Abstract: By means of a Burkard Seven Day Recording Volumetric Spore Trap located in central Stockhom, about 20 m above ground level, pollen was sampled between March and August for eight consecutive years (1973–1980). The pollen spectra with special reference to trees, in particular Betula and Pinus, were compared as to amount and distribution of taxa. No co-variation between the two latter genera was noted. Betula showed a ± distinct biennial periodicity. The main pollen season is defined. Betula and Pinus showed slightly different patterns regarding beginning and duration of the pollen season; mean intensity is compared.

Abstract: In angiosperms selection has led to the utilization of numerous substances other than pollen and nectar that help to insure repeated visitation by pollinating animals. Here, we group the various substances into nonnutritive and nutritive rewards and discuss within each group the specific kinds that occur. In our discussion of nutritive rewards, we emphasize floral oils, lipids produced by one of two types of specialized secretory organs called elaiophores and which serve as nutritive rewards for certain New World anthophorine bees. Although discovered only within the last 15 years, the syndrome of oil production now appears to be one of the most widespread kinds of floral rewards. We report here for the first time the occurrence of oil production in the Solanaceae (Nierembergia). It is apparent that oil production has evolved independently many times, but plants which produce oils that are collected by female anthophorine bees show similarities in the chemistry of the oils and the types of structures that produce them. It is not clear whether other groups of plants reported to produce oils but which are not pollinated by anthophorine bees possess an analogous system or not. Floral rewards can be considered any component of a flower or inflorescence that is used by animals and, because of this use, insures repeated visitation that will lead to pollination. Without doubt, pollen and nectar are the primary rewards offered by flowers to visiting animals in order to buy their services as pollinating agents. Of the two, nectar is sought by a wider array of animals than pollen. On the other hand, pollen is the primary reward for which bees, probably the single most important group of pollinators, visit flowers. The role of pollen and nectar in the attraction of potential pollinators has been appreciated for hundreds of years, but we have only recently begun to realize the complex nature of these two rewards. Nectar, for example, formerly considered to be a simple sugar solution, has been shown to consist of a variety of chemicals dissolved, or suspended, in an aqueous solution. These range from mixtures of one to three common sugars (glucose, sucrose and fructose) to more complex sugar solutions (Percival, 1961) or combinations of sugars, free amino acids, "vitamins," lipids, and other compounds (Baker & Baker, 1975; Baker, 1978). The complex chemical nature of pollen has been realized for a century (refs. in Barbier, 1971), but only in the last twenty years have researchers begun to explore the varied nature of specific enzymes contained in the pollen walls and their possible roles in incompatibility reactions (Stanley & Linskens, 1974). These same enzymes may play a role in pollen recognition by specific pollinators. The chemistry of pollen is in fact so complex that it has been impossible to provide a precise description of pollen chemistry that is all-inclusive. The continued elucidations of the intricate nature of these common rewards has spurred studies of pollination biology and provided an impetus for the investigation or reinvestigation of other floral rewards.

Abstract: SUMMARY Failure of regeneration of Tilia cordata in north-west England is associated with almost complete sterility of the seeds. Between 1964 and 1979 significant numbers of fertile seeds were recorded only after the exceptionally warm summer of 1976. In contrast, large or moderate crops of fertile seed were produced at sites in central and southern England in at least 8 of these years. Comparative studies of pollination, fertilization and seed development at sites in north-west England, central England and northern France show relatively small differences in the proportions of flowers which are pollinated but significant differences in the rates of extension of pollen-tubes. In samples collected in 1977 from north-west England germinated pollen was present on most receptive stigmas but many pollen-tubes extended only a short distance down the style and the few which reached the base appeared to be arrested in the ovary wall. In French samples pollen had germinated on all receptive stigmas and numerous pollen-tubes had reached the ovary within 2 days of pollination. These differences cannot be attributed to variation in the incidence of self-pollination, as at least some trees of T. cordata in northern populations are almost certainly self-fertile. The differences are correlated with temperatures at the time when the samples were collected. When pollen-tubes are growing in sucrose solutions, their rate of extension shows a large response to temperature over the same range (15 to 25°C). Analysis of records shows that temperatures in north-west England at the time of flowering are frequently too low to permit fertilization. This is confirmed by studies of the development of ovules. Although a high proportion of ovules in T. cordata lack embryo sacs, normally at least one is functional in each ovary. In over 90% of fruit formed in north-west England, embryos are contained in none of the 10 ovules. In less than 10% of fruit partly developed embryos are present, suggesting that temperatures are also too low in late summer to allow completion of their development.

