Another tangle of tubes in chert
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The nematophytes, from palaeobotany monographs also known as Enigmatic Organisms, are not often seen in the Rhynie chert. Judging from the few samples hitherto found, they come in tangles of tubes which can be more or less aligned, or even strictly aligned as with Pachytheca. There are several species, among them apparently unnamed ones. Some of them seem to consist of smooth-walled tubes only, as those presented in
 Rhynie Chert News 13, 30, 40, 46, 92, 98, 99Others consist of a combination of tubes with smooth walls and tubes with a pattern of spirals or annular rings on the walls [1].
Fig.1: Nematophyte tube fragment, diameter 26Ám, with
spirals or annular rings on the wall, spacing mostly 5-6Ám. (Part of the tube is hidden in the depth.) Width of the image 0.8mm.

The logic behind the different types of tubes and their possible mutual relation remains obscure. With
Nematoplexus [1], the tubes are thought to somehow originate within "branch knots" but the present sample does not provide evidence for this although a few branch knots surrounded by smooth-walled screw-like tubes are seen only 3cm away. The tubes with patterned walls are found as scattered fragments only, similar as in Fig.1, with one quite unexpected exception seen in Fig.2, where the large tubes seem to be embedded, together with a tangle of poorly visible tiny filaments, in a separate lump which had probably been organic gel before silicification.
As noticed by P. Strother [2], the fossil in Fig.2 strongly resembles Nematothallus pseudo-vasculosa known from compressions [3]. The size data are roughly compatible, including the dimly seen tiny filaments in Fig.2 which seem to correspond with "tubes between 1.5 and 3Ám in diameter" seen on the lectotype of that organism [3,4].
Similar as with the tube fragments scattered sparsely throughout the chert, the tubes in the gel lump do not show branching nor other remarkable features, perhaps except for one peculiarity poorly seen above left: A big tube suddenly reduces its diameter to less than half.
What looks like a series of orderly turns of a screw in Fig.1 is often interrupted by disorder due to merging or branching turns, as repeatedly seen in Fig.2.

tube patch
Uncommon assemblage of nematophyte tubes as a separate patch, probably of silicified organic gel, with tube diameters centered around an average of 20Ám,
        and a wide variety of spacings between turns. Width of the image 1.9mm, same scale as above.

Drawing conclusions from only one sample may not be justified here but asking questions may be appropriate:
Why do patterned tubes often grow not far from or even emerge from branch-knots among smooth-walled tubes like those of Nematoplexus ? Why are the conspicuous tubes in Fig.2 not seen emerging from branch-knots ? Why does this veritable 3D-version of Nematothallus pseudo-vasculosa, too,  prefer a place where Nematoplexus is near ?
Finally it may be mentioned that this sample of mere 0.28kg found in 2003 has offered several remarkable items: Nematoplexus with tubes larger and smaller than hitherto known, Castracollis eye (? 2015) and unidentified moults, an unknown archetypal charophyte (2016), and possibly the first 3D-version of Nematothallus pseudo-vasculosa (2017).
Annotation 2018: The tube wall patterns, more clearly seen in
 Rhynie Chert News 122, resemble the tracheid wall patterns of land plants. This has led to the following conclusion: "The study of the nematophytes will become more central to the issue of the rise of the earliest land plants because they clearly have developed a diverse and somewhat complex tubular anatomy, which in many ways appears to be analogous to vascular tissue [3]".

H.-J. Weiss    2017
    (modified: June 2017)  2018

[1]  A.G. Lyon: On the fragmentary remains of an organism referable to the nematophytales, from the Rhynie chert, Nematoplexus rhyniensis.
      Trans. Roy. Soc. Edinburgh 65(1961-62), 79-87, 2 plates.        (Scale error on Plate I Fig.1: not x19 but x1.5)
[2]  P.K. Strother: private communication (2017).
[3]  P.K. Strother: Clarification of the genus Nematothallus Lang: J. Paleont. 67(1993), 1090-1094.
[4]  W.H. Lang: On the plant-remains from the Downtonian ... . Phil. Trans. Roy. Soc. London B 227(1937), 245-291.

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