Ventarura performing as a flower
deutsche Version

Ventarura cross-section The Rhynie chert has not only provided several species of plants and creatures not seen elsewhere but, along with them, also peculiar structures conjuring up funny faces, leafy vegetables, or strange flowers. One of the latter is shown here. Its overall aspect and its details are so strange that it could well represent „The Dark Flower“, a symbol of fascination and longing in the novel of that title by 
J. Galsworthy.
This image, as one may guess, has got much more to offer than the appearance as a flower. It shows a cross-section from a quite uncommonly preserved lower or subterranean part of Ventarura, the last-discovered land plant in the Lower Devonian Rhynie chert. It would not have been recognized as such if there were not lots of other Ventarura sections around. In fact, there is no other plant species seen on the 6 cut faces of the 4 parts into which this sample has been divided. Hence, one can safely assume that the section seen here is really Ventarura although its state of preservation is so peculiar that none of the other about 500 sections seen on the cut faces of this sample compares to this image. Nevertheless it may be worth trying to partially explain how the peculiar aspect is related to the structure of the plant.
To begin with, the preservation in this case is such that several concentric zones can be distinguished. The xylem in the very centre is decayed but a few of its small cells are still there, arranged in a small dark ring with gaps. The eye is attracted to the tiny bright dots which greatly contribute to the illusion. They are mineral precipitates formed around the xylem strand for reasons unknown. 
Next comes a broad ring which is usually regarded as phloem. It consists of cells with thin walls forming a clearly seen network. The dark dot or spot in the middle of every cell seems to be the remains of the more or less shrunken plasma.
The outermost cells of this ring are much larger and probably belong to the adjacent main part of the tissue called cortex. Further out in the cortex, the aspect is quite different. The former cellular structure can only be guessed from the pale grey spots with randomly distributed dots like dust grains possibly related to some fungus. Judging from experience, the ubiquitous fungi thriving in the Lower Devonian habitat, as there are parasitic, symbiotic, and saprophytic ones, are able to greatly modify the aspect of the living and dead plants before they become solid chert. Hence the effect of fungus activity has to be considered in this case, too. Some fungus known to invade a  part of the cortex of other plants in the Rhynie
chert, appearing as a ring-shaped zone on cross-sections, could be involved here, too. Still farther out, the cortex tissue looks more normal again, with cell walls seen.
Note that this section does not show the ring of well-preserved cortex tissue which is characteristic for the upper parts of this plant. Hence it can be assumed that this image shows a section of a rhizome or of a lower part of a shoot. Perhaps that ring is even more enigmatic than the combination of effects contributing to this concentric pattern.

H.-J. Weiss     2016
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