Abstract: . 1. Previous accounts of the feeding behaviour of hoverflies (Diptera: Syrphidae) are contradictory and in many cases do not correspond with field observations. 2. Patterns of feeding on nectar and pollen differ between species: these patterns are correlated with morphological differences. 3. The data indicate that there are two correlates of increasing tongue length: first, the proportion of pollen in the diet decreases; and second, the flies concentrate on visiting flowers with longer corollae, which contain more nectar sugar. 4. Reasons for these effects are discussed.

Abstract: (1) An analysis of the relationship between pollen frequency and plant numbers in a given area is an essential step if pollen diagrams are to be used as records of past tree populations. This relationship was studied by comparing the pollen content of moss samples with the vegetation within 20-m radius of each sample site, at seventy-eight sites in the New Forest, Hampshire, The Mens and the Cut, Sussex, and Bradfield Woods, Suffolk. (2) Linear regression analysis was used to analyse the relationship between the intensity of pollen deposition and tree basal area, and between pollen percentages and percentages of total basal area per plot for the major tree species. (3) The rank-order of taxa for number of pollen grains deposited per unit of tree basal area for all sites was Betula > Pinus > Taxus > Alnus > Quercus > Fraxinus - Fagus Salix. The correlations between pollen and basal-area data were significant for all tree taxa except Fraxinus, Fagus and Salix; the correlations for these taxa were higher when the data were expressed as percentages. There was a wide range of pollen representation for different shrub and herb taxa. (4) With the exception of Quercus, a consistent order of pollen representation for the major forest trees of northern Europe can be recognized. Senescent Quercus populations are a contributory factor to the low pollen representation of this taxon in south-east England. (5) The regression coefficients derived in this study can be used to convert fossil pollen counts into estimates of tree basal area for areas of 20-m radius around very small sedimentary basins. An example is given for a small woodland pond in Suffolk.

Abstract: Male gametes ofPlumbago zeylanica were examined in pollen grains and tubes using light and electron microscopy of chemically and physically fixed tissues, and Nomarski interference microscopy of isolated, living sperm cells. Male gametes are elongate, spindleshaped cells containing a nucleus, mitochondria, ER, ribosomes, vesicles, dictyosomes, probable microfilaments, and a variable number of plastids. In mature pollen grains ofP. zeylanica, the two sperm cells are directly linked; they share a transverse cell wall with plasmodesmata and are enclosed together by the inner vegetative cell plasma membrane. One of these two sperms is also associated with the vegetative nucleus as a consistent feature of pollen grain organization. The basis of this association appears to be a long, narrow projection of the sperm cell (averaging < 1 μm wide and about 30 μm long) which wraps around the periphery of the vegetative nucleus and occupies embayments of that nucleus. This association is maintained throughout pollen tube growth but becomes less extensive near the completion of tube growth and is severed following tube discharge. The consistent occurrence of the sperm-vegetative nucleus association in pollen grains, tubes and isolated pollen cytoplasm suggests that the two structures may be directly connected, but attempts to visualize this type of connection were unsuccessful. Possibly, the entwining nature and extent of complementary interfaces between vegetative nucleus and sperm may have a role in stabilizing their association. Functionally, the two sperms and vegetative nucleus appear to travel as a linked unit within the pollen tube, possibly increasing the effectiveness of gamete delivery and helping to ensure nearly simultaneous transmission of sperms into the receptive megagametophyte.

Abstract: Pollen flow in a population of Delphinium virescens was examined by experimentally investigating the foraging behavior of the pollinators, Bombus americanorum. When bumblebees visited inflorescences with copious nectar they picked up more pollen and flew a shorter distance than when they visited infloresences with little nectar. Thus, short flights were more effective pollen dispersal flights and pollen flow was thereby reduced. These results and other factors are discussed as to their potential effects on gene flow within the plant population.

