Peculiar voids in the tissue of Rhynie chert plants

Conspicuous patterns of radially arranged voids on cross-sections of Rhynie chert plants, like those in Figs.1-5, had been explained as shrinkage cracks of the decaying tissue [1] before the suspicion arose that fungi present in the growing plant might somehow have affected growth.
void pattern
void patternvoid patternvoid patternvoid pattern









Figs.1-5:  Void patterns on Aglaophyton cross- sections with degraded or well-preserved tissue. All same scale.
Fig.5 square 6mm.

Extremely shrunken and kollapsed tissue is obviously present between the large voids seen in Figs.1,2,3,5 but this does not mean that the formation of patterns of this kind is merely an effect of degradation. An early stage of void formation (Fig.4) suggests that more complex processes must have been at work. The tissue beside the voids does not look decayed but deformed as a result of the expanding voids. Apparently there had been tissue throughout before, and it became squeezed by the expanding voids while alive. The well-preserved tissue near the tip of the voids is clearly seen in Rhynie Chert News 4.
Other related information comes from enigmatic "twin patterns" where the two prongs of a forking shoot show essentially the same pattern. Since it is highly improbable that they developed independently, they must have been inherited from the base of the fork. (See Rhynie Chert News 21, 54.) Some tendency or inclination towards void formation had probably become divided along with the forking axis and got into the branches before the voids really formed there.
It is remarkable but confusing that the arrangement of the voids may vary between chaotic as in Fig.5 and highly pre-determined as in Fig.4.
different holes in Aglaophyton As a disturbing fact, the idea of some fungus being involved in the formation of the above patterns is not immediately supported by fossil evidence. However, supposedly related phenomena as in Fig.6 may be interpreted in favour of this idea.

Fig.6: Aglaophyton cross-section with two types of damage in the live plant: one hole caused by some unknown herbivore, the other one probably by fungus activity. Picture 4mm square.

The symmetrical void in Fig.6 has something in common with the voids in Fig.4: While expanding, it squeezed the adjacent tissue. The analogy is spoiled, though, by the observation that the surrounding tissue in Fig.6 is affected by abnormal growth while the tissue looks normal in Fig.4. Since abnormal growth in plants is often due to fungus infection, it can be assumed that a fungus had been involved here, too. Disregarding the different aspect of the expanding cavities in Fig.6 and Fig.4, one may suspect that both are a result of fungus action.
Chytrid fungi, which had been present in the Devonian habitat at Rhynie, are known to be able to bloat plant cells enormously [2]. Hence, the idea suggests itself that all of the peculiar voids in Figs.1-6 represent hypertrophy due to fungus action. What remains enigmatic is the way in which the fungus governs the complex process. 

H.-J. Weiss    2017

[1]  www.abdn.ac.uk/rhynie
[2] T.N.Taylor, M. Krings, E.L. Taylor: Fossil Fungi, Elsevier 2015, p.64.








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