462 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
tlie radiating cellular laminse are seen at d enclosing the large lacunae at d these, in 
turn, being invested by the thick outermost parenchymatous cortex, e. 
At the opposite end, B, of the section we find another brandy intersected very 
obliquely, and which is evidently tending outwards, in opposite directions. We here 
discover a central vascular axis, a, dividing dichotomously into a larger one, a, and a 
smaller one, a". These branches are successively surrounded by the inner hark, c, the 
radiating laminae, d, with their enclosed lacunae, d", and the outermost cortex, e. At 
C a yet smaller vascular bundle, a", is passing laterally outwards. We thus have 
four branches passing in as many separate directions in this one specimen. None of 
these branches display any indication of a distinct central medulla, though cells appear 
to intermingle with the irregularly grouped vessels at A, a. It is thus clear that this 
section belongs to a plant in which, as in fig. 1, we have axial vascular bundles unsur¬ 
rounded by an exogenous zone, whilst in figs. 5 and 6 we have the same plant in which 
such a zone is fully developed. 
The vessels of the vascular bundles present some peculiarities, examples of which 
are represented in figs. 8-14. In describing the Oldham Astromyelon in my memoir, 
Part IX., I mentioned the extreme indistinctness if not almost entire absence of all 
traces of structure in the walls of these vessels, though in some few there were sugges¬ 
tions that they had been barred. The Halifax specimens differ from the Oldham ones 
in this respect, though there is room for doubting whether or not the latter shows 
fully their original nature. In all the figures, from 8 to 13 inclusive, a considerable, 
and often by far the greatest, part of the walls of the vessels are homogeneous and 
structureless. Thus in fig. 8 we have a single vertical series of small translucent, 
slightly oval, areolae, the longer axes of which cross the vessel somewhat obliquely. 
In fig. 11 we have a similar arrangement, only the areoles are still more oblique, and 
more elongated transversely. In fig. 9 the areolae are still small but almost circular. 
In fig. 10 the areolae are more irregular both in size and number, but they still occupy 
the central area of the vessel. In fig. 12 the larger vessel approaches more nearly to 
an ordinary reticulated modification of the scalariform type of vessel, whilst in the 
smaller one the areolae are larger in proportion to the diameter of the vessel than in 
most of the other examples, but in both the striking obliquity of the areolae, seen in 
figs. 8 and 11, is again observable. The forms here described are those which charac¬ 
terise all the specimens figured, as well as others in my cabinet, except fig. 7 ; the 
vessels in the branching vascular bundle, B, a, of that section resemble figs. 13 and 14, 
wdiich approach nearer to the barred type ordinarily met with amongst the fossil 
plants of the Coal-measures; but even fig. 14 lacks the extreme regularity which 
ordinarily characterises these barred forms. Do these figures represent the actual 
state of these vessels w’hen living, or has mineralisation destroyed the details of the 
structure of their walls save along certain lines ? Such specimens as figs. 8, 9, and 11 
are so peculiar that I incline to adopt the former explanation, and the more so because 
at some future period I shall have to call attention to some similarly remarkable 
