50 
Scott*— On a Palaeozoic Fern , the 
The Aphlebiae. 
Scale-leaves or aphlebiae are borne indiscriminately on the stem and 
the leaf-bases, unless indeed we regard the whole surface as covered with 
leaf-bases, an interpretation which the form of the transverse section scarcely 
seems to justify. The numerous aphlebia-traces which traverse the 
cortex give the best idea of the number of these appendages (PI. I, 
Phot. 4). 
The Shore specimen shows several aphlebiae in connexion with the 
stem, but not many after they become free. Fig. 7, PL IV, represents one 
just detached from the cortex, with which it is connected lower down in 
the series. There are two gaps in the tissue, symmetrically placed, in one 
of which a vascular bundle is contained ; no doubt the second bundle has 
been lost. In another case an aphlebia contained three bundles, and there 
was some evidence of a lateral lobe having been given off. The extreme 
tangential extension of the bundle in the aphlebiae still attached to the 
stem (cf. PI. Ill, Fig. 6) is no doubt preparatory to division ; in some cases 
the fission had begun. 
From the evidence of the Shore fossil and of the second Williamson 
specimen we may conclude that the aphlebiae were lobed bodies containing 
as many as three vascular strands — possibly more. 
The origin of the aphlebia-trace has been investigated, confirming 
Paul Bertrand’s statement that they are; given off from the leaf-traces, even 
before the complete individualization of the latter. They spring from the 
arms of the stele below as well as above the point where these become free 
as definitive leaf- traces. Thus Plate III, P'ig. 5, shows an aphlebia-strand 
just given off from, and still connected with, one of the peripheral loops of 
a leaf-trace (No. 5) just detached from the stele. The level of the section 
figured is immediately below that of Phot. 4, PL I. On the other hand, 
in PL III, Fig. 4, an aphlebia-strand is shown which has separated from 
an arm of the stele, still far below the point where the leaf-trace will be 
given off, and indeed at a level where the peripheral loops are not yet fully 
differentiated. 1 The strand is well preserved and appears to show some 
remains of phloem. Other cases of stele-borne, as distinguished from 
trace-borne, aphlebia-strands have been observed. 
The course of the strand is steeply ascending, as is well shown in the 
longitudinal section (Pl. IV, Fig. 8), where such a strand can be followed 
almost the whole way from the stele through the cortex. Numerous 
aphlebia-strands are given off, in succession, from each leaf-trace or 
stelar arm. They form four series, two to each peripheral loop. 
1 The drawing is from the section next above that represented in PI. I, Phot. 6, and the 
arm is No. 2 . 
