In this genus the general habit agrees with that of Calamostachys, and in imperfectly preserved specimens it may be impossible to discriminate between Calamostachys and Palaeostachya. The latter form is characterised by the attachment of the sporangiophores in the axil of the sterile bracts, or immediately above them, as shown in figs. 97 and 98.

Examples. Palaeostachya vera sp. nov., P. pedunculata Will. afford examples of this form of strobilus. The genus Palaeostachya includes several species previously described under the genus Volkmannia[734].

Strobili of this generic type are known in organic association with Annularian branches, as well as with Calamocladus and Calamites.

This generic name was originally applied by Schimper[735] to certain forms of Calamitean stems, of the type afterwards referred to the sub-genus Calamitina by Weiss, bearing long and thick cones. The name is, however, more appropriately restricted to strobili, which differ from the two preceding genera in their greater length (14–16 cm.) and in the more crowded and imbricating whorls of bracts. The internodes of the cones are very short, and each whorl of bracts consists of about 20 coherent members separated at the periphery of the disc into short pointed teeth. The internal structure of Macrostachya has not been satisfactorily determined. An account by Renault[736] of a petrified specimen does not present a very clear idea as to the structural features of this form of Calamitean strobilus.

The generic name Huttonia, suggested by Sternberg[747] in 1837, is applied to cones which closely resemble Macrostachya in habit, but differ—so far as our scanty knowledge enables us to judge—in the arrangement of the members. The student must refer to Weiss[748], Solms-Laubach[749] and other writers[750] for a further account of these types, and of another rare and little-known form of cone, called by Weiss Cingularia[751].

Macrostachyan cones have been found attached to stems of Calamites which are included in the sub-genus Calamitina (p. 367). The larger size of Macrostachya as a distinguishing feature is not always a safe test; some cones which belong to Palaeostachya [e.g. P. arborescens Sternb.] and Calamostachys (e.g. C. Solmsi) are much thicker and larger than the majority of species of these two genera.

It would appear from the examples selected to illustrate the connection between strobili and vegetative shoots, that the Annularia type of branch usually bears cones which conform to the genus Calamostachys (Stachannularia); while the Asterophyllitean branches—Calamocladus—are associated with Palaeostachya and Macrostachya. But this rule is not constant, and we are not in a position to speak of cones of a particular type as necessarily characteristic of definite types of Calamitean shoots.

Although it is admitted by the great majority of Palaeobotanists that the Calamites were all true Vascular Cryptogams, the older view that some members of the Calamarieae are gymnospermous has not been given up by Renault[752]. This observer has recently described some seeds which he believes were borne by Calamitean stems; he admits, however, that no undoubted female cones of Calamodendron have so far been found. In view of the unsatisfactory evidence on which Renault’s opinion is based, we need not further discuss the questions which he raises.

[The following specimens in the Williamson Cabinet in the British Museum, may be found useful in illustration of the structure of Calamites.

Stems. (i. Arthropitys.) Young twigs and small branches 1, 2, 6, 10, 14, 19, 116*, 1002, 1007, 1020.

Older stems (transverse sections) 15–17, 62, 77–87, 115 a, 117*, 118*, 120, 122*–124*, 1933 A, 1934, 1941.

(Tangential sections) 20, 24, 26, 37, 38, 49, 90, 91, 130, 138, 1937, 1943.

(Radial sections) 20, 20 A, 21, 22, 48, 65–68, 83–91, 137*, 138*, 1937.

(ii. Arthrodendron) 36, 37, 38, 52, 54.

Roots. 1335, 1347, 1350, 1356.

Strobili. i. Calamostachys Binneyana. 991, 996, 997, 1000, 1003, 1005, 1007, 1008, 1011, 1013, 1016, 1017, 1022, 1023, 1037 A, 1043.

ii. C. Casheana. 1024, 1025, 1587, 1588.

iii. Palaeostachya vera. 110, 1564, 1567, 1569, 1579, 1583.]

III. Pith-casts of Calamites.

Palaeobotanical literature contains a large number of species of Calamites founded on pith-casts alone. Many of these so-called species are of little or no value botanically, but while we may admit the futility of attempting to recognise specific types in the same sense as in the determination of recent plants, it is necessary to pay attention to such characters as are likely to prove of value for descriptive and comparative purposes. From the nature of the specimens it is clear that many of the differences may be such as are likely to be met with in different branches of the same species, while in others the pith-casts of distinct species or genera may be almost identical.

