STUDIES IN THE FLORAL ANATOMY OF THE

By V. S. Rao and Arati Ganguli Rammrain Ruia College, Bombay-19

fRcceivcd for publication on November 22, 1961)

I ntroduction

T h e Apocynaceae is a natural taxon having a close affinity with Asclepia- daceae. This family is characterised by a deeply iive-lobed imbricate calyx, often with glands or squamellae at the base on its inner surface; a 5-lobed contorted corolla, often hairy or appendaged within; 5 epi- petalous distinct stamens, often with an apical prolongation of the con­ nective ; anthers either free or adherent by viscid exudates to the stigma; granular pollen; a bicarpellary, superior to half-inferior pistil with the two carpels cither free or united in the ovary portion; and a single style. In syncarpous, bilocular ovaries in this family the placentation is axile, whereas in syncarpous unilocular states it is parietal. In the apo­ carpous condition the placentation is marginal. A nectariferous disk is present at the base of the gynoecium in most Apocynaceae.

Schumann (1895) divided Apocynaceae into the two subfamilies, Plumeroideae and Echitoideae. In Plumeroideae the stamens are either free or only slightly attached to the stigma, the anthers are generally without tails and the seeds are usually without a coma. In Echitoideae the stamens are closely attached to the stigma, the anthers have tails, and the seeds arc generally with a coma. This subfamily is believed to show affinities with Asclepiadaceae. Woodson and Moore (1938) recognized three subfamilies, namely the Plumeroideae, Echitoideae and .

There have been only a few investigations on the floral anatomy o f Apocynaceae., W oodson (1930) studied this group chiefly in its general morphological aspect. Apart from brief references in the papers of Van Tieghem (1875) and Grelot (1897), it was Woodson (1935) and Woodson and Moore (/oc. cir.) who paid attention to the floral ana­ tomy of Apocynaceae. Saunders (1939) gave a very short account only of a few genera. Woodson and Moore {lot. cit.) interpreted the calycine squamellae as well as the corolline scales o f Apocynaceae as stipular in nature. The nectaries have been considered to be carpellodes. On the basis of an ontogenetical study, Boke (1948) interpreted the lower portion of the corolla tube of Vinca rosea L. as receptacular in nature, being formed by toral growth, while its upper part is appendicular. The same author (1949) studied also the development of the stamens and carpels of this species. The carpellodes are said to arise later than the carpels but on the same morphological level. It was suggested that the ancestors of V. rosea might have had four carpels. Agarwal (1951) interpreted non- vascular squamellae at the base of Asclepiadaceae flowers as receptacular outgrowths and were not considered to be stipular in origin. Coronal outgrowths receiving vascular supply from the stamina! bundles were regarded as outgrowths from the stamina! filaments.

The species listed below are studied, following the paraffin-infiltra- tion method. Subfamily: Plimieroideae

(1) Carissa congesta Wight,

(2) AUamanda cathartica Linn., (3) * alba Linn., (4) Holarrhena antidysenterica Wall.,

(5) A Is ton ia scholar is R.Br., (6) Tabernaemontana divaricala (Linn.) R.Br. Syn. Ervatamia coronaria S tap f, (7) Kopsia fruticosa Wall.,

(8) Cerhera thevetia Linn. . Subfamily: Echitoideae (9) Aganosma cymosa G.Don..

(10) Nerium indicum Mill. Syn. N. odorum Soland.,

(11) tinctoria R.Br., (12) Vallaris solanacea O. Ktze. Syn. K. heyneii Spreng.

D e s c r ip t io n In Carissa congesta (Text-Figs. 1 and 2) and Alsionia scholaris the calyx is supplied by five midrib traces and five commissural traces which branch and supply adjacent sepal margins. In Tabernaemontana divaricala also there are five midribs and five commissural traces, but in addition there may be one or two small sepal lateral traces arising directly from the stele. In all these three species the petal traces are fused at their base with the commissural traces of the calyx. The com­ posite traces formed by the fusion o f the petal traces and the sepal com ­ missural traces have been called petal-sepal cords. In AUamanda cathartica (Text-Fig. 3), Plumeria alba (Text-Fig. 6). Holarrhena anti­ dysenterica, Aganosma cymosa (Text-Fig. 25). Nerium indicum (Text- Fig. 30), Kopsia fruticosa, Cerhera thevetia. Wrightia tinctoria, and

• As- pelt by Hutchinson, 1959. Vallaris solanacea the calyx is supplied by five sepal traces which branch. In Cerbera theveHa, in addition to five sepal traces, a smaller branches arise directly from the stele. In Holanhena antidysenterica and Vallaris solanacea the five traces arise as two sets. Firstly three traces are borne and just above these two more traces are given out.

