SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 885 
than of the walls of the tubes.* The cylindrical brown threads may appear as if 
cracked across, but there is no satisfactory evidence of the filament having been 
septate. At places a beaded appearance, possibly due to contraction of the contents, 
is found. Careful search reveals tubes in which the wall is preserved and which, 
therefore, appear wider than the brown threads. There has been much breaking- 
down and rearrangement of the substance during preservation, and the clear 
intervals or matrix between the tubes often exhibits pseudo-cellular structure ; this 
is most marked where the decay is most advanced and the tubular structure has 
disappeared. 
A feature of considerable interest in the preservation of some of the tubes is the 
appearance of a fine spiral marking. This runs round the inside of the thick wall 
of the tube. In favourable examples (fig. 118) the thickness of the wall can be 
traced, and the spiral marking seen in section to be due to a regular ridging of the 
innermost layer of the wall, f In other specimens only the spiral is evident. This 
mode of preservation, revealing a potential structure, is also found in the narrower 
tubes of zone b (fig. 117). 
Certain oval or spherical thin-walled vesicles are met with at places in the regions 
between the brown tubes— one of them is seen below the tube in fig. 118. They 
suggest comparison with some of the fungal types already described, and in some 
cases have been observed to be borne on slender branched hyphse. In the light 
of the common presence of such fungi in the portions of all the plants in this deposit, 
we are probably justified in regarding these vesicles as belonging to a saprophytic 
fungus, and not as a part of the structure of the organism under consideration. 
Their presence is noted, however, since in such an anomalous organism as Nema- 
tophyton they might prove to be of importance. 
The small areas of different texture dotted through the inner region are fre- 
quently ill preserved and difficult to analyse. In fig. 116 they appear as dark 
masses owing to their greater opacity, the only structural feature that is indicated 
being the entrance of some of the wide tubes into the dark mass. 
Careful examination of the best preserved examples shows that these wider 
tubes, which may have their rather thick wall preserved, resemble in cross-section 
the large tubes of the other specimen of Nematophyton. These wide tubes are 
accompanied by others of moderate fineness, and the bulk of the area seems to be 
made up of numerous still finer tubes closely entangled. The general resemblance 
in construction between these areas and the “medullary spots” in the other 
specimen is striking, and we have no doubt as to their being corresponding 
structures. 
The region (figs. 113, 114, b) with the tubes arranged parallel to one another, 
* A similar mode of preservation was met witli in N. Hiclcsii ( cf . Penhallow, loc. cit., 1889, p. 20). 
f A very similar spiral marking, due to contraction and ridging of the inner layer of the cell-wall, is often met 
with in the cells of Laminaria. It has there been interpreted as an artefact due to drying or dehydration (cf. 
Thoday, Mrs M. G., New Pliytologist, x (1911), p. 69). 
