Casts of Calamites Suckowi are characterised by flat or slightly convex internodal ridges separated by shallow depressions, the ridges are rounded at the upper end of each internode, and usually bear circular casts of infranodal canals. There are some unusually large examples of casts of this species in the British Museum from the Radstock Coal-Measures; one of these has a length of 81 cm., and a diameter of 27 cm. Specimens are not infrequently found with verticils of slender roots in close proximity to the nodes of the cast; figures of such root-bearing casts have been given by Lindley and Hutton[808], Weiss[809], and other authors.
Renault[810] has drawn attention to the thinness of the layer of wood which is often associated with large casts of C. Suckowi; he concludes that the stems must have possessed little or no secondary wood. In a more recent work by Grand’Eury[811] Calamites Suckowi is spoken of as having had wood of the Calamodendron type, but as wood of this kind has not been found in England, it is suggested that the plant may not have assumed an arborescent habit until late in the Coal-Measure period. During the Lower and Middle Coal-Measures, at which horizon it commonly occurs in England, it may have been herbaceous. This suggestion has little to commend it; the close agreement between C. Suckowi from English and French localities points to a plant of the same form, and we have no satisfactory evidence as to any difference in stem-structure in the two cases.
Stur has figured a specimen of a Calamite cast, which he compares with C. Suckowi, surrounded by a band of silicified wood apparently of the Arthropitys type. From this and other facts it would appear probable that some of the English stems with the Arthropitys structure possessed casts referable to Calamites (Stylocalamites) Suckowi.
We are not in a position to speak with confidence as to the strobili of C. Suckowi, but Stur adduces evidence in support of a connection between this species of Calamite and certain Asterophyllitean branches (Calamocladus equisetiformis) bearing Calamostachyan cones. He does not appear to have found the foliage-shoots and stems in organic contact, but draws this conclusion from the association of the fertile branches and stems in the same rocks[812]. This species is abundant in the Lower, Middle and Upper Coal-Measures; it has also been recorded from the Millstone Grit[813].
C. Eucalamites.
In this sub-genus branch-scars occur on every node; the scars never form a contiguous whorl as in Calamitina, but there may be from 3 to 10 on each node. The scars of successive nodes often alternate in position, and thus form more or less regular vertical series as shown in fig. 102. The most obvious feature as regards the arrangement of the branch-scars is their spiral disposition on the surface of the pith-cast. The internodes are fairly uniform in length, and there is no periodic recurrence of narrower internodes as in Calamitina. From an examination of specimens of Eucalamites in which the pith-cast is covered with a coaly layer representing the carbonised remains of the wood and cortex, it would appear that the surface of the stems was practically smooth. The coaly investment on Eucalamites casts varies considerably in thickness[814]; it is very unsafe to make use of the thickness of this layer as a test of the breadth of the wood in Calamitean stems. The branch-scars as seen in a surface-view of a stem are situated a little above the nodal lines, while depressions on the pith-casts occur in the slight nodal constriction or immediately above it. Small leaf-scars have been described as occurring on the nodes between the branch-scars in specimens showing the surface features[815].
The species long known as Calamites cruciatus Sternb. is usually taken as the type of the sub-genus Eucalamites. Weiss[816] has subdivided this species into several ‘forms,’ which he bases on the number of branch-scars on each node and on other characters; a more extended subdivision of C. cruciatus has recently been made by Sterzel[817], who admits the impossibility of separating the specific forms by means of the data at our disposal, but for purposes of geological correlation he prefers to express slight differences by means of definite ‘forms’ or varieties. The more comprehensive use of the specific name cruciatus as adopted by Zeiller in his Flore de Valenciennes[818] is, I believe, the better method to adopt. The specimen shown in fig. 102 affords a good example of a typical Calamites cruciatus, it was found in the Middle Coal-Measures near Barnsley, Yorkshire.
Fig. 102. Calamites (Eucalamites) cruciatus, Sternb.
From a specimen in the Barnsley Museum, Yorkshire. ½ nat. size.
Calamites (Eucalamites) cruciatus (Sternb.). Fig. 102.