Abstract: All main types of pollen grains in Rosaceae seem to be variations of the same theme: a tricolporate pollen, with or without operculum. In most cases the exine sculpture is the best feature for classification; and combined with other characteristics, it is possible to separate some species earlier considered undistinguishable.

Abstract: The pollination biology of angiosperms affects the quantity and qual- ity of seeds produced by an individual. The amount of genetic variability present in the seeds of a single fruit is dependent on the number of male parents involved in fertilization. The variation in genetic relatedness of developing siblings in an ovary may lead to varying degrees of competition among young seeds for maternal nu- trients. Kin selection theory predicts that closely related seeds resulting from fertil- ization by a single paternal parent will compete less with each other than seeds fertilized by different fathers. Ramdom dispersal of single pollen grains character- istic of wind pollination tends to produce less closely related seeds in multi-ovulate ovaries. Pollen transferred between flowers in large aggregations by specialized an- imal pollinators gives rise to seeds that are full siblings. The evolution of animal pollination, large pollen unit size, and multi-ovulate ovaries in some angiosperms may be understood in terms of competitive interactions among the developing seeds. The multi-seeded angiosperm fruit contains a unique collection of in- dividuals. These individuals are young sporophytes that share a common maternal parent. The group is special because of the relatively high ge- netic relatedness of its members. The high genetic similarity is important in two ways. First, within a single fruit it sets an upper limit to the amount of genetic variation controlling the rate and quality of seed development. Second, the large number of genes "identical by descent" shared by these sporophytes will augment the inclusive fitness component of offspring reproductive success and influence their competitive interactions. Inclu- sive fitness is defined here as the total reproductive value of an individual including personal production of offspring plus the individual's effects on the reproduction of relatives (Hamilton 1964; West Eberhard 1975). Haldane (1923) originally noted that the pollination system in angio- sperms determines the number of paternal parents involved in fertiliza- tion. Later Hamilton (1964) suggested that seeds in the flowering plant ovary can be half-sibs, full-sibs, or genetically identical individuals de- pending on the manner in which pollen is transferred between plants. He also pointed out that the variation in genetic relatedness of sibs might influence the degree of competition and cooperation among them. To date there has been no experimental confirmation of the hypothesis that kin selection has led to the evolution of cooperative interactions among fertilized ovules in the angiosperm ovary. The difficulties encountered in studying kin selection as an evolutionary process in the laboratory have been pointed out by Wade (1980). In the present paper I attempt

Abstract: Maize (Zea mays L.) plants subjected to severe deficiency of boron (0.0026 ppm B) failed to produce tassels with functional flowers. In plants subjected to moderate deficiency of boron (0.013 ppm B), emergence of tassels and anthesis was suppressed and delayed. In a large percentage of boron deficient plants the stamens lacked sporogenous tissue and appeared as staminodes or floral appendages that either lacked or had branched vascular supply. The apparently normal stamens of these plants also failed to dehisce and showed a marked decrease in pollen producing capacity, pollen size and pollen germination. Even in plants that were only marginally deficient in boron (0.066 ppm B), without any foliar symptoms of boron deficiency, pollen grains showed poor germination and changes in enzyme activities. Pollen grains of such plants had low activities of catalase, acid phosphatase, starch phosphorylase and invertase and high activities of ribonuclease and amylase.

