Abstract: more frequently (Fragaria), and removal of floral biomass causes a reduction in the frequency of insect visits proportional to the fraction of biomass removed (Impatiens). (ii) Removal of attractive structures may cause a decline in the probability that a fruit will be formed but has no effect on the number of seeds set per fruit; thus, mutilation of essentially solitary flowers has no effect on seed-set per fruit (Impatiens), while removal of flowers from inflorescences in a species that forms several many-seeded fruits per inflorescence reduces fruit-set per inflorescence but has no effect on seed-set per fruit (Asclepias), and removal of sterile flowers from an inflorescence in which the fertile flowers yield one-seeded fruits is effective in reducing seed-set per inflorescence (Viburnum). (iii) Larger flowers may disperse a greater fraction of their pollen in unit time (Impatiens) and the removal of flowers from inflorescences causes a steep reduction in total pollen exported and a weak decline in the quantity of pollen exported per flower (Asclepias). These results are consistent with the hypothesis that a single insect visit (or a very few visits) suffices to fertilize almost all available ovules and is procured by a very small allocation to attractive structures, while much greater allocation is necessary to procure the numerous visits required to disperse a large fraction of the pollen. This inference is supported by a comparative survey of sexually dimorphic plants, in which male flowers are generally larger than female flowers, male inflorescences bear more flowers, and male plants bear more inflorescences. It is concluded that the flower is primarily a male organ, in the sense that the bulk of allocation to secondary floral structures is designed to procure the export of pollen rather than the fertilization of ovules. This conclusion may be sensitive to whether it is the flower or the inflorescence as a whole that represents the primary unit of attraction to insects. It was found that the performance of a given flower was substantially affected by other flowers in the same compact inflorescence (Asclepias), though not by other inflorescences on

Abstract: The two DNA-specific fluorochromes DAPI and mithramycin have been found to be extremely useful dyes in studies of pollen development and growth. Both fluorochromes stain nuclei brilliantly either in fixed or in living tricellular and bicellular angiosperm pollen, thereby permitting rapid scanning for pollen abnormalities and easy observation of nuclear details. These water soluble dyes can be incorporated into the germination medium for studies of pollen germination in vitro, facilitating observation of the movement of generative, sperm and tube nuclei during pollen growth. In fixed pollen, the fluorochromes bind quantitatively with DNA and thus may be used to quantitate ploidy changes and to study cell cycles during pollen development, germination and fertilization.

Abstract: A pollen analytical study of New Zealand honey provides a basis for identifying the origins of a honey in terms of locality and floral source: The information may be used to develop analytical standards for pollen, contributing to quahty control of a product offered for export or for the home market. General principles outlined by the International Commission for Bee Botany have been used as a guide, although in practice these are considerably modified. Samples were processed by acetolysis, and absolute pollen counts were obtained by spiking with a known number of Lycopodium spores. Most New Zealand honey falls within the “normal” category (20 000-100 000 pollen grains in a standard 10 g sample). Clover honey is in this category. Thyme honey with a pollen content less than 20 000 grams per 10 g sample, and manuka honey where the pollen content exceeds 100 000 grams, are examples of “under-represented” and “over represented” categories respectively. The analyses confirm the importance of white clo...

Abstract: The effects of pollination and resource levels on seed-set in Polemonium viscosum were evaluated at three elevations: 3528, 3640, and 4025 m in the Rocky Mountains of Colorado. Resource levels were enhanced by weeding out heterospecific neighbors ofthe plants studied. Flowers are either sweet- or skunky-scented, and the morphs are ecotypically adapted to differences in resource and pollination availability. At the low site, where bumble bees are uncommon and flies common, sweet flowers set fewer seeds than skunky ones; at the highest elevation where bumble bees are common and flies uncommon, sweet flowers set more seeds than skunky ones. Hand pollination increased seed- set, indicating that seed-set was pollen limited at all sites. The effects of weeding on seed-set were less consistent than those of hand pollination. Nonetheless, weeding enhanced seed production in sweet- scented flowers at the low elevation, and in concert with pollen supplementation also enhanced seed- set in skunky-scented flowers at the medium elevation. This pattern is consistent with the hypothesis of ecotypical differentiation between the floral morphs.

