ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MBASURES, 905 
vascular bundle (see Plate 80, figs. 23 and 24; Plate 81, figs. 27 and 28). Where 
two distinct spaces are present at each corner of the stele, we are therefore justified 
in assuming that two distinct vascular bundles existed, as is especially clear in fig. 23. 
Often however these spaces are not distinct from one another, and it may be impos- 
sible to say, in such cases, whether one or two protoxylem-groups were present. We 
have noticed that the bundles at each corner are most evidently separate at the level 
of the sporangiophores, as for example in fig. 23. They seem to have diverged a 
little from one another at the points where the traces of the sporangiophores were 
given off. 
We find then that each prominent angle of the triquetrous stele contains either 
one vascular bundle, or a pair of bundles in close proximity, the total number of 
bundles thus being either three or six.* 
The amount of primary xylem must have been very small. Some of the prepara- 
tions show only a single iayer of tracheides, to the outside of the protoxylem-gap. 
In the less perfectly preserved specimens the wood has often broken away altogether, 
and only the pith is left in position. 
The later-formed tracheides were reticulated or scalariform. 
Before going further, it will be well to describe shortly the quadrangular type of 
stele, for much of what remains to be said applies equally to both forms. 
In the four-cornered stele the pith shows precisely the same structure as in the 
type already described (see Plate 80, fig. 25, and Plate 74, photograph 14). At each 
angle there is a vascular bundle, with a well-marked intercellular space at its inner 
margin. In this space the remains of the protoxylem-elements can be detected, 
just as in the previous type. There is no reason to suppose, in this case, that more 
than one bundle was present at each corner. The somewhat peculiar form of the 
stele in the beautiful specimen from which Photograph 14 was taken has already been 
noticed. 
The structure of the xylem is identical with that in the triquetrous form.t In the 
figure referred to in the footnote it will be noticed that the two bundles on the left 
show no spaces at their internal edge, but are solid strands of tracheides. In the text 
of the memoir cited,{ it is pointed out that this part of the section approached a node. 
As a matter of fact, we have always found, in both types of cylinder, that the inter- 
cellular spaces come to an end at the sterie nodes, but are continued without 
interruption through the nodes at which the sporangiophores are borne. This is one 
of the points in which the sterile, or bract-nodes, of Calamostachys resemble the 
ordinary nodes of Calamites (see Plate 81, fig. 28, which shows the structure at a 
sterile node). 
* The structure and arrangement of the vascular bundles are well described, from independent 
specimens, by Mr. T. Hick, ‘ Proceedings of the Yorkshire Geological and Polytechnic Society,’ vol. 12, 
1893. 
+ See Wiitiamson, “ Organization,” Part XV., Plate 2, fig. 7. 
$ Loc. cit., p. 160. 
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