Each whorl contains 16–32 segments, which are connected basally into a collar or narrow sheath; the lateral segments are usually longer than the upper and lower. The branches are about 6–20 mm. broad, with finely ribbed internodes 3–7 cm. long, bearing verticils of leaves; the ultimate branches arise in pairs in the axils of the lateral segments of the verticils.

The strobili are of the Calamostachys[670] type and are borne on the main branches or possibly on the stem; they have a long and narrow form and are attached in verticils at the nodes. Each strobilus consists of a central axis bearing alternate whorls of linear lanceolate sterile bracts and sporangiophores, about half as numerous as the sterile bracts; each sporangiophore bears four ovoid sporangia.

The anatomical structure of a specimen referred to Annularia stellata has been described by Renault[671]. The cortex consists of parenchyma traversed by lacunae and limited peripherally by a denser hypodermal tissue. In the stele Renault describes 14 xylem strands, each with a large carinal canal. The pith was apparently large and hollow. The same author describes an Annularia strobilus in which the lower sporangiophores bear macrosporangia, and the upper microsporangia.

The references in the footnote should be consulted for figures of this species of Annularia; it is from the examination of such specimens as are referred to in the note that the above diagnosis has been compiled[672].

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.

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.

There are certain external characters by which one may often recognise a Calamitean root. There is no division into nodes and internodes as in stems, and as the pith of the root was usually solid the parallel ribs and grooves of stem-casts are not present. In smaller flattened roots there may sometimes be seen a central or excentric black line representing the stele, and the surface of the root presents a curious wrinkled or shagreen texture, probably due to the shrinkage of the loose lacunar cortex. The occasional excentric position of the stele is no doubt due to the displacement of the vascular cylinder as a result of the rapid decay of the cortical tissues. In the Bergakademie of Berlin there are some unusually good examples of Calamite casts bearing well-preserved root-impressions; these include the original specimens figured by Weiss[691].

No doubt some of the roots figured by various writers under the names Pinnularia[692] and Hydatica[693] belong to Calamites, but it is often impossible to identify detached specimens with any certainty.

The section figured diagrammatically in fig. 91 A shows the characteristic single series of large lacunae, l, in the middle cortical region. In the centre there is a wide solid pith surrounded by a ring of vascular tissue, x. The appearance of the middle cortex is very like that of the stem of a water-plant such as Myriophyllum, the Water Milfoil; it shows that the Calamite roots grew either in water or swampy ground. In fig. 91 B, the root characters are clearly seen; the centre of the stele is occupied by large parenchymatous cells which are rather longer than broad in longitudinal view; at the periphery there are four protoxylem groups px, alternating with four groups of phloem, ph, the latter being situated a little further from the centre of the stele. The structure is therefore that of a typical tetrarch root. In the example represented in the figure secondary thickening has begun, and the cambial cells internal to each phloem group have given rise to a few radially disposed tracheids, x². Beyond the phloem there are two layers of parenchyma representing, as regards position, a pericycle and an endodermis. In the ordinary pericycle and endodermis of the roots of most plants the cells of the two layers are on alternate radii, but in the Calamite root, as in Equisetum roots, the cells of these layers are placed on the same radii, as seen in the neighbourhood of x² in the figure. This correspondence of the radial walls of the endodermal and pericyclic cells points to the development of both layers from one mother-layer, and suggests the ‘double endodermis’ or phloeoterma of Equisetum (p. 254). The cells in the outer of these two layers have slight thickenings on the radial walls recalling the usual character of endodermal cells. The phloeoterma is succeeded by a few layers of parenchyma, constituting the inner cortex, and beyond this we have the large lacunae separated from one another by slender trabeculae of cells. The outer cortex is limited by a well-defined layer of thick-walled cells, which may be spoken of as the epidermoidal[694] layer. Roots possessing this superficial layer of thicker cells have no doubt lost the original surface-layer which produced the absorptive root-hairs.

The xylem elements have the form of spiral, reticulate and scalariform tracheids.

In roots or rootlets smaller than that shown in fig. 91 B, the primary xylem may extend to the centre of the stele, and form a continuous axial strand; in such examples the structure may be diarch, triarch or tetrarch. The origin of the cambium agrees with that in recent roots, the cells immediately external to the protoxylem tracheids become meristematic, as also those internal to the phloem. Another root-character is seen in the endogenous origin of lateral members. Good examples of branching roots are figured by Williamson[695] and by Williamson and Scott[696].

