Showing papers on "Pollination published in 1976"

Foraging behavior of solitary bees : Implications for outcrossing of a neotropical forest tree species

Abstract: Most flowering plants of neotropical forests display adaptations for animal pollination (see references cited by Frankie, Baker & Opler (1974a) and by Frankie (1975, 1976)), but, since little information is available on the foraging behaviour of the animals involved, there has been considerable speculation as to whether widely spaced, conspecific plants in these forests are selfor cross-pollinated (Corner 1954; Baker 1959; Fedorov 1966; Ashton 1969; Bawa 1974). Bees constitute one of the major groups of visitors to a large proportion of tree species occurring in certain lowland forests (Janzen 1967; Frankie 1975). The potential for interplant movement of bees in Central America has been emphasized by Janzen (1971, 1974), who found that certain euglossine bees in Lowland Wet forests may forage over distances of several kilometres. Janzen has also suggested that members of other bee genera (e.g. Bombus, Centris, Ptiloglossa and Xylocopa) may forage over similar distances. Experimental studies on the nature of breeding systems of tree species in a Costa Rican Dry forest indicate that of the tested species (many of which are bee-pollinated), most have obligate outbreeding systems (Bawa 1974). Bawa's findings strongly imply that bees and other anthophilous animals effect pollination through inter-plant movement. However, patterns of pollinator foraging behaviour in relation to breeding systems have yet to be experimentally investigated for any neotropical plant species. In this paper experimental data are presented on the breeding system of a papilionaceous tree, Andira inermis (Swartz) H.B.K., and on the movements of its pollinators. Early experiments (detailed below) showed that A. inermis is self-incompatible. The flowers show clear adaptation for pollination by bees. The specific questions asked in this study were as follows. (i) What kinds of bees visit Andira flowers and what are their patterns of inter-tree movements ?

Plant‐Pollinator Interactions in Hawaii: Pollination Energetics of Metrosideros Collina (Myrtaceae)

Abstract: The most abundant tree species in much of the undisturbed Hawaiian forest was the subject of a 2—yr study on plant—pollinator interactions and energetics. The purposes of the study were (1) to determine the roles of insects and of some endemic Hawaiian birds in the pollination of the tree Metrosideros collina, (2) to test the hypothesis that maximal outbreeding and seed set occur at intermediate levels of nectar availability, (3) to understand the adaptive significance of profuse flowering in this species, and (4) to determine the degree of specialization in the pollination ecology of this species. Endemic Hawaiian birds (Drepanididae) are essential for high levels of fruit—set and outbreeding in M. collina. Fruit—set was much higher in red—flowered individuals when birds were allowed to use inflorescences than when only insects used them. This is apparently caused by partial self—incompatibility, such that maximal fruit—set occurs only with outbreeding, the primary agents of which are the birds. The pred...

Intraspecific variation in pollen-ovule ratios and nectar secretion-preliminary evidence of ecotypic adaptation'

Abstract: Because pollen-ovule ratios (P/O's) reflect the predictability of pollinators in a habitat and the efficiency of pollination, large intraspecific differences in P/0's suggest differences in pollinator numbers and/or their efficiency. Plants of Heracleum lanatum, which is andromonoecious, from forests have larger percentages of male flowers than those outside of forests, hence a higher P/0. This difference is associated with differences in the kinds of flower visitors. I suggest the pollen removal by small bees that forage on Heracleum in but not outside the woods may be the selective force that accounts for the larger percentage of male flowers of woods plants. In andromonoecious Caesalpinia the percentage of hermaphroditic flowers in a population ranges from 8-83%, and appears to be ecotypically adapted to levels of pollinator, i.e., butterfly, activity. Nectar secretion is continuous and is the key to successful reproduction, especially in populations with low pollinator activity. Pollination is proportional to foraging time and a function of the pollen carried. The amount of nectar in the flowers reflects pollinator activity; thus in low activity populations there will be more nectar and visits will be longer, thus increasing the likelihood of pollination. Because there are large numbers of male flowers in such populations the pollinators presumably carry more pollen, which also increases the likelihood of pollination. In populations with high pollinator activity large numbers of visits balance the shortness of individual visits. A consequence of this balanced system is that the fecundity of hermaphroditic flowers in quite dissimilar populations is equivalent. Deviations from predicted levels of seed set and fruit set are consistent with below normal levels of pollinator activity. Nectar production in two populations of Calliandra anomala are quite different, with a high elevation population producing far less nectar than a lower elevation population. The low rate of nectar production in the high elevation population is undoubtedly an adaptation that forces the pollinators, i.e., hawkmoths, to visit large numbers of flowers to obtain sufficient nutrients, thus increasing fruit set and maximizing fecundity. The breeding system and pollination biology of Leonotis nepetaefolia are used to explain the distribution of this African plant in Mexico, where it is a roadside weed.

