Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 63. (Budapest 1971)
Kováts, D.: Some histological observations on Lihospermum purpureo-coeruleum L. seedlings
For the purposes of the present paper, I propose to submit on a graph only the growth of the organs of the seedlings (cotyledon, radicula, hypocotyl, epicotyl; Fig. 1). The measured seedlings were raised between September and December, at 15 C° room temperature and 50 — 60% humidity content. The only exceptions were the oldest seedlings (35 days old), which have been raised in the field in May—June. The longitudinal growth of the cotyledons fall back naturally only on two occasions: first at the appearance of the primary root and secondly at that of the hypocotyl. Then a greater longitudinal and latitudinal increase follows. By the appearance of the epicotyl, dimensions do not decrease as in the two preceding cases, but the intensive growth appears to slow down and become rather uniform (Fig. 1). To determine the rate of growth, still many, day by day, measurements are to be taken. In the present paper, I should like to give only a general information on the changes in the longitudinal growth of the seedlings. Manifestly, the longitudinal measurements of the main radix and the roots originating from the hypocotyl are the greatest, and their longitudinal growth also the most rapid. The radicle itself often stops its growth, or indeed becomes atrophied; 1 experienced this in already three weeks old seedlings of my research material —the lateral rootlets and then the hypocotylous roots exceed it. The longitudinal development of the hypocotyl is not uniform. After about three weeks, it does not increase further (indeed its length decreases in several cases), but becomes thicker, lignifies (see below, Figs 4, 5), and develops lateral roots. Histological observations 1. The radicula The outermost cellular row of the young radicle is a uniseriate rhizoderm, many cells of which develop long radicular hairs (Pl. II, Fig. 1). The primary cortex is about 8—10-seriate. The parenchymatous cells are thin-walled, isodiametric in cross section, and slightly elongate parallel with the longitudinal axis (Pl. II, Figs. 1, 2; Pl. III, Fig. 1). Inwards from the rhizoderm the dimensions of the cells increase, greatest in the median line of the primary cortex, then decreasing towards the endoderm (20X24 u.; 31x40 u.; 18x21 u.). In accordance with the cellular arrangement, the intercellulars are triangular, rarely quadrangular. The inner border of the cortex is a uniseriate Caspari-punctate endoderm (15x19 u.) (Pl. II, Figs. 1, 2). In the dicotyledons, a multiseriate pericambium —multiseriate above both the xylem and phloem fascicles —is rare. A multiseriate pericambium above either the phloem or the xylem fascicles is more frequent (KAUSMANN, 1963). This latter is the case in the radicle of the young Lithospérmum purpureo-coeruleum L's seedlings. In other words, the pericambium constituting the external border of the central cylinder is multiseriate above the xylem fascicles (2—5-seriate), whereas it is generally uniseriate above the phloem fascicles (Pl. II, Figs. 1, 2). The vascular bands are simple. The radicle is diarchic. The plane of the two xylem fascicles passes through the insertional points of the cotyledons, hence I propose to designate this plane as cotyledonary in the followings. I have also encountered a triarchic structure; its study needs further observation. The cross section of both the proto- and metaxylem vessels is 5—6-angular (Pl. II, Figs. 1—4). The cell wall thickening of the protoxylem vessels is spiral (PI. III, Fig. 1). The elements of both xylem fascicles are arranged in generally radial rows, but I also
