[Illustration: FIG. 52. _Equisetum maximum_ Lam. A. Fertile shoot with strobilus and sterile leaf-sheaths [after Luerssen (89); slightly less than nat. size]. B. Sporophyll bearing open sporangia (after Luerssen; slightly enlarged). C. Part of a transverse section (diagrammatic); _v_, vallecular canals, _e_, endodermis, _c_, carinal canals (after Luerssen; × 20). D. _Equisetum arvense_ L. Part of a transverse section of an internode of a sterile shoot. _v_, cortex, _e_, endodermis, _x_, xylem tracheids, _a_ remains of annular tracheids of the protoxylem, _c_, carinal canal (after Strasburger; × 90).] _Equisetum._ The plant consists of a perennial underground creeping rhizome, branching into secondary rhizomes, divided into well-marked nodes and internodes. From the nodes are given off two sets of buds, which may develope into ascending aerial shoots or descending roots. At each node is a leaf-sheath more or less deeply divided along the upper margin into teeth representing the tips of coherent leaves (fig. 52, A). In some species one or more internodes of underground branches become considerably swollen and assume the form of ovate or elliptical starch-storing tubers, which are capable of giving rise to new plants by vegetative reproduction. Tubers, either singly or in chains, occur in _E. arvense_ Linn., _E. sylvaticum_ Linn., _E. maximum_ Lam., among British species. [Illustration: FIG. 53. Rhizome (R) of _Equisetum palustre_ L. with a thin shoot giving off roots and tuberous branches from a node [after Duval-Jouve (64)].] In the example shown in fig. 53 (_Equisetum palustre_ L.[487]) the stout rhizome R gives off from its node, marked by a small and irregular leaf-sheath, two thin roots and a single shoot. The latter has a leaf-sheath at its base, and from the second node, with a larger leaf-sheath, there have been developed branches with tuberous internodes; the constrictions between the tubers and the tips of the terminal tubers bear small leaf-sheaths. Branched roots are also given off from the upper node of the erect shoot.