Fossil fungus-related spheres that come in pairs
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fungus spheres in pairs
Spheres related to fungi are a common sight in the Rhynie chert. Usually they are separate and randomly distributed but the small spheres of one species come in dense clusters. Quite uncommon is the phenomenon of big spheres in pairs. Considering that the cut would not show connected spheres unless their position and orientation with respect to the cut plane is within narrow limits, it may be concluded from Fig.1 that most of the spheres are arranged in pairs here but not all are seen so.
There is no obvious reason for this pair formation. The problem will not be resolved here but by looking at the details one may be guided along the way towards an explanation.

Fig.1: Cut plane of a small sample of Rhynie chert with fungus- related spheres up to 0.7mm, mostly arranged in pairs, connection not always in the cut plane. Image width 5.54mm.

A phenomenon not related to the fungus connection but nevertheless interesting is the formation of dark deposits at the bottom and /or at the top of the spherical cavities. Apparently there had been different suspensions (of mineral precipitates, dead microbes etc.) in water that were either heavier or lighter than water and settled accordingly.

Additional evidence for the conspicuous pair formation is provided by Figs.2-6. Level deposits of suspensions are seen in Figs.2-5.
The deposit in Fig.5 consists of a stack of layers, which indicates that the deposition took some time with periodically changing conditions.
The highly symmetrical aspect of the fused spheres in Fig.2 indicates that (1) the spheres are of nearly equal size, (2) incidentally the axis of rotational symmetry is well within the cut plane. For comparison, the axis is slightly inclined to the cut plane in Fig.3, where the upper sphere is slightly larger than its circular section on the cut face.
Rather well symmetrical cuts, except for the sphere size, are seen in Figs.4,6, each one with a remarkable detail: There is a small stub, possibly a broken-off or budding hypha, on the smaller sphere close to the symmetry axis.

Figs.2-6: Fused spheres of equal or moderately differing sizes.
     Same scale as above, width of the pictures 1 or 2 mm.
spheres pair of spheres2 pairs of spheresspheres and germination tube

Figs.7,8 (below): Spheres with outgrowths. Picture width 1mm. All pictures have been taken from the same chert sample, same scale.                                     
spheres spheres
The seemingly clear principle prevailing in this peculiar sample of Rhynie chert, which is fungus-related spheres fused into dumbbells, becomes less clear in several ways.
It is not clear whether the outgrowths in Figs.7,8 become as large and round like another sphere, as possibly indicated by two "would-be dumbbells" in Fig.1 (above left). Dark dots are distinctly seen on the surface of spheres excentrically cut, as in Figs. 5,7.
A small globule in Fig.5 (above left) seems to be germinating, thereby producing a 50Ám-tube with a bulging end of 85Ám. 

As a disturbing fact, charophyte tubes and whorls, probably Palaeonitella, are present in this sample, often quite near to these spheres, as in Fig.7, where a tube is partially filled with a dark former suspension. Since it is known that charophyte tubes can be induced to grow big globules under the influence of fungi [1], the suspicion arises that the spheres seen here might be bloated charophyte cells like those in [1] but about twice as big. (See Rhynie Chert News  119, 120. ) However, the 40Ám-tubes seen as stubs in Figs.4,6 and elsewhere are much smaller than the charophyte tubes of 90Ám - 300Ám in this sample but compatible with big fungus tubes of 35Ám in this sample so that an interpretation as expanded fungus hyphae or chlamydospores rather than charophyte cells seems appropriate.
Large spheres with diameters up to 0.75mm and more, some with adhering hypha, have been found in several samples but this sample has been the only one with dumbbell-like formations.
Further details are expected from other cut planes of this sample of 0.35kg obtained from
Barron in 2007, labelled Rh14/17. 

H.-J. Weiss    2017,  2018

[1] T.N.Taylor, M. Krings, E.L. Taylor: Fossil Fungi. Elsevier 2015, p.64.

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