Intra-inflorescence variation in floral traits and reproductive success of the hermaphrodite Silene acutifolia

BACKGROUND AND AIMS: Intraspecific variation in floral components and reproductive success is often located at the intra-individual level. The arrangement of flowers within inflorescences may explain a great deal of this variation. The variation in number of ovules, fruit set, number of seeds per fruit, seed set, seed weight and seed germination is investigated at different positions within the inflorescence of Silene acutifolia. METHODS: Data were obtained in natural populations, and germination experiments were conducted in a germination chamber. KEY RESULTS: The number of ovules, fruit set, number of seeds, seed set and seed weight, showed a significant decline from early (primary) position to later (tertiary) position. The patterns of intra-inflorescence variation were consistent in different populations and years of study. Seed germination showed an opposite pattern, seeds from primary position showed the lowest germination percentages and seeds from tertiary position the highest, although the effect of position on germination was only marginally significant. There was significant among-population variation in number of ovules per flower. Fruit set also varied significantly among populations, with lower fruit set in the smaller and more isolated population. No significant among-population differences were detected in number of seeds per fruit and seed set. Seeds from the smallest and more isolated population (Arnado) were the lightest. Seed germination showed strong differences between populations, seeds from Arnado started to germinate later, and showed the lowest final germination percentages. CONCLUSIONS: Architectural effects or resource competition are the most commonly proposed hypothesis to explain these patterns. Data suggest that there is less pollen available to pollinate tertiary flowers, and that there is not enough outcross pollen in Arnado. The germination percentages suggest that there is variation in the source of pollen within inflorescences, with high probability of receiving outcross pollen in flowers from primary position, and higher probability of geitonogamous crosses in tertiary flowers.     

Synchronicity of pollination and inoculation with Claviceps africana and its effects on pollen-pistil compatibility and seed production in sorghum

Sorghum ergot (caused by Claviceps africana) is a disease that affects sorghum seed development and yield. The interaction between pollen tube growth and hyphal development determines whether ovaries will be fertilized or colonized. Thus their respective deposition times on the stigma are critical. The effect of the time interval between pollination and inoculation on stigma receptivity and seed production was measured under field conditions in the male-sterile line A9 at Montecillo, State of México (2240m altitude). Pollination and inoculation treatments, from simultaneous application to 2 and 4h difference, were imposed when all stigmas on the panicle had emerged. Control panicles were either only pollinated or only inoculated. Eighteen hours later, pollen grains that adhered to, and germinated within the stigma, pollen tubes in the style and ovary, and fertilized pistils were counted. Pistils showing some disease expression (germinated spores, mycelium growth, or tissue necrosis) at 18, 48, and 72h were recorded. The number of diseased florets was registered at the dough growth stage, while number of seeds, grain yield and 100-seeds weight was measured at the physiological maturity. The pathogen applied in a water suspension of macro and secondary conidia caused a decrease in stigma receptivity; the greatest decrease (40-60%) occurred when the pollen and the inoculum were deposited almost simultaneously, regardless of which was deposited first. The route of the pollen tube was also the route for fungal infection. On average, treatments first inoculated had 60% more diseased florets and 36% less grain yield, 30% fewer seeds and seed size decreased 8%, than those first pollinated.     

PATTERNS OF PRE- AND POSTFERTILIZATION RESOURCE ALLOCATION WITHIN AN INFLORESCENCE: EVIDENCE FOR INTEROVARY COMPETITION

I investigated the distribution of ovules and seeds on the inflorescence of Solanum Carolinense L. (Solanaceae). Ovules did not appear to vary in size, but the number of ovules per ovary and the size of ovaries decreased significantly along the inflorescence (from basal to distal positions). Experimental removal of basal ovaries at an early stage resulted in increased ovary size and number of ovules in distal ovaries, suggesting a dynamic system of control. Mature fruits displayed a similar pattern of decreasing mass and seed number with position along the infructescence. It is not clear whether the patterns of allocation to fruits are related to the patterns of allocation to ovaries in a simple cause-and-effect relationship. However, a satisfying hypothesis that explains these and other patterns of allocation is that they are all manifestations of, or adaptations to, interovary competition along the inflorescence.     

