INFLUENCE OF MANURE. 15 



or the wood in a forest receives its carbon, since 

 there no manure no carbon has been given to it 

 as nourishment ? and how it happens, that the soil, 

 thus exhausted, instead of becoming poorer, becomes 

 every year richer in this element ? 



A certain quantity of carbon is taken every 

 year from the forest or meadow, in the form of 

 wood or hay, and, in spite of this, the quantity of 

 carbon in the soil augments ; it becomes richer in 

 humus. 



It is said, that in fields and orchards all the carbon 

 which may have been taken away as herbs, as 

 straw, as seeds, or as fruit, is replaced by means of 

 manure ; and yet this soil produces no more carbon 

 than that of the forest or meadow where it is never 

 replaced. It cannot be conceived that the laws 

 for the nutrition of plants are changed by culture, 

 that the sources of carbon for fruit or grain, and 

 for grass or trees, are different. 



It is not denied that manure exercises an influ- 

 ence upon the development of plants ; but it may 

 be affirmed with positive certainty, that it neither 

 serves for the production of the carbon, nor has 

 any influence upon it, because we find that the 

 quantity of carbon produced by manured lands is 

 not greater than that yielded by lands which are 

 not manured. The discussion as to the manner in 

 which manure acts has nothing to do with the 

 present question, which is, the origin of the carbon. 

 The carbon must be derived from other sources ; 



