Volume 3

The natural history of plants : their forms, growth, reproduction, and distribution / from the German of Anton Kerner von Marilaun ; translated and edited by F.W. Oliver, with the assistance of Marian Busk and Mary F. Ewart ; with about 2000 original woodcut illustrations and sixteen plates in colours.

  • Kerner von Marilaun, Anton, 1831-1898.
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: The natural history of plants : their forms, growth, reproduction, and distribution / from the German of Anton Kerner von Marilaun ; translated and edited by F.W. Oliver, with the assistance of Marian Busk and Mary F. Ewart ; with about 2000 original woodcut illustrations and sixteen plates in colours. Source: Wellcome Collection.

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    be remarked that the water absorbed by the plants only partly enters into chemical combination with the materials of the cell-body and cell-wall; that another part, which we have called the water of imbibition, is not chemically combined. The cell-wall and cell-body are saturated with this latter, and the cell-sap in the vacuoles of the protoplasm also contains a large quantity of such water. In the cell-sap it appears as the solvent of the acids, salts, and other materials there present. The water by which the protoplasm and cell-walls are saturated, and which we must imagine filling the interstices, like capillary spaces, between the groups of molecules, is indeed held fast by the molecules of the protoplasm and cell-wall, and the water in the cell-sap by the molecules of acids and salts, but yet certainly not so energetically as the chemically-combined water in the albuminous substances of the protoplasm. What happens now in a body which holds fast the water in its smallest interstices, like paste, for example, or in which the water appears as a solvent as in an alum solution, when warmth is withdrawn, and when it is cooled down to the freezing point of water? It is very remarkable that the water does not immediately stiffen into ice as long as it is retained in the capillary spaces, or as a solvent, and many salt-solutions can be cooled down to 5° C., some even to 10°, below zero without freezing. When at length under the influence of still lower temperatures a stiffening occurs, a separation has always taken place previously; the water has run together from the finest interstices of the paste into its larger spaces; it is first changed into ice in these cavities, and the water of the salt solution has separated from the molecules of salt, and is -then first changed into ice-crystals. The same thing occurs, however, with the water saturating the cell-wall and protoplasm, and serving as solvent of certain materials contained in the cells. The formation of ice occurs in a very few species only on cooling the plant-tissues down to —1°; in most instances the temperature must sink to — 2° or —3° in order that ice may be formed in the cooled tissue. And indeed the water here has sepa- rated from the molecules by which it was hitherto held fast before it congealed, and it does not freeze in the interior of the cells, but outside them in the inter- cellular spaces. In order that the water should get from the interior of the cell into the adjoining intercellular spaces, a pressing and squeezing is necessary, and this pressure can only proceed from the living protoplasm in the cell-chambers; consequently the process of freezing can be most correctly represented in this way, viz. that the protoplasm becomes stimulated and roused by the lowering of the temperature to transport a portion of the water from the interior to the exterior of the cell, by means of contraction and pressure. What happens there is accordingly not unlike the excretion of watery sap into the intercellular spaces in the stimulated pulvini on the leaf-stalk of Mimosa', but the advantage obtained by the excretion of water in the two cases is very different. In the cooled leaves the benefit of course is to be sought for in the fact that the living portion of the cells is protected from destruction as long as possible by the formation of ice-crystals in the inter-