CYCADOFILICES FROM THE CALCIFEROUS SANDSTONE SERIES. 815 
As the vascular axis is not well petrified in the example figured (Pl. I. fig. 1), we 
shall turn to the other stem from Pettycur in order to examine that part more closely. 
In this specimen the xylem cylinder is about ‘7 cm. in diameter, and sections of it are 
represented in Pl. I. figs. 2 and 7. As in the former example, two regions may be 
noted in the xylem—the inner, primary wood, and the periphera] secondary zone (PI. I. 
fig. 2, x, and a, respectively). The primary wood consists of anastomosing groups 
of tracheides scattered in a parenchymatous ground tissue (PI. I. figs. 3 and 5, a’). In 
the parenchyma numerous secretory sacs and ducts may be seen, their deeply coloured 
contents imparting a dark appearance to this central zone (Pl. I. fig. 7, s.s.). Sur- 
rounding the primary xylem is a zone of secondary wood with its radially distributed 
elements, and, in both specimens, this tissue attains a fair thickness (Pl. I. figs. 1 and 2, 
x). It is traversed by medullary rays which vary greatly in height and breadth. 
These rays sometimes spread out when they enter the phloem region as they do in 
Heterangium tilixordes. 
The various tissues which succeed the wood externally are each well preserved at 
one or other part of the specimen.. In one stem the phloem is seen to consist of 
elongated elements, but sieve plates have not been detected with certainty. No peri- 
eycle or endodermis can be separated from the inner cortex, which appears to have been 
a zone of rather delicate tissue containing numerous resin ducts and cells with dark 
contents (Pl. II. figs. 10 and 11,7.¢.). These latter elements may have acted as storage 
or even mucilage cells, and this would account for their dark colour. No stone cells or 
other strengthening elements occur in the inner cortex. The outer cortex, on the other 
hand, contains numerous strengthening fibres, and these give a characteristic appearance 
to the whole zone. Pl. II. fig. 15 gives an excellent idea of this tissue; in the inner 
part a rather thick-walled parenchyma is seen, but the hypodermal part contains a 
reticulum of elongated sclerotic bands or threads. The meshes of the reticulum are 
narrow but they are exceedingly long. Associated with the fibres themselves are long 
secretory ducts. 
The general outer surface of the stem is rendered irregular by the decurrent petioles. 
These swell out enormously at their junction with the stem, their outer cortex loses its 
sclerotic fibres, and so the cortex of the leaf base consists entirely of a mass of uniform 
small-celled parenchyma through which the petiole-trace passes to join the central axis 
(Pl. I. fig. 4, pet. b.). As a result, the petioles are readily torn from the stem, and 
this, no doubt, accounts for the fact that the outer cortex often appears broken up into 
separate segments. Usually three petiole-traces are seen departing from the stem in 
any transverse section. They show a succession in their development, but the stems 
are so crushed that the phyllotaxy has not been determined. 
When the petiole-trace leaves the xylem axis it is rather peculiar in form and does 
not resemble the trace in any known genus of the Pteridospermex. The xylem 
consists of a more or less continuous, corrugated mass while still in the cortex of the 
stem. In the free petiole the xylem still appears continuous though the outline is 
