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).
Fig. 94. Calamostachys Binneyana (Carr.) in longitudinal (radial and tangential) section.
Sp, sporangiophores; S, sporangia.
(From specimen no. 1022 in the Williamson Collection, British Museum.)
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.
Fig. 95. Calamostachys Binneyana (Carr.).
- A sporangiophore and one sporangium. t, vascular bundle. × 45.
- Tangential section showing portions of two sterile discs, b, b; a sporangiophore, a, with its four sporangia, in two of which are seen the spores; t, vascular bundle. × 35.
- Surface-view of cells of a sporangium wall. × 130.
- Spores and remains of mother-cells. × 130.
(After Williamson and Scott.)