[Illustration: FIG. 88.—Trunk of a Devonian Tree-fern (_Caulopteris Lockwoodi_, Dn.). Gilboa, New York. One-third natural size.] [Illustration: FIG. 89.—Frond of _Archæopteris Jacksoni_ (Dn.). Devonian, of Maine.] [Illustration: FIG. 90.—Portion of a branch of _Leptophleum rhombicum_ (Dn.). A Lycopodiaceous tree of the Devonian of Maine. Natural size.] [Illustration: FIG. 91.—_Calamites radiatus_ (Brongniart). Middle Devonian of N. Brunswick.] In the Devonian age we meet with no land plants of the two lower classes of the Cryptogams, and with scarcely any that can be referred to the two higher classes of Phænogams, so that the vegetation of this period presents a remarkable character of mediocrity, being composed almost entirely of the highest class of the flowerless plants and the lowest class of those that flower. Of the former there are Tree-ferns and vast numbers of herbaceous forms (Figs. 88, 89), great Lycopodiaceous plants, immensely better developed than those now existing (Fig. 90), and gigantic _Calamites_, allied to the Mares’-tails (Fig. 91), along with humbler members of the same group (Fig. 95). Of the latter there were Pines of great stature, known to us at present only by their wood (Fig. 92); and that other allied trees existed we have evidence in numerous seeds which must have belonged to this class (Fig. 93), and in long flag-like leaves[29] which modern discoveries would refer to the same group. As yet we know no Devonian Palms or Grasses; and only a single specimen has been found indicating the existence of a plant of the highest vegetable class, that of the true exogens. This unique specimen, found by Hall in the Devonian of the shores of Lake Erie, is a fragment of mineralised wood, the structures of which are represented in Fig. 94. The large ducts seen in cross section in Nos. 1, 2, and 3, and in longitudinal section in Nos. 4 and 5, and the medullary rays, seen in Nos. 1, 4, and 6, testify to the fact that this chip of wood must have belonged to a tree of the same type which contains our oaks, maples, and poplars; a type which does not appear to have become dominant till near the close of the Mesozoic, but which already existed, though perhaps only in few species, and only in upland and inland positions, as far back as the Middle Devonian. Perhaps one of the most interesting discoveries in the Erian or Devonian rocks has been that of the immense abundance of spores of those humble plants the Rhizocarps, represented in modern times by the Pillworts and Salviniæ, &c. To these it is believed that _Sphenophyllum_ and _Psilophyton_ were allied; but in addition to this there are thick and vastly extended beds of bituminous shale which owe their inflammable properties to countless multitudes of Macrospores (_Sporangites_) of the genus _Protosalvinia_.[30] In Ohio there are beds of this kind 350 feet thick, and extending across the State. They occur also in Canada, where