In the following account of the Calamites, the generic name Calamites is used in a wide sense as including stems possessing different types of internal structure; when it is possible to recognise any of these structural types the terms Calamodendron, Arthropitys or Arthrodendron are used as subgenera. The reasons for this nomenclature are discussed in a later part of the Chapter.
| Genus Calamites, Suckow, 1714 | This term was originally applied to the common pith-casts of Calamitean stems, without reference to internal structure. |
| Subgenera | Calamodendron, | Brongniart, | 1849 | These names have primarily reference to internal structure. | |
| Arthropitys | Göppert, | 1864 | |||
| Arthrodendron | Scott | 1897 | |||
| (= Calamopitys | Williamson, | 1871 |
II. Description of the anatomy of Calamites.
a. Stems. b. Leaves. c. Roots. d. Cones.
No fossils are better known to collectors of Coal-Measure plants than the casts and impressions of the numerous species of Calamites. In sandstone quarries of Upper Carboniferous rocks there are frequently found cylindrical or somewhat flattened fossils, varying from one to several inches in diameter, marked on the surface by longitudinal ridges and grooves, and at more or less regular intervals by regular transverse constrictions. Similar specimens are still more abundant as flattened casts in the blocks of shale found on the rubbish heaps of collieries. The sandstone casts are often separated from the surrounding rock by a loose brown or black crumbling material, and the specimens in the shale are frequently covered by a thin layer of coal.
Most of the earlier writers regarded such specimens as the impressions of the ribbed stems of plants similar to or identical with reeds or grasses. Suckow, and afterwards Dawes and others, expressed the opinion that the ordinary Calamite cast represented a hardened mass of sand or marl, which had filled up the pith of a stem either originally fistular or rendered hollow by decay. The investigation of the internal structure confirmed this view, and proved that the surface-features of a Calamite stem do not represent the external markings of the original plant, but the form of the inner face of the cylinder of wood. The ribs represent the medullary rays of the original stem or branch, and the intervening grooves mark the position of the strands of xylem which are arranged in a ring round a large hollow pith[604].
With this brief preliminary account we may pass to a detailed description of the anatomical characters of Calamites.
The genus Calamites may be briefly defined as follows:—
Arborescent plants reaching a height of several meters, and having a diameter of proportional size. In habit of growth the Calamites bore a close resemblance to Equisetum; an underground rhizome giving off lateral branches and erect aerial shoots bearing branches, either in whorls from regularly recurring branch-bearing nodes, or two or three from each node; and in some cases the stems bore occasional branches from widely separated nodes. The leaves were disposed in whorls either as star-shaped verticils on slender foliage shoots, or in the form of a circle of long narrow leaves on the node of a thicker branch. Adventitious roots were developed from the nodal regions of underground and aerial stems. The cones had the form of long and narrow strobili consisting of a central axis bearing whorls of sterile and fertile appendages; the latter in the form of sporangiophores bearing groups of sporangia. The strobili were heterosporous in some cases, isosporous in others. The stems had a large hollow pith bridged across by a transverse diaphragm at the nodes in the centre of the single stele; the latter consisted of a ring of collateral bundles separated from one another by primary medullary rays. Each group of xylem was composed of spiral, annular, scalariform and occasionally reticulate tracheids, the position of the protoxylem being marked by a longitudinal carinal canal. The shoots and roots grew in thickness by means of a regular cambium layer. The cortex consisted of parenchymatous and sclerenchymatous cells, with scattered secretory sacs. The increase in girth of the central cylinder was often accompanied by a considerable development of cortical periderm. The roots differed from the shoots in having no carinal canals, and in the possession of a solid pith and centripetally developed primary xylem groups alternating with strands of phloem.