Radial striation of the S2 layer in mild compression wood tracheids of Pinus radiata

The fine structure of the tracheid walls in Pinus radiata mild compression wood was examined by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). On transverse-fractured surfaces the S-2 layer of tracheid walls exhibited distinct radial structures when observed with the FE-SEM. The TEM observations of ultrathin sections of samples from similar regions showed the S-2 layer with radial striations, corresponding in their direction to the radial structures seen with the FE-SEM. The observations are discussed in relation to the information on the structure and composition of compression wood cells.