OF THE BRITISH COAL MEASURES. 63 
In the hypoderma the radial bands of sclerenchyma are well marked, and 
sometimes anastomose across the intervening tracts of cellular tissue, as in 
Lyginopteris. On the prominent leaf-base the proportion of sclerenchyma to 
parenchyma is greater than elsewhere (Pl. 8. fig. 2). The leaf-base is delimited 
on either side by a barrier of sclerenchyma, resembling that of the hypoderma 
on which it abuts (figs. 1, 2). The whole structure of the cortex is typical 
of a Heterangium and shows the various tissues in a well-developed form. 
The elements commonly described as “secretory sacs” are, however, 
obscure. There are a certain number of cells, especially in the cortex, with 
dark contents, but, owing to the state of preservation and the absence of any 
longitudinal sections, it has not been possible to distinguish with certainty 
between differentiated sacs and disorganised cells. 
The Leaf-traces. 
We now come to the most characteristic point in our plant—the arrange- 
ment and course of the leaf-traces. Several traces are present in each 
transverse section, but no one section shows them all perfectly. That repre- 
sented in fig. 1 may serve to give an idea of their distribution. Four leaf- 
traces are shown in the section. 
At the top of the figure is the large leaf-base, in which three bundles are 
preserved (Trace A). The full number, however, is four, as shown in fig. 2, 
which represents the same leaf-base several sections higher up the stem. All 
four are likewise shown in a section eut lower down than that represented in 
fig. 1, so the presence of three only in the latter is merely due to accidents 
of preservation. 
The first fact, then, which we learn as to the leaf-traces is that no less than 
four bundles entered the base of the leaf. 
In the petiole itself still further division took place, as shown in fig. 3, 
which represents the section of a detached petiole clearly belonging to the 
same plant. Here each of the four original bundles has divided into two, the 
division being more advanced in the middle than in the lateral pairs. This 
plurality of bundles is a new feature for the genus Heterangium and a marked 
difference from the Lower Carboniferous species, M. Grievii, where only a 
single bundle enters the petiole. 
How, then, do the four bundles entering the leaf-base originate? Turning 
to fig. 1, we see in the “ S.E.” of the figure, in the inner cortex, a pair of 
bundles close together, and above them another, ill-preserved, pair. In other 
sections this second pair is quite well shown ; the space between the two 
pairs is about 1*6 mm. There is thus a strong presumption that the two pairs 
of strands together constitute a single leaf-trace (Trace Bj. This is con- 
firmed on observing the bundles on the left of the figure (Trace C). There 
are two on the inner edge of the cortex, and each is evidently in the act of 
division. The lower of the two is shown on a larger scale in fig. 6. The 
