hiehigs Organic Chemistry applied to Agriculture. 565 



contains. It must be obvious how little science will be promoted 

 by a book so evidently written without consideration, and, in fact, 

 made up of unconnected accidental conceptions. 



In the chapter on Cultivation, little could be expected of interest 

 to vegetable physiologists ; and having been as badly arranged as 

 the remainder of the work, at least half its contents consist of isolat- 

 ed physiological observations. First, humus is again taken up, and 

 found to be an inexhaustible source of carbonic acid, which feeds 

 the plants. By this process, the quantity of humus contained in the 

 soil is, he says, subject to a continual diminution. Dr. Liebig has 

 forgotten that, in another place, he had asserted the reverse to take 

 place. Then comes a most surprising statement. He says (p. 109), 

 that in a soil which communicates a yellow colour to water, no 

 plants thrive ; and that few plants flourish on barren peat- soil, or 

 marshy meadows, whose soil has that quality. One would think 

 that Dr. Liebig had never seen a peat-moss, or a marshy meadow, or 

 the dense mass of vegetation which is spread over it ; or that he had 

 never heard of peat being continually reproduced by the perishing 

 vegetation that it bears, and which quickly shoots up again ; or, that 

 on this peculiar quality of peat-moors depends the inexhaustible na- 

 ture of peat-pits. The matter, however, stands thus : Farmers call 

 that soil barren in which those plants do not thrive which they culti- 

 vate, notwithstanding that it may otherwise produce a most luxuriant 

 vegetation. On the soils named by Dr. Liebig there do, in fact, 

 grow as many plants as on any other soil, but of peculiar kinds. 

 Many of them, doubtless, require a large quantity of humus, as, for 

 instance, many kinds of Moss ; while Reeds and Sedges do not seem 

 to thrive at all, except in soil containing a large quantity of free 

 humic acid. Dr. Liebig had already settled, as we thought, all that 

 is requisite for the growth of plants ; but (at p. 109) he suddenly 

 produces quite a new requisite, namely, the existence of free oxygen 

 in the soil ; without, however, mentioning for what purpose it serves, 

 and whether or in what way it is introduced into plants, and what 

 changes it undergoes there. Further on, amidst a number of well- 

 known observations, are more erroneous conceptions. In a preced- 

 ing page of his book (p. 23), he had asserted that " no matter can 

 be considered as nutritious, or as necessary to the growth of plants, 



