Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 62. (Budapest 1970)

Kováts, D.: Quantitative xylotomic investigations on the xylem of our home ash trees

The codecurrences and counterdecurrenees of the graphs relating to the tension and pression woods concerning growth ring width (STIEBER, 1967) were plotted on the accessory graphs of Figs. 6-10. The number of parallel courses, though at diverse rates, is greater in all 5 trees; the greatest in tree Fr. 9|~=4.80| and Fr. 151—= 4.50 32 18 18 less in Fr. 5 and nearly equalized in Fr. 11/a Accordingly, the heterogeneity of the countermovements is the greatest and Fr. in the two latter cases (STIEBER, 1967). The most frequent changes in growth ring width appear to be those lasting for a short period, namely 1-2 years (Fig. 4). The frequency of growth ring width increases or decreases lasting for several years diminishes with the increase of the number of years. If there occurs a growth ring width increase, it is interrupted by decreases, and vice versa, decreases lasting for several years alternating with increases. It is owing to the years of stagnation (no changes in growth ring width) that the graphs of increase and decrease are not wholly symmetrical (Fig. 4). As regards the strength of the trees, the sclerenchymatous or libriform fibrils and fibre-tracheids (many relegate them to the fibrils) are of great significance. In light and soft woods, the cell walls are thin, their number small, and the lumens duration of change in years