534 PTERIDOSPERMS, ETC. [CH. 



parts of the leaf is much less evident. The primitive leaf was 

 probably a dichotomously branched axis provided with a 

 continuous lamina which eventually became broken up into 

 separate lobes or pinnules. 



As the dichotomy of the frond became less regular, a pinnate 

 habit was acquired, as is clearly seen in many Palaeozoic tj^es 

 which constitute connecting links between forked and pinnate 

 fronds (fig. 354, D). The Aphlebiae may be remnants of the 

 once-continuous lamina on the petiole, and the normal pinnules 

 borne on the rachis may be regarded as the attributes of fronds 

 in which the division of physiological labour had not reached 

 the stage which characterises the leaves of recent ferns. 



Mariopteris. 



This name, which is due to Zeiller^ is applied by him to 

 Palaeozoic fronds characterised by a double bifurcation of the 

 rachis of the primary pinnae. Mariopteris muricata (= Peco- 

 pteris muricata Schloth.) may be taken as the type of the genus. 

 This species is common in the Lower and Middle Coal-Measures 

 of Britain and rare in the Upper Coal-Measures'". It is 

 described by Kidston" as one of the most polymorphic and 

 widely distributed Coal-Measure species. The pinnules as 

 seen in fig. 364, B, are of the Sphenopteroid type. No fertile 

 specimens are known, but it is significant that Grand'Eury* 

 has recorded the association of Mariopteris muricata and seeds. 



The main rachis gives off alternate naked branches, each of 

 which bifurcates at its apex into two short naked axes, and these 

 are again forked, the ultimate branches having the form of 

 bipinnate pinnae provided with large Sphenopteroid pinnules 

 (fig. 354, B). Zeiller includes in Mariopteris some species 

 which Stur" referred to his genus Diplotmema. Possibly some 

 of the Palaeozoic fronds with a zigzag rachis may have been 

 climbers like Lygodium. 



1 Zeiller (79=). ^ Kidston (Ol") p. 195. 



3 For synonymy, see Kidston (03) p. 771. 



*■ Grand'Eury (08). » Stur (75) A. p. 120. 



