Bark anatomy of Pteroceltis tatarinowii, Cannabaceae

Pteroceltis tatarinowii, , a tertiary relic plant, has a long and fascinating history in China due to its irreplaceable role in traditional papermaking. In this study, the anatomical differences between young and old bark were analysed by light microscopy (LM), fluorescence microscopy (FM), and polarized light microscopy (PLM). Both the young and old bark contain periderm, cortex, and phloem. In the non-conducting phloem, the curved radial phloem rays were perpendicular to bands of sieve-tube elements and axial parenchyma cells, forming a net-like pattern. Primary phloem fibres only occurred in young bark, and both primary and secondary phloem fibres contained a gelatinous layer (G-layer). Transmission electron microscopy (TEM) showed that the thickness of the G-layer in the primary phloem fibres was about 1.5-4 times higher than that of the secondary phloem fibres. The thick G-layer might be an important potential reason for the absorption of ink by paper made from P. tatarinowii phloem fibres, due to the good water absorption of the gelatinous layer.