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.

Figs. 13, 14). In the older shoot apices (several months old), the xylem ring is not only contiguous, but also secondarily considerably incrassate (Plate II., Fig. 15, Plate III., Fig. 17), in cross-section resembling a triangle lying on its hypotenuse (Plate II., Fig. 16). The cross-section of certain young shoot apices is also triangular, especially if two shoot apices originate from one plane of section in the young shoot. The pressure of the roots presumably also interacts in forming the shape of the xylem. We have observed the origin of also 3 roots from the cross-section of older, secondarily already strongly lignified shoot apices. We propose to discuss here some observations made on the development dj'tiamism of stem-borne roots of Lithospermum purpureo-coeruleum L. Owing to the extremely variable circumstances of this development, already discussed in part in the foregoings, we cannot undertake on the present occasion to expose and discuss the complete dynamism of root development from the shoot, even within one plant species. Based on observations, we should like to draw certain inferences which are, in our opinion, important moments in root development. Anatomical observations In our research material we have observed two, in certain relations apparently different, types of root development. One of them was found in 3-40 mm long, young roots, often composed of primary tissues only (Fig. 1; Plate I., Figs. 3, 4; Plate III., Fig. 18 ; Plate IV., Fig. 27). The other one was observed in longer (several cm long) older roots (Fig. 2; Plate I., Fig. 7; Plate IL, Fig. 12, Plate IV., Fig. 29; Plate VIL, Fig. 62). In all probability, the two types of development are temporally subsequent during the spatial elongation of the root (Fig. 4). In the subapical levels of roots, still in the early phase of development and merely some mm long, there are only phloem bundles (mostly 6) and the cross-section of the entire root is oval. It is presumably owing to the resistance of the shoot tissues that the emitted root becames flattened where it is exposed to greater pressure. The primary bundles also take up this oval form, as well as the central pith enclosed by them (Plate III., Figs. 18-24, Plate IV., Figs. 26, 27, Plate VIT, Fig. 54), and thus the oval form persists also in the older, secondarily already strongly thickened roots (Fig. 1. k, 1; Fig. 2. m; Plate VI., Figs. 45, 46). In the upper levels of the young roots, two xylem bundles are differentiated opposite each other, along the longer axis of the oval cross-section (Fig. 1. b). Still further up, the subsequent primary xylem bundles enter, in our observations regularly yet not symmetrically but apparently disarranged, among the existing pholem bundles. The simple bundles enclose a pith parenchyme, the endoderm is Caspary-punctate (-striate), and the root is enveloped in rhizoderm (Fig. 1. b-h; Plate III. Figs. 18-23). In our experience, the number of bundles is different near the shoot level in the various roots. Together with a greater number (8-10 rays) of the transporting bundles, they are also partly tangentially situated (Plate III., Fig. 24), so that the primary xylem bundles form an apparently contiguous ring (Fig. 1. g; Plate IV. Fig. 25). In this spatial section, the metaxylem element are often arranged not on the pith side of the bundles but in their centre (Fig. 5; Plate IV., Fig. 28). This phenomenon appears in that part of the root which is in the cortical section of the shoot axis ; presumably the effect of the shoot influences the direction of differentiation in this latter case (see also below).