[Illustration: Fig. 49.--Erect _Calamites_ (_C. Suckovii_), showing the mode of growth of new stems (_b_), and different forms of the ribs (_a_, _c_). (Pictou, Nova Scotia.) Half natural size.] There is every reason to believe that all these various and complicated stems belonged to higher and nobler types of mare's-tails than those of the modern world, and that their fructification was equisetaceous and of the form known as _Calamostachys_. We have already seen that noble tree-ferns existed in the Erian period, and these were continued, and their number and variety greatly extended, in the Carboniferous. In regard to the structure of their stems, and the method of supporting these by aërial roots, the tree-ferns of all ages have been nearly alike, and the form and structure of the leaves, except in some comparatively rare and exceptional types, has also been much the same. Any ordinary observer examining a collection of coal-formation ferns recognises at once their kinship to the familiar brackens of our own time. Their fructification is, unfortunately, rarely preserved, so that we are not able, in the case of many species, to speak confidently of their affinities with modern forms; but the knowledge of this subject has been constantly extending, and a sufficient amount of information has been obtained to enable us to say something as to their probable relationships. (Figs. 51 to 55.) [Illustration: Fig. 50.--Stems of _Calamodendron_ and tissues magnified (Nova Scotia), _a_, _b_, Casts of axis in sandstone, with woody envelope (reduced). _c_, _d_, Woody tissue (highly magnified).] The families into which modern ferns are divided are, it must be confessed, somewhat artificial, and in the case of fossil ferns, in which the fructification is for the most part wanting, it is still more so, depending in great part on the form and venation of the divisions of the fronds. Of about eight families into which modern ferns are divided, seven are found in a fossil state, and of these, four at least, the _Cyathaceæ_, the _Ophioglosseæ_, the _Hymenophyllaceæ_, and the _Marattiaceæ_, go back to the coal-formation.[CD] [CD] 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. [Illustration: Fig. 51.--Group of coal-formation ferns, A, _Odontopteris subcuneata_ (Bunbury), B, _Neuropteris cordata_ (Brongniart). C, _Alethopteris lonchitica_ (Brongniart). D, _Dictyopteris obliqua_ (Bunbury). E, _Phyllopteris antiqua_ (Dawson), magnified; E^1, Natural size, F, _Neuropteris cyclopteroides_ (Dawson).] [Illustration: Fig. 52.--_Alethopteris grandis_ (Dawson). Middle coal-formation of Nova Scotia.] [Illustration: Fig. 53.--_Cyclopteris_ (_Aneimites_) _Acadica_ (Dawson), a tree-fern of the Lower Carboniferous. _a_, Pinnules. _b_, Fragment of petiole. _c_, Remains of fertile pinnules.]