708 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
Plate 21, fig. 1 the relative position of these bundles is evident and is indicated by 
numbers, /.t.! being the most internal, and /.t.5 the most, external of the five leaf-traces. 
The innermost leaf-trace, J.t.1, is still within the general contour-line of the 
secondary wood, while /.t.2 has only just passed beyond it. Both these traces are 
solitary bundles, and each has a secondary arc, which is more developed in /.t. than 
in 1.t.% The next outer trace, 1.2.3, is already double, and has no secondary tissues ; 
l.t.4 is similar, but lies a little further out, while /.t.° is still nearer the periphery. 
This last trace, like the rest, is within the pericycle, which, however, here shows a 
marked outward protrusion. It will be noticed that, behind each of the four inner 
strands, there is a gap in the secondary wood occupied by parenchyma, while, behind 
the outermost leaf-trace, U.¢.5, this yap has already been filled up by intercalated 
secondary tissues. We will speak of this gap as the trace-gap. 
The order of the outgoing bundles can be traced in a similar manner in the stem 
shown in Plate 18, photograph 1. The same general rules hold good for all transverse 
sections, where the preservation is sufficiently perfect. 
We now have a number of specimens showing the leaf-trace bundles actually 
passing out into the base of the leaf. Previous figures (Part IV., Plate 16, fig. 25 ; 
and Part XVIL.,* Plate 12, fig. 1) show the twin bundles in transverse section as they 
traverse the cortex and enter the leaf-base. Plate 18, photograph 3 and Plate 23, 
fig. 10 in the present paper represent two transverse sections from the same specimen 
showing a petiole in connection with the stem. The vascular bundles have here 
passed out so far as tu belong definitively to the petiole. In Plate 18, photograph 4, 
a corresponding radial section from another specimen is shown. Here the foliar 
vascular bundle can be traced from the pericycle of the stem, through the cortex, 
and can be followed for a long distance in the petiole itself. 
There is in the Wittramson collection a series of eight successive transverse 
sections from the same stem.t Considerations of space have prevented us from 
figuring the series, which throws great light on the course of the vascular bundles. 
The lowest section shows the base of a petiole attached to the stem, and a second 
petiole makes its appearance towards the upper end of the series, which thus extends 
through one internode. The divergence between these two successive leaves is 4, 
and this seems to have been the most usual phyllotaxis in Lyginodendron. The trace, 
which passes out into the upper of the two leaves, can be followed throughout the 
series ; it is a double bundle ail through this part of its course. In the sixth section 
from below it begins to bend out into the leaf-base, and, as it does so, its two bundles 
unite somewhat, forming a V with the angle outwards ; this very frequently happens 
at the base of the petiole, though sometimes the bundles remain quite distinct (see 
* These references ave to the WitLtAMson Memoirs fully cited above (p. 705, footnote). 
+ C.N. 1191-1198. ‘The proper order of these sections from beluw upwards is as follows: C.N. 1198, 
1192, 1193, 1194, 1195, 1197, 1196, 1191. 