Some members of Apocynaceae have scales called as squamellae which are usually glandular, associated with the basal parts of the calyx. The sepals o f Nerium iiidicum bear many such non-vascular outgrowths in median and lateral positions on their inner surface near the base (Text-Fig. 31). A somewhat similar condition is also seen in Cerhera thevelia (Text-Fig. 19) but with just an indication of some of the sepal traces bearing short faint inward branches which, however, do not actually enter the squamellae. In Holanhena anlidysenierica (Text- Fig. 10) and Wrigluia tinctoria (Text-Fig. 35) there are only five squamellae alternating with the sepal lobes and they arise from those five margins of the imbricate calyx which are towards the inside. In Holarrheim antidysenterica the five glands show also a division. In both these species they are vascularized by small branches from the sepal marginal traces. Aganosma cymosa also has a few glandular scales in similar positions but they are non-vascular (Text-Fig. 27). Tabernaemontana divaricata has 3-4 non-vascular scales opposite every sepal arising from its inner surface (Text-Fig. 14). The calyx of Vallaris solanacea has less than five .scales alternating with sepal fobes, with a faint vascularization from sepal marginal traces.

In all the Apocynaceae studied there are five traces for the corolla. In AUamanda aitliartica, Holarrhena antidysenterica, Nerium indicuin, Kopsia fruticosa, Cerbera thevetia, Wrightia tinctoria and Vallaris solanacea the five petal traces arise directly from the vascular cylinder just above: the origin of the sepal traces. In Holarrhena antidysenterica they run upwards for some distance very closely adn^fe-^ihe .yascdar cylinder and travel then only outwards. In Aganosma cymosa the foetal traces arise at the same level as the five sepal traces. In Carrissa con- gesta, AJstonia schoJaris and Tabernaemontana divaricata there is a fusion of the five petal traces at their base with the five commissural bundles of the calyx (Text-Fig. 1). In Plumeria alba the five petal traces arise at the-^ame level as the stamen traces. The petal traces bear lateral branches sooner or later within the corolla tube. In Cerbera f/ieV'e^' tf^sre^are peculiar inward projections of the corolla tube for ■'som e'^i^nce alternating with the petals and these cannot be inter- r>reited in (any way other than as partial inward projections of the petal 'rti^ in s even where the corolla lube is still entire (Text-Fig. 23).

From among the species of Apocynaceae studied here, Nerium indicum and Wrightia tinctoria have a corolline corona. In Nerium indicum the antepetalous corona divides into a number of filiform struc­ tures and is supplied by many branches from the vascular bundles of the petals (Text-Figs. 33 and 34). In Wrightia tinctoria, somewhat similar corolline outgrowths which are vascularized are present, and in addition, just below the splitting of the corolla into five segments are Text-Figs. 1-10. Figs. 1 and 2. Carissa congesta, x22. Figs. 3-5. AUa> manda calhartica, xl2. Figs. 6-8. Pbimeria alba, xl2. Figs. 9 and 10. ffolar^ thtm anUdysenterica, X 20, T ext-F ios. 11-18. FigB. 11 and 12. Abionia siMaris, 14. TqberngenHmtanf, O ^kam , x29. Fifs. 15-18. KopsI* fruticosa. x « . five outgrowths alternating in position witii tiie corolla lobes (Text- Figs. 36 and 37). Each of these outgrowths receives a vascular branch from adjacent petal margins. The antepetalous outgrowths of Wrightia tinctoria are present both beneath and above the level of splitting of the corolla. The antepetalous corona of Nerium indicum is adnate to the corolla for a considerable length and the division into filiform parts , occurs only above the level o f splitting o f the corolla into its five segments.

