On the Structure of Sigillaria scutellata, ete. 149 
rather smaller than those of the primary xylem, but, unlike them, they are 
arranged radially. The outer margin of this zone was crenulated, the 
ridges and grooves corresponding in position to those of the primary wood. 
The medullary rays usually consist of a single row of cells of varying height, 
of which the walls are sometimes thickened transversely. 
The phloem and inner cortex of thin-walled elements are not preserved. 
A well developed band of phelloderm is found near the surface of the ribs. 
This is regarded as having arisen on the inner side of a meristematic zone. 
No definite cambial layer is to be found, and it is suggested that the 
meristematic activity here took place periodically. Cells are to be seen in this 
region which appear to have undergone division shortly before preservation 
took place, and rings of growth are to be observed in the older portions of 
the phelloderm. The secondary tissue consists of prismatic fibres, often 
chambered. 
The ribs are really formed of cortical tissues, and not by fused leaf-bases. 
They consist largely of phelloderm, and externally what is probably a small 
zone of primary cortex, which lay without the region of secondary merister- 
matic activity, still persists. The stems were probably ribbed long before 
the formation of the periderm. The leaf-bases, consisting of thin-walled 
parenchymatous elements, merely form bracket-like projections from the ribs; 
those of the same vertical series being sufficiently distant from each other 
to leave a small gap of primary cortex between them. The ribbing of the 
stem in the Eusigillariz, being entirely independent of the form and arrange- 
ment of the leaf-bases, appears to be a natural feature of importance in 
classifying the Sigillariz. No sign of branching has been observed in any 
specimen. The presence of a heule and a lgular pit has been detected 
for the first time. 
The course of the leaf-traces in the leaf-bases and cortical tissues has been 
followed with important results. The bundle is collateral, and without 
secondary wood. In the leaf-bases the trace consists of a double xylem strand, 
the two xylem groups being widely separated. These two strands unite as - 
they pass through the phelloderm. The structure of the trace is almost 
identical with the foliar bundle of the leaf described by Scott as Sigillariopsis 
sulcata, which is obviously simply the leaf of a Eusigillarian stem. 
The parichnos—the two strands of thin-walled elements, which accompany 
the leaf-trace through the leaf-base and cortex—increases greatly in size, as 
we pass from the exterior of the stem to the inner margin of the periderm. 
The two strands further unite, first below and then above the trace, so that, 
at a deep level in the periderm, the trace is completely surrounded by a broad 
zone of this tissue. 
N 2 
