CARBON. 173 



verted into portions of their own substance than 

 when this element is combined with oxygen in the 

 form of water. 



"We may conclude generally, in regard to the 

 source of the oxygen of plants, that though there 

 are undoubtedly several other forms of combination 

 in which this element may enter their circulation 

 in uncertain quantity, yet that all-pervading water 

 is the main and constant source from which the 

 hydrogen of vegetable substances is derived. 



3. Carhon. " We have reason to believe that 

 carbon is incapable of entering directly, in its solid 

 state, the circulation of plants. There are two 

 sources from which it can be obtained, — the soil 

 in which the plant grows, and the air by which its 

 stem and leaves are surrounded. In most soils 

 much vegetable matter is present, and large quan- 

 tities are added by the manures used. It is true, 

 however, that plants are really fed by the vegetable 

 matter existing in the soil. 



[a) " We know from sacred history, what reason 

 and science confirm, that there was a time when no 

 vegetable matter existed in the soil. The first 

 plants must have grown without the aid of either 

 animal or vegetable matter ; that is, they must have 

 been nourished from the air. 



(h) " It is known that certain marly soils, raised 

 from a great depth beneath the surface, and con- 

 taining apparently no vegetable matter, will yet, 

 15* 



