NITROGEN. 177 



the experiments hitherto made with the view to 

 investigate the action and function of the leaves. 

 "We are not at liberty, consequently, to assume that 

 any of the nitrogen which plants contain has been 

 derived in this way directly from the air. It may 

 be the case, but it is not yet proved. 



" There is little doubt, however, that nitrogen 

 enters the roots of plants in a state of solution, but 

 the quantity they thus absorb is uncertain. When 

 water is exposed to the air in an open vessel, it 

 gradually absorbs oxygen and nitrogen, though in 

 proportions different from those in which they exist 

 in the atmosphere. The whole quantity of the 

 mixed gases thus taken up, according to Humboldt 

 and Guy Lussac, amounts to about four per cent, of 

 the bulk of the water, and in rain-water about two- 

 thirds of this consists of nitrogen. One hundred 

 cubic inches of rain-water will therefore carry into 

 the soil about two and two-third inches of nitrogen 

 gas." 



These organic substances were all originally pos- 

 sessed by the air. The first forms of vegetation 

 which existed upon the earth were those whose 

 roots simply served to hold them in position, or to 

 draw very slightly from the earth. All the organic 

 elements of growth were to be easily absorbed by 

 those which were aquatics from the water which 

 surrounded them, and by land-plants from the 

 atmosphere. These, by their death, imparted to the 



