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.
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.