.XVI FOSSIL ARCHEGONIATES 589 



have closely resembled, except for their much greater dimen- 

 sions, such species of Lycopodium as L. cernuum or L. den- 

 droideum. The branching was prevailingly dichotomous, and 

 the shoots thickly set with acicular leaves of a size correspond- 

 ing to the dim-cnsions of the shoots. Sigillaria seems to have 

 been much less freely branched than Lepidodendron, and it 

 has even been supposed that in some species branching was en- 

 tirely suppressed. Of the living species of Lycopodium, L. 

 mundattmi or L. sattritrus may be compared in habit to Sigil- 

 laria. Trunks of Lepidodendron a hundred feet in length have 

 been found, show^ing the genuine tree-like proportions of these 

 giant Club-mosses. 



The base of the stem in both Lepidodendron and Sigillaria 

 is often found connected w^ith forking structures, which were 

 originally described as distinct fossils under the name Stig- 

 maria. It is clear, however, that these were the underground 

 parts of Lepidodendron and Sigillaria, probably rhizomes 

 rather than true roots. The name Stigniaria is given them be- 

 cause of the very regular scars upon the surface, and these have 

 been shown to be the points of attachment for roots — or root- 

 lets, if the main SHgmaria branches are true roots and not rhi- 

 zomes (see Scott (i), Fig. 82). 



The slender pointed leaves were often of considerable 

 length, 15 centimetres or more, and resembled those of Selagi- 

 nclla rather than Lycopodium in having a ligule near the base. 

 (See Scott (i), Figs. 48, 58). 



The internal structure is w-ell known in a good many forms, 

 especially among the Lepidodendraceae ( Scott ( i ) ) , and it is 

 evident that there was a good deal of difference among them, 

 especially in the degree of secondary thickening which occurred. 



In all know^n species of Lepidodendron (Scott (i), p. 123) 

 there is always a single stele with centripetally developed pri- 

 mary wood. There may or may not be a central pith. In the 

 larger stems there is usually a central medulla about which the 

 primary w^ood forms a ring. Probably the phloem, W'hich is 

 rarely well preserved, formed a ring outside the xylem. The 

 cortex is relatively very thick, as it is in the living Lycopo- 

 dinese, and through it passed obliquely the leaf-trace bundles, 

 one being given off from the central stele of the stem to each 

 leaf-base. 



While in some species, e. g.^ L. parvnlum, there w^as appar- 



