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

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

wide. In general, the radially interconnected fibrils are thin-walled in the young wood, whereas the fibril walls are more robust in late wood. The tensile and bending stress of the tree, its hardness and resistance depend also on the length of the fibrils. The length of the ligneous fibrils and fibril-tracheids depends as well in the ash as in all other trees on the age of the given specimen, and also at which height the fibrils are situated in the trunk. According to KALLMANN'S (1941) investigations, the length of the fibrils increase from the pith towards the bark. I found its very opposite, however, in my research material. Fibril length shows a decrease, with some fluctuations, from the pith towards the bark: I observed this state of affairs in all five examined trees (Fig. 5). The high fibre length of the European Ash tree Fr. 15 is rather conspicuous; the specimen derives from Fertőrákos, a locality outside of its area in Hungary. Comparing the variability of fibre length with the evolvement of growth ring width, I found a direct proportion: the fibre length is greater in a wider growth ring and smaller in a narrower one. This is especially well demonstrable in Fraxinus ornus L. trees (Fr. 15 and 11/a; Figs. 6, 7). The direct proportion between fibre length and growth ring width prevails also in my Fraxinus excelsior L. research material, but in a less expressed state (Fr. 5 and 9 ; Figs. 8, 9). This ratio connot be detected, however, in the Fraxinus excelsior L. specimen marked Fr. 32 (Fig. 10) wherein fibre length decreases comparatively evenly, whereas the growth ring width displays rather strong fluctuations. Fibre length data derive from every fifth growth ring, hence their graph exhibits a less even decurrence than that of the growth ring widths based on all respective data. Accordingly, the above inference is of a conditional character and still requires many measurements to make it a definite statement; however, the general course of the graph appears to be well founded. According to SZÁLAI et VARGA (1955), it is a general trend in trees, and valid for all height levels, that the number of medullary rays, as related to the unit area, gradually decreases from the pith towards the cambium. These authors investigated the proportion of the several histological elements in the xylem of ash trees originating from diverse localities. Their measurements show that the number of the narrow medullary rays (1-2 cells wide) near the pith represents more than 90 per cent of the number of all other medullary rays. In growth rings adjacent to the bark, 2-3 cells wide medullary rays still predominate (70 per cent). In tangential longitudinal sections, there are 25-60 medullary rays per mm

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, and the rays are smaller near the pith than in the outer portions of the xylem. And it is not so much the age of the tree which influences, according to the above authors, the quantitative evolvement of the tissue elements but the ecological conditions (climate, substrate, stand density, etc.). With respect to my measurements, also the medullary ray percentage decreases from the pith towards the bark, yet not evenly but with fluctuations (Fig. 11). In tree Fr. 9, the medullary ray percentage is, on the other hand, the highest in a growth ring (20) nearer to the bark than in the pith. Similarly, in the Fraxinus ornus L. tree, marked Fr. 11/a, high medullary ray percentages appear in growth rings 25 and 30, far exceeding the values obtained for other years and hardly less than the maximum prevailing at the pith (72 years old tree; Fig. 11). Again according to SZÁLAI & VARGA'S investigations, a direct proportion was obtained between growth ring width and the number of medullary rays, hence the ratio of the number of medullary rays is greater in a wider growth ring. In my own 11 TT. Múzeum Évkönyve 1970