OF THE BRITISH COAL MEASURES. 87 
the pericycle or cortex is hard to say, the two tissues not being at all sharply 
delimited here—at any rate, it is separated from the disorganized phloem of 
the stele by several layers of more or less sclerotic parenchyma. The two 
double bundles of the trace are about 120 u apart; they are fairly large 
strands, measuring 615 w and 820 p respectively in tangential diameter, and 
each is manifestly double, for the xylem is lohed and divided radially down 
the middle by a band of collapsed cells. This section, then, proves that the 
leaf-trace consisted of two bundles, each of which prepared to divide before 
it had got far on its outward course. The adventitious root figured by 
Williamson shows no obvious relation to any leaf-trace. 
In specimen 2 the order of the sections from below upwards proves to be : 
W.1885 HH, W. 1915 N, W. 1885 H, W. 1915 M, W. 1915 0, S. 236, R. 642. 
So long a series seems promising, but the stem is in many sections incom- 
plete and the crushed condition perplexing. It is doubtful whether the two 
“ leaf-traces ” marked on our fig. 21, of 1895, were really of that nature; 
the only undoubted traee is near the broken end of the section. In the 
present fig. 16 (Pl. 4), from this specimen, the double strand v.b. may be a leaf- 
trace. So far as the evidence goes, it confirms that from the type-specimen. 
In specimen 2 a, which appears in five sections of the same series, a double 
leaf-trace can be followed through the whole thickness of the cortex. [n 
the section figured (fig. 17) the bundles are far out and may have been entering 
the leaf-base ; the tissue, however, is damaged and one of the two strands 
(v.b.!) lies in the débris. The signs of division in each bundle are less marked 
here than in the other cases mentioned. 
So far as the available data show, the behaviour of the leaf-trace in the a 
form of stem seems to have been much the same as in the *cylindricum 
form, already described, the trace consisting of two large strands which 
pass out without separating very widely, and do not complete their subdivision 
till after they have entered the leaf-base ; in both cases more than one trace 
may be met with in the transverse section, 
A word may be added about the branching, already described and figured 
in the joint memoir *. The branch appears in three successive sections of 
specimen 2. In the lowest section the continuity between branch and stem 
is more complete than in that figured (the middle one); the stele of the branch 
is smaller, and its zone of secondary wood thicker. At this level there is a 
little secondary wood on the main stele also—a small arc 620 u broad and 
about 6 cells thick on the side towards the branch. It dies out higher up the 
stem. In the third section (W. 1885 H; above that figured) the branch is 
free from the stem, but still shows no leaf-traces of its own ; it is, however, 
not quite complete. At this level, the secondary wood of the branch has all 
* Williamson & Scott, 1895, p. 753, pl. 26. fig. 21. 
T W.1885 HH, 1915 N, 1885 H. 
