Anatomy and chemical composition of Pinus pinaster bark

Abstract

The secondary phloem of Pinus pinaster Aiton bark has sieve cells and axial and radial parenchyma, but no fibres. Resin ducts are present in fusiform rays. Stiloid crystals, starch granules and tannins occur inside sieve and parenchyma cells. The rhytidome of P. pinaster bark has a variable number of periderms forming scale-type discontinuous layers over expanded parenchyma cells. Phellem comprises 4-6 layers of thick-walled and little suberized cells and phelloderm a layer of 2 or 3 thickened lignified cells and a layer of expanded cells. Ash content of P. pinaster bark is low and pH slightly acid. Total extractives amount to 11.4% and tannins correspond to 4.5% of oven-dry weight. Content of lignin and unhydrolysable phenolic acids is 43.7% and polysaccharides amount to 41.7% with the following monosaccharide composition: glucose 51.8%, mannose 13.4%, xylose 26.1%, galactose 4.1% and arabinose 4.6%. No statistical significant differences were found between the structure of the bark from trees at five sites.