Enigmatic voids in the tissue of early
land plants
Conspicuous
patterns of radially arranged voids on plant cross-sections had been explained as shrinkage cracks
of the decaying tissue [1] before own samples (Figs.1-5) gave rise to the
suspicion that some fungus
present in the growing plant might somehow have affected growth. (See
Rhynie
Chert News
54.)
Figs.1-5: Void patterns on Aglaophyton
cross-sections with degraded or well-preserved tissue. All
same scale.
Fig.5: 6mm square.
Extremely
shrunken and collapsed tissue is obviously present between the large
voids seen in Figs.1,2,3,5 but this does not mean that the patterns of this kind are merely a result 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. Well-preserved
tissue near the edges of the voids is clearly seen in Rhynie
Chert News
4.
It
is remarkable but confusing that the void pattern may vary
between chaotic as in Fig.5 and ordered as in Fig.4.
Other
related information comes from enigmatic "twin patterns" where the two
prongs of a forking shoot show essentially the same pattern of voids. (See
Rhynie
Chert News 21, 54.) Apparently the patterns in the prongs have
been inherited from the base of the fork.
The idea of some fungus
being
involved in
the formation of the above patterns is not immediately supported by
fossil evidence. The ubiquitous fungus Glomites
rhyniensis, whose tiny arbuscular hyphae are
seen as dark clots inside cells in Figs.3,4, is most probably not
involved. Possibly the symmetrical hole in Fig.6 with affected tissue
is due to misguided growth caused by another fungus.
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.
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 activity.
Parasitic 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, 2018
[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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