In examining sections of calcareous nodules from the coal seams one meets with numerous fragments of small Calamitean twigs with little or no secondary wood; in some of these there is a small number of carinal canals, in others the canals are much more abundant. The former probably represent the smaller ramifications of a plant, and the latter may be regarded as the young stages of branches capable of developing into stout woody shoots[606]. Longitudinal sections of small branches teach us that the xylem elements next the carinal canals are either spiral or reticulate in character, the older tracheids being for the most part of the scalariform type, with bordered pits on the radial walls. This and other histological characters are admirably shown in the illustrations accompanying Williamson and Scott’s memoir on _Calamites_. The student should treat the account of the anatomy of _Calamites_ given in these pages as introductory to the much more complete description by these authors. They thus describe the course of the vascular bundles in a Calamitean branch:— “The bundle-system of _Calamites_ bears a general resemblance to that of _Equisetum_. A single leaf-trace enters the stem from each leaf, and passes vertically downwards to the next node. In the simplest cases the bundle here forks, its two branches attaching themselves to the alternating bundles which enter the stem at this node. In other cases both the forks attach themselves to the same bundle, so that, in this case, there is no regular alternation. In other cases, again, the bundle runs past one node without forking, and ultimately forms a junction with the traces of the second node below its starting-point. These variations may all occur in the same specimen. The xylem at the node usually forms a continuous ring, for where the regular dichotomous forks of the bundles are absent their place is usually taken by anastomoses[607].” As in _Equisetum_, the xylem at the nodes possesses certain characteristic features which distinguish it from the internodal strands. It has already been pointed out that the xylem of _Equisetum_ increases in breadth at the nodes (p. 251, fig. 55, 4); the same is true of _Calamites_. In fig. 72, _C_, we have part of a radial section of a Calamite twig in which the broad mass of short nodal tracheids is clearly shown; this nodal wood forms a prominent projection towards the pith. In the lower part of the section the remains of some spiral protoxylem tracheids are seen in a carinal canal. [Illustration: FIG. 72. _A._ External xylem elements and cambium, _c_, with imperfect phloem, × 100. _B._ Carinal canal containing protoxylem, _px._ × 65. _C._ Radial longitudinal section through nodal xylem, _px._ × 35. _D._ Phloem elements; _s_, sieve-tubes; _p_, _p_, parenchymatous cells. (_A–C._ After Williamson and Scott. _D._ After Renault.)]