- Transverse section; t, vascular bundle; x, sheath of cells. × 35.
- Vascular bundle consisting of a few small tracheids, t.
- A tracheid and a few parenchymatous cells, the latter with nuclei.
- A stoma; s, s, guard-cells.
- Pallisade cells and intercellular spaces.
From a section in the Manchester Museum, Owens College.
The nature of the assimilating tissue, the comparatively thick band of thin-walled cells with intercellular spaces, and the exposed position of the stomata suggest that the plant lived in a fairly damp climate; at least there is nothing to indicate any adaptation to a dry climate.
In the Binney collection of plants in the Woodwardian Museum, Cambridge, there is a species of a very small shoot bearing three or four verticils of leaves which possess the same structure as those of fig. 86. We may probably regard such twigs as the slender terminal branches of Calamitean shoots.
α. Calamocladus (Asterophyllites).
The generic name Asterophyllites was proposed by Brongniart[641] in 1822 for a fossil previously named by Schlotheim[642] Casuarinites, and afterwards transferred to Sternberg’s genus Annularia. In 1828 Brongniart[643] gave the following diagnosis of the fossils which he included under the genus Asterophyllites:—“Stems rarely simple, usually branched, with opposite branches, which are always disposed in the same plane; leaves flat, more or less linear, pointed, traversed by a simple median vein, free to the base.” Lindley and Hutton described examples of Brongniart’s genus as species of Hippurites[644], and other authors adopted different names for specimens afterwards referred to Asterophyllites.
At a later date Ettingshausen[645] and other writers expressed the view that the fossils which Brongniart regarded as a distinct genus were the foliage-shoots of Calamites, and Ettingshausen went so far as to include them in that genus. In view of the generally expressed opinion as to the Calamitean nature of Asterophyllites, Schimper[646] proposed the convenient generic name Calamocladus for “rami et ramuli foliosi” of Calamites. Some recent authors have adopted this genus, but others prefer to retain Asterophyllites. In a recent important monograph by Grand’Eury[647] Calamitean foliage-shoots are included under the two names, Asterophyllites and Calamocladus; the latter type of foliage-shoots he associates with the stems of the subgenus Calamodendron, and the former he connects with those Calamitean stems which belong to the subgenus Arthropitys.
It is an almost hopeless task to attempt to connect the various forms of foliage-shoots with their respective stems, and to determine what particular anatomical features characterised the plants bearing these various forms of shoots. We may adopt Schimper’s generic name Calamocladus in the same sense as Asterophyllites, but as including such other foliage-shoots as we have reason to believe belonged to Calamites. Those leaf-bearing branches which conform to the type known as Annularia are however not included in Calamocladus, as we cannot definitely assert that these foliage-shoots belong in all cases to Calamitean stems. Grand’Eury’s use of Calamocladus in a more restricted sense is inadvisable as leading to confusion, seeing that this name was originally defined in a more comprehensive manner as including Calamitean leaf-bearing branches generally. We may define Calamocladus as follows:—
Branched or simple articulated branches bearing whorls of uni-nerved linear leaves at the nodes; the leaves may be either free to the base or fused basally into a cup-like sheath (e.g. Grand’Eury’s Calamocladus). The several acicular linear leaves or segments which are given off from the nodes spread out radially in an open manner in all directions; they may be either almost at right angles to the axis or inclined at different angles. Each segment is traversed by a single vein and terminates in an acuminate apex.
As a typical example of a Calamitean foliage-shoot the species Calamocladus equisetiformis (Schloth.) may be briefly described. The synonymy of the commoner species of fossil plants is a constant source of confusion and difficulty; in order to illustrate the necessity of careful comparison of specimens and published illustrations, it may be helpful to quote a few synonyms of the species more particularly dealt with. The exhaustive lists drawn up by Kidston in his Catalogue of Palaeozoic plants in the British Museum will be found extremely useful by those concerned with a systematic study of the older plants.