76 Seward . — ^4 Contribution to our 
small sections (1185) in the Williamson Collection shows the 
strongly marked curvatures of the tracheids remarkably well. 
It has been pointed out by Williamson and Scott that in 
Lyginodendron Oldhamium the internal cambium may arise 
£ partly from the parenchyma of the primary xylem, so that 
some of the tracheae belonging to the latter have been carried 
inwards into the pith V By this means the original position 
of the primary xylem-elements would be altered, and their 
subsequent recognition rendered more difficult. This possi- 
bility should be borne in mind in connexion with the apparent 
absence of primary xylem-strands in Nield’s stem. 
To compare, briefly, Lyginodendron Oldhamium and the 
larger stem described above, as regards the centrifugal wood, 
there is on the whole a very close agreement ; but a careful 
comparison of sections from the British Museum stem with 
numerous examples of Lyginodendron Oldhamium confirms 
the opinion expressed by Williamson and Scott, that in Nield’s 
specimen the tracheids are somewhat smaller than in the 
undoubted examples of Lyginodendron . In Lygmodendron 
Oldhamium the medullary rays are usually narrower, and 
smaller in proportion to the breadth of the tracheid-bands 
than in the larger stem. The anomalous wood described by 
Williamson and Scott in some examples of Lyginodendron is 
precisely similar in structure to the ring of centripetal wood 
in Nield’s stem. In some examples of Lyginodendron Old- 
hamium the tissues of the pith present the same regular 
radial arrangement of parenchymatous cells as in the large 
stem. The sclerous nests and secretory sacs are practically 
identical in distribution and appearance in Lyginodendron 
Oldhamium and Nield’s stem. 
In transverse sections of Lyginodendron Oldhamium one 
occasionally finds that the secondary centrifugal wood and 
the primary xylem assume the appearance of an almost con- 
tinuous band without any obvious division between them ; 
stem, figured by Renault in a ‘Notice sur les Calamariees.’ Autun, 1895, 
Plate IV, Fig. 6. 
1 Loc. cit. , p. 723. 
