Dr. Hugo Mohl, on Liebig s Organic Chemistry. 79 



deavours to prove this position by comparing, from tables made by 

 De Saussure, the quantity of oxygen absorbed by the leaves of 

 Pinus abies, Quercus robur, and Populus alba, as compared with the 

 quantity absorbed by the Agave americana. Mohl remarks on this 

 statement, that, in the first place, the quantity of oxygen absorbed 

 by the Agave is put down at 0.3, when it ought to have been at 

 0.8, so as to affect the calculations very considerably ; and that, in 

 the second place, those plants in De Saussure's table which contain 

 neither oil nor tannic acid in any quantity, as the Triticum sestivum 

 and Robinia pseudacacia, are altogether omitted, although they ab- 

 sorbed more oxygen than those mentioned by Liebig; whilst the 

 oily Juniper and Rue, which are also omitted, absorbed less. 



Again, Liebig states on this point, that the absorption of oxygen 

 has nothing at all to do with the processes of life. How is it, then, 

 asks Mohl. that plants begin to be blighted when oxygen is with- 

 drawn ; that seeds will not germinate ; that leaves lose their irrita- 

 bility ; that the motions of leaves and flowers cease ; that leaf-buds 

 and flower- buds will not open when brought into an atmosphere 

 without oxygen ? But the way to settle the question of respiration 

 would appear to be to determine whether the asserted relation be- 

 tween the quantity of oxygen absorbed and the quantity of carbonic 

 acid given out was wrong. In De Saussure's experiments, there was 

 found to be an exact relation in all cases. This would not be the 

 case, were Liebig's theory of the origin of the carbonic acid correct. 



These few general remarks, observes Dr. Mohl, will serve to in- 

 dicate the claim of Liebig to become a reformer of botanical science. 



The next part of Dr. Mohl's observations relates to the chapters 

 of Professor Liebig's book, inscribed " The Assimilation of Carbon." 

 The question at issue is, whether the plants owe their carbon to the 

 absorption of organic or inorganic substances, Prof. L. having given 

 his sanction to the latter opinion. The reasons which seem to have 

 weighed most with him are, 1st, Humic acid loses its soluble 

 character by exsication as well as by freezing ; 2d, Even conceding 

 that all the bases found in the ashes of plants should have been con- 

 veyed to their substance in the form of humates, yet the amount of 

 humic acid thus conveyed to plants is not sufficient to explain the 

 amount of carbon they contain ; moreover, 3d, Even all the rain 



