Pseudo-cells in Rhynie chert

pseudocells in Nothia rhizomeOccasionally, cherts with or without silicified higher plants may show confusing structures resembling plant tissue while being no such. In Fig.1, the "cells" seen in the odd-shaped areas of decayed and vanished tissue in a Nothia rhizome do not seem to differ
much from the cells of the latter, at least with respect to shape and size distribution. The conspicuous horizontal boundary above the structure indicates the former presence of a watery suspension.
pseudocells
 Fig.1 (right): Nothia rhizome cross-section with central strand, surrounding tissue decayed and replaced by coated fungus hyphae and pseudo-cellular structure grown in formerly water-filled places.

Fig.2 (left):
Formerly water-filled cavity with thick lining of silica gel, grains of irregular shape grown inside.

What seems to be mutually contradictory, a horizontal boundary above some structure in Fig.1 but below in Fig.2, may be surprising. In Fig.2, a pale brown watery suspension had settled at the bottom of the water-filled cavity, making a horizontal surface, and eventually solidified into gel. Then the remaining cavity got a thin white lining all around, clearly seen only at the bottom where it appears in cross-section. Then came a thick pale white lining, appearing unevenly thick owing to varying orientation with respect to the cut plane. The granular structure within does not look as much like tissue as the structure in Fig.1 does. It seems that the horizontal boundary of the latter, as well as a similar boundary in Fig.3, had been brought about by some watery suspension settling in the lower part of the cavity but there is no obvious reason why the structuring had been restricted to that area.

Fig.3 (below): Pseudo-cellular structures grown in 3 formerly water-filled cavities between silica gel. Width of the picture 4.3mm.
Figs.4,5: (below right): Details of Fig.3
pseudocells in 3 spotspseudocells
pseudocells
pseudocells
Fig.6 (right): Detail of Fig.3, possibly leading the way to a partial explanation of the phenomenon of pseudocells.

The pseudo-cellular structure is seen in Fig.6 above and below. Apparently it has originated from whitish clots abundantly seen in  the middle of the cavity. The growing globular clots would not fuse when touching but keep their individuality and mutually squeeze into a pattern resembling plant tissue. The illusion is favoured by the fact that the pseudo-cells are separated by dark boundaries which possibly consist of microbes living on the surface of the clots or pushed ahead by the expanding surface and getting trapped.

Microbes could even be the primary cause of the phenomenon. This is suggested by the observation that the pseudo-tissue is often much darker than its surroundings. On the left of Fig.5 there is a dark fill of a narrow former cavity between whitish silica gel (all chalzedony now), with only one small globular clot, apparently retarded in growth compared to the bigger clots on the right of Fig.5. Hence, one can assume that first came the dark, then the clots.
Dark deposits, layers, and crusts occasionally seen in Rhynie chert are most probably due to microbial activity (See
Rhynie Chert News 87 .)
It is not known how the microbes, which are not often present in water-filled cavities left during silicification, can trigger the formation of globular clots with sizes incidentally like those of plant cells, thus making pseudo-tissue. Judging from the available samples, they would not trigger the formation of clots of much deviating sizes.

H.-J. Weiss      2017
112

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