Le 
BRANCH OF LEPIDOPHLOIOS FULIGINOSUS. 229 
longitudinal view showing the continuity between the parichnos and the middle cortex is 
seen on a slide (No. 796) from the specimen now under consideration, kindly lent me by 
Dr. Scott. Pl. 26. fig. 15 is taken from this slide. In this figure the continuity is very 
well seen, as also the fact that the outer cortex runs for some distance down the leaf- 
trace on the upper side. 
Potonié's (1893) researches on the nature of the parichnos have led him to the con- 
clusion that the parichnos running out into the leaf-base was an organ to promote active 
transpiration, but, from the structure of the tissue, it is quite as possible to argue that 
it was a respiratory organ allowing a passage of air from the leaves into the inner 
portion of the stem and down to the roots. Considering the structure of the roots and 
the supposed habitat of the plants, this would seem to me a more natural explanation. 
The trabecular tissue of various species of Selaginella, which also accompanies the leaf- 
traces, probably has the same function as the middle cortex and the parichnos. But the 
persistence of the parichnos on the leaf-scars of the old stems of Lepidodendra enabled 
them also to supply the place of the lenticels of the recent dicotyledonous trees; for 
stems with secondary thickening, like the recent Dicotyledons and extinct Vascular 
Cryptogams, would require some such organs to supply the actively growing cells of the 
interior with the necessary oxygen. 
The cells of the outer cortex are short and closely set together, and this tissue, which 
is about a third of the thickness of the middle cortex ( Pl. 24. fig. 6), was no doubt largely 
of a protective nature and would have prevented any air from reaching the inner tissues, 
except where penetrated by the parichnos strands. Near the outside of the outer cortex, 
just on the periderm, there may be seen irregular patches of a darker colour running more 
or less tangentially. On closer examination it will be seen that they have the appearance 
of groups of secretory cells with thin walls and dark cell-contents. These are described 
and figured by Seward (1899) for Lepidophloios fuliginosus (fig. 6, p. 4 & p. 148) and 
also for Lepidophloios Harcourtii (Seward, 1900, pl. 1. fig. 3). In PI. 24. fig. 14 will be 
seen the early stages of development of this tissue, and the perfection of the preservation 
of these delicate tissues can be gathered from this drawing. These patehes tend to 
become continuous in a tangential direction. An examination of this tissue is not only 
convincing as to their secretory nature, but also shows it to be of a very different nature 
from the phloem-tissue to which Seward attributes a secretory character. 
Close to these seeretory patches we have the secondary tissue produced from the outer 
cortex. As will be seen trom the section shown in Pl. 24. fig. 6, this tissue is only 
preserved in a portion of the section. It commences with fairly large square cells, 
and then near the outside the cells get smaller and more compressed. As the outer 
portion of the tissue is much disorganized it is impossible to distinguish an actual 
phellogen. In all probability this tissue will be morphologically a phelloderm with a 
phellogen on the outside; but the appearance of its cells, both in transverse and longitu- 
dinal section, suggests a function agreeing more with that of true cork. In longitudinal 
view the cells are seen to be much more elongate than the cortical cells and arranged 
in fairly close alternating series. 
