58 QUARTERLYJOURNAL. 



that makes both the soil and the atmosphere the sources from which 

 these elements are drawn. It is well known that the roots will 

 absorb them if presented to them in a liquid form, and if intro- 

 duced into the circulation they will no doubt be appropriated by 

 the plant. 



Nothing in a solid form can enter into the circulation of plants. 

 It is by means of water that they receive all their food which they 

 take in by their roots, that fluid being the solvent of all they re- 

 quire. By their leaves they absorb gases and probably water also. 

 But before any thing can enter the minute pores of the roots, it 

 must be dissolved in water. But this is not the only use of water. 

 It is composed of two of the gases mentioned above, viz., oxygen, 

 and hydrogen, and is an abundant source from which the plant can 

 receive them. And it may be proper before closing this paper, to 

 consider in a few words the sources whence the plant derives its 

 organic constituents. 



Carbon constitutes a very large portion of the vegetable. From 

 forty to fifty per cent, nearly or quite one-half, of all plants consists 

 of this substance. This is derived from several sources. First, 

 by their leaves from the atmosphere. When wood or coal is 

 burned in the open air, the principal product is carbonic acid, i. e. 

 carbon united with oxygen. During the process of respiration, 

 animals give off from their lungs this same substance. About 

 eleven ounces of this gas are said to be thrown off from the lungs 

 of a healthy man in twenty-four hours. This mingles with the air, 

 constituting about xolo P^"^^ °^ ^^^ weight, the quantity varying 

 somewhat under different circumstances ; in the vicinity of large 

 bodies of water, it being less, and at night more than in the day. 

 From this source it is absorbed by the leaves of plants, which are 

 furnished with numberless pores, serving as mouths. It is the 

 opinion of one class of vegetable physioligists that it is in this way 

 that they obtain all their carbon, making no use of their roots for 

 this purpose. 



But it is probable that it is taken up largely by the roots, both 

 that which is brought down from the atmosphere in rain, and also 

 that which is formed in the soil by the decomposition of animal 

 and vegetable matters. These organs indeed, may be considered 

 the true mouths of plants, by which they receive by far the greater 

 part of their food, both organic and inorganic. 



