. On the structure and affinities of Sigillaria, Calamites and Calamodendron [microform]. Paleobotany; Paléobotanique. ir>2 1'1U)CEKI>IX08 OF THE GKOLOOICAL SOClTrTT. ami Cycads, or with two, three, or four rows of such pores Bome- times iiiHcribed in hexagonal ureoles in the manner of Datloaiilon. This woody cylinder is traversed by medullary rays, which arc short, and comiwhcd of few rows of cells superimposed. It is also traversed by obli(iue rudiatinf; bundles of pscudo-scalariform tissue proceeding; to the lenves. In some Si^lllario' this outer cylinder was itself in ])art conii)ose
. On the structure and affinities of Sigillaria, Calamites and Calamodendron [microform]. Paleobotany; Paléobotanique. ir>2 1'1U)CEKI>IX08 OF THE GKOLOOICAL SOClTrTT. ami Cycads, or with two, three, or four rows of such pores Bome- times iiiHcribed in hexagonal ureoles in the manner of Datloaiilon. This woody cylinder is traversed by medullary rays, which arc short, and comiwhcd of few rows of cells superimposed. It is also traversed by obli(iue rudiatinf; bundles of pscudo-scalariform tissue proceeding; to the lenves. In some Si^lllario' this outer cylinder was itself in ])art conii)osed of psendo-scalariform tissue, as in Brong- niart's specimen of tS. tle(/aii8; and in others its jdace may liave been taken by nnilti\)orous tissue, as in a case above referred to; but I have no reason to believe that eitlier of these variations occurred in tho typical ribbed species now in (luestion. The woody fibres of the outer cylinder may be distinguished most readily from those of Conifers, as already mentioned, by the thinness of their walls, and the more irregular distribution of the pores. Additional characters arc furnished by the medullary rays and tho radiating bundles of Bcalariform tissue when these can be obseiTed. (d) An inner cylinder of pscudo-scalariform tissue. I have adopted tho term pscudo-scalariform for this tissue, from the con- viction that it is not homologous with the scalariform ducts of Ferns and other Acrogens, but that is merely a modification of the disci- gcrous wood-cells, with pores elongated trjmsversely, and sometimes separated by thickened bars, corresponding to the hexagonal arco- lation of tho ordinary wood-cells. A similar tissue exists in Cycads, and is a substitute for the spiral vessels existing inordinary Exogens. (e) A largo medulla, or pith, consisting of a hollow cylinder of cellular tissue, from which proceed numerous thin diai)hragm8 to- ward the centre of the stem. The structures above referred to may undoubtedly exist in di
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