The genetics and ecology of seed size variation in a biennial plant,Hydrophyllum appendiculatum (Hydrophyllaceae)

The goal of this study was to elucidate the sources of seed size variation in Hydrophyllum appendiculatum, an outcrossing, biennial plant. The genetic basis of seed size variation was examined with a diallel breeding design. The analysis did not reveal any evidence for additive genetic variance, suggesting that seed size could not evolve in response to natural selection. A series of greenhouse experiments was conducted to determine the sensitivity of seed weight to a number of ecological variables. Seed weight was affected by inbreeding depression: seeds produced by self-pollinations were significantly lighter that outcrossed seeds. Maternal plants did not differentially provision seeds that were the result of crosses between subpopulations (separated by 300 m) or between populations (separated by 1.7 km). Mean seed size was independent of the number of outcrossed pollen donors (one vs. many) that sired seeds on an inflorescence; however, the variance was greater on inflorescences pollinated by multiple donors. Direct manipulations of the abiotic environment showed that seed size was greater on plants growing under full sunlight compared to shaded plants. Seed size was unaffected by soil type, fertilizer addition, or defoliation. Finally, I determined the effect of varying pollination intensity at the level of a single inflorescence, and at the whole plant level. Seed weight was greatest on plants that had only 1 and 5 inflorescences pollinated, and least on those that had 10 and 20 pollinated. At the inflorescence level, seed weights were greatest on those where all flowers were pollinated, compared to inflorescences where only half of the flowers were pollinated. Perhaps the greatest contributor to variance in seed size in this species was the temporal decline within plants through the flowering season. These results indicate that maternal plants are not capable of producing uniform seed crops. Rather, the final distribution of seed size produced by plants within a population will necessarily vary and be the result of pollination effects, heterogeneity in the abiotic environment, and developmental constraints.     

Seed size,pollination costs and angiosperm success

Summary Seed plants capture pollen before seeds are dispersed and abort unpollinated ovules. As a result, each seed is associated with an accessory cost that represents the costs of pollen capture and the costs of aborted ovules. Accessory costs may explain the minimum seed size among species, because these costs are likely to comprise a greater proportion of total reproductive allocation in species with smaller seeds. For very small propagules, the costs of pollination may not be worth the benefits, perhaps explaining the persistence of pteridophytic reproduction at small propagule sizes. The smallest angiosperm seeds are much smaller than the smallest gymnosperm seeds, both in the fossil record and in the modern flora. This suggests that angiosperms can produce pollinated ovules more cheaply than gymnosperms. Pollination becomes less efficient as a species decreases in abundance, and this loss of efficiency is greater for species with a higher accessory cost per seed. We propose that the greater reproductive efficiency of angiosperms when rare can explain why angiosperm-dominated floras were more speciose than the gymnosperm-dominated floras they replaced.     

Application of a probabilistic model for analysing the abortion of seeds and pods in winter oilseed rape (Brassica napus)

In winter oilseed rape (WOSR), only a subset of ovules can develop into seeds in the majority of pods. Any difficulty during the process of seed production may result in seed or pod abortion. This study aimed to reproduce the process of seed development in WOSR based on a limited number of parameters. As a result of the complexity of the developmental patterns of WOSR, it is challenging to identify the roles of various factors that influence seed production using an experimental approach. Here, we present a stochastic probabilistic model of seed development. The generalised least squares method was implemented to estimate the model parameters using the experimental data. Experiments were done in Grignon (France) in 2008 and 2009. The variations in the parameters were analysed according to the following four factors: year, pod rank, inflorescence position and ramification‐clipping treatment. The year had no effect on the number of ovules per ovary (μ) and the probability of seed viability (p). The proportion of effective pollen grains (k) significantly decreased with pod rank at the end of the main stem. Inflorescence position influenced the number of ovules per ovary (μ: 30.8–33.8 from top to bottom) and the parameter k. The mean number of seeds per pod on the main stem and the bottom ramification along the stem was larger than the other ramifications within one plant. Ramification‐clipping treatment increased the number of ovules per ovary (μ: 31 for control plants and 32 for clipped plants), the parameter k and the number of seeds per pod (p). This effect could be due to the competition for assimilates between the pods and seeds. Furthermore, the distribution parameters of the pollen number per stigma (m) remained stable, and the probability of pod survival (Bo) varied with different factors, including the year, pod rank and inflorescence position. Our results indicate that pollen germination is a factor that determines final seed number. This model can identify the impact of each of the factors that lead to the abortion of seeds and pods in WOSR, which include the position effect, assimilate competition and pollination limitation. However, further studies on the pollination process in WOSR should help to refine this model.     