Preferential pollination of yellow-flowered morphs of Raphanus raphanistrum by Pieris and Eristalis spp.

Abstract: COROLLA-COLOUR polymorphisms occur in wild populations of many angiosperms, but little is known of the selective factors that maintain them. Valentine has suggested that yellow/white corolla-colour polymorphisms may be adaptively neutral1. I have observed extremely strong discrimination by some insect pollinators between the yellow and white corolla-colour forms of polymorphic wild radish. These observations, which are described below, indicate that corolla-colour differences are of adaptive importance in this and similar cases.

Pollination and fruit-set in asclepias: a reappraisal

Abstract: Experimental pollinations of Asclepias tuberosa L., the first for this species and second largescale effort for the genus, reveal trends toward local population differentiation. The species possesses a low level of self-compatibility, the first documented report for the genus. Analysis of flowers visited by natural pollinators in populations across the eastern half of the United States demonstrated a linear relationship between pollinia removal and pollinia insertion. Clarifications in older literature regarding the specificity of the pollination mechanism, effective levels of pollination in natural populations, and the performance of experimental manipulations are made, and it is concluded that fruit-set in Asclepias is regulated by the interaction of both mechanical aspects of pollination and physiological aspects of fertilization and fruit development. A model incorporating these restraints is seen to predict fairly well the observed fruit to flower ratio of about 1:100 in natural populations. WITH MORE RECENT attempts to quantify and explain pollination biology in evolutionary terms (e.g., Faegri and van der Pijl, 1966; Heinrich and Raven, 1972; Proctor and Yeo, 1972), there has been a resurgence of interest in the reproductive biology of asclepiads. The reproductive biology of the Asclepiadaceae, or milkweed family, is rivalled only by that of the Orchidaceae in its floral complexity (Fig. 1). The five antisepalous stamens have undergone extreme modification; the anther connectives extend upward to partially overlap the stigmatic head. In addition, coronal extensions (hoods) containing arching structures (horns) retain the nectar secreted by nectaries located inside the stigmatic chamber within the flower (Galil and Zeroni, 1965). The stigmatic surfaces have been shifted laterally and are enclosed by the closely adjoining anther wings. The pollen sacs (pollinia) of two adjacent anthers are joined by translator arms to a black body (corpusculum or gland) located just above the slit of the stigmatic chamber formed by the projecting anther wings. Pollinia removal is effected when a groove in the corpusculum catches on a hair of an insect leg. When the insect flies to another flower on a different plant the pollinium lodges in the chamber, thus effecting cross-pollination. Quantitative studies of the reproductive biology I Received for publication 26 June 1975. I wish to thank Janis Antonovics for supplying encouragement, ideas, and criticism. Gordon Whitaker provided able assistance in the field during the re-collection of the transect. Henry M. Wilbur and Mary F. Willson suggested improvements in an earlier draft of the manuscript. The line drawings were executed by Karen Teramura. Funds for use of the Duke University Phytotron were supplied by NSF Grant GB-28950 and for travel by an NSF Graduate Fellowship. of the Asclepiadaceae were first attempted in the 1940's when commercial use of species of Asclepias was proposed (Fischer, 1941; Whiting, 1943; Stevens, 1945; Moore, 1946, 1947; Sparrow and Pearson, 1948). These early studies raised many questions regarding reproductive biology, but no general agreement could be reached on even such basic matters as the precise mechanism of pollinia removal and insertion, the relative importance of mechanical versus physiological interspecific isolating mechanisms, the possibility of self-compatibility, and factors limiting fruit-set to levels of 1 %. Floral morphology (Safwat, 1962; Galil and Zeroni, 1965, 1969), specificity of pollinia transfer (Macior, 1965), and temporal and spatial aspects of the floral display (Willson and Rathcke, 1974) have all been re-examined. Life history characteristics (Wilbur, 1976) and interspecific variation in ovule and pollen production (Bell, 1974) have also been analyzed recently. This paper reports detailed studies on pollination, breeding system, and fruit-set in Asclepias tuberosa L., the common roadside "butterflyweed." This species was studied previously by Woodson (1947, 1953, 1962, 1964). MATERIALS AND METHODS-In July, 1973, twenty flowering individuals were taken from each of five populations located more or less equidistantly along Woodson's (1947, 1962) 1200-mile west-to-east transect. The populations were therefore separated by average distances of about 300 miles. The plants were cut back to the rootcrown, established in pots in a controlled environment greenhouse and grown under natural light in a temperature regime of 23 C day and 20 C night. The plants flowered after two months, and all