Older roots[697] are usually found in a decorticated condition. A transverse section of root in which secondary thickening has been active for some time presents on a superficial view a close resemblance to a stem of Calamites, but a careful comparison at once reveals important points of difference. The specimen diagrammatically sketched in fig. 92 illustrates very clearly the origin of a root from the node of a Calamite stem. The section has passed through a stem in a tangential direction, showing the characteristic arrangement of the vascular bundles x, and principal medullary rays m. The small leaf-traces, t, t, afford another feature characteristic of a Calamite stem. The portion of stem to the right of the figure has been slightly displaced, and between this piece and the root R, one of the ubiquitous Stigmarian appendages, s, has inserted itself. At R a fairly thick and decorticated root is seen in oblique transverse section; at the upper end the root tracheids are seen in direct continuity with the xylem of the stem. In the centre of the root is the large solid pith surrounded by twelve bluntly pointed xylem groups, composed in the main of radially disposed scalariform elements with narrow secondary medullary rays like those in a stem. Between each xylem group there is a broad medullary ray, which tapers rapidly towards the outside, and is soon obliterated by the formation of interfascicular secondary xylem. At R′ a portion of another root is seen in transverse section, and R″ the inner part of a single xylem group is shown more clearly. The solid pith and the absence of carinal canals are the two most obvious distinguishing features of the roots.

As Renault points out, roots of Calamites have been figured by some writers[698] as examples of stems, but it is usually comparatively easy to distinguish between roots and stems. On examining the xylem groups more closely, one notices that the apex of each is occupied by a triangular group of centripetally-developed primary tracheids, the narrow spiral protoxylem elements occupying the outwardly directed apex. The protoxylem apex is usually followed externally by a ray of one or two radially disposed series of parenchymatous cells. This ray is not distinguished in fig. 92 R″ from the rows of xylem tracheids. Each xylem group is thus formed partly of centripetal xylem and in part of secondary centrifugal xylem; the latter is associated with secondary medullary rays, as in stems, and contains a broader ray (fascicular ray of Williamson and Scott[699]) immediately opposite each protoxylem strand. In the roots of recent plants (e.g. Cucurbita, Phaseolus, &c.) a broad medullary ray is often found opposite the protoxylem, and such an arrangement is a perfectly normal structure in roots[700].

Renault has recently described several species of Calamite roots which he designates by specific names, some of them belonging to stems with the Arthropitys structure, and others to Calamodendron. Some of the roots figured by the French author have an axial strand of xylem with 7–15 projecting angles of protoxylem[701]. These he considers true roots, but the larger specimens with a wide pith he prefers to regard as stolons. In the latter he mentions the union of the primary centripetal with the secondary centrifugal wood as a distinguishing feature. It has been shown, however, that each group of secondary xylem includes a median ray of parenchyma, and that the whole structure is essentially that of a root, and not that of a modified stem or stolon. The organs described by Renault as true roots are probably rootlets, and as Williamson and Scott have demonstrated, there is every gradation between the smaller specimens with a solid xylem axis and those with a large central pith.

It is interesting to note that Renault’s figures of Calamodendron roots show the closest resemblance to those of the subgenus Arthropitys.

d. Cones.

The occurrence of fossil plants in the form of isolated fragments is a constant source of difficulty, and is well illustrated by the numerous examples of strobili which cannot be connected with their parent stems. We are, however, usually able to recognise Calamitean cones if the impressions or petrified specimens are fairly well preserved, but it is seldom possible to correlate particular types of cones with the corresponding species of foliage-shoots or stems. Palaeobotanical literature contains numerous illustrations and descriptions of long and narrow strobili designated by different generic terms such as Volkmannia, Brukmannia, Calamostachys, Macrostachya and others; many of these have since been recognised as the cones of Calamites, while some species of Volkmannia have been identified with Sphenophyllum stems. Before further considering the general question of Calamite cones, a few examples may be described in detail as types of fructification which are known to have been borne by Calamites. The examples selected are species of the two provisional genera Calamostachys and Palaeostachya.

The usual form of a Calamite cone is illustrated in fig. 93, which represents a fertile shoot bearing a few narrow linear leaves of the Calamocladus type; in the axils of some of these are borne the long strobili.

