FROM THE LOWER COAL-MEASURES, 55 
It is unfortunate that neither the position of the meristeles nor the arrangement of 
the leaf-bases themselves gives any certain clue to the phyllotaxis. The most definite 
leaf-base is that which occupies the lower left-hand portion of the transverse sections, in 
the position in which they are figured. At the top of the series, in Section XVII. 
(Pl. 8. fig. 6), the individuality of this leaf-base is well-marked, and it appears to have 
been approaching its separation from the stem *. No other appendage shows any 
definite demareation at this level, so that we may assume that the se baton was spiral 
and not verticillate. The appearances are not inconsistent with a 2 arrangement, such 
as exists in Medullosa anglica, but no positive conclusion ean be drawn. 
Histology. 
1. Structure of the Wood.—The wood of the stele has essentially the same structure— 
apart from the position of the protoxylem—as in Medullosa anglica, and requires no 
detailed description. The primary tracheides, which, as already mentioned, are of 
exceptionally large size, sometimes reaching 350 » in diam., bear the multiseriate 
bordered pits which are so common a character in Palsozoie woods. In the stele itself 
the details of structure are not usually well-preserved, owing perhaps to too slow 
penetration by the petrifying substance, but in the more external bundles the preserva- 
tion is all that could be desired, as shown in Pl. 10. fig. 18. The exarch character of the 
protostele of Sutcliffia at once suggested a comparison with the JMegaloxylon of Seward ; 
it is therefore of importance to point out that throughout the stele in Swtcliffia the 
tracheides are of the ordinary elongated form (Pl. 9. fig. 12), and there is no trace of 
the short and broad xylem-elements, adapted probably for water storage, which are so 
characteristic a feature in Mr. Seward's fossil (Seward, 1899). 
The comparatively thin-walled wood-parenchyma forms a continuous network among 
the tracheides, separating them into small groups or sometimes single elements (Pl. 9 
fig. 11. The parenchymatous cells are transversely elongated in a direction parallel to 
the walls of the adjacent tracheides, so that a longitudinal section sometimes shows a 
Structure remotely suggestive of medullary rays (fig. 13). Among the ordinary cells of 
the xylem-parenchyma there are numerous scattered elements with dark contents, 
perhaps of a secretory nature; these sacs may resemble the neighbouring cells, or may 
be larger in one or other dimension. 
The position of the protoxylem, as already pointed out, is, generally speaking, external. 
Àn example of this is given in Pl. 8. fig. 10, where a group of tracheides is shown with 
the smallest elements towards the outside (pz.). Another illustration is given in Pl. 9. 
fig. 11; here the right-hand group becomes smaller-celled towards the exterior, and 
terminates in one or two crushed elements, clearly the collapsed protoxylem. On the . 
left the most external element is rather larger than some of those to the inside of it— 
an occasional irregularity, which appears too trifling to justify us in applying the 
* The fact that the limit of -this leaf-base lies so near the stele is no doubt due to the intervening cortical tissue 
being lost. 
L2 
