120 THE MORPHOLOGY OF PTERIDOPHYTES 



from stem and the term 'Phyllophore' is sometimes used 

 for intermediate orders of branching. 



Austroclepsis, occurring in Lower Carboniferous rocks of 

 AustraUa, was first described^® as a species of Clepsydropsis, 

 on account of its clepsydroid petioles. However, the mode of 

 growth of the plant and the internal anatomy of the stem 

 show that it was not a member of the Cladoxylales. It had a 

 stout trunk, at least 30 cm in diameter and 3 m high, that 

 must have looked superficially like modern tree ferns, but it 

 differed fundamentally from these in that, within the mass of 

 roots constituting the main bulk of the trunk, there were 

 several stems instead of just one. These branched within the 

 trunk and gave off numerous petioles in a 2/5 phyllotactic 

 sequence and these, too, continued to run up within the 

 trunk. Each of the many stems had a single stele, usually 

 pentarch, in which there was a central stellate region of 

 mixed pith surrounded by a zone of tracheids. The petioles 

 had a rather narrow clepsydroid stele with two islands of 

 parenchyma bounded by ^peripheral loops' of xylem, and it 

 was from these peripheral loops that pinna traces were given 

 off from alternate sides at distant intervals, each associated 

 with aphlebiae. 



Metaclepsydropsis duplex, from Lower Carboniferous 

 rocks of Pettycur, Scotland, ^^ had a creeping dichotomous 

 stem, from which erect *fronds' arose at intervals. Its stele 

 was circular in cross section or (just before a dichotomy) oval 

 (Fig. 17J), with an inner region of mixed pith and an outer 

 zone of large tracheids. The only protoxylem present was 

 that associated with the origin of a leaf trace, there being no 

 cauHne protoxylem at all. The leaf trace was at first oval in 

 cross section (Fig. 17K) but soon became clepsydroid (Fig. 

 17L). Pinnae were borne in alternate pairs, along with 

 aphlebiae (i). In giving rise to a pair of pinna traces, the 

 peripheral loop (2) became detached and then split into 

 two (3). A new peripheral loop then quickly re-formed. 



Diplolahis Roemeri occurs in the same rocks and was very 