Nectar Robbing and Pollination of Lantana camara (Verbenaceae)

Abstract: Floral robbers are categorized as nectar-foraging, nectar-foraging-perforating, and pollen-foraging. Trigona fulviventris is a nectar-foraging-perforating robber of yellow flowers of Lantana camara. Flower head maturation of L. camara is centripetal and flowers turn from yellow to reddish-orange, resulting in inflorescences of central yellow flowers with peripheral orange and reddish-orange ones. In the laboratory, seed set occurs only after cross-pollination; in the field, the presence of orange and reddish-orange flowers is related to decreased nectar robbery of yellow flowers. Co-evolution of L. camara, its butterfly pollinators, and T. falviventris has presumably involved increased nectar production of this plant to feed both its pollinators and robber. THIS STUDY WAS MADE because of our limited knowledge of the pollination ecology of Latana camara; furthermore, it is the first record of nectar robbery by the stingless bee, Trigona (Trigona) fulviventris, or any other meliponine apid. T. fulviventris is a nectar-foraging-perforating robber of L. csmara which bites holes below the bases of the stamens (fig. 1) and probably effects little if any cross-pollination. Possible effects of its robbing behavior on butterfly pollinators and the general pollination ecology of this plant in Costa Rica were investigated. L. camara is a woody shrub distributed throughout tropical Central America; it has also become naturalized in other tropical and subtropical areas. Flowers gradually turn from yellow to reddish-orange in three days in the plants studied. Dronamraju (1958, 1960) reported that butterflies preferentially visit yellow flowers of Lantana and Muller (1877) hypothesized that having varicolored flowers makes inflorescences more visually attractive in potential pollinators. In Costa Rica, in addition to Lawtana, Trigona spp. rob nectar by perforation from Hamelia patens, Clerodendrum paniculatum, Rondeletia, and Malvaviscus. In other parts of the world, other genera of bees (e.g. Bombus, Apis, Xyloco pa, and Megachile) are or are likely to be nectar-foraging-perforating robbers of various genera of plants having flowers with tubular corollas (see for examples, Sprengel 1793, Darwin 1876, Kerner 1895, Porch 1924, Meidell 1944, Schremmer 1955, Meeuse 1961, Hurd and Linsley 1963, Macior 1966, 1970, 1971, Faegri and van der Pijl 1971).

