252 Theory of Lucases Experiments 



Art. II. Theory of M. Edward Lucas's Experiments on the Effect 

 of Charcoal on Vegetation. By Dr. A. Buchner, Sen. (Trans- 

 lated from the " Garten Zeitung " for the " Gardener's Magazine," 

 by M. L.) 

 The numerous experiments and observations mentioned in this treatise appear 

 to me to be very important contributions, not only to vegetable physiology 

 and dietetics, but also to the founding of a vegetable therapeutic system, 

 which, if I am not mistaken, has not hitherto been taken into consideration. 

 I take leave, therefore, to make a small addition in a theoretical point of view, 

 in order to introduce a clear scientific notion of the effects of charcoal on 

 vegetable life. These effects are founded, undoubtedly, on several causes, of 

 which the following appear to me the most important. 



1. Absorption of Light, and Generation of Heat. It is well known that bodies 

 receive the light of the sun the more perfectly, the darker, duller, and looser 

 they are, and that the consequent developement of heat is in proportion to 

 this absorption of light ; hence, a black light soil is, under the same circum- 

 stances and relations, much more favourable to vegetation than a light- 

 coloured, grey, heavy earth. Heavy clayey soil, with a deficiency of humus, is 

 less suitable to vegetation, inasmuch as it soon loses its porosity through rain 

 and snow, and assumes a smooth surface, by which it is prevented from ab- 

 sorbing air and light and generating heat. Hence agriculturists justly name 

 these clayey soils, which are deficient in humus, cold soils. As charcoal dust 

 is one of the darkest, dullest, and most porous of bodies, it must, on account 

 of its peculiar capacity of receiving the sun's light and changing it into heat, 

 be particularly favourable to vegetable life. M. Lucas, in his experiments 

 next summer, will, no doubt, not omit making comparative thermometrical ex- 

 periments. 



2. Absorption of Atmospherical Air. Among all porous bodies that have the 

 capacity of absorbing gases and vapours, charcoal has been proved by nu- 

 merous experiments to hold the first rank. If, therefore, clayey soil, deficient 

 in humus, is in general less suitable to the growth of plants than rich loose 

 garden mould, the reason lies, not only in the latter receiving more light and 

 creating warmth, but also in its more readily condensing, by its greater poro- 

 sity, the constituent parts of the atmospheric air, and consequently supplying 

 oxygen, nitrogen, and carbonic acid gas for the nourishment of the spongioles. 

 We come here to a very important point, the nourishment of plants, which I 

 cannot slightly pass over in elucidating the theory of the effects of charcoal in 

 this respect. Modern vegetable physiologists are, for the most part, of opinion, 

 that plants can receive no solid nourishment from the earth ; that is, that 

 every thing that they can assimilate (or digest) must be in a liquid and gaseous 

 or vapoury state. If we, therefore, meet with siliceous earth, chalk, magnesia, 

 oxide of iron, in short, such substances in plants as could only be received 

 from the soil, we may always consider it certain that these sorts of matter can 

 only be absorbed by the roots in proportion as they are in a fluid or dissolved 

 state in the soil. These sorts of matter, and particularly the different organic 

 salts which we find in the ashes of vegetables, are not actually to be con- 

 sidered sources of nourishment, but stimulants to assist in digesting, as salt 

 and spice are to the higher animals and man ; we also not unfrequently 

 observe that a superfluity or mixture of certain inorganic substances in the 

 soil, prejudicial to certain families and species of plants, is the cause of disease 

 when this inorganised matter is in a dissolved state and capable of being ab- 

 sorbed by them. 



If we analyse the nourishment of plants, we shall find it is only the con- 

 stituent parts of air, water, and charcoal. The experiments of Boussingault 

 on the oi'igin of nitrogen in organic bodies show, 1st, that no plant exists 

 without a proportion of nitrogen ; and 2d, that, while men and animals receive 

 the portion of nitrogen of their bodies not from the air by breathing, but from 

 food by assimilation, plants on the contrary draw their supply of nitrogen, not 