Abstract: Pollinators that forage indiscriminately can transfer pollen from one species to another, reducing the amount that reaches conspecific flowers. I present evidence that the presence of another plant species visited by the same pollinators can also reduce pollen dispersal distances and outcrossing. This has the potential to influence gene flow and reproductive success. Pollen carryover and movement patterns were measured for the shared insect pollinators of Stellaria pubera and Claytonia virginica in North Carolina. Bee flies deposited similar amounts of Stellaria pollen on a series of pistillate Claytonia flowers as on a series of pistillate Stellaria flowers. In arrays of potted plants, flies and solitary bees visited most flowers on a plant before leaving and then flew to a nearby plant chosen independently of species; 95% of moves were to one of 12 nearest neighbors. These measures of pollen carryover and movement patterns were used in a set of computer simulations to predict pollen dispersal distances. The simulations suggested that C. virginica substantially reduces outcrossing and pollen flow in S. pubera. These predictions were tested by tracking dye movement from anthers in populations of potted plants. Addition of C. virginica reduced the mean squared distance moved by dye to receptive S. pubera flowers by 23% and reduced the amount of dye moved by 51%. The estimated pollen component of gene flow was also much lower in a natural population of 5. pubera mixed with C. virginica than in the synthetic single-species populations.

Abstract: In the field of regeneration of plant in vitro cultures, haploid formation from pollen is the scientifically most advanced, but at the same time very controversial system. In the present state of transition from basic research to commercial application, a sound scientific basis of pollen embryogenesis would make this transition much easier. New discoveries in recent years have made it possible to develop a new view of pollen embryogenesis. The new view includes recognition-theoretical aspects, provides a model for a number of problems in plant development, and has consequences for strategies for haploid production. The accumulated knowledge in the field of pollen plant formation is critically analyzed against this new view.

Abstract: We compared the frequencies of multiply and singly sired fruits produced from simultaneous and sequential depositions of different pollen types in order to examine the mechanisms by which high frequencies of multiple paternity are produced in wild radish, Raphanus sativus. We found that most multiply sired fruits result from simultaneous pollen deposition (pollen carryover) and that the first pollen donor in a series of sequential pollen applications sires most seeds. Frequent sequential pollinations could produce multiply sired fruits, but insect visits to individual flowers in the field occur only at long intervals. We conclude, therefore, that multiple paternity in the field is a result of pollen carryover. Additional data on the sequence of seeds by father within field-collected fruits and on the number of fathers per fruit confirm this conclusion. Given the high frequency of multiply sired fruits in the field, most insects must carry pollen from several pollen sources. Our results suggest that there ...

Abstract: Repeated bronchial histamine challenges before, during, and after the birch pollen season were performed in 22 allergic patients with bronchial hyperreactivity (BHR) treated for 6 wk with sodium cromoglycate (SCG), 20 mg, four times a day, or placebo in a double-blind, randomized group comparison. Clinical assessments of the asthmatic symptom score and peak expiratory flow revealed less symptoms and less use of bronchodilators in the SCG group. Responsiveness to histamine was significantly increased in the placebo group after 14 days with high pollen counts. After the season there was an immediate return to preseasonal value. There was no change in responsiveness in the SCG group, demonstrating significant protection against pollen-induced increase of BHR. The results support the hypothesis that inhibition of mediator release, which is demonstrated for SCG, leads to a reduction of the nonspecific BHR.

Abstract: Darwin proposed that the function of the stamen-style polymorphism in heterostylous plants is to increase the probability of legitimate (compatible) pollinations among the floral morphs. Conspicuous pollen trimorphism in tristylous Pontederia cordata enables a test of the hypothesis. Comparison of the composition of pollen loads in naturally pollinated stigmas of intact and emasculated flowers were made at a population in Paugh Lake, Ontario, which was visited primarily by bumblebees. The magnitude of legitimate pollination was analyzed by ANOVA. In intact flowers, significant legitimate pollination was detected in the long-styled morph only. Following emasculation legitimate pollination was evident in the long- and short-styled morphs, with the mid-styled morph just short of displaying significant legitimate pollination. Similar results were obtained by chi-square analysis. It has been suggested that heterostyly may reduce mutual interference between maternal and paternal reproductive function. Two aspects of pollen-stigma interference were investigated in P. cordata. The potential importance of stigmatic or stylar clogging by incompatible pollen was examined by controlled field pollinations and measurements of seed set. The results indicate that prior application of large amounts of incompatible pollen has no significant effect on the seed set of open-pollinated inflorescences. Comparison of legitimate pollen capture in intact and emasculated flowers provided no evidence that the presence of stamens within flowers of the floral morphs interferes with the receipt of legitimate pollen. Pollen-stigma interference remains to be demonstrated in heterostylous plants.