In 1867 Carruthers[702] gave an account of the structural features of the species of cones named by him Volkmannia Ludwigi and V. Binneyi, the generic term having been originally used by Sternberg[703] for some impressions of Carboniferous strobili. Brongniart[704] in 1849 referred to the various forms of Volkmannia as cones of Asterophyllitean branches, and the latter he regarded as the foliage-shoots of a Calamite stem. In 1868 Binney[705] published a description, with several illustrations, of the cones named by Carruthers Volkmannia Binneyi, and referred to them as the fructification of that type of Calamite stem spoken of in a previous section of this chapter (p. 311) as Calamites (Arthropitys) communis (Binney). This cone is now usually spoken of as Calamostachys Binneyana; the specific name Binneyana being suggested by Schimper[706] in 1869 as more euphonious than that proposed by Carruthers. In recent years our knowledge of both C. Binneyana and C. Ludwigi has been considerably extended. We shall confine our attention in the following account to the former species[707]. Some excellent figures of the latter species may be found in Weiss’ Memoir[708] on Calamarieae.

One of the largest examples of Calamostachys Binneyana so far recorded has a length of 3–4 cm. and a maximum diameter of about 7·5 mm. The axis of the cone bears whorls of sterile leaves or bracts at equal distances; the linear bracts of each whorl are coherent basally as a disc or plate of tissue attached at right angles to the central axis of the cone. The periphery of each of these discs divides up into twelve linear segments, which curve upwards in a direction more or less parallel to the strobilus axis, and at right angles to the coherent portion of each whorl. The manner of occurrence of the whorls is shown in fig. 94, which has been sketched from a large section in the Williamson collection. The segments of the successive sterile verticils alternate with one another, so that in the surface-view of a cone the long and narrow free bracts appear spirally disposed. Midway between these alternating sterile verticils there is a series of fertile appendages, also given off in regular whorls. Each fertile whorl consists of about half as many members as the segments of a sterile whorl, and the members of the several fertile whorls are superposed and not alternate. Each member has the form of a stalk or sporangiophore given off at right angles from the cone axis; this is expanded distally into a peltate disc bearing four sporangia attached to its inner face. In fig. 94 we can only see the basal portions of the sporangiophores, which are shown in the upper part of the sketch as pointed projections, Sp, from the cone axis. Each sporangiophore is traversed by a vascular strand which sends off a branch to the base of a sporangium (fig. 95, A, t).

The axis of the cone is occupied by a single stele, usually triangular in section; the stele consists of a solid pith of elongated cells surrounded by six vascular bundles, two at each corner. A somewhat irregular gap marks the position of the protoxylem of each strand, and portions of spiral or annular tracheids may occasionally be seen in the cavity. These cavities, which may be spoken of as the carinal canals, disappear at the nodes, where there is a mass of short reticulately pitted tracheids, as in a Calamite stem. Vascular bundles pass upwards in an oblique direction from the central stele to supply the bracts, each of which is traversed by a single strand of tracheids. The coherent portion, or disc, of each sterile whorl consists of sclerenchymatous elements towards the upper surface, and of parenchyma below. The pedicel of the sporangiophores consists of fairly thick-walled cells traversed by a single vascular strand, and the peltate distal portions are made up of parenchymatous cells arranged in a palisade-like form at right angles to the free surface of the sporangiophores. The vascular strand of the pedicel forks into two halves just below the peltate head, and these branches again bifurcate to send a branch to each sporangium. The four sporangia of each sporangiophore are attached by a narrow band of tissue to the shield-shaped distal expansion (fig. 95, A).

In a tangential section of a cone, such as the lower portion of fig. 94 and in fig. 95, B, the sporangiophores present the appearance of narrow stalks (fig. 95, B, a) in the middle of a cluster of sporangia, and the latter appear more or less square in outline. The wall of a sporangium is made of a single layer of cells (fig. 95, B) which present a characteristic appearance in surface-view (fig. 95, C), the thin walls being crossed at right angles by small vertical plates. In the tangential section of the coherent sterile whorls (fig. 95, B, b and b) the vascular strands are occasionally seen in transverse section (fig. 95, B, t), as they pass outwards to the several free bracts.

