77 



Dr. Justus Liebig in his Relation to Vegetable Physiology. By Dr. 

 Hugo Mohl. (Dr. Justus Liebig's Verhdltniss zur Pflanzen- 

 Physiologie.) Tubingen. Frues. 1843. 



This is the pamphlet of Dr. Mohl to which we referred in a 

 leading article of May the 20th, and which consists of a critique on 

 the work of Dr. Liebig, so well known in this country under the 

 title of " Chemistry, in its applications to Agriculture and Physi- 

 ology." Dr. Mohl says that work was anxiously looked for by 

 botanists both on account of the reputation of Liebig as a chemist, 

 and from a knowledge of the fact that they had much to look for 

 from the aid of Chemistry in their investigation of the phenomena of 

 the nutrition of plants. But Dr. Mohl observes that throughout 

 the whole work there is a want of original experiment, which is the 

 more wonderful, since it is written by the greatest experimenter of 

 his day, and the possessor of one of the largest laboratories in 

 Europe. Nevertheless Liebig every where insists on the importance 

 of experiments, and is continually appealing to those of Theodore 

 De Saussure. Under these circumstances the work can only be 

 looked upon as an attempt to construct a theory from data already 

 known to the world. 



The next general remark by Dr. Mohl refers to the style in which 

 the book is written. If not always correct, it is energetic and clear ; 

 the thoughts are propounded in short determinate propositions, and 

 there is not the slightest indication of doubt or uncertainty about 

 anything; the author seems to know everything for certain, and 

 says it boldly out. This sort of style is apt to mislead the uniniti- 

 ated, and frequently leads the author himself into positive contradic- 

 tions ; in fact, a thing is stated to be black or white according as it 

 suits the author's purpose. For instance, in one place (p. 22)* he 

 says that leaves do not decompose carbonic acid in the shade, (in 

 which he is wrong,) and in another place (p. 121) he says the leaves 

 do decompose carbonic acid in the shade, (in which he is right). 

 Such contradictions are frequent, and prove that the author is 

 neither well-grounded in the subjects on which he has undertaken to 



* These numbers refer probably to one of the German editions. 



