Lignin staining in a basal-section of the flax stalks grown in a field. Arrows point at places where lignification of the fibre cell wall has just started to happen. These are three representatives of 20 specimens prepared for each line and the control plants (wt). Magnificent: x40. EP–epidermis, CP–cortical parenchyma, BF–bast fibre cells, PH–phloem, X–xylem.