OF THE FOSSIL PLANTS OF THE COAL-MEASURES.—PART XIII. 295 
Plate 24, fim 22, is a form from Halifax, in which the central axial bundle is in 
process of development, but in which no exogenous growth has yet taken place. Its 
thick cortical layer, r, from its hypodermal portion to within a short distance from the 
vascular bundle, has been very uniform in its composition. This structure was, as I 
have already observed, imperfectly preserved in the Oldham specimens, but soon after 
my description of the latter was published I obtained from Halifax several of those 
now described. The parenchyma of this cortex has been thin-walled, and the forms 
of its cells apparently rather irregular; but scattered amongst the latter are numerous 
long, narrow, longitudinally arranged canals, r. It is not quite easy to determine 
whether these canals are true tubes or merely intercellular passages. Plate 23, 
figs. 24 and 25, demonstrate that each canal is enclosed by a wall, r, within which we 
constantly find a black substance, evidently moulded upon the interior of this wall, 
either in the form of a solid rod, as in fig. 24, r", or as a hollow cylinder, as in fig. 25, 
r". The wall, r, may either be a true one belonging to the canal, or it may only 
consist of the coalesced walls of the surrounding cells. Seeing how long different 
opinions prevailed respecting the structure of such organs as the so-called laticiferous 
vessels, a determination of such a point in the case of fossil plants may well be doubtful. 
That these passages have been gum or resin canals may be inferred from the large 
amount of the black carbon which they so often contain. Fig. 26 is a section of a 
specimen from Halifax, in which five vascular wedges have undergone a considerable 
development, though much less than fig. 20. The inner ends, d', d', of the vascular 
laminae composing each wedge curve away from its centre, converging towards similar 
laminae belonging to contiguous wedges to form a series of semicircular curves. I 
further discover in similar specimens a few parenchymatous cells creeping in amongst 
the vessels, e, of the central axis. Such examples constitute connecting links between 
the type represented in fig. 20 and others yet to be described. The phloem masses 
are again visible at k, k. The epidermal layer, p", so extremely characteristic of this 
plant, is here thicker than usual, consisting of from three to four cells in breadth, the 
ordinary number being two or occasionally three. 
The specimen just described conducts us to fig. 27, which is an excellent example of 
the type most frequently obtained from the Plalifax deposits. Its medullary axis, 
which is of large size compared with that of fig. 20, has an undulating peripheral 
outline of a pentagonal or hexagonal form ; some specimens having the former, others 
the latter contour. The conspicuous bundles of vessels, e, are now largely inter¬ 
mingled with a delicate parenchyma, a. We find here no exogenous growths, unless 
the single continuous line of vessels, e , seen bounding each peripheral concavity with 
more or less regularity, is to be regarded as the first of a series of such growths. 
This vasculo-cellular axis is completely invested by a zone of extremely delicate 
parenchyma, p, the innermost portions of which, especially where they fill the con¬ 
cavities, p', of the peripheral outline, consist of very minute cells. Other specimens, 
resembling fig. 27 in most of their features, exhibit a wavy line of cortical cells, 
