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



ing been prepared by the leaves before the period of flowering, have 

 been deposited in the stem or other organs, and are subsequently 

 conveyed to the fruit. We know that some bulbous plants will fruit 

 even when taken out of the soil. But general assertions, taken from 

 special facts, can only lead to absurd conclusions. Let Profes- 

 sor Liebig cut plants in bloom above their roots {unnecessary, 

 he says, at that period), and expose them to as much dew and rain 

 as he likes, and see what will happen ; or, as he is fond of 

 experiments on a large scale, let him take the hay harvest for a test 

 of this theory ; which, after all (concludes Dr. Mohl), seems 

 to be nothing more than a distorted and overdone copy of the doc- 

 trine of the development of plants given by Schwerz, in his treatise 

 on Practical Agriculture (Anleiitung zum Pract, Ackenbau, hi. 56). 



Besides the formation of humus, Liebig adduces another reason for 

 the rotation of crops, viz., the relation which plants bear to the in- 

 organic constituents of the soil. As every plant deprives the soil of 

 certain ingredients, it thus makes it unfit for feeding similar plants, 

 until by subsequent decomposition a fresh amount of such ingre- 

 dients is again set free. To this proposition (says Dr. Mohl) no 

 one will object ; but it has long been known. 



Having thus examined in detail the work of Dr. Liebig, Dr. Mohl 

 concludes with the following general recapitulation. It appears up- 

 on the whole that Liebig has not availed himself of his chemical re- 

 sources to clear up doubtful points in the nutrition of plants. Con- 

 trary to the spirit of a true investigator of nature, he has not formed 

 his conclusions on the detailed facts of vegetable phenomena, but on 

 random observations, or vague operations on a large scale, destitute 

 of all precision. His calculations are based on arbitrary assump- 

 tions. His book, therefore, far from being a consistent and well- di- 

 gested theory, swarms with contradictions and false reasoning. He 

 does not possess a knowledge of the most elementary doctrines 

 of vegetable physiology. His assertion that physiologists have 

 hitherto considered humus as the chief food of plants is untrue. 

 The assumption that plants live merely on inorganic substances 

 is by no means new, but has long been one of the controverted 

 points of vegetable physiology. The assertion that all Botanists 

 have doubted the absorption of carbon by plants by bheir decomposi- 



