DISTRIBUTION OF PLANTS. Ill 



branching form has received the generic name of Buthotre- 

 phis (Fig. 129). In the Upper Silurian, besides many marine 

 species, there were a number of true land-plants, among which 

 may be mentioned the genus Psilophyton, which is a represen- 

 tative of the Club-mosses or Lycopods. 



3. A very marked advance is exhibited in the vegetation of 

 the Devonian Bra. The fucoidal plants of the Silurian con- 

 tinue in this age, but they were accompanied with a multi- 

 tude of Vascular Cryptogams, and even some Phenogams 

 (Gymnosperms). For the first time there was a true forest 

 vegetation ; and the great size and number of the plants thus 

 early foreshadowed the remarkable development that took 

 place in the next age. The groups existing were as follows : 



(a) The Equisetacese were represented by Calamites and As- 

 terophyllites (Fig. 130). The Calamites had long, slender, 

 tapering, and jointed stems, sometimes two feet in diameter 

 and thirty feet high. The surface was finely striated, or fluted, 

 and at all the joints were situated whorls of scale-like or thread- 

 like leaves. They were, except as regards size, like our living 

 Equiseta, which grow generally less than three feet high and 

 no thicker than the finger. The Asterophyllites were herba- 

 ceous, flexible species, with leaves arranged in whorls at the 

 joints as the name indicates. 



(6) The Ferns were represented by such genera as Cyclopteris 

 and Neuropteris. In these the leaflets or pinnae have no midrib. 



(c) The Lycopods were Psilophyton, already introduced in 

 the Upper Silurian, Lepidodendron and Sigillaria. The Lepi- 

 dodendra were gigantic plants, the surface of whose trunks 

 and branches was regularly marked in rhomboidal patterns, 

 or quincuncially, representing the leaf arrangement (Fig. 131) ; 

 the branches were clothed with squamous, spinous or acicular 

 leaves, and terminated by scale-cones, which bore spores like 

 the Club-mosses. The Sigillariee were likewise arboreous, but 

 their trunks exhibited longitudinal ribbing or fluting, and ver- 

 tical rows of seal-like impressions representing the leaf ar- 

 rangement ; thej' were but little, if at all, branched, and clothed 

 with numerous long, tapering leaves. 



