OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
687 
branch. In the bark investing these bundles we can still trace the various elements seen 
in the larger stems ; but the individual layers of cells are comparatively few in number. 
The transverse sections of these branching examples thus exhibit some important 
features. Before a stem is about to branch, there is obviously a decided increase in the 
number of smaller vessels at the ends and corresponding side of the two arms of the 
crucial bundle from which the branches are about to proceed. Then these additional 
vessels, along with others not additional, become detached in two distinct bundles. 
Sometimes transverse sections of these detached bundles exhibit the same crucial form 
as that seen in the parent stem ; but they much more frequently assume the trifid form 
seen in fig. 22. Though in making a longitudinal section like fig. 27 we can only pass 
in the same plane through the main stem and one of its branches, it is obvious that 
two branches of equal size are given off at each of these ramifications. Hence it would 
appear as if these branches had been given off in pairs, as in many species of Pteris. 
The question remains to be asked whether or not this is a fern. In favour of this 
conclusion we have its general aspect, the arrangement of its vessels in each bundle, 
the fern-like mode of increase in the dimensions of the vascular bundles on the side 
from which branches are about to be given off, and the detachment of those bundles in 
two coequal groups, indicating a different mode of branching to what is common 
amongst the Lycopods. I have seen no Lycopod, transverse sections of which exhibit 
this mode of orientation of the secondary bundles from the primary ones. The single 
bundle given off in the Lycopods separates into two parts in the young shoot ; but 
these two bundles always go into the same branch, continue closely parallel to each 
other, and are but the common points of departure for new vessels, which continue to 
develop centripetally until the two temporarily separated vascular foci are again united 
into one elliptical bundle. This is very different from what occurs in the plant just 
described. But in the latter case, on the other hand, we have the remarkable succes- 
sion of divisions and subdivisions continued until we obtain clusters of minute twigs like 
fig. 24, and which look much more like cylindrical rootlets than twigs or ultimate 
branches of a rachis. It seems strange, supposing them to be the ultimate subdivisions 
of the petioles of ferns, that we should reach these ultimate divisions without discovering 
any trace of a leaf or of a leaf-attachment. If they bore leaves they must have been very 
small terminal ones, resembling in their positions those of some of the Adiantums. 
But notwithstanding the difficulty just stated, the arguments in favour of the affinity 
of this plant with ferns appear to me to preponderate over the opposite ones. I would 
therefore retain it in my genus Rachiopteris, associating with it Mr. Binney’s specific 
name of Oldhamia. 
Amongst the specimens sent to me from Burntisland by Mr. Grieve, I found one or 
two full of branching fragments of a plant apparently undistinguishable from this 
Oldham one. Both in size and organization the two appear to be identical. 
The next plant to be described is also one which I discovered amongst the Burntis- 
land specimens, but which I have not yet found at any other locality. It is beyond 
