Seward — The A natomy of L epidodendron aculeatum , Sternb. 377 
and middle cortex is clearly defined by the junction of the vertical rows of 
the short cells of the former with the loose tissue of irregularly branched 
and hypha-like cells of the latter, which tend to assume a horizontal rather 
than a vertical direction. 
Numerous leaf-traces in slightly oblique transverse section occur in the 
middle cortex. A leaf-trace as seen in this region (Fig. 4, PI. XXVI) consists 
of a somewhat tangentially elongated xylem-strand (x) separated by a 
few layers of delicate elongated and narrow cells ( b ) from a patch of dark 
disorganized tissue in continuity with the secretory zone. The whole trace 
is enclosed by a few layers of parenchymatous cells (peridesm), of which those 
on the adaxial side often assume a radially elongated form (Fig. 4, p). The 
structure of a leaf-trace is shown in longitudinal section in Fig. 3, PI. XXVI. 
In the actual specimen the spiral protoxylem-elements are clearly seen, 
while the scalariform metaxylem-tracheids show a slight tendency towards 
a reticulate form of pitting. The xylem is shown at # and the disorganized 
cells of the secretory zone at s in Fig. 3, PI. XXVI. The contrast between 
the compact peridesm (p) and the loose cortex is seen at/, c. 
The clear line near the surface of the transverse section, reproduced in • 
Fig. 5, PL XXVI, represents a break in the tissue filled with mineral sub- 
stance, immediately internal to the sharply defined junction between the 
outer edge of the middle and the inner edge of the firmer and much more 
compact outer cortex. 
The cells at the inner edge of the outer cortex are short and rather 
flat and in longitudinal sections exhibit a fairly regular vertical arrange- 
ment, but they gradually assume a more elongated and prosenchymatous 
form towards the outer surface of the stem. No signs of phelloderm can 
be detected, nor are there any indications of the secretory canals which 
often occur immediately internal to the secondary cortical tissue of other 
lepidodendroid stems. Fig. 6, PI. XXVI represents a portion of the outer 
edge of a transverse section. The superficial tissue has been converted into 
a patch of pure coal, which sends irregular threads between the disorganized 
cortical cells. The gradual passage from coal to well-preserved tissue 
reminds one of the appearance presented by sections of silicified Liassic 
wood partially converted into jet 1 . It may be that the branch under 
consideration had not reached the stage of producing a phelloderm, or 
possibly the conversion into coal of the superficial tissue has destroyed the 
results of phellogen activity. 
Fig. 2, PI. XXVI shows a leaf-trace in the outer cortex accompanied by 
a large crescentic parichnos which is simply an accompanying strand of 
middle cortex. In structure the leaf-traces appear to be identical with 
those described in sections from the Binney Collection referred to, Lepido- 
phloios fidiginosus 2 . The boundary between the parichnos and outer 
1 Seward (’04), p. 66, PI. VIII, Figs, i and 2 . 2 Seward (’99). 
