While several species possess a cortex of three distinct zones (fig. 125, H, _c_, _c_′, _c_″), in others the extra-stelar tissue is much more homogeneous, consisting of thin-walled parenchyma or in some cases of thick-walled elements; as a general rule, however, there is a tendency towards a more compact arrangement in the inner and outer portions of the cortex as contrasted with the larger and more loosely connected cells of the middle region. In certain types the middle cortex contains fairly large spaces, as in the swamp-species _L. inundatum_, which with _L. alopecuroides_ exhibits another feature of some interest first described by Hegelmaier[99]. If a transverse section of the stem of _L. inundatum_ be examined the leaf-traces are seen to be accompanied by a circular canal containing mucilage which extends into the lamina of the leaf. In a specimen of _L. cernuum_[100] obtained at a height of 2500 ft. by Professor Stanley Gardiner in the Fiji Islands, the leaf-traces (fig. 125, B _lt_) were found to be accompanied for part of their course by a well-marked secretory space (fig. 125, B, _s_). There is little doubt that the presence of these mucilage canals is directly connected with a certain type of habitat[101] and attention is called to them in view of a resemblance which they offer to a characteristic strand of tissue, known as the parichnos, which is associated with the leaf-traces of _Lepidodendreae_ and _Sigillarieae_. In the section shown in fig. 125, H, the xylem of the stele forms more continuous bands than is often the case in _L. cernuum_ which has already been described as having its xylem in small detached groups. The presence of the smaller branch-stele (fig. 125, H, _b_) affords an example of monopodial branching. The outer cortex of _L. saururus_ (fig. 125, C) exhibits a somewhat unusual feature in the distribution of the thicker-walled tissue (_b_) which encloses a patch of more delicate parenchyma (_a_) with large lacunae (_lc_) in the region of the leaf-bases, and presents the appearance of an irregular reticulum. This arrangement of the mechanical tissue in the outer cortex is comparable with that in stems of some species of _Sigillaria_. In certain species of _Lycopodium_ the roots[102], which arise endogenously from the axial vascular cylinder, instead of passing through the cortex of the stem by the shortest route, bend downwards and bore their way in a more or less vertical direction before emerging at or near the base of the aerial shoot. The transverse section of _L. dichotomum_ represented in fig. 125, A, shows several roots (R) in the cortex; they consist of a xylem strand of circular or crescentric form accompanied by phloem and enclosed by several layers of root-cortex. The roots of _Lycopodium_ do not always present so simple a structure as those of _L. dichotomum_; the xylem may have an irregularly stellate form with as many as ten protoxylem groups.