On the Relative Advantages of Cross-and Self-Fertilization

Abstract: An optimality model based on the tradeoffs between seed set efficiency and outbreeding is presented that predicts under what conditions selfing should be favored over outcrossing. The model predicts that local density and distributional pattern, degree of environmental predictability, and adult and seed longevity are the independent variables that determine the shape of the marginal benefit curves for seed set and offspring heterogeneity. Some data supporting the model are presented derived from a study of species of the genus Leavenworthia (Cruciferae). Flowering plants can reproduce in two basic ways. All species have the capacity to produce new individuals by vegetative means, such as runners, stolons, bulbs, corms, etc. Nearly all species in addition reproduce by seeds. The embryo contained in the seed is normally the result of the union of the egg cell with a gamete produced by a pollen grain from another plant and transported to the style by some pollinating agent. However, in a number of species, pollen from the same plant occasionally, or habitually, fertilizes the egg. Finally, seeds can also be produced apomictically without recourse to fertilization. From an evolutionary standpoint, the latter is better viewed not as a form of reproduction, but

Plant dispersion, pollination and gene flow in Viola.

Abstract: The effect of pollinator activity on gene flow in colonies of Viola were examined by measuring pollinator flight distances, the frequency of interplant flights and percent pollination under different plant spacing patterns. Pollinator flight distances were directly proportional to spacing parameters while the frequency of interplant flights and percent pollination were inversely proportional to spacing parameters. These findings show that gene flow is reduced by pollinator activity over a wide range of spacing parameters but in populations with low spacing means highly localized gene exchange can occur within the colony. Isolation of colonies may be expected under these circumstaces and cleistogamy may be the optimal breeding system. However, chasmogamous flowers may be important both in promoting within-colony gene exchange and long distance between-colony gene exchange corresponding to the sexual functions proposed in several recent models. Viola colonies appear to be semi-isolated demes with pollinator service which can bring adaptive genes to high localized frequencies, but which maintains low frequency, long-distance gene dispersal. This pattern corresponds to the "Shifting Balance" view of evolution.

Inbreeding in neighboring trees in two White Spruce populations.

Abstract: ELDRIDGE, K. G.: Genetically improved eucalypt seed for Australian pulpwood forests. Appita 25: 105-109 (1971). HEIMBITRGER, C.: Breeding for disease resistance in forest trees. Forestry Chronicle 38: 356-362 (1962). LEPISTO, M.: Accelerated birch breeding in plastic greenhouses. Forestry Chronicle 49: 1-2 (1973). NEL, P. M.: The breeding of eucalypts in South Africa. South Afr. For. Jour. 54: 17-21 (1965).

Pollination, fecundity, and the distribution of moth-flowered plants.

Abstract: The upper altitudinal limits of moth-pollinated plants are correlated with temperatures that restrict the activity of their crepuscular pollinators. The activity of hawkmoths decreases with temperature below 15'C. The number of Calliandra flowers visited and pollinated and the amount of pollen on Oenothera stigmas decrease with elevation. Fruit set and fecundity of most Calliandra populations and fruit set of Yacca are also negatively correlated with elevation. We suggest that the upper altitudinal limits of hawkmoth-flowered plants in tropical montane regions are restricted by low temperatures which restrict the activity of their pollinators. Because the hawkmoth-flower interaction may be diurnal in temperate regions and tropical habitats without hummingbirds, we speculate that a shift in the interaction from a nocturnal to a diurnal rhythm in New World tropical montane regions is inhibited by competitive interactions with hummingbirds. FECUNDITY IN XENOGAMOUS (OUT-CROSSING) PLANTS iS, in part, a function of the interaction between their flowers and pollen vector (s). In some animal-pollinated plants, maximum fecundity occurs only if each flower is visited a number of times. In Oenothera fraticosa L. a minimum of three or four visits by honey bees is required to transfer enough pollen to achieve maximum fecundity (Primack and Silander, pers. comm.). Environmental factors that limit the activity of a plant's pollinator(s) decrease the plant's fecundity (Cruden 1972) because each flower receives less than the number of visits required to maximize fecundity. Three sets of observations suggest that low temperatures may influence the fecundity and thus limit the distribution of moth-flowered plants in montane regions. First, low temperatures resulted in poor pollination of Mirabilis nyctaginea (Michx.) MacMill. flowers (Cruden 1973). Second, field observations in Mexico indicated that hawkmoth-flowered plants, which are relatively common in lowand mid-elevation ecosystems, are absent or rare in high-elevation ecosystems. This observation was corroborated by a survey of specimens of hawkmoth-flowered species in five genera (fig. 1). Finally, various species of Yucca in the western United States reach their upper elevational limits at 2600 m (Harrington 1964, McCleary and Wagner 1973), and in California most Yucca populations occur below 2000 m, with a few found up to 2450 m (Munz 1965). These observations suggest a testable hypothesis. Because temperatures decrease with increased elevation and moth activity decreases with decreased temperature (Harling 1968), moth activity should decrease with elevation resulting in a negative relationship between plant fecundity and elevation. We present data on pollination success, fruit set, and fecundity in moth-flowered species of Calliandra (Leguminosae: Mimosoideae), Oenothera (Onagraceae), and Yicca (Agavaceae) that support the above hypothesis and discuss the distribution of moth-flowered plants with respect to pollinator acti-

