Each vascular bundle has its own sclerenchyma sheath, and very often the stronger veins are accentuated owing to the vascular bundle having a girder-like band of sclerenchyma running conjointly with its sheath and joining the latter above and below--or below only--to the epidermis (Figs. 24 and 25). In many cases these lower girders spread out laterally below--fan-shaped in section--and nearly join the neighbouring girders. In other cases the strands of sclerenchymatous supporting tissue do not join the bundles, but run parallel to them, above or below, as separate strands just beneath the epidermis. Finally, these strands may separate from the bundles, and fuse below into a continuous layer under the epidermis; this occurs especially in leaves of xerophytes where the cuticle is well developed--e.g. in varieties of _Festuca ovina_ (Fig. 18), _Aira flexuosa_ (Fig. 28). The distribution of the strands of isolated sclerenchyma affords good characters. While there are none in _Mibora_, we find one large strand at the ridge of the keel and one at each margin, in addition to smaller ones subtending each vascular bundle, in _Avena pubescens_, _Sesleria_, _Poa annua_ (Fig. 21), _P. bulbosa_, _P. compressa_ and _Dactylis glomerata_. In _Festuca ovina_, _F. rubra_, _F. heterophylla_ (Figs. 18, 27) there are groups more or less pronounced at the keel and margins, or even a continuous band below, but none above the bundles. [Illustration: Fig. 26. Transverse section of leaf of _Nardus stricta_ (× about 50). The upper surface is represented by the four grooves and five ridges, each of the former with traces of motor-cells at its base. The deep shaded portions are sclerenchyma, strong girders of which join the vascular bundle of each ridge to the lower surface. This type is obviously derived from that in Fig. 19, and may be regarded as a permanently rolled leaf.] [Illustration: Fig. 27. Transverse section of leaf of _Festuca ovina_, var. _duriuscula_ (× about 50), the type of a permanently folded leaf. Seven ridges and six intervening grooves are seen: each of the latter with traces of motor-cells below. In each ridge is an isolated vascular bundle, and a narrow sclerenchyma band below.] Many grasses have an isolated band above and below each primary bundle only--e.g. _Panicum_, _Cynodon_--or above and below each of the other bundles as well--e.g. _Spartina_, _Arundo_, _Polypogon_, _Agrostis alba_, _Aira cæspitosa_ (Fig. 23), _Holcus lanatus_, _Glyceria aquatica_, _G. fluitans_, _Digraphis_, _Elymus_ (Fig. 25), _Agropyrum_ (Fig. 24), _Brachypodium_, _Nardus_ (Fig. 26). In _Psamma arenaria_ the lower bands join into a continuous layer. In the following there is a band like a girder above and below each bundle, and contiguous with it, joining it to the epidermis above and below--_Leersia_, _Phleum pratense_, _Calamagrostis Epigeios_, _Bromus erectus_, &c.