# Atlas of Micromorphological Degradation of Archaeological Birch Bark
## 3 Results  
The micromorphology of cell structure and degradation was investigated on transverse and radial sections. To facilitate the comparison among the results, mostly radial sections are shown in this paper. We first present a careful description of the micromorphology of the reference material and the contemporary bark decayed in nature, followed by an analysis of the 13 archaeological samples. The morphological features were systematically described, and 13 degradation characteristic patterns were identified and named with abbreviations to facilitate their localisation on the LM and TEM images (Table 2). For each feature, example LM and TEM images are presented. Macroscopic images of the samples are shown in the previous section. The occurrence of degradation features in the samples is summarized in a table. The following features may be associated with fungi or bacteria, or overall in the sample. To distinguish among these cases, the suffix fu (fungi), ba (bacteria) or ov (overall) is added to the abbreviation:  
* Fra: Fracture of radial cell walls;
* Un: Unfolding of compressed thin-walled cell; if it is in conjunction with stretching of the thick-walled cells, it is marked as Un-st;
* No-bi: Absence of birefringence of secondary wall of thick-walled cell;
* In-st: Intense toluidine blue staining;
* Swe: Swelling and/or disaggregation of the secondary cell walls;
* Ir: Increased irregularity of cell shape and size leading to irregular cell arrangement;
* Det: Detachment, either of cells from each other (Det-cl) or secondary cell walls from the compound middle lamella (Det-wl) or the tertiary wall;
* Rem: Removal of phenolic compounds in the lumen of thick-walled cells or the compound middle lamella or in the secondary cell walls;
* Re-th: Reduced cell wall thickness;
* Hy: Hyphea in thin-walled cell lumen;
* Vo: Circular/oval voids in the corners of secondary thick-walled cell walls with a diameter of about 0.6 um, or smaller voids in the secondary cell walls with diameter of about 1.2 um aligned along or in the compound middle lamella; the former are \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & **Fra** & **Un** & **No-bi** & **In-st** & **Swe** & **Ir** & **Det** & **Rem** & **Re-th** & **Hy** & **Vo** & **Me** & **Acc** \\ \hline Ref & x & x & & & & & & & x-fu & x-fu & x-fu & x & x-fu & x-fu \\
0 & x & x & x & x-fu & x-fu & x & wl & x-fu & x-fu & x-fu & & & x-fu \\
1 & & x & x & x-fu & x-fu & & & x-fu & x-fu & x-fu & & & x-fu \\
2 & x & x & x & x-ov & x-fu & & & x-fu & & x-fu & & & \\
3 & x & x & x & x & & x-ov & x & x-ov & & & x & & \\  & & & & & & x-ov- & & & & & (rarely) & & \\
4 & x & x, x-st & & & & x-ov, & & & & & & & \\  & & & & & x-fu & x & & & & & & & \\  & & & & & & x-fu-cl & & & & & & & \\  & & & & & & x-ov- & & & & & & & \\
5 & & & x & & & & & & wl, x-ov & & & & & \\  & & & & & & & x-fu-cl & & & & & & \\
6 & x & x & x & x-fu & x-fu & & & x-fu & & x-fu & & x & x-fu & x-fu \\  & & & & & & & & & & & & & \\  & & & & & & & & x-fu & & & & & \\
7 & x & x & x & x & x-fu & x-fu & & & x-fu- & & & x & x & x \\  & & & & & & & wl & & & & & & \\
8 & x & x & x & x-ov & x-ov & x & x-ov & x & x-ov & & & & & \\
9 & x & x & & & & & & & & x-fu & & (rarely) & & \\
10 & x & x & & & x-ov & x-fu, & & & & x-ov, & & & x & x-fu & \\
11 & x & x & & & & x-fu & & & x-fu & & & x-fu & & \\  & & & & & & & x-fu?- & & & & & & \\
12 & x & x & x & x-ov & x-ov & & & wl, x-fu?- & x-fu? & x-fu & & x-ba & x-ba & \\  & & & & & & & & x-fu?- & & & & (rarely) & & \\  & & & & & & & & & & & & \\
13 & x & x & x & x-ov & x-fu & & x-fu & & x-fu & & & & \\  & & & & & & & & & & & & (rarely) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Occurrence of degradation features in samples. x indicates the feature was present in the analysed sample. Fractures, unfolding of thin-walled cells and hyphae are also present in the reference material, a piece of contemporary intact birch bark.