Characterization of the common wheat (Triticum aestivum L.) mutation line producing three pistils in a floret

In a normal wheat (Triticum ssp.L.) spike, one floret carries only one pistil that will further develop into one grain after fertilization. The cultivated common wheat (T. aestivum L.) mutation line Three Pistils (TP) carried three pistils in a floret. Although one or two of the pistils died out before seed set in some florets, there were exist many florets that set three seeds. Normally, it was observed that there were one to three seeds in different florets of the same spike. Therefore, this mutation trait could raise considerably the number of grains per spike. The weight of 100 grains in three seeds set florets was lower than that of in one seed set florets. But three seeds set florets were significantly to surpass the one seed set florets in grain(s) weight per floret. Based on these results, the three pistils trait was suggested to be an interesting germplasm resource. Localisation of the gene controlling the three pistils trait was carried out by the method of crossing TP with the Chinese Spring disomic substitutions. F2 population segregation analysis revealed that only the 5B F2 population did not show homogeneity to control population. chi2-test analysis indicated that 5B F2 population, and only this population, was deviated from the Mendelian segregation ratio (3:1). As a conclusion, the gene for three pistils trait was located on chromosome 5B. According to the Recommended rules for gene symbolization in wheat, the name of the dominant gene for three pistils trait in the line TP was suggested as Pis1.     

Differential self‐fertilization rates in response to variation in floral traits within inflorescences of Aquilegia buergeriana var. oxysepala (Ranunculaceae)

To assess variation in the proportion of self‐fertilized seeds among flowers within inflorescences and the relationship between floral traits and the rate of self‐fertilization, the proportion of self‐fertilized seeds among individual flowers was estimated using ten microsatellite markers in self‐compatible plants of Aquilegia buergeriana var. oxysepala. Within‐inflorescence variation in floral traits, such as the duration of the male and female phases, flower size, herkogamy and the number of pollen grains and ovules in two natural populations, were investigated. The first flower in an inflorescence produced more seeds and a higher proportion of self‐fertilized seeds than the second flower. The higher proportion of self‐fertilized seeds in the first flowers was accompanied by a higher number of pollen grains and ovules in the bud stage and the female phase. These results indicate that the high proportion of self‐fertilized seeds in the first flowers in an inflorescence may be due to the high number of remaining pollen grains in the female phase. This suggests that variation in floral traits within inflorescences affects seed quality and quantity among flowers within inflorescences.     

FERTILIZATION DYNAMICS AND PARENTAL EFFECTS UPON FRUIT DEVELOPMENT IN RAPHANUS RAPHANISTRUM: CONSEQUENCES FOR SEED SIZE VARIATION

Seed weight varies significantly within and among fruits of wild radish (Raphanus raphanistrum). To determine sources of this variation, we studied fertilization and seed development following controlled pollinations. Within fruits, central ovules were fertilized prior to distal ovules and attained greater seed size. Ninety-seven percent of the variation in mean seed wt per fruit was explained by an analysis of variance incorporating parental effects, pollination date, and the number of seeds per fruit. We document strong maternal effects on the number of ovules per ovary, the number of fertilized ovules per ovary, the number of seeds per fruit, and mean individual seed wt per fruit. Across females, pollen donor had a slight but significant effect on seed wt; no paternal effects on fertilization rate, zygote number, or seed number per fruit were detected. Within females, with one exception, pollen donor had no significant effect on these components of seed development. Stronger maternal main effects may be due to donor x recipient interactions, cytoplasmic factors, the genetic inequity within triploid endosperm, and/or strict maternal control over resource allocation. The large maternal effects relative to paternal effects may limit the rate at which natural selection acts on paternal traits expressed prior to seed maturation.     