Abstract: The relative efficiencies of native bees and honey bees in pollinating sunflower were compared with male sterile and male fertile lines. Wild bees as a group and some oligolectic females were more effective in pollinating florets than were the apids (hon ey bees and bumble bees). In comparisons of the fidelity of bee visitation to either sterile or pollen varieties, apids preferred male sterile rows, some wild bee species were evenly distributed be tween sterile and pollen rows, and other wild bees preferred pollen rows. In comparisons of the amount of pollen carried on a bee body, oligolectic sunflower bees carried more pollen than did other kinds of bees. Few researchers have examined the role of bees in the production of sunflower seed since this plant has become an important oil seed crop (Car ter, 1978). In fact, so little is known concerning the diversity of bee species and their relative efficiency as pollinators of this crop that most commercial sunflower producers use self-fertile varieties (Fick and Rehder, 1977). Some researchers have suggested the use of honey bees, Apis mellifera L., as pollinators, but the recommended numbers of colonies vary from 1 to 51 hectare (McGregor, 1976). The sunflower is a native North American crop species with which many native bee species have probably co-evolved (Hurd et al., 1980). Many species of native bees are commonly observed associated with commercial plantings of sunflower, but their role in seed production has not been in vestigated. Parker (1980) found that sunflower oligoleges (bees restricted in pollen utilization to sunflower or closely related composites) carried more pollen on their body hairs than did sunflower polyleges (bees that visit many crop species including sunflower). However, relative effectiveness of these groups as sunflower pollinators was not determined in his study. This study was conducted 1) to compare different species of native bees with honey bees as pollinators of sunflowers, and 2) to compare the fidelity of bee species to male fertile or male sterile lines (most commercial self-fertile Received for publication 24 May 1980. This content downloaded from 40.77.167.48 on Thu, 15 Dec 2016 04:57:19 UTC All use subject to http://about.jstor.org/terms 62 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY varieties are produced by hybridization of male sterile and male fertile lines, and bees are the mechanism of pollen transfer). Methods and Materials plots: Sunflower was grown at the North Farm at Logan, Utah in Mill ville silt loam. Northrup King Co., Woodland, California, supplied 6 male sterile lines (SW 504, 506, 509, 517, 526) and 1 male fertile line (RW 637). Twenty-four rows (.7-m apart and 16-m long) were planted. Rows 1, 2, 9, 16, 23, and 24 were sown with the male fertile line and the remaining 3 blocks (rows 3-8, 10-15, and 17-22) were divided in half and sown with the 6 male sterile lines. counts: Bloom began on August 13 and ended on September 4. Polli nators were counted and changes in abundance and diversity of pollinators noted on early blooming heads 3 times daily (9:00 am, 11:00 am, and 1:00 pm) on Mondays, Wednesdays, and Fridays to determine any changes in abundance and diversity of pollinators during the day. Just prior to bloom, 20 randomly chosen plants of each variety were bagged with cheesecloth to exclude insect visitors; when these heads were in full bloom, the bags were removed to allow bee visitation. After one bee visit/head, the bag was re placed to prevent additional visits. During each visit, a sketch of the flower and the route taken by the bee on the florets was made (Fig. 1). To determine if pollen was accidentally transferred with the bagging technique, we treated 10 heads as above except that no bees were allowed to land before the flower was rebagged. Any male fertile plants in the sterile plots were rogued. However, the actual number of heads used was 86; some heads were un visited and others were fertile instead of male sterile. Data on single visits/ head were lumped because of inconsistent bee visitation/variety and simi larities among varieties in percentage seed set when open-pollinated. harvesting: In October, we collected all bagged heads and recorded the number and pattern of mature seed set by opening the seed. Mature (pollinated) seed was easily distinguished by size from immature (unpolli nated) seed (Fig. 2). We determined seed yield/head of unbagged heads by sampling 12 heads/variety. Each head was sampled by removal of 6 arcs (a single row of seed from the outer edge of a head to the center) of seed at the 2, 4, 6, 8, 10, and 12 o'clock positions (Fig. 3). The number, per centage, and weight of the mature seed in each arc were recorded. An additional 102 heads (17/row) sampled randomly from each plot were used to estimate yield/hectare. pollen: To estimate the amount of pollen carried on a bee body, we collected samples of bees from male sterile and male fertile lines by catching a single bee in a long tube, adding distilled water, vigorously shaking the vial up and down until no more pollen could be seen on the bee, and then removing the bee. Only one female (Megachile parallela Smith) died when This content downloaded from 40.77.167.48 on Thu, 15 Dec 2016 04:57:19 UTC All use subject to http://about.jstor.org/terms VOLUME 54, NUMBER 1 63 Figs. 1-3 1. Pattern of bee visit on male sterile sunflower. 2. Male sterile sunflower head showing large, mature seeds at bottom. 3. Male sterile sunflower head with 6 arcs (rows) of seed removed (arrows), illustrating sampling method. This content downloaded from 40.77.167.48 on Thu, 15 Dec 2016 04:57:19 UTC All use subject to http://about.jstor.org/terms 64 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY Table 1. Average number of sunflower seeds produced per bee visit on male sterile lines of sunflower. Logan, Utah, 1979. Species and sex Observations x number of seeds Range Control Bombus 9 Apis 9 Agapostemon Melissodes 6 Andrena 9 Melissodes 9 10 6 22 13 14 5 5 0.00 0.83 2.55 3.15 7.21 12.60 27.80 (0-2) (0-23) (0-15) (0-57) (6-15) (6-70) treated in this manner. After the bees dried sufficiently, they flew off, and many treated bees were seen a short time later gathering nectar from sun flower heads. The washed pollen was centrifuged in the vial, and the number of pollen grains/insect was counted with a hemocytometer.

