480 PAL^EOBOTANY. 



genuine Sea-weeds. Besides these problematical fossils, how- 

 ever, the Upper Silurian Rocks have been shown to contain 

 the remains of genuine land-plants. Thus, remains of the 

 Lycopodiaceous genus Lepidodendron (Sagenaria) have been 

 discovered in the Upper Silurian of Germany and Bohemia. 

 At the summit of the Upper Silurian series in Britain have 

 been detected numerous seed-vessels or " sporangia " referred 

 by Hooker to a Lycopodiaceous plant under the generic title 

 of Pachytheca. Lastly, the Upper Silurian of North America 

 has yielded remains of the characteristic Devonian genus Psilo- 

 phyton, which will be described immediately. 



DEVONIAN PLANTS. The plants of the Devonian period 

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

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

 fer a the whole constituting an abundant terrestrial vegetation. 

 Besides the above, however as already mentioned the re- 

 mains of a true Angiospermous Exogen have in one instance 

 been detected in Devonian strata (Dawson). 



The Equisetacece are represented by species of the remarkable 

 genus Calamites, the characters of which will be briefly spoken 

 of when treating of the Coal-plants. 



The Lycopodiacea are represented by the genera Lepidoden- 

 dron, Lycopodites, Leptophlaum, Lepidophloios, Cordaites, and 

 Psilophyton. The Lepidodendroids will be shortly discussed 

 under the head of the plants of the Carboniferous series ; but 

 Cordaites and Psilophyton merit special notice here. The 

 genus Cordaites is common both to the Devonian and the 

 Carboniferous formations, and includes broad, striated, parallel- 

 veined leaves, which are extremely abundant in certain beds. 

 They possess broad clasping bases, and may attain a length of 

 a foot and a breadth of as much as three inches. Their affini- 

 ties are disputed j but they are regarded by Dr Dawson as 

 referable to some Lycopodiaceous plant. 



The genus Psilophyton of Dawson (fig. 380) 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 inter- 

 rupted 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 decor- 

 ticated specimens represented by minute punctate scars. Young 

 branches circinate ; rhizomata cylindrical, covered with hairs 

 or ramenta, and having circular areoles irregularly disposed, 



