Knowledge of Lyginodendron . 75 
mineralization of the tissues in this region, renders it im- 
possible to make use of such characters as the nature of the 
pitting as a distinguishing feature of the primary xylem- 
tracheids. In Lyginodendron Oldhamium , for example, the 
scalariform character of the tracheids affords a convenient 
distinguishing feature of the primary xylem in longitudinal 
section. In one or two longitudinal sections imperfectly 
preserved tracheids have been detected of which the faint 
traces of pitting suggest the scalariform type, such as occurs 
in the primary xylem of Lyginodendron Oldhamium , but the 
evidence is insufficient to be cited as absolute proof. 
In Plate V, Fig. 6, at / and t'\ is shown a group of 
tracheids in contact laterally and distally with the main mass 
of centrifugal xylem ; these groups are probably leaf-trace- 
bundles on their way to the surface of the stem. In Plate VI, 
Fig. 15, a single leaf-trace is seen under a higher magnifying 
power ; the dark lines indicate the direction of the rows of 
tracheids, and the centripetal xylem is represented at x 2 . It 
is not possible to recognize at the proximal end of the out- 
going leaf-trace-bundle any definite indication of primary 
xylem-elements ; the space may be in part the result of 
tearing of the tissues in the immediate neighbourhood of the 
primary tracheids. In another section showing a leaf-trace- 
bundle in a similar position to that represented in Fig. 1 5, 
there are groups of fairly thick-walled elements lying about 
internal to the fan-shaped trace ; these may be portions of 
the primary xylem. At the distal end of a somewhat 
obliquely-cut leaf-trace, as seen in a transverse section of 
the stem, there is a mass of narrow and radially-elongated 
parenchymatous cells. In tangential sections of the stem 
the leaf-trace-bundles are seen passing through the centrifugal 
xylem, and in their immediate neighbourhood the tracheids 
of the wood exhibit extraordinary contortions. In Fig. 11 
some of the strongly curved centrifugal tracheids are shown 
in connexion with an outgoing leaf-trace 1 . One of the 
1 A very similar appearance is presented by a tangential section of a Calamitean 
