A convenient classification of Calamite casts was proposed by Weiss in 1884, founded chiefly on the number and manner of occurrence of branch-scars—or rather branch-depressions—on the surface of pith-casts. Weiss[758] recognised the imperfection of his proposed grouping, and Zeiller[759] has also expressed reasonable doubts as to the scientific value of such group-characters. Weiss instituted three subgenera—Calamitina, Eucalamites and Stylocalamites, which are made use of as convenient terms in descriptive treatment of Calamite casts. The following account of a few of the more typical casts may serve to illustrate the methods employed in the description of such specimens; the synonomy given for the different species is not intended to be complete, but it is added with a view to drawing attention to the necessity for careful comparison in systematic work.
A. Calamitina.
Fig. 99. Calamites (Calamitina) Göpperti (Ett.). b, branch scars.
From a specimen in the Manchester Museum, Owens College. ¼ nat. size.
This sub-genus of Calamites, as instituted by Weiss[760], includes Calamitean stems or branches, which are characterised by the periodic occurrence of branch-whorls usually represented by fairly large oval or circular scars just above a nodal line (figs. 99, 100 and 101). The branch-scars may form a row of contiguous discs, or a whorl may consist of a smaller number of branches which are not in contact basally. A form described by Weiss as C. pauciramis, Weiss[761], has only one branch in each whorl, as represented by a single large oval scar on some of the nodes of the cast. A stem of this form is by no means a typical Calamitina, but it serves to show the existence of forms connecting Weiss’ sub-genera Calamitina and Eucalamites. The number of internodes and nodes between the branch whorls varies in different specimens, and is indeed not constant in the same plant. Each nodal line bears numerous elliptical scars which mark the points of attachment of leaves; each branch-whorl is situated immediately above a node, and in some forms this nodal line pursues a somewhat irregular course across the stem, following the outlines of the several branch-scars[762]. The surface of the internodes is either perfectly smooth or it is more frequently traversed by short longitudinal ridges or grooves probably representing fissures in the bark of the living stem; these are indicated by lines in fig. 99 and by elongated elliptical ridges in fig. 101. On young stems the leaves are occasionally found in place, as for example in an example figured by Weiss[763] (C. Göpperti), or we may have leaf-verticils still in place in much older and thicker branches[764] (cf. fig. 85, p. 330).
It occasionally happens that the bark of Calamitina stems has been preserved as a detached shell[765] reminding one of the sheets of Birch bark often met with in forests, the separation being no doubt due in the fossil as in the recent trees to the manner of occurrence of the cork-cambium.
In a few cases branches have been preserved still attached to a stem or branch of higher order; examples of such specimens are figured by Lindley and Hutton[766], Stur[767], and others. Grand’Eury[768] has given an idealised drawing of a typical Calamitina bearing a whorl of branches with the foliage and habit of Asterophyllites equisetiformis. The specimen on which this drawing is based is in the Natural History Museum, Paris; it shows Asterophyllitean branches in organic connection with a Calamitean stem, but it is not quite clear if the stem is a true Calamitina. A large drawing of this interesting specimen is given by Stur[769] in his monograph on Calamites, also a smaller sketch by Renault[770] in his Cours de botanique fossile. Similar branches of the Asterophyllites type attached to an undoubted Calamitina are figured also by Lindley and Hutton. There is, in short, good evidence that stems of this sub-genus bore branches with Asterophyllitean shoots.
The wood of stems of the Calamitina group of Calamites, in some instances at least, was of the Arthropitys type; this has been shown to be the case in some French specimens from the Commentry coal-field[771] and in others described by Stur[772]. The pith-casts of Calamitina are characterised by comparatively short internodes separated by deep nodal constrictions, as shown in fig. 100. From Permian specimens from Neu Paka in Bohemia, described by Stur[773], we learn that there were the usual Calamite diaphragms bridging across the wide pith-cavity at each node. Such a cast as that shown in fig. 100 is often referred to as Calamites approximatus Brongn.; the length of the internodes and the periodic occurrence of branch-scars in the form of circular or oval depressions along a nodal line enable us to recognise the Calamitina casts. Weiss[774] points out that in pith-casts of this form the branch-scars occur on the nodal constriction, and not immediately above the node as is the case on the surface of a typical Calamitina. This distinction is however of little or no value; the point of attachment of a branch may be above the nodal line, while on the pith-cast of the same stem the point of origin of the vascular bundles of the branch is on the nodal constriction[775].
The specimen shown in fig. 100 illustrates the appearance of a Calamitina cast. There is a verticil of branch-scars on the lowest nodal constriction; on the right of the pith-cast the broad band of wood is faintly indicated by the smooth surface of the rock (x). Other examples demonstrating the existence of a broad woody cylinder in Calamitina stems have been figured by Weiss[776] and other writers, and some good examples may be seen in the British Museum.
