230 PROF. F. E. WEISS ON A BISERIATE HALONIAL 
Leaf-traces. 
The giving off of the leaf-traces from the primary wood was described in’ connection 
with that tissue. The mesarch bundles thus given off pass nearly vertically at first 
through the ground-tissue and the secondary elements lying between the xylem and 
phloem. This portion of their course is seen in Pl. 25. fig. 11. As they pass out through 
the phloem (Pl. 25. fig. 18) they carry outwards a portion cf the phioem, which always 
remains separated from the xylem elements by a few rows of undifferentiated cells. In 
passing through the inner cortex the leaf-traces still retain their steeply inclined position, 
but when they reach the middle cortex (see Pl. 24. fig. 6) they become much more 
horizontal in position. "l'his is more particularly the case with the leaf-traces passing in 
the direction of the longer diameter of the stem. These very oblique or horizontal leaf- 
traces in this region are very characteristic of most specimens of Lepidophloios fuliginosus 
in the Manchester Museum, and are not generally so found in other Lepidodendracee. 
An examination of the bundles whilst running through this middle cortex will show that 
they are surrounded by a firm sheath of cells, similar to those of the inner cortex through 
which the bundle has previously passed. 
'The course of the leaf-traces through the outer cortex is much the same as that in the 
middle cortex, and here too it is quite horizontal. 
As the leaf-cushions are absent, we cannot follow the leaf-traces beyond this layer. 
Branching of the Stele. 
The branching of the stele to supply the halonial tubercle agrees in all respects with the 
cases described by Williamson (1873), (1881), (1893). The stele does not divide equally 
as in the case of ordinary branching, but displays a somewhat horseshoe-shaped segment 
in the case of halonial branches with two rows of tubercles at the two ends of the longer 
axis of the elliptical stele. This is well figured by Williamson (188 1) for Lepidophloios 
Juliginosus (pl. 52. fig. 9), and is also seen in our figure of the transverse section of 
Lepidophloios fuliginosus (Pl. 24. figs. 6 & 7). In this specimen of Lepidophloios, 
however, the branch of the stele takes, like the leaf-trace bundles, a more horizontal 
course soon after separating from the central stele, so as to be seen more horizontally 
in subsequent sections where it is nearer the outside. This very oblique course gives 
us a less clear picture in the transverse sections, while longitudinal sections, such as 
that figured by Williamson (1893) (pl. 2. fig. 25), give us a better idea both of the course 
and of the structure of this stelar branch. 
The commencement of the branching of the stele is characterized by the breaking up 
of the cylinder of primary xylem by intruding bands of medullary tissue. At the din 
time a corresponding piece of phloem is separated off by strands of cortical cells, which 
ultimately meet the projections from the pith. 
The horseshoe-shaped piece of primary wood which is thus detached gives off numerous 
leaf-traces on the outside, as can be seen in Pl. 24. fig. 7. The gap in the stele becomes 
bridged over by a tissue the cells of which have dark contents, and which appears con- 
tinuous with what I have described above as a possible endodermis. A similar dark 
