OF THE BRITISH COAL MEASURES. 71 
cortex ; all four bundles are shown, forming two pairs, about 2:5 mm. apart. 
The strands of each pair are quite separate, with about 200 p of cortical 
tissue between them. The section is important, as proving the complete 
division of the leaf-trace into four while in the cortex ; unfortunately one of 
the pairs of bundles is damaged (see Phot. 2). The attached leaf-base is 
still shown, but no bundle is visible. The three traces and leaf-base mark 
the position of four successive leaves: their arrangement is in agreement 
with a 2 phyllotaxis. 
There are two transverse sections of specimen 4 (S. 1323 and R. 633) ; 
they were cut near together. It is a beautiful specimen of a young stem, 
showing all the stelar tissues perfectly (Pl. 1. Phot. 8, & Pl. 4. fig. 12), but, 
owing to the loss of the cortex, is notof much value for the course of the leaf- 
traces. In the not quite complete sections two traces are shown, both in the 
pericycle. In the lower section (S. 1323) the inner trace (T. 1) lies in 
the inner part of the wide pericycle, and consists of two bundles nearly 1 mm. 
apart. They have no secondary wood at this level, but it is not much 
developed on the stele itself. Behind them the stelar wood is beginning 
to close up in the form of small tracheides, which for the most part run 
horizontally. The outer trace (T. 2), at about 2 divergence from the former, 
lies in the extreme outside of the pericycle, which forms a great protrusion 
round each of the two bundles; they are over 2 mm. apart (Phot. 8). In 
the upper section (R. 633) the strands of the inner trace are about 1:5 mm. 
apart, but there is otherwise little change. 
Taking the whole of the evidence from the four specimens, we arrive 
at the following conclusions regarding the course of the leaf-traces in 
H. tiliwoides. 
Two distinct strands start from the stele to form a leaf-trace. Each has 
at first its own secondary tissues, which it loses in traversing the pericycle. 
The strands diverge rapidly, and before the pericycle is passed each begins 
to divide. The division is completed in the cortex, and four bundles enter 
the leaf-base and petiole. It will be noticed that the facts are essentially 
the same as in H. shorense, except that in H. tiliwoides no further subdivision 
of the four bundles in the petiole has been observed. This may merely be 
correlated with the smaller size of the specimen. The phyllotaxis appears 
to be 2. 
Adventitious Roots. 
The evidence as to the roots of Heterangium is meagre*. It is therefore 
of interest to find that in H. tiliwoides the structure of the root can be deter- 
mined with a near approach to certainty, a point not hitherto noticed. The 
best evidence is provided by specimen 8. At the bottom of the series 
(Phot. 7; section Q. 60) the stem bears an appendage (7.) embedded in the 
* See Williamson & Scott, 1895, pp. 764, 765; Scott, 1909, p. 410. 
