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



quantity of a certain base, which may be absolutely required for the 

 prosperity of one plant, may act as a poison to another, &c. In this 

 respect, lime more especially is conspicuous, as the flora of the cal- 

 careous Alps, compared with that of primitive rocks, clearly proves. 

 In this respect some plants are very fastidious, and will only bear 

 one certain sort of soil, whilst others grow in both. In the species 

 which may be called fastidious of soil, the substitution of one 

 base for another cannot be supposed to take place. 



In a subsequent part of his book, Dr. Mohl examines what Liebig 

 has stated or retracted in his late work, " Organic Chemistry in its 

 Relation to the Doctrines of Dr. Grubes and Sprengel." Dr. M. 

 considers the explanations of L. in that place only as additional proofs 

 of his inconsistency, and another sample of the uncertain style of his 

 writings, " which leaves the reader, on almost every important topic, 

 in perfect uncertainty what it really is that Liebig means." In only 

 one instance, concludes Dr. M., the author has spoken plainly ; viz., 

 in alluding to silica, of which he says that it is the first solid 

 substance that is taken up by plants, and is that, moreover, whence 

 the formation of wood takes its origin : acting, therefore, like one of 

 those particles of a solution on which the first crystals are formed, 

 and that in Equisetum and the Bamboo silica assumes the form and 

 functions of the wood. This theory Dr. M. calls a physiological 

 blunder, (as it certainly is,) proving Prof. Liebig's absolute ignorance 

 of everything connected with the physiology of plants. 



Another important point, says Prof. Mohl, (p. 37,) which L.'s 

 theory does not explain, is, that the saline bases absorbed by plants 

 are not only absorbed in the shape of carbonates, (which are easily 

 decomposed by the mere vegetable acids,) but often also in the shape 

 of phosphates, sulphates, &c. According to all experience, these 

 salts are not less essential to vegetation than those bases combined 

 with organic acids. Silica, also, is an ingredient equally essential to 

 the growth of most, if not all, plants. Which part these substances 

 take in the vital process, is (says M.) almost unknown, unless, 

 indeed, we may presume that the sulphates yield plants the sulphur 

 required for some of their organs. Of the phosphates we know still 

 less ; we are ignorant why they chiefly occur in young plants, and in 

 their seed ; and we are perfectly ignorant of the quantity required for 





