The specimen represented in fig. 68, A, was originally described by the Italian palaeobotanist Zigno[564]; it serves to illustrate the points of difference between this genus and the ordinary Equisetum. The open and spreading sheaths clasping the nodes and the erect solitary branches give the plant a distinctive appearance.
Fig. 68.
- Phyllotheca Brongniarti, Zigno. Nat. size. (After Zigno.)
- Calamocladus frondosus, Grand’Eury. (After Grand’Eury.) Slightly enlarged.
- Phyllotheca indica, Bunb. Part of a leaf-sheath. From a specimen in the Museum of the Geological Society. Slightly enlarged.
3. Phyllotheca indica Bunb. and P. australis Brongn. Fig. 68, C.
Sir Charles Bunbury[565] described several imperfect specimens from the Nagpur district of India under this name, but he expressed the opinion that it was not clear to him if the plant was specifically distinct from the Phyllotheca australis Brongn. previously recorded from New South Wales. Feistmantel[566] subsequently described a few other Indian specimens, but did not materially add to our knowledge of the genus. Bunbury’s specimens were obtained from Bharatwádá in Nagpur, in beds belonging to the Damuda series of the Lower Gondwana rocks, usually regarded as of about the same age as the Permian rocks of Europe.
Phyllotheca indica is represented by broken and imperfect fragments of leaf-bearing stems. The species is thus diagnosed by Bunbury:—“Stem branched, furrowed; sheaths lax, somewhat bell-shaped, distinctly striated; leaves narrow linear, with a strong and distinct midrib, widely spreading and often recurved, nearly twice as long as the sheaths.” An examination of the specimens in the Museum of the Geological Society of London, on which this account was based, has led me to the opinion that it is practically impossible to distinguish the Indian examples from P. australis described by Brongniart[567] from New South Wales. The few specimens of the latter species which I have had an opportunity of examining bear out this view. In the smaller branches the axis of P. indica is divided into rather short internodes on which the ridges and grooves are faintly marked. In the larger stems the ridges and grooves are much more prominent, and continuous in direction from one internode to the next; a few branches are given off from the nodes of some of the specimens. The leaves are not very well preserved; they consist of a narrow collar-like basal sheath divided up into numerous, long and narrow segments, which are several times as long as the breadth of the sheath, and not merely twice as long as Bunbury described them. Each leaf-sheath has the form of a very shallow cup-like rim clasping the stem at a node, with long free spreading segments which are often bent back in their distal region. The general habit of the leafy branches appears to be identical with that of P. australis as figured by McCoy.
Prof. Zeiller informs me that in the type-specimen on which Brongniart founded the species, P. australis, the sheath appears to be closely applied to the stem with a verticil of narrow spreading segments radiating from its margin. It may be, therefore, that in the Australian form there was not such an open and cup-like sheath as in P. indica; but it would be difficult, without better material before us, to feel confidence in any well marked specific distinctions between the Indian and Australian Phyllothecas.
On the broader stems, such as that of fig. 67, we have clearly marked narrow grooves and broader and slightly convex ridges, which present an appearance identical with that of some Calamitean stems. In the specimen figured by Bunbury[568] in his Pl. X, fig. 6, there is a circular depression on the line of the node which represents the impression of the basal end of a branch; on the edges of the node there are indications of two other lateral branches. The nature of this stem-cast points umnistakeably to a woody stem like that of Calamites. The precise meaning of the ridges and grooves on the cast is described in the Chapter dealing with Calamitean plants.
CALAMOCLADUS.