, In all the Apooynaceae investigated there are only five stamen traces. These arise jtrst above the petal supply in Carissa congesta, AUiimanda cathartica, Holarrhena antidysenterica, Alslonia scholgn's, Tabemaemontaria divaricata, Nerium indicum, Kopsia frulicosa, Cerbera ihevetia, Wrightia tinctoria and Vallaris solanacea. In Holarrhena antidysenterica the five staminal traces run perpendicularly upwards very close to the axial vascular cylinder for some distance, like its sepal traces and petal traces. In Plumeria alba the stamen traces arise along with the petal traces. In Aganosma cymosa the stamen traces arise either directly from the stele or conjoined with the sepal traces. (In this species the vascular supply to the calyx and corolla arises at the same level.) The filaments of Kopsia fruticosa arise from small pouches in the corolla tube, a condition not seen in the other members (Text- Fig. 18). In Allamanda cat hart ica, Aganosma cymosa, Wright ia tinctorja and Vallaris solanacea the outer anther cells form spurs. In Nerium indicum the outer and inner anther cells on either side together form a spur. The tips of the anthers are prolonged into shorter or longer, somewhat cylindrical, structures in Allamanda caihartica, Ptumeria alba. Tahernae- montana divaricata, Cerbera thevetia (Text-Fig. 24), Aganosma cymosa, Nerium indicum and Wrightia tinctoria.

Text-Fkjs. 25-29. Aganosma cymosa, X'20'.

In Cerbera thevetia, the filaments are extremely reduced. The anthers of Allamanda cathartica (Text-Fig. 5), Aganosma cymosa (Text- Fig. 29), Nerium indicum (Text-Fig. 32) and Wrightia tinctoria (Text- Fig. 37) laterally adjoin each other very closely forming a tube-like struc­ ture. In Aganosma cymosa (Text-Fig. 28), Nerium indicum (Text- Fig. 32), Wrightia tinctoria and Vallaris solanacea the anthers become somewhat adherent to the stigma for a short distance. All these four species belong to the subfamily Echitoideae.

The prominent disk in the flowers of Allamanda cathartica (Text- Fig. 4), Alstonia scholaris (Text-Figs. 11 and 12), Tabernaemontana divaricata (Text-Fig. 13), Cerbera thevetia (Text-Fig. 20) and Vallaris solanacea (Text-Fig. 39) receives vascular branches from the axial vas­ cular cylinder above the origin of the stamen traces or from the basal- most portions of the gynoecial traces. The disk of Cerbera thevetia receives a large number of traces which lie scattered within it. That of Allamanda cathartica, Alstonia scholaris, Cerbera thevetia and Vallaris solanacea is more or less annular, while that of Tabernae­ montana divaricata is fully adnate to the gynoecial base. The lower part o f the disk in Aganosma cymosa is adnate to the inner surface of the floral tube (Text-Fig. 26) while its upper part is free. It is supplied by the axial vascular cylinder. The disk of Kopsia fruticosa is usually described (Bailey, 1953) as of two glands. The present study very clearly proves that these two glands are actually sterile carpels alter­ nating in position with the two fertile carpels and having a vascular supply closely resembling that of the fertile carpels (Text-Figs. 15-17).

The vascular organization in the carpels of Apocynaceae conforms to the normal method. Each carpel has a dorsal strand, a varying number of lateral bundles and two ventral or marginal bundles which may be either separate or fused together. The ovules are supplied by branches from the ventral strands, which are usually exhausted at the top of the ovuliferous zone.

The ovary wall of Cerbera thevetia receives in addition to the car- peliary traces, a number of scattered bundles that run on the outside of the carpellary bundles for a considerable distance (Text-Figs. 21 and 22). These scattered bundles are apparently “ disk traces” being borne along with those that run into the disk, but which, instead of entering the disk, run in the ovary wall.

