Principles of scientific botany, or, Botany as an inductive science / by J.M. Schleiden ; translated by Edwin Lankester.

Date:
1849
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Licence: Public Domain Mark

Credit: Principles of scientific botany, or, Botany as an inductive science / by J.M. Schleiden ; translated by Edwin Lankester. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    These changes require no further explanation than the decomposition of water, the setting free of oxygen, and the separation of a smaller or larger number of equivalents of water; processes which we know con- stantly present themselves in the decomposition of organic substances. One of the most important of the proximate principles is undoubtedly dextrin. In all formative fluids, according to Mitscherlich. and Mulder, dextrin presents itself as the primary substance out of which all the other assimilated matters are formed. In the various changes which these matters undergo, the nitrogenous bodies seem to be the means of effecting changes in the other bodies, whilst they themselves remain unchanged. This phenomenon has got various names without any ex- planation of it being given. Berzelius calls the process catalysis; Mitscherlich, the contact of substances ; and Liebig the activity of ap- prehending bodies. A number of such chemical facts are known ; thus — sulphuric acid, with heat, converts starch into dextrin and sugar and alcohol into ether ; diastase changes starch into dextrin and sugar; albu- men, protein, &c. convert sugar into alcohol. Liebig’s explanation of the phenomenon as a communication of motion is founded on the notion of the existence of ultimate atoms, and is otherwise untenable. Could we explain better this phenomenon of one of the assimilated substances facilitating the changes which go on in the others, we should have yet to explain the changes which produced the nitrogenous substances. The most important of these changes appears to be the decomposition of water, but we are at a loss to know whose calculations to adopt. Almost all plants need for their growth the influence of light. Here also we have a need of experiments to determine the action of the par- ticular rays of the sun-light, as of the coloured, the calorific, and the chemical. Only thus much is known from De Saussure’s experiments : that under the influence of light the carbonic acid of the air is fixed in the cells, and combines also with hydrogen ; a process which will not go on when light is excluded. That in this case light can be supplied through hydrogen, appears to be proved by an interesting experiment of Humboldt’s.* § 34. In the formation of the assimilated matters, many sub- stances become free, which, either through their natural affinities, or the effect of contact, or predisposing affinity, form new com- binations either amongst themselves, or with the non-assimilable substances which may have been absorbed at the same time. All substances formed in this way I call secretions (materia secreta) of the cells. Some of these are universally present, as free oxygen, oi at least when they have vegetated under definite circumstances, as the green colouring matter (chlorophyll). There are others whose formation depends on especial circumstances, as conia, so- lania, and the like. Lhc chemical changes by which such sub- stances are produced are for the most part concealed. Two points lemain to be noticed here:—1. That these secretions would be frequently injurious to the cells were they not neutralised by in- organic substances taken up from without or by newly formed oi game mattei s. thus, oxalic acid combines with lime, and the * Flora) Fribergensis Specimen, p. 180. [See also, on this subject, Hunt’s Reports m the transactions of the British Association, 1847 ; and Draper on the Chemistry of Plants—Tit a ns.]