Abstract: We studied the reproductive ecology of Clintonia borealis, a clonal understory species, in eastern Ontario. Flowers are protogynous and require insect pollination for outcrossing and maximum seed set. Most pollination is done by nectar-gathering bumble bees. We recorded pollen deposition and flowering patterns in 1983. Flowering lasted for about 10 days in midJune. Stigmatic pollen loads were lowest at the onset of blooming, reflecting the scarcity of male-phase flowers. Pollination increased significantly by peak bloom and subsequently remained high. However, since bees fly mostly between neighboring stems, much of the pollen transferred may have been geitonogamous. In 1983, seed set per flower was not increased by supplementing pollination or by reducing the number of fruits competing for resources per stem. Rather, flowers set more seeds (14%) only if both treatments were performed simultaneously. Seed size was increased by 25% when competitive fruits were removed and by 5% more when pollen was added under the removal treatment. Further work in 1984 showed that pollination effects may be related to changes in pollen source. Selfed flowers set fewer and smaller seeds than outcrossed ones when screened from insects and hand pollinated. Outcrossing distance had little effect on seed set or seed size. Thus, in C. borealis seed number and seed size are limited by a balance between maternal resource availability and the amount of outcrossing provided by pollinators. SEED PRODUCTION in flowering plants is constrained by two prsnciple factors: 1) the amount of resources available for flower (Van Andel and Vera, 1977; Solbrig, 1981; Meagher and Antonovics,1982), ovule (Snow,1982; Wolfe, 1983), seed (Kawano, Hiratsuka and Hayashi, 1982; Lee and Ba7:zaz, 1982), and fmit production (Willson and Price,1979; Stephenson, 1980, 1981; Udovic, 1981; Udovic and Aker, 1981); and 2) the amount and source of pollen that a plant's flowers receive (Willson, Miller andRathcke, 1979;PrimackandLloyd, 1980; Schemske, 1980; Bierzychudek, 1981; Galen, 1985). The relative importance of resource and pollination levels to seed set not only varies among closely related species (Gross and Werner, 1983), but also within species, with flowering date (Schemske, 1977), habitat (Udovic, 1981), and floral attractiveness (Galen, 1985). ' Received for publication 23 May 1984; revision accepted 3 May 1985. We acknowledge with gratitude H. G. Weger's assistance in the field. L. Wolfe, D. M. Waller, and two anonymous reviewers made helpful comments on the manuscript. Discussions with S. C. H. Barrett, J. A. Shykoff, and G. Thaler were valuable in many phases of the work. The research was funded by a Natural Sciences and Engineering Research Council of Canada grant to R. C. Plowright. 2 Send correspondence to: Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403. 3 Ecology and Evolution Department, State University of New York, Stony Brook, NY 1 1794. Seed size has been viewed as less responsive to environmental conditions than seed number (Harper, Lovell and Moore, 1970). However, recent studies (e.g., Thompson,1984; Stanton, 1984a; Schaal, 1984) show that much phenotypic variation in seed size occurs in at least some plant species. Seed number and size are often negatively correlated at an interspecific level (Salisbury, 1942; Primack, 1978) as well as within populations of the same species (Primack, 1978; Janzen, 1982; Stanton, 1984a) indicating that intrinsic resource levels may limit investment in total seed mass of individual fruits. Little information is available on the importance of pollination levels to seed weight. High pollen receipt could reduce seed weight indirectly by augmenting seed number. Alternatively, excess pollination might allow maturation of selected, perhaps heavier, seeds in a manner analogous to selective fruit production (Bookman, 1984). If genes expressed in pollen tube growth are also active in embryo development, then competition among pollen tubes at high levels of pollen deposition could eliminate paternal genotypes that otherwise would yield small seeds. This prediction agrees with findings that male gametophytic competition can affect later stages of oispring development (Mulcahy, Mulcahy and Ottaviano, 1975; Ottaviano, Sari-Gorla and Mulcahy, 1980). Regardless of pollination intensity, pollen genotype influences seed weight in those