The gynoecium of Kopsia fruticosa differs from the other species studied. There are clearly four dorsal bundles for the gynoecium instead of the usual two (Text-Fig. 15). There are two carpels which are fertile and ovuliferous. The other alternating two are com­ paratively small and sterile but basically the vascular supply to the sterile carpels is on the same plan as that of the fertile carpels. The sterile carpels are usually described as comprising a disk of two glands. The sterile carpels have, however, no ventral bundles differentiated but have only the dorsal bundles and their branches. It may be empha­ sized that the term “ sterile carpel” is used in its obvious sense and not in the specialized meaning of Saunders as used in her theory of carpel polymorphism. The present authors do not find any anatomical 8ui^rt to the carpel polymorphism theory except that an obvious T ext-Figs. 30-37. Figs. 3<>-34. Nerim tndicum, x20. Figs. 35-37. Wrighha tinctoria, x2Q, sterility of carpels is seen in like Kopsia fruticosa as in some mem­ bers of Verbenaceae (Rao, 1952). In most angiospermic genera, the strand of transmitting tissue is prominent in the stigma also and in many cases it is even connected with the receptive surface of the stigma. In Apocynaceae it is peculiar that the transmitting tissue disappears near the base of the stigma. From among the Apocynaceae studied, Carissa congesta, Alla- manda cathartica, Alstonia scholaris, Tabernaemontana divaricata, Kopsia fruticosa, Cerbera thevetia and Wi ightia tinctoria have superior ovaries. An adnation, at least for a very short lenjgth, of the calyx, corolla and androecium to the basal part of the ovary is seen in Plumeria alba (Text-Figs. 7 and 8), Holarrhena aniidysenterica (Text-Fig. 9), Aganosma cymosa (Text-Fig. 25), Neriiim indicum (Text-Fig. 30) and Vallaris solanacea (Text-Fig. 38), producing a short hypanthium or floral tube through which run the vascular bundles of the calyx, corolla and androecium on circumferences external to that occupied by the car- pellary bundles. In Nerium indicum and Vallaris solanacea the calyx separates out quite at a low level, leaving the corolla and androecium adnate for short distance more to the ovary. Thus in all these species the basal part of the ovary appears embedded while the upper part is free. The ovary, therefore, has to be termed as semi-inferior.

Text-Fios. 38 and 39. Vallaris solanacea, x 20.

Varying degrees of fusion of the carpels is seen in Apocynaceae and the variation is most in the ovary portion. There is a single ovary of two carpels in Carissa congesta, Allamanda cathartica, Nerium indi­ cum and Vallaris solanacea. In Tabernaemontana divaricata and Cer­ bera thevetia, the carpels separate in the apical part of the ovary. The ovary of Carissa congesta, Nerium indicum and Cerbera thevetia is bilocular wfth axile placentation. The ovary of'Tabernaemontana. divaricata is bilocular at the base and unilocular above; and that of AUamanda cathariica is unilocular with parietal placentation. In all cases, including forms where in the ovuliferous zone the carpels are free, the placentas are clearly developed from the carpellary margins.

