| 1833. | Galium sphenophylloides, Zenker[673]. |
| 1865. | Annularia brevifolia, Heer[674], Strobilus. |
| 1876. | Calamostachys (Stachannularia) calathifera, Weiss[675]. |
Principal branches 8–12 mm. wide, with internodes 8–10 cm. in length, giving off two opposite branches at the nodes; from the secondary branches arise smaller branches in opposite pairs. The leaf-verticils and branches are all in one plane. Each verticil consists of 12–18 spathulate segments, 3–10 mm. long, cuneiform at the base and broader above, with an acuminate tip; the lateral segments are slightly longer than the upper and lower members of a whorl.
The small and crowded leaf-whorls give to this species a characteristic appearance, which readily distinguishes it from the larger-leaved forms such as Annularia stellata. A fossil figured by Lhwyd[676] in 1699 as Rubeola mineralis is no doubt an example of Annularia sphenophylloides.
Annularian branches are occasionally found with cones given off from the axils of some of the leaf-whorls. An interesting specimen, which is now in the Leipzig Museum, was described by Sterzel in 1882[677], showing cones attached to a vegetative shoot of Annularia sphenophylloides. The long and narrow strobili—2·5 cm. long and about 6 mm. broad—appear very large in proportion to the size of the vegetative branches. A fertile shoot consists of a central axis bearing whorls of bracts alternating with sporangiophores, to each of which are attached four sporangia. The specimen in fig. 89, A, does not show the details clearly; each transverse constriction represents the attachment of a whorl of linear bracts; the whole cone appears to consist of a series of short broad segments. The divisions in the lower half of each segment mark the position of the sterile bracts, while those of the upper half represent the outlines of the upper sporangia of each whorl of sporangiophores, the lower sporangia being hidden by the ring of linear bracts[678]. On some portions of the specimen of fig. 89, A, it is possible to recognise the outlines of cells on the coaly surface-film; these probably belong to the sporangium wall. This type of cone is included under the genus Calamostachys, a name applied to Calamitean strobili with certain morphological characters, as described on p. 351.
c. Roots.
In 1871 Williamson[679] described some sections of what he considered to be a distinct variety of a Calamite stem. The chief peculiarity which he noticed lay in the absence of carinal canals, and in the solid pith. Some years later the same observer[680] came to the conclusion that the specimens were probably those of a plant generically distinct from Calamites; he accordingly proposed a new name Astromyelon. Subsequently Cash and Hick[681] gave an account of some examples of apparently another form of plant, to which they gave the name Myriophylloides Williamsonis; and Williamson[682] suggested the term Helophyton as a more suitable generic designation. It was, however, demonstrated by Spencer[683] that the plant described by Cash and Hick was identical with Williamson’s Astromyelon. Williamson[684] then gave an account of several specimens of this type illustrating various stages in the growth and development of the Astromyelon ‘stems,’ which he compared with the rhizome of the recent genus Marsilia.
In 1885 Renault[685] published an account of Astromyelon in which he brought forward good evidence in favour of regarding it as a Calamitean root. The same author has recently given some excellent figures and a detailed description of certain specific types of these Calamite roots, and Williamson and Scott’s memoir on the roots of Calamites has rendered our knowledge of Astromyelon almost complete. Some of the finest specimens, in which the organic connection between typical Calamite stems and Astromyelon roots is clearly demonstrated, are in the Natural History Museum, Paris. There are several sections also from English material which show the connection between root and stem very clearly.
Fig. 90. Pith-cast of a Calamite stem, with roots; embedded in sandstone and shale. (After Grand’Eury.) Much reduced.
Casts of the hollow pith of Calamite rhizomes or aerial branches are occasionally found in which slender appendages are given off either singly or in tufts from the nodal regions. Many examples of such casts have been figured by Lindley and Hutton[686], Binney[687], Grand’Eury[688], Weiss[689], Stur, and other writers[690]. The large stem-cast of fig. 90 illustrates the manner of occurrence of long branched roots on the nodes of a Calamite growing in sandy or clay soil. The lower and more darkly shaded portion of the specimen is covered by a layer of coal representing the carbonised wood and cortex, which has been moulded on to the sandstone pith-cast. In fig. 77 (p. 316) a fairly thick root is seen, in organic connection with one of the nodes, N 3, and on N 2 there is a scar of another root.