Calcium Oxalate Crystals in the Bark of Quercus robur, Ulmus glabra, Populus tremula and Betula pendula

Abstract

Barks of different developmental stages of oak ( Quercus robur L.), elm ( Ulmus glabra Huds.), poplar ( Populus tremula L.) and birch ( Betula pendula Roth) were analysed with regard to the variability of presence, type, location, dimension, and quantity of calcium oxalate crystals. Solitary crystals were present in all bark samples. In oak and poplar they were located in thick-walled, chambered, lignified cells adjacent to fibre groups and in sclereids. In birch they were mostly present in sclereids and occasionally in axial phloem parenchyma cells. In elm, thin-walled, chambered axial phloem parenchyma cells contained solitary crystals. Druses were present in oak, poplar and birch, but not in elm. They were located in thin-walled, chambered axial phloem parenchyma cells in the vicinity of the vascular cambium, in axial phloem parenchyma cells of the secondary phloem and in cortical cells. Presence, type and location of bark crystals did not vary between bark samples of different age. Therefore, these bark crystal characteristics may form reliable features for a diagnostic description of the barks investigated. The dimensions and quantity of bark crystals varied considerably and may not serve as diagnostic features.