D isc u ssio n

The basic vascular supply for a sepal is assumed by most botanists to be of three traces (Puri, 1951). The commissural strands of the calyx seen in some of the species are formed by the fusion of adjoining mar­ ginal traces of adjacent sepals. As compared with those species where the calyx is supplied by only five traces, the species with median traces and commissural traces are primitive so far as the calyx is concerned. This is on the assumption that a reduced number of traces indicates an advanced nature. In Plumeria alba and Holairbena antidysenterica, the sepal traces travel somewhat perpendicularly upwards in the thalamus for some distance and then travel outwards. In the other species they run more or less outwards. Woodson and Moore (1938) recognized the following four types for the organization of the vascular supply to the calyx. (1) Calyx midribs leave with a single gap in the stele and the two lateral traces of each sepal are also associated with the same gap. This three-trace, one-gap system was supposed by them to be primitive. (2) Adjoining lateral traces of adjacent sepals, either separately or fused together, are adnate to the petal midribs. (3) A single trace for each sepal which bears lateral branches. (This condition is suggested to be probably more advanced than the first two types.) (4) This type incorporates features of types (1) and (3) or of types (2) and (3). Woodson and Moore {loc. cii.) also believed that the one-trace condition is derived from the three-trace condition. An adnation of the basal parts of petal traces to the commissural bundles of the calyx is seen in Carissa con- gesta, Alstonia scholaris and Tabermemontana divaricata by the present authors. The four species of the subfamily Echitoideae namely Aganosma cymosa, Nerium indicum, Wrightia linctoria and Vallaris solanacea have five traces for the calyx. In the species belonging to Plumeroideae the authors find not only this condition but also the supply by five median traces and five commissural traces. Woodson and Moore (loc. cit.) found a three-trace, one-gap condition in Tabernae- inonlam accutissima and T. arbores. In T. divaricata, however, there are five median traces and five petal-sepal cords arising from as many gaps. In addition, there may be one or two small lateral traces arising directly from the stele. Woodson and Moore (1938) recognized three chief types of relation­ ship of the squamellae with the calyx lobes. (1) Squamellae alter­ nating with the calyx lobes on their margins, to which they appear to be attached either singly or in groups. (2) Opposite the lobes, either singly or in groups. (3) Indefinitely distributed when they seem to form a fringe of many scale-like structures around the very base of the calyx. On comparison with small glandular structures seen at the base of petioles in many Apocynaceae (that may be alternate or opposite or indefinitely distributed in relation to the petiole), which have been interpreted as stipular (Gluck, 1919), in spite of the fact that the of Apocynaceae are described as exstipulate, the calycine squamellae of Apocynaceae have been interpreted by Woodson and Moore {loc. cit.) as stipular in nature. Although in general they found no vascular tissue in the squamellae, they reported in Strophanthus gratus and Funtumia elastica small bicollateral bundles derived from the marginal veins of the sepals. They suggested alternate squamellae as representing the basic condition and solitary opposite squamellae as advanced while the indefinitely distributed squamellae were suggested to be derived from either the alternate or the opposite condition. Woodson (1930) origi­ nally interpreted the squamellae as staminodes but Woodson and Moore (loc. cit.) discarded this view in favour of a stipular theory. The present authors find antesepalous squamellae in Tahernaemontana divaricata, Nerium indicum and Cerhera tlievetia, and in all these three, no vascular bundles enter the squamellae. In Holarrhena antidysenterica, Aganosma cymosa, Wrightia tinctoria and VaUaris solanacea the squamellae alter­ nate more or less in position with the sepals. A fact which has not been noticed by any of the earlier workers is that, at least in those plants with alternisepalous squamellae studied by the writers there is a definite relationship of the squamellae with the imbricate nature of the calyx. In the imbricate calyx of five sepals, both the margins of two sepals and one margin of a third sepal are towards the inside and it is these margins that bear the squamellae. In Holarrhena antidysenterica, Wrightia tinctoria and VaUaris solanacea these outgrowths are vas­ cularized by branches from the sepal marginal bundles. In Aganosma cymosa they are non-vascular. In Nerium indicum and Cerhera thevetia there are many antesepalous squamellae which appear to correspond to what Woodson and Moore {loc. cit.) described as “ indefinitely distri­ buted when they seem to form a fringe of many individuals uniformly distributed around the base of the calyx.” This description of Wood­ son and Moore (loc. cit.) seems to imply that they are present alround the calyx base. But their figure cited to illustrate this point shows the squamellae close to the base on the upper side of the calyx and the words “around the base of the calyx” would mean an entirely different posi­ tion, namely near the lower surface of the calyx at its base. Such a meaning does not appear to be intended by Woodson and Moore (loc. cit.). Many of their figures are also purely diagrammatic.

