FLORAL MORPHOLOGY OF HORSFIELDIA (MYRISTICACEAE)

The pistillate flowers of Horsfieldia are morphologically similar to those of Myristica and Knema, and are composed of a single whorl of thick, fleshy tepals, and an unsealed, monocarpellate pistil bearing a single ovule. The carpel is vascularized by two ventral bundles, a pair of dorsal bundles, and several supernumerary bundles. The ovule vascularization is derived from the supernumerary bundles. Paired dorsal vascular bundles are an uncommon feature of uncertain significance. Carpels of Myristica and Knema lack any clearly defined dorsal vasculature, and the ovule vascular supply is derived from both the ventral and supernumerary bundles. The organization of the staminate flowers of Horsfieldia agrees with the myristicaceous pattern observed in Myristica and Knema. Each androecium consists of a single whorl of anthers fused or partially fused to a massive connective column. Each anther consists of a pair of bisporangiate lobes and a single vascular bundle. The androecial forms observed are interpreted as forming a series of intermediates between the monadelphous type of androecia of two South American genera, Compsoneura and Dialyanthera, and one African genus, Brochneura, and the solid, columnar androecia which are predominate in the family. Accumulating evidence supports a proposed South American or west Gondwanaland origin of the Myristicaceae.     

STUDIES ON THE FLORAL ANATOMY OF THE CUNONIACEAE

Twenty-two genera representing sixty-two species of Cunoniaceae and Davidsonia were examined with respect to floral anatomy. Sepals are vascularized by three traces with the lateral traces of adjacent sepals united. Pancheria is unique for the family with species in which the sepals are vascularized by a single, undivided bundle. Petals, when present, and stamens, are uniformly one-trace structures. A general tendency exists within the family for the principal floral bundles to unite in various ways, with fusions evident between calyx, corolla, and androecial vascular supplies. Carpel number ranges from two to five and the gynoecium is generally surrounded by a prominent disc. Gynoecia of Ceratopetalum and Pullea are “half-inferior.” The number of ovules per carpel locule ranges from one to numerous. Ventral carpel sutures range from open to completely sealed at the level of placentation. Carpels of the apocarpous genus Spiraeanthemum (incl. Acsmithia) are vascularized by a dorsal bundle and either three or four bundles constituting the ovular and wing vasculation in the ventral position, a condition unlike other members of the family. Ovules are supplied by the median ventral bundle. More advanced bicarpellate gynoecia within the family are predominately vascularized by a dorsal and two ventral bundles although a variable number of additional lateral wall traces may be present. A major trend exists toward fusion of the ventral bundles of adjacent carpels in the ovary of both bicarpellate and multicarpellate plants. At the base of the styles the fused ventral strands separate and extend along with the dorsal carpellary bundles into styles of adjacent carpels. In Pullea the ventral bundles terminate within the ovules. The united ventral carpellary bundles in Aphanopetalum, Gillbeea, and Aistopetalum lie in the plane of the septa separating adjacent carpels. Ovules are vascularized by traces originating from the vascular cylinder at the base of the gynoecium or by traces branching from the ventral bundles. Ovular traces in each carpel are united, or remain as discrete bundles, prior to entering the placenta. Tannin and druses are common throughout all floral parts. Although floral anatomy generally supports the position of Cunoniaceae near Saxifragaceae and Davidsoniaceae, the evolutionary relationship of the Cunoniaceae to the Dilleniaceae is uncertain.     

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. II. PRUNOIDEAE: MADDENIA,PYGEUM; OSMARONIA

A survey of species of the prunoid genera, Maddenia and Pygeum, and of the genus Osmaronia has been made. The ovules of all are pendent, campylotropous, and epitropic. In the prunoids, the ovular supply is intimately connected with a central vascular plexus in the base of the carpel; that plexus is absent from Osmaronia. The prunoid carpels are marked by an extensive degree of fusion among the ovular and wing bundles, by fusion of the sutural margins, by fusion of the 2 integuments of the ovule to a single massive one, and by the presence of 3 or 5 well-developed bundles in the base. The carpel of Osmaronia also has a strongly fused bipartite ovular supply, separate bundles of which, however, become very much attenuated before reaching the funiculus; it has independent ovular and wing bundles, completely separate carpellary margins, 2 clearly separate integuments in the ovule, and 6 distinctive bundles in the carpel base. At the funiculus, the wing bundle of Osmaronia is connected with the adjoining weak ovular bundle by a well-developed vascular branch. Various particularities in the morphology of Osmaronia lend support to its segregation into a unique tribe, the Osmaronieae of Rydberg.     

