Nematophyte big tubes with precipitate 
deutsche Version

Nematophytes with tubes wider than those of Prototaxites
are worth being noticed even without the rare phenomenon of mineral precipitates seen in some of the tubes as in Figs.1,2. The tube widths of Prototaxites are said to be below 50Ám but are usually pictured as about 25Ám [1,2] while those of this specimen reach 65Ám. The yellow and red precipitates most probably consist of iron oxides. Since the tiny grains are seen here settled at the bottom of the tube sections, it can be concluded that they had formed while the interior of the tubes was fluid. The transient existence of a fluid fill of the tubes is unexpected since they had been filled with protoplasma while alive, and with silica gel while becoming silicified.
Apparently, the decaying cell content became watery and its silicification was delayed inside because the still present cuticle on the tubes hindered the diffusive inflow of silica.
deposits in big nematophyte tubes
Fig.1: Cross-section of unknown nematophyte in Rhynie chert, with well aligned tubes, width up to 65Ám, with mineral precipitates at the bottom of a few tube sections. Width of the image 1.4mm.

deposits in big nematophyte tubes
Fig.2: Detail of Fig.1 below left.
Width of the image 0.3mm.

There is no indication why the precipitates did not form in every tube or outside. Perhaps it is another manifestation of the fact well known from agates that tiny differences of the chemical composition of the watery solutions inside cavities can result in largely differing aspects after silicification.

Judging from its aspect, this nematophyte lived as an assembly of aligned tubes within a lump of organic gel, most probably produced by the tubes themselves. From the spacing of the tubes one may conclude that the gel had not decayed before silicification. The presence of some soft gel before and during silicification is also suggested by the gap in Fig.1.

Unrelated to the tiny mineral grains incidentally formed and settled in some of these nematophyte tubes is the unsettled dispute concerning the relation between the big fossil Prototaxites and the usually small nematophyte fragments in Rhynie chert. Since one of the latter, Nematophyton taiti [3], has been thoroughly inspected anew and renamed Prototaxites taiti [4], other small nematophyte fragments found in the Rhynie chert (see Rhynie Chert News 46, 86, 92, 9899, 153), like the one above, should be considered potential relatives of Prototaxites and inspected accordingly. This might help to find out where the various nematophytes belong.
 Sample: Rh2/81.1, 0.63kg, obtained from Shanks in 2003.

H.-J. Weiss    2020  

[1]  T.N. Taylor, M. Krings, E.L. Taylor: Fossil Fungi. Elsevier 2015.
[2]  H. Steur:  Prototaxites. Google:
[3]  R. Kidston, W.H. Lang : On Old Red Sandstone plants showing structure ..., 
      Part V, Trans. Roy. Soc. Edinburgh 52(1921), 855-902.
[4]  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.
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