304 



LYCOPODIALES 



similar in their general characters, as also in their clear definition, to 

 those of the more differentiated types of Lycopodium or to Selaginella. 

 The general structure of the strobilus is, as in other Lycopods, essentially 

 the same as that of the vegetative shoot, excepting in the presence of the 

 sporangia. These are of very large size, and are commonly extended radially 

 outwards from the axis, being interposed between the axis and the 

 ligule : the latter then appears on the upper surface of the sporophyll, 

 beyond the distal limit of the sporangium (Fig. 153). In Lepidodendron 

 the cones thus constructed were borne on the ends of the ordinary 



B 



FIG. 152. 



Lepidophloios, sp. A = tangential section from the outside of a stem, passing through 

 the leaf-bases, and showing their characteristic form, slightly enlarged. = a single 

 leaf-base, to show details; = collateral vascular bundle; /a = the two parichnos- 

 strands; lg= ligule in its pit. x 10. Will. Coll., 1974 A. (After Scott.) 



branches; but in Sigillaria they appear to have arisen laterally upon the 

 main axis, from which after maturity they were deciduous, and each was 

 borne upon an elongated pedicel covered with acicular bracts, while the 

 cone itself showed a construction essentially similar to that of a small 

 Lepidodendron . 



Though the type with a definite cone marked off from the sterile 

 region was usual for the fossil Lycopodiales, it was not universal. In the 

 imperfectly known plant, Pleuromoia from the Trias, the whole main axis 

 seems to have been a strobilus (Fig. 154), borne upon a Stigmarian base 

 (compare Fig. 151). But a much more satisfactory example, from the 

 Westphalian series (Middle Coal Measures) is that of Ptnakodendron 

 musivitm, Weiss, specimens of which, discovered by M. Hector Delteure 



