On the forms and structure of fern-stems / by George Ogilvie.

  • Ogilvie, George
Date:
1859
Catalogue details

Licence: Public Domain Mark

Credit: On the forms and structure of fern-stems / by George Ogilvie. Source: Wellcome Collection.

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    form tissue, ensheatlied in a layer of brownish pleurenchynia, and separated by large open meshes, through which the cellular tissues of the central and cortical regions are freely continuous with each other (PI. X. fig. 11). The pile of superposed trun¬ cated cones, diagrammatically representing the Exogenous stem —already cut down all to one length, and more opened at the top to adapt them to the Endogenous type—must now be re¬ duced to a series of simple rings placed one upon another. On a longitudinal section along the axis, a fern-stem presents a uniform expanse of cellular tissue, marked only by an inter¬ rupted line near each margin, indicating the position of the fibro-vascular bundles of the reticulated cylinder, the interrupted spaces answering to the meshes of the network (fig. 10). On a horizontal section we have a corresponding interrupted circle formed by the cut extremities of the fibro-vascular anastomosing cords (fig. 12). This circle divides the section into a large central and a smaller cortical region, both composed of cellular tissue, as in the Monocotyledonous stem, but without the descending fibres which form so conspicuous a feature in the interior of the latter. In a certain point of view, these regions correspond to the pith and cellular bark of a young Dicotyledonous stem, in which the cellular tissue has not yet been displaced by the fibro-vascular element; and the interspaces of the reticulations may be held to represent the medullary rays. Indeed, in all the fibrous tissues of Dicotyledonous plants a tendency may be observed to such an interlacement about the medullary rays: it is quite ob¬ vious to the naked eye in the bast-fibres of the Lime and many other trees; it has been noticed in the medullary sheath of Conifei’se, and it may be seen with great distinctness under the microscope, in tangental sections of mahogany and other hard woods. The stems of Tree-ferns are said to be generally hollow, but the eharacter is not an essential one. Fistulous stems are well known to occur both in Endogenous and Exogenous plants*, and ])robably always depend on the shrinking of a lax cellular tissue originally filling the space. Hollow stems are not described as occurring in any of our indigenous Ferns, but it may generally be observed that in the decayed portions of a rhizome the central cellular tissue is the first to disappear. The most elegant and instructive preparation of a fern-stem is made by dissecting off the outer cortical layer so as to expose the reticulated structure of the fibro-vascular cylinder. Two sets of fasciculi will then be seen to be connected with its exterior, * Til Endogens, the Cocoa-nut and other Palms and most grasses, in Exogens, many Umbelliferaj, Compositac, and Labiatae furnish instances of this.
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