The peculiarities of the genus have been emphasised by Solms-Laubach by the institution of a family-name Protopityeae: the genus is essentially a generalised type exhibiting in the structure of its stem both Filicean and Coniferous features. The bordered pits differ from those in recent Conifers in their flatter form, but in this respect they exhibit a closer agreement with the transversely stretched pits of _Xenoxylon phyllocladoides_ Goth.[536], a Mesozoic species. CHAPTER XXXIII. CORDAITALES. A. =POROXYLEAE=. =Poroxylon=. Renault. In 1879 Renault[537] briefly summarised the anatomical features of some silicified vegetative shoots from the Permian of Autun for which he instituted a new family, the Poroxyleae. The more complete account contains a description of two species, _Poroxylon Boysseti_ and _P. Duchartrei_: the latter was afterwards recognised as a stem of _Heterangium_. Renault considered this new genus to be closely allied to _Sigillaria_ and _Sigillariopsis_ and pointed out its resemblance to _Cordaites_. Additional species have since been described but as yet the genus has not been found outside France in Permo-Carboniferous strata of Autun and the St Étienne district. The results of a more detailed investigation of the anatomy of the genus were published by Bertrand and Renault in 1882 and since then[538] Bertrand, Renault, and Scott have added to our knowledge of this interesting type. In several respects _Poroxylon_ stems present a striking resemblance to _Lyginopteris_, but the recent discovery of the genus _Mesoxylon_ has given greater significance to the characters in which _Poroxylon_ agrees with representatives of the Cordaitales. Our knowledge of the genus, though exceptionally full with regard to the anatomy of vegetative shoots, does not include any precise information as to the reproductive organs. The slender cylindrical stems, not exceeding 2–3 cm. in diameter in specimens so far recorded, bore large broadly linear leaves similar in form and venation to those of some species of _Cordaites_ which were attached singly to slightly swollen nodes separated from one another by internodes several centimetres long. The base of the rather fleshy lamina passes imperceptibly from the narrow lower portion into a tangentially expanded petiole which forms a decurrent ridge on the stem. Axillary buds frequently occur. Little is known of the leaf-impressions, but if Grand’Eury[539] is correct in his identification of certain specimens from French Stephanian beds as the leaves of _Poroxylon_, the lamina reached a length of 1 met. and a breadth of 15–20 cm. In habit the stems probably resembled some of the larger-leaved Bamboos. The only evidence bearing on the nature of the reproductive organs is furnished by Grand’Eury who believes that some _Rhabdocarpus_ seeds and bractless inflorescences associated with the leaves assigned to _Poroxylon_ belong to that genus.