Resource allocation patterns in Spinifex sericeus R.Br.: A dioecious perennial grass of coastal sand dunes

The resource allocation patterns within populations of Spinifex sericeus R.Br, were studied on the mid north coast of NSW. Sand burial and nutrient availability were two major factors influencing the allocation of resources to roots, culms, tillers and inflorescences, resulting in different growth forms in different sections of the dune. The data suggest that pollen availability may affect allocation to seeds late in the flowering season. Spinifex sericeus was found to have a greater below- than above-ground biomass, especially on the crest of the incipient foredune where sand accretion was high. The ability of culms of S. sericeus to grow upwards at a rate that generally prevents complete burial of the tillers is one mechanism which allows S. sericeus to vary resource allocation patterns in response to a varying environment. Differences in the inflorescence characteristics of males and females indicate their different functions. The much greater floret number of males indicated the importance of pollen dispersal. Female inflorescences consisted mainly of structures other than florets and suggested the importance of the female inflorescence in seed dispersal. Addition of nitrogen and phosphorus increased the number of spikelets and seeds but not the proportion of spikelets which produced seed.     

A comparison of ovule abortion in self-incompatible and self-fertile lines of white clover (Trifolium repens L.)

Plants of white clover (Trifolium repens L.) cv. Olwen and three genotypes of each of three self-fertile inbred lines of white clover were grown from seed in a bee-proof glasshouse. When in flower, a series of crosses within and between the self-incompatible (SI) and self-fertile (SF) lines was made and ovule growth and seed production measured 7 and 28 days after pollination (DAP) respectively. At harvest, the SF plants had a lower proportion of ovules aborting and more seeds per floret than the SI plants, though the mean seed weight of the SI plants was greater. Ovule abortion was observed in both the SF and SI plants though the number of aborted ovules was greater in the SI plants. The stage when abortion occurred also differed. All of the ovule abortion in the SI plants occurred within a 7-day period after pollination. In the SF plants, some abortion was observed in this period but also between 7 and 28 DAP, when the seed was harvested. This suggested that abortion, up to 7 DAP, is due primarily to genetic factors whilst subsequent abortion, between 7 and 28 DAP, is due to non-genetic factors.     

Effect of exogenous plant growth regulators on in vitro seed growth,embryo development,and haploid production in a cross between H. vulgare (L.) and H. bulbosum (L.)

Exogenous plant growth regulators are known to increase the efficiency of interspecific and intergeneric crosses. In vitro floret culture provides a defined system for assessing the importance of various plant growth regulators on the determinants of haploid production efficiency (seed set, embryos per seeds, and plants per embryos) in Hordeum vulgare × Hordeum bulbosum crosses. The individual and combined effects of three plant growth regulators (2,4-D, GA₃ and kinetin) on in vitro seed growth, embryo development and haploid production efficiency were tested in floret culture of the cross H. vulgare, cultivar Klages × H. bulbosum. All treatments, except kinetin alone, produced larger seeds and more embryos/100 seeds than the control (no plant growth regulator). 2,4-D alone was superior to GA₃ alone in haploid production efficiency (70.6 vs. 51.5) as measured by the number of plants regenerated/100 florets pollinated. Although kinetin +2,4-D+GA₃ produced the largest seeds and embryos, no advantage over 2,4-D alone was observed in haploid production efficiency. 2,4-D alone or kinetin +2,4-D are recommended for the purpose of barley haploid production in floret culture using the bulbosum method.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid     

Effect of ovular receptivity on seed set and fruit development in cucumber (Cucumis sativus L.)

Summary Seed set and fruit development in cucumber (Cucumis sativus L.) were studied in relation to female flower receptivity from day — 2 before anthesis to day + 2 after anthesis. The female cucumber flower is protogynous. The pistil was receptive 2 days before anthesis. The iso-electric focusing (IEF) patterns of the stigma/style proteins, were identical from day -5 to day +2. In pollinated flowers in vivo germination and pollen-tube growth in the ovary were affected by pistil age from day -2 to day +2. In addition, differences in sectorial filling in full seeds were observed within the fruits. A negative correlation was observed between the frequency of fertilized ovules in the pedoncular part of the fruit and ovary length at the time of pollination. In the whole fruit, significant differences in the number of full seeds and fruit size at maturity were found, and these were observed to be correlated with the various stages of female flower maturation at pollination. The day -2 and day +2 stages yielded the smallest fruits with few full seeds compared to the day -1, day 0 and day +1 stages, which had the biggest fruits and a large number of full seeds. A strong positive correlation was found between total seed number (including full and empty seeds), fruit length and weight at maturity. All these results suggest that both seed set in the different parts of the fruit and fruit development are controlled by ovular receptivity rather than by stigma/style receptivity.     

