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QUARTERLY JOURNAL. 



ted by the decomposition of vegetable matter, and from the at- 

 mosphere. The main source of carbonic acid is, however, the 

 atmosphere. " How can this be otherwise when the enormous 

 quantities of carbon which trees, the growth of centuries, for ex- 

 ample, have laid up, are contrasted with the very limited extent 

 to which their roots extend ? Very certainly where the acorn, 

 whence sprung the oak which is now our admiration, geriAinated 

 a hundred years ago, the soil where it fell and struck not did not 

 contain the millionth part of the charcoal which the oak now in- 

 closes. It is the carbonic acid of the atmosphere which has fur- 

 nished all the rest ; that is to say, almost the whole mass of the 

 noble tree." 



" But what can be more clear or conclusive upon this subject 

 than the experiment of M. Boussaingault, in which peas sown in 

 sand, watered with distilled water and fed by the air alone, never- 

 theless found in this air all the carbon necessary to their develop- 

 ment, flowering and fructification."* 



Liebighas insisted strongly on the fact that the vegetable mould 

 is of much less consequence in furnishing carbonic acid to the nits 

 of plants than has been previously supposed. According to him, 

 this vegetable mould is more important as furnishing the inor- 

 ganic constituents of plants in a soluble state than as furnishing 

 carbonic acid. 



Plants are, however, dependent to a great extent on the carbo- 

 nic acid of the soil. During germination the plant derives its 

 nourishment from the supply laid up in the seed. By the time 

 this supply is exhausted the roots and first green leaves are 

 formed. The latter organs can now take in carbonic acid from 

 the atmosphere, but the quantity absorbed will be in proportion to 

 their surface, which is very small. If then the plant is vegetating 

 in a soil which furnishes no carbonic acid to the roots, so that the 

 whole supply must be derived from the atmosphere by its leaves, 

 its early growth will be slow and the season far advanced before 

 it arrives at maturity. But if the roots can take in carbonic acid 

 the process of growth is more rapid, the leaves are formed in 

 greater abundance, and as the leaves increase, the capacity for 

 taking in carbonic acid from the atmosphere is increased, and thus 



• Dumas' Balance of Organic Nature. 



