252 



On the Application of Manures. 



that important oflFice which is assigned to them in the economy of 

 nature — of purifying the atmosphere polluted by the breath of so 

 many millions of animals, as well as by other operations con- 

 nected with the existence of the human species. 



It is remarked by Liebig that, in early periods of the earth's 

 history, the gigantic monocotyledonous plants — the ferns, palms, 

 and reeds, with which the surface of the globe was overspread — 

 belonged to a class to which nature has given the power, by means 

 of an immense extension of their leaves, to dispense with nourish- 

 ment from the soil. Hence the enormous amount of carbon 

 locked up within the earth in the shape of coal, the whole of 

 which Avas originally obtained from the carbonic acid aflbrded 

 by the atmosphere. 



But it would seem necessary to attribute to the living vegetable 

 the power of decomposing not merely carbonic acid, but also 

 water. 



This indeed has been shown by MM. Colin and Edwards, in 

 their experiments on the respiration of plants, and likewise by 

 INI. Boussingault ; nor can we otherwise account for the fact that 

 wax, resin, and several other vegetable products, contain an ex- 

 cess of hydrogen over and above that required to constitute water 

 with the oxygen present. 



It would seem, I think, from the late important researches of 

 M. Payen, that the decomposition of water commences subse- 

 quently to that of carbonic acid ; whether it be that the former 

 process requires a greater development and energy in the vege- 

 table functions, or that it takes place in organs of a different de- 

 scription and of later growth. 



M. Payen seems to have established, that under the general 

 term of ligneous fibre, or lignin, we have hitherto confounded at 

 least two distinct substances — namely, that which constitutes the 

 walls of the cells, and that which, by being deposited afterwards 

 on the surfaces of the latter, imparts to them the solidity of tex- 

 ture which woody fibre possesses. 



He has succeeded in isolating the two by chemical means, and 

 has found that, whilst the cellular matter has exactly the same 

 composition as starch — being composed of 44*9 carbon, 6' I 

 hydrogen, 49 oxygen, or 44*9 carbon and 55*1 of water — the 

 incrusting matter afterwards formed consists of 53*76 carbon, 

 40 • 2 oxygen, and 6 of hydrogen ; or of 53 • 76 carbon, 45 of 

 water, and 1 of hydrogen.* 



The composition of the ligneous matter of different kinds of 

 wood will therefore vary according to the relative proportion 



* Payen has since stated that this incrusting matter probably consists 

 of two or three different principles. 



