9G 
PROFESSOR W. C. WILLIAMSON ON THE ORGANISATION 
Ileterangium Grievii. 
In the Memoir, Part IV., already referred to, I also described under the above 
name a plant from the ClilT of Petticur, near Burntisland, in Fifeshire. Some months 
ago my young friend, Mr. Lomax, of Ratcliffe, found, for the first time, specimens of 
the same plant from Dulesgate, in Lancashire. But along with these he brought from 
the same localit}^ a series of sections of what at first seemed to be a different species 
of Ileterangium. But long and careful comparison of all the examples of that genus 
in my cabinet convinced me that the supposed new forms were merely the II. Grievii 
in a younger state of growth. The specimens previously described were characterised 
by the existence of a central mass composed of irregular clusters of trachere, imbedded 
amongst numerous parenchymatous cells [loc. cit., Plate 28, fig. 30, a), surrounded by 
an exogenously developed zone of trachefe {ibid., h). This plant was also invested by 
a well-defined zone of sclerous prosencliyma, which, in the transverse sections, was seen 
to be more or less subdivided radially into cubical masses {loc. cif., fig. 30, Jc, and Plate 
29, fig. 35, /;). 
The central ])art of the transverse section (Plate 14, fig. 14, a) resembles the Petticur 
plant in consisting of numerous clusters of trachere aggregated into a large axial mass, 
into the composition of which many parenchymatous cells enter. That these cells may 
have become carbonised is probable from the fact that, when examined under a higher 
power, the appearances shown in fig. 15 are observed. Two of the clusters of tracheae, 
enlarged 75 diameters, are here i-epresented. In the centre of each cluster we have a 
number of larger tracheae, a, a, surrounded by still more numerous smaller ones, inter¬ 
mingled w'ith some cells, d, d. ddie investing zones, c, c, seem to me to be the carbonised 
remains of the inter-tracheaeal cells which occupy similar positions in the Petticur 
plant. At fig. 14, o', a tracheaead bundle is paissing outwards from the central mass to 
some externail appendage. 
A thick cortex, fig. 14, J), h, invests these central tissues : it is fundamentally paren¬ 
chymatous, hut the forms and arrangement of its component cells vary much in difierent 
portions of it, ais will be shown when describing longitudinal sections of this tissue. 
The outer cortical zone is a layer of sclerous fibres, e, e. The aspect ])resented by 
these fibres, ais seen in transverse sections, is shown in fig. 16. The lignified wadi and 
central lumen of each cell aire very distinctly seen. These fibres reappear at e in fig. 17, 
which represents a longitudinal section tlirough the centre of a stem like fig. 14. At a 
we have the central vasculo-medullary axis, consisting of intermingled barred tracheae 
and vertical rows of cells, the latter having chiefly rectangular trainsverse septa. Imme¬ 
diately external to this vasculair axis we find an innermost layer, h, h, of the cortex, the 
cells of winch are arranged in rather regular perpendicuhir lines, but more externally 
these cells become larger and more in’egular in size, form, and arrangement, though still 
retaining a tendency to dispose themselves in vertical rows. This zone of the cortex is 
bounded externally by an irregularly undulating, ill-defined line, b', b'. Outside this 
