Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 63. (Budapest 1971)

Kováts, D.: Some histological observations on Lihospermum purpureo-coeruleum L. seedlings

diagonal plane and enter, together with the xylem fascicles, the cotyledons. Thus a collateral open fascicle each arrives in the cotyledons (Fig. 3a). In these seedlings and at such a stage of development, the epicotyl (if at all developed already) has still a meristematic character, without differentiated vascular bands. In the roots with a differentiated procambium, about three types of fascicular rearrangement types might be distinguished in my research material (Fig. 3b, c, d). In these roots, the waved cambium has already closed into a ring. In the first type (Fig. 3b), the tracheal row divides and widens (Pl. IV, Fig. 2). The two tracheal rows turn from the radial into tangential and again bifurcate. The discontinuous line of the phloem fascicles follow this arrangement of the xylem fascicles. The four collateral open fascicles, formed in this wa}^, settle in a diagonal plane. In approaching the insertional points of the cotyledons, the four fascicles also concomitantly align themselves in the cotyledonary plane, to continue in the cotyledons, two for each cotyledon (Pl. IV, Figs. 3, 4). At the same time, a phloem fascicle each enters in the transverse plane on both sides. A trachea each joins the phloem, first on the one and then on the other side (Pl. IV, Fig. 3). The two new collateral open fascicles, formed in this way, continue in the epicotyl (Pl. IV, Figs. 3, 4). In the other two types of fascicular rearrangements, the tracheal row, extending in the cotyledonary plane, passes unaltered into the hypocotyl (Fig. 3c, d). At a higher level, a tracheal ring evolves by the entrance of probably other tracheae. There are cells of a parenchymatous character within the xylem ring, their row medially seperated by the still extant tracheal row. In some roots it is the xylem ring which first divides (along the transverse plane) and then the tracheal row (Fig. 3d), but the inverse case also occurs. In these latter cases the tracheal ring disunites into four parts, to tangentialand radial rows of vessels both in the cotyledonary and in the transverse planes (Fig. 3c). Subsequently, the above mentioned four, then six, collateral open fascicles evolve in the corresponding sequence. Passing into the hypocotyl from the older roots with a compact xylem cylinder, the xylem (Fig. 3e) divides medially, leaving an ovally shaped pith centrally, at the cotyledonary level. The appearance and extension of the pith are gradual, but in general it retains its oval, dumb-bell-shaped form in the hypocotyl. At the insertion of the cotyledons, a part of the (6—10-seriate) xylem ring branches off on both sides, together with the respective cambial and phloem parts (Pl. V, Fig. 1). This latter is still discontinuous, though the number of phloem elements have increased as compared to the younger stage (Pl. V, Fig. 2). Thus a collateral open fascicle each arrives in the cotyledons, where they immediately separate. I found meristematic groups of cells at the level of the cotyledons (in their axils) in several seedlings. On some specimens of seedlings older than one month, also an axillary young shoot appeared, bearing two leaves. Also in the axils of young leaves such axillary meristems and shoots could be found (Pl. VI, Fig. 2). On the vegetative, recumbent shoots of the old, developed plants, I have frequently seen axillary branches below the leaves, even more than one on a single vegetative shoot. These will take root in the autumn, similarly to the main axis. The hypocotyl lignifies already at a young stage as compared to the other organs (Fig. 4). It is from this part of the shoot that the rhizome characteristic of Lithospérmum purpureo-coreuleum later evolves. From the hypocotyl of even one month old hypocotyl roots evolve endogeneously (Pl. I, Fig. 3). I have measured the areas of the xylem and the pith in the several organs,