ON THE EOSSIL PLANTS OF THE COAL-MEASURES. 
239 
intervening between the medullary vascular cylinder and the woody zone of the latter 
one. The large primary medullary rays are composed of barred cells, which are some- 
times mural, but more frequently prosenchymatous ; through the upper part of each 
of these large rays there proceeds a bundle of true barred vessels. I have not succeeded 
in tracing one of these bundles to its medullary extremity, consequently I cannot yet affirm 
how it originates ; but I have seen sufficient to confirm what I have already stated in the 
body of the memoir, that we need only remove the central cellular medulla of the plant 
in question to convert it into a true Diploxylon ; the identity of the two, so far as struc- 
tural type is concerned, is as close as it can be, even in its minuter details. Such being 
my conviction, I propose to designate the plant represented in figs. 8-11 Diploxylon 
vasculare , and to apply Gouda’s name of D. cycadeoideum to figs. 21-23. The plant repre- 
sented by figs. 33, 34, distinguished by its large medullary axis and by the deeply fluted 
aspect of the interior surface of its ligneous zone, I propose to designate Diploxylon 
cylindricum, whilst a fourth form, exhibiting some different features yet to be noticed, I 
would term I), stigmarioideum. So far as the general structure of the stem is concerned 
the last-named plant does not differ from the other Diploxylons. The cellular medulla 
has disappeared, but there remains the medullary ring of barred vessels, surrounded by 
the exogenous ligneous zone. The primary and secondary medullary rays also appear ; 
but neither of them occurs so abundantly as in the other species. Moreover, in the radial 
vertical sections, the vascular bundles occupying the primary rays exhibit a different 
aspect to those of the other species described, and approach nearer to what exists in Stig- 
maria Jicoides. This is represented in fig. 23 b. The vascular bundle (to) appears to 
be derived from the body of the ligneous zone and not from its medullary surface. It 
is composed of smaller vessels than those seen at e ; but we find that at e' these vessels 
diminish in size and approach in magnitude those of the bundle to ; not only so, but 
whilst the upper extremities of the small vessels of to exhibit the perpendicular arrange- 
ment indicating that they belong to the part of the woody zone in which they occur, 
tire lower extremities of the large vessels ( e ) are deflected in the direction of those of the 
foliar bundle, which is never the case with the corresponding ones of the other forms of 
Diploxylons. The lower margin of the foliar bundle is cut off in this section by an 
oblique, sharply defined line ; this indicates that the large vessels at e" have been sharply 
deflected to the right and left of the bundle to allow the latter to pass between them. 
All these appearances correspond so closely with what we find in Stigmaria, that for a 
long time this plant seriously perplexed me ; but it appears to be a true Diploxylon, 
since it has the vascular medullary cylinder of that genus as well defined as in any other 
species. This cylinder is never found in Stigmaria Jicoides. It has been more espe- 
cially in connexion with this species of Diploxylon, though not exclusively, that I have 
found the peculiar bark represented in figs. 54-57. It is possible that this plant may, 
like Stigmaria , prove to be the uppermost part of a root of some of the other forms, 
though I have never yet found it associated with any rootlets ; or it may be a fragment 
from the base where stem and roots united. 
