospheric nitrogen cut 

 off, the free nitrogen of the air takes no part in the 

 food supply of the plant. 



113. Boussingault's Third Experiments. — In 1854 

 Boussingault again repeated his experiments; this 

 time he grew the plants in a glass case so constructed 

 that there was a free circulation of air from which all 

 combined nitrogen had been removed. These exper- 

 iments were similar to his second series ; the plants, 

 however, were not grown in a limited volume of air. 

 The results, without going into detail, showed that 

 the free nitrogen of the air, under the conditions of the 

 experiment, took no part in the food supply of plants. 



