THE ORGANIZATION OF THE VASCULAR SYSTEM IN THE STEMS OF THE NYMPHAEACEAE. II. NYMPHAEA SUBGENERA ANECPHYA, LOTOS, AND BRACHYCERAS

The anatomy and organization of the stem vascular system was analyzed in representative taxa of Nymphaea (subgenera Anecphya, Lotos, and Brachyceras). The stem vascular system consists of a series of concentric axial stem bundles from which traces to lateral organs depart. At the node each leaf is supplied with a median and two lateral leaf traces. At the same level a root trace supplies vascular tissue to adventitious roots borne on the leaf base. Flowers and vegetative buds occupy leaf sites in the genetic spiral and in the parastichies seen on the stem exterior. Certain leaves have flowers related to them spatially and by vascular association. Flowers (and similarly vegetative buds) are vascularized by a peduncle trace that arises from a peduncle fusion bundle located in the pith. The peduncle fusion bundle is formed by the fusion of vascular tissue derived from axial stem bundles that supply traces to certain leaves. The organization of the vascular system in the investigated taxa of Nymphaea is unique to angiosperms but similar to other subgenera of Nymphaea. CONARD (1905) divided the genus Nymphaea into five subgenera (Castalia, Hydrocallis, Anecphya, Lotos, and Brachyceras) on the basis of floral morphology, general morphology of the stem, leaf, and seed, and geographic distribution. The organization of the vascular system in the stems of subgenera Castalia and Hydrocallis was described in a previous paper (Weidlich, 1976). This present paper represents an extension of the analysis of the vascular system in the stems of the Nymphaeaceae by considering the Nymphaea subgenera Anecphya, Lotos, and Brachyceras. Subgenus Anecphya consists of one species, Nymphaea gigantea, that is endemic to Australia and New Guinea, whereas subgenus Lotos consists of four night-blooming species that are native to the Old World tropics. The subgenus Brachyceras contains twelve species which are found in the tropics of both the New and Old World (Conard, 1905). MATERIALS AND METHODS-Seeds of N. gigantea (subgenus Anecphya) were obtained from the Missouri Botanical Garden and were germinated 'Received for publication 14 January 1976. Parts of this investigation represent portions of a dissertation submitted in partial fulfillment for the Ph.D. degree, Duke University, Durham, NC 27706. The author wishes to express appreciation to Dr. P. B. Tomlinson and Dr. Usher Posluszny for their critical evaluation of the manuscript, and to Dr. M. H. Zimmermann for his assistance in photography. This research has been supported in part by a Research Fellowship from the Atkins Garden Fund, Harvard University. 2Present address: Dept. of Botany and Plant Pathology, Mich. State Univ., East Lansing, 48824. in a tank at the Duke University greenhouses. Preserved stems of N. lotos (subgenus Lotos) were acquired from Sierra Leone and from an introduced colony in Costa Rica. Living material of N. rubra (subgenus Lotos) was obtained from Van Ness Water Gardens, California, and raised at the Duke University greenhouses. N. caerulea (subgenus Brachyceras) and the hybrid N. X daubenyana (subgenus Brachyceras) were also obtained from the Van Ness Water Gardens and raised at the Duke University greenhouses. Specimens of all taxa used in this study were deposited in the Duke University Herbarium. Entire lengths of stem, often exceeding 5 cm in diam and 15 cm in length were treated with 48 % HF after fixing in FAA, and embedded in 52 C TissueMat after dehydration in ethyl alcohol, and were sectioned on either a rotary or a sliding microtome at 10 um, 25 ym, or 50 ym. Each dehydration step (Johansen, 1940) was protracted to five days to allow complete infiltration of both the dehydration and clearing fluids. The stems were evacuated several times during dehydration in ethyl alcohol, clearing in xylene, and paraffin infiltration to assure complete removal of air from the air chambers and aerenchyma of the stem. Special trays were constructed for the embedding of these large stems. Large stems were then sectioned on a Reichert sliding microtome equipped with a modified chuck, containing rollers that allow continuous feed of long paraffin blocks. Sections were stained in safranin and fast green (Johansen, 1940) or toluidine blue (O'Brien, Feder, and McCully, 1964). Serial sections were first analyzed with conventional techniques