356 MR. M. D. ZALESSKY ON NEW 
the phloem ; here, too, the cells have brown contents. In this part of its 
course the leaf-trace has a clearly marked horseshoe shape, and there are 
about six protoxylem groups on its inner face. 
On the outer side of the leaf-trace there are no longer any of the tracheæ 
resembling protoxylem elements, which were present during its passage 
through the inner cortex. When the leaf-traces leave the outer cortex as 
they pass into the petioles, a portion of this cortex is seen behind them as a 
ring, and next to this ring is a parenchymatous tissue which belongs to the 
wings of the stipules and is pierced in many places by rootlets. 
The Structure of the Roots. 
The root arises either from the leaf-traces as they become apparent on 
the periphery of the stele, or after they have become detached from it; in 
the latter case they can often be seen passing out in pairs on each side of the 
oval section of the leaf-trace, or one by one from its anterior surface. The 
root has a central vascular bundle of diarch structure which usually lies in a 
cavity left on the destruction of the phloem and inner cortex. This cavity 
is surrounded by the outer cortex and, nearer to the periphery, by a ring of 
sclerenchyma. 
ZALESSKYA Kidston y Gwynne- Vaughan. 
(Trans, R. Soc. Edinb. vol. xlvi. 1908, p. 213.) 
ZALESSKYA URALICA Zalessky, n. sp. (Pl. 84. figs. 1-3.) 
We have only one transverse section of the stem of this species ; it was 
prepared from a specimen belonging to the artist Denisov-Ouralsky, and is 
from the Permian rocks of the Ural Mountains. Being unable to obtain a 
whole specimen I had to be satisfied with a single section which the owner 
kindly presented to me. The centre of the stem is occupied by a stele, 
slightly compressed along one diameter, which measures 10 mm. The other 
diameter is 12 mm. In the protostele is a space formed by the destruction 
of the central tissue of the stele, which undoubtedly occupied the whole 
space during the life of the plant. The stele consists of two kinds of xylem— 
an outer portion of long tracheæ of the usual width with multiseriate 
scalariform pits, and an inner portion composed of wider and shorter 
elements with irregularly distributed multiseriate and transversely elongated 
pits which give to the tracheæ a reticulate appearance. In the peripheral 
portion of the stele along its circumference, and at some distance from the 
edge, there are about 20 protoxylem groups of two or three elements each, 
which represent the mesarch protoxylems of the ends of the leaf-traces 
immersed in the stele. At a higher level these assume the form of 
prominences of the stele, each with a mesarch protoxylem : the prominences 
are eventually separated from the main part of the stele by the xylem-sheath 
and the phloem. The xylem is surrounded by a zone of elongated narrow 
