Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 64. (Budapest 1972)

Kováts, D. ; Stieber, J.: Some observations on the dynamism of structural development in the stem-borne root of Lithospermum purpureo-coeruleum L.

Fig. 5. Schematic cross-section pictures of xylem bundles of stem-borne roots, from subsequent levels, and their long-section projection. Direction of fascicular differentiation indicated by arrows. At lower levels metaxylem part of primary xylem bundles usually touching along axis (1-3). In higher sections, adjacent to shoot, central pith appears (hatched, 2-3) and gradually widens (4-10). Direction of differentiation gradually reverses, 1-3 occurring still interiorad, in middle (4-8) from two directions, and in the higher section, adjacent to shoot, already exteriorad (9-10). Accordingly, also metaxylem shifting gradually exteriorad. Both in the seedling and in the great majority of stem-borne roots, the temporal sequence in assuming the secondary character of the xylem, the endoderm, and the rhizoderm is general, occurring from in side to outward. But also deviating types exist, of which two are discussed here : mirror images, as it were, of each other. Type I is frequent mainly in seedling roots. In this type, by the formation of the cambium it is the secondary xylem which first occurs, followed by the desorganization of the rhizoderm and thereby the appearance of the exoderm, the sequence terminated by the endoderm transforming into septate, thick-walled cells (Fig. 6). Type II was observed mainly in stem-borne roots which have been collected in early spring (March). Especially in a sheltered position it was not only the rooting shoot apex and the roots which overwintered, but the entire vegetative shoot, under the protection of the leaf litter. The effect of other factors should also be considered in the evolvement of the anatomical structure. In these roots, the cell walls of the endoderm thicken first (Plate VII., Figs. 53-56), followed by the appearance of the exoderm, while the formation of the secondary xylem begins last (Fig. 7). The difference against type I is illustrated also by the formula of temporal changes expressed in figures (Fig. 7). The difference in structural changes presumably affects the water uptake and ion exchange abilities of the root in the various types. Therefore the approach of these phenomena seems advisable not only from the anatomical but also from the biochemical and physical aspects.