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. C, Palæopteris Harttii, scars half natural size. D, Acadica, scars half natural size.
Some of these ferns have the more complex kind of spore-case, with a jointed, elastic ring. It is to be observed, 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 Carboniferous. Some of the forms in these old rocks are somewhat difficult to place in the system. Of these, the species of Archæopteris, of the Upper and Middle Erian, are eminent as examples. This type, however, scarcely extends as high as the coal-formation.[CE] 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]).
[CE] The pretty little ferns of the genus Botrychium (moonwort), so common in American and European woods, seem to be their nearest modern allies.
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, represented 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 Saportea.
Fig. 57.—Noeggerathia disbar (half natural size).
