SPECIES OF PERMIAN OSMUNDACE./E. 200 
Thamnopteris Kidstoni are shorter and blunter than those of T'hamnopteris 
Sehlechtendalii, and, so far as one can see in tlie specimen, there is only one 
group of sclerenchyma in the form of a dot on each side of the stipule, and 
not two or three as in J'hamnopteris Schlechtendalü. Thamnopteris Kidstoni 
is also characterized by the fact that the sides of the sclerenchymatous border 
in its outer portion are bent in the form of an are curved outwards, while in 
Thamnopteris Schlechtendali they are curved slightly inwards. 
The Structure of the Roots. 
The xylem bundles of the roots emerge from the periphery of the stele 
almost vertically, so that in this part of the transverse section of the stem 
they appear as if cut lengthwise. The bundle is diarch with obvious proto- 
xylem trachez. Usually the roots arise from the stele of the leaf-trace either 
singly or in pairs. Sometimes they are given off from the leaf-traces on the 
posterior and lateral parts of the xylem bundles as these bundles are 
becoming detached from the stele, or after they have been detached and lie 
in the inner cortex. The root bundles traverse the cortex of the stem in all 
possible directions, and in the transverse section of this regicn of the stem 
they appear cither in longitudinal or transverse section. The transverse 
section reveals a diarch xylem bundle surrounded by a zone of thin-celled 
tissue sometimes filled with brown content. This zone contains about eight 
layers of cells which no doubt represent phloem ; it is surrounded in its turn 
by a ring of four to five layers of empty cells which apparently represent 
the tissue of the inner cortex of the stem—orientated in relation to the root 
and forming its sheath. In longitudinal section the cells of the inner zone 
enclosing the vascular bundle of the root appear to be prosenchymatous ; 
their walls are penetrated by irregularly distributed and rounded perforations 
varying in diameter and similar to the pits in the prosenchymatous cells of 
the outer cortex of the stem. The outer zone of light-coloured tissue in 
longitudinal section appears to consist of prosenchymatous cells with similar, 
irregularly distributed perforations in their walls—a fact that demonstrates 
that these perforations, wherever they occur, do not represent the structure 
of the wall but are due to a particular state of preservation. The vessels of 
the root, like those of the leaf-traces, are provided with multiseriate pits. As 
the root passes from the inner cortex to the outer part of the stem it is 
surrounded by its own cortex, the inner portion of which consists of thin- 
walled parenchyma and the outer part of sclerotic prosenchymatous cells. 
The roots as they traverse the parenchyma of the stipules of the petioles are 
provided with these two kinds of cortex and enclose in the centre a well- 
marked diarch vascular bundle surrounded by phloem which is not always 
well preserved, 
