Delicate anatomical structures of fossil plants preserved in chert are often hardly seen unless the optical contrast is greatly enhanced by some peculiarity in the processes of decomposition and mineralisation. The quite uncommon aspect of the epidermis of Aglaophyton in Fig.1 may serve as a conspicuous example of such phenomena (see also the contribution A rare aspect of Aglaophyton). Apparently the inner edges of the epidermis cells, and only those lying just below the surface, are neatly lined with a dark substance such that an array of individual elongated polygons with nearly equal spacing is formed. The outer edges of the epidermis cells are seen as faint thin lines forming a polygon network right between the dark frames as indicated in Fig.2.

						Fig.1: Aglaophyton epidermis pattern
						Fig.2: drawing of epidermis pattern

In some places where the frames have been cut, a tiny bright spot of reflected light is seen in Fig.1. This means that the polished face is not plane there. Hence one can conclude that the dark matter is mechanically different from the surrounding chalcedony.
As an intriguing fact, the lining seems to keep a rather even distance from the cell wall. Note also the stoma with its opening. The black lining is less distinct in the cells surrounding the stoma.
No explanation is proposed here for these observations. Suggestions are welcome.

text & photographs: H.-J. WEISS/Rabenau