886 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
and at right angles to the surface, shows similar elements to the inner zone 
differently arranged; the “medullary spots” are not, of course, represented. 
The vesicles and fine hyphse mentioned above and regarded as a saprophytic 
fungus in connection with the inner zone, occur between the tubes of the 
outer zone also. 
The tubes in the outer region are represented by their homogeneous brown 
contents, and can be traced from the irregularly running tubes of the inner region 
which bend outwards and branch. The free ends form the parallel tubes of the 
outer zone, which vary in thickness. They tend to widen slightly at their outer 
ends, where their tips stand at about the same level. Some of these tubes showed 
the same spiral marking as was described for the wider tubes of the inner tissue 
(fig. 117). 
Between the vertically running tubes, and at places appearing to separate them . 
into bundles, a granular mass is such a regular constituent of this outer zone as 
to suggest that it might have been based on a real structure, but the appearance 
is never decisive. When the clear evidence of breaking down and rearrangement 
afforded by the pseudo-cellular structure is taken into consideration, we are not 
prepared to attach significance to the brown granular masses in the outer zone, 
though attention may be directed to them. 
The narrow, clear outer zone (figs. 113, 114, a) above the summits of the vertical 
tubes is structureless, but the pseudo-cellular structure, that can be traced through- 
out much of the fragment, comes out very clearly here. It seems reasonable, in 
the light of the rest of the structure, to interpret this outermost zone as having 
been a structureless,- and perhaps mucilaginous, layer during life. It has no 
sharply defined outer limit, though this is marked as a dark line owing to a 
granular deposit. 
Although there is no continuity and the condition of decay or preservation is 
somewhat different, the second fragment described above has been treated as the 
peripheral region of Nematophyton. This peripheral region in previously known 
specimens of the genus has, at best, been represented by a thin coaly layer.* The 
demonstration of the general structure of the peripheral region is the main addition 
to our knowledge of Nematophyton that is afforded by these specimens. 
The affinities of Nematophyton with its remarkable and very consistent type of 
construction must still be regarded as an open question. The general opinion 
since Carruthers’ paper t has been that they were to be sought for in the Algae, 
although there has always been difficulty in recognising a clear relationship to any 
algal group. There are difficulties in the way of a close comparison with Lamin- 
ariacese, although in some respects the Bhynie specimens afford additional points 
* This layer is described as “ very thin, hardly exceeding 3 mm.” for N. Logani (Penhallow, Trans. Canad. Roy. 
Soc., vol. vi, 1888, p. 38), and as l - 5 mm. in iV. Ortoni (Penhallow, Ann. Bot., vol. x, 1896, p. 42). 
f Monthly Microscopical Journal , vol, viii, 1872. 