Abstract: Soybean plants were cultured in solution with and without silicon application (silicon-supplied plants and silicon-free plants). Both silicon-free and silicon-supplied (l00 ppm SiO2) plants grew normally in the earlier growth stages. At the flowering stage, however, the newly-developed leaves (7th and 8th leaves) of the silicon-free plants showed malformations such as curling and curving to the outside, while the silicon-supplied plants grew normally. In severe cases, numerous necrotic spots were observed on the leaves of the plants. The growth of the silicon-free plants was markedly inferior to that of the silicon-supplied plants. The pollen fertility rate of the silicon-free plants was lower than that of the silicon-supplied plants. As the Ca content of the soybean plant was much higher than the SiO2 content, the soybean plant is rated as a Ca-type plant like the tomato plant. However, unlike the tomato plant in which most of Si is retained in the roots, the soybean plant translocates Si freely from the...

Abstract: (1) We tested whether seed production in the perennial monocarpic plant Ipomopsis aggregata (Polemoniaceae) was pollen-limited by adding outcross pollen to open stigmas of plants on three occasions at weekly intervals. We compared fruit set and seed set per fruit with a set of adjacent, untreated plants of the same average height and flower number. (2) Experimental pollination doubled the number of flowers producing seed after each occasion and increased the average seed set per fruit for the first one. (3) Plants treated with pollen showed correlations between seed production and height and aborted seed production consistent with resource limitation, but untreated, naturally pollinated plants did not.

Abstract: Previous reconstructions of the late Quaternary biogeographical history of lodgepole pine (Pinuscontorta Dougl.) have been based upon inferences from the modern geographical distribution of morphological and genetic variation. These studies have led to the widely accepted conclusion that relict populations of the Rocky Mountain subspecies of lodgepole pine (ssp. latifolia Engelm.) persisted in glacial refugia located in northwestern Canada. New fossil pollen evidence of the late Pleistocene and Holocene distribution of lodgepole pine in the western interior of Canada contradicts this view. Pinuscontorta ssp. latifolia migrated northward into Canada from refugia located south of the continental glacial limits and did not reach its northern range limits in the southern Yukon until the late Holocene.

Abstract: This report summarizes a 6-yr study of male and female cone production in a population of 216 ponderosa pines whose ages, diameters, and genotypes at 7 protein polymorphisms are known There are different schedules of male and female reproduction The majority of cones are produced by the same few trees each year There is a tradeoff between growth rate and female cone production but not pollen production Differential female (but not male) cone production is associated with protein genotype The variance of female reproductive effort declines with increasing protein heterozygosity LONG-LIVED, iteroparous species tend to have complex life histories and variable schedules of reproduction Reproduction is often highly varzable from year to year, and years of abundant seed production, called "mast" years, are characteristic of many forest trees Masting seems to be advantageous in reducing seed destmction by various animals (Harper, 1977; Silvertown, 1980) While such yearly variation in reproduction is a recognized characteristic of long-lived plants, it is seldom known what proportion of a population reproduces and whether specific individuals are consistently low or high reproducers year after year Relative allocation to pollen and seed production are also variable in long-lived species Monoecious species are particularly interesting in this respect because they can be very flexible in their timing and allocation of energy to male and female reproduction This flexibility is just beginning to be explored in an ecological context (Charnov, 1982; Willson, 1983; Willson and Burley, 1983) The role played by genetic variation in all this complexity is poorly known and only beginning to be documented (Dingle and Hegmann, 1982) Here we describe the associations between male and female cone production, growth rate, and protein genotypes The data were collected

