SOIL NOT CHIEF SOURCE OF CARBON. 361 



If these facts are considered, it will become 

 apparent, that the true source of the carbon of 

 plants cannot be in the carbonaceous matter of 

 the soil, seeing that vegetation is luxuriant even 

 upon soils which contain little or none of this 

 element. 



The carbonic acid furnished to the air by the 

 various processes of combustion, respiration, and 

 putrefaction, and from volcanic craters, is the 

 true source of the carbon of the vegetable 

 world. The composition of this gas is one 

 equivalent of carbon, united to two of oxygen 

 gas. If we could remove the two proportions 

 of oxygen, carbon is left. Wood is composed 

 of carbon, together with the elements of water, 

 oxygen, and hydrogen ; it contains other prin- 

 ciples, but it is sufficient for our present purpose, 

 to consider wood to be chiefly carbon. If there- 

 fore any structure is supposed to have the power 

 of decomposing carbonic acid, of rejecting its 

 oxygen, and of appropriating its carbon, model- 

 ling it for the peculiar purpose of its organ- 

 ization, the atmospheric origin of wood is ren- 

 dered perfectly feasible. All we have to do is 

 to show that plants possess this decomposing 

 power; that is, they really are able to destroy 

 the union between carbon and oxygen in car- 

 bonic acid. If it should appear that plants are 

 really endowed with this power, it is not diffi- 

 cult to believe that they should be able to use 



