Wilting nematophytes in Rhynie chert
deutsche Version
(largely revised version 2020)
Nematophytes, literally "filamentous plants", are still so poorly understood that they go under the heading Enigmatic Organisms in [1]. Therefore, any newly observed detail is potentially relevant and worth being reported.
There are not many details seen in the small nematophytes usually preserved as coaly compressions [2]. 3D-preservation in chert provides the possibility to see more. Several insights have already been obtained from the very few nematophyte specimens found in the Rhynie chert hitherto. Own contributions are listed here.
The filaments of the nematophytes appear mostly as structureless tubes, as in Fig.1. One may ask whether it is really tubes what is seen here or merely the tube-shaped cavities left after the organism had decayed and vanished, together with its tube, after silicification of the space between them. The aspect of the deformed tubes suggests that real tubes surrounded by organic gel became silicified here.
Here the colloquial term "wilting" is to refer to degradation and decay of the live filaments and the organic gel in between.
Nematophyte: tangle of limpid tubes
Fig.1: Nematophyte tubes in organic gel, non-described species.
A kinked tube (above left) allows conclusions to be drawn concerning mechanical properties. Image width 1.75mm.

Independent of whether or not there is wall substance left in Fig.1, one can derive information on the mechanical properties of the components before silicification. One tube (above left) got a kink when it was bent by contact with others. Hence, it must have consisted of a material with some flexibility and strength. If it had been more brittle, or soft and weak, it would have broken or torn. The gel must have been so weak that it did not preclude kinking.
nematophyte

Fig.2: Nematophyte, non-described species with uncommonly large tubes up to 70Ám across and well aligned in organic gel, smaller ones inside indicating shrinkage. Image width 1.4mm.

The smaller cross-sections seen inside some of the larger ones in Figs.2 pose a problem. They could possibly be degraded and shrunken tubes within the cavities in the silica gel preserving the size of the original tubes. (Such phenomena are known from fossil plants, see
Rhynie Chert News 31.) 
A different possibility has to be considered: The smaller section inside may not be the shrunken tube but the cell plasma with enclosing membrane shrunk away from the tube wall.
The question remains why the phenomenon is restricted to some of the tubes in some part of the specimen. For reasons unknown, silicification might have been not equally fast throughout the sample so that various stages in the succession of decay have become preserved.
Also in Fig.2, the organic gel keeping the tubes in a compact lump below left is seen to be degraded and fragmented above right. The decay of gel may release some of the tubes into the surrounding water where they float away, which explains why separate tubes are occasionally seen scattered in the chert.
Also worth mentioning in Fig.2 are sections of two big clots known from other nematophytes as "medullary spots", which are assumed to somehow produce the tubes.

Fig.3 (below): Nematophyte, same sample as Fig.1. Below right: tubes in organic gel silicified. Above left: gel disappeared before silicification after an enigmatic de-jellifying front had passed, leaving loose broken tube fills behind.
Image width
2.8mm. 
nematophyte
A different mode of decay is suggested by Fig.3: Apparently the organic gel keeping the nematophyte tube assemblage together and protecting it against exsiccation had been dissolved by an enigmatic decay process spreading in a front-like way, down right in Fig.3. Above left there are the broken fills of the tubes which had settled in the water. These fragments indicate that there had been a transient stage of fossilisation with silicified tube content and non-silicified organic gel between the tubes.
Also the final stage of fossilisation as seen in Fig.3 shows that there had been differential paths of silicification inside and outside the tubes, also among the tubes, as apparent from the different colouring.
Finally it can be stated that, before silicification, the organic gel between the nematophyte tubes may become fragmented (as in Fig.2) or completely removed (as in Fig.3). In either case, the tubes or fills get deranged. Apart from these details, the nematophytes shown here are remarkable for their comparatively huge tube diameters up to 70Ám.

Samples: Rh13/7, 0.25kg, found by S. Weiss  in 2005, Part1: Figs.1,3.
              Rh2/81, 0.63kg, obtained from Shanks in 2003, Part3: Fig.2.

H.-J. Weiss
     2011, 2016, 2020

[1]  T.N. Taylor, E.L. Taylor, M. Krings: Paleobotany, Elsevier 2009.
[2]  P. K. Strother: Clarification of the genus Nematothallus, J. Paleont. 67 (1993), 1090-94.

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