57 
Zygopteris Grayi of Williamson . 
I think it probable, however, that there was a slight difference between 
the later Williamson specimen and that from Shore, the peripheral loops 
not becoming clearly differentiated so low down in the course of the leaf-trace 
in the former as in the latter. Dr. Bertrand’s own description clearly 
points to a rather late differentiation in this respect. 
The petiolar bundle of the type-specimens (PI. II, Phot. 1 6) is almost 
identical in form with that of Zygopteris di-tipsilon (Williamson, ’ 80 , PI. XXI, 
Fig. 90), with which Dr. Kidston identified Z . Grayi (Kidston, TO). The 
resemblance is so striking that this conclusion appeared well founded at the 
time. Dr. Kidston, like myself, had not then recognized the presence of 
peripheral loops in Z. Grayi. Z. di-upsilon is a typical Etapteris (P. Ber- 
trand, ’ 09 , p. 148 ; PI. I, Fig. 6 ; PI. XVI, Fig. no), and, as such, has no 
peripheral loops and gives off four series of secondary strands from the 
foliar bundle. It cannot therefore belong to Zygopteris Grayi , which is 
shown to be an Ankyropteris by the presence of peripheral loops, and 
by there being (so far as the available evidence shows) only two series of 
secondary rachis-strands. 
Dr. P. Bertrand (’ 09 , p. 106) suggested, with much reserve, the possi- 
bility that the petiole of Z. Grayi might be identical with the well-known 
Z. bibractensis , var. westphaliensis. The differences in the form of the foliar 
bundle are obvious ; the middle band of the xylem (‘ apolar ’) is straight in 
Z. Grayi , curved in Z. westphaliensis ; the lateral bands (antennae) are 
long and but little curved in Z. Grayi , while in Z. westphaliensis they are 
strongly bent inwards towards the plane of symmetry ; further, the antennae 
are of approximately equal length in Z. Grayi , while in Z. westphaliensis 
those on the convex (presumably adaxial) side of the median band are con- 
siderably longer than those on the concave (abaxial) side. Nothing has 
yet been observed to indicate that the one form passed over into the 
other, and there is a strong presumption that the species are distinct. 
The Morphology of the Leaf-trace and Axillary Stele. 
There are two views of the nature of the organ which throughout this 
paper has been called the ‘ leaf-trace ’ or the ‘ undivided trace ’. On the 
one view, which was that of Stenzel, 1 the first to observe the facts, this 
strand is essentially a leaf-trace, directly continuous with the foliar bundle, 
but modified, to a certain extent, by the presence of a branch, the stele of 
which is given off from the leaf-trace on its adaxial side and a little above 
its base. From its position the branch is consistently termed the axillary 
shoot, and its vascular strand the axillary stele. 
On the alternative view, the meristele which we have called the leaf- 
trace is, from its base, of an axial nature, constituting the stele of a branch ; 
the true leaf-trace is given off from it as a lateral appendage. On this 
1 ’89, p. 35 5 ’96, p. 31 . 
