ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 689 
The general structure of the secondary wood is identical with that of the stem of 
Calamites. The fascicular wood abuts directly on the external elements of the 
primary xylem (see fig. 2). The interfascicular wood is soon formed across the whole 
width of the primary rays, which, consequently, cannot be traced far outwards (see 
Plate 15, photographs 3, 6, and 7). In some cases the cells of the primary ray show 
tangential dilatation, exactly as we described in the case of the stem in our last paper.* 
In these, as in other roots, the primary interfascicular rays are necessarily limited 
to the wood, for each of them corresponds in position to a strand of primary phloém. 
A characteristic feature of the secondary wood is the regular presence of a ray one or 
two cells in thickness, exactly opposite each protoxylem-angle (see Plate 16, fig. 2, fr.). 
These rays, which often consist of cells rather broader than the trachez, can some- 
times be traced for a long distance through the wood. In some cases they become 
subdivided by intercalated series of trachew. We may call them fascicular rays, to 
distinguish them from the broader interfascicular rays which lie between the bundles 
of primary xylem. ‘The fascicular rays can be recognized in radial sections also, 
wherever the plane of section exactly passes through the protoxylem (see fig. 3, 
fr.). They can also be distinguished in tangential sections which pass through 
the inner part of the wood. These rays were observed by Renavtt, in his Astro- 
myelon augustodunense, in 1885.t 
The formation of a ray opposite each protoxylem-group is a well-known pheno- 
menon in recent roots.{ 
The wood also contains numerous secondary rays of the ordinary type.§ 
The trachez agree in all respects with those of the stem. Their pits are usually 
limited to the radial walls, and are distinctly bordered, as can best be seen in good 
tangential sections. 
Remains of the cambium and phloém have been observed in several of the more 
advanced specimens, as well as in the younger roots already mentioned. Perhaps the 
best specimen in this respect is that illustrated in Plate 15, photograph 3, and in 
Plate 17, figs. 10 and 11. This root shows a distinct layer of phloém (fig. 10, ph.), 
which has split away from the wood, and remains attached to the cortical zone. Here 
and there a tabular cambial cell is seen at the outer edge of the wood (cb.). We 
cannot be certain that the whole thickness of the pbloém remains ; the part preserved 
is six or more cells in width, and its elements show traces of a radial arrangement. 
Most of this tissue, no doubt, belonged to the secondary phloém ; some more irregular 
groups in the outer part of the zone probably represent the primary phloém. 
The structure of the cortex has been fully described in formér memoirs.|| Only a 
* “Purther Observations,” Part I., p. 884. 
+ Loc. cit., “ Nouvelles Recherches,” p. 98. 
t Dr Bary, ‘Comparative Anatomy of Phanerogams and Ferns,’ Engl. ed., p. 474. 
§ See WinLiamson, “ Organization,” Part IX., Plate 19, fig. 6, ¢. 
|| See especially ‘* Organization,” Part XII. 
MDCCCXCV.— B. 4U 
