864 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
with the usage of most English and German paleobotanists, under the generic name 
of Calamites, are characterized anatomically by the following features : 
1. The axis is traversed by a well defined central cylinder, consisting of a large 
pith (which became fistular in all but the smallest specimens), and of a ring of 
distinct, collateral vascular bundles, separated from one another by broad radial 
bands of interfascicular tissue, or primary medullary rays (see Plate 72, photographs 1, 
2,and 3; Plate 77, figs. 1, 2, and 3). Each vascular bundle has an intercellular space, 
or canal, on its inner side, and from the outer margin of this canal the radial series of 
xylem-elements extend. 
The bundles run parallel to one another, without anastomosis, through the inter- 
node. At each node they turn outward, taking an almost horizontal course. The 
out-going bundles are all situated at the same level, forming a whorl. There can be 
no doubt from their position and course that they were leaf-trace bundles, supplying 
a whorl of leaves (see Plate 72, photographs 5 and 6 ; Plates 77 and 78, figs. 6, 7, 8, 11). 
As all the bundles of a whorl are alike, and they are equidistant one from another, 
there is a strong presumption that each leaf received a single bundle only. This 
presumption is fully confirmed by all that we know, from other sources, of the foliage 
of Calamites.* 
The course of the vascular bundles in some cases follows the well-known simple 
type characteristic of Hquisetum, those of successive internodes alternating regularly 
with each other. Considerable deviations, however, from this type are met with, and 
will be considered below. 
2. The central cylinder is surrounded by a cortex, only preserved in comparatively 
few specimens (see Plate 72, photographs 1, 2,3; Plate 77, figs. 1, 2, 3; Plate 78, 
fig. 12; Plate 79, fig. 18). In some cases the cortex is but little differentiated, showing 
only a few thick-walled elements among the parenchyma, while in others it consists 
of two distinct zones, of which the outer is more sclerotic than the inner. 
3. The branches are placed immediately above the node, each branch being so 
situated, in almost all cases, that its centre-line lies midway between two of the 
leaf-traces which pass out at that node (see Plate 72, photographs 5 and 6, and 
Plate 80, fig. 21). The number of branches developed is very variable, but seems to 
be always much less than that of the leaf-traces. Although placed above the node, 
the wood of the branch is directly continuous with that of the bundles below it. 
4. Neither leaves nor roots have been found, so far, in connection with the 
specimens investigated by us, in which the internal structure is preserved. As 
regards the roots, however, we have now some important information from other 
sources, which we shall consider at a later stage. 
“Tntroduction to Fossil Botany” (Hnglish Translation, 1891, chapters 13 and 14), where the literature 
is very completely cited. Only the most necessary references are given in the present paper. 
* See, for example, Wuiss, “ Steinkohlen-Calamarien,” vol. 2, p. 26, plate 1; Renavuur, ‘“ Cours de 
Botanique fossile,” vol. 2, plate 17. 
