root cortex of the nymphaeaceae, cabombaceae, and nelumbonaceae1, The

Journal of the Torrey Botanical Society, Jan-Mar 2002 by Seago, James L Jr

Results. NYMPHAEACEAE. The developmental and structural features of the root cortex in Nymphaea odorata (Seago et al., 2000b) have recently been reported in more detail than in previous studies. The stele of most members of the family normally has 5-9 strands or poles of primary xylem with a small parenchymatous pith in most Nymphaea species (Fig. 1 ) or with metaxylem elements occupying the stele center (e.g., in Victoria Fig. 2, and Euryale Fig. 3). Roots of Nuphar luteum are distinctly different in having 10-18 strands or poles of primary xylem and a large pith (Fig. 4), depending on root size.

The endodermis of the members of the Nymphaeaceae is characterized by the occurrence of Casparian bands only (Fig. 1, 2, 3, 4, 5), except for a few, apparently old roots of N. tuberosa and N. tetragona in which light Fluorol yellow staining indicates suberin lamellae (Fig. 6). The wavy walls of endodermal Casparian bands are best demonstrated by acid digestion (Fig. 7).

The hypodermis is generally two or three cell layers thick in the Nymphaeaceae. Its outermost layer is always a uniseriate, uniform exodermis (Fig. 1) with Casparian bands (Fig. 8), that sometimes appear as two bands in N. odorata (see Seago et al., 2000b), and with suberin lamellae (Fig. 9) in every cell. The wavy walls of exodermal Casparian bands are also demonstrated by acid digestion (Fig. 10). In N. odorata there are cellulosic secondary wall thickenings in the exodermis of long, large roots, and the non-exodermal layer(s) of the hypodermis are typically parenchymatous and may be thick-walled with cellulose (see Seago et al., 2000b, Fig. 5E, 5F). In old roots, the exodermis is often the outermost layer of the root, except that remnants of the epidermis trichoblasts are a common and characteristic feature of the root surface (see Seago et al., 2000b).

The aerenchyma in members of this family has characteristically hexagonal-shaped lacunae with lacunar walls of cells which always have SRH cells (semi-regular hexagon-shaped cells) at the angles (Fig. 11, 12), and there appear to be transverse diaphragms of a uniseriate layer of small cells with perforations (intercellular spaces) in the diaphragm in all genera examined (Fig. 11, 12, 13), although they are rare in Nuphar luteum (Fig. 4). In the middle of the aerenchyma, sclereids (idioblasts in Conard, 1905) are typical; astrosclereids, as they are often termed because they seem star-shaped in transverse sections, are found in Nymphaea species (Fig. 1, 6, 12) and Nuphar (Fig. 4). I observed only one sclereid in Euryale and none in Victoria; this is undoubtedly due to the lack of mature root specimens. The arms of the sclereids are elongated somewhat vertically (Fig. 14) and protrude into lacunae (Fig. 12) and diaphragms (Fig. 12, 13). Where they occur adjacent to the endodermis, the sclereids arusually very long and narrow and appear like fibers in transverse section (Fig. 1 ). The astrosclereids. which are always derived from the SRH cells of the lacunar walls (Seago et al., 2000b), have long arms in, e.g., N. odorata (Fig. 1), N. 'Wood's Blue Goddess' (Fig. 12), and N. tuberosa (Fig. 6), and slightly shorter arms in Nuphar (Fig. 4). The endodermis and hypodermis lack sclereids.