Carbonic Acid a gaseous body consisting of 

 one part of carbon and two of oxygen is the 

 source from which all plants derive their carbon, 

 and it claims our attention first. The natural 

 philosophers of a former generation, even the 

 celebrated Sir Humphrey Davy, believed that the 

 organic food of plants carbon of course included 

 was directly derived from the decaying vegetable 

 matter contained in the soil, and they considered 

 the relative presence or absence of such as the sole 

 reason for the fertility or sterility of the soil. 

 When leaves, branches, trees, or any other vege- 

 table matter in short, are heaped together and left 

 exposed to the action of moisture and atmospheric 

 air, a gradual decay or slow combustion takes 

 place, on account of the affinity which the oxygen 

 of the atmospheric air possesses to the carbon and 

 hydrogen of vegetable matter. In course of time 

 the whole becomes a black mouldy mass, which 

 some chemists have called humus. The so-called 

 " Humus Theory" rested on the erroneous belief 

 that, as stated above, plants derived their organic 

 food directly from this substance. The fallacy of 

 this theory was, however, soon demonstrated, and 

 Liebig showed by extensive experiments the 

 mistake that was made. 



From an acre of good meadow or grass land 

 there is obtained year after year, on the average, 

 2,500 Ibs. of hay, which contain 984 Ibs. of carbon 