The most striking differences observable in Calamite casts are in the character of the internodes, the infranodal canals, the number and disposition of branch-scars, and other surface features. Occasionally it is possible to recognise certain anatomical characters in the coaly layer which often surrounds a shale- or sandstone-cast, and the surface of a well preserved cast may give a clue to the nature of the wood in the faint outlines of cells which can sometimes be detected on the cast itself[753]. The breadth of the carbonaceous envelope on a cast has been frequently relied on by some writers as an important character. It has been suggested[754] that we may arrive at the original thickness of the wood of a stem by measuring the coaly layer and multiplying the breadth by 27; the explanation being that a zone of wood 27 mm. in thickness is reduced in the process of carbonisation to a layer 1 mm. thick.

The breadth of the coal on the same form of cast may vary considerably; on this account, and for various other reasons, such a character can have but little value. Our knowledge of anatomy may often help us to interpret certain features of internal casts and to appreciate apparently unimportant details. One occasionally notices that a Calamite pith-cast has large infranodal canals, and in some specimens each internodal ridge may be traversed by a narrow median line or small groove; large infranodal canal casts suggest the type of stem referred to the subgenus Arthrodendron, and the median line on the ridges may be due to bands of hard tissue in each principal medullary ray.

In attempting to identify pith-casts the student must keep in view the probable differences presented by the branching rhizome, the main aerial branches and the finer shoots of the same individual. The long internodal ridges of some casts may be mistaken for the parallel veins of such a leaf as Cordaites, a Palaeozoic Gymnosperm, if there are no nodes visible on the specimen. The fossil figured by Lindley and Hutton[755] as Poacites, and regarded by them as a Monocotyledon, is no doubt a portion of a Calamite with very long internodes. An interesting example of incorrect determination has recently been pointed out by Nathorst[756] in the case of certain casts from Bear Island, originally described by Heer as examples of Calamites; the vertical rows of leaf-trace casts on a Knorria were mistaken for the ribs of a Calamite stem. The specimens in the Stockholm Museum fully bear out Nathorst’s interpretation. The undulating course of internodal ridges and grooves is not in itself a character of specific value. If a Calamite stem were bent slightly, the wood and medullary-ray tissues on the concave side might adapt themselves to the shortening of the stem by becoming more or less folded, and a cast of such a stem would show undulating ridges and grooves on one side and straight ones on the other[757].

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.

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.

We have so far noticed the connection of certain forms of pith-casts (e.g. Calamites approximatus), and Asterophyllitean shoots with stems of the sub-genus Calamitina.

As regards the strobili our knowledge is far from satisfactory. Stur[777] figures some fertile branches bearing long and narrow strobili, either Palaeostachya or Calamostachys, in close association with Calamitina stems, and Renault and Zeiller[778] give illustrations of the association of Calamitina stems with large strobili of the Macrostachya form.

Before Weiss proposed the term Calamitina, various authors had figured this form of Calamite under a distinct generic name (e.g. Hippurites of Lindley and Hutton[779], Cyclocladia[780], Macrostachya[781], &c.). Stems of this type have also been described by more recent writers under different names, and considerable confusion has been caused by the use of numerous generic designations for forms of Calamitina. Some small fragments of Calamitina stems were described by Salter[782] in 1863 as portions of a new species of the Crustacean Eurypterus (E. mammatus). In 1869 Grand’Eury proposed the generic name Calamophyllites[783] for stems bearing verticils of Asterophyllites shoots; his description of such stems agrees with Weiss’ Calamitina, but as Grand’Eury’s name is used in a narrower sense as implying a connection with Asterophyllites, it is more convenient to adopt Weiss’ term in spite of the priority of Calamophyllites. In the Fossil flora of Commentry we find some flattened stems of the Calamitina type described under different generic names, as Arthropitys approximatus[784] and as Macrostachya[785].

The determination of distinct species of the sub-genus Calamitina is rendered almost hopeless by the variation in the different branches of the same individual, and by the difficulty of connecting surface-impressions with casts of the pith-cavity.

