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XX. On the Evolution of Nitrogen during the growth of Plants, and the Sources 

 from whence they derive that element. By Robert Rigg. Communicated hy the 

 Rev. J. B. Reade, MA. F.R.S. 



Received June 14, — Read June 21, 1838. 



An this communication I shall have the honour of submitting to the Royal Society 

 a series of experiments, which not only confirm the principles I have already laid 

 down in the investigations of the influence of nitrogen on the growth of plants, but 

 also enable us to trace this important element to its source. 



By what mysterious process of natural chemistry the living principle of the plant 

 obtains this product, we must be content to remain ignorant ; but to what extent a 

 supply can be procured from the compounds upon which its agency is directed, is 

 within the compass of legitimate experimental research. 



With respect to the entire volume of nitrogen connected with the process of vege- 

 tation, it will be observed that my former Tables show that the quantity appropriated 

 by the plant varies from -roVo to 4~ of their weight of carbon ; and the important ex- 

 periments of Dr. Daubeny, Saussure, Sir Humphry Davy and others, have abun- 

 dantly established the fact that there is a considerable evolution of nitrogen during 

 the growth of plants. Experiments, however, upon the quantity of nitrogen evolved 

 are so beset with difficulties, that our best efforts in this department of vegetable phy- 

 siology have not enabled us to speak with certainty as to the absolute or relative 

 quantities of the gases which are given off during the healthy action of the functions 

 of vegetable life. And in corroboration of this remark it is only necessary to state, 

 that the natural course of vegetation is unavoidably interrupted, by the necessity we 

 are under of excluding plants from the free action of the external atmosphere, when 

 we attempt to collect the gases they give off. 



Sir Humphry Davy made his experiments under as favourable circumstances as 

 the nature of the case will admit of; and he found that when the oxygen decreased 

 in quantity about two per cent, the nitrogen increased four per cent., and that when 

 the oxygen increased about thirty-five per cent, the nitrogen increased about seven 

 per cent. Some of my own experiments have been conducted on the principle adopted 

 by Sir Humphry Davy. I have also introduced whole branches of trees, as well as 

 stems and leaves of more tender plants, under water, without removing them from 

 the parent stock, and collected their gaseous products in inverted glass vessels. Upon 

 examining these products, I find, that the gaseous volumes are perceptibly affected by 

 the brightness of the sun's rays, though their variation appears to be subject to no 



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