The pollination biology of tilia

Abstract: A B S T R A C T An anthecological study of Tilia in the Great Plains and New England was undertaken for both native and introduced species. The floral bracts are postulated as being at least as important in pollinator attraction as they are in fruit dispersal. A characteristic sweet odor is always present, but becomes stronger at dusk. Flowers are protandrous with anthers opening for the first time late in the afternoon and releasing pollen abundantly for about 24 hr. Initial nectar production coincides with stigma receptivity which begins late in the afternoon, but on the second day a flower is open. Sixty-six species of insects in 29 families were collected. Bees and flies are the most common diurnal visitors and moths are the primary nocturnal visitors. Samples of pollen taken from the insects indicate a relatively high constancy. Experimental tests show that Tilia is not apomictic or self compatible. Anemophily plays a secondary role to entomophily in pollination. Nocturnal pollinators are slighly less effective than diurnal pollinators in effecting fruit set. Although nocturnal pollinators are favored by the syndrome of floral characteristics, it is concluded that Tilia is a generalist in regard to pollination. It is proposed that the lack of clear morphological differences between Tilia species leads to pol

Silene otites (caryophyllaceae) pollinated by nocturnal lepidoptera and mosquitoes

Abstract: SUMMARY Indications of the existence of plants of Silene otites in the dunes in The Netherlands (Coastal plants), with wind pollination additional to insect pollination, gave rise to this study. Morphological evidence, such as stickyness of pollen, together with field observations on the wind dispersal of pollen and experiments with bagged flowers, prove the absence of wind pollination. Insect visitors mainly belonged to the Lepidoptera (Microlepidoptera, Geometridae and Noctuidae) and to the Diptera (Culicidae). Observations of the dusting with pollen and of the flower visiting behaviour indicate that insects of these two types pollinate. This has finally been proved by experimental confinement of insects with bagged flowers. Neuroptera are visitors but are not pollinators. The pollination of flowers by mosquitoes is new for Europe.

The Pollination and Androphore Structure of Some Amazonian Lecythidaceae

Abstract: Pollination observations were made for six Amazonian species of Lecythidaceae from five genera. Large bees were found to be the pollinators in five species and wasps in one species, Couroupita subsessilis Pilg. The species studied were allogamous, and flowers lasted only a single day. The diversity of androphore structure is discussed. The complex androphore structure is concluded to have evolved to protect the fertile stamens and to increase efficiency of pollination rather than as an adaptation to new pollinators. THE NEOTROPICAL LECYTHIDACEAE have an interesting series of androecium structures. These vary from the actinomorphic circles of stamens united only by a basal annular ring in Gustavia, or almost free in Grias, to the complex, highly zygomorphic androphore of Eschweilera, Couroupita, and other genera (fig. 1). With this large amount of variation in the staminal apparatus of the family, the type of pollination should be interesting for the inrterpretation of trends in the evolution of the flower. There is little published on pollination in the family, probably because of the difficulty of observation in large forest trees. In recent field work I have observed the pollination of species in several genera of the family. These pollination data are presented here with a summary of the androecium structure of the family.

