8 Seward. — On the genus Myeloxylon (. Brong .). 
material 1 . Fig. 3 shows this partial mineralization of the 
tissues as seen in a transverse section cut parallel to the base 
on which the block rests in Fig. 2. In this section we have a 
number of isolated islands of tissue, in each of which the 
xylem-portions of the vascular bundles are well preserved, 
whilst the phloem is always absent ; and in the immediate 
neighbourhood of the bundles are a few layers of parenchyma, 
with here and there distinct canals. At the periphery of the 
section are seen darker patches which indicate the position of 
thick-walled hypodermal cells arranged in radiating bands 
and alternating with radial extensions of the parenchymatous 
tissue. In many of the groups of tissue seen in Fig. 3, the 
parenchyma surrounding the vascular bundles is limited by a 
distinct dark line ; this is due to the brown walls of the 
compressed parenchyma which represent the extent of the 
mineralization of the tissues. Similar dark lines, cutting up 
the parenchyma into a kind of network, are shown in Cotta’s 
figure of Medullosa elegans , and also in a figure of Myelopteris 
given by Renault: I have already alluded to such lines as 
probably accidents of fossilization in speaking of Felix’s note 
on Myeloxylon. In Fig. 3 a second fragment is represented, 
smaller than the first and cut longitudinally. To describe in 
detail the larger transverse section, which measures 2*5 cm. 
by 2*2 cm. : in looking at the peripheral bundles, where the 
ground-tissue has not been destroyed, and their original 
position has therefore been retained, we notice that they are 
regularly arranged concentrically with the circumference of the 
section ; towards the centre this concentric disposition is 
much less obvious. The individual bundles, when examined 
in detail, appear under various forms. In some cases we have 
a group of xylem almost in the centre of a space bordered by 
parenchymatous cells : this type is shown in Fig. 4, in which 
case the position of the xylem suggests a partially preserved 
concentric bundle, the space having been originally occupied 
by the more delicate tissue of the phloem. In Fig. 5, we 
2 There is a striking example of this in a large stem of Araucaroxylon in the 
British Museum (Geological Department). 
