MORPHOLOGICAL AND ANATOMICAL STUDIES IN HELOBIAE VII. Vascular Anatomy of the Flower of Butomus umbellatus Linn.* BY V. SINGH (School of Plant Morphology, Meerut College, Meerut) Received August 4, 1965 (Communicated by Prof. V. Purl, F.A.Sc.) ABSTRACT The vascular anatomy of the flower of Butomus umbellatus--a member of the Butomaceae--has been described. The perianth and stamens remain fused with the gynoecium up to the level of the locules and thus showing a tendency towards epigymy. The six carpels are also adnate among them- selves at the base for some distance. The vascular supply of a carpel con- sists of a dorsal bundle and two ventral bundles. The latter ramify repeatedly and the branches are distributed on the lateral walls of the carpel. The placentation in Butomus has been described as 'superficial' since the ovules are distributed almost throughout the inner carpel wall except the dorsal suture. It is considered that in cases like Butornus where carpels are free, the superficial placentation might have originated from marginal placentation by the unequal extension of the ventral surface of the carpellary margins. The present study also brings out certain resemblances in between Butomaceae and Hydrocharitaceae, while on the other hand vasculature of the flower hardly shows any resemblance to that of Alismaceae THE vascular anatomy of the flower of some species of Potamogetonaceae, Najadaceae, Aponogetonaceae, Scheuchzeriaceae and Alismaceae has already been worked out by the author (Singh, 1965, a, b, c, d, 1966). The present paper deals with the vascular anatomy of the flower of Butomus umbellatus--a member of the Butomaceae, F.A.A. fixed material of which was obtained through the courtesy of the Director, National Botanic Gardens, Lucknow, India, and Professor Ernst C. Abbe, Minnesota, U.S.A. * Research contribution No. 73 from the School of Plant Morphology, Meerut College, Metnart. 313 314 V. Sn,,lGx.i OBSERVATIONS The monotypic genus Butomus represented by B. umbellatus is distributed in temperate Asia and Eurasia. It is a freshwater slender emersed herb with a short rhizome and basal rosettes of erect, linear and triquetrous leaves. The scape is very long, erect and terete bearing numerous flowers on long slender pedicels in simple umbels. Before anthesis the inflorescence is enclosed by an involucre of three large, scarious bracts. The six subequal persistent perianth segments are petaloid and are arranged in two whorls of three each. The stamens are nine, free with flattened filaments and red- coloured, 2-celled, basifixed anthers opening by lateral slits. The six carpels are connate only at the base. The ovary of each carpel is unilocular with numerous, anatropous ovules scattered all over the inner surface of the carpel wall excepting the dorsal suture. The style is apical with the stigma on the inner side. The ripe carpels are free or nearly so and are crowned by persistent styles. The fruit is a many seeded inflated follicle. Anatomy of the Inflorescence and Flower.--The vascular supply of the peduncle consists of a large number of scattered collateral vascular bundles. Each bundle is surrounded by a bundle sheath of lignified cells. The sheath is more prominent especially in the outer region of the peripheral bundles. The phloem of the bundle is normal while the xylem is represented by a cavity associated with a few lignified elements. The outer seven or eight layers of the cortex are composed of small thin-walled rounded cells with diamond- shaped intercellular spaces while the inner cortex is very lacunaceous The epidermis is covered by a distinct layer of cuticle, and is beset by numerous stomata with small accessory cells. At the base of the umbel the vascular bundles of the peduncle branch and anastomose freely and then many traces diverge for each of the three involucral bracts. Thereafter many traces enter into the base of the pedicel of each flower and these soon organise almost into a ring of about 12 vascular bundles (Fig. 2). At the base of the receptacle the xylem cavity is completely replaced by lignified elements and the vascular bundles frequently split and anastomose to form a complete vascular cylinder (Figs. 3-5). Three traces for each of the six perianth segments diverge out from this vascular cylinder (Fig. 6). The traces for the outer whorl of perianth segments z_rise at a slightly lower level than those of the inner whorl. These traces may divide in their outward course through the cortex of the receptacle. The laterals further resulting in seven to nine bundles. The perianth lobes separate from the central part slightly above the level where the locules arc present (Fig. 12). Morphological and Anatomical Studies in Helobiae--.VI! 315 BUTOMUS UMBELLATUS " Zt .d_..,d ~t ; " ~! • st , ,d "d .st " " ~st 16 /f '" %N "d 13 . d "vs ;: d d. '°~'td 5~ x.