82 THE CULTURE OF FARM CHOPS. 



to any appreciable extent, than carbonic acid, and thnf tbia 

 compound is everywhere diffused throughout the atmos- 

 phere and is always found in solution in water, the con- 

 clusion cannot be avoided, that it is from carbonic acid 

 that the carbon of plants is derived, primarily. This con- 

 clusion is supported and confirmed by the knowledge that 

 plants absorb carbonic acid through their leaves in the sun- 

 shine, and that they will die in an atmosphere from which 

 carbonic acid is wholly excluded. 



Again supposing that plants derive their carbon wholly 

 from the soil or are able to do so, then, knowing that the 

 most abundant product of the decay of vegetable matter is 

 carbonic acid; and that in a well manured soil filled with 

 decaying vegetable matter, this gas must be quite abun- 

 dant; and that water dissolves it freely, we must be satisfied 

 that it is from this carbonic acid, absorbed with the water 

 of the soil by the -roots that the carbon of plants is derived. 

 In either case it is the carbonic acid which supplies the car- 

 bon, and it is most probable that this enters the plant both 

 by the roots, and leaves. Thus whether from the earth or 

 the air, this gas furnishes an unfailing supply of food for 

 plants from which their carbon is derived. 



But when water passes through the soil it takes up what- 

 ever soluble substance it may meet potash; soda; lime; 

 magnesia; silica; &c. ; and conveys them into the plants by 

 the medium of their roots. Do the roots exercise a super- 

 vision over the absorbed waters and reject every soluble 

 form of carbon but that of carbonic acid ? This is a ques- 

 tion of interest too to the farmer and applies directly to the 

 practice of manuring the land. This subject is out of place 

 as yet, but the question is pertinent to the present enquiry. 

 It is known that plants do not exercise such a watch and 

 have no discretionary power over the water which they ab- 

 sorb; for various coloring matters as madder and the juice 

 of poke root berries have been absorbed into the circulation 

 of plants and have imparted their color to the flowers, and 

 other parts. These coloring matters then undergo a chem- 

 ical change in the plants and even afford nutriment. Sugar 



