2 ‘OF THE BRITISH COAL MEASURES. 91 
4 
thickness of about seven elements, is small-celled, as usual, the tracheides 
seldom exceeding 36 u in diameter. The phloem is destroyed ; the pericycle 
tolerably preserved in places. No sclerotic nests have been detected either 
in the pericycle or the cortex—one would not expect a strong mechanical 
construction in so smalla stem. The cortex is parenchymatous, with a rather 
feeble Sparganum zone on the outside. 
In the section figured a leaf-trace is seen in the’ pericycle. — It is a single 
strand, though somewhat lobed ; other sections show that the trace divided 
into two strands further out on its course, but they have not been seen to 
diverge. In one section (S. 1805) a second trace is seen, just separating 
from the wood, as a single strand, with two protoxylem groups. 
It thus appears that /Jeterangium minimum differs from all other forms 
described in this paper in having a leaf-trace consisting of a single bundle 
where it starts from the stele. In this point it agrees with M. Grievii, but 
differs in the fact that the trace divided into two in the cortex. Of course, 
it cannot be strictly proved that /7. minimum may not have been a minute 
twig of some other species ; there is, however, nothing to indicate that this 
was the case, and on present evidence the plant must be regarded as distinct. 
The specific characters may run as follows :— 
Heterangium minimum, sp. nov. 
Stem minute, under 3 mm. in diameter. ! 
Primary wood consisting chiefly of tracheides with a few parenchymatous 
bands. Peripheral xylem-strands not well defined ; mesarch, with a layer or 
two of centrifugal wood. i 
Sclerotic tissue apparently absent from both pericycle and cortex. Leaf- 
trace a single bundle where it leaves the stele, dividing into two in the 
cortex. : 
Locatity. Dulesgate, Lancashire : Lower Coal Measures. 
Found by Mr. James Lomax in 1903, 
A New SUBGENUS. 
If for the moment we leave /Jeterangium minimum out of account, we find 
that the other three British Coal-Measure species of the genus, while differing 
only in trivial points, agree in the following characters: the distinetness of 
the peripheral xylem-strands, and consequently of the principal medullary 
rays; the tendency towards exarchy in the primary xylem-strands, the 
centrifugal primary wood being little developed ; the compound leaf-traces, 
double on starting from the stele, quadruple or more on entering the petiole. 
The first of these characters may reasonably be considered as an advance 
on the structure of the H. Grievii type, in which the peripheral strands of 
the stele are not sharply delimited. Their greater distinctness is a departure. 
from the pure protostelic structure, and indicates a progressive downward 
differentiation of the leaf-trace system. 
H2 
