33& PALAEONTOLOGY 



by trees which attained a height of fifty feet or more and 

 a thickness of several feet, the latter attained by a 

 process of secondary thickening like that of modern 

 trees. Like the little Equisetum of to-day, they had a 

 hollow stem, and are most frequently represented by 

 internal casts (pith-casts), the markings on which are 

 very like those of the exterior of Equisetum vertical 

 flutings, alternating in position at the nodes (where 

 leaf- whorls arose). Chief genera: Archceocalamites (U. 

 Dev.-L. Carb.), Catamites (U. Carb., Fig. 100, /, leaves 

 known as Anrmlaria, Asterophyllites, Calamocladus, repro- 

 ductive cones as C alamo stachys, etc.), Schizoneura (Perm.- 

 Trias.), Equisetites (Rhaetic-Wealden). 



Lycopodiales. The post-Carboniferous members of 

 this group are all herbaceous plants, of little geological 

 importance, but in the Devonian and Carboniferous 

 periods it was also represented by forest-trees of great 

 size and with secondary thickening. Genera : Lepidoden- 

 dron (Dev.-Carb., Fig. 100, d), Sigillaria (U. Carb., Fig. 

 100, e). These two genera are readily distinguished by 

 the leaf-scar pattern on the bark the former having 

 large rhomboidal scars covering the whole surface, the 

 latter having small scars of varying shape in vertical 

 rows: in both, the full pattern is only shown on the 

 exterior of the bark, its internal surface or the decorti- 

 cated stem showing a ghost of the same pattern. The 

 roots of both are alike, branching dichotomously (Stig- 

 maria)', the reproductive cones of Lepidodendron are known 

 as Lepidostrobus, those of Sigillaria as Sigillariostrobiis. 

 In some species of Lepidodendron the megasporangium 



