The stem is traversed by a central fibro-vascular cylinder that separates easily from the surrounding tissue, owing to the rupture of the cells of the bundle sheath, this being particularly frequent in dried specimens. When slightly magnified the arrangement of the tissues may be seen (Fig. 73, _E_). Within the epidermis is a mass of ground tissue of firm, woody texture surrounding the central oval or circular fibro-vascular cylinder. This shows a number of white bars (xylem) surrounded by a more delicate tissue (phloem). On magnifying the section more strongly, the cells of the ground tissue (_G_) are seen to be oval in outline, with thick striated walls and small intercellular spaces. Examined in longitudinal sections they are long and pointed, belonging to the class of cells known as "fibres." [Illustration: FIG. 73.--_A_, a club moss (_Lycopodium_), × ⅓. _x_, cone. _r_, root. _B_, a cone, × 1. _C_, single scale with sporangium (_sp._). _D_, spores: i, from above; ii, from below, × 325. _E_, cross section of stem, × 8. _f.b._ fibro-vascular bundle. _F_, portion of the fibro-vascular bundle, × 150. _G_, cells of the ground tissue, × 150.] The xylem (_F_, _xy._) of the fibro-vascular bundle is composed of tracheids, much like those of the ferns; the phloem is composed of narrow cells, pretty much all alike. The spores (_D_) are destitute of chlorophyll and have upon the outside a network of ridges, except on one side where three straight lines converge, the spore being slightly flattened between them. Almost nothing is known of the prothallia of our native species. The second order (_Ligulatæ_) is represented by two very distinct families: the smaller club mosses (_Selaginelleæ_) and the quill-worts (_Isoeteæ_). Of the former the majority are tropical, but are common in greenhouses where they are prized for their delicate moss-like foliage (Fig. 74, _A_). [Illustration: FIG. 74.--_A_, one of the smaller club mosses (_Selaginella_). _sp._ spore-bearing branch, × 2. _B_, part of a stem, sending down naked rooting branches (_r_), × 1. _C_, longitudinal section of a spike, with a single macrosporangium at the base; the others, microsporangia, × 3. _D_, a scale and microsporangium, × 5. _E_, young microsporangium, × 150. The shaded cells are the spore mother cells. _F_, a young macrospore, × 150. _G_, section of the stem, × 50. _H_, a single fibro-vascular bundle, × 150. _I_, vertical section of the female prothallium of _Selaginella_, × 50. _ar._ archegonium. _J_, section of an open archegonium, × 300. _o_, the egg cell. _K_, microspore, with the contained male prothallium, × 300. _x_, vegetative cell. _sp._ sperm cells. _L_, young plant, with the attached macrospore, × 6. _r_, the first root. _l_, the first leaves.]