228 PROF. F. E. WEISS ON A BISERIATE HALONIAL 
Cortical Tissues. 
In many parts of the transverse section we find, outside this apparently meristematic 
layer, a few layers of cells more or less longitudinally drawn out with black contents, and 
these, though not always clearly marked, have much resemblance to an endodermis. 
The dark cells go over into the inner cortex, of which they probably represent the inner 
layers, possibly specialized for storage of carbohydrate material, as is the case in those 
plants which possess a well-marked starch-sheath, The inner cortex as a whole is 
formed of a close and compact tissue, the cells of which are more or less elongated in a 
tangential direction and show few intercellular spaces, and seem to form a protective 
sheath to the stele. In longitudinal sections the celis are seen to be short and rounded. 
The next portion of the cortex, the middle cortex, which is more or less clearly marked 
off from the inner cortex, consists of a very different tissue. Its cells are not at all 
closely set together, and thus leave very considerable intercellular spaces. The cells, 
moreover, are not all arranged with their long axis in a vertical position, but run obliquely 
and even horizontally, and have the appearance of a spongy parenchyma, or, when the cells 
are considerably drawn out, even of a felted mass of hyphæ. This trabecular cortex forms 
the bulk of the tissue of the stem, being 25 mm. thick in the direction of the broader | 
diameter of the stem and 15'8 mm. in the narrower direction. Its extent is well shown 
in Pl. 24. fig. 5 (m.e.), and the structure in Pl. 26. fig. 15 (m.e.), in which it is seen 
in longitudinal section. Owing to the irregularity of its cells, it presents much the same 
appearance both in transverse and in longitudinal sections. It will be noticed that the 
cells are not all of the same diameter, there being larger light r cells and smaller cells with 
dark contents. ‘These latter are met with in various parts of the stem, but they are found to 
be very numerous and running horizontally close to the passage of the leaf-trace bundles 
from the middle to the outer cortex (see Pl. 26. fig. 15). The narrower and darker cells 
have often an appearance not unlike a laticiferous tissue, though it is impossible in the 
case of a fossil plant to make this identification complete. his loose middle cortex, 
generally defective or absent in other Lepidodendracec, is usually well preserved in Lepi- 
dophloios fuliginosus, so that it is a tissue of some importance in the identification of the 
specimen. The demarcation between the middle cortex and the outer cortex is marked in 
longitudinal section (Pl. 26. fig. 15) by the very small cells of the latter, which are drawn: 
out tangentially and which are therefore very short in longitudinal view. An interesting 
feature of the longitudinal sections is the passage, in connection with each EE 
bundle, of a group of cells from the middle cortex through the outer cortex to the leaves, 
where they form the so-called parichnos. Bertrand (1891) and Hovelacque (1892) had 
traced the parichnos strand in Lepidodendron to the middle cortex, but by means of 
transverse sections, Unfortunately this delicate tissue is often defective in the Lepido- 
dendra. But where, as in Lep. fuliginosus, the middle cortex is generally well preserved, 
the delicate parenchymatous nature of the parichnos tissue can readily be seen. It is 
well figured in transverse section by Binney (1872) *, and on a more enlarged scale by 
Seward (1900), in whose figure the hypha-like tissue can be seen. But the best 
.* Binney, E. W. (1872), pl. 15. fig. 4. 
