Abstract text: Mechanical performance of a plant body throughout its life is built on combination of two skeleton types: the dispersed hydrostatic skeleton based on turgor pressure and primary cell wall resistance and the accentuated skeleton based on the deposited in specialized tissues thickened cell walls. Usually, young tissues have hydrostatic skeleton, while later complex system of specialized cells with secondary and sometimes tertiary cell walls, is developed. We have employed complementary approaches to characterize the transition from hydrostatic to accentuated skeleton and further establishment of biomechanical system in flax - the model plant that hires all three cell wall types and develops sophisticated system of mechanical tissues. Stem splitting experiments were used to reveal present tensions and their origin, atomic force microscopy - to check cell wall nanoindentation moduli in various tissues, and an original device for the inverse three-point bending test - to trace the changes in mechanical properties of the whole stem portion within a wide range of elastic moduli. Combined with deep anatomy, immunocytochemistry, and transcriptomics, the obtained data permitted to characterize the major events and principles in the establishment of whole plant mechanical system and the involvement of various cell wall types. Supported by the RSF #24-14-00383.