[PENHALLOW] OSMUNDITES SKIDEGATENSIS Ti 
approach to completeness, the fourth and most external being repre- 
sented by a small fragment only. (Plate I. fig. 2.) 
The Pith.—The pith is prominent and 13 mm. broad in its greatest 
diameter. It consists of rather large, parenchyma cells in which local- 
ized groups often show a tendency to greater thickening of the walls. 
These groups of sclerenchyma are dark in colour, but devoid of starch. 
There is a general absence of starch in the medulla proper, except in the 
region bordering upon the stele and in certain radial extensions which 
lie between the folds of the horseshoe-shaped xylem bundles. These pro- 
iections, when narrow, are composed of thin-walled parenchyma cells 
which show remnants of nuclei, but they are devoid of starch. When 
broad, they commonly enlarge toward the free end. (Plate IT. fig. 3.) 
The border cells are then seen to be thin walled, usually with nuclei, 
and devoid of starch; but the cells of the central region are con- 
spicuously thicker walled and filled with large starch grains which are 
more or less completely carbonized, and thus impart to such structures a 
very dark appearance which is most conspicuous. (Plate IT. fig. 3.) 
The Medullary Rays—The medullary rays are very variable in 
width. In the narrower ones, the structure has been pretty completely 
obliterated. In the broader rays, the cells bordering upon the xylem 
are thin walled and contain nuclei, but they show no evidence of starch. 
The central region of such rays consists of rather thick-walled cells 
filled with starch. Outwardly the rays spread out laterally along the 
face of each of the xylem bundles (Plate IT. fig. 4) in such a way as 
to connect with the inner phloem between the xylem and the sieve cells. 
The Stele.— The stele is conspicuous, and it is made up of about 
twenty-six bundles of the collateral type. It has an external diameter 
of 19 mm. and an average thickness of 3 mm. 
The xylem bundles are conspicuous for their peculiarly curved or 
horseshoe form (Plate II. fig. 3), a feature which at once suggests 
comparison with Osmunda, in which similar bundles are a well-known 
and characteristic feature. The xylem elements consist of broad 
vessels of considerably greater diameter than in Osmunda Claytoniana 
or O. cinnamomea, and they are more nearly comparable with those 
of Todea barbara. The wall, at a point midway of its width, gen- 
erally shows a constriction (Plate III., fig. 6) where the opposing 
plates are joined laterally and vertically. Between this point and 
the lateral limits of the wall, the two plates are split away so as to 
leave a narrow slit-like opening in the median plane, such as may be 
observed ‘in Osmunda and more conspicuously in Todea. In 
longitudinal section the vessels are seen to be of the scalariform type 
common in ferns (Plate III. fig. 5), and identical with those which 
occur in Osmunda. 
