The water-ferns (Hydropteride) contain but few forms, and grow either in water or marshy places. They are of particular interest from the morphological standpoint, because they are hetero spo•ons There are two distinct families. Marsiliacerc, represented by the common Slarsilia, contains semi-aquatic species with slender stems, which send down numerous roots into a mucky soil, and give rise to comparatively large leaves, each of which has a long erect petiole, and a blade of four wedge-shaped leaflets like a four leaved clover. From near the base of the petiole another leaf-branch arises in which the blade is modified as a spo•c-bearing structure. which in the spo•e-ease and becomes hard and nut like. The other family is the Salvinincete, repre sented by Salvinia, whose species are floating forms.
Fossil, FERNS, Leaves and stems of fossil ferns are common in all geological formations above the Silurian, and they are especially in the Coal Measures of the Carboniferous age. Indeed. ferns may he MI1S1111•1*(41 to have been the dominant forms of the Paleozoic land flora, not alone by reason of thcir abundance. but also be enu•e of their large size. Ma Ily of them were tree ferns that grew in the vast forests along the swampy shores of later Paleozoic seas. A large number of the Paleozoic genera seem to have had their sporangia inclosed by the tissue of the fer tile lea f. as seen in the modern adder's•tomple fern (Ophioglossum), and its allies the Marat tias. Because of this structure, these genera are included in a suborder. the Eusporangia.
Although fragmentary fern-leaves and some supposed stems are found in Lower Devonian rocks, well-preserved specimens are not found until the Upper Devonian (Catskill) sandstones are reached, where Archa-opteris is obtained. In the Coal Measures, where ferns are abundant, the principal genera are Peeopte•is, a tree-fern; Neu ropteris, Archa-opteris, Dictyopteris, Odontop teris, .Alethopte•is, etc., which are herbaceous ferns of large size; and Hymenophyllnin and Sphenopteris, which are delicate ferns that must have formed the undergrowth of the forest vege tation. In the Permian and Triassic periods the
most important genus was Glossopteris (q.v.) ; and an allied genus, Tteniopteris, is very com mon in the Jurassic rocks. During Cretaceous time the ferns began to resemble more closely those of to-day, and in Tertiary time a large number of modern species appeared.
Consult: Lyell, Geographical Handbook of All the Known Ferns (London, 1869) ; Baker, Sum mary of New Ferns Discovered Since 1874 (Lon don. 1892) ; Hooker and Baker, Synopsis Filieunt (London, 1874) ; Eaton, The Ferns of North Amer ica (Boston. ISSO) ; Goebel, Outlines of Classifica tion. and Special Morphology of Plants, trans. by Garnsey (Oxford, 1887) ; Solms-Lanbach, Fossil Botany (Oxford. 1891), contains a full bibliog raphy of paleobotany, including works on ferns. Consult also: Zittel, Schimper, and Barrois, Traite de Part II. Paleophytologie ( Paris, 1891 ) ; Bernard, Elements de paleontologic (Paris, 1895) ; Gardner, "Monograph of the Brit ish Eocene Flora, Vol. I. Filices," Monographs of the Palwontographical Society (London, IS79 82) ; Feistmantel and others, "FosSil Flora of the Gondwana System," Pal•ontologica Indica, Series 11. and XII. (Calcutta, 1876-81). The most im portant works describing the fossil ferns of North America are: Fontaine and White, "The Permian or Upper Carboniferous Flora of West Virginia end Pennsylvania," Second Geological Survey of Pennsylvania, vol. PP (Harrisburg, 1880) ; Les quereux, "Description of the Coal Flora of the Carboniferous Formation in Pennsylvania and Throughout the United States," Second Geologi cal of Pennsylrania. Report of Progress P. vols. i.. ii., and V. (Harrisburg, ISSO-S4) ; D. White, "Fossil Flora of the Lower Coal Measures of Missouri," Monographs of the United States Geological Surrey, vol. xxxvii. (Washington, 1899).