444 PALEOBOTANY. 



the Upper Silurian of North America has yielded remains of 

 the characteristic Devonian genus Psilophyton, which will be 

 described immediately, together with true Terns (related to 

 Ncurojpterii), and two forms allied to the great Devonian and 

 Carboniferous family of the Calamites (namely, Anmdaria 

 and Sphenopltyllmn). 



Devonian Plants. — The plants of the Devonian period 

 belong to the groups of the Equisetacece (Horse-tails), Lyco- 

 podiacece (Club-mosses), Filiccs (Ferns), Sigillarioids, and Coni- 

 ferce — the whole constituting an abundant terrestrial vegeta- 

 tion. Besides the above, however — as already mentioned 

 — the remains of a true Angiospermous Exogen are stated 

 to have been in one instance detected in Devonian strata 

 (Dawson). 



The Equisetacem are represented by species of the remark- 

 able genus Calamites, the characters of which will be briefly 

 spoken of when treating of the Coal-plants. 



The Lycopodiacem are represented by the genera Lcpidodtn- 

 dron, Lycopodites, Leptopthlwuiii, Zepidophloios, and Psilophyton. 

 The Lepidodendroids will be shortly discussed under the head 

 of the plants of the Carboniferous series ; but the genus 

 Psiloplmjton merits special notice here. 



The genus Psilophyton of Dawson (fig. 699) commences its 

 existence in the Upper Silurian rocks ; but it is character- 

 istically Devonian, and is not known to be represented in the 

 Carboniferous period. The following is given by Dr Dawson 

 as the definition of the genus : — 



" Stems branching dichotomously, and covered with in- 

 terrupted ridges. Leaves rudimentary, or short, rigid, and 

 pointed ; in barren stems, numerous and spirally arranged ; 

 in fertile stems and branchlets, sparsely scattered or absent ; 

 in decorticated specimens represented by minute punctate 

 scars. Young branches circinate ; rhizomata cylindrical, 

 covered with hairs or ramenta, and having circular areoles 

 irregularly disposed, giving origin to slender cylindrical root- 

 lets. Internal structure — an axis of scalariform vessels, 

 surrounded by a cylinder of parenchymatous cells, and 

 Ijy an outer cylinder of elongated woody cells. Fructifi- 

 cation consisting of naked oval spore-cases, borne usually 