Abstract: Eichhornia paniculata (Spreng.) Solms. (Pontederiaceae) is a short-lived perennial or annual of marshes, seasonal pools and ditches of lowland tropical South America, primarily NE Brazil, and the Caribbean islands of Cuba and Jamaica. Comparisons, made under uniform glasshouse conditions, of populations originating from seed collected in the two regions revealed striking differences in their floral biology and breeding systems. The majority of populations sampled in NE Brazil are tristylous. Floral trimorphism is associated with pollen trimorphism and minor differences in anther size and pollen production among the three stamen levels. Unlike the majority of heterostylous plants the floral morphs of E. paniculata are highly self-fertile. Populations sampled on the island of Jamaica are composed exclusively of self-pollinating, semi-homostylous, mid-styled forms. Flowers from these populations are smaller and less showy, with reduced pollen heteromorphism and significantly fewer pollen grains and ovules per flower, in comparison with trimorphic populations from Brazil. Individual genotypes from Jamaican populations display considerable developmental instability in floral expression, particularly with respect to filament elongation of the lower stamen level. It is proposed that self-pollinating populations of E. paniculata are evolutionarily derived from tristylous ancestors and that the shift in breeding system is favoured at low density, following population bottlenecks, where pollinator service is unreliable.

Abstract: Climatic changes in East Africa have been well documented although the record is far from complete Palaeoclimatic data for both the Holocene and Pleistocene1–7 and the Pliocene1–8 are available through fossil pollen studies However, these data extend in a continuous manner only as far back as 37 Myr BP (ref 11) largely because of the emphasis on studies related to human origins Fragmentary data from macrofossils also exist for older periods from Eastern14–20, Central and Southern Africa21,22 although the scarcity of material and the lack of isotopic dates makes it difficult to define continuity in the patterns of climatic fluctuations in East Africa The late Miocene pollen/spore flora described here represents the first data from East Africa for this time period and provides new information on the pre-Pliocene flora and climate of the continent The pollen flora comes from a post-8-Myr lacustrine deposit in the heart of the Northwestern Ethiopian Plateau (12° 35′ N, 37° 06′ E) and contains ‘exotic’ taxa that are now extinct The pollen diagram is characterized by abundant wet lowland rainforest taxa and pteridophytes, a very weak representation of grasses and the total absence of conifers, indicating warm and humid climates towards the close of the Miocene Post-depositional uplift of the Chilga area (∼1,000m) is also implied from the fossil pollen/spore assemblage

Abstract: Pollinators that forage indiscriminately can transfer pollen from one species to another, reducing the amount that reaches conspecific flowers. I present evidence that the presence of another plant species visited by the same pollinators can also reduce pollen dispersal distances and outcrossing. This has the potential to influence gene flow and re- productive success. Pollen carryover and movement patterns were measured for the shared insect pollinators of Stellaria pubera and Claytonia virginica in North Carolina. Bee flies deposited similar amounts of Stellaria pollen on a series of pistillate Claytonia flowers as on a series of pistillate Stellaria flowers. In arrays of potted plants, flies and solitary bees visited most flowers on a plant before leaving and then flew to a nearby plant chosen independently of species; 95% of moves were to one of 12 nearest neighbors. These measures of pollen carryover and movement patterns were used in a set of computer simulations to predict pollen dispersal distances. The simulations suggested that C. virginica substantially reduces outcrossing and pollen flow in S. pubera. These predictions were tested by tracking dye movement from anthers in populations of potted plants. Addition of C. virginica reduced the mean squared distance moved by dye to receptive S. pubera flowers by 23% and reduced the amount of dye moved by 5 1%. The estimated pollen component of gene flow was also much lower in a natural population of S. pubera mixed with C. virginica than in the synthetic single-species populations.