The spores in Calamostachys Binneyana are all of the same size, and no macrospores have ever been seen. In well preserved specimens tetrads of spores may be seen, still enclosed by the wall of the spore-mother-cell (fig. 95, A and D); and the torn remnants of the mother-cell sometimes simulate in appearance the elaters of an Equisetum spore. In surface-view a spore often shows clearly the three-rayed marking, which is a characteristic feature of daughter-cells formed in a tetrad from a mother-cell. The spores of a tetrad are in some cases of unequal size, some having developed more vigorously than others. This unequal growth and nourishment of spores is clearly shown in fig. 96, which represents a sporangium of a heterosporous Calamitean strobilus, C. Casheana. Williamson and Scott[709] have described striking examples of spores in different stages of abortion, and these authors draw attention to the importance of the phenomenon from the point of view of the origin of a heterosporous form of cone. The abortion of some of the members of a spore-tetrad and the consequent increased nutrition of the more favoured daughter-cells, might well be the starting-point of a process, which would ultimately lead to the production of well defined macrospores and microspores. The young microsporangia and macrosporangia of recent Vascular Cryptogams such as Selaginella, Salvinia and other heterosporous genera are identical in appearance[710]; it is not until the spore-producing tissue begins to differentiate into groups of spores, that the sporangia assume the form of macrosporangia and microsporangia. During the evolution of the various known types of pteridophytic plants heterospory gradually succeeded isospory, and this no doubt occurred several times and in different phyla of the plant kingdom. In the mature sporangia of some of the Calamitean strobili we have in the inequality of the spores in one sporangium an indication of the steps by which heterospory arose; and in the immature sporangia of some recent genera we are carried back to a stage still nearer the starting-point of the substitution of the heterosporous for the isosporous condition.

To Williamson[711] again is largely due the information we possess as to the structure of this type of Calamitean strobilus. Its special interest lies in the occurrence of macrospores and microspores in the same cone.

The strobilus axis agrees in structure with that of C. Binneyana, but in C. Casheana a band of secondary xylem forms the peripheral portion of the triangular stele. Were any further proof needed of the now well-established fact that secondary growth in thickness is by no means unknown as an attribute of Vascular Cryptogams, the co-existence in the same cone of a cambium layer producing secondary wood and bark, and cryptogamic macrospores and microspores, affords conclusive evidence[712]. The dogma accepted by many writers for a considerable number of years that the power of secondary thickening is evidence against a cryptogamic affinity, has been responsible for no little confusion in palaeobotanical nomenclature.

On the axis of Calamostachys Casheana there are borne alternate whorls of fertile and sterile appendages similar to those in the homosporous C. Binneyana, but they are inclined more obliquely to the axis of the cone. Macrospores and microspores have been found in sporangia borne on the same sporangiophore.

The spore-tetrads in the macrosporangia occasionally include aborted sister-cells like those noticed in C. Binneyana; this phenomenon is well illustrated by the unequally nourished spores in the sporangium of fig. 96, but no such starved spores have been found in the microsporangia. In this cone, then, heterospory has become firmly established, but the occurrence of undersized spores in a macrospore-tetrad leads us back to the probable lines of development of heterospory, which are seen in C. Binneyana at their starting-point.

In the two species of strobili which have been described, Calamostachys Binneyana and C. Casheana, the sporangiophores or sporophylls are given off at right angles to the axis, and midway between the sterile whorls. These are two of the most important distinguishing features of the Calamitean cones included under the generic term Calamostachys. In another form of cone, which also belongs to Calamitean stems, the sporangiophores arise in the axil of the sterile leaves, and are inclined obliquely to the axis of the cone. To this type the generic name Palaeostachya has been applied by the late Prof. Weiss[713] of Berlin. The portion of a cone shown in fig. 97 shows the arrangement of the sterile and fertile appendages characteristic of Palaeostachya.

It is practically impossible to distinguish between cones of the Calamostachys and Palaeostachya type in the case of imperfectly preserved impressions; indeed we cannot assume that all long and narrow cones with spirally disposed verticillate bracts are Calamitean. We must have the additional evidence of internal structure or of the direct association of the cones with Calamitean foliage.

In 1869 Williamson[714] described a fragment of a strobilus which showed certain anatomical features indicative of a close relationship or even identity with Calamites. Some years later[715] a much more perfect example was obtained from the Coal-Measures of Lancashire, and the additional evidence which it afforded definitely confirmed the earlier views of Williamson. The cone was more fully described by Williamson in 1888, as “the true fruit of Calamites.” It is clearly a form of Weiss’ genus Palaeostachya; Williamson and Scott[716] refer to it in their Memoir as Calamites pedunculatus. It is preferable, however, to retain the generic designation Palaeostachya for cones of this type. As the name P. pedunculata has previously been adopted by Weiss[717] for a cone figured by Williamson[718] in 1874, and afterwards referred to by that author in writing as P. pedunculata, it is proposed to substitute the specific name vera; this specific name being chosen with a view to put on record the fact that it was this type of cone that Williamson first proved to be the true fructification of the Calamite.

