Nematophyte twice protected
deutsche Version
Since the most disputed nematophyte Prototaxites has been sorted among the fungi
[1-3], these "enigmatic organisms" [4] may have lost part of their attraction as something mysterious among the living beings. Nevertheless it seems appropriate to have a close look at the rare species found in the Rhynie chert, some of which have probably never been seen before.
The unique nematophyte specimen shown in Rhynie Chert News 98 is considered here anew. As there and in Figs.1,2 here, the nematophyte, as a lump of gel with tubes inside, is not seen as a whole but as a fragment with distinct details which allow conclusions to be drawn.
nematophyte fragment in chert with protective crustnematophyte in Rhynie chert

Figs.1,2: Nematophyte:  
a former brittle fragment
as a component
in Rhynie chert:
upper left part (left) and lower part,
same scale,
widths 5.5mm and 11mm.



Tubes surrounding themselves with organic gel to live in is obviously a favourable way of life. In water, the gel keeps the tubes together, and it keeps them moist when transiently exposed to air.
During drought, some gel near the surface dries, some tubes collapse, forming a hard layer protecting the gel and tubes below, as seen in Rhynie Chert News 98, there
Fig.3, and in this Fig.1, where it appears as a dark crust above. A wide gap between two fragments of the thick brown crust in Fig.2 below indicates that the crust had been hard and brittle while everything else was still soft.
Apparently the local damage of the crust served as a starting point of a destructive process spreading through the nematophyte. Possibly some microbe had entered, consuming the organic gel between the tubes and the tube walls as well.
nematophyte in chert, partially damaged
Evidently, the decay spread as a front of certain depth, seen here as a light-coloured zone (Figs.3,4). The bluish-white organic gel turned into a dark fluid in this process. What is seen in the affected area does not look like tubes without gel but rather like some tube fill fragments. Possibly the interior of all tubes had become slightly silicified while the gel was not yet, then the gel and the tube walls were consumed by the decay process, and the tube fills settled down, where they are seen as whitish "worms" in dark "brine".

It is readily seen in Fig.1 that the nematophyte, which originally had been gel with tubes, must have hardened into a mechanically homogeneous solid material, then broken in a brittle way, judging from the smooth fracture faces. The edgy fragment must somehow have gotten into the then fluid swamp matter with remains of land plants, where all together turned into chert.
nematophyte in Rhynie chert, decay
Fig.3 (left): Locally rotting nematophyte, with rot spreading from the broken protective crust below into the lump of gel with tubes; detail of Fig.2, width 5mm.

Fig.4 (right): Locally rotting nematophyte; detail of Fig.3,
width 2mm.

mineral precipitates in big nematophyte tubes
Fig.5 (left): Broken fills of nematophyte tubes with mineral precipitates; detail of Fig.4, width 0.3mm.

The yellow (and red) mineral grains in some of the tube fills (Fig.5), which had not settled into a deposit at the bottom, indicate that the tube content was not fluid when they grew. Settled mineral grains in nematophyte tubes have been reported in Rhynie Chert News 154.
That sample has something else in common with this one, which is the uncommonly large tubes, mostly about 50Ám or larger. The diameter of the tubes with yellow fill in Fig.4, for example, is about 60Ám. Other tubes in this sample reach 70Ám.

Finally it can be stated that this unnamed nematophyte with large tubes, and probably others, too, had been able to successfully protect themselves with a hard crust against exsiccation and microbial attack as well.

Sample Rh13/7 (0.25kg), Part 2, described in Rhynie Chert News 13.

 
H.-J. Weiss    2020  

[1]  T.N. Taylor, M. Krings, E.L. Taylor: Fossil Fungi. Elsevier 2015.
[2]   H. Steur:  Prototaxites. Google: steurh.home.xs4all.nl/engprot/
[3]  R. Honegger, D. Edwards, L. Axe, Ch. Strullu-Derrien: Fertile Prototaxites taiti: a basal ascomycete with inoperculate, polysporous asci lacking croziers.
      Phil.Trans. Roy. Soc. B 373 (2017): 20170146.

[4]  T.N. Taylor, E.L.Taylor, M. Krings: Paleobotany, Elsevier 2009.
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