This species, which Zeiller[1070] has investigated from sections of Unger’s material, illustrates a type in which the vascular tissue is very richly developed and forms crowded concentric series of curved plates associated, in the more peripheral series, with bands of mechanical tissue. The outermost part of the vascular region consists of (i) a series of loops or variously curved bands of conducting tissue representing leaf-traces at different stages in their outward course, (ii) a series of similar vascular strands (peripheral steles of Zeiller) confined to the stem (cauline) and from which roots are given off, and (iii) bands of mechanical tissue associated with the leaf-traces and peripheral steles. The peripheral steles ([fig. 296], A, B, p) form anastomoses with the leaf-traces and contribute to their formation.
The form of some of the vascular bands in the section of Psaronius infarctus shown in [fig. 296], A, illustrates the occasional anastomosing of one dictyostele with another: the different degrees of looping of other bands represent stages in the giving off of leaf-traces which eventually pass out as V-shaped meristeles. Beyond the leaf-traces and sclerenchymatous bands the section consists of transverse sections of adventitious roots.
The surface-features of Psaronius infarctus are probably represented, as Zeiller points out, by the cast described by Lesquereux as Caulopteris peltigera ([fig. 298], A).
Fig. 297. Pecopteris Sterzeli: a, pinnule. (After Renault and Zeiller. ¹⁄₁₁ nat. size.)
The Psaronius shown in [fig. 297] is one of the few examples illustrating the connexion between fronds and stem. The leaf (Pecopteris Sterzeli Zeill. and Ren.[1071] is quadripinnate and is described as reaching a length of at least 3 metres; the ultimate segments are entire or lobed. The stem is characterised by elliptical scars, 6–8 cm. x 3·5–4 cm., with leaf-traces like those in Caulopteris peltigera. The fronds of Pecopteris Pluckeneti, a Pteridosperm, bear a very close resemblance to those of P. Sterzeli, which are as yet known only in a sterile state.
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Psaronius brasiliensis Unger, a species founded by Unger on a piece of silicified stem acquired by Martius in Brazil and now in the Rio Museum, is a good example of a tetrastichous species. Solms-Laubach[1072] has recently told the history of this type, which is represented by sections, cut from the Rio stem, in several European collections. A well-preserved section in the British Museum is figured by Arber[1073] in his catalogue of the Glossopteris flora and by other authors. Scott gives a concise description of the species in his Studies in Fossil Botany[1074]. The roots of P. brasiliensis are stated by Pelourde[1075] to have a lacunar cortex.
Psaronius musaeformis Corda[1076]. Fig. 296, D.
This species from the Lower Permian of Chemnitz and the Coal-Measures of Bohemia affords an example of the distichous type in which the leaves are borne in two rows. The vascular bands, as seen in a section of the dictyosteles, occur in regular parallel series. The stelar region is separated from the cylinder of encasing roots by a sclerenchymatous sheath, broken at intervals where roots pass out from the vascular region.