80 Dr. Hugo Mohl, on Liebig's Organic Chemistry. 



which falls on a certain area is not sufficient to explain the large 

 quantity of carbon they contain : but the chief argument against the 

 plants deriving carbon from humus is, 4th, That manured and bar- 

 ren ground will yield nearly the same amount of carbon in the plants 

 growing thereon. It is, in fine, to be observed, that 5th, Humus and 

 the carbon of plants must have the same origin, as it is impossible 

 that there could have existed any primitive humus, for plants must 

 have existed before humus. Plants receive, therefore, their carbon 

 from the atmosphere, where it exists in sufficient quantity to supply 

 all plants with carbon. Dr. Mohl says, then, that L. has arrived, in 

 these remarks, at one or two results correct in the main ; but he also 

 shows that most of it (or at least as much as is true) has been known 

 to Saussure 40 years ago. As the above axiom, however, is one of 

 great importance in botanical physiology, Dr. Mohl proceeds to ex- 

 amine the doctrine of Liebig in detail. The argument stated under 

 No. 1 proves, he says nothing — because the combination of humic 

 acid with alkailies, stated under No. 2, is in direct contradiction to 

 it. These parts of the question have been, however, already sifted 

 by Schleiden ; and the utmost which can be conceded is, that plants 

 do not obtain all their carbon from the soil. 



Liebig concludes one of hi3 remarks relating to humus in the 

 following words : — " As plants grown on an acre of unmanured 

 meadow or forest-land will assimilate an equal amount of carbon to 

 those grown on manured and cultivated fields, — as, moreover, the 

 former soil will not become, by the process of vegetation, poorer in 

 humus, but, on the contrary, richer ; there must be a source dif- 

 ferent from humus or manure, whence plants receive their carbon, 

 and this is the atmosphere." — This mistaken argument of Liebig, 

 (says Dr. Mohl,) arises out of his confounding the origin of carbon 

 in the whole of vegetation with that in a single plant, as well as on 

 his placing unmanured soil on a par with that which is deficient in 

 humus. A plant might require a certain amount of humus for its 

 nourishment, and still prepare and yield, by the decay of its foliage 

 or herbage, the same quantity, or even more than it has absorbed, 

 for the growth of subsequent generations. 



The next argument of Liebig discussed by Dr. Mohl (relating 

 always to the origin of carbon in plants) is, that in antediluvian 



