13 OF THE ASSIMILATION OF CARBON. 



26,910 square feet of wood-land produce of carbon . . 1007 lbs. 



" " meadow-land " . . 1018 lbs. 



" " arable-land, beet-roots without leaves 880 lbs. 



" " corn . .... 1020 lbs. 



It must be concluded from these incontestable facts, that equal 

 surfaces of cultivated land of an average fertility are capable 

 of producing equal quantities of carbon ; yet, how unlike have 

 been the different conditions of the growth of the plants from 

 which this has been deduced ! 



Let us now inquire whence the grass in a meadow, or the 

 wood in a forest, receives its carbon, since there, carbon has not 

 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 leaves, 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, in meadows and forests, 

 are different. 



It is not denied that manure exercises an influence upon the 

 development of plants ; but it may be affirmed with positive cer- 

 tainty, that to its carbon is not due the favorable influence which 

 it exercises, 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 ; and as the soil does not yield it, it can only be 

 extracted from the atmosphere. 



In attempting to explain the origin of carbon in plants, it has 

 never been considered that the question is intimately connected 