Abstract: Sympatric plant species can compete for pollination services in several ways. For example, pollinators may move between species and deposit heterospecific pollen on stigmas, which in turn may reduce the efficacy of conspecific pollen. We explored this possibility by determining the effect of Delphinium nelsonii poIlen on seed set in Ipomopsis aggregata. These montane herbs are pollinated by hummingbirds, experience heterospecific pollen deposition in nature, and suffer reduced seed set in each other's presence. We hand-pollinated flowers of I. aggregata with either pure conspecific pollen or a mixture of pollen of the two species. Resulting pollen loads on stigmas ranged from 0-865 D. nelsonfi grains and from 10-336 I. aggregata grains; mean seed set per flower was 11.3. There was no detectable effect of D. nelsonii pollen load on I. aggregata seed set. It is possible that seed set reductions seen in previous studies of competition for pollination between these species were caused by pollen wastage, pollen layering on the pollinatorl or the temporal sequence of pollen arrival at the stigma. This content downloaded from 207.46.13.85 on Sat, 28 May 2016 06:02:42 UTC All use subject to http://about.jstor.org/terms 1145 July,1985] KOHN AND WASER-EPPECT OF DELPHINIUM POLLEN ON IPOMOPSIS METHODS In June 1983, we dug up 29 I. aggregata plants in bud stage from a pasture near Almont, Gunnison Co., Colorado (elevation 2,450 m). Plants were potted in native soil and moved 35 km to a greenhouse at the Rocky Mountain Biological Laboratory, Gothic, Colorado (RMBL, 2,900 m elevation). Ten plants were subsequently used as conspecific pollen donors and the rest as pollen recipients. We also potted 20 D. nelsonii plants from a meadow near the RMBL to serve as heterospecific pollen donors. Potting at different elevations was necessary to obtain plants of the two species that would flower simultaneously. We removed the first 10 flowers that opened on each of the 19 recipient I. aggregata plants and counted ovules by examining squashed ovaries at 25 x . Subsequent flowers were handpollinated as described below, except that ovules were again counted for up to 10 flowers per plant that developed after the pollination experiment was terminated. We also counted ovules of the first and last 10 flowers produced by 10 plants in the field in 1984. Recipient flowers were emasculated before anthers dehisced to avoid contaminating stigmas with self pollen, which is incompatible (Waser and Price, 1983). We pollinated almost daily, between 0800 and 1230 hours, from 27 June to 16 July. Pollen was collected from most male-phase flowers on donor plants and usually came from flowers that had opened on the day of collection. We mixed pollen from all donors and applied it with fine watercolor brushes, with each flower receiving either pure conspecific pollen or a mixture of conspecific and heterospecific pollen. We alternated pollination treatments (i.e., pure-mixed) to flowers on each recipient; if an odd number of flowers were receptive, first and last flowers received mixed loads. We used reflexed stigma lobes as an indicator of receptivity. Tests for the presence of esterase (1-ANS, Mattson et al., 1974; FDA, Heslop-Harrison and HeslopHarrison, 1970) indicate that this is as accurate as possible, but there may have been some variation in receptivity that remained uncontrolled. Three days after flowers were pollinated, we removed and stained stigmas, squashed them gently, and counted pollen at 100 x . Grains of the two species are different shapes and sizes (45-55 ,um diam for I. aggregata vs. 20-25 ,um for D. nelsonfi). Subsequently, we removed undehisced fruits and counted seeds. We excluded from analyses fruits attacked by fly larvae (Zimmerman, 1979), but included undamaged flowers that failed to set fruit or seed. Finally, we assessed natural conspecific and heterospecific pollen loads by examining 240 stigmas from five diffierent I. aggregata patches near the RMBL. We also counted pollen loads on 46 I. aggregata stigmas from Waser's (1978a) previous hand-pollination experiment. These values were then compared to those obtained in the present experiment. RESULTS-Mean ovule number was higher for the first 10 flowers on pollen recipients than for flowers measured after the end of pollinations(means = 28.1 vs.21.8; paired t = 11.8, df= 18, P < 0.001, two-tailed). Thus, the maximum number of seeds a flower could set declined on average during the experiment. Mean ovule counts in the field in 1984 were 23.3 for early flowers and 19.7 for late flowers on the same plants (paired t = 3.50, d.f. = 9, P < 0.01, two-tailed). Of 454 hand-pollinated stigmas from the 19 pollen recipients, 172 contained I. aggregata pollen alone and 282 contained pollen of both species. Pollen loads ranged from 0-865 D. nelsonii grains (x = 108.1, SD = 141) and from 10-336 I. aggregata grains (x = 87.3, SD= 51.1). Amounts of pollen of the two species on individual stigmas were positively correlated (r = 0.26, df = 281, P < 0.001). The mean seed set of hand-pollinated fruits was 11.3 (SD = 5.6, N= 454). Stigma loads of D. nelsonii and I. aggregata pollen produced by our experiment fell within the ranges of 1-977 and 3-357 obtained for the two species, respectively, in Waser's (1978a) hand-pollinations. Field-collected stigmas from 1983 carried 0-309 heterospecific grains, a somewhat smaller range than in the experiment, and 0-478 conspecific grains (x = 119, SD = 80.5, N = 240), some of which were certainly incompatible self grains. Similarly, R. Mitchell (pers. comm.) found 0-156 D. nelsonii grains and 36-372 I. aggregata grains on I. aggregata stigmas collected during natural flowering overlap of the species in 1984. The dose-response relationship for seed set resulting from pure I. aggregata pollen (Fig. l) should be fit reasonably well by a negative exponential function of the form y = a [1expf-bx)], which is asymptotic to some maximum value of y (seed set) as x (pollen load) increases. The values in Fig. 1 are poorly fit by a linear model (Table 1). Log-transfolnzation of pollen loads and an exponential function do explain slightly more of the variance (Table 1). Even the best-fitting model explains very little of the variance in seed set, however. Multiple linear regressions with log-transformed pollen loads (Table 2) indicate that there is no detectable effect of D. nelsonfi pollen on This content downloaded from 207.46.13.85 on Sat, 28 May 2016 06:02:42 UTC All use subject to http://about.jstor.org/terms TABLE 2. Multiple regression of log-transformed pollen load on seed set in the 454 flowers receiving mixed conspecific and heterospecific pollen. The regression model is y = alogx + blogz + c, where x = number of I. agegats pollen grains, y = seed set, z = number of D. nelsonii grains, and a and b = partial regression coefficients. The table includes tests of the null hypothesis that regression parameters equal zero I. REGRESSION PARAMETERS Parameter Variable df estimate SE t P a 1 6.7 1.1 6.1 0.0001 b 1 -0.01 0.06 0.1 0.9 c 1 1.2 2.0 0.6 0.5

