THE INTERNAL STRUCTURE OF SIGILLARIA ELEGANS. 543 
out through a medullary ray in an almost horizontal direction. Once free of the 
secondary xylem it suddenly bends upwards again (Pl. Il. fig. 15, /..). 
By the time the leaf trace emerges from the secondary wood one or two additional 
rows have been added, mostly on the side next the axis, but a few may have been 
added to the opposite side, and the leaf trace now shows a distinct mesarch structure 
(Pl. IL fig. 15, /.¢.). On another leaf trace, which is slightly further removed outward 
from the axis, a greater number of.tracheides have been added, and the increase seems 
to have been more equally placed on all sides of the primary group (PI. IL. fig. 16, /.t.). 
_ The course of the leaf traces through the xylem, and their behaviour on their 
emergence from it, seems to be similar to that so well represented in the figure of the 
radial section of Sigillaria Menard: given by Renavu.r.* 
It was impossible to discover any annular or spiral tracheides in the leaf trace, but 
their structure is very much effaced in their passage through the secondary xylem. 
Sigillaria elegans does not show any secondary wood in connection with the leaf 
trace up to their entrance into the inner cortex and in the outer layer of the bark (the 
only portion of the cortex preserved) ; the leaf traces are too imperfect to permit of their 
structure being made out. 
Cortex.—The only part of the cortex which has been preserved is that formed 
by the ribs, which must probably be regarded as composed of the confluent persistent 
leaf bases and a small portion of the underlying periderm. 
Fig. 18, Pl. I., shows the outer surface of a specimen of Sigillaria elegans, 
collected by Mr W. Hemineway from the Yorkshire Middle Coal Measures. In 
this condition the leaf cushions are usually compressed. ‘They are arranged on 
the ribs in vertical rows, the leaf scars of one row alternating with those on the 
contiguous rows. The leaf scars are subhexagonal, with prominent lateral angles, 
which alternate with those of the neighbouring leaf scars, and thus impart a zigzag 
course to the furrows between the ribs. The cones are borne in a verticil formed 
of a single row, and some of the cone scars are seen in the figure at c.s. 
In the uncompressed condition the leaf cushions slope outwards, and their lower 
margin becomes considerably elevated. This is shown on Pl. III. fig. 19, which 
is a radial section through a rib of Sigillaria elegans. The leaves are attached 
to the sloping surfaces, s.a. This figure is from a specimen received from Mr 
JamMEs Lomax, and was derived from the Halifax Hard bed. 
The surface of the leaf scar is formed of a stratum of dark broken - down 
parenchymatous tissue. The main body of the leaf cushion below this consists of 
fairly thick-walled parenchyma, the cells of which are more or less oval, with their 
longest diameter directed outwards. Towards the upper adaxial side of the cushion 
these cells become smaller, and seem to contain a dark-coloured material, which causes 
_ the tissue in this region to become opaque (PI. III. fig. 5). The lower margin is also 
formed by similar small opaque cells, but not developed to the same extent. 
* Flore fossile, Bassin howiller et permien d Autun et d’Epinac, Deux. part, Atlas, pl. xxxvii. fig. 6, 1893. 