The axis of P. vera is practically identical in structure with a Calamitean twig. There is a hollow pith in the centre of the stele surrounded by a ring of 16–20 collateral bundles, each of which is accompanied by a carinal canal as in a vegetative shoot. As the pedicel of the strobilus passes into the cone proper it undergoes some modification in structure, but retains the characteristic features of a Calamite. The diagrammatic longitudinal section of fig. 98, which is copied from a drawing by Williamson[719], shows the broadening of the vascular strands at the nodes, and here and there a carinal canal is seen internal to the wood.

The axis of the cone bears whorls of bracts at right angles to the central column. Each whorl consists of about 30–40 segments coherent basally into a disc of prosenchymatous and parenchymatous tissue. The free linear bracts curve sharply upwards from the periphery of the disc, approximately parallel to the axis of the cone. From each of these sterile whorls there are given off 16–20 long and slender obliquely-inclined sporangiophores, sp, which arise from the upper surface of the disc close to the axis. Each sporangiophore no doubt bore four sporangia, S, containing spores of one size,—about ·075 mm. in diameter. The specimens of Palaeostachya vera so far obtained do not show the actual manner of attachment of the sporangia, but more complete examples of other species of Palaeostachya[720] enable us to assume with certainty that the sporangiophores terminated in a distal peltate expansion bearing four sporangia on its inner face.

A transverse section of the axis of the cone in the region of the sterile and fertile appendages shows the vascular bundles arranged in pairs. In a section through the peduncle of the cone, below the lowest whorl of bracts, the bundles of the stele are situated at equal distances apart. The cortical tissue of the peduncle is traversed by a ring of large canals[721] similar to the vallecular canals of an Equisetum stem.

Isospory is not a constant characteristic of Palaeostachya; some forms have been found with macrospores and microspores[722].

It would be out of place in an introduction to Palaeobotany to attempt an exhaustive account of the various cones which were probably borne by Calamitean plants, but there are a few general points to which the attention of the student should be directed. The examples dealt with in the foregoing description illustrate the fact, that plants included under the comprehensive genus Calamites bore cones possessing distinct morphological features. There are, however, other types of strobili which have been found in organic connection with Calamites; and some of these must be taken into account in dealing with Calamarian plants. The genera Volkmannia, Brukmannia, Huttonia, Macrostachya, in addition to Calamostachys and Palaeostachya and others, have been applied by different writers to Calamitean cones. As Solms-Laubach[723] has suggested, it is wiser to discard Volkmannia and Brukmannia, as they have been made to do duty for cones of widely different forms. It is better to adhere to the provisional generic names used by Weiss, as they enable us to conveniently systematise the various Calamarian strobili.

The following classification may be given of the better known cones, some of which we are able to describe in considerable detail, while others are still very imperfectly known. We have good evidence that all these strobili were borne by vegetative shoots of the type of Calamites, Calamocladus or Annularia.

Cones long and narrow, consisting of a central axis bearing alternate whorls of sterile and fertile appendages, the latter having the form of sporangiophores attached at right angles to the axis midway between the sterile verticils, and bearing four sporangia on the inner face of a peltate distal expansion.

Calamostachys Binneyana Schimp., C. Ludwigi Carr., C. Casheana Will., may be referred to as examples of this type of cone; also some of the strobili described by different authors as species of Volkmannia[725], Brukmannia[726], &c.

Although one cannot make out the detailed structure of a Calamite cone in the absence of internal structure, it is often possible to recognise the essential features in specimens preserved in ironstone nodules, such as those from Coalbrook Dale in Shropshire, or by carefully examining the carbonised impressions on shale under a simple microscope.

Weiss applies the term Paracalamostachys[727] to cones of the Calamostachys form, but in which the manner of attachment cannot be made out. Such a cone as that of fig. 93 should probably be referred to this sub-type of Calamostachys in the absence of definite evidence as to the position of the sporangia.

Another term Stachannularia, originally used by Weiss as a genus[728], was afterwards[729] applied to cones of the same general type as Calamostachys, in which the sporangiophores have the form of thorn-like structures bearing on their upper side a lamellar expansion. There is however some doubt as to the correct interpretation of the features associated with cones included in Stachannularia; for an account of such forms reference must be made to the writings of Weiss, Renault[730], Solms-Laubach[731] and others[732].

Calamostachys cones have been found in organic union with branches bearing leaves of the Annularia type, also with Calamocladus foliage, and the branches bearing such cones have been found in actual connection with Calamitean stems. The association of cones and vegetative stems and branches is shown in tabular form on p. 363.