. A handbook of cryptogamic botany. Cryptogams. FOSSIL VASCULAR CRYPTOGAMS 117 Although the genus Sigillaria is still placed by some writers among Gymnosperms, its true place is undoubtedly near to Lepidodendron in the order Selaginellacese; the structure of the stem presents no important difference ^ ^ from that of Lepido- dendron, while the fructification known as Sigillariostrobus bears a remarkable resemblance to Lepidostrobus. The remains of various species of Sigil- laria occur in enormous quantities in the coal measures ; and they constituted one of the predominant forms of vegetation o
. A handbook of cryptogamic botany. Cryptogams. FOSSIL VASCULAR CRYPTOGAMS 117 Although the genus Sigillaria is still placed by some writers among Gymnosperms, its true place is undoubtedly near to Lepidodendron in the order Selaginellacese; the structure of the stem presents no important difference ^ ^ from that of Lepido- dendron, while the fructification known as Sigillariostrobus bears a remarkable resemblance to Lepidostrobus. The remains of various species of Sigil- laria occur in enormous quantities in the coal measures ; and they constituted one of the predominant forms of vegetation of the period. The stems rivalled in height and thickness those of Lepidoden- dron, and were covered, like them, with the scars of fallen leaves in linear series. They were simple or dichotomously branched. The scars are circular, ovate, or hexagonal from mutual compression. In the section known as Leiodermaria the cushions which occur in other forms are wanting, and the scars stand out at a considerable distance from one another on the smooth surface of the stem. The leaves, which are occasionally found still attached to the branches, were narrow, linear, and sedge-like, up to as much as one and a half feet in length, with a projecting midrib. According to Van Tieghem the stem of Sigillaria differs from that of the Lepidodendrese, and indeed from that of all other Vascular Cryptogams, in the leaf-trace bundles being ' diploxy- lous'—that is, in the central cylinder having an external secondary and centrifugal as well as an internal primary and centripetal xylem. Renault regards the RhytidokpidcB, or Sigillarise with stem exhibiting raised cushions as well as scars, as Cryptogamic ; the Leiodermariea^ or smooth- stemmed Sigillariae, as Gymnospermic; but this view is not supported by a careful examination of the A, B, C, portions of surface of stem of different species of Sigillaria ; D, Leiodetmaria. (After Solms-Laubach. ] Fic-. Please note that these images are e
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