Androecium and floral nectaries ofHarungana madagascariensis (Clusiaceae)

The mature flower ofHarungana madagascariensis (Choisy)Poir. has an androecium of five antipetalous fascicles, consisting of four stamens each. The stamen fascicles alternate with five indented nectary scales. A SEM-study of the floral development, as well as a study of the floral anatomy was carried out to understand whether the nectariferous scales represent staminodia or are receptacular in nature and consequently whether or not the androecium ofHarungana, and theClusiaceae in general, is originally diplostemonous. The five petals originate by the splitting of petal-stamen complexes. Next the upper part of each complex differentiates basipetally in four stamens. The stamens remain fascicled and are lifted on a long stalk at maturity. Five carpel primordia are initiated united in a low ringwall. The five nectary scales appear after carpel inception and develop an external morphology reminiscent of anthers. The floral anatomy reveals an independent origin of sepal median traces and common sepal lateral traces, free petal traces, stamen fascicle traces and alternating vascular tissue which supplies the nectaries. The petal-stamen complexes are the result of a retardation in petal inception, linked with the absorption of petal tissue into the stamen primordia. The development of the stamen fascicles is discussed; it is suggested that they are of a secondary nature and do not appear as a reduction from a multistaminate androecium. The external morphology and vascular anatomy of the scales speaks in favour of a staminodial nature. The comparison with some other species of theClusiaceae gives evidence of a diplostemonous ancestry of the androecium.     

THE AFFINITIES OF PRINSEPIA (ROSACEAE)

Sterling, C. (U. California, Davis.) The affinities of Prinsepia (Rosaceae). Amer. Jour. Bot. 50(7): 693–699. Illus. 1963.—Anatomical study of the carpels of 4 species of Prinsepia has shown that at flowering the 2 ovules are erect and pleurotropic. The funiculus is on the dorsal and lower side of the ovule; the micropyle faces a large obturator on the ventral side. The carpellary margins are separated by a fissure below the funicular insertion, but above this level they are fused. The style is laterally inserted on the ventral face of the carpel; it is vascularized only by the wing bundles and the recurving dorsal bundle. At the base of the ovary, 2 ovular bundles depart from the vascular cylinder and run separately, each to its respective ovule. In carpel morphology, ovular position, ovule structure, and vascular anatomy, Prinsepia is not a prunoid type. Although its features on the whole resemble those of chrysobalanoid plants, there are notable differences. Consequently, Prinsepia is assigned to a new subfamilial group in the Rosaceae, the Prinsepioideae. Some phylogenetic considerations are discussed briefly.     

FLORAL ANATOMY IN THE SAXIFRAGACEAE SENSU LATO. II. SAXIFRAGOIDEAE AND ITEOIDEAE

The floral anatomy and morphology of 26 species from the Saxifragoideae and three from the Iteoideae are described and compared. The flowers of the Saxifragoideae are predominantly actinomorphic, partially epigynous and/or perigynous, and pentamerous, with two carpels which bear numerous ovules. There is usually some degree of independence between carpels, and the normally separate styles possess both a canal and transmitting tissue. Generally, staminodia are absent and nectariferous tissue, which is not vascularized, is present. The subfamily is characterized by large multicellular trichomes with globular, often glandular, heads. Placentation may be parietal, axile, or transitional between the two; parietal appears to be a derived condition in the subfamily. The vascular cylinder in the pedicel generally consists of several to many discrete bundles from which diverge ten compound traces at the base of the receptacle, leaving an inner cylinder of vascular strands that coalesce at a higher level into either as many ventral bundles as carpels or twice that number. In the former case, each ventral bundle consists of one-half of the vascular supply to each adjacent carpel and separates into individual ventral strands in the distal half of the ovary. The ventral bundles provide vascular traces to the ovules and, along with the dorsals, extend up the style to the stigma. Each trace diverging in a sepal plane typically supplies one or more carpel-wall bundles, a median sepal bundle, and a stamen bundle. Each petal-plane trace usually provides one or more carpel-wall bundles, a lateral trace to each adjacent sepal, a petal bundle and, in flowers with ten stamens, a stamen bundle. Dorsal carpel bundles are usually recognizable and may originate from traces in either perianth plane. While the position of Ribes remains problematical, its floral structure does not easily exclude it from the Saxifragoideae. Floral structure in the Iteoideae is remarkably similar to that in the Saxifragoideae, the main differences being a lesser degree of independence between carpels, generally narrower placentae with somewhat fewer ovules, and the presence of only unicellular, acutely pointed epidermal hairs as opposed to the relatively complex, multicellular trichomes prevalent in the Saxifragoideae.     

