446 PAL^EOBOTANY. 



in pairs on slender curved pedicles, either lateral or ter- 

 minal." 



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, hav- 

 ing rhizomata resembling those of some ferns, stems having 

 the structure of Lycopodium, and rudimentary leaves also 

 resembling those of Lycopodiaccm, branchlets with circinate 

 vernation like that of Ferns, and sporangia of a type quite 

 peculiar to themselves." The genus, as has been seen, begins 

 in the Upper Silurian. 



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 Gydopteris, Ncuropteris, Sphenop)teris, Alethop- 

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

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

 Psaronius or Stcmmatoptcris, Caulop)tcris, and Protoptcris. Sub- 

 joined is an illustration of a Fern from the Devonian of 

 Europe (fig. 700). 



The SigiUarioids of tlie Devonian series comprise forms 

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

 and Calcniiodendron ; 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 remains of Conifer ce are by no means unknown in 

 the Devonian rocks, and various generic types of this group 

 are represented. The two principal genera of this period 

 are Dadoxylon and Ornioxylon, both of which are exogenous 

 trees with concentric rings of growth, their woody tissue 

 exhibiting " discs " under the microscope. We may also 

 place here the genus Prototaxites (fig. 701), which is found 

 in the Lower Devonian of Canada, and which is regarded by 

 Principal Dawson as being Coniferous. The trunks of 

 Prototaxites vary in diameter from one to three feet, and 

 exhibit concentric rings of growth ; but its woody fibres have 

 not yet been incontestably proved to possess discs. Mr 

 Carruthers does not consider the Coniferous nature of Pro- 