Pollination as a factor limiting the yield of field beans (Vicia faba L.)

Abstract: Self-pollinating and cross-pollinating by hand samples of flowers in field bean crops usually gave an increased set of seed compared with control flowers left to be pollinated naturally. Hence, insect pollination of field bean crops is often inadequate. In large fields of more than 12 ha the seed yield was greater by plants near the edge than near the centre. Fewer pods were produced from nodes at the upper than the lower parts of a stem, and they contained fewer seeds which were of a smaller size.

Pollination Ecology of Platanthera (Habenaria) Ciliaris and P. blephariglottis (Orchidaceae)

Abstract: The pollination ecology of Platanthera (Habenaria) ciliaris and P. blephariglottis in Booth Lake Bog, Berrien County, Michigan, was investigated during 1973 and 1974. Platanthera ciliaris was pollinated mainly by Papilio troilus (spicebush swallowtail) and P. blephariglottis mainly by several species of moths; the main difference between these orchids was color. Butterflies apparently were attracted by the bright orange color of P. ciliaris, whereas moths appeared to be attracted more by scent than by color. The evaluation of capsule set indicated that in P. ciliaris half as many flowers were pollinated in a semiopen habitat compared with an open habitat, whereas in P. blephariglottis nearly equal pollination occurred in the open and semiopen habitats. Platanthera ciliaris had a higher mean number of flowers per raceme, which may indicate some selection pressure for larger racemes due to the visual requirements of the butterfly pollinators. Autogamy did not occur in these two Platantherans; however, artif...

Breeding systems and pollination in New Zealand Parahebe (Scrophulariaceae)

Abstract: New Zealand species of Parahebe are homogamous, self-compatible hermaphrodites. P. canescens, P. catarractae, P. decora, P. hookeriana, P. linifolia ssp. linifolia, P. lyallii, and P. olsenii are predominantly entomophilous, whereas P. birleyi, P. cheesemanii, P. laxa, P. linifolia ssp. brevistylis, P. plano-petiolata, P. spathulata, and P. trifida are predominantly autogamous. The morphological syndromes associated with entomophily and autogamy are described. In Parahebe, lowland, widely distributed species are adapted to entomophily, whereas most species occupying various subalpine, alpine, and nival habitats are adapted to autogamy.

Pollen flow in distylous populations of Amsinckia (Boraginaceae)

Abstract: Stigmatic pollen loads were analyzed from naturally pollinated pin and thrum form flowers of Amsinckia douglasiana and A. vernicosa var. furcata. Pin stigmas captured more total pollen than thrum stigmas. Pins experienced either net self-pollination or random pollination. Thrum stigmas experienced significant disassortative pollination. Comparing pollen loads from intact and emasculated thrum flowers of A. douglasiana indicated that self-pollination and geitonogamy were relatively unimportant in the pollination of the thrum form. The level of disassortative pollination of A. vernicosa var. furcata does not appear to be high enough to account for the level of disassortative mating observed by progeny testing, suggesting that this species may possess an incomplete stylar self-incompatibility system such as has been reported in A. grandiflora.

A study on the pollination mechanism in field beans (Vicia faba L.)

Abstract: Inbred lines and hybrids of English tick and horse beans and exotic stocks were studied with respect to pod set, floral structure and pollen production and germination to find out why most inbred lines set few or no seeds without tripping whereas most hybrids and some inbred lines set equally well with or without tripping. The most important outcome was new information on variation between genotypes in flower structure and pollen quantity and on how these two characters affect the mechanics of self-pollination. Though heterosis in terms of abundant pollen production could be a factor in the self-pollinating ability of hybrids, some of the inbred lines were capable of self pollination despite limited pollen production, because the structure of the flower permitted the pollen to reach the stigma via a short route. The floral features associated with the ability to self-pollinate in the inbred lines included a relatively short style bending at more or less a right angle, few and short stylar hairs and stigmatic papillae, and less pronounced ridges on the inside of the keel petals. The implications of these findings to the development of self-pollin ated varieties of field beans are briefly discussed.

