AGRICULTURAL CHEMISTRY. 145 



understanding of the processes by which the element nitrogen is 

 made assimilable to vegetation. 



Within a few years numerous investigations relative to this subject 

 have been made. Luca has observed that when air (freed from am- 

 monia) is passed through a solution of potash, nitrate of potash is 

 formed, in case the air has been in previous contact with the foliage 

 of plants, but not otherwise; thus indicating that the oxygen is ozon- 

 ized by the oxydations going on in or about living vegetation (espe- 

 cially when ethereal oils are exhaled ?) and, according to Pless and 

 Pierre, ozone is also produced in the decay of the organic matters of 

 the soil. 



If, as thus appears probable, it is the case that the very existence 

 of living plants, and certain later stages of their destruction by 

 decay, are means of recombining nitrogen to an extent equal to or 

 slightly greater than that to which this element is placed beyond the 

 reach of vegetable assimilation in the earlier steps of organic decom- 

 position, we see that the vegetable germ carries with it, so far as this 

 element is concerned, the possibility of an almost unlimited, reproduc- 

 tion or expansion. 



Allusion has already been made to the possibility of the occurrence 

 of nitrous oxide in the atmosphere, but we have as yet no positive 

 evidence of the fact. 



Having thus shown the origin of the compounds out of which, for the 

 most part, the plant organizes itself, and explained, so far as the 

 present state of science allows, how the supplies that are continually 

 being consumed are as continually maintained, we now come properly 

 to consider the question, Are the atmospheric stores sufficient for the 

 purposes of vegetation ? 



To this inquiry we must undoubtedly reply, that while the quantity 

 of carbonic acid absolutely contained in the atmosphere is so large as 

 to feed an abundant vegetation, it being experimentally shown that 

 some plants are able to grow well with none other than the ordinary 

 atmospheric supplies, it appears that a concentration of this substance 

 in the vicinity of the absorbing organs not only develops, but is essen- 

 tial to the intense growth which characterizes agricultural production. 



Liebig and others have instanced forests and prairies as proving the 

 sufficiency of the atmosphere in this respect, for, say they, under the 

 occupancy of trees and grasses the soil is constantly enriched in car- 

 bon drawn from the atmosphere by these plants and annually deposited 

 upon the soil as fallen foliage. In our view, however, the fact that a 

 forest does not come into its most vigorous growth before the soil has 

 been covered with decaying leaves, proves that the general atmos- 

 phere is insufficient, not indeed in the amount, but in the rapidity of 

 its provision, and that an atmosphere more highly charged than usual 

 with the products of vegetable decay, near or in the soil, is essential 

 to the full supply of carbonic acid. The same doctrine must obtain 

 with reference to the other forms of plant-food. It is, in fact, needful 

 that the soil become a medium for the condensation and more speedy 

 transmission into the plant of the originally purely atmospheric sup- 

 plies. We shall recur to this subject in subsequent pages. 

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