254 SIGILLARIEAE. 



the other. He accordingly considers the central wood also of Lepi- 

 dodendron to be composed of these leaf-traces. The secondary wood 

 of Sigillaria spinulosa forms a firmly-closed ring of considerable thickness 

 traversed by numerous rays of more than one kind, and has no special 

 features ; there is one point only to be noticed, that its primary rays do not 

 always coincide on the inner boundary with the places where the tracheal 

 ring of the central cylinder is interrupted, and that in this point also there 

 is less dependence of the two systems on one another in this species, than 

 appears to exist in Sigillaria Menardi. The inner cortical layer, consisting 

 of delicate tissue and inclosing the transverse sections of the ascending 

 leaf-trace-bundles, is only rarely and imperfectly preserved ; the contiguous 

 layer on the outer side shows exquisite Dictyoxylon-structure throughout 

 up to close beneath the surface ; this is caused by the undulated plates of 

 sclerenchyma approaching each other and uniting together here and there, 

 and then again separating from one another. This layer is also termed 

 by Renault in his accustomed way the ' couche sube"reuse.' How far it really 

 belongs to the periderm I am unable to determine ; the question must be 

 left to further investigation. 



While the scarcity of the Sigillariae in the upper beds of the Car- 

 boniferous formation makes it easy to understand why well-preserved 

 remains of them should be so rare in the French deposits, it is very sur- 

 prising to find that they are equally rare in the English coal-fields, though 

 impressions of Rhytidolepis-forms are abundant enough, and even their 

 outer rinds with the structure preserved cannot be said to be scarce. Only 

 one specimen has been found up to the present time, as far as I know, 

 which shows the rind and the woody body in connection. This comes from 

 Oldham and is in Carruthers's possession. Since the well-preserved surface 

 shows that it belongs to a species of the section Rhytidolepis, probably 

 Sigillaria Saullii, it is most desirable that it should speedily be submitted 

 to the examination which has hitherto been deferred. Its owner, however, 

 has been kind enough to show me the rough specimen, and I can only 

 confirm the statements of Williamson and Hartog l . The latter authors 

 say: ' The fragment has the continuous cylinder and all the internal organisa- 

 tion of Corda's Diploxylon ' ; it has therefore a structure, which, if we dis- 

 regard the secondary wood, answers perfectly to that of the central cylinder 

 of Lepidodendron Harcourtii. This only confirms us in the view which has 

 been already explained respecting the pith and the tracheal zone surround- 

 ing it in Sigillaria spinulosa and Sigillaria Menardi, and we shall be 

 able perhaps to set this view in a still clearer light, when once the details 

 of the structure of this Sigillaria Saullii have been laid before us. The 

 little that Williamson 2 has said about Rhytidolepis concerns only the outer- 



Hartog (5). * Williamson (1), n, t 29. 



