[AW] For descriptions of these ferns, see reports cited above. [AX] "Reports on Fossil Plants of the Devonian and Upper Silurian of Canada," 1871, &c. [Illustration: Fig. 23.--Erian ferns (New Brunswick), B, _Cyclopteris valida_, and pinnule enlarged, D, _Sphenopteris marginata_, and portion enlarged. E, _Sphenopteris Harttii_. G, _Hymenophyllites curtilobus_. H, _Hymenophyllites Gersdorffii_, and portion enlarged. I, _Alethopteris discrepans_, K, _Pecopteris serrulata_, L, _Pecopteris preciosa_. M, _Alethopteris Perleyi_.] [Illustration: Fig. 24.--_Archæopteris Jacksoni_, Dawson (Maine). An Upper Erian fern, _a_, _b_, Pinnules showing venation.] [Illustration: Fig. 25.--An Erian tree-fern. _Caulopteris Lockwoodi_, Dawson, reduced. (From a specimen from Gilboa, New York.)] Some of the Erian ferns attained to the dimensions of tree-ferns. Large stems of these, which must have floated out far from land, have been found by Newberry in the marine limestone of Ohio (_Caulopteris antiqua_ and _C. peregrina_, Newberry),[AY] and Prof. Hall has found in the Upper Devonian of Gilboa, New York, the remains of a forest of tree-ferns standing _in situ_ with their great masses of aërial roots attached to the soil in which they grew (_Caulopteris Lockwoodi_, Dn.).[AZ] [AY] "Journal of the Geological Society," 1871. [AZ] _Ibid._ [Illustration: Fig. 26.--_Megalopteris Dawsoni_, Hartt (Erian, New Brunswick), _a_, Fragment of pinna. _b_, Point of pinnule, _c_, Venation, (The midrib is not accurately given in this figure.)] These aërial roots introduce us to a new contrivance for strengthening the stems of plants by sending out into the soil multitudes of cord-like cylindrical roots from various heights on the stem, and which form a series of stays like the cordage of a ship. This method of support still continues in the modern tree-ferns of the tropics and the southern hemisphere. In one kind of tree-fern stem from the Erian of New York, there is also a special arrangement for support, consisting of a series of peculiarly arranged radiating plates of scalariform vessels, not exactly like those of an exogenous stem, but doing duty for it (_Asteropteris_)[BA] Similar plants have been described from the Erian of Falkenberg, in Germany, and of Saalfeld, in Thuringia, by Goeppert and Unger, and are referred to ferns by the former, but treated as doubtful by the latter,[BB] This peculiar type of tree-fern is apparently a precursor of the more exogenous type of _Heterangium_, recently described and referred to ferns by Williamson. Here, again, we have a mechanical contrivance now restricted to higher plants appropriated by these old cryptogams. [BA] "Journal of the Geological Society," London, 1881. [BB] "Sphenopteris Refracta," Goeppert; "Flora des Uebergangsgebirges." "Cladoxylon Mirabile," Unger; "Palæontologie des Thuringer Waldes." [Illustration: Fig. 27.--_Calamites radiatus_ (Erian, New Brunswick).]