THE CARBONIFEROUS FLORA OF BERWICKSHIRE. 267 
ture of the trace leaves no gap in the secondary xylem, which closes in immediately 
behind it. 
The leaf-trace continues to possess a certain amount of secondary xylem for some 
time after it has become free from the xylem of the stem, although that on the adaxial. 
side is very scanty and soon disappears. It was possible also to recognise in our sections 
the leaf-trace that immediately preceded the one just described (figs. 6-7, /.t.," and 18). 
In this trace the primary xylem had just divided into two approximately equal portions, 
which are at first still surrounded by a certain amount of secondary xylem common to 
both. Even after they have become completely separate, the secondary wood on the 
abaxial side is retained for a considerable time (fig. 7, /.¢.'). 
There is no doubt that all the traces occurring in the space formerly occupied by the 
cortex were derived by the continued subdivision of primary leaf-traces such as those 
just described. Several leaf-traces, both large and small, were observed in actual division 
(fig. 21). It is therefore certain that all the vascular strands given off from the stele 
are primary leaf-traces, which in their passage through the cortex divide repeatedly to 
supply the petioles. ‘There is also clearly an entire absence of any meristeles probes to 
the stem such as those occurring in Sutcliffia insignis.* 
The xylem of the leaf-traces consists mainly of porose tracheze without any xylem 
parenchyma. The trachez at the periphery are markedly smaller than those at the 
centre, and are scalariformly pitted (figs. 20,21, 22, and 23, from the petiole). The 
scalariform trachez are present in greatest number towards the side of the trace on which 
the protoxylem is situated. he traces usually show a single very distinct and definite 
protoxylem, except just below a point of division of the trace where there are two (figs. 
21-22). In the immediate neighbourhood of the stele the protoxylems appear to be 
exarch, but at some distance out they are distinctly immersed, and are represented by 
small cavities situated some little distance within the periphery of the xylem (figs. 20, 
21, and 22). Owing to the shifting and displacement of the leaf-traces due to collapse 
of the cortex, it is impossible to determine their proper orientation with regard to the 
periphery of the stem. Most probably, however, the protoxylems pointed to the outside. 
No indication of phloem could be discovered in relation to any of the leaf-traces. 
Descruption of the Leaf. 
In the sections of the block which contained the stem there also occurred several other 
fragments of vegetable tissue. Most of these were portions of leaf lamina, and one of 
these was found to be in organic connection with an axis which is no doubt the petiole, 
rachis, or midrib of Stenomyelon (fig. 1, L., and text fig. 1). As seen in longitudinal 
section, the connection between the lamina and the rachis of the petiole extended over 
a considerable distance, which suggests that the leaf was a simple and not a divided one, 
* Scort, “On Sutcliffia insignis, a new type of Medullosex from the Lower Coal Measures,” Trans. Linn. Soc., vol. vii. 
p. 49, 1906. 
