Abstract
Flax is one of the oldest cultivated plants and one of the most important fiber crops in the world. Thousands of years of selection have resulted in the unique biomechanics of this plant, the principles of which are not yet fully understood. Detailed anatomical analysis of flax stems at different heights and at different stages of plant development (herringbone, fast growth, flowering) allowed us to follow the dynamics of primary and secondary growth of these plants. The evaluation of the mechanical properties of the stems and their individual parts at the same stages made it possible to identify the tissues that take on the main mechanical load at different periods of the plant’s life. In the younger parts of the stems, this tissue is the fiber-enriched phloem, whose fibers rapidly acquire a considerable elastic modulus. Xylem, which takes longer to develop, provides the main mechanical load in more mature parts of the stems and at later stages of plant development. Fast growth of flax stems occurs against the background of delayed xylem development. The onset of cell wall thickening in phloem fibers (the position of the snap point) is not determined by the mass of the plant part above it. The results obtained highlight the contribution of different tissues to the functioning of the plant as a holistic biomechanical system.