Abstract: In incompatible (intramorph) pollinations of the heterostylousPrimula vulgaris, pollen germination or tube growth may be partially inhibited in several sites associated with the stigma or style. Blockage may occur, a) on the stigma surface through the failure of germination or of pollen tube penetration after germination, b) in the stigma head during the passage of the tube through the specialized transmitting tissue of the head, or c) in the transmitting tract of the style. None of the barriers is complete, and the prohibition of selfing or intramorph crossing depends upon the cumulative screening effect of one following upon the other. In both morphs, the germination of incompatible pollen on the stigma is enhanced in high ambient relative humidity, but many tubes still fail to penetrate the stigma. Those that do are retarded or blocked in their growth in the transmitting tissues of the stigma head and style. Crude extracts from the tissues of the stigma head and style show some differential effect on the growth of pollen tubesin vitro, and dialysates of extracts containing high molecular weight fractions show a consistent differential effect, those from thrum tissues retarding thrum tubes while having a lesser effect on pin tubes, and those from pin tissues retarding pin tubes while having lesser effect on thrum. It is suggested that the factors influencing tube growth are present in the intercellular secretions of the transmitting tract.

Abstract: Protoplasts from a nitrate reductase-deficient mutant of Nicotiana tabacum L. were fused with protoplasts from a stamen-less, cytoplasmically malesterile cultivar of tobacco containing the cytoplasm from N. suaveolens Lehm. Plants were regenerated from the fused protoplasts and characterized with respect to stamen development, chromosome number, and chloroplast composition. Of 29 regenerated plants, stamen production was restored in 26 plants and pollen production in 22. One plant was male sterile and two plants have never flowered. Analysis of the electrophoretic mobility of ribulose-1,5-bisphosphate carboxylase (RuBPcase) showed that 19 of the plants contained RuBPcase of the N. suaveolens type, six plants contained enzyme of the N. tabacum type, and four plants contained both types. Analysis of resistance to tentoxin in seedlings from 20 of the plants demonstrated that 14 had N. suaveolens-type chloroplasts, three had N. tabacum type, and three contained both types. Many of the plants which produced stamens and pollen still contained chloroplasts of the N. suaveolens type. Thus, the trait of cytoplasmic male sterility in tobacco is not an expression of the type of chloroplast genetic material.

Abstract: Pollen analysis of a 115-m sediment core from Clear Lake, Lake County, California, provides a climatic record that is continuous for the past 130,000 yr. The pollen record reflects migrations of the tree species of the California Coast Ranges in response to the climatic changes of the last glacial cycle. During interglacials, the Clear Lake pollen rain was dominated by Quercus (oak) pollen. During cooler periods, oak pollen was replaced by pollen of coniferous species. The curve for Quercus pollen strongly resembles and is used to correlate with both deep-sea oxygen-isotope curves and the climatic record from certain European pollen studies.