VASCULAR SUPPLY AND STRUCTURE OF THE OVULE AND ARIL IN PEONY AND OF THE ARIL IN NUTMEG

Camp , Wendell H., and Mary M. Hubbard . (U. Connecticut, Storrs.) Vascular supply and structure of the ovule and aril in peony and of the aril in nutmeg. Amer. Jour. Bot. 50(2): 174–178. Illus. 1963.—Examination of the placental region in the carpel of Paeonia indicates a complexity and super-abundance of vascular supply beyond that usually found in angiosperms and certainly more than is necessary for adequate nutrition and water supply of the ovules. From this it is concluded that the ovules once were borne on a larger and more complex structure than the present carpel. Vascular strands leading to the aril and the hypostase are interpreted as being relictual. The large multifid aril of Myristica has a well-developed vascular system composed of several sizes of branched bundles.     

THE COMPARATIVE MORPHOLOGY OF THE CANELLACEAE. IV. FLORAL MORPHOLOGY AND CONCLUSIONS

The morphology and anatomy of 105 flowers representing 13 species and 6 genera of the Canellaceae are summarized. The flowers are borne in axillary or terminal racemes, cymes, or small groups, or solitary, in an axillary or terminal position. The flowers are characterized as follows: bisexual, hypogynous; sepals 3, thick and leathery; petals, 5–12, free or united into tube at base, rather thick, in 1 or 2 whorls and/or spirals; androecium of 6–12 stamens united by their filaments forming a tube, anthers with longitudinal extrorse dehiscence; gynoecium of 2–6 carpels fused by their ventral margins; 2–6 placentae. There are 2 vascular bundles (rarely 3) to each sepal, 3 to each petal (some of the inner petals have only 1), 1 to each stamen and 1 trace to each carpel. The petal and stamen bundles have a common origin. All the data accumulated in this series on the Canellaceae indicate that the correct systematic placement of the Canellaceae is in the woody Ranales, perhaps in a complex with the Myristicaceae.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE SENSU LATO. XVII. FLORAL ANATOMY OF ONDINEA PURPUREA SUBSPECIES PURPUREA (NYMPHAEACEAE)

Classification and phylogeny of the Nymphaeaceae are unresolved. This study provides floral anatomical data that will assist in elucidating generic interrelationships and systematic relationships to other taxa of angiosperms. The floral anatomy of Ondinea purpurea den Hartog subsp. purpurea has been examined utilizing light microscopy. The peduncle possesses stelar vascular bundle complexes and cortical vascular bundles. Cortical bundles terminate within the peduncle. Each bundle complex consists of 2 collateral bundles on the same radius, the inner bundle inverted; 2 protoxylary lacunae occur yet differ in structure and function. Progressing acropetally, the inner xylary lacunae become discrete mesarch strands surrounded centrifugally by a vascular cylinder formed by divisions and anastomosing of the bundle complexes. Together these become the massive receptacular vascular plexus. The plexus provides collateral traces to the floral organs. Each sepal receives 3 traces that separate from the plexus as 1–3 lateral traces. Petals are absent and no vestigial petal traces have been observed. Distally, the plexus forms several large strands of connate gynoecial and androecial traces termed the principal vascular bundles (PVBs). Ventral veins separate from the PVBs and the latter extend acropetally through the outer ovary wall. Branches of the ventrals and PVBs contribute to septal vascular reticula from which each ovule is supplied by one vascular bundle. Each stamen receives 1 trace from branches of the PVBs. The ventrals and PVBs terminate within the carpellary lobes. A comparative anatomical study is offered that supports the inclusion of Ondinea in the Nymphaeaceae sensu stricto.     

