SPECIES OF PERMIAN OSMUNDACEÆ. 357 
cells in four to five layers, and in this zone occur cells with brown con- 
tents ; these are either scattered singly among the elements that have no 
brown contents or in groups. Next to this zone, serving as a xvlem-sheath, 
is a band of wider phloem elemeuts. These are sieve-tubes, and with them 
are sometimes seen small cells which represent phloem-parenchyma. The 
phloem is succeeded by a band of cells almost as large as the sieve-tubes, 
enclosing a brown mass. This band consists of five not quite regular layers. 
The inner series of these cells may be regarded as the pericycle, although 
the characteristic cells of the endodermis have not been found. The thick- 
ness of the inner cortex generally reaches 13 mm.; it is thus 7 mm. less 
than the thickness of the same tissue in Zalesskya gracilis. The outer cortex 
seen in my preparation, on a small extension of the circumference of the 
stem, is preserved only in its inner portion, and the thickness of this part 
does not exceed 6 mm. The leaf-traces, as seen in section near the stele, 
have an oval outline, and are separated from the cells of the inner cortex by 
a band of cells with brown contents. The protoxylem, even in leaf-traces 
that are very near the stele, occurs on the edge of the adaxial side so that 
the trace, which at its departure from the stele was mesarch, soon becomes 
endarch. The xylem-sheath of the vascular bundle and the phloem 
surrounding it are sometimes well enough preserved to show the sieve-tubes 
and, in the sheath, cells with brown contents. Nearer the periphery the leaf 
trace becomes reniform and the vascular bundle crescentic, first with one 
then with two protoxylem groups on its adaxial side. In the outer cortex 
the leaf-trace is surrounded by a sheath of parenchymatous cells of the inner 
cortex, and this is sickle-shaped. There are four protoxylem groups on its 
adaxial side. 
The roots leave the periphery of the stele singly or in pairs. In the 
centre of the root is a diarch vascular bundle surrounded by phloem, beyond 
which is a thick cortex of parenchymatous cells stained a deep brown and 
sharply distinguished from the cells of the inner cortex of the stem throngh 
which the root passes. A few of the outer layers of the cortex are very 
deeply stained and have brown contents; it is possible that they are 
thick-walled cells. Zalesskya uralica is practically identical in structure 
with Z. gracilis and may be only a younger stem of that species. The 
difference consists in the smaller diameter of the stele, which is about 10 mm. 
broad, while Z. gracilis has a stele of 14 mm. and a narrower zone of inner 
cortex which reaches a breadth of 13 mm., while in Z. gracilis it is 20 mm. 
broad. The leaf-traces of Z. uralica are much smaller than those of 
Z. gracilis (Pl. 84. fig. 4). In view of the difficulty of deciding the question 
of relationship, it is more convenient to describe the Denisov-Ouralsky 
specimen under a separate name, 