Effect of flower number on the pollinator attractiveness and the threshold plant size for flowering in Pertya triloba (Asteraceae)

Pertya triloba (Asteraceae) is a perennial herb growing in the understory of deciduous broad-leaved forests in central Japan. Its capitulum consists of a single floret that differs from those of most other Asteraceae species. A bagging experiment clearly showed that breeding of P. triloba required cross-pollination. By using female fertility as a measure of pollination success, the effect of an attractive floral display on the threshold plant size for flowering in P. triloba was surveyed. The number of florets per plant in a P. triloba population was artificially adjusted between one and 30. In both control plants and experimental plants with adjusted floret number, the seed set increased with an increase in the number of florets per plant and became constant (60%) when the floret number per plant was more than 10. Thus, the number of florets per plant has an important role in attracting pollinators, and more than 10 florets per plant must be the effective floral display size. In the P. triloba population, 98.5% of the flowering plants had 10 or more flowers. The effective floral display size might be determined through the mutual relationship between plants and pollinators. The number of florets per plant increased with an increase in the plant leaf area. Therefore, the threshold plant size for flowering might be determined by the productivity needed to support an attractive floral display.     

影响黄帚橐吾种子生产的因素Ⅰ.生境和花序结构

 通过对黄帚橐吾(Ligularia virgaurea)自然种群在不同生境和种群密度下的种子生产的研究,结果显示：1）黄帚橐吾的种子生产无论是在种群水平,还是在总花序上同一部位头状花序水平,均受到生境条件的影响,其种子数量、种子均重和种子总重量等特征在不同生境间表现出沙地＞滩地＞坡地,在同一生境内则为高密度种群＞低密度种群和植被盖度较低＞植被盖度较高的趋势（滩地例外）;2）种子生产中的种子数量和种子总重与总花序大小、头状花序数量以及无性系株大小多呈显著正相关,与个体密度无关,但种子均重与上述因素（除无性系株大小外）的关系不显著;3）在总花序内不同部位头状花序间表现出的种子生产变化趋势（顶部＞基部）不受生境条件、种群密度等因素的影响; 4）种子生产在总花序上所表现出的这种部位依赖性可能是由于不同部位头状花序间开花时序上的差异引起种子从母体获取资源上的不同所致。     

Longevity, early emergence and body size in a pollinating fig wasp--implications for stability in a fig-pollinator mutualism

1. Fig trees (Ficus) are pollinated only by agaonid wasps, whose larvae also gall fig ovules. Each ovule develops into either a seed (when pollinated) or a wasp (when an egg is also laid inside) but not both. 2. Ovipositing wasps (foundresses) favour ovules near the centre of the enclosed inflorescence (syconium or 'fig'), leaving ovules near the outer wall to develop into seeds. This spatial stratification of wasps and seeds ensures reproduction in both partners, and thereby enables mutualism persistence. However, the mechanism(s) responsible remain(s) unknown. 3. Theory shows that foundresses will search for increasingly rare inner ovules and ignore outer ovules, as long as ovipositing in outer ovules is sufficiently slow and/or if inner ovules confer greater fitness to wasps. The fig-pollinator mutualism can therefore be stabilized by strong time constraints on foundresses and by offspring fitness gradients over variation in ovule position. 4. Female fig wasps cannot leave their galls without male assistance. We found that females in outer ovules were unlikely to be released. Inner ovules thus have added value to foundresses, because their female offspring are more likely to mate and disperse. 5. For those offspring that did emerge, gall position (inner/outer) and body size did not influence the order in which female pollinators exited syconia, nor did early emerging wasps enjoy increased life spans. 6. We also found that the life spans of female wasps nearly doubled when given access to moisture. We suggest that conflict resolution in the fig-pollinator mutualism may thus be influenced by tropical seasonality, because wasps may be less able to over-exploit ovules in dry periods due to time constraints.     

Efficient floret inspection by honeybees in capitula of Carduus acanthoides

Abstract. 1. The floret inspection by honeybees Apis mellifera ligustica on inflorescences of Carduus acanthoides was studied in a natural patch. First-day stage capitula were protected with a net hood against insect visits. The next day, the net hood was removed at the time of maximal nectar accumulation, allowing a bee to visit the inflorescence. Walking trajectories on the capitula, the number of florets inspected and the duration of the visit were recorded. After the bee's departure, the inflorescence was cut off and analysed in the laboratory to determine the presence or absence of nectar in each of its florets.
2. Bees made inspection trajectories without a defined systematic pattern.
3. The number of floret inspections performed represented a high percentage of the available florets (57.37 ± 2.81%; mean ± SE; n = 8).
4. The number of depleted florets coincided with the number of floret inspections.
5. The number of times a floret is visited in a bee's trajectory is non-random.
6. Strategies that might account for this high foraging efficiency are discussed.     

