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.

of its bundles during elongation, so that there remains a tetrarchal, triarchal, and diarchal structure (Fig. 4). All three structures are encountered in the subapical levels of the older root (Fig. 2. a-c; Plate IV, Fig. 29; Plate V., Fig. 35). These levels have probably not yet developed in the younger roots (Fig. 4). In contrast to the development of the seedling roots, wherein the procambium differentiated mostly in a diarchal structure in our research material (KOVÁTS, 1971), the tetrarchal structure without pith is the more frequent in stem-borne roots (Fig. 2. h, Plate IV. , Fig. 30 — Plate V., Fig. 35). Several phases of the differentiation of the tetrachal procambium bundle were observed, and their various possible aspects illustrated in Figure 3 (Plate IV., Fig. 32, Plate V., Figs. 33, 34). By the termination of bundle differentiation, the waved cambium closes into a ring (Fig. 2. h; Plate V., Fig. 35). By the strengthening of the secondary xylem, the compact xylem cylinder evolves, its original oval shape (assumably owing to the robust xylem bundle arranged in the longer axis) gradually rounds out (Fig. 2. i-k; Plate V., Figs. 36-40). At higher levels but still prior to the appearance of the annual rings, the level of the sclerotized pith appears. The polyarchal procambium bundles are generally discernible on the outer margin of the pith (Fig. 2. m ; Plate VI., Figs. 45, 46). Also in older roots the secondary evolvement of the xylem is generally followed by that of the endoderm and thus the desOrganization of the rhizoderm is left to the last, but a sequence in assuming the secondary stage, deviating from the general one, was also encountered (see below). With respect to the anatomy of root development in Lithospermum purpureocoeruleum L., we discussed separately some characteristics, and their changes, of the xylem, endoderm, and rhizoderm. The primarily differentiated tissue of the dermal layer of the root is the rhizoderm, at whose desorganization alterations in the inferior cell rows in the exoderm, with certain changes in function. In short, one might designate a primary and a secondary character of the dermal layer. The endoderm of Lithospermum purpureocoeruleum L. is initially a typically Caspary-punctate (-striate) endoderm (to be called primary endoderm), becoming later, by the incrassation of the cell walls and eventually by anticlinal (septum) walls, a secondary endoderm (Plate V., Fig. 40, Plate VI., Figs. 41-44). The pericambium is here 2-5-seriate, being often uniseriate only above the phloem bundles (Plate IV., Figs. 29-31). It is partly this which later differentiates the equally many-layered cambium producing the secondary xylem (Plate V., Figs. 35, 36). The spiral tracheae of the metaxylem show simple perforations, but porous or sieve-like perforations are also frequent (Plate V. , Fig. 39). The metaxylem parts of the primary xylem bundles meet usually along the axial lines (Fig. 5, 1-3; Plate IV, Fig. 32, Plate V., Figs. 33-35). In the section adjacent to the shoot of roots originating from shoots there appears, however, a central pith (Fig. 5. 2-3) gradually widening in the direction of the shoot (Fig. 5. striated part 4-10; Plate III., Fig. 17, Plate VI., Figs. 45, 46). Along this section (Fig. 5. 3-10), the xylem is fascicular, as is characteristic to roots, but in contrast with the lower levels (Fig. 5.1) the direction of the primary differentiation gradually turns round, partly still before the spatial rearrangement of the bundles. In the lower half of this section (Fig. 5. 2-3) differentiation occurs inwardly, in the middle section (Fig. 5. 4-8) from both directions (Plate IV., Fig. 28), and in the upper part (Fig. 5. 9-10) outwardly. Accordingly, the metaxylem is still interior in the lower part of the section, transposing cxteriorad gradually in the upper levels (Fig. 5, right side sketchy series of figures 1—10).