259 
Medullas a from the Lower Coal Measures . 
very like transfusion tissue, is present in section A, lying close to an out- 
going leaf-trace bundle. This group is of interest when it is recalled that 
Scott noted in two cases in M. anglica 1 that a leaf-trace after diverging 
from the stele was connected with it for a considerable distance by radial 
bridles of short tracheides, and he suggested that the peculiarity was 
correlated with the insertion of adventitious roots. 
V. The Periderm. 
A continuous zone of well-preserved tissue encloses the vascular tissues 
of the stem (cf. pd., PI. I, Figs, i and 4). The zone, which is very irregular 
in outline, is usually about five or six cells in thickness, and the more or less 
regular seriation of the cells points to its secondary origin, while here and 
there traces of a cambium can be detected (c.b., PI. I, Fig. 4) ; secretory 
sacs are occasionally present (m.c., PI. I, Fig. 3). The tissue strongly 
recalls the secondary cortex of Sutcliffia insignis , 2 though the development 
is far less than in that fossil. 
Since none of the external tissues show sign of death or of ‘ drying up *, 
it is obvious that the zone, though morphologically periderm, cannot 
function as does the cork of the present day. The conclusion arrived at by 
Kisch, 3 in an investigation into the physiological anatomy of the periderm 
in the fossil Lycopodiales, applies equally well here : that, ‘ whatever the 
morphological nature of the secondary tissue, there is no evidence to show 
that any of it was other than secondary cortex.’ 
VI. The Leaf-Bases. 
The leaf-bases which are present are in all cases still in continuity 
with the stem. Their ground tissue is composed of thin-walled parenchy- 
matous cells, throughout which are scattered numerous secretory canals 
(m.c., PI. I, Fig. 3). A well-marked hypodermal zone lies at the limit of 
the section, but the external layers are not in any case preserved ; the 
hypoderma is of Renault’s Myeloxylon Landriotii type (hy., PI. I, Figs. 1, 
2, and 3). 
The sclerotic strands of the hypoderma are usually two, occasionally 
three deep, and are somewhat irregular in form ; they are similar to those 
of Medullosa anglica ; the hypoderma thus differs from the simpler form 
in M. pusilla , where usually the strands are single, at the most two 
deep, and at the same time more regular in form. Corresponding with the 
1 M. anglica , loc. cit., p. 93. 
2 de Fraine, E. : On the Structure and Affinities of Sutcliffia , in the Light of a newly discovered 
Specimen. Ann. of Bot., vol. xxvi, No. civ, Oct. 1912, p. 1051 and Text-fig. 17. 
3 Kisch, M. H. : The Physiological Anatomy of the Periderm of Fossil Lycopodiales. Ann. of 
Bot., vol. xxvii, No. cvi, April 1913, p. 296. 
