MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE. XII. THE FLORAL BIOLOGY OF CABOMBA CAROLINIANA

Observations have been made on the pollination ecology of Cabomba caroliniana Gray in Texas. Flowers are trimerous with morphologically similar perianth parts. The adaxial corolla spurs are nectariferous and attract small Diptera (e.g. Notiphila cressoni and Hydrellia bilobifera). Anthesis occurs for 2 consecutive days with flowers opening about 10:00 a.m. and closing around 4 p.m. on each day. First-day flowers have short, indehiscent stamens and longer pollen-receptive stigmata which arch outward over the nectaries. In 2nd-day flowers the stamens have elongated to the level of the stigmata and extrorse dehiscense occurs above the nectaries. Stigmata of 2nd-day flowers are pressed together at the center of the flower and are nonreceptive to pollen. Insects attracted to 2nd-day flowers in search of nectar become dusted with pollen (due to the position and extrorse dehiscence of the anthers) and as insects fly to 1st-day flowers, achieve cross-pollination by virtue of the stigmata position over the nectaries. Seed anatomy is similar to that of other nymphaeaceous genera (i.e., abundant perisperm, little cellular endosperm, a haustorial nucellar “tube,” and a small dicotyledonous embryo). Pollination morphology and comparative xylem anatomy support the segregation of Cabomba from the Nymphaeaceae, sensu stricto. The anatomical correlations between seeds and the myophilous pollination syndrome (found elsewhere in Nymphaeaceae, sensu lato), however, suggest a phyletic relationship.     

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.     

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.     

MORPHOLOGICAL AND EMBRYOLOGICAL STUDIES ON THE LEMNACEAE. I. THE FLORAL STRUCTURE AND GAMETOPHYTES OF LEMNA PAUCICOSTATA

Maheshwari, Satish C., and R. N. Kapil. (U. Delhi, Delhi, India.) Morphological and embryological studies on the Lemnaceae. I. The floral structure and gametophytes of Lemna paucicostata. Amer. Jour. Bot. 50(7): 677–686. Illus. 1963.—In Lemna paucicostata, a locally occurring member of the Lemnaceae, the plant body is represented by a frond which is devoid of lignified elements. The root shows a winged root sheath but does not have root hairs. There are no distinctive layers like the endodermis and xylem. The male archesporium is hypodermal and differentiates normally as in other angiosperms into parietal and sporogenous layers. The tapetum is single-layered and plasmodial. The partition walls of the anther are not derived by sterilization of the sporogenous cells as believed earlier. The microspore tetrads are isobilateral and decussate, the meiotic divisions being successive. The pollen grains are shed at the 3-celled stage. The ovary contains a single hemianatropous, bitegminal and crassinucellar ovule. The development of the embryo sac conforms to the Allium type.     

FLORAL BIOLOGY OF MAGNOLIA

The floral biology of eight species of Magnolia native to the United States is described. The flowers are protogynous. They are pollinated by several species of beetles that enter buds as well as closed and open flowers to feed on nectar, stigmas, pollen, and secretions of the petals. Individual flowers persist from two to four days and undergo a series of petal, stigma, and stamen movements that assure pollination by beetles. It is suggested that the flowers of Magnolia are highly specialized for exclusive pollination by beetles. These specialization mechanisms produce large quantities of food for the beetles and deny other types of insects (bees, moths, etc.) access to the flowers at critical stages in the pollination process, i.e., when stigmas are mature and pollen is shed.     

STUDIES OF THE BIOLOGY OF SCLEROTIUM CEPIVORUM BERK.

Sclerotium cepivorum did not grow from agar into unsterile soil, but growth of restricted duration and extent was observed from infected onion tissue. Growth depended on the food reserves and its extent was determined by the size and age of the infected tissue. In sterile soil the mycelium grew only very slowly even in the presence of organic supplements. In addition to being inadequate nutritionally, unsterile soil has a microflora that interferes with the growth of S. cepivorum. It is concluded that S. cepivorum does not persist as growing mycelium in natural soils.     

STUDIES OF THE BIOLOGY OF SCLEROTIUM CEPIVORUM BERK.

Sclerotia from 6-week-old pure cultures of Sclerotium cepivorum germinated immediately in soil only after abrasion of their rinds, but after burial in soil for a month or more, unabraded sclerotia became capable of germination.
Marked stimulation of germination occurred in the presence of host plants (onion, leek and shallot). Little or no germination occurred in soil alone or in the presence of non-host plants (barley, cabbage, carrot and white clover). Sclerotial germination was observed in a number of soils of widely differing pH and over a wide range of soil water content. Germination of sclerotia on uninjured onion roots was greatest at the tip region. On artificially injured roots sclerotial germination was enhanced but the effect of position was lost.
Sclerotial germination was independent of contact between roots and sclerotia. It was induced by root extracts of all Allium spp. tested, but of no other plants. Boiling or autoclaving root extracts did not destroy the active principle and it is concluded that under field conditions sclerotia are induced to germinate by a thermostable chemical substance from Allium roots.
The process of germination of sclerotia is described.     

