ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 763 
the sclerotic masses are limited to the cortex, while it agrees with Lyginoden- 
dron.* 
The outer layers of the pericycle have generally undergone somewhat irregular 
tangential cell-divisions. Beyond these layers we often tind a zone of flattened cells, 
which may represent an incipient periderm.t 
Elements of the kind which we regard as secretory sacs are excessively abundant 
throughout the soft tissues of H. tilieoides, especially in the medullary rays and 
pericycle. 
The cortex, the outer layers of which are usually much shattered, bears a general 
resemblance to that of H. Grievii, especially to the specimens of that type from 
Dulesgate.t 
The leaf-trace bundles are seen in all the transverse sections at various points of 
their outward course. Sometimes they are met with in the pericycle, sometimes in 
the cortex. Their close agreement in structure with those of H. Grievii or of Lygino- 
dendron leaves no doubt as to their nature, though in the present species we have no 
specimens actually showing their passage into a leaf. One specimen (C.N. 1301) 
shows a petiole in connection with the stem ; the stem is seen in transverse section, 
the petiole is cut obliquely, but in a nearly longitudinal direction. The continuity of 
the cortical tissues between petiole and stem is evident. The vascular bundle is well 
shown in the petiole, but the plane of section does not allow us to trace it into the 
stem. The structure of the petiole is essentially the same as in H. Gvevit. 1+ is 
remarkable that it appears to contain a single vascular bundle only, for the leaf-traces 
in the stem of this species are nearly always in pairs, as in Lyginodendion.§ The 
twin bundles may have completely fused on entering the leaf. We think there is no 
doubt that the pair of bundles imbedded in the pericycle, figured in Memoir XIII, 
Plate 22, fig. 5, are leaf-trace bundles, which are just separating from the stele, and 
each of which still retains its own external arc of secondary tissue. Exactly parallel 
cases are well known in Lyginodendron and have been fully described above. 
Beyond the fact that the stem bore adventitious roots, we have no information as 
to these organs. We regard the body represented in Memoir XIII., Plate 23, fig. 12, 
as the base of an adventitious root at its junction with the wood of the stem. It is 
very probable that the structure represented in Plate 22, fig. 13, is also connected 
with the base of a root. 
* Some doubt was expressed in Memoir XIIL., p. 293, as to these elements being really thick-walled 
cells. Tt was suggested that their appearance might be due to the conditions of mineralization producing 
inorganic deposits on the cell-walls. We now find that the structure of these cells is the same as that 
of the undoubtedly sclerotic elements which constituted the horizontal plates of the cortex. Like the 
latter they persist when the surrounding soft tissue has perished. Similar cells occur in the dilated 
phloém-rays. 
+ C.N. 1302, 1619, 1627. 
t See Wituramsoy, “ Organization,” Part XIII., Plate 21, figs. 1 and 6,7,t; Plate 22, figs. 2 and 11,1, ¢. 
§ See Witu1aMson, “ Organization,” Part XIII., Plate 22, figs. 7 and 8. 
5 F 2 
