Pseudo-cells in Rhynie chert
deutsche Version

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.
 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 a water-filled cavity whose former contour can only be guessed, 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 as a bright line. 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.

Fig.3 (below): Pseudo-cellular structures grown in 3 formerly water-filled cavities between silica gel. Width of the picture 4.3mm.
Figs.4,5,6: (below right): Details of Fig.3
pseudocells in 3 spotspseudocells
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. Possibly it originated from
the abundant whitish clots. 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 growing clots 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 chalcedony now), with only one small globular clot, apparently retarded in growth compared to the bigger clots on the right of Fig.5. Hence, one may assume that first came the dark, then the clots.
Dark deposits, layers, and crusts occasionally seen in the Rhynie chert are most probably due to microbial activity (See
Rhynie Chert News 87 .) If looked at superficially, pseudo-tissue produced by microbes could be confused with real tissue.

H.-J. Weiss     

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