48 DR. D. H. SCOTT ON A NEW TYPE OF MEDULLOSEA 
number of scattered vascular bundles. The most striking feature in their arrangement 
is the presence of a definite peripheral rank of bundles, adjacent to the hypoderma 
(PL 7. fig. 5; Pl. 9. fig. 16). Towards the interior the bundles are rather sparsely 
scattered, in smaller numbers than is usual in a Myelorylon. It must, however, be 
remembered that in Meduliosa anglica also the leaf-bases attached to the stem are at 
first poor in bundles compared with the petioles, and only gradually receive their full 
complement (Scott, 1899, p. 100). In Suteliffia the petiole itself has more numerous 
vascular strands than the leaf-bases. 
In all cases the bundles, as already mentioned, are of concentric structure (see PL. 9, 
figs. 14 & 15; Pl. 10. fig. 22). The details of their organisation will be discussed later. 
Each bundle is surrounded by a ring of small strands of sclerenchyma, and similar 
strands are also scattered in the ground-tissue. Secretory organs, probably of the 
nature of gum-canals, though no clear evidence of an epithelium has been obtained, are 
frequent in the cortex, especially in association with the fibrous strands. 
So far the structure described, apart from the concentric bundles, has been of a 
Medullosean type. The vascular system of the stem, however, is quite different from 
anything hitherto described in Medulloseze. The stem contains a single main stele of 
large size and simple structure. In Prof. Weiss's slide (Pl. 7. fig. 5) its transverse 
section measures 47 em. in length by 1:8 em. in maximum breadth, taking the wood 
only into consideration. The dimensions of the stele undergo little change throughout 
the specimen, except where vascular strands are given off. There is no pith; the wood 
extends to the centre, and is in all parts uniformly composed of tracheides interspersed 
with parenchyma. In this respect the stele of Sutcliffia resembles that of Heterangium, 
or a single stele of Medullosa anglica *. A vascular cylinder of this type, when only 
one is present, has been called a protostele (Jeffrey, 1902, p. 144). : 
In Swiclifia the smallest elements, shown by longitudinal sections to be spiral | 
tracheides, lie at the outer edge of the primary wood (Pl.9. fig. 11; Pl. 10. fig. 18).  . 
Hence the structure is exarch, as in the genus Megaloxylon (Seward, 1899) or in the 2 
recent Fern Lygodiwm (Boodle, 1901). The stelar tissue is almost wholly primary; — | 
secondary growth had only taken place to a trifling extent, and indications of it are for — | 
the most part limited to sections from the lower portion of the specimen (Pl. 8. fig. 10). 
The outer region of the wood is very perfectly preserved, but the middle part shows j 
obvious signs of crushing or collapse, for here the elements are more or less flattened 
in the plane of the long axis (figs. 1-6 & 9). It thus appears that the narrow 
form of the stele in transverse section is in part due to the collapse of its more - 
central tissues. "The change of form, however, does not seem to have been very — 
considerable ; in some sections comparatively v 
middle part of the stele (PL. 7. fig. 4). 
a 
y 
a 
x 
little sign of collapse is shown, even in the — 
The natural form can never have been - 
* I am inclined to agree with the view of Mr. Boodle and Prof. Tansley that throughout the Fern-series, at any 
rate, the structure of the stem is essentially monostelie. I see no reason to suppose that the Medulloses are an 
exception to the rule, Consequently, it is incorrect, from a morphological point of view, to speak of the parts of 
the SES NH in a dialystelic Medullosa as steles. I continue to do so, however, in a purely descriptive sense, 
until a more consistent terminology shall have been established. 