Abstract: A stratigraphic study was undertaken to determine the historic role of watershed and sea—level changes on the development of Fresh Pond Marsh on Long Island's north shore. Pollen analytic, radiometric, and macrofossil techniques were aimed at differentiating among marsh, watershed, and regional changes over the last 1000 yr. A study of surface pollen distribution was conducted to determine pollen source and tidal influences on pollen deposition and to evaluate comparability of fossil pollen records from various intertidal environments. Regional and local inputs along a transect that included several tidal regimes were identified. Pollen counts from these different environments were comparable and proved useful for marsh reconstructions. Pollen analyses from the coastal marsh and a nearby lake distinguished changes in upland vegetation and cultural patterns within the watershed from those occurring regionally. Records of local pollen, foraminifera, macrofossils, rhizomes, and lithology indicated that the history of Fresh Pond Marsh has included periods of both tidal and freshwater conditions. Close dating control provided by 210Pb measurements and historically documented changes in indicator pollen taxa identified marsh responses to external influences, including dynamics of a baymouth bar, land clearing, agriculture, mosquito ditching, and sea—level fluctuations. Results showed that (1) tidal marsh sections can provide sensitive records of both upland and marsh vegetation histories, (2) pollen and macrofossil records can be closely linked to tide—gauge records and are responsive to short—term changes in sea level with a high degree of temporal resolution, and (3) upland influences can play an important role in determining the course of plant succession in the intertidal environment. Pollen provides the most sensitive record of marsh and upland development, as long as pollen source is accounted for.

Abstract: The postglacial history of the forest-tundra zone in Labrador is inferred from the pollen stratigraphy of sediment cores from four lakes which differ considerably in the size and relative relief of their hydrologic catchments. Local pollen-assemblage zones are established independently for each pollen sequence by numerical methods. The relative pollen stratigraphies, interpreted through multi- variate statistical comparison with modem pollen spectra from the region, show an overall increase in the tundra component of the forest-tundra vegetation since z3000 BP. Decreasing absolute fre- quencies of Picea pollen in the sediments are interpreted as evidence of the decline in tree numbers within the lake catchments, and therefore as a potential record of lowering of the altitudinal tree limit. The records show diachronous changes between sites because of differences in catchment elevation and relief. Tree limit has apparently fallen at least 40 m between 3000 and 1000 BP. A further fall of 30 m may have taken place by 250 BP. High ground in northern Laborador makes it unlikely that any equivalent southward displacement of latitudinal tree line can be identified.