Submarine pollination in seagrasses

Abstract: THERE is great interest in water plants and their adaptation to the aquatic environment. Seagrasses, in the family Cymodoceaceae, are the only wholly marine group of flowering plants which carry out their entire life cycle in the sea1. The male and female flowers are borne on different plants. Consequently, their pollination mechanism presents intriguing problems, for terrestrial angiosperms, from which seagrasses presumably arose2,3, shed dry pollen. This becomes hydrated only after alighting on the female stigma, where recognition events determine acceptance or rejection of the pollen4. These events seem to involve interactions between surface proteins or glycoproteins borne by both pollen and stigma5. The pollen proteins are released on to the stigma during normal pollination6,7, but are lost from the surface whenever pollen is wetted8. The system found in terrestrial species could thus hardly operate with submarine pollination. We have found that adaptations have occurred in both pollen and stigma of the seagrasses, accommodating the pollination system to the marine environment. Changes in the shape and form of the pollens, together with the loss of the outer wall layer, make it possible for the pollen to be carried in water currents as long, rope-like masses. The receptive stigma cells secrete a proteinaceous surface layer that is not dispersed in seawater, providing a suitable medium for trapping the pollen during submarine pollination.

Early seed development after crossing of Trifolium ambiguum and T. repens

Abstract: Hand pollination of Trifolium ambiguum Bieb. (2n = 4x = 32) with pollen from T. repens L. (2n = 32) resulted in fertilisation and pod enlargement, but no mature viable seed was produced. Hybrid embryos and endosperms were developmentally more advanced than those of T. ambiguum (4x) controls for the first 2 days after pollination. Subsequently hybrid embryo growth slowed, and although an advanced globular or early “heart” stage was attained at 5–6 days after pollination normal differentiation did not proceed beyond this stage and almost all embryos were visibly degenerating by 7–9 days after pollination. Occasional abnormal undifferentiated or partially differentiated embryos were found still showing substantial numbers of cell divisions at 10–13 days after pollination. Hybrid endosperms varied in their development, but never exceeded the 128-nucleate level. By 5 days after pollination all were degenerating. Endosperm failure appears to be a major cause of seed failure in this cross.

Heat production and pollination in Araceae

Abstract: The ecological role of heat production in Araceae has not been extensively investigated. The possibility that carbon dioxide and heat production are components of a carrion, dung, and mammal mimicry syndrome deserves consideration. Warm inflorescences might also serve as significant shelters for pollinators of species flowering during cold seasons.

The Pollinating Efficiency of Honeybee and Bumblebee Visits to Flowers of the Runner Bean Phaseolus coccineus L.

Abstract: In Britain, the runner bean (Phaseolus coccineus L.) is almost entirely insect pollinated. Darwin (1858, 1876), Free (1966) and Free & Racey (1968) showed that plants enclosed in cages or glasshouses to exclude insects set very few pods compared with plants in the open or plants caged with honeybees and bumblebees. However, Tedoradze (1959) in Russia, obtained more variable results. In one year, a plot of beans visited by honeybees produced more seed than one from which bees were excluded, but this was not so in another year. Similar experiments by Mommers (1971) in Holland, also showed that pollination by insects was not always needed. He suggested that pollination requirements may differ between varieties. Free & Racey (1968) demonstrated that in cages honeybees and bumblebees were more effective pollinators of runner bean flowers than blowflies. Blackwall (1971) stated that several small insects, e.g. pollen beetles (Meligethes spp.) and Thrips spp. may contribute to pollination, but that bumblebees were probably the chief pollinators. We have now examined in more detail, and under more natural conditions, the relative value of honeybee and bumblebee visits to the flowers. Previous workers enclosed insects and plants continuously during the flowering period, conditions that could have affected insect behaviour and adversely affected plant growth and yield (Free 1966). Also, Blackwall (1969) demonstrated an inverse relationship between pod-load and pod-setting (i.e. flower fertility), suggesting that plants could partly compensate for inadequate pollination of early flowers by producing relatively more pods on flowers pollinated later in the season. Thus, comparing total yields from plots caged with different insects may not provide valid comparisons of their value as pollinators. Our method, although using cages, partly avoided these problems: first, cages were removed for specified periods to allow insect visits and minimize any effect on insect behaviour; secondly, uncovering the plots periodically should have reduced direct effects on plant growth; and thirdly, the proportion of flowers capable of setting pods was kept more or less constant.

