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

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

quotient one. Ascending in the epicotyl, the area of the whole central cylinder concomitantly decreases (see later: Fig. 5): the xylem ring disunites and its area decreases together with the pith. The pith area enlarges and does not diminish to the same extent as the xylem, and thus the value of the quotient falls below zero (Fig. 4). 3. The epicotyl. In the examined seedlings, the vascular bands have already differentiated in the epicotyl above the insertions of the cotyledons, at about the tenth day of growth. Thus the two collateral open fascicles, passing over from the hypocotyl could be detected (Pl. IV, Fig. 4). In the older seedlings (aged about a month), the xylem ring, the cambial and discontinuous phloem rings, incomplete owing to their branching off into the cotyledons, are now completed again in the epicotyl (Fig. 3e; Pl. V, Fig. 3). There is a central parenchymatous pith parenchyme consisting of large, isodiametric cells (42x49 u.). The xylem ring is 4—6-seriate, the cambium 4—5-seriate. The phloem is only 1—2-seriate, and still not completely whole but discontinuous. An 1—2-seriate pericyclus lies between the phloem and the starch sheath. The primary cortex is 5—6-seriate. The biggest cells are in the median line (from outward to inwards: 23X25 \i, 47x56 p., 23x37 [x), a characteristic retained from the radicula. The external border of the cortex consists of epidermal cells (20x20 it), with large hairs containing cystoliths (Pl. V, Figs. 3, 4). In the transverse plane, therefore diagonally opposite to the cotyledons, two collateral open fascicles pass into the first leaves (Fig. 3e; Pl. VI. Figs. 1, 2). The other leaves show a diffuse, 2/5 phyllotaxis. Adjacent to the shoot apex, the xylem ring breaks up into several parts, leaving solitary tracheae or rows composed of 2—3 tracheae. At this stage, the cambium is a still continuous, 5—6-seriate ring (Fig. 3e; Pl. VI, Figs. 3, 4). I have followed in cross sections the areal changes of the cortex and the stele in the several organs of 35 days old seedlings, at levels of various stages of development (Fig. 5). Naturally, owing to the secondary vessels appearing in ever greater numbers by the activity of the waved cambium, the areas of the stele and cortex also considerably increase in the root. The great dimensions of especially the primary cortex is the most conspicuous in the hypocotyl, being more than four times greater than that of the stele. The surface of this latter one is the greatest also here, in the hypocotyl. This thickening in the hypocotyl is ascribable to lignification. The surface of the stele decreases evenly from the hypocotyl to the epicotyl and further on towards the shoot apex. The decrease of the cortical area is uneven, diminishing considerably from the hypocotyl towards the epicotyl, but this decrease slows down in the epicotyl. The quotient of the two areas is the greatest in the primary root, then it decreases, with some fluctuations, towards the shoot apex. Summary In the course of histological investigations on seedlings of Lithospérmum purpureo-coeruleum L., I have followed the development of principally the vascular bands, and especially that of the xylem (that of the phloem is insignificant), in the radicula, the hypoctyl, and the epicotyl.