THE SOUECES OF THE NITROGEN OF VEGETATION, ETC. 465 



considered, appropriated carbonate of ammonia from the atmosphere by then - leaves. 

 Graminaceous crops, on the other hand, he supposed, only took it up in solution by 

 their spongioles. He further supposed that the free Nitrogen of the air was not appro- 

 priated by the leaves of plants, but that Nitrogen dissolved in water, and so taken up, 

 by their roots, could be assimilated. He concluded that, in the case of M. Boussln- 

 gault's plants grown in limited air, there woidd be but little passage of solution of 

 Nitrogen by their roots, and evaporation of water from their leaves, and that, hence, the 

 necessary conditions did not exist for the assimilation of free Nitrogen. M. Ville's 

 rapid current of air would, on the other hand, cause a considerable amount of solution 

 of Nitrogen to be drawn into the plants. 



E. — The Experiments of MM. Cloez and Geatiolet. 



In 1850, MM. Cloez and Gratiolet published the results of some experiments made 

 with Water-plants. They found that, carbonic acid and air being both present, the 

 plants gave off oxygen slowly, or very rapidly, according to the condition of the sunlight 

 and the temperature. In water deprived of common air, but containing carbonic acid, 

 the evolution of oxygen rapidly declined, Nitrogen was given off, and the plant contained 

 less Nitrogen than a similar plant in water not deprived of its air. The evolution of 

 Nitrogen diminished as the experiment proceeded. They considered that, in the vege- 

 tation of Water-plants, Nitrogen is given off from their nitrogenous constituents and 

 that there must be restoration either from free or combined Nitrogen. And as their 

 experiments showed that ammonia-salts were injurious to the plants, they concluded 

 that they take up free Nitrogen dissolved in water. 



In 1855* M. Cloez published the results of some experimental inquiries on nitrifica- 

 tion, with a view to the question of the source of the Nitrogen of plants. He made 

 twenty experiments, passing washed air through as many different combinations of 

 porous, earthy, and alkaline matters. The experiments continued from September 1854 

 to April 1855, when, in some cases, efflorescence was observed. He found nitrates to 

 be formed in notable quantity in calcined brick, or pumice, impregnated with alkaline 

 or earthy carbonates ; also, in uncalcined brick similarly impregnated. In chalk, marl, 

 a mixture of kaolin and precipitated carbonate of lime, &c, only traces of nitrate were 

 formed. 



M. Cloez concluded that nitrates would be formed when a current of air was passed 

 over porous bodies, alkalies being present. He considered, therefore, that the porosity 

 of the pots and brick fragments, the alkalinity of the ashes, the moisture, and the cur- 

 rent of air, in M. Ville's experiments with plants, provided the conditions for the forma- 

 tion of nitric acid. He asks, can such formation take place in limited air 1 



F. — The Experiments of M. de LucAf. 

 M. de Luca found that, on passing moist ozonous air over potash and potassium, 

 nitrate of potash was formed. He further found that the oxygen given off by plants 

 * Compt. Rend. xli. t Ibid. 1856. 



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