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

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

found roots in which the trachea of one of the xylem fascicles appeared in a tangential row (Pl. II, Figs. 1, 2). Mainly in these latter cases, the pericambium was, in one plane of section, more multiseriate above the tangentially situated xylem fascicle than above the radially situated xylem fascicle opposite to it. In serial (manual) slides, an alternation of the cell rows occurs also in layers above of below one another: the pericambium changing from biseriate to triseriate or vice versa. The two phloem fascicles consist of sieve tubes and companion cells. During the initial stage of development, there is in the centre still a thinwalled region of tissue rich in plasm; this contains the still undifferentiated part of the medially touching procambial fascicle and the pith parenchyme (4—5seriate). In the centre, there is generally a single, large, undifferentiated procambial cell (18x10 surrounded by a ring of smaller cells of a parenchymatous character (9X11 u.) (Pl. II, Figs. 1, 2). Within the phloem fascicles, a declifferentiation occurs in the parenchymatous pith parenchyme, the cells dividing along one zone by tangential walls (Pl. II, Fig. 3). A part of the waved cambium forms in this section (JODIN, 1903). The differentiation of the procambium (metaxylem) terminates generally after the evolvement of this waved cambium part. Thereby a tracheal row comes into being in the cotyledonary plane, with protoxylem vessels at its two ends (Pl. II, Fig. 4). The cross section measurements of the trachea, from one end of the tracheal row to the other, are as follows: 5x8 u., 6x8 p., 6x10 [x, 11x14 u., 18x18 u,, 16x18 (x, 16x19 u,, 11x11 [X, 8X8 u., 5x6u., 5X5 p., 3X3 p.. A certain synchronism, with some temporal overlap, can be detected between the differentiation of the procambium and the formation of the waved cambium. The wall of the metaxylem vessels becomes bordered-pitted (Pl. Ill, Fig. 1). After the differentiation of the metaxylem, but in some cases also before it, the waved cambium forms also outside of the xylem fascicles, continuing in the inner level of the pericambial zone and soon closes into a continuous ring, consisting of 4—6-seriate cells dividing by tangential walls (Pl. II, Figs. 3, 4). The narrow and insignificant phloem (JODIN, 1903) extends, in 2—3 strands, as a discontinuous line, parallel with and on the two sides of the tracheal row (Pl. II, Fig. 4). The pericambium constricts to uniseriate also above the xylem fascicles, because its inner cellular rows became parts of the waved cambium closing into a ring (Pl. II, Fig. 4). By closing into a continuous ring, the waved cambium forms secondary tracheae so that those decurrent in the cot}dedonary level distend and become 2—3-seriate (Pl. Ill, Fig. 2). More and more secondary vessels appear in the transverse plane, until the xylem becomes cross-shaped. The waved cambium is really "undulating", following the shape of the cruciform xylem (Pl. Ill, Fig. 3). The number of the sieve tubes and the companion cells of the discontinuous phloem increases. The uniseriate pericambium divides by tangential walls. The endoderm is still Caspari-punctate, but the outermost cellular row of the cortex is already an exoderm. The new secondary vessels become larger and larger, of more rows and bigger masses than those of the primary row; they slowly exceed them also in size and close around them. Thus a compact xylem cylinder evolves, chiefly from the more or less radially arranged (13—15-seriate) tracheae (Pl. Ill, Fig. 4). Together with the xylem, also the waved cambium rounds out and widens, becoming 3—5-seriate. The number of phloem elements further increases (Pl. Ill, Fig. 4). The pericambium regains its ability to divide. The cells of the pericambial