COMPARATIVE STUDIES OF FLORAL MORPHOLOGY OF THE LABIATAE

Hillson , Charles J. (Pennsylvania State U., University Park.) Comparative studies of floral morphology of the Labiatae. Amer. Jour. Bot. 46(6): 451–459. Illus. 1959.—Comparative vascular studies of 39 species of mints from 27 genera reveal 2 basic stelar patterns: those in which the dorsal carpellary bundles are terminal in origin and those in which the dorsal carpellary bundles are basal in origin. Gradations of intermediate dorsal carpellary bundle divergence exist. Steles exhibiting terminal dorsal carpellary bundles are always associated with laminal ovules and are interpreted as being primitive. Marginal ovules are associated with floral steles exhibiting basal divergence of dorsal carpellary bundles and are regarded as being advanced. Adnation of traces seems to be a more reliable character in determining phylogenetic relationships than is connation. On the basis of 3 characters, viz: (1) position of dorsal carpellary bundle divergence, (2) ovule position and (3) degree of concrescence, a phylogenetic series of the 8 sub-families of Labiatae from advanced to primitive is proffered.     

THE FLORAL BIOLOGY OF CASSIA DIDYMOBOTRYA AND C. AURICULATA (CAESALPINIACEAE)

The flowers of Cassia didymobotrya and C. auriculata have three types of fertile anthers that differ in orientation, size, shape, and pollen production. Flowers with right-handed or left-handed style deflections, i.e., enantiostylous flowers, occur in the same raceme. In Israel, both species are pollinated by pollen collecting buzzing females of Xylocopa pubescens. Vibrations of the carpenter bee are necessary for release of pollen from poricidal anthers and, in C. didymobotrya, also for absorption of pollen through the stigmatic opening into a cavity of the style tip. The largest anthers supply pollen for pollination. Pollen for consumption by the bee, on the other hand, appears to be supplied by all fertile anthers. This is in contrast to the accepted view of a complete separation of functions in the heteromorphic anthers in Cassia. The pollen/ovule ratio in C. didymobotrya was 55,200, and that in C. auriculata 32,000. Only 0.01% of the pollen produced by a flower was found in the stigmatic pollen load, and this fraction allows for high seed sets. From a comparison of the pollen production and utilization in the Cassia species and in certain distylous plants, it is concluded that heteranthery in Cassia does not confer an advantage in pollen economy. The high pollen/ovule ratios are explained by lack of nectar as well as by the large area on which pollen is deposited on the bee's body relative to the small size of the stigma. Enantiostyly in Cassia is considered as part of a pollination syndrome whose characteristics are outlined. The function of enantiostyly as an outbreeding strategy is discussed. In the two Cassia species, opportunities for self- and geitonogamous pollinations and self-compatibility minimize an effect of enantiostyly in promotion of outcrossing. Instead, it is proposed that style deflections may clear access of the pollinator to the anthers and protect female parts from injury by a vibrating heavy-bodied visitor.     

激光生物学效应的研究

本文较系统地报道了CO_2激光,He-Ne激光的生物学作用,证明激光确能导致生物体内生理生化的变化,确能诱发染色体畸变和基因突变。作者认为激光作为育种上一种新的诱变因素是有根据的。     

STUDIES ON THE FLORAL HISTOGENESIS AND PHYSIOLOGY OF PERILLA. II. FLORAL INDUCTION IN CULTURED APICAL BUDS OF P. FRUTESCENS

Raghavan , V., and W. P. Jacobs . (Princeton U., Princeton, N. J.) Studies on the floral histogenesis and physiology of Perilla. II. Floral induction in cultured apical buds of P. frutescens. Amer. Jour. Bot. 48(9): 751–760. Illus. 1961.—The morphological and histological changes induced in apical buds and explants of P. frutescens (L.) Britt. var. ‘Tall Late’ in short days and long days when cultured in White's medium have been followed. When photoinduced in culture, apical buds showed visible signs of changes in 30.9 days, and produced normal flowers in 81.6 days. Apical buds in LD showed similar transformations at the apices, but with continued LD treatment, they elongated to form sterile structures, superficially resembling Selaginella cones. The normal flowers formed in culture were similar to those formed on the intact plant, while the individual florets of the LD-cone differentiated only the non-sporogenous tissues in them. A less pronounced sequence of changes resulted when apical buds stripped of their older pairs of apical leaves were LD- or SD-treated. When explants with the 1st pair of unfolded leaves or with the 1st and 2nd pairs of unfolded leaves were photoinduced in vitro, the responses were relatively fast. However, explants with the 1st and 2nd pairs of unfolded leaves in LD remained entirely vegetative. When unfolded leaves were implanted in the same medium separated from the buds and both were photoinduced or given LD, the buds formed the typical 1st signs, but did not differentiate into normal flowers. This inhibition of flowering resulted in the formation of sterile cones, consisting of florets with non-sporogenous tissues only. The results have suggested the possibility of the sterile cone-like structures being an intermediate stage in the flowering of Perilla. The role of a possible inhibitor produced by mature leaves of SD plants in LD is discussed.     

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.