Abstract: Pollen analysis of a 36 m deep core from the Niger delta was carried out with a view to obtaining direct, botanical evidence of the Late Quaternary vegetation of West Africa, particularly Nigeria and Cameroon. Radiocarbon dates were obtained for five layers in the core. Practically all the pollen was riverborne, there being no evidence of long-distance wind transport. Pollen representation seemed to decrease with increasing distance of pollen source from site. Rhizophora, the dominant component of the creek vegetation in the vicinity of the site, was over-represented all through, except for the lowest portions of the core in which the pollen spectra were dominated by fresh-water swamp forest. Variations in the pollen of Rain forest plants and fern spores and that of Northern Guinea and Sudanna savanna, respectively, were regarded as reflecting climatic changes inland. Human impact on the natural vegetation was noted, beginning from c. 2800 years BP.

Abstract: Surface pollen studies across a small, wooded raised bog at Bankhead Moss in Fife, Scotland, have revealed a pattern of pollen dispersal and accumulation showing how representative the present pollen record of the bog is of the surrounding area. Pollen accumulation in the central open area of the bog is dominated by local pollen, mainly Calluna, and Betula pollen from the woodland. Of all the pollen types produced outside the bog only Gramineae is well represented, and of all the weed taxa found locally only Plantago and Rumex consistently appear. The implications of this work for the interpretation of early periods of forest clearance using such deposits are also discussed emphasizing the likelihood of not recognizing or underestimating the extent of land cleared, particularly if clearance was taking place some distance from the site.

Abstract: Extensive analyses were made of surface soil samples and extant vegetation from Argentina, where palynological reconstructions of paleoenvironments over the last 15,000 years is underway. The major vegetation zones in the desert northwest and the sub‐antarctic southwest and south of Argentina are discernible in the relative frequency of their respective pollen assemblages. Where quantitative comparisons of plant and pollen data are possible, representation factors for the pollen taxa are calculated. In addition to the conventional approach using percentage values, principal component and cluster analysis prove to be excellent and complementary techniques in that they reduce the data set into definite groups of representative taxa, both for plants and pollen. The comparison of these groups and their respective dominance along transects indicate that, for example, in the treeless vegetation zones of the desert northwest of Argentina, the transition zone between the grassland and desert scrub (Punen...

Abstract: Southern Chile (41–56 °S), in the belt of westerly winds, receives mostly heavy precipitation, reaching 8,500 mm yr−1 near 50 °S and decreasing northwards and southwards from this latitude to ≤1,500 mm; mean January (summer) temperatures near sea level along the latitudinal gradient are 8–16 °C (refs 1, 2). Dense rain forest covers much of the region to 48 °S; south to Cape Horn, magellanic moorland prevails and rain forest becomes limited. Modern pollen measured in surface samples reflects the distribution of plant species in the vegetation. We have now applied regression equations relating present-day pollen to temperature and precipitation to fossil pollen data at Taiquemo to assess climatic conditions during the Quaternary. The results extend our previous record of the past 16,000 yr at Alerce3 beyond the lateglacial to ∼43,000 yr BP. For the 27,000-yr interval, they show mean January temperatures of 10–12 °C and mean annual precipitation centred around 1,000 mm except during the time span of ∼31,000–43,000 yr BP when amounts increased to 4,000 mm. In general fluctuations correspond to the isotopic climatic reconstruction in Antarctica4 and to changes inferred from pollen data at comparable latitudes in Tasmania5–8 and New Zealand9,10.

Abstract: Pollen of trees extracted from surface sediments of the Potomac estuary represent all components of the arboreal vegetation, with the exception of Liriodendron tuZipiJeru (tulip poplar), and reflect the major forest gradients in a broad band adjacent to the estuary. Pollen of common trees restricted to the upper watershed, 60 km upstream of the limit of tidal influence, are not present in downstream estuarine deposits. A comparison of the statistical variability in pollen data from estuarine sediments with tree data in the area adjacent to the estuary suggests that atmospheric or estuarine transport processes erase the local patchiness of the trees from the pollen distributions in the sediment. Although dispersion is selective for different pollen types, none of the pollen is transported far enough to mask regional forest gradients. Pollen distributions in Potomac estuary sediments suggest that once particles of approximate hydraulic equivalence become part of the suspended sediment load, they are not widely dispersed within the estuary before initial deposition.