Surprising aspects of Devonian fungus hyphae
deutsche Version
cave with hyphaeTiny air bubbles emerged slowly from the murky depth of an oil-filled cavity in Rhynie chert and arranged themselves such that the reader may feel an intense questioning look from some alien with keen eyes: Fig.1. They detract the attention from the quartz-coated fungus hyphae in the foreground but, serving as reduction lenses, reveal more coated hyphae behind.

Fig.1: Quartz-coated straight fungus hyphae crossing a cavity in Rhynie chert. Image width 5mm.

Straight hyphae crossing small cavities are not rare. They are mostly not seen but coated with quartz crystals, thus appearing as straight rods.
As an extremely rare coincidence, a cut plane had unwittingly been chosen such that it cuts through a cave with coated hyphae where it follows right along the coating of a hypha, thereby keeping at such a small distance from the hypha that the latter is dimly seen through the quartz all along: Fig.2.

straight coated hypha
Fig.2: Quartz-coated straight fungus hyphae crossing a cavity in Rhynie chert. Note the very thin horizontal hypha seen through the quartz.
Image width 4.5mm.

The hyphae growing in the water-filled caves were virtually "weightless", hence weight did not interfere with growth. However, this is not a satisfactory explanation of the observed straightness. Coating with chalcedony and quartz made the hyphae heavy but also stiff so that they could remain straight if stiffness was high enough. Otherwise the hypha could sag like a slack rope, as seen in Rhynie Chert News 63As another possibility, silica gel could have stabilised the hypha being coated and dissolved later. (There are examples of cavities once filled with silica gel but empty now.)
It is well known that there are numerous fungus species in the Rhynie chert [1]. A tendency to straight hyphae is more or less distinct among them. No attempt is made here to assign the straight hyphae to some species.
The hyphae of some fungi branch and interconnect profusely without distinct straight parts in between. Also without straight parts are the wavy or spiralling hyphae of the recently (2017) discovered Devonian mycoparasite resembling the recent Trichoderma.  
The quartz coatings in Figs.1,2 indicate slow silicification with low supersaturation of silica. With higher supersaturation, the whole water-filled space may turn into silica gel and later into chalcedony, as still seen in Fig.3.

straight hyphaFig.3: Straight fungus hyphae in chalcedony, connecting rotten plant debris in the former swamp water turned into Rhynie chert.
Image width 2.8mm, hypha thickness about 12Ám.

This magnificient structure might remind the attentive reader of a "bridge over troubled water".
Apparently the "bridge" is made of two parallel hyphae touching mutually up to the "pillar" on the right. Like with Fig.2, the reason for the perfectly straight growth remains obscure. Fig.3 is even more enigmatic for the slight but distinct change of direction at the "pillar".

The illusion of a seashore slope with lush vegetation is brought about here by a thicket of microbes
 which are not rare on former silica gel surfaces where they had apparently formed a slimy layer before all turned into Rhynie chert.

Samples:  Rh14/17.5 and Rh14/18.4, obtained from Barron in 2007: Figs.1,2;    Rh9/61.1 (0.13kg), found in 2004: Fig.3;

H.-J. Weiss     2021

T.N. Taylor, M. Krings, E.L. Taylor: Fossil Fungi. Elsevier 2015.
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