Influence of post-flowering temperature on seed development, and subsequent performance of crisp lettuce

Crisp lettuce plants cv. Saladin were grown from the time they started flowering, at 20/10°C (16 h day, 8 h night), 25/15°C and 30/20°C in glasshouses on two occasions in 1985. Yields of seed increased from, on average, 15 g to 27 g and then fell to 20 g per plant with progressive increases in temperature. The number of mature florets per plant increased with temperature but the number of seeds per mature floret was lower at 20/10°C and 30/20°C than at 25/15°C. An increase in temperature reduced mean seed weight by up to 45%, seed volume by 15%, cell numerical volume density (N_v) by 27% and the number of cells per seed by 39%. Percentage seed germination reached a maximum early in seed development at the stage when the pappus appeared through the involucral bracts. Differences in percentage germination and vigour of seeds (slope test) from different temperatures were accounted for largely by the effects on mean seed weight. However, when germinated at 30°C seeds produced at 30/20°C germinated more readily than those produced at 25/15°C or 20/10°C. Seed vigour gradually increased with an increase in the length of storage after harvest, reaching a maximum after 260 days. In general, seeds produced at 25/15°C exhibited a greater variation in numbers of seeds per floret, N_v, seed weight, times of seedling emergence, seedling and mature head weight than seeds produced at lower or higher temperatures.     

EFFECTS OF POLLEN AND RESOURCES ON SEED NUMBER AND OTHER FITNESS COMPONENTS IN AMELANCHIER ARBOREA (ROSACEAE: MALOIDEAE)

Most Amelanchier arborea flowers have 10 ovules, but the number of filled (embryo-containing) seeds per fruit is usually less than 10 and is highly variable within each individual plant. Because fruit developmental time correlates with seed number, this variation in seed number results in asynchronous fruit ripening. Field experiments tested whether seed number was pollen- or resource-limited. Manipulation of resources in the shoot at the time of fruit initiation by defoliation, girdling, fruit thinning, or foliar feeding had no significant effect on seed number per fruit, although fruit set and seed weight were affected. Supplemental cross-pollination also had no demonstrable effect on seed number. Most ovules that do not become filled seeds are visible as small “undeveloped seeds”; these are not necessarily aborted seeds as this was also the fate of ovules in unpollinated carpels. Alternative hypotheses for the determination of seed number are proposed and discussed.     

Plasticity of reproductive components at different stages of development in the annual plant Thlaspi arvense L.

Summary This study examines the effect of different densities and the removal of all neighbours at different stages of development on all components of reproduction in the inbreeding annual Thlaspi arvense L. A 64-fold increase in density significantly reduced all repooductive components. The number of flower buds per plant was decreased most strongly; the order of decreasing plasticity among the other components was number of capsules per flower, individual seed weight, ovule number per capsule, flowers per flower bud and seeds per ovule. Removing neighbours at all stages of development increased seed yield of plants in comparison to the control without density reduction, but patterns of plasticity depended strongly on time of treatment. The main effect of the removal of neighbours at the vegetative stage was to increase the number of flowers per plant, but the number of ovules per capsule and seed weight increased also, and abortion of capsules decreased. Removing neighbours at the onset of flowering initially failed to affect flower number per plant, instead it resulted in a strong reduction of capsule abortion and an increase in seed weight. However, several weeks after flowering had initially ceased, fresh lateral inflorescences were produced, resulting in a second flush of reproduction. Removing neighbours at the stage of fruit ripening resulted at first only in an increase in seed witht, but later a second reproductive phase occurred. Fresh lateral branches were produced, but the apical meristem was also reactivated. The overall pattern of plasticity among all reproductive components in response to a removal of neighbours was the same as in response to density. The position of a capsule along the inflorescence influenced its number of ovules, the rate of seed abortion and the mean weight of seeds, with the type of effect depending on the developmental stage at which neighbours were removed. Significant negative correlations were found between the mean weight of seeds and the number of seeds in a capsule under all treatments.