55 
Zygopteris Grayi of Williamson. 
laterally extended, forming a band coincident with the major axis of the 
elliptical section, and tangential to the parent stem. The row of internal 
tracheides almost reaches the surface at either end of the band, while the 
main zone of xylem appears divided into two arcs ; the large sieve-tubes 
are now limited to the adaxial and abaxial arcs, and are absent opposite the 
ends of the internal band. The structure strongly suggests that leaf-traces, 
distichously arranged, are about to be given off. The bilateral anatomy of 
the axillary shoot at this level presents the closest analogy with that of the 
stem in some recent Hymenophyllaceae, especially Trichomanes radicans 
and T. reniforme (Boodle, ’00, PI. XXVI, Figs. 22 and 24). 
Unfortunately, in the section next above that from which Phot. 10 was 
taken, the axillary stele is destroyed ; in the second section above, it is seen 
in oblique section and not quite complete ; 1 it shows a relatively large 
‘ mixed pith with at least four prominent angles, and corresponding groups 
of internal tracheides ; on the adaxial side, corresponding to one of the 
protrusions of the central tissue, there is a projecting arm or incipient leaf- 
trace, with an evident island of internal xylem near its end. It is thus clear 
that at this level the axillary shoot was already preparing to assume 
mature structure, with leaves in several series ; 2 the distichous stage, 
indicated at a lower level, must have been passed through very rapidly. 
Intermediate conditions between that of the axillary stele (as seen at its 
base) and the normal stellate form have been previously figured by Williamson 
(’88, PI. I, Fig. 5, see p. 157) and Stenzel (’89, Taf. VI, Fig. 53 ; see 
’96, p. 71). 
Zygopteris Grayi an Ankyropteris. 
We have seen that the Shore fossil is clearly an Ankyropteris , as shown 
by the manifest presence of the peripheral loops, characteristic of that genus, 
on the leaf-trace, confirmed by such slight indications as we have of the 
arrangement of the pinnae on the rachis (see above, p. 46). 
The question remains whether the A nkyropter is characters are common 
to all the specimens known. Dr. P. Bertrand includes the plant in Ankyro- 
pteris , and in his description, based immediately on the later Williamson 
specimen, he states that the leaf-trace has two poles, interior to the wood , on 
its posterior (abaxial) side, situated exactly at its extremities. He adds 
that, after the separation of the axillary strand, each of the poles divides 
into two, and that this division is the point of departure of thp formation of 
two peripheral loops (Bertrand, ’09, pp. 108, 109). 
In a letter dated September 25, 1911, Dr. Bertrand informed me that 
1 The three sections are W. 1919 a, R. 443, and Kidston 308. See list above, p. 52. 
2 It is interesting to find that in this section (Kidston 308) the cortex of the axillary shoot 
contains several aphlebia-bundles, which are absent from it at a lower level. Evidently, as soon as 
the first leaf-traces of the shoot began to be differentiated, the inevitable aphlebia-strands appeared 
with them. 
