82 Dr. Hugo Moldy on Liebig's Organic Chemistry, 



divided into three classes. 1st, plants were reared in soil destitute 

 of humus, either with distilled water or such as contained carbonic 

 acid. Under both these circumstances they do not prosper ; still, 

 this does not prove the necessity of organic food, because they are 

 here equally deprived of other inorganic substances, which they are 

 in contact with, under common circumstances. 2d, Or, plants have 

 been reared in powdered charcoal. L. says, (p. 58,) that they will 

 attain in this material the most luxuriant growth, flower, and bear 

 fruit ; but he merely quotes in evidence the experiments of Lucas, 

 reprinted in his Appendix. But the reasoning of L., under this 

 head, is illusory. Lucas speaks of vigorous vegetation of plants 

 reared in a mixture of charcoal powder and decayed leaves ; of such 

 as are grown in charcoal powder alone, he merely says that they 

 speedily become rooted. Of their further vegetation he says nothing ; 

 and it has been proved by the experiments of Zuccarini that plants 

 will not grow at all, or very badly, in this substratum. The same 

 is stated by Saussure (Bibl. univ. xxxvi., p. 352,) who relates, that 

 Peas reared in charcoal did not grow much better than those planted in 

 mere sand. The third class of experiments relates to the question, 

 whether plants will- absorb organic substances dissolved in water, 

 and especially humates ; and whether they will prosper under these 

 circumstances. The experiments of Saussure, Davy, and Sprengel 

 are affirmative ; but L. has reprinted (as stated before) those of 

 Hartig, which are negative. The whole question, therefore, is, to 

 say the most of it, one yet undecided. At any rate, it cannot be 

 solved by experiments upon a single species of plants; and it is 

 begging the question to state (p. 122) that, "All plants are the 

 same in the chemical nature of their nutritive process." 



Dr. Mohl then proceeds, at some length, to refute this unqualified 

 assertion of Liebig. There is a considerable number, he says, of 

 true parasites, which require for their food the juices of living plants. 

 It cannot be doubted that such plants require substances of a pecu- 

 liar chemical combination and quality for their food. Many such 

 parasites are not green, and therefore cannot decompose carbonic 

 acid, so that their food must necessarily consist of substances already 

 assimilated by other plants, and stand in the same relation to the 

 mother plant as the flower and fruit of other vegetables to their 



