GO NUTRITION*. 



the oxygen, hydrogen, carbon, and nitrogen, of 

 which plants are chemically composed (1) are 

 thus derived. The oxygen is abundantly fur- 

 nished by the decomposition of carbonic acid, 

 by the surrounding atmosphere, and by the 

 water taken up into the system. The carbon, 

 which constitutes so large a part of the texture 

 of plants that it retains the form and character 

 of the species when the other portions have 

 been separated from it, and it alone remains as 

 charcoal,* is also mainly derived from the de- 

 composition of carbonic acid. The hydrogen is 

 partly obtained from the water the plant takes 

 up by its roots and leaves, and also from the 

 same source as the nitrogen, which although so 

 abundant in our atmosphere as to constitute 

 four fifths of its whole composition, does not 

 appear to be thence imbibed in its simple form 

 by plants, but to be supplied to them combined 

 with hydrogen in the form of ammonia, the 

 great ingredient in those animal manures so 

 important in agriculture. " It appears," says 

 Dr. Carpenter, " from recent inquiries, that the 



* A remarkable instance of this may be noticed in 

 the triangular pith of the alder used in the manufacture 

 of gunpowder. 



