168 D. H. Scott. 



of this nature are among the very commonest Carboniferous specimens, 

 both as casts and petrifactions. The difficulty is that it is still im- 

 possible to refer the various specimens of Stirpnarki to the species, or 

 even the genus to which they belonged. Stigmaria has been found in 

 connection with the stems both of Sigillaria and Lepidodendron : four 

 main Stigmarian branches were usually given off from the base of the 

 upright stem; they are dichotomously branched, and bear numerous, 

 spirally arranged rootlets, which, like the main axis, are repeatedly 

 forked. In the common British form, S. ficoides, the main axis has a 

 ring of centrifugal Avood, accompanied by phloem and surrounding a 

 pith; centripetal xylem is wholly absent and there is no clear dis- 

 tinction between primary and secondary wood. In other species, 

 however, centripetal primary wood is present. Periderm was formed 

 abundantly as in the stem. The rootlets have a totally different 

 structure, each containing a monarch stele as in the roots of a recent 

 Isoetes or Selaginella. A peculiar feature is the presence of radial 

 vascular strands, connecting tlie protoxylem of the stele with groups 

 of cortical tracheides (Weiss, 1902). The morphology oî St ig maria 

 has been much disputed; so far as the main axis is concerned the 

 best analogj^, though a somewhat remote one, appears to be with thé 

 rhizophores of Selaginella; the rootlets agree so nearly with the roots 

 of some recent Lj^copods that there seems little doubt as to their 

 homologies, though their peculiar arrangement has led some authors 

 to interpret them as modified leaves. 



Anatomically the Lepidodendreae are a well-characterised group, 

 as to the affinities of which there can be no doubt, even apart from 

 the evidence of fructification. The primary anatomy is of simple 

 Lycopodiaceous type, comparable to that of the aerial stem of SeJagi- 

 nella spinosa or a large stem of Psilotum — the higher anatomical 

 organization is chiefly expressed in the general occurrence of second- 

 ary growth. Except for the very different arrangement of tlie foliar 

 traces there is a certain resemblance between the stelar structure 

 of a Lepidodendron and that of Cheirostrohus among the Sphenophyll- 

 ales. Otherwise there is little in the vegetative cliaracters which 

 throws any new light on the affinities of the class. 



The Fructifications of the Lepidodendreae are grouped under se- 

 veral generic names. In Lepidostrohm. the most extensive and oldest- 

 established of these genera, the organization is essentialh' that of a 

 Lycopodiaceous cone (Fig. 9). The axis, resembling a vegetative twig 

 in structure, bears numerous spirally arranged sporophylls, each of 

 which has a single large sporangium on its upper surface, attached 

 almost throughout its whole length. The sporophyll has an up- 

 turned lamina, between which and the end of the sporangium a ligule 

 is situated, showing that the whole of the long horizontal pedicel on 