The fact that in some cases the squamellae arise from near the margins of the sepals and in other cases from their inner surface reminds one of stipules in angiosperms which are either free-lateral or adnate or axillary. As mentioned earlier, some workers aid call the squamellae as stipule-like in nature. The adaxial squamellae which are actually attached to the inner surface of the sepals can perhaps more appro­ priately be compared with ligules seen in a few dicotyledons and some monocotyledons, specially the grasses. Parkin (1948) regarded the ligule of dicotyledons as being formed by the fusion of two adnate stipules on the adaxial face of the petiole. The vascular supply to the lig u lc is from the foliar lateral traces, as in the case of stipules. Arber (1925) interpreted the ligule of grasses as an axillary stipule. Majuradar (1956) interpreted it as a composite structure composed of the margins of the -sheath and its stipules. The squamellae of the calyx seen by the present authors in Apocynaccae are either non-vascular or vascu­ larized by the sepal marginal bundles, thus apparently more or less con­ firming their stipular nature when they are so vascularized. But the adaxial corona of the petals in some Apocynaceae which has also been interpreted by some (Woodson and Moore, 1938) as stipular, casts a serious doubt about the correctness of this view. This aspect is further discussed in connection with the corolline corona. The corolla of Nerium indicum has an antepetalous corona supplied by branches from the midrib and lateral bundles of the petals. The corona at its base occurs as five very short plates adnate to each petal lobe on its inner surface and dividing into a number of filamentous pro­ cesses, each one of which receives a small vascular bundle. Jn Wrightia /hidoria also there is a corolline corona of a number of filiform out­ growths which arise chiefly in antepetalous positions but also occur in positions alternaling with the petal lobes. These are also vascularized by branches from the median and the lateral (including the marginal) bundles of the petals. Woodson and Moore (!oc. cit) described pairs of scales alternating with corolla lobes in Slrophanlhus\ single scales alter­ nating with the petals in Presionia\ and antepetalous scales in Apocynum. The corolline corona of Apocynum and Traclwmilum is said to be non-vascular but in Strophanthus sarmentosus and Prestonia, marginal bundles of the petals are described as sending branches into the corona. Although Nerium indicum is listed by Woodson and Moore {loc. cit.) among the plants studied by them there is no mention of it in the description about corolline corona in this species. They had inter­ preted the corona of the corolla also as stipular in nature more or less similar to the squamellae of the calyx. The corolline corona of Nerium indicum and Wrightia tinctoria is supplied not only by the marginal bundles but also by the median bundles of the petals. A stipular supply is only from the lateral traces of a leaf. On the basis of vascular supply at any rate, the interpretation of the corolline corona as stipular seems very doubtful. Corolline scales of some Boraginaceae (Lawrence, 1937) have been interpreted as folds from the inner surface of the corolla, and those of Lychnis (Arber, 1939) also in almost the same manner, being considered as “ hollow lateral invaginations” . Anther prolongations seen in a number of families are usually formed from the connective. The vascular bundle of the stamen runs at least into its basal part. The protrusions in this family, at least in their basal part, are clearly seen to be derived not only from the con­ nective but also from the sterile terminal portions of the anther lobes. Hence it seems more appropriate to call them as sterile prolongations of the anther tips rather than as connective protrusions. In many Compositae there are apical protrusions sometimes referred to as appendages, as well as basal appendages which correspond somewhat to the spurs. Small (1917) considered apical and basal appendages of anthers of Compositae as formed by sterilization of sporogenous tissue. Parkin (1951) expressed the view that Small {!oc. ci'i.) did not distinguish between apical prolongations which are merely of the connective, and basal outgrowths which are sterile prolongations of the pollen sacs independent of the connective. Parkin, therefore, believed that apical and basal appendages of Compositae are different in nature. In Apo- cynaceae the present authors find that the terminal prolongation of the anther is composed not only of the tissues of the connective but also of the sterile tip of the anther and hcnce it is better to call them as anther-tip prolongations instead of as connective prolongations. This, however, does not apply to species of other families with terminal pro­ longations of the stamens or even to those members of Apocynaceae not studied by the writers. It is well known that in a number of plants like Annona and Nelumhium only the connective is prominently pro­ longed. Small (loc. cii.) considered anthers with only apical appendages as primitive when compared with anthers having both basal and apical appendages. Parkin {loc. cil.) agreed with this view.

