482 PAL^iOBOTANY. 



giving origin to slender cylindrical rootlets. Internal structure 

 an axis of scalariform vessels, surrounded by a cylinder of 

 parenchymatous cells, and by an outer cylinder of elongated 

 woody cells. Fructification consisting of naked oval spore- 

 cases, borne usually in pairs on slender curved pedicles, either 

 lateral or terminal." 



Species of Psilophyton occur all through the Devonian series 

 of North America, and they are also not wanting in the Old 

 Red Sandstone of Britain. The genus is regarded by Dr 

 Dawson as comprising "synthetic or generalised plants, having 

 rhizomata resembling those of some ferns, stems having the 

 structure of Lycopodium, and rudimentary leaves also resem- 

 bling those of Lycopodiacece, branchlets with circinate verna- 

 tion like that of Ferns, and sporangia of a type quite peculiar 

 to themselves." 



The Ferns of the Devonian period are very numerous, and 

 upon the whole present a close resemblance to those of the 

 Carboniferous period. The smaller forms are represented by- 

 such genera as Cyclopteris, Neuropteris, Sphenopteris, Alethop- 

 tcris, Pecopteris, &c. Besides these, however, there occur the 

 trunks of large Tree-ferns, which are referred to the genera 

 Psaronius, Caulopteris, and Protopteris. Subjoined is an illus- 

 tration of a Fern from the Devonian of Europe (fig. 381). 



The Sigillarioids of the Devonian series comprise forms 

 referable to the well-known genera Sigillaria (with Stigmaria) 

 and Calamodendron ; though the affinities of the last are not 

 well understood. The characters of these genera will be 

 noticed in treating of the plants of the Carboniferous series. 



The Coniferte of the Devonian Rocks belong to the genera 

 Dadoxylon, Ormoxylon, and Prototaxites. All of these are 

 exogenous trees with concentric rings of growth, and the two 

 former are undoubtedly Coniferous, as their woody tissue 

 exhibits discs under the microscope. Prototaxites, unlike the 

 preceding, occurs in the Lower Devonian series, and is there- 

 fore the oldest Exogenous tree at present known to us. The 

 woody fibres do not exhibit punctations, and there is there- 

 fore some doubt as to the exact position of this genus. 



In addition to the preceding forms, the Devonian Rocks have 

 yielded examples of the fossils known as Stcrnbergia, Cyperites, 

 Asterophyllites, Annularia, Pinnularia, Cardiocarpon, and Tri- 

 gonocarpon. Of these, the genus Stembergia comprises cylin- 

 drical, transversely-marked fossils, which are now known to 

 be nothing more than the casts of the pith-cylinders of other 

 plants. They seem chiefly to belong to Conifers of the genus 

 Dadoxylon, but they are referable also to Sigillaria, and even 



