84 Dr. Hugo Mo hi, on Liebig's Organic Chemistry. 



world by their scanty roots. L. says further, that in hot climates 

 the succulent plants require but a slight connexion with the soil, and 

 develop themselves without its co-operation, in proof of which he ad- 

 duces the slender roots of Sedum, Cactus, and Sempervivum. L. 

 believes, in fine, that in lactescent plants the humidity absorbed from 

 the air, and indispensable to their growth, is protected from evapora- 

 tion by the very nature of their sap, as humidity is surrounded by 

 caoutchouc and is protected by a sort of impermeable integument ! 

 Risum teneatis, amici — exclaims Mohl, in allusion to these opinions. 

 The assertion that antediluvian plants lived on a soil devoid of 

 humus is so extraordinary, that M. refutes it at some length. We 

 know, he says, that monocotyledonous and cryptogamic plants 

 possess no tap-roots, but merely fibres, which, although they are 

 slender, still are very numerous. The assertion, therefore, that 

 plants with thick, branchy roots (like our trees) obtain their food 

 from the soil, and those plants which possess fibrous ones are nourish- 

 ed by the air — is untenable. L. himself " considers the absorption 

 of inorganic substances to be necessary for the nourishment of 

 plants ; those, however, can only be absorbed by the roots." " The 

 reader" — concludes M. — " will, I trust, not expect from me a refu- 

 tation of Liebig's assertions on tropical vegetation, which are really 

 beneath criticism. If the luxuriant vegetation of the tropics, with 

 their virgin forests, Palms, and arborescent Grasses, is to be typified 

 by a few Sedums, Cacti, or Sempervivums, and if lactescent plants 

 are to be looked upon as surrounded by a coat of Indian-rubber ; 

 then, certainly, anything may be proved — and, not least, the igno- 

 rance of the propounder." 



Professor Liebig's third chapter, inscribed " The Assimilation of 

 Hydrogen," proves pretty well that all which Chemistry has made 

 out about chemical processes in the interior of plants amounts to 

 almost nothing. L. states, in the first instance, that woody fibre 

 consists of carbon and the component parts of water, or of carbon 

 plus a certain quantity of hydrogen. Here, therefore, the very first 

 proposition in the progress of assimilation contains an either and 

 an or. L. thinks (p, 60.) that decomposition of water is the more 

 likely to take place, because water is the easier of decomposition ; 

 and this is plausible enough. But what shall we think of the con- 