Abstract: In coastal heath, 12 km north of Sydney, Banksia ericifolia set fruit after cross-pollination but not after controlled self-pollination. Animals removed nectar and pollen from inflorescences during the day but not overnight. Introduced honeybees (Apis mellifera) and native birds (Meliphagidae, Zosteropidae) visited flowers frequently during the day, carried pollen on their body surfaces and were likely to transfer pollen between plants. Native bees, nocturnal moths and ants also visited flowers but were too infrequent, did not move between plants or foraged inappropriately to be important pollinators. No mammals were seen visiting flowers and the small mammals we caught carried no pollen. Exclusion experiments confirmed that pollination occurred during the day and not at night, but the experiments were insufficient to determine the relative importance of honeybees versus birds as pollinators. Only about 3% of the flowers of Banksia ericifolia developed follicles under natural conditions. Follicle production in this species was limited by resources and not by pollinators, since multiple cross- pollinations of flowers did not increase follicle production above the natural rate.

Abstract: A method for the induction of a high rate of cell division and embryogenesis of Nicotiana rustica pollen was developed. Binucleate pollen grains were fractionated by Percoll density gradient (35/45%) centrifugation and cultured in 0.4 molar mannitol at 30°C (the first culture). After 3 days in culture pollen was recollected by a second Percoll fractionation (0/30%) and transferred to and cultured in a medium containing the Murashige-Skoog macro-elements, 0.4 molar mannitol, 40 millimolar galactose, 3 millimolar glutamine, and 5 micromolar ABA for 10 days (the second culture). The cell population consisting of about 80% dividing pollen was transferred to a Murashige-Skoog medium containing 0.4 molar mannitol, 3 millimolar glutamine, and no phytohormone (the third culture), where about 40% of dividing pollen developed into embryos or embryogenic calli.

Abstract: In a riparian population of Erythronium americanum (Liliaceae) in central New Jersey, experimentally self-pollinated plant produced markedly fewer fruit and fewer seeds per fruit than hand-outcrossed and open pollinated plants, even though differences were not evident between pollen tubes that penetrated stigmas from self or foreign pollen. This weak self-compatibility and a positive relation between the percentage of seeds set by outcrossed plants and the distance between pollen donor and recipient plants indicate that this population could be susceptible to inbreeding depression.Limited resources for seed development apparently constrained maximal seed production, based on low seed set (40.6%) by hand-pollinated plants and positive correlations for these plants between plant size and the number and size of seeds set. In contrast, naturally-pollinated plants set a smaller proportion of their ovules, suggesting that limited pollinator service reduced the quantity of seeds produced in this population. Free-foraging bees usually removed more than half of the available pollen in a single visit, so that individual plants probably have few opportunities to disseminate their pollen.Even though sexually reproductive ramets produce only a single flower per year, less than a third of variation in floral morphology is associated with variation in plant size. Within the flower, the sizes of some closely associated structures, such as the style and ovary, and the anthers and filaments, vary essentially independently of one another. Production of nectar and pollen, the ultimate attractors of pollinating insects, was positively correlated with flower size.

Abstract: The primitive and vesselless angiosperm Zygogynum (Winteraceae), which is restricted to New Caledonia, is pollinated by a moth, Sabatinca (Micropterigidae). Fossil records of both the moth and the plant families extend to the Early Cretaceous. Adult Sabatinca have grinding mandibles and usually feed on the spores of ferns and on pollen. The insects use the flowers as mating sites and eat the pollen which is immersed in a dense pollenkitt. This mode of pollination in which flowers serve as mating and feeding stations with floral odors acting as cues may have been common in the early evolution of flowering plants.

Abstract: Pollen and spores form a significant part of the suspended organic load of a New Forest stream. Flood concentrations reach 230 grains ml−1 while baseflow carries under one grain ml−1. Hydrographs from different seasons show differing hysteretic loops for pollen and spore concentrations against discharge and suspended sediment. These variations reflect not only factors of production, but the type and distance of the contributing sources. This investigation suggests that variations in flood pollen and spore concentrations may be used to trace such suspended sediment sources as: eroding bedrock, channel banks, or hillslopes under specific vegetation covers.