OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
209 
fig. 33*. It is of precisely the same type, so far as its general organization is concerned, 
as Plate XXVIII. fig. 21, consisting of a hollow central cavity surrounded by a ring of 
medullary vessels (c). The line of demarcation between these two tissues is crenulated 
with great regularity ; not only so, but at d, where the ligneous zone has been broken 
away from the zone of medullary vessels, we see that the exterior of the latter is fluted 
like the medullary cast of a Calamite, for which the specimen might very easily be 
mistaken. The more minute details of the transverse section are shown in the enlarged 
segment of it represented in Plate XXIX. fig. 34. In this figure it will be seen that the 
woody zone presents the convexities of its outline (d!) towards the medullary axis ; whilst 
the vessels of the latter, filling up the angles (d) between the convex projections of the 
former, are very small compared with those composing the rest of the medullary zone (c). 
The cellular tissue of the medullary rays has disappeared, but the cavities which mark 
their position are almost identical with those of fig. 21. In both this specimen and that 
previously described, vascular bundles ( m ) pass outwards to the leaves. 
We must now pass to some allied genera of the Lepidodendroid family. One of the 
most interesting of these is a very small specimen of Ulodendron, for which I have been 
indebted to Mr. Nield, of Oldham. Plate XXVI. fig. 24 represents a transverse section 
of this stem, magnified two diameters. Plate XXVII. fig. 25 is a longitudinal section 
of its central axis, enlarged twelve diameters. Plate XXVII. fig. 26 is a transverse 
section of the same portion, and Plate XXVIII. fig. 27 is a longitudinal section of the 
outer bark and epidermis, with the bases of its petioles attached. 
The structure of the central axis (figs. 25, 26) is identical with that of the Lejpidoden- 
dron represented in figs. 12, 13 & 14. We have at a the same vertical piles of cells, 
devoid of any indication of spiral structure, their transverse septa being, as before, 
sometimes rectangular and sometimes oblique. The transverse diameter of each of these 
piles varies from ’0025 to "005. The cavity (a!) in the centre of this medulla is clearly 
not fistular, but a mere rupture, the result of desiccation. Surrounding this is a circle 
of barred vessels ( c ) with about eight or nine tubes, counting radially ; these are not 
arranged in rows, but represent the medullary vessels of the Lepidodendra. The 
ligneous zone (figs. 25, 26, d) is very feebly represented. A great portion of its circum- 
ference has disappeared through disorganization, but it remains at one or two points ; 
nowhere, however, in such measure as to present a lineal arrangement of its small barred 
vessels. It is chiefly in the longitudinal section that they can be distinguished by their 
small size. External to the central axis is a large space from which the tissues have 
wholly disappeared, comprehending most of the inner and middle portions of the bark. 
Externally we meet with some of the latter in the shape of coarse parenchyma, the cells 
of which have a diameter of "003. This passes through an exceedingly narrow layer of 
common prosenchyma (Plate XXVI. fig. 24 & Plate XXVIII. fig. 27, i), but a few cells 
in thickness, into the tubular prosenchyma (Plate XXVII. fig. 25 & Plate XXVIII. 
* I have more recently obtained a second fine example of this species from Mr. James Whittaker, of 
Watersheddings, near Oldham. 
