44 
Scott . — On a Palaeozoic Fern , 4 ^ 
cases, as already mentioned, the undivided leaf-trace has a somewhat 
triangular transverse section, as shown in PI. IV, Fig. 12; in the Shore 
specimen the section may be described as crescentic (PI. I, Phots. 4-6, 
8 ; PI. Ill, Fig. 1) with the concavity outwards and the ends obliquely 
truncated. The bundle here, however, is obviously of the same nature as in 
the Z. Grayi type, for in PI. I, Phot. 1 (/./., a.s.), we see it in the act of 
dividing to form the axillary stele and foliar bundle, though the latter is 
imperfectly shown. The form of the undivided trace, though a striking 
feature of the new specimen, is not peculiar to it ; a similar crescentic leaf- 
trace occurs in one of Williamson’s type-specimens, as shown in PI. II, 
Phot. 15, l.t. The | phyllotaxis is obvious on comparing the successive sec- 
tions (Phots. 1-6) and observing the position of the stelar arms from which 
leaf-traces depart. The phloem and inner cortex are badly or not at all 
preserved ; in this respect the Shore fossil is inferior to the best Williamson 
specimen (see PI. IV, Fig. 12; PI. V, Fig. 13). The wide outer cortex has 
the same general character as in the latter, and is traversed by numerous 
aphlebia-bundles. In both plants the epidermis bears great numbers of 
multicellular uniseriate hairs (PI. IV, Fig. 7). The adventitious roots appear 
to be given off in the same way in all the specimens (see PI. V, Fig. 14, 
from Williamson’s later specimen). 
Structure of the Stele. 
The general ground-plan of the wood is not at all unlike that in 
the Williamson type-specimens (Williamson, ’ 89 , PL I, Figs. 1 and 2, and 
PI. II, Phot. 15, in the present paper) ; the resemblance to his later 
specimen is not quite so exact (cf. PI. II, Phots. 11-13). The central tissue 
(‘ mixed pith ’) has a diameter of little over 1 mm., and a pentagonal outline 
(PL I, Phot. 7). The internal system of tracheides forms an interrupted 
zone in the outer region of the mixed pith, enclosing a considerable amount 
of parenchyma (PL I, Phot. 7). 
PL III, Fig. 3, is from a longitudinal section of the stele, cut somewhat 
tangentially, so that the plane of section coincides with one side of the zone 
of internal xylem, and several groups of internal tracheides are shown (x.i.). 
From the central zone extensions of the internal xylem extend 
outwards, up each of the xylem-arms, forming the internal rays, the length 
of which varies according to the level at which the arm is cut. The internal 
rays are narrow in this specimen and the tracheides in them much com- 
pressed. The tangential diameter of the tracheides in the outer part of the 
internal ray ranges from 12 to 20 /x, the radial diameter from 18 to 60 jx. 
Some of these compressed tracheides show a spiral thickening, and no 
doubt represent the protoxylem of the stele. 1 
1 The protoxylem elements are best shown in the axillary stele. See PI. IV, Fig. io, px . 
