876 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
node it bends out in a horizontal direction, forming the foliar bundle, which is therefore 
cut transversely in a tangential section. At this point branch-bundles are given off 
to the right and left, which unite with the corresponding branches of the neighbour- 
ing strands, and thus constitute the bundles of the next internode above. Here, 
therefore, we have a regular alternation in successive internodes, and each leaf-trace 
extends through one internode only. This simple arrangement is, however, by no 
means constant. Thus, we often find the bundles of adjacent internodes lying nearly 
in the same straight line; the forks of a bundle at the node curve round the outgoing 
leaf-trace, and unite on its opposite side (see one of the bundles in photograph 5, on 
Plate 72). This may occur in the same specimen which in other parts shows regular 
alternation.* 
In other cases, the bundles at the node are about twice as numerous as the out- 
going foliar bundles—or, in other words, only about every alternate bundle passes out 
at a given node. (See Plate 78, fig. 11.) Here each bundle must pass through two 
internodes, instead of one, before joining on to the trace of another leaf. In all the 
tangential sections, including those of Calamopitus, similar variations occur.t 
We may sum up the facts considered as follows :—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 alter- 
nating 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. Occasionally, how- 
ever, the ring is interrupted. (See photograph 5, on Plate 72.) 
The nodal xylem, «¢., the commissural ring of primary wood, composed of the 
forks and amastomosing branches of the bundles, differs considerably from the primary 
xylem of the internode. In the first place, the former is much greater in amount 
than the latter. The nodal wood projects conspicuously into the pith, forming the 
well-known constriction, so familiar in the medullary casts. It is also somewhat 
prominent on the outer side, so that the secondary trachez deposited upon it are 
arched outward at the node, as has often been described in former memoirs.{ (See 
Plate 72, photograph 4; Plate 78, figs. 7 and 10.) It may, indeed, be questioned 
whether this mass of wood at the node is properly to be regarded as altogether 
* Asin O.N. 20, A and B, 24, &e. 
+ See Wituamson, “Organization,” Part I., Plate 26, fig. 25, dc. In these figures m indicates the 
foliar bundle. 
{ See Wittramson, “ Organization,” Part L, p. 483. 
