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menophyllaceœ, and the Marattiacea, go back to the coalformation.*
Some of these ferns have the more complex kind of spore-case, with a jointed, elastic ring. It is to be ob
FIG. 54.-Sphenopteris latior, Dawson. Coal-formation. a, Pinnule magnified, with traces of fructification.
served, however, that those forms which have a simple spore-case, either netted or membranous, and without annulus, are most common in the Devonian and lowest
FIG. 55.-Fructification of Paleozoic ferns. a, Theca of Archæopteris (Erian). 6, Theca of Senftenbergia (Carboniferous). c, Thecæ of Asterotheca (Carboniferous).
Carboniferous. Some of the forms in these old rocks are somewhat difficult to place in the system. Of these, the
* Mr. R. Kidston has recently described very interesting forms of fern fructification from the coal-formation of Great Britain, and much has been done by European palæobotanists, and also by Lesquereux and Fontaine in America.
FIG. 56.-Tree-ferns of the Carboniferous. A, Megaphyton magnificum, Dawson, restored. B, Leaf-scar of the same, two thirds natural size. B1, Row of leaf-scars, reduced. o, Palæopteris Hartii, scars half natural size. D, Palæopteris Acadica, scars half natural size.
species of Archæopteris, of the Upper and Middle Erian, are eminent as examples. This type, however, scarcely extends as high as the coal-formation.* Some of the tree-ferns of the Carboniferous present very remarkable features. One of these, of the genus Megaphyton, seems to have two rows of great leaves, one at each side of the stem, which was probably sustained by large bundles of aërial roots (Fig. 56).
In the Carboniferous, as in the Erian, there are leaves which have been referred to ferns, but are subject to doubt, as possibly belonging to broad-leaved taxine trees. allied to the gingko-tree of China. One of these, repre
sented in Fig. 57, has been found in the coal-formation of Nova Scotia, and referred to the doubtful genus Noeggerathia. Fontaine has proposed for similar leaves found in Virginia the new generic name Suportea.
Ferns, as might be inferred from their great age, are at the present time dispersed over the whole world; but their headquarters, and the regions to which tree-ferns are confined, are the more moist climates of the tropics and of the southern hemisphere. The coal-swamps of the northern hemisphere seem to have excelled even these favoured regions of the present world as a paradise for ferns.
I have already stated that the Carboniferous constitutes the headquarters of the Cordaites (Fig. 58), of which a large number of species have been described, both in
FIG. 57.-Noeggerathia dispar
(half natural size).
The pretty little ferns of the genus Botrychium (moonwort), so common in American and European woods, seem to be their nearest modern allies.
Europe and America. We sometimes, though rarely, find their stems showing structure. In this case we have a large cellular pith, often divided by horizontal partitions into flat chambers, and constituting the objects which, when detached, are called Sternbergia (Fig. 62). These Sternbergia piths, however, occur in true conifers as well, as they do in the modern world in some trees, like our common butternut, of higher type; and I showed many years ago that the Sternbergia type may be detected in the young twigs of the balsam - fir (Abies balsamifera). The pith was surrounded by a ring of scalariform or barred tissue, often of considerable thickness, and in young stems so important as to have suggested lycopodiaceous affinities. But as the stem grew in size, a regular ring of woody wedges, with tissue having rounded or hexagonal pores or discs, like those of pines, was developed. Outside this was a bark, often apparently of some thickness. This structure in many important points resembles that of cycads, and also approaches to the structure of Sigillaria, while in its more highly developed forms it approximates to that of the conifers.
On the stems so constructed were placed long and often broad many-nerved leaves, with rows of stomata or breathing-pores, and attached by somewhat broad bases to the stem and branches. The fruit consisted of racemes, or clusters of nutlets, which seem to have been provided
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FIG. 59.-Fruits of Cordaites and Taxine Conifers (coal-formation, Nova Scotia.) A, Antholithes squamosus (two thirds). B, A. rhabdocarpi (two thirds). B1, Carpel restored. c, A. spinosus (natural size). D, Trigonocarpum intermedium. E, T.
num. G, Rhabdocarpus insignis, reduced. H, Antholithes pygmæus. 1, Cardiocarpum fluitans. K, Cardiocarpum bisectum. L, Sporangites papillata, lycopodiaceous macrospores (natural size and magnified).