CMT ONERE NAR Sl 
OF THE BRITISH COAL MEASURES. 89 
petiole the sclerotic nests appear, and the dense hypoderma is also that of a 
fleterangium*. The tissues are much permeated by roots and rootlets, but 
the vascular bundles belonging to the petiole are easily recognized in all the 
sections. There are four large bundles, two widely separated in the section 
figured, and two close together. The two more median bundles are clearly 
dividing; where the structure is well enough preserved, the bundle is evidently 
mesarch with little centrifugal wood, and is thus completely of the Heterangium 
Lomacii type. This petiole is much compressed, and measures where complete 
about 6x1 mm. There is no doubt that it belongs to the Heterangium, 
and it thus proves that the bundles completed their division into four after 
entering the petiole, and even initiated further subdivision. 
Another larger and much crushed petiole t (75x1 mm. in diameter) 
shows, in the best section, four bundles, two of which are dividing. A third 
specimen f, of about the same size (6 x 1:5 mm.), contains four large bundles, 
quite separate, but not obviously dividing further. All these show the 
Heterangium characters unmistakably. It is a pity that we have no petiole 
in continuity with the stem, but the evidence is enough to show that in 
H. Lomawii, as in H. shorense and H. tiliwoides, the petiole was polydesmic, 
the minimum number of bundles being four. 
It is evident that the three species of Heterangium which have now been 
described were nearly allied; they agree among themselves in having 
polydesmie petioles, and are the only species recorded in which this 
character has been observed, though it may be found to extend to others. 
The forms now grouped under H. Lomasii appear, for reasons already 
given, to constitute a single species, distinct though not very different, from 
H. shorense and H. tilieoides. The specific characters may be summed up as 
follows :— 
Heterangium Lomacii, Will. in litt. 
Stem from about 5 or 6 mm. to about 198 mm. in diameter. 
Primary wood consisting of somewhat irregular groups of tracheides, with 
parenchyma between the groups. 
Tracheides without any spiral bands between the pits. 
Peripheral xylem-strands and leaf-trace bundles inesarch with little 
centrifugal wood. 
Secondary phloem sometimes well developed, but phloem-rays not much 
dilated. 
Pericycle generally of moderate breadth, but much enlarged where leaf- 
traces or roots pass out. 
* This petiole occurs in five sections of the specimen 2 (æ form) series, namely 
W. 1915 N, 1885 H, 19150; S. 236 and R. 642. 
T Occurring in the sections W. 1915, 1915 B, 1915 A. 
t In the University College slide, N. 3. 
LINN. JOURN.—BOTANY, VOL. XLIV. H 
CT SC TORTE NN 
