FUNCTION.] NITROGEN. 273 



It has already (p. 261.) been shewn that Messrs. Edwards 

 and Colin have proved experimentally that plants decompose 

 water by their vital force, fixing the hydrogen and parting 

 with the oxygen, which combines with carbon, forming 

 carbonic acid. 



As it has been supposed that all the oxygen given off by 

 plants is produced by the decomposition of carbonic acid, it 

 has been inferred that, if the water which is consumed by 

 plants is ever decomposed, it is in the formation of the various 

 secretions which contain more oxygen (acids), or more 

 hydrogen (oils), than water : but, as the greater part of vege- 

 table substances, such as gum, sugar, fsecula, &c., contain 

 oxygen and hydrogen in the same proportions as water, it has 

 been thought that the greater part is undecomposed and 

 simply fixed ; but the experiments of Edwards and Colin, 

 above referred to, prove the contrary. 



It was formerly thought that nitrogen, or azote, has nothing 

 to do with the nutrition of plants ; and that, in those cases 

 where it was met with, it was merely in a state of separation 

 from the atmospheric air which had been inhaled and deprived 

 of oxygen and carbonic acid. But M. Boussingault long 

 since proved, that it is in fact a constant element of vegeta- 

 tion, most concentrated in seeds, to the maturation of which 

 it is essential, and dispersed through the other parts of the 

 tissue. (Comptes rendus, vi. 105.) 



In the form of carbonate of ammonia it is greedily taken 

 up by plants, which obtain it naturally through the interven- 

 tion of rain water or snow. It is found everywhere in tissues, 

 very abundantly in the youngest parts of plants, sparingly in 

 the oldest, and probably contributes to the rapid decay of the 

 former, as it does to that slower rotting process which is 

 observed in timber. Chemists have in fact ascertained that 

 by washing away the soluble azotised matter of timber, its 

 power of resisting decay is much increased. Mr. Rigg finds 

 the youngest parts of plants richest in nitrogen, the germ of 

 Peas and Beans containing by weight about 200 parts of that 

 gas for 1000 parts of carbon, while the cotyledons contain 

 only from about 100 to 140 parts. He is disposed to believe 



VOL. II. T 