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. I. PRUNOIDEAE: PRUNUS

A study of the carpel in 27 species of Prunus has shown certain notable structural relationships associated with the extent of closure of the carpellary margins. These relationships involve the degree of fusion of the 2 integuments, the number of vegetative bundles in the base of the carpel, the extent of fusion of the ovular bundles with one another and with the wing bundles, the relative size of the ovular bundles, and the relative development of the central vascular plexus. The comparative evidence strongly supports a primitively separate state of ovular and vegetative bundles. The significance of this finding is discussed.     

PATTERNS OF FLORAL DEVELOPMENT IN AGALINIS AND ALLIES (SCROPHULARIACEAE). II. FLORAL DEVELOPMENT OF AGALINIS DENSIFLORA

Initiation of floral primordia begins in Agalinis densiflora with production of two lateral adaxial calyx lobe primordia followed by a midadaxial primordium, and then primordia of two abaxial calyx lobes. Initiation of three abaxial corolla lobe primordia is succeeded by that of two stamen pairs and then by primordia of two adaxial corolla lobes. The primordium of the abaxial carpel appears before the adaxial one. Except for the calyx, initiation of primordia proceeds unidirectionally from the abaxial to the adaxial side of the floral apex. Zygomorphy in the calyx, corolla, and androecium is evident during initiation of primordia and is accentuated during organogenesis. The calyx undergoes comparatively rapid organogenesis, but the inner three floral series undergo a protracted period of organogenesis. The perianth series reach maturation prior to meiosis in the anthers. Maturation of the androecium and gynoecium are postmeiotic events.     

ANATOMY OF THE GYNOECIUM IN TWO SPECIES OF BAKERIDESIA (MALVACEAE)

Structure of the gynoecium is described in two species of Bakeridesia, subgenus Bakeridesia (Malvaceae, tribe Malveae). The dorsal wall of each carpel bears a winglike projection with a marginal pair of pubescent, bluntly dentate wings. The projection arises as a single, solid ridge of tissue after the ovules are initiated and after the ventral carpellary margins are fused with the receptacle. Two multiseriate layers of fiber-sclereids line each locule and continue into the winglike projection where they are separated by parenchyma. Gynoecial vascularization is described in detail. The richly vascularized carpels are supplied by five traces: a median dorsal trace, which bifurcates into two dorsal bundles; two lateral traces; and two ventral traces. Adjacent ventral traces, lateral traces, and septal bundles are fused—i.e., they are held in common by neighboring carpels. The presence of lateral carpellary traces may be a primitive character in the tribe Malveae.     

STUDIES IN THE FLORAL ANATOMY OF POLYGALA (POLYGALACEAE)

Flowers of Polygala are irregular, each having three small and two long winglike sepals, three petals, eight stamens, and a bilocular ovary. These flowers have been considered pentamerous, and placentation has been subject to various interpretations. Development and anatomy of flowers of Polygala alba, P. lanceolata, and P. lutea were studied to see if evidence of pentamery and change in placentation could be found. These studies reveal no evidence of vestigial petals or stamens nor of vascular traces to organs that are missing in the three species studied. Neither are there abortive sporangia in the bisporangiate anthers. Observations on development of carpel primordia and on the vascular plan of mature carpels indicate that placentation is fundamentally parietal rather than axile. Speculation is offered as to the derivation of this type of placentation.     

Floral development of Kingdonia (Ranunculaceae s. l., Ranunculales)

The flower of Kingdonia has a terminal position, thus the rhizome is sympodial. The floral organs initiate in spiral phyllotaxis. The androecium is centripetal in initiation but the sterile stamens are retarded in development compared with the fertile ones. The apex of the young carpel does not participate in the conduplication. The floral organs have single vascular traces and unilacunar nodes.The study was supported by the National Nature Science Foundation of China (No. 30370095 and 30130030).     

POSTGENITAL CARPEL FUSION IN CATHARANTHUS ROSEUS (APOCYNACEAE) IV. SIGNIFICANCE OF THE FUSION

The ontogenetic and phylogenetic significances of the postgenital carpel fusion in Catharanthus roseus were investigated experimentally. When one of the two carpel primordia was surgically destroyed prior to carpel fusion, the remaining carpel differentiated nevertheless; however, the tissue development on the adaxial (normally fused) carpel face appeared aberrant. Possible reasons for this modified ontogeny are discussed. The suggestion that syncarpy is phylogenetically significant because any pollen tube can potentially reach any ovule was verified in C. roseus by monitoring pollen tube growth following spatially controlled pollinations. The suture formed by the postgenital fusion was no barrier to pollen tube growth, and the pollen tubes rapidly became distributed throughout the stigmatic tissue.     

