Sclerification in the bark tissues of common fir (Abies alba Mill.)

The sclerification process in bark tissues of common fir (<em>Abies alba</em> Mill.) has been described. The sclerification begins in 3 years old stems. Sclereids differentiate from cortical parenchyma cells and from secondary phloem parenchyma cells that do not contain phenolic deposits. The first single sclereids are formed at the interface of the cortex and nonfunctional phloem. Hereafter, a continuous layer of them is formed. Later, new sclereid layers are formed successively in nonfunctional secondary phloem and cortex. The consecutive layers are separated tangentially by phloem parenchyma cells, that accumulate large amounts of phenolic substances, and by compressed phloem cells. Laterally they are separated by phloem rays that except of some dislocations are continuous. Structural net of the cortical phloem ray cells and phloem parenchyma delineates the areas where the formations of sclereid layers occurs in nonfunctional secondary phloem. Older cortex contains more sclereid layers and the time period of their formation extends continuously.