448 COENOPTERIDEAE [CH. 



situated between the two metaxylem zones. As Mr Gordon 

 says : this type of stem occupies a position " in the Zygopteroid 

 alliance " corresponding to that which Thamnoptefis Schlech- 

 tendalii (p. 329) occupies in the Osmundaceous series. The 

 discovery of this stem supplies another link between the two 

 fern groups, Osmundaceae and Coenopterideae. Pelourde^ has 

 described an imperfectly preserved vascular strand from a 

 locality near Autun as the type of a new genus Flicheia esnostensis. 

 Mr Gordon has pointed out to me that this is a partially rotted 

 petiole of Diplolabis esnostensis (= Zygopteris Roemeri). 



In their recent account of fossil Osmundaceous genera, Kid- 

 ston and Gwynne-Vaughan^ speak of the central parenchyma of 

 the existing medullated stele as being derived from tracheal 

 tissue. They add that if the Zygopteroid line of descent is at 

 all close to the Osmundaceous, we must be prepared for the 

 existence of a Zygopteris with a solid xylem like that of 

 Thamnopteris : " such a discovery, in fact, we hopefully antici- 

 pated" The new Pettycur stem amply justifies this prophecy. 

 It is noteworthy that Mr Gordon's stem affords an instance of 

 the occurrence of a type of stele, similar in its cylindrical form 

 and in the absence of parenchyma to that of Botryopteris, in a 

 plant bearing leaves characterised by the Zygopteris type of 

 vascular strand. 



Metaclepsydropsis duplex (Will.) fig. 310, A^ {= Rachiopteris 

 duplex, Williamson 1874. Asterochlaena (Clepsydropsis) 

 duplex, Stenzel 1889. Clepsydropsis, Renault 1896.] 



The vascular axis of the main axis of the frond is charac- 

 terised by the hour-glass shape of the xylem which consists 

 entirely of tracheae, most of which are reticulately pitted. In 

 a transverse section (fig. 310, A) the two ends of the stele are 

 dissimilar ; at one end of the long axis is a small bay of thin- 

 walled tissue (phloem) enclosed by a narrow band of xylem, and 



1 Pelourde (09). 



2 Kidston and Gwynne-Vaughan (08) p. 230. 3 Ibid, (09) p. 664. 



* A Culm species Rachiopleris aphyllus (Unger) is closely allied to Meta- 

 clepsydropsis duplex. [See Solms-Laubach (96) p. 30.] 



