Liebig's Organic Chemistry applied to Agriculture. 569 



in how hasty and superficial a way Dr. Liebig draws conclusions. 

 According to the experiments of Saussure, plants of wheat yield 

 before they are in blossoms 0,070, whilst they are in blossom 0,054, 

 and when the corn is ripe 0,035 of ashes. Hence the author infers 

 that plants, from the time when they begin to blossom, return to the 

 soil a portion of their inorganic matter ; which certainly is a false 

 conclusion. These facts only shew, that the relative proportion 

 between the organic and inorganic constituents has been changed ; 

 and this may have taken place whilst the absolute quantity of in- 

 organic constituents in each single plant has been increased tenfold, 

 or in any other proportion. I am decidedly of opinion, that a great 

 increase of this matter takes place, if we consider the absolute weight 

 of plants in blossom, and when loaded with seeds. It is quite dis- 

 tressing to mention such things to a chemist, for he at least should 

 know how to estimate them. 



The chapter on the Rotation of Crops and Manure contains little 

 to interest a physiologist. The author first mentions excretions by the 

 roots, respecting which there exist no experiments of any value, except 

 those of Macaire Prinsep. Although we poor physiologists may not 

 have acquired the art of experiment in chemical laboratories, yet we 

 know, I trust, what are the requisites of a scientific experiment ; 

 and we think those of Mr. Prinsep not made with such skill as enti- 

 tles them to form the foundation of a theory, as is evident from the 

 weighty objections made to them by Meyen in his " Physiology." 

 A theory founded on such experiments can only be a plaything. 

 Scientific naturalists are aware that in the complicated processes 

 of vegetation, many things are to the considered, of which Dr. 

 Liebig has not the most remote idea. A few propositions in this 

 chapter, placed side by side, will show with what facility shallow 

 people can explain things that are inscrutable to those who penetrate 

 below the surface of the subject. *' According to Macaire Prinsep, 

 it is by their excretions that plants return to the soil such consti- 

 tuents as have been introduced into them during their growth. 

 These excretions cannot be assimilated by any plants, until they 

 again have been converted into humus. Clover secretes matter which 

 becomes humus with great difl[iculty. All Clover-like plants, especi= 



