THE CARBONIFEROUS FLORA, 



ir,i 



and cycads, or with two, three, or four rows of siioh pores sometimes 

 inscribed in hexagonal areoles in the manner of Mu/orv/ora, This 

 woody cylinder is traversed \>y medullary rays, which tire short, and 

 composed of f(!W rows of ca-Ws su[U'riinposed. It is also traversed by 

 ol)li(pio radiating bundles of pseudo-sealariform tissue proceeding to 

 the leaves. In soiu(! Sit/if/nrun this outer cylinder was iiself in part 

 com[)osed of pscudo-sciilariform tissue, as in Jirongniart's specimen 

 of .S'. elcf/aiiM ; and in others its plucc; may have l)een taken by mul- 

 tiporous tissue, as iti a case alK)ve n^ferred to ; but I have no reason 

 to Ixdieve that either of these variations occurred in the typical 

 ribbed sjiecic^s now in question. Tfie woody filires of the outer 

 cylinder nuiy b(? distinguished most readily from tliosi; of conifers, 

 as already mentioncid, by the thinness of their walls, and the more 

 irregular distribution of the pores. Additional charact(!rs are fur- 

 nished by the nietlidlary rays and the radiating bundles of 8calari- 

 form tissues when these can be observed. 



d. An innifr cylinder of ps(!udo-scalariform tissue, I have 

 adopted the term ftseudo-scidariform for this tissue, from the con- 

 viction that it is not liortiologous with the scalar! fffrri' ducts of ferns 

 and other acrogi'iis, but that it is merely a modification of tin; dis- 

 c ,gerf)us wood-cells, wit h pores elongated t ransversely, and sonuitimes 

 separated by thic^kened bars, corres{)onding to the hexagonal areo- 

 lation of the ordinary wood-cells. A similar tissut; exists in cycads, 

 and is a substitutt; for the spiral vcssc^ls existing in (ordinary ex- 

 ogens. 



e. A large medulla, or pith, consisting of a hollow cylinder of 

 cellular tissue, from which proceed numc^rous thin diaphragms to- 

 wards the cent Hi of the stem. 



These structures of the highest type of Sigillaria are on the 

 one hand scarcely advanced b(!yond those of (JalninnpHun, as de- 

 scribed by Williamson, and on the other a[)proach to those of 

 (jordaitPH, as seen in specimens presented to mr- by Renault. 



Finally, as to the fruit of JSir/illarid', I Imvo no new facts to 

 ofT(!r. The strobiles or sjiikes associated with these trees have Ijcen 

 variously described as gymno.^permous (]((;nault) or cryptogamous 

 ((loldenberg and Williamson). I have never seen them in plaoe. 

 Two considerations, however, have always weighetl with me in refer- 

 ence to this subj(!ct. One is the constant abundance of Trigotiocarpa 



hexagonal rim of thickenod wall ; but in all cases these Htnicturcs arc 

 less pionoimeed than in I)tiilori//i>n, and less regidar in tlie walls of the 

 liuiiie ceil, aa well us in dilTcrcnt layers of the tiesucs of the axia. 



