Dr. Hugo Mo/tl, on Liebig's Organic Chemistry. 89 



vegetable growth — for analysis shows that the amount of phosphates 

 varies considerably even in the same organ in plants grown on differ- 

 ent soils, as is best seen in the different sorts of grain. 



In that chapter which is devoted to the Culture of Plants, Pro- 

 fessor Liebig puts forth a regular theory of vegetable nutrition — as 

 far, namely, (observes Dr. Mohl,) as L.'s unconnected way of writing 

 admits of any systematic arrangement. He again starts from the 

 assumption, that humus cannot be absorbed and used as food by 

 plants ; for two reasons — one chemical, and the other physiological. 

 He, in the first instance, denies that the humus of vegetable mould 

 possesses the properties ascribed to it by chemists, it being absolute- 

 ly insoluble in water, and not combining with earth into soluble salts. 

 The latter, he says, may be seen in calcareous caves, whose stalac- 

 tites, instead of consisting of humate of lime, do not contain a trace 

 of vegetable matter. Dr. M. says that he does not intend to settle 

 these opinions, for he has no doubt that chemists will take them up 

 in due time. He merely throws out the following remarks : — " It 

 cannot be positively asserted that the humates contained in vegetable 

 mould are insoluble in water, because water will dissolve out of the 

 soil a certain amount of an organic, brownish substance — an experi- 

 ment which can be made with any garden soil ; still coal of humus 

 seems to possess the property of subtracting these substances from 

 a solution passing or filtering through soil, otherwise (as L. has 

 stated) all our springs would contain brown water. It appears, more- 

 over, that besides coal of humus, the inorganic substances of the soil 

 themselves possess (although in a lesser degree) the property of 

 withdrawing from water the substances dissolved in it — a circum- 

 stance to which the greater purity of springs coming from a great 

 depth may be ascribed. Still this withdrawal of organic substances 

 is obviously only a partial one, for our spring- water is never free 

 from organic substances — a fact borne out by analysis, as well as by 

 the putrescence to which spring- water is subject. This perfectly 

 agrees with the new experiments of Saussure, who found in all 

 waters an azotised substance soluble in water." All these facts, 

 therefore, give quite another result from that which L. has arrived 

 at, viz. that <the water which niters through vegetable mould will 

 always supply plants with some portion of organic matter. How far 



