256 de Frame . — On Medullosa centroflis , a New Species of 
of steles also. The well-marked peripheral strands of spirally marked 
tracheides are also characteristic of the steles of M. anglica , but the 
protoxylem in this case is undoubtedly mesarch in development. 1 
The conjunctive parenchyma of the primary wood is composed of thin- 
walled tissue, which on the whole is very badly preserved. 
A zone of secondary wood occurs around each stele, its dimensions 
vary somewhat, and the thickness is usually greater on the side of the stele 
adjacent to the star-ring. 2 The number of secondary tracheides in a row is, 
on an average, eight to ten. The sculpturing of the secondary tracheides 
consists of multiseriate bordered pits which appear to be limited to the radial 
walls of the elements. 
Medullary rays run from the primary wood of the stele to the limit of 
the secondary xylem, separating the radial series of tracheides into segments 
which are usually two to three cells broad (Text-fig. 2, xy 2 ). The rays are 
usually very narrow and appear to be composed of narrow thin- walled 
parenchyma cells, considerably longer than they are wide ; each ray is 
generally two or three cells in width. Here and there the rays appear to 
broaden out towards the periphery of the stele into wedge-shaped masses. 
In addition to the primary rays, secondary ones may arise in the secondary 
wood at varying distances from the central mass of primary tissue. 
No trace of any phloem surrounding any of the steles can be dis- 
tinguished, but lying immediately beyond the secondary wood is a narrow 
zone in which the tissue as a whole is not preserved, but in which secretory 
canals occur with great frequency ( m.c Plate XV, Fig. 3). This zone 
probably represents the phloem and the pericycle of the stem ; it is bounded 
on the outer side by the periderm ( p.d ., PI. XV, Fig. 3). 
The Star-ring . — The tissues of the star-ring are, on the whole, very well 
preserved, and show quite clearly that the structure here is precisely similar 
to that of the peripheral steles, but on a smaller scale. 
In the Permian Medullosas, in which £ star-rings ’ form so characteristic 
a feature, their preservation is, as a rule, far from good, and the structures 
are described as possessing a ‘ partial pith ’ surrounded by a zone of 
secondary wood and bast ; the ‘ partial pith ’ consists of scattered primary 
tracheides and parenchyma, 3 though occasionally, as in M. Solmsii , Schenk 
y lignosa } ‘ die markstandigen Sternringe lassen kein deutliches Centralmark 
mit Primartracheiden, auch keinen ausseren Bastbelag erkennen.’ 4 It seems 
extremely probable that the star-rings of this last named species are of the 
1 M. anglica , loc. cit., p. 89. 
2 Cf. M. anglica , loc. cit., p. 89, and M. pusilla, p. 223, both ot which show a similar pheno- 
menon. 
3 Weber, O., und Sterzel, J. T. : Beitrage zur Kenntniss der Medulloseae, loc. cit., cf. Text-fig. 23, 
‘ Sternring ’ of Medullosa Leuckarti , Gopp. und Stenz., with Text-fig. 9, ‘ Sternring ’ of M. stellata v. 
Cotta 8 lignosa . 
4 Loc. cit., p. 78 and Text-fig. 13. 
