ioi8 
Scott . — The Structure of 
Another stem, incompletely shown in slide 2397, may probably belong 
to this species, and is interesting from its close association with numerous 
leaves of the so-called ‘ Cordaitean * type (see p. 1022). A third stem (slide 
2609) closely resembles the type, though not so well preserved. These are 
rather small stems from 2 to 3 cm. in diameter. A much larger specimen 
(slide 2608), of which the radius , measured only to the outer edge of the 
wood, exceeds 4 cm., has some points in common with M. poroxyloides, 
but in such large and incompletely preserved stems specific identification 
becomes very uncertain. 
In the type specimen (PL LXXXVIII, Fig. 8), the pith measures 
about 12 x 4 mm. (8 mm. mean diameter), that of the whole, stem being 
about 2*5 cm. In slide 2397 (the second specimen) the stem is too incom- 
plete to measure accurately : the diameter may have been about 2 cm. ; the 
stem is young and the pith therefore proportionately larger than in the 
type. The stem in slide 2609 approaches 3 cm. in diameter, that of the 
pith being little more than 6 mm. It thus appears that a comparatively 
small pith may be regarded as characteristic. 
The pith, as in other species, has a persistent outer zone and a discoid 
middle (PI. LXXXVIII, Fig. 13; PI. XC, Fig. 22). In the convergence 
and early fusion of the twin-bundles of the leaf-trace as they reach the 
pith (PI. LXXXVIII, Figs. 9 and 10) M. poroxyloides comes nearest to 
M. Lomaxii , from which it differs in the absence of a definite sheath round 
the primary xylem. 
The centripetal xylem is well developed and is retained for some 
distance below the point of fusion of the strands (PI. XC, Fig. 23). The 
secondary wood has the small tracheides and narrow medullary rays usual 
in the genus. 
The phloem, chiefly secondary, forms a broad zone, well preserved in 
the type-specimen. The pericycle contains numerous large elements with 
dark contents, which may have been secretory sacs. 
The Dictyoxylon zone of the cortex is wider than in other species. 
The leaf-traces subdivide in passing through the cortex, and on entering 
the leaf-base the full number of eight bundles is attained (PI. XC, Fig. 24). 
No axillary shoots or steles have yet been observed. 
The Pith. 
The pith is decidedly well preserved in places ; the most favourable 
section for showing it as a whole is slide Q 6 c in the University College 
collection. The section illustrated in PI. LXXXVIII, Fig. 13, and 
PI. XC, Fig. 22, is not quite radial and the pith is somewhat broken and 
displaced, but the discoid structure is sufficiently evident. It is of rather 
a peculiar kind and may be described as compound, for the thick horizontal 
plates stretching inwards from the persistent zone subdivide towards the 