THE PALM GYNOECIUM

The morphology, anatomy, and histology of the gynoecia at or close to anthesis are described for 20 genera of palms selected to represent different taxonomic alliances and to include major gynoecial types within the family. Palms may have 1–10 carpels, but most have three. Fifteen genera, including 14 coryphoid palms and the monotypic Nypa fruticans, are apocarpous and the remainder, approximately 190, are syncarpous. Fusion of carpels in some gynoecia begins in the base, in others in the styles. Pseudomonomerous pistils occur in several different alliances: the ovarian parts of two carpels are reduced but three usually equal and functional styles and stigmas are present. The carpel is often follicular in shape with the ventral suture open or, more frequently, partially or completely closed. The carpel may be stipitate or sessile and usually has a conduplicate laminar part. Most carpels are spirally and laterally inserted on the receptacle, but the carpel in some unicarpellate genera (e.g., Thrinax) appears terminal. Stipes, ovarian parts, styles, and stigmas vary in structure and development. Septal nectaries which differ in size, in the presence or absence of specialized canals, and in position, characterize all genera of some groups but only some genera of others. Diverse vascular configurations in the bases of gynoecia vary according to the extent of the floral axis, the development of carpellary stipes, and the connation of the carpels and their adnation to the tip of the floral axis. Four types of carpellary vascular systems are present in the genera described: (1) most palm carpels have three major traces consisting of a dorsal bundle and two ventral bundles, and they may also have up to four pairs of lateral bundles or occasionally more; (2) in certain cocosoid palms no ventral bundles can be distinguished, but a dorsal bundle, many parallel lateral bundles, and a row of immature ventral strands vascularize each carpel; (3) carpels of Phytelephas have a dorsal bundle, two pairs of major lateral bundles and about four pairs of shorter lateral bundles, with no identifiable ventral bundles; (4) carpels of Nypa have many dichotomously branched bundles but none that are recognizable as dorsal, ventral, or lateral strands. Additional peripheral bundles or systems may be present in each of the above types. Ovules are supplied by 1–15 bundles. These are derived either from the carpellary stele; from ventral bundles only; from ventral, lateral, and dorsal bundles; or from a combination of these origins. Certain areas of the gynoecia or certain parts of dorsal carpellary walls in some genera are much less mature at anthesis than surrounding tissues. Implications for floral biology and relationships within the palms and of palms to other groups are discussed.     

兰花蕉花部维管束系统的解剖学研究

兰花蕉花梗的维管束分散排列．子房基部的维管束排成两部分,外方为一轮大维管束环,中央为分散排列的小维管束区。前者的纸管束进入子房壁,后者进入子房的中轴,形成股座纸管束;及至延长都以后,股座维管束逐渐消失．子房壁上的维管束较易识别的有心皮背束、心皮背束伴束和隔膜束．三束心皮背束经延长部最终进入花柱和柱头．心皮背束指心皮背束务与其紧靠的大维管束,三枚心皮背束伴束最终分别进入三枚外轮雄蓝．三枚隔膜束中远轴面的两枚分别进入两校内轮雄蕊,而近轴面的一枚伴随着第六枚雄蓝的缺失最后进入唇瓣中央．子房壁其余的维管束进入延长部后,先向外分出一轮纸管束进入花幕,余下的中央部分排成一轮心形的线管来环．该环远轴面的维管束分为两半分别进入两枚侧生花瓣;近轴面即心形凹陷一侧初为两轮即外轮大的维管束与内轮小的维管束,后排成一轮并与近轴面的隔膜束一同进入唇瓣．兰花蕉的唇瓣既为花瓣成员,又含一枚缺失的雄蓝维管束,与姜目已报道的只来自退化雄蕊的竹芋科的兜状结构和美人蕉科、姜科、闭鞘姜科的唇瓣有明显区别．在旅人蕉科尚未有研究资料的情况下,作者根据已有资料,对姜目雄蕊维管束系统来源和结构进行比较,初步认为在姜目的系统演化上,兰花蕉科与芭蕉料更近．     

