78 
Seward. — A Contribution to our 
present paper, should be placed in the genus Lyginodendron , 
but is in all probability not specifically identical with Lygino- 
dendron Oldhamium (Binney). No actual proof of the 
occurrence of primary xylem-tracheids has been discovered, 
but such evidence as is available is favourable rather than 
opposed to the original existence of such primary strands. 
As a convenient designation of Nield’s large stem, of which 
the diameter must have been very considerably greater than 
in any previously known specimen of the genus, we may 
adopt the name Lyginodendron robustum. 
With reference to the numerous examples referred to 
Lyginodendron Oldhamium , Williamson and Scott write : 
‘All the forms with which we are concerned may be pro- 
visionally referred to the same species, or rather type, Lygino- 
dendron Oldhamium .’ As these words imply, it may be 
possible with more complete knowledge to recognize additional 
specific types among the numerous examples of the genus. 
As regards a comparison with recent plants, the most striking 
resemblance is that between the centrifugal wood of Lygino- 
dendron robustum and the wood of Cycadean stems. An 
examination of sections of the secondary wood of Cycas, 
Stangeria , and Macrozamia reveals the closest possible 
resemblance with Lyginodendron. In the stems of Cycas 
and Macrozamia , however, the wood does not form a broad 
continuous band as in Lyginodendron robustum , but consists 
of concentric zones developed from successive meristems. 
The cycadean nature of the centrifugal wood of Lyginodendron 
Oldhamium has been previously pointed out by Williamson and 
Scott 1 and others 2 , but the much larger size of the stem of Lygi- 
nodendron robustum makes the resemblance still more striking 
than in the much smaller form, Lyginodendron Oldhamium. 
In 1879 Renault described a new type of a Palaeozoic 
plant from the well-known silicified beds of Autun, to which 
he gave the name Cycadoxylon Fremyi 3 . A comparison of 
1 Loc. cit., p. 767. 2 Solms-Laubach, Fossil Botany (1891), p. 361. 
3 Structure comparee de quelques tiges de la Flore Carbonifere (Nouv. Arch. 
Mus. Paris, Vol. ii [2], 1879, p. 283. See also Cours de botanique fossile, Vol. i. 
(1880), p. 74, Plate XT. 
