FOOD OF PLANTS IN GENERAL. 483 



constant loss ? The carbon consumed by breathing yearly alone cor- 

 responds to the full produce of 500,000,000 acres of the finest wheat- 

 land, or a surface more than twice as large as France.* 



Whatever may have been the manner of the first production of plants, 

 few will be inclined to assume that the mountains, when they first rose 

 from the sea, were thickly covered with humus. It is much more pro- 

 bable that they were at first quite naked, and that they were but very 

 gradually covered with mould by means of vegetation. 



Upon this earth, at first void of humus, the vegetation of the coal for- 

 mation was first developed, the extent of whose remains still fill us with 

 amazement. Should the store suffice to cover the present demand for 

 yet 2000 years to come, as some English geologists f have assured us 

 that it will, then these mineral coals, assuming that in decomposition 

 their loss would only be 20 per cent, of carbon, would have a weight of 

 1290 billion Ibs. of carbon, which manifestly could not be derived from 

 the original earth void of humus. 



If we consider now the cultivation of individual plants, we find such 

 data as follows : The sugar-cane requires a good damp soil, but which 

 is never manured. The acre produces about 4700 Ibs. of cane, which 

 contains at a minimum 700 Ibs. of carbon in sugar, 500 Ibs. of carbon 

 in the pressed cane ; the sugar is taken away and the cane is burned in 

 the sugar-making houses ; 1200 Ibs. of carbon are thus yearly drawn from 

 the earth without any return (Boussingault). The soil in the French 

 colonies, used in the culture of sugar, must in this way yield yearly 

 225 million Ibs. of carbon, which would correspond to a loss of 325 

 million Ibs. of humus. J We may reckon, on the whole, that the tropical 

 regions produce, from coffee and sugar alone, annually about 2300 mil- 



* The produce of the acre amounts, according to Block, to 475 Ibs. of grain, and 

 2970 Ibs. of straw. The quantity of the carbon of the grain amounts to 46 per cent., 

 and of the straw to 48 per cent., according to Boussingault. 



f Mr. Taylor, one of the most extensive proprietors of coal mines in England, 

 reckons that the store of coals in Durham and Northumberland alone would suffice 

 for the consumption of these provinces for 2,500 years yet to come ; or, in case of 

 falling off, at least for 1700 years. Bakewell, in his Geology, reckons that the coal- 

 beds of South Wales alone would suffice for the present necessities of all England 

 for nearly 5000 years. Both these reckonings are accepted by distinguished geolo- 

 gists, and only objected to by some practical men, in so far as they conceive that too 

 little allowance has been made for loss in working, an objection which does not affect 

 our present case. According to the statements of Lindley and Hutton, in the " British 

 Fossil Flora," the coal-beds of the State of Ohio, covering an extent of 12,000 square 

 miles, calculated at an average thickness of five feet, would give a quantity of carbon 

 arnounting to 70,000,000,000,000 Ibs. We cannot estimate with great exactness the 

 contents of the various coal-beds upon the earth ; but when Liebig supposes that the 

 carbonic acid now present in the atmosphere contains by far more carbon than all the 

 coal-beds in existence, he manifestly errs greatly. The carbon contained in the car- 

 bonic acid of the atmosphere certainly cannot amount to a tenth part of that contained 

 in the whole of the coal-beds upon the globe ; and we do not assuredly over-estimate 

 the loss during decomposition and putrefaction, if we rate it at a twentieth part of the 

 carbon which this past vegetation contained during life. 



\ The sugar-cane contains on an average . 



Of dry Vegetable fibre . . . 1 1 '0 



Sugar 15-5 



Water 73-5 



In the pressing, 8 per cent, of sugar is the maximum obtained ; thus 8 Ibs. of prepared 

 sugar, and 26 '5 Ibs. of dry organic substance, corresponds with 40 per cent, of carbon. 

 The French colonies produce yearly 80 mill, kilogr. The islands of Bourbon and 

 Mauritius yield annually about 100 mill. Ibs., and thus lose yearly about 130 mill. 

 Ibs. of carbon. 



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