RE-EVALUATING THE SIGNIFICANCE OF CORRELATIONS BETWEEN SEED NUMBER AND SIZE: EVIDENCE FROM A NATURAL POPULATION OF THE LILY,CLINTONIA BOREALIS

The basis for the negative correlation between seed number and seed size was experimentally investigated in a natural population of Clintonia borealis. Clones of this species vary significantly in estimated self-compatibility (ratio of seed set with selfing to that with outcrossing) and this appears to affect the number and size of seeds set in individual flowers of each. Clones estimated to be largely self-compatible set more seeds per flower than incompatible ones under natural pollination. However, naturally pollinated flowers of self-compatible clones set smaller seeds than those of incompatible clones, and the significance of the negative relationship between seed number and size in individual flowers was removed by holding variation due to compatibility constant. Supplementing resources per flower (by reducing the number of fruits competing for resources per stem) significantly increased total seed mass but had no effect on the negative relationship between seed number per flower and seed size. In contrast, supplementing cross pollination did not significantly influence total seed mass per flower but changed the relationship between seed number and size to positive, regardless of resource level. In other words, with plentiful cross pollination maternal genets capable of setting more seeds per flower also produced heavier ones. Thus, evidence is provided that the balance between seed number and seed size in this population is regulated by the interaction of maternal self-compatibility with natural pollination.     

Selective fruit filling in relation to pollen load size in Alstroemeria aurea (Alstroemeriaceae)

 We conducted an experiment in a natural population of Alstroemeria aurea, a clonal perennial, to determine (1) if reproduction was resource limited, and (2) if fruits would be selectively filled based on differences in pollination intensity when pollen loads were adequate for full seed set. Under these conditions, differences in pollination intensity are unlikely to affect seed number, but could affect seed quality, providing an interesting test of the gametophytic competition hypothesis. To test for resource limitation, percent fruit maturation, number of seeds per fruit and average seed weight were compared to paired controls for ramets in which all but one fruit was removed. To test the effect of pollination intensity on selective resource allocation, three types of pollination treatments were performed: (1) all flowers of the single inflorescence received a low pollen load, (2) all flowers received a high pollen load, (3) alternate flowers of the inflorescence received either a high or a low pollen load. We determined the percentage of fruit that reached maturity, counted the number of seeds and ovules and calculated the average seed weight for all capsules in each treatment. Resources appeared to limit reproduction in this population since seed number and weight were significantly higher than in controls when competing capsules were removed. At the whole ramet level, a four fold difference in pollen loads had no significant effect on any of the parameters measured. However, when pollination intensity varied within an inflorescence, the number of seeds per fruit increased by about 10% in flowers that received the higher pollen load. We observed the same trend in each of 2 years, but the increase was significant in only 1 year. The differences, although not great, were only slightly smaller than when all competing fruits were removed, and were consistent with selective resource allocation based on pollination intensity independent of seed set. Received: 28 September 1997 / Accepted: 30 April 1998     

Pollination of greenhouse tomatoes by the Australian bluebanded bee Amegilla (Zonamegilla) holmesi (Hymenoptera: Apidae)

The pollination effectiveness of bluebanded bees of the species Amegilla (Zonamegilla) holmesi Rayment (Hymenoptera: Apidae) was evaluated in tomato plants, Lycopersicon esculentum Miller (Solanaceae), cultivated in two greenhouse chambers. Bluebanded bee pollination was compared with mechanical pollination and no supplementary pollination. Pollination effectiveness was compared between treatments by using the percentage of fruit set, fruit weight, fruit diameter, fruit roundness, and the number of seeds per fruit. Both the bluebanded bee pollination and the mechanical pollination treatments significantly increased fruit set, individual fruit weight, and diameter compared with the control treatment. Fruit were also significantly rounder and contained significantly more seeds. Positive correlations were found for fruit weight versus seed number, maximum diameter versus seed number and minimum diameter versus seed number. We conclude that the use of A. holmesi for pollinating greenhouse tomatoes in Australia may be an effective alternative to the use of mechanical pollination.     

