(A, B, after Renault; C–G, after Stur; H, I, after Strasburger; K, after Sterzel.)

Hawlea.

Stur[1002] retains this generic name for sori in which the sporangia are free and united only by the proximal end to a central receptacle ([fig. 291], F, G). He describes the individual sporangia as possessing a rudimentary annulus, a comparatively strong wall, and terminating in a pointed distal end. He emphasises the greater degree of cohesion between the sporangia of Asterotheca as the distinguishing feature of that genus; but this is a character difficult to recognise in some cases, and from the analogy of recent ferns one is disposed to attach little importance to the greater or less extent to which sporangia are united, at least in such cases as Asterotheca and Hawlea when the cohesion is never complete.

Scolecopteris.

Zenker[1003] gave this name to detached fertile pinnules from the Lower Permian of Saxony, which he described as Scolecopteris elegans. He recognised the fern nature of the sori and suggested that the pinnules might belong to the fronds of one of the “Staarsteinen” (Psaronius), a view which subsequent investigations render far from improbable. The sori, which occur in two rows on the lower surface of the small pecopteroid segments with strongly revolute margins ([fig. 291], H–K), contain 4–5 sporangia attached to a stalked receptacle comparable with that of Marattia Kaulfussii. These pedicellate synangia were fully described by Strasburger[1004], who decided in favour of a Marattiaceous alliance. The lower portions of the distally tapered sporangia are concrescent, the distal ends being free ([fig. 291], H). Stur includes in Scolecopteris the common species Pecopteris arborescens ([fig. 376]), but Kidston[1005] states that the British example of Scolecopteris is S. polymorpha, Brongn. from the Upper Coal-Measures.

Scolecopteris elegans Zenk. furnishes an example of a plant, or plant fragment, which has been assigned to the animal kingdom. Geinitz[1006] described silicified pinnules as Palaeojulus dyadicus, the generic name being chosen because of the resemblance to Millipedes such as the genus Julus. The mistake is not surprising to anyone who has seen a block of siliceous rock from Chemnitz crowded with the small pinnules with their concave surfaces formed by the infolding of the edges. Sterzel[1007], who pointed out the confusion between Myriapods and Filices, has published figures which illustrate the deceptive resemblance of the pinnules, with their curved lamina divided by lateral veins into segments, to the body of a Millipede (fig. 291, K). He points out that Geinitz searched in vain for the head and legs of Palaeojulus and expressed the hope that further examination would lead to fresh discoveries: the examination of sections revealed the presence of sporangia and demonstrated the identity of Palaeojulus and Scolecopteris.

Discopteris.

Stur[1008] instituted this genus for fertile fronds from the Upper Carboniferous Schatzlarer beds, including two species Discopteris karwinensis and D. Schumanni. He described the small Sphenopteroid pinnules as characterised by disc-shaped sori made up of 70–100 sporangia attached to a hemispherical receptacle: the absence of a true annulus led him to refer the genus to the Marattiaceae. In his memoir on the coal-basin of Heraclea (Asia Minor), Zeiller[1009] instituted the species Sphenopteris (Discopteris) Rallii and figured sporangia resembling those described by Stur in the possession of a rudimentary “apical annulus.” He compared the sporangia with those of recent Osmundaceae and Marattiaceae. In the later memoir on the Upper Carboniferous and Permian plants of Blanzy and Creusot, Zeiller[1010] gives a very full and careful description of fertile specimens of Sphenopteris (Discopteris) cristata, a fern originally described by Brongniart as Pecopteris cristata[1011]. Many of the Sphenopteroid pinnules of this quadripinnate fern frond show the form and structure of the sori with remarkable clearness in the admirable photographs reproduced in Plates I.–III. of Zeiller’s Blanzy memoir. The lobed pinnules of this species are of oval-triangular form, 5–15 mm. long and 2·5–6 mm. broad[1012]. An examination of the type-specimens of Discopteris from Vienna enabled Zeiller to correct Stur’s original description of the sori: he found that the Austrian and French specimens, though specifically distinct, undoubtedly belong to one genus. The sori in Discopteris cristata are globular, as in the recent genera Cyathea and Alsophila, and frequently cover the whole face of the lamina. The individual sporangia are 0·4–0·5 mm. long and 0·15–0·2 mm. in diameter; they are exannulate, but for the annulus is substituted a group of thicker-walled and larger cells in the apical and dorsal region. The description by Stur of a hemispherical receptacle seemed to indicate an important difference between the Austrian and French species; but Zeiller found that this feature does not actually exist and that it was so described as the result of misinterpretation. Zeiller succeeded in isolating spores, 40–50 μ in diameter, from some of the sporangia of D. cristata and found that they exhibited the three-rayed pattern characteristic of fern-spores and which is indicative of their formation in tetrads. The conclusion arrived at is that the genus Discopteris, as represented by D. karwinensis, D. cristata etc., may be regarded as a true fern and included in the Marattiaceae. As Zeiller points out, the sori of Discopteris differ from those of recent Marattiaceae in their pluriseriate construction and agree in this respect with those of the Cyatheaceae. The comparison already made[1013] between the sporangia of D. Rallii and those of recent Osmundaceae holds good: the genus affords another example of a generalised type, in this case probably a fern, combining features which are now distributed among the Marattiaceae, Osmundaceae and Cyatheaceae.

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