296 
PROFESSOR W. C. WILLIAMSON ON THE ORGANISATION 
indicative of the beginnings of exogenous development by the formation of phloem 
elements like those of fig. 26, k. 
The specimen before us possesses additional interest from displaying a longitudinal 
section of what appears to be a rootlet, y, springing from the periphery of the 
medullary axis at y', and pursuing its outward way through the bark. We see no 
vessels in this rootlet, since the section has only passed through the cellular zones 
forming its cortical cylinder; but another similar specimen in my cabinet exhibits 
such vessels in their normal central position. 
I may now call attention to a remarkable series of objects, chiefly from Oldham, 
which are certainly organs of the plant under consideration. They vary in relative 
size from that represented at Plate 24, fig. 28, to fig. 37. So far as their general 
features are concerned, these objects differ but little from each other. In all we have 
the epidermal layer p" enclosing the cortex r, in the centre of which latter is a 
vascular bundle e. The chief interest of these specimens resides in the illustration 
they afford of the gradual development of this vascular bundle, and the conclusions 
suggested by that development as to the nature of the objects to which the bundles 
belong. Being from Oldham, the cortex r of each of these specimens is in the 
same imperfect state of preservation as characterised those figured in my Memoir, 
Part VII. ; but, as the vascular bundle is now the object under consideration, this 
defect is of no present importance. 
In Plate 24, fig. 28, we find the section of the bundle e of an oblong form. There 
are faint traces of small vessels given off from each side of the centre of this bundle, 
but they are too indistinctly preserved to be relied upon. In Plate 23, fig. 29, we again 
discover the bundle ate, and at Plate 24, fig. 29a, this bundle is enlarged 182 diameters. 
Most of the structures in this latter figure are certainly vessels or tracheids. A few of 
those marked p, p, may possibly be inner cortical cells. We here see the section of the 
bundle approaching a triangular, if not a quadrangular, contour. In Plate 24, fig. 30, 
e, we have a fine bundle from a Halifax specimen, enlarged 156 diameters, enclosed 
within a mass of small cells, p, which in turn are surrounded by the ordinary cortical 
parenchyma, p'. In this bundle w ? e have a striking resemblance to that of a tetrarch 
rootlet which had developed centripetally ; the vessels at the four primitive points 
of apparent protoxylem being very small, whilst the central ones, assumably of later 
growth, are of much larger size. Such was long my interpretation of this and similar 
specimens, but we shall see that the further study of other examples throws serious 
doubt upon the accuracy of this determination. Plate 24, figs. 31 and 32, represents 
transverse sections of two other bundles, the former enlarged 77 and the latter 99 
diameters. Both these bundles, which are from Halifax specimens, present the 
same quadrate form, suggestive of a tetrarch origin, as fig. 30, and each bundle is 
imbedded in an investment of extremely delicate parenchyma, obviously identical 
with that [p') surrounding the vasculo-cellular axis of Plate 24, fig. 27. 
Plate 24, fig. 33, is a still smaller specimen of the type of fig. 28, from Oldham, 
