(b) Eligulatae. This group of lycopods of which Lycopodium the type are not so well represented as fossils; Spencerites, of :arboniferous age is the only certain eligulate Lycopod known in he Palaeozoic but it is possible that Cyclostigma, a Devonian enus, is eligulate, for no one has yet been able to show that a gule is present, although poor preservation might account for hat.
Filicales (Ferns).—One of the striking features of the assem dage of plants found in the Carboniferous rocks is the frequency ,f fragments of fern-like plants. Up to the end of the 19th cen ury these were all considered to be true ferns ; since then, how ver, evidence has been accumulating to show that many of them )elong to a higher group of plants and our present knowledge of hese fossils indicates that the majority of these fernlike fronds )elong to an extinct group, the pteridosperms, plants which pro luced seeds and which cannot therefore be classed with the ferns. addition to seeds the pteridosperms had microsporangia which :ontained microspores the equivalents to the pollen grains in the lowering plants. These microsporangia bearing fronds, unless heir relation to the rest of the plant is established may easily be aken for fertile fern-fronds. No known pteridosperms had nicrosporangia bearing the specialised group or band of cells :ailed the annulus which is part of the dehiscence mechanism of nost fern sporangia; so that fronds found with annulate spo -angia are almost certainly fronds of ferns. On the other hand 'ertile fronds with ex-annulate sporangia are known which are ilso certainly ferns but here it may be due to the difficulty of letecting the annulus where the plant is preserved in the form of in incrustation and the sporangia are very small. The best known Palaeozoic ferns are preserved in the form of petrifications. Un like the Equisetales and Lycopodiales the formation of secondary tissues was as of rare occurrence in fossil ferns as among the liv ing and no certain examples of heterosporous ferns are known from the Palaeozoic. The Botryopteridaceae fall into two groups: (a) Zygopterideae. This family contains over a dozen genera and one of them, Asteropteris, was found in Upper Devonian rocks in the State of New York while Anky ropteris, the best known genus, is represented by both Carbonifer ous and Permian species. Anky ropteris Grayi from the Lower Coal Measures of England had stems about 2CM. in diameter and
of considerable length; in fact it was probably a climber. Large fronds were attached at fairly wide intervals and their petioles or stalks must have nearly equalled the stem in thickness. They were arranged in spiral se ries on the stem and a short cylin drical branch was present in the aril of each leaf. It is possible that the axillary branch is just the smaller of the two branches of a forking of the stem effected close above the point of attachment of a leaf. The section of the coal-ball shown in Plate I., fig. 4, contains a stem cut transversely. The centre of the stele (vascular cylinder) appears as a small dark narrow-rayed star which consists of a mixture of parenchymatous tissue and tracheids ; while surrounding this are the large tracheids of the periphal xylem whose outer limit retains the star-shaped outline. The annular space surrounding the xylem was produced by the decay of the phloem and the wide zone of tissue occupying the greater part of the section is the cortex. The vascular struc ture of the leaf-stalk is peculiar, the xylem is in the form of a doubly grooved strand which appears like a double anchor in section (hence the name of the genus). The leaflets were given off alternately on each side of the petiole. In some zygopterids these leaflets were forked at their bases so that the petiole appar ently bears four rows of leaflets and has a bushy habit. The — sporangia in some of the generae.g., Etapteris (fig. I I) have a multiseriate annulus and are comparatively large; they were grouped in small bunches on the smaller divisions of the frond. In Stauropteris the stalk or rachis of the frond had four distinct rows of secondary stalks or rachises and each of these bore four rows of tertiary rachises.
All the rachises are cylindrical and were presumably green as they have well developed photo-synthetic-tissue. Each frond thus con sisted of a bush of small green twig-like divisions. The sporangia of Stauropteris had no annulus but germinating spores have been found (fig. 12) and the preliminary stages in prothallus formation is so essentially fern-like that there is no doubt that Stauropteris is a fern and not the pollen bearing part of a Pteridosperm, for pollen grains would behave differently on germination.