~~ 17 • ~ .,/ ..~, 14 >. Lit • • J /-/II~L-~A( ))~%~-- 18 @4 5 t 15 FIGs• 1-18. Butomus tmtbellat.s. Fig. 1. Semi-diagrammatic longitudinal section of flower showing vaseular ground plan. Figs• 2-15. Serial cross-sections of flower-bud from base upward showing vascular supply to different organs. Fig. 16. A portion of longitudinal section of stigma showing glandular hairs• Fig. 17. Cross-section of an abnormal flower with ten stamens. One of the anther lobes of extra stamen is transformed into perianth segment (ps). Fig. 18. Cross- s-~ction of gynoecium with seven carpels from an abnormal flower. (d---dorsal bundle of carpel; psmperianth segment; st--staminal tra~; vs--ventral strand of carpel.) 316 V. SINGH After the departure of the perianth traces, and before the gaps are com- pletely filled up, nine traces diverge for the stamens almost simultaneously (Figs. 7, 8). Each stamen receives a single concentric vascular bundle which extends almost up to the top of the connective unbranched. The filaments separate from the central part simultaneously with the perianth. Two stamens lie opposite each perianth segment of the outer whorl and one each of the inner whorl. The vascular tissue left constitutes the gynoecium supply and gets re- organised into a more or less complete vascular cylinder. Six carpellary dorsals arise from this cylinder and take the midrib position in the six carpels (Figs. 9, 10). Then the vascular tissue breaks up into six V-shaped bundles arranged on radii alternating with those of carpellary dorsals (Fig. 10). These are the ventral strands of the carpels. Slightly above the level of the locules each of the two arms of a V-shaped ventral strand, which extends on either side of a locule, splits generally into five to seven bundles (Figs. 11, 12). The bundles thus derived from the two arms of a ventral strand lie on the lateral walls of the two adjacent carpels. These bundles give rise to traces for the numerous anatropous ovules scattered on most of the inner surface of the ovary walls of the carpels except the dorsal suture (Fig. 13). The cells present on the lateral sides of adjacent carpels are glandular and densely staining. They mark the limits of the two adjacent carpels. The separation of the carpels starts from the centre and extends towards the periphery (Fig. 13). The carpels remain coherent for about half of their length before they become completely free. Each free carpel is open on the adaxial side (Fig. 14) and the two arms are closely placed. The locule extends into the style and the style is also open on the adaxial side. The dorsal bundle as well as the ventrals after supplying the ovules continue into the style and the stigma (Figs. 1, 15). The stigma is covered by two to three celled glandular hairs arising from the cells of the internal lining (Fig. 16). The cells are densely staining and have distinct nuclei. Some variations in the number of stamens and of carpels have been observed. In one case there were ten stamens instead of nine. One of the anther lobes of the extra stamen was transformed into a perianth part (Fig. 17). Flowers with seven or eight carpels were also noticed. In such cases the vascular cylinder gives off corresponding number of dorsal bundles and ventral strands for the carpels. In one flower with seven carpels (Fig. 18), two of the carpels were fused throughout their length but their styles were free. There were two dorsal bundles in the fused carpels. Morphological atul Anatomical Studies bt Helobiae--Vll 317 DISCUSSION AND CONCLUSIONS In Butomus the perianth and the stamens remain fused with the gynoecium up to the level of the locules and thus showing a tendency towards epigyny. The six carpels are also adnate among themselves through the tissue of the floral axis at the base for some distance. Eber (1934) while studying the development of the gynoecium in Butomus described it as " Falsches Coenocarpes Gynaeceum" (Pseudosyncarpous gynoeeium). The side walls of carpels are glandular on their outer surface by whic'a the carpels become coherent at the base. Saunders (1929) compares these glandular surfaces with the septal glands of Liliaceae. The vascular supply of a carpel consists of a dorsal bundle which extends into the stigma and two ventral bundles which branch several times. These branches are distributed on the lateral wall of the carpel. The profuse branching of the ventral bundles can be attributed to the fact that the ovules are distributed throughout the inner wall of the carpel except along the dorsal suture. The ventral bundles of the adjacent halves of two different carpels arise conjointly. Very recently Melville (1962) proposed a new theory of angiosperm carpel on the basis of the comparative morphology but he finds some support for it in anatomy.