FERTILITY OF DIFFERENT SOILS. 39 



38 per cent, of carbon; therefore 1961 lbs. of straw- 

 contain 745 lbs. of carbon. One hundred parts of 

 corn contain 43 parts of carbon; 882 lbs. must 

 therefore contain 379 lbs., — in all, 1124 lbs. of car- 

 bon. 



26,910 square feet of wood and meadow land pro- 

 duce, consequently, 1109 lbs. of carbon; while the 

 same extent of arable land yields in beet-root, 

 without leaves, 1032 lbs., or in corn, 1124 lbs. 



It must be concluded from these incontestable 

 facts, that equal surfaces of cultivated land of an 

 average fertility produce 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 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 nutri- 

 tion 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 influence 

 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 influ- 

 ence upon it, because we find that the quantity of 

 carbon produced by manured lands is not greater 



