Notes. 
613 
A leaf-trace, as seen near its entrance into the secondary wood, 
presents the appearance of an oval group of comparatively narrow 
elongated tracheal elements and vertical rows of parenchyma, with 
about six external protoxylem groups. Each leaf-trace on passing 
vertically downwards through the primary tissues of the stem becomes 
less compact and spreads laterally in a fan-shaped manner ; the 
elongated tracheids become shorter and more irregular in shape, and 
finally merge into the short and large tracheids of the more central 
region or metaxylem. Between the metaxylem and the xylem of the 
leaf-traces there is no sharp line of division, as each foliar strand 
in its downward course gradually loses its individuality and becomes 
indistinguishable from the metaxylem. An examination of the 
transverse sections leads to the conclusion that the stem had 
a phyllotaxis of two-fifths. The secondary wood agrees in structure 
with that of recent Cycads and with Lyginodendron , Medullosa and 
other Palaeozoic genera. The characteristic features of the plant, 
which it is proposed to name Megaloxylon Scotti l , may be summarized 
as follows : — 
Megaloxylon Scotti , gen. et sp. nov. The primary single stele 
consists of a peripheral leaf-trace region and a central metaxylem 
region; the metaxylem consists of tracheids varying in shape from 
isodiametric and somewhat flattened to more or less elongated 
elements with numerous bordered pits on their walls. With the 
large isodiametric or even horizontally elongated tracheids occur 
some smaller short tracheids and occasionally irregularly-shaped 
longer tracheal elements. The metaxylem tracheids occur in groups 
of varying size and form scattered through a parenchymatous ground- 
mass, which includes small secretory cells. 
At the periphery of the primary stele numerous strands of spirally 
pitted protoxylem tracheids occur in an exarch position ; these 
strands of protoxylem occupy different positions in regard to one 
another in different parts of the stem, according to the position in 
its vertical course at which a leaf-trace is seen. A leaf-trace has the 
sectional form of an elliptical mass of long tracheids — with bordered 
pits on their walls and of somewhat larger diameter than the tracheids 
1 I have associated this new species with the name of my friend, Dr. D. H. Scott, 
whose researches have so materially extended our knowledge of the Cycadofilices 
and demonstrated the importance of this extinct group from a phylogenetic 
standpoint. 
S S 2 
