276 CORDAITEAE [CH. 



Scott and Maslen Mesoxylon 1 . A separation of Cordaites from 

 Mesoxylon, which no doubt extended far beyond the British 

 area, is possible only if well-preserved petrified material is 

 available. The leaves of Mesoxylon, so far as our imperfect 

 knowledge of them enables us to express an opinion, are con- 

 structed on a plan almost identical with those of Cordaites and, 

 as already stated, it is almost certain that many of the impressions 

 referred to Cordaites were borne on Mesoxylon stems. An addi- 

 tional source of confusion is supplied by the Cordaites-like leaves 

 of Poroxylon. It is evident, therefore, that even within the limits 

 of the Carboniferous and Permian formations the recognition of 

 true Cordaites leaves must often be attended with considerable 

 risk of error. Apart from the possible confusion between the 

 foliage of Cordaites and Mesoxylon there are other difficulties as 

 regards detached leaves which depart more or less widely from 

 the typical Cordaitean form. Leaves such as C. circularis (fig. 

 468, B) and C. grandifolius emphasise the lack of any thoroughly 

 satisfactory dividing line separating single pinnules of Cardio- 

 pteris or Cyclopteris on the one hand and leaves of Psygmophyllum 

 on the other from Cordaites. The petrified buds described as 

 Dolerophyllum 21 have been quoted by several authors as examples 

 of unexpanded shoots of Cordaites though anatomical evidence 

 warrants a generic separation. In the case of species founded on 

 leaves described in this chapter as Cordaites it should be remem- 

 bered that further research may necessitate an alteration in 

 nomenclature. 



Among the species included in Cordaites is Noeggerathiopsis 

 Hislopi 3 (figs. 470 472), a type widely spread in India and in 

 other parts of Gondwana-Land : if the change of generic name is 

 accepted it involves the extension of the geographical range of 

 Cordaites from Northern Europe and North America to the southern 

 botanical province. We have as yet no proof of the existence of 

 Cordaites in the Arctic regions. The range in time of Cordaites 

 or of the Cordaitales has generally been stated to be from the 

 Upper Devonian to the Permian. It is, however, by no means 

 certain that the genus flourished before the Carboniferous period, 

 though it is clear that closely allied types must have lived in 



1 See page 270. 2 See page 132. 3 See page 238. 