Woodson (1930) and Woodson and Moore (1938) interpreted the disk or nectaries of Apocynaceae as carpellodes on the ground that their vascular supply is associated with that of ihe gynoecium. This interpretation is quite correct in the case of Lochnera rosea, Pleiocarpa mmica. Vinca major and V. minor studied by them and Kopsia fruticosa studied by the present writers in which the vascular supply to the disk and to the carpels is very similar and also organized at the same level. These carpellode nectaries do not take any part in the formation of the style. In AHamanda catliariica, Arstonia scliolaris, Tabernae- montana divaricata, Cerhera Ihcvelia and Vallaris solanacea the disk is annular, surrounding the gynoecial base and partly or fully adnate to it. It is surprising that Woodson and Moore (/oc. ci/) reported the absence of a nectary in Cerhera tangliin. Cook (1905) mentioned that a disk is absent in Alstonia scholar is. Jt is not obvious in an external examina­ tion but sections reveal the presence of a definite disk. There are numerous traces for the disk which are borne by the axial vascular strands even before they are definitely arranged as the supply for the two carpels. Among the nectary traces of these species, absolutely no distinction can be made between the dorsal, lateral and marginal bundles as can be done in the case of carpels and carpellodc nectaries. Woodson and Moore ( oc, cii.) also found some species like Stemmadenia alfari in which the nectary is annular and adnate to the base of the gynoecium. They did not give any detailed reasons but interpreted these also as being of the nature of carpellodes. They state that poly- desmy is frequently characteristic of the nectaries but never of the carpels proper. But how they correlate this statement with their inter­ pretation that all nectaries of Apocynaceae are carpellodes is not explained by them. Moreover, the fact that the vascular supply to these annular nectaries is organized just below that of the two carpels would involve a further difficulty which has not been considered by the earlier workers. One has to assume an ancestral condition with two whorls of carpels, the outer one of which has become modified into the nectary. This assumption has no justification in fact. A further objec­ tion for interpreting the nectaries of Apocynaceae as carpeliodes is pro­ vided by the condition seen in Aganosma cymosa. In this species the lower part of the disk is adnate to the floral tube while its upper part is free. At levels where the disk is fully adnate to the floral lube the carpels lie in the centre, separated from the floral tube. It is difficult to interpret such a disk in the way in which Woodson and Moore (1938) interpreted it. It seems least objectionable to interpret the annular type of disk in this family as developed through a proliferation of the receptacular tissue between the androecium and the gynoecium and which is vascularized by branches from the axial vascular cylinder. In connection with the disk of Boraginaceae, Lawrence (1937) writes: “ It has been suggested that the disk is formed from the receptacular tissue. Since a dorsal trace is clearly differentiated well below the disk, it seems more correct to consider the disk, part of the ovary. However, the development of some regions far faster and to a greater degree than others makes it difficult to state with any degree of surety the exact limitation of the rcceptacic or of the ovary." The disk traces in Apocynaceae usually arise at a lower level than the dilTerentiation of the dorsal and other traces of the carpels. Hence the interpretation that the disk of Apocynaceae is formed through a proliferation of the receptacular tissue which becomes vascularized is logical. In Aganosma cymosa the gynoecial supply is by inward traces from the vascular cylinder, the latter supplying the disk which is adnate to the inner face of the floral tube for some distance. This also is rather in favour of the receptacular nature of the disk and cannot in any way support Wood­ son and Moore's (lor. cil.) general interpretation of the disk in this family as being of carpeliodes. Saunders (1939), in her expositions of floral morphology in relation to her almost universally rejected theory of carpel polymorphism, described the gynoecium of Apocynaceae and Asclepiadaceae as of two median sterile carpels and two lateral fertile carpels. The term “ sterile carpel’" in her account is not identical in meaning with the same term as commonly understood. In view of the fact that the theory of carpel polymorphism is not accepted these days by the vast majority of botanists it is not further discussed. The ovary in Apocynaceae is known to be either superior or partly inferior (Bailey, 1953; Rendle, 1938; Willis, 1955). The basal portion of the so-called ovary wall in those species with semi-inferior ovaries in this family must be regarded as appendicular in nature and not receptacular because there is no downward turning of the gynoecial or any other traces (Douglas, 1944; Puri, 1952). Boke (1948) interpreted the corolla tube of Vinca rosea as receptacular belo\v and appendicular above. The present anatomical study does not provide any evidence for it. The semi-inferior condition of the ovary in Nerium indicum and Vallaris solanacea differs from the typical type of semi-inferior condition in the fact that the calyx is separated from near the base of the ovary itself, leaving only the corolla and androecium adnate to the ovary wall for some distance. Some authors like Hanf (1935), use the term stylodium for the style­ like portion of each carpel in apocarpous gynoecia, the term style being confined to syncarpous forms. Although the apocarpous condition is acknowledged to be primitive, Hutchinson (1959) states that in the order Apocynales the tendency to free carpels is probably a secondary attain­ ment and not a primitive character, on the basis of the presence of a common style and stigma. Woodson (1930) and Woodson and Moore (1938) believed that in Apocynaceae the unilocular condition and parietal placentation of-the ovary have been derived from a bilocular ovary with axile placentation. As they themselves noticed, in some species one finds the bilocular condi­ tion with axile placentation at the base and apex of the ovary, but with the unilocular condition and parietal placentation in the middle. Puri (1951) suggested that “ recent work seems to indicate that the distinction which is sometimes maintained between parietal placentation and axile placentation is untenable, there being a graded series between them”.

S u m m a r y

The vascular anatomy of the flowers of twelve species of Apocynaceae has been studied. The ovary is semi-inferior in a few species. The calycine squamellae, the corolline corona, and the disk have been discussed in detail. The interpretations of Woodson and Moore (1938) of a number of features are shown to be untenable.

A CK NO W^LEDGEMENTS

The authors express their thanks to Mrs. K. Gupte for help during the progress of this work.

R e f e r e n c e s

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------and Moore, J. A. 1938. The vascular anatomy and comparative morpho* logy of Apocynaceous flowers. Ibid. 65: 135-66.

* Not consulted in the original.