CYCADOXYLEAE 487 



tracheides occur, and at its inner limit are the spiral 

 elements of the protoxylem. It would thus appear 

 that the whole normal wood was centrifugally developed, 

 as is usual in recent Cycads. Professor Seward, how- 

 ever, states that at one place he detected a distinct strand 

 of primary xylem ; this may indicate that some trace of 

 the mesarch structure of the Lyginodendreae still per- 

 sisted in Cycadoxylon, though much reduced. The wide 

 phloem-zone consists of alternating concentric bands of 

 parenchyma and sieve-tubes. 



Within the normal vascular ring, are two or more 

 interrupted zones of anomalous wood and bast, with 

 inverted orientation, the phloem facing inwards. These 

 medullary vascular arcs are separated by parenchyma 

 from the normal centrifugal wood. The whole structure 

 is thus comparable to that of Cycadoxylon robustum, 

 except that the normal zone is much less developed, 

 which may simply be a matter of age. 



Curiously enough, no leaf-trace bundles have so far 

 been found in Cycadoxylon Fremyi. The characters, as 

 at present known to us, strongly suggest Cycadean 

 affinities, though the characteristic anomaly of Cycado- 

 xylon, the formation of inverted zones of secondary 

 wood and bast in the pith, is not known in the same 

 form among recent Cycads. On the other hand, it is 

 identical with the most frequent anatomical variation 

 occurring in stems of Lyginodendron oldhamium. 



Another silicified stem from the Permian of Autun, 

 the Ptychoxylon Levyi of M. Renault, presents a some- 

 what similar combination of characters. In this fossil 

 the dimensions are greater than in Cycadoxylon Fremyi, 

 the stem of Ptychoxylon attaining a diameter of 5 or 6 



