236 
" forth, and the old plants die. Vegetable matter accurau- 
lates, a bog, and finally a thick bed of peat is formed. 
" Whence have all these plants derived their carbon ? The 
" original quantity contained in the soil is increased ten 
" thousand fold. Has dead matter the power of reproducing 
" and multiplying itself ? You will answer at once that the 
" plants have grown at the expense of the air," — and he 
then arrives at the following conclusion " that plants derive 
" their carbon from the atmosphere^ that carbonaceous matters 
" accumulate, Sfc'* Now here is a most incorrect comparison 
and inference, that a monocotyledonous plant, the sphagnum 
palustre, of vvhich peat principally consists, and which has 
the property of throwing up new shoots in its upper parts, 
while its lower extremities are decaying, and which ma}/ 
derive its carbon from the atmosphere ; therefore all other 
cultivated plants must do the same ! Why, the tribe of 
orchideae will grow suspended by a string from the ceiling. 
Cacti, 8 feet high and 12 feet broad, will grow in the same 
pot of earth, not weighing two pounds, for ten years, and 
must therefore derive their carbon from the air ; yet surely I 
am therefore not to arrive at the conclusion that all plants 
derive their carbon from the air in the like proportion. 
Liebig also institutes a similar incorrect comparison between 
the carbon produced by a forest which is unmanured, and 
that derived from crops of manured land, and thence con- 
cludes that carbon must be derived by all plants from the 
atmosphere, and " that the quantity of carbon produced by 
" manured land is not greater than that yielded by land not 
" manured." Every farmer knows the latter proposition to be 
untrue, and that it would at once be refuted by the produce 
of a turnip crop unmanured, and one manured ; but if it were 
ever proved that a forest did produce more carbon than 
cultivated plants, the general application would by no means 
follow; for there is every reason to believe that the source of 
