In situ imaging nanoindentation was used to characterize the differences in longitudinal Modulus of Elasticity(MOE) and hardness of different cell wall layers of softwood tracheids.It was found that the deformation of cell wall was mainly plastic when tips were indented in longitudinal direction.The distribution of longitudinal MOE and hardness along cell wall thickness was uneven with much lower values at the interface between S_3 layer and cell cavity as well as S_1 layer and compound middle lamella(CML) ...