THE ORGANIZATION OF THE VASCULAR SYSTEM IN THE STEMS OF THE NYMPHAEACEAE. I. NYMPHAEA SUBGENERA CASTALIA AND HYDROCALLIS

The vascular system in the stems of Nymphaea odorata and N. mexicana subgenus Castalia, and N. blanda subgenus Hydrocallis consists of continuing axial stem bundles with eight being the usual number. The stem bundles are concentric and xylem maturation is mesarch. Xylem elements consist of tracheids with spirally or weakly reticulated secondary wall thickenings. The phloem is made up of companion cells and short sieve tube members with simple sieve plates that are nearly transverse. At the node each leaf is supplied with two lateral leaf traces and a median leaf trace. A root trace is also present and supplies a series of adventitious roots borne on the leaf base. Flowers and vegetative buds develop directly from the apical meristem and occupy leaf sites in a single genetic spiral. Each flower or vegetative bud is related to a leaf through specific spatial and vascular association. The related leaf is separated from the related flower by three members of the genetic spiral and occupies an adjacent orthostichy. Vascular tissue for the related flower arises from the inner surfaces of the four stem bundles supplying leaf traces to the related leaf and extends through the pith to the flower or vegetative bud via a peduncle fusion bundle. The vascular system organization in the investigated species of Castalia and Hydrocallis is not typically monocotyledonous or dicotyledonous, nor can it be considered transitional between them. The ontogeny of the vascular system is similar to typical dicotyledons and the investigated species of Nymphaea can, therefore, be considered to represent highly specialized and modified dicotyledons.     

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.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE (SENSU LATO). XIII. CONTRIBUTIONS TO THE VEGETATIVE AND FLORAL STRUCTURE OF CABOMBA

Six species of Cabomba have been examined although the anatomy of the vegetative axes is based on the study of only C. caroliniana and C. palaeformis. A plant consists of an erect short shoot with decussate leaves which bears axillary flowering shoots and rhizomes. A rhizome bears decussate leaves and may also form axillary flowering shoots or turn upward and become a new short shoot. The phyllotaxies of the flowering shoots are proximately decussate or ternate (C. piauhyensis). The flowering shoots with decussate phyllotaxy change to 1/3 phyllotaxy distally; they bear axillary flowers proximally, and extra-axillary flowers distally. Flowering shoots with ternate phyllotaxy do not change distally but each produces first axillary and then extra-axillary flowers. Decussate vegetative axes and flowering shoots have four vascular bundles; ternate vegetative axes and flowering shoots have six vascular bundles, distantly paired into two or three vascular bundle-pairs, respectively. An elliptical vascular plexus occurs at each node. Each leaf receives one bundle-pair from one trace and each flower three bundle-pairs. A two-level receptacular vascular plexus occurs in flowers; the proximal, larger portion provides traces to perianth and stamens and the distal, smaller portion becomes carpellary traces. Each of the three sepals typically receives five branch traces from a basal principal trace, and each of the three petals receives, typically, three branch traces from a basal principal trace. Sepals and petals generally occur in a single, basally connate whorl. Each stamen receives one trace. Each stamen of three-stamen flowers is opposite a petal; each stamen of six-stamen flowers is aligned with an interval between a petal and adjacent sepal. Each staminal trace, which is just above the principal petal trace, in a three-petal flower, is frequently adnate to the latter trace. Each carpel receives one principal trace from the distal, small extension of the receptacular plexus, and each principal trace becomes three conventional veins of a carpel. Ovules may be borne directly over one of the veins or in any position between veins and are supplied by branches of the nearest vein or nearest two veins. All traces, ovular supply veins and the proximal portions of all veins are amphicribral. The several anatomical and morphological differences in vegetative axes and flowers between Cabomba and Brasenia suggest a greater taxonomic distance between the two genera than commonly supposed. It is suggested that extra-axillary flowers in 1/3 helical and ternate flowering shoots of Cabomba might be advantageous in preventing anthesis of flowers beneath peltate leaves. The aberrant position might be the initial evolutionary step toward what, in other nymphaeaceous genera, has shifted each flower to an adjacent helix. It is proposed that the zigzag stem accompanying the trigonal and sympodial flowering shoots may offer greater stability and floatability in water than the monopodial form. Several suggestions are offered for the variability of ovular positions: 1) the variability is a vestige of former laminar placentation in conduplicate carpels; 2) it is a vestige of a primitive condition antedating the current close association of ovules with ventral carpellary veins; 3) it is an early stage of evolution which might have terminated in laminar placentation and cantharophily, but which was replaced by a trend toward myophily.