8o 
Seward. — A Contribution to our 
Fremyi is represented, showing an internal and narrow band 
of centripetal xylem, composed of tracheid-rows separated 
by broad medullary rays, and external to this a narrow zone 
of parenchyma, followed by a broader zone of centrifugal, 
xylem. The broad band of the latter wood consists of rows of 
tracheids and broad medullary rays practically identical with 
the corresponding xylem of Lyginodendron robustum , the 
centripetal wood is also precisely alike in the two plants. The 
absence of any cortical tissues in Lyginodendron robustum 
prevents any comparison with the cortex of Cycadoxylon. 
1 Gum-canals ’ are fairly numerous in the tissues of the latter 
genus, as in Lyginodendron. 
In the pith of Cycadoxylon there appear to be no sclerous 
nests, and in the cortical tissues there are none of the radially- 
disposed bands of sclerenchyma characteristic of Lyginodendron 
Oldhamium. As at present defined, the genus Cycadoxylon 
is no doubt distinct from Lyginodendron ; the resemblance, 
which is indeed particularly close between the centrifugal and 
centripetal wood of the two plants, Cycadoxylon Fremyi and 
Lyginodendron robustum , is one based on secondary structures. 
There is no evidence of any similar agreement as regards the 
more important primary structures 1 . 
In 1878 2 Williamson figured and described three sections 
of a fragment of wood from the volcanic ash of Arran which 
he named Lyginodendron anomalum. A re-examination of 
the sections by Williamson and Scott led them to regard 
the specimen as having ‘ nothing in common with the genus 
Lyginodendron 5 but as rather comparable with Renault’s 
Cycadoxylon 3 . In transverse section the Arran fragment 
shows bands of reticulately pitted tracheids and broad medul- 
lary rays, with some of the tracheids occasionally cut across 
in an obliquely longitudinal direction. In tangential section 
3 The existence of a group of primary xylem, referred to in a previous footnote, 
makes the agreement still closer. 
2 Phil. Trans., 1878 (Memoir IX of Williamson), p. 252, Plate XXV, 
Figs. 90-92. The specimen from which the sections were obtained is in the 
Geological Museum of the University of Glasgow. 
3 Williamson and Scott, loc. cit., p. 770 (footnote). 
