726 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
petiole after it has become free, where it presents all the characteristics of Rachiop- 
teris aspera. * 
The leaf is attached to the stem by a massive base, which, however, is not at all 
sheathing (see photographs 3 and 4, fig. 10). The leaf-trace bundles, which had 
traversed the pericycle almost vertically through about five internodes, bend out 
somewhat sharply into the base of the leaf (see photograph 4). It has already been 
mentioned that the bundles, which are collateral in the stem, become concentric 
as they enter the leaf. The extent to which the two bundles of the trace fuse 
on entering the petiole varies in different specimens; in that represented in fig. 10 
they partially fuse; in other cases (e.g., C.N. 1984) they remain distinct. All the 
primary tissues, vascular bundles, pericycle, inner and outer cortex are, as we should 
expect, perfectly continuous between stem and leaf. The limit between cortex and 
pericycle is, however, difficult to trace at the point of junction. The sclerotic nests, 
which in the stem are almost always limited to the pericycle, become distinctly 
cortical in the petiole, forming a conspicuous feature which helps to characterize 
the species. t 
There is always a great development of these sclerotic masses in the axillary 
region, a fact which is worth noticing because these conspicuous groups of cells 
might be mistaken for rudimentary axillary buds. We find no evidence that 
such buds existed. 
Exactly below the axil a characteristic transverse hypodermal band of black 
sclerotic tissue is found (see photograph 4 and fig. 10). This helps us to fix very 
exactly the position of the transverse as compared with the longitudinal sections of 
the node. The outer cortex of the stem closes in again almost immediately above the 
level of the sclerotic band. 
The subject of phyllotaxis has already been dealt with. The arrangement is 
evidently 3 in all the larger stems, in which the relative position of the leaf-trace 
bundles is clear. In the smallest stems the divergence seems to have been 3. 
2. Form of the Leaf: 
This subject was discussed in Memoir VI., at a time when the relation of Rachiop- 
teris aspera to Lyginodendron had not yet been determined. 
The stems of Lyginodendron are almost invariably found to be surrounded by a 
multitude of fragments of foliage, among which petioles of all sizes, often in the act 
of branching, are to be recognized, as well as portions of leaflets. Wherever the 
structure is sufficiently well preserved, the characters of Rachiopteris aspera are 
* C.N. 1983 and 1984; also three sections from this series in the possession of D. H. Scorv. 
Numerous single sections in the Wintiamson collection also show the connection between petiole and 
stem, as O.N. 1140, 1144,B, 1144 D, 1190, 1191 and 1198 (two nodes of the same stem), 1885 G, 1915 C. 
+ See Wintiamson, Part VI, p. 682. 
