FROM THE LOWER COAL-MEASURES. 49 
cylindrical, but the transverse section may have been more markedly triangular than at 
present. 
The most peculiar feature in the structure of the stem is the presence of large, 
irregular masses of wood (surrounded by phloem) around the stele, sometimes detached 
from it, sometimes still in connection (Pl. 7. figs. 1-5; Pl. 8. fig. 6). "These masses vary 
much in size and form, and at first sight give an uncouth appearance to the transverse 
section, different from anything met with in other stems, though offering some remote 
analogy with certain anomalous structures in Dicotyledonous lianes *. These vascular 
masses, subsidiary to the main stele and arising from it, will be called the meristeles ; 
the question of their relation to the steles of Medullosa will be discussed further on. 
The meristele marked « in fig. 5 (Pl. 7) measures 7X 45 mm.; that at 9, on the 
opposite side of the stele, is much longer, measuring 14X4 mm.f The origin and 
course of the two meristeles will be traced in the following paragraphs. Other meri- 
steles are seen scattered round the stele, some of comparable dimensions to those already 
indicated, others smaller, and graduating in size between the former and the ordinary 
leaf-trace bundles. The smaller groups arise, as we shall see, by the subdivision of the 
main meristeles. The structure of the meristeles is in all respects similar to that of 
the stele, and, like the latter, they sometimes show slight indications of secondary 
thickening. ! 
A curious feature in all the transverse sections (best shown in those from No. IX. 
upwards) is the occurrence of two conspicuous double rows of vascular bundles, one 
(d.r.) extending from near the left-hand end of the stele (see figs. 5 & 6) to the periphery 
of the stem, while the other (d.7.') starts just below the stele and likewise runs out 
towards the surface. The bundles are accompanied by a multitude of fibrous strands. 
The structure in these regions is well preserved, and there is no possibility of two leaf- 
bases having been accidentally crushed together, though the series d.7. has probably 
been pushed in a little towards the stele. It is noticeable that in each double row the 
bundles of the lower or left-hand series (figs. 5 & 6) are larger than those of the 
adjacent series. Unfortunately, the remarkable slowness with which structural changes 
take place in this stem prevents us from seeing what becomes of | these bands above or 
below; I ean only suppose that they represent the downward continuation in the stem of 
the inner surface of a leaf-base which would become detached at a higher level. Fig. 6 
(Pl. 7), from the uppermost section of the series, is favourable to this interpretation. 
It will be best to postpone histological detail, and to endeavour first to gain a general 
idea of the vascular system of the plant. For this purpose it is necessary, 80 far as the 
material allows, to trace the course of the meristeles and their relation to the foliar 
bundles. | : 
* Especially with the “lignum circumseptum " of Radlkofer, mee “ — wood," —: m - 
Sapindaceous genus Thinouia (Solereder, 1899, fig. 53, C-E). This is, of course, a secondary anomaly, and has, 
therefore, no homology with the structure in Sutcliffia. dee | ud Queis oe 
+ In all such measurements the wood only is included, as the limits of the phloem may be difficult or impossible 
to trace. 
"io. Bot. Garden 
1913 