Birds as Possible Pollinators of Acacia pycnantha

Abstract: Acacia pycnantha, like many members of its genus, produces nectar from a gland at the base of the petiole. Nectar is apparently produced only when the plant is flowering and only on petioles close to the inflorescences. The nectary seems poorly placed to attract insect pollinators, but honeyeaters and silvereyes take the nectar, brush against the flowers and could effect pollination. Insects also visit the nectaries and flowers and may act as an additional attractant to the birds.

Pre-fertilization barriers to hybridization in the Poplars

Abstract: Artificial hybridization has played a lengthy and important role in the domestication of the poplars. Contributing factors include the convenience of reproductive manipulation, the short time required for superior hybrids to be recognized, and the ease with which successful cultivars can be propagated. While the breeder's intuition played a major factor in early hybridization efforts, attempts at capturing heterosis or combining desirable traits have become increasingly systematic and during the past 40 years have resulted in thousands of hybrid cultivars being tested on an extensive scale in many parts of the world (e.g. STOUT and SCHREINER, 1933; HEIMBURGER 1940, 1968; HYUN and HONG, 1959; ZUFA, 1968; STEENACKERS, 1969; CHUNG and SON, 1972). However, the transfer of genes among certain poplar species, particularly those belonging to different sections of the genus, is constrained by barriers whose site and action are still unknown in all but a few cases (reviewed in ZSUFFA, 1975). The observation by STETTLER, 1968; STETTLER and BAWA, 1971, that pollen mixes of killed compatible (= \"mentor\") lected from trees in Seattle, Washingon; pollen of the remaining species was provided by L. ZSUFFA, Ministry of Natural Resources, Ontario, Canada, and D. EINSPAHR, Institute of Paper Chemistry, Appleton, Wisconsin, receipt of which is gratefully acknowledged. Female branches were maintained in water culture as previously described (STETTLER and BAWA, 1971). Flowers were usually receptive 3-5 days after being brought into the greenhouse. Pollination was performed by inserting attached catkins into a small glass via1 containing pollen and lightly dusting the flowers using a camels-hair brush.

Honeybee Behaviour as Affected by Plant Height and Flower Colour in Brussels Sprouts

Abstract: SummaryDifferences in plant height and flower colour of the parent lines involved in the production of hybrid seed of Brussels sprouts affected the behaviour of honeybees during pollination. Where the inbreds were of somewhat similar plant height but differed in flower colour, the effective self to cross movement of bees was 23: 1. Where plant height was very different but flower colour the same, the effective bee self to cross movement was 33: 1. Bees crossed freely between tall plants and between short ones, but rarely between tall and short, thus encouraging selfing and sibbing (sister-brother mating).These results suggest that, when honeybees are used as pollinators in hybrid seed production, parent plants should be of similar height and flower colour if crossing between the inbred lines is to be improved.

Increased atmospheric humidity post pollination: A possible aid to the production of inbred line seed from mature flowers in the Brussels sprout (Brassica oleracea var. Gemmifera)

Abstract: In two highly self incompatible inbred lines of Brussels sprouts the effect of increased atmospheric humidity post pollination was examined immediately following 1) hand pollination of green buds and open flowers, and 2) blowfly pollination of open flowers. Data were obtained for mean number of seeds set per pollination, mean number of fruits setting seed, and mean number of seeds produced per fruit which set for both varieties. Measured as number of seeds produced per minute spent pollinating, it was clear that open flower pollination followed by high humidity conditions was a much more efficient method of producing inbred line seed (46 seeds/minute) than green bud pollination (27 seeds/minute).