LIFE ON THE EARTH. 133 



germination draw from the atmosphere the Carbon 

 which is fixed in their tissues, and combined with 

 Oxygen, Hydrogen, and in some cases Mtrogen, 

 constitutes the main part of their substance. The 

 chemical composition of the atmosphere is every- 

 where nearly the same; the stimulus of light which 

 is the great determinant of the chemical processes 

 in plants, and which specially governs the absorption 

 of carbonic acid by them, acts with much equality 

 on the various races of plants. Hence much equa- 

 lity in the amount of Carbon taken from the atmo- 

 sphere, and fixed in the substance of plants in a 

 given time. Liebig has found that the annual pro- 

 duct of Carbon fixed in plants so different as Fir- 

 wood, Hay, Beet-roots, and Straw, is the same in 

 weight, for the same extent of ground. This quan- 

 tity is about 1000 Hessian Ibs. for 40,000 square feet 

 of surface 1 ; in English weight and measure 10 Ibs. 

 for 244 square feet. 



Supposing the whole of this quantity to be stored 

 up year by year, and converted to Anthracite, the 

 variety of Coal richest in Carbon, such as occurs in 

 South Wales and North America, it would amount 

 to about one inch in 170 years. If converted to or- 

 dinary Coal, with about 75 per cent, of Carbon, it 

 would yield one inch in 127*5 years. In South Wales 

 1 * Organic Chemistry, 1840. 



