148 M. Boussingault on the influence of Nitrates on Vegetation. 



acid added to it, and was purified from ammonia by being passed 

 through sulphuric acid and through bicarbonate of soda. The 

 weight of the cress-seeds was determined, and the quantity of 

 nitrogen contained therein ascertained, by comparative experi- 

 ments. When the plant was fully developed, it was weighed, and 

 the quantity of nitrogen contained in it was estimated. The 

 latter was always greater than the quantity of nitrogen which 

 could have been derived from the soil and from the quantity of 

 ammonia contained in the water used for irrigation. The deter- 

 minations of the nitrogen contained in this water were rather 

 uncertain, but the Commission thought itself fully justified in 

 concluding, that the free nitrogen of atmospheric air was assi- 

 milated by plants. 



That plants could assimilate nitrogen from nitrates, was 

 shown by the success with which the use of nitrate of soda in 

 maniu'e has been attended. Liebig* believed that the nitrogen 

 of nitric acid, like the carbon of carbonic, and the sulphur of 

 sulphuric acid, could become a constituent of the vegetable 

 organism. Salm-Horstmar arrived at the conclusion, that in 

 the development of plants the alkaline nitrates could replace 

 ammonia. Kuhlmann thought that the nitrates were first re- 

 duced to ammonia by the deoxidizing influence of decomposing 

 organic substances. George Wilson was of opinion that the 

 nitrogen was obtained by the reducing action of the plants on 

 the nitrates. 



Boussingault t made a series of experiments on the action of 

 nitrates on vegetation. If the presence of puti'cscible organic 

 matters in the soil were not necessary for the assimilation of the 

 nitrogen of a niti'ate by a plant, two conclusions might be drawn : 

 the first, that the nitrogen of nitric acid need not previously be 

 transformed into ammonia outside the plant in order to be fit to 

 be assimilated by the organism ; secondly, that the nitrates do 

 not merely act in virtue of their being potash or soda salts. The 

 method adopted consisted in growing a plant in a soil rendered 

 barren by calcination, and to which a known quantity of an 

 alkaline nitrate was added. When the plant was developed, the 

 quantity of nitrogen which it had absoi'bed was estimated, as 

 well as the residual nitrate in the soil. 



In an experiment made with sunflower in a soil free from 

 ammonia and organic matter under the conditions indicated, he 

 came to the conclusion that the nitrogen of the nitrate is assimi- 

 lated by the plant, and that for each equivalent of nitrogen assi- 

 milated by the organism, an equivalent of alkali is assimilated ; 

 that almost the entire quantity of the still unabsorbed nitre is 



* Jahresbericht, 1856. 



t Annates de Chimie et de Physique, January 1856. 



