246 NITROGEN IN PLANTS. 



wheat of the same variety, but of which one sample was taken 

 from garden ground, very rich, and the other from the ordinary 

 soil of his field, and of course comparatively poor. The growths 

 were of the same year, and the same farm, and therefore the influ- 

 ences of weather the same. 



"FROM THE OPEN FIELD. FROM THE GARDEN GROUND. 



Carbon, . 46.10 



Hydrogen^ . 5.80 . 



Oxygen, . 43.40 



Azote, . . 2.29 



Ashes, . 2.41 .... 



100.00 100.00 



"In the produce of the garden ground there were 21.94 per 

 cent, of gluten and albumen [the products of wheat which only 

 contained azote] ; in that of the open field no more than 14.31 per 

 cent, of the same principles." (Rural Economy, &c., p. 176.) 



The cursory reader would perhaps be struck only by the general 

 agreement of the proportions of the constituents of these two 

 samples of wheat grown on such different soils. But while there 

 is such near approach to equal proportions of the three larger con- 

 stituents, the azote, smallest in quantity, but the most important 

 for its quality, is shown to be increased in proportion more than 

 50 per cent, by the richer soil. 



Thus the smallest but richest element, azote, would seem to be ob- 

 tained by plants principally or entirely through their roots, and from 

 the soil. Therefore, the supply to plants is in no degree increased by 

 the prodigious quantity of azote in the atmosphere. On the other 

 hand, the carbon, which constitutes about half the dry weight of 

 all plants, is supplied, for much the larger part, from the carbonic 

 acid gas of the atmosphere, through the leaves, and thus is fixed 

 in and assimilated to the plant. Carbon is the only one of the 

 four great elements found in air or water which is presented (by 

 the atmosphere) to plants in small quantity, and apparently in in- 

 sufficient quantity for the supply of their leaves. Therefore, I 

 infer that to increase the nourishment and growth of plants it is 

 not only necessary to increase the supply of azotized manures 

 through the soil to their roots, but also (if possible), to increase 

 the supply of carbonic acid to the leaves; or to increase their 

 power to take up the supply actually present in the surrounding 

 atmosphere.* As to the oxygen and hydrogen, they will be sup- 



* Professor Liebig maintains that all the azote taken up by plants is 

 through their roots, and of course derived immediately from the soil. 

 Boussingault infers, from some very interesting experiments, to which I 

 shall again advert, that some azote is also taken directly from the atmos- 

 phere, at least by leguminous plants. The latter author, agreeing with 



