614 
Notes. 
of the secondary wood, but much narrower than the large metaxylem 
tracheids — associated with short parenchymatous cells ; several groups 
(at least six) of protoxylem elements occur on the external edge of 
the trace. As a leaf-trace passes deeper into the stem the tracheids 
become less compactly arranged, and the whole leaf-trace becomes 
wider and less well defined ; its long and narrow tracheids are 
gradually replaced by shorter elements of more irregular and variable 
form, and these are eventually linked on to the short and large 
tracheids of the metaxylem region; the peripheral leaf-trace region 
and the axial metaxylem regions of the stele are in close organic 
connexion. 
The secondary wood of the stem is made up of regular rows of 
tracheids, with multiseriate bordered pits on their radial walls, and 
broad and deep medullary rays composed of short parenchymatous 
cells. 
As a leaf-trace passes through the secondary xylem of the stem its 
primary tissues become enclosed by a zone of secondary tracheids and 
medullary rays. 
The structure of the primary wood recalls that of Heterangium and 
Medullosa anglica Scott, but there are certain important peculiarities 
in the present species which constitute well-marked differences and 
render advisable the institution of a new generic name. The primary 
peri-medullary strands in the stele of Heterangium , as also in 
Medullosa anglica , are distinctly mesarch in structure, whereas in 
Megaloxylon the protoxylem groups occupy an exarch position. 
Another distinctive feature of the new type is the unusually large 
size and the peculiar short form of the metaxylem tracheids — 
elements which probably served for water-storage rather than for 
transport. 
In Megaloxylon we have a type of stem in which the primary xylem 
is distinctly of the fern type; the protoxylem is external, and not 
internal as in Heterangium ; but in recent ferns the xylem may be 
endarch, mesarch or exarch, and no great importance from the point 
of view of affinity to the ferns as a group should be attached to this 
point. On the other hand the mesarch structure of the xylem of 
Heterangium , Lyginodendron and other Cycadofilices affords an 
important Cycadean character, which is not met with in Megaloxylon. 
Megaloxylon adds another connecting link between the Palaeozoic 
Cycadofilices and recent ferns ; in anatomical characters the two 
