The small drawing in fig. 55, 3 shows part of the ring of thick nodal wood; the section cuts through two bundles about their point of bifurcation, the strand _x_ is passing out in a radial direction to a lateral branch, the strand to the right of _x_ and the separate fragment of a strand to the left of _x_ are portions of leaf-trace bundles on their way to the leaf-sheath. Reverting to fig. 54, B, the other structures seen in the section are the leaf-sheaths (_l_ and _m_), the vallecular canal (_f_), the epidermis, cortex and pith (_k_, _e_ and _a_) of the stem. The epidermis which has been ruptured by the root and branch is indicated at _i_, _i_; the dotted lines traversing the upper part of the pith of the lateral branch mark the position of a nodal diaphragm. [Illustration: FIG. 55. 1. Transverse section of a root of _Equisetum variegatum_ Schl., _e_ endodermis, or outer layer of the phloeoterma (after Pfitzer; × 160). 2. Transverse section of rhizome of _E. maximum_, slightly enlarged. 3. Transverse section through a node of _E. maximum_, _x_, branch of vascular strand (slightly enlarged). 4. Transverse section through a node of _E. maximum_ showing the mass of xylem, _px_ protoxylem (× 175). (Figs. 3 and 4 after Cormack.)] Immediately external to each vascular strand, as seen in transverse section, there is a layer of cells containing starch, and this is followed by a distinct endodermis, of which the cells show the characteristic black dot in the cuticularised radial walls (fig. 52, D). Beyond the endodermis there is the large-celled parenchyma of the rest of the cortex. Tannin cells occur here and there scattered among the ground tissue. On the same radius on which each vascular strand occurs, the cortical parenchyma passes into a mass of sub-epidermal thick-walled mechanical tissue or stereome. Alternating with the ridges of stereome, the grooves are occupied by thin-walled chlorophyll-containing tissue which carries on most of the assimilating functions, and communicates with the external atmosphere by means of stomata arranged in vertical rows down each internode. The continuity of the cortical tissue is interrupted by the occurrence of large longitudinal _vallecular canals_ alternating in position with the stem ridges and vascular strands (fig. 52, C, _v_). The epidermis consists of a single layer of cells, containing stomata, and with the outer cell-walls impregnated with silica.