THE CARBONIFEROUS AND PERMIAN FLORAS. 49! 



and the branches are given off in a regular, bifurcating manner. 

 The bark is marked with numerous rhombic or oval scars, 

 arranged in quincunx order, and indicating the points where 

 leaves were formerly attached. The branches were covered 

 with slender, pointed leaves, closely crowded together; and 

 the fructification was carried at the ends of the branches in 

 the form of cones or spikes. These cones have generally been 

 described under the name of Lepidostrobi ; and they consist of 

 a central axis, surrounded by imbricated scales or bracts, each 

 of which supports a sporangium or spore-case. 



In internal structure, Lepidodendron possesses a large cen- 

 tral pith, surrounded by a continuous sheath of scalariform 

 vessels. Outside this, again, is a thick bark, composed mainly 

 of elongated fibres or " bast-tissue," with a thin dense outer 

 rind. 



The genera, or sub-genera, Sagenaria, Knorria, and Aspidiaria, 

 are properly to be referred to Lepidodendron. The genus Le- 

 pidophloios, however, is represented in both in Devonian and 

 Carboniferous Rocks by forms which are generically distinct 

 from Lepidodendron. The genus includes Lycopodiaceous 

 trees which have " thick branches, transversely elongated leaf- 

 scars, each with three vascular points, and placed on elevated 

 or scale-like protuberances, long one-nerved leaves, and large 

 lateral strobiles in vertical rows or spirally disposed" (Daw- 

 son). 



e. Sigillarioids. The three chief genera included under this 

 head are Sigillaria, Rhytidolepis, and JFhvularia, of which the 

 first is the most important. The Sigillarioids commence their 

 existence, so far as known, in the Devonian period, but they 

 attain their maximum in the Carboniferous ; and unlike the 

 Lepidodendroids they are not known to occur in the Per- 

 mian period. They are comparatively gigantic in size, often 

 attaining a height of from thirty to fifty feet or more; but 

 though abundant and well preserved, great divergence of 

 opinion prevails as to their true affinities. The name of Sigil- 

 larioids (Lat. sigilla, little seals or images) is derived from the 

 fact that the bark is marked with seal-like impressions or leaf- 

 scars (fig. 388). 



According to Dawson, Sigillaria proper is distinguished by 

 its strong ribs, " which are usually much broader than the 

 oval or elliptical tripunctate areoles, and are striated longi- 

 tudinally." The stem consists of a central pith, which is trans- 

 versely partitioned, as in the so-called Sternbergice. The pith 

 is surrounded by a woody cylinder, consisting of ligneous 

 wedges, composed of punctated (discigerous) and scalariform 