A typical example of the Calamitina type of Calamites was figured by Sternberg[786] in 1821 as Calamites varians. This has been adopted by Weiss[787] as a comprehensive species including several different ‘forms’ of stems, which differ from Sternberg’s fossil in such points as the number of nodes between the branch-whorls and the number of branches in each whorl. The result of this system of nomenclature is the separation of portions of one specific type under different form-names. It must be clearly recognised that accurate specific diagnoses are practically impossible when we have to deal with fragments of plants, some of which are mere pith-casts, while others show the surface features. The specimen represented in fig. 99 agrees with a stem described by Ettingshausen[788] in 1855 as Calamites Göpperti, and as a matter of convenience a member of the Calamitina group showing such characters may be referred to as Calamites (Calamitina) Göpperti (Ett.). The following list, which includes a few synonyms of this form, may suffice to illustrate the difficulties connected with accurate systematic determinations.

This species is characterised by the smooth bark, which may be traversed by a few irregular longitudinal fissures; most of the nodes bear a series of small leaf-scars, and at fairly regular intervals a node is immediately succeeded by a circle of contiguous branch-scars, 8–12 in a whorl. The pith-cast of this type of stem has short ribbed internodes separated by rather deep nodal constrictions; the branch-whorls being represented by a series of pits on the nodal constrictions recurring at corresponding intervals to the whorls of branch-scars on the surface of the stem. Leaves narrow and linear in form, like those on Asterophyllitean branches, are occasionally associated with this type of stem.

The fragment of a Calamitina stem shown in fig. 101 is the counterpart of a specimen originally figured by Steinhauer[798] in 1818 as a species of Phytolithus. This may be specifically identical with C. Göpperti; but it is better to speak of so small a specimen as merely one of the Calamitina stems, to be compared with Calamites (Calamitina) Göpperti. The specimen measures 14·5 cm. in length and 7 cm. in breadth.

The form of pith-cast represented in fig. 100 is no doubt that of one of the Calamitina species, but as it is seldom possible to determine the connection between such casts and the particular species of stems to which they belong, they are often referred to as Calamites (Calamitina) approximatus (Brongn.). The specimen of which fig. 100 is a photograph was originally described and figured by Mr Kidston[799] from the lower Coal-Measures of Ayrshire. Both Calamites (Calamitina) Göpperti (Ett.) and C. (Calamitina) approximatus (Brongn.) are recorded from the Transition, Middle and Lower Coal-Measures[800].

In the members of this sub-genus the branch-scars are either irregular in their occurrence or absent. In some Calamites the branch-scars are very few and far between, and other species appear to have been almost without branches; pith-casts of such stems may be referred to the sub-genus Stylocalamites[801].

An exceedingly common Calamitean cast, C. Suckowi Brongn. (fig. 82) affords a good illustration of this type of stem. In the specimen shown in fig. 82 we have a cast of a rhizome, which is rather exceptional in showing three branches in connection with one another. The appearance of the fossil suggests a rhizome, rather than an aerial shoot, bearing lateral branches; the narrowing of the branches and the rapid decrease in the length of the internodes towards the point of attachment being features associated with rhizomes rather than with aerial branches.

For more complete lists of synonyms of this species reference should be made to Kidston[806], Zeiller[807], and other authors.

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].

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.

This species occurs in the Upper, Middle and Lower Coal-Measures[827]. The casts of the cruciatus type have been found associated with wood possessing the structural features of the sub-genus Calamodendron[828], but our knowledge of the structure of the stem, and of the fertile branches of C. cruciatus is very imperfect. A restoration of Calamites (Eucalamites) cruciatus is given by Stur[829] in his classic work on the Calamites, but he does not make quite clear the supposed connection with the stems and the fertile shoots of the Asterophyllites type[830] which he describes. Another member of the Eucalamites group, which is better known as regards its foliage-shoots, is Calamites ramosus, a species first described by Artis[831] in 1825. Stems of this species have been found in connection with the branches and leaves of the Annularia[6] type, bearing Calamostachys[832] cones. In all probability pith-casts included in the sub-genus Eucalamites belonged to stems with foliage-shoots and probably also with cones of more than one form.