PRESIDENT HITCHCOCK'S ADDRESS. 163 



which shows how infinitely Divine transcends human skill and 

 benevolence ! 



We have seen that the largest part of the carbon of plants is 

 absorbed directly by the leaves from the atmosphere. But car- 

 bonic acid is carried down in a state of solution by drops of 

 rain, and this, being absorbed by the roots, furnishes of course a 

 further supply of carbon. Again, the manure in the soil fer- 

 ments, and furnishes another portion of the same gas, which, 

 in like manner, is carried into the plant. Most chemists sup- 

 pose that carbon is furnished to the plant in no other state than 

 that of carbonic acid. But some of the organic matter in the 

 soil is certainly soluble in water ; and what should prevent its 

 being carried into the vessels of the plant, and its carbon from 

 being there extracted by the same chemistry which decom- 

 poses the carbonic acid? Indeed, Professor Johnston has shown 

 most conclusively, that this is one of the modes in which carbon 

 is supplied. (Lectures on Agricultural Chemistry. Lecture 3, 

 p. 87. Wiley &• Putnam's edition.) 



So much for the carbon which forms the principal part of the 

 solid portion of the plant. Whence does it obtain its oxygen 

 and hydrogen? Nearly all of it, no doubt, from the water 

 pumped up by the roots, or absorbed by the leaves ; for water 

 is entirely composed of these two elements. Nitrogen, also, the 

 least abundant ingredient, might, it would seem, be derived 

 directly from the air by absorption, since four fifths of the at- 

 mosphere consists of it : but there is no evidence of any such 

 absorption. Yet a small quantity of it is absorbed by the water 

 taken up by the roots. Ammonia also, a compound of nitrogen 

 and hydrogen, sometimes exists in small quantity in the air, 

 and is produced still more abundantly by fermenting manures. 

 Nitric acid likewise is sometimes found in minute quantity in 

 the atmosphere, and its absorption would furnish nitrogen as 

 well as oxygen. 



As to the inorganic matter of plants, the sulphur, phosphorus, 

 lime, silex, iron, manganese, &c., it must nearly all be derived 

 from the soil, since water alone can hold it in solution. Chlo- 

 rine perhaps may, as Dr. Dana suggests, be derived from the 

 atmosphere in the condition of common salt, which he has 

 shown to exist probably in the air. 



