354 MR, M. D. ZALESSKY ON NEW 
THAMNOPTERIS GWYNNE- VAUGHANT Zalessky, n. sp. (Pl. 88. figs. 1-5.) 
The transverse section of the stem of this fern, represented by a single 
specimen from the Permian deposits of the River Kozva in the basin of the 
Petchora River, has a central stele 11 mm. in diameter; the xylem reaches 
a diameter of about 9 mm., and consists of two distinct regions, an inner and 
an outer (Pl. 88. figs. 2& 3). The inner xylem, about 7 mm. in diameter, 
oecupies the central part of the vascular eylinder, and consists exclusively of 
short, wide xylem elements with reticulate pitting. There are no traces of 
parenchymatous tissues among the xylem elements present in the central 
part of the stele of  Thamnopteris Kidstoni. The outer xylem, which 
encircles the inner, is composed of long and narrow tracheæ with multiseriate 
transversely elongated pits; its periphery is somewhat irregular in outline 
because of the prominences caused by the exit of leaf-traces which are given 
off at a wider angle than are those of T. Aidstoni. Asa result of the course 
followed by the leaf-traces those next the stele in a transverse section of the 
stem are cut obliquely, and show multiseriate pits in the walls of the xylem 
elements. The angle at which the leaf-traces leave the stele varies from 
22° to 30°. The xylem cylinder is surrounded by a sheath consisting of 
narrow and long cells. This sheath, which is badly preserved, includes three 
or four layers of cells, and is surrounded by another zone of four to six layers 
of cells made up of equally long but wider elements, in which it is not 
difficult to recognize the sieve-tubes of the phloem. This tissue is also badly 
preserved, and occurs only in some places on the circumference of the stele. 
The next zone of tissue has not been preserved, and beyond this is a single 
layer of badly preserved cells sometimes represented only by an irregular 
brown line representing the remains of the endodermis. The vacant space 
between this line and the phloem was occupied, one must suppose, by the 
pericycle, which is nowhere preserved. The endodermis was succeeded by 
the inner cortex, the tissue of which is only occasionally preserved. The 
cortical cells are parenchymatous and their diameter is much larger than that 
of the sieve-tubes. In the specimen examined the inner cortex occupies a 
zone about 9 mm. wide, and is clearly distinguished from the outer cortex 
(10 mm. broad) composed of thick-walled prosenchymatous elements, The 
leaf-traces passing through the inner and outer cortex enter the petioles 
which are at first in close contact, but nearer the periphery they are only 
slightly attached to one another. The petioles form a fairly thick covering 
to the stem. 
The Departure of the Leaf-traces. 
The leaf-traces leave the periphery of the stele at the places where 
prominences have been previously formed as a first step towards separation 
of the foliar bundles. As I have already pointed out, the sections of these 
