760 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE . 
ii. HereraANcium Tintao0rpEs, Will. 
This species of Heterangium (from the coal-measures of Halifax) was first 
described in 1887, when a full account of its general structure was given.* The 
specimens are few, but are remarkable for the astonishing perfection with which the 
anatomical details are preserved. We are enabled to add some information on the 
minute structure to the facts previously brought forward. 
The stem in its general organization and dimensions resembles that of H. Griewi. 
We do not propose in this case to give a detailed description of the whole structure, 
which is unnecessary in view of what has already been done, but merely to state in 
order the fresh points which our renewed examination of the specimens has brought 
to light. . 
The first point to which we desire to call attention is the great distinctness of the 
primary xylem-strands at the periphery of the central mass of wood. They at once 
strike the observer as definite bundlest (see Plate 28, fig. 32) and can easily be 
counted. Thus in one of the larger stems{ they number 20, and in a smaller 
specimen§ they number 16. The structure of each of these strands is perfectly 
clear, as shown in transverse section (see figs. 32 and 33), and exactly agrees 
with that of the corresponding strands in H. Grievit or with that of the peri- 
medullary strands of Lyginodendron (cf. Plate 21, figs. 2, 8, and Plate 26, fig. 24). 
The spiral or annular protoxylem-elements are placed in the interior of the xylem- 
strand, but near its outer margin, and are usually accompanied by parenchyma (see 
the radial section shown in Plate 29, fig. 34). To the outside of the protoxylem we 
find more densely spiral elements, which evidently still belong to the primary wood, 
while on the inside tracheides with bordered pits at once appear. It would be 
quite legitimate to compare the central cylinder of this Heterangiwm to that of 
a Lyginodendron, supposing the primary bundles of the latter to be connected 
together throughout the pith by a network of metaxylem. The analogy with 
Lyginodendron is more evident in H. tiliewoides than in H. Grievii, though the 
structure is essentially similar in these two species. The great majority of the 
peripheral xylem-strands show the structure described ; a few, however, appear to be. 
destitute of spiral elements. ; 
The secondary growth bore a definite relation to the peripheral strands of the 
primary wood. Opposite each of the latter a fan-shaped mass of secondary tissue 
was developed (see fig. 32).| 
* Wiuuiamson, “ Organization,” Part XIII. 
+ Witramson, “ Organization,” Part XTII., Plate 21, fig. 1, and Plate 22, fig. 2. 
ft C.N. 1619, 
§ C.N. 1620, 
|| Also Wituiamson, loc. cit. 