Seed germination patterns of Salvia mellifera in fire-prone environments

Summary I examined the effects of pollen loads containing pollen from one, three and five donors on fruit production and fruit quality in Campsis radicans. Number of pollen donors had no significant effect on % fruit production, seed number, seed weight or seed germination. In singledonor pollinations the identity of the donor did have a strong effect on the above parameters. Furthermore, the best single donor sired fruits with more seeds and heavier seeds than any mixture containing this donor. This pattern indicates interference of pollens or preemption of some ovules by the inferior pollen. In Campsis, therefore, the number of pollen donors contributing to a pollen load is less important than the identity of these donors in determining fruit production and fruit quality. Seeds from fruits resulting from mixed pollination were slightly more variable than seeds from fruits resulting from single-donor pollinations.     

Influence of nutrient availability and tree wildling density on nutrient uptake by Oxalis acetosella and Acer saccharum

The different weight-number strategies of seed production displayed by individuals of a Mediterranean fire-prone plant species (Cistus ladanifer) were investigated in relation to seed germination responses to pre-germination heating. A control (no heating), a high temperature during a short exposure time (100 degrees C during 5 min) and a high temperature during a long exposure time (100 degrees C during 15 min) were applied to seeds from different individual plants with different mean seed weight. These pre-germination treatments resemble natural germination scenarios for the studied species, absence of fire, typical Mediterranean shrub fire, and severe fire with high fuel load. Seed germination was related to heat treatments and seed mass. Seed heating increased the proportion of seeds germinating compared with the control treatment. Mean seed weight was positively correlated to the proportion of germinated seeds but only within heat treatments. These results suggest that in periods without fire, the relative contributions to the population dynamics are equal for all seeds, regardless of their mass, whereas heavier seeds would be the main contribution after wildfire events. Since lighter seeds can be produced in higher quantities than heavier ones within a given fruit, the number of seedlings produced per fruit depended strongly on the germination conditions. In the absence of wildfire, fruits producing lighter seeds gave rise to more seedlings; nevertheless, they were numerically exceeded by those producing heavy seeds after a wildfire. The implications of these results are discussed in relation to their consequences on the population dynamics of this species, considering also additional information on stand flammability and changes in seed mass with plant age.     

Plants,position and pollination: Planting arrangement and pollination limitation in a revegetated eucalypt woodland

The spatial arrangement of plants is a key determinant of pollination services in natural ecosystems. Despite this, plant arrangements are rarely considered an important characteristic of revegetated communities and this may be limiting successful pollination dynamics in these re‐created systems. We assessed if aggregated South Australian Blue Gum (Eucalyptus leucoxylon, F. Muell) had greater pollination success than more dispersed trees by measuring fruit set, seed production and germination in a revegetated eucalypt woodland. The proportion of buds that developed into fruit (fruit set) was similar between aggregated (five flowering Blue Gum within 30 m) and dispersed (no flowering Blue Gum within 30 m) trees (<14%). Aggregated and dispersed trees produced a similar number of seeds per fruit in 2015, when fewer trees flowered and those that flowered produced fewer flowers (ca 8 seeds/fruit). In 2016, when flowering was more abundant, aggregated trees produced more seeds per fruit than dispersed trees (12 seeds/fruit compared to 4 seeds/fruit). Despite differences in seed number, there was no difference in the quality of seed produced, indicating outcrossed pollen was received by both aggregated and dispersed trees. Although outcrossing was likely, this did not prevent pollination limitation, with the addition of outcrossed pollen increasing fruit and seed set for trees in both arrangements. Consequently, we propose that planting individuals of the same species (conspecifics) in clumps, rather than intermixing species, can increase seed set in revegetated eucalypts, particularly in good flowering years. However, aggregated plantings will be most effective if the needs and foraging behaviour of pollinators are also considered, to attract and sustain pollinators in revegetated systems, thereby minimizing the risk of pollination limitation.     

人工授粉对火龙果果实发育的影响

于开花期对红皮红肉类型火龙果进行人工授粉与自然授粉处理,并对不同发育阶段的子房或果实进行解剖观察,以研究人工授粉对果实发育的影响.结果表明:人工授粉可提高火龙果的平均单果重和商品果率,平均单果重与果实内种子数呈显著正相关关系;火龙果子房为多胚珠结构,子房内有若干“珠柄-胚珠”单元,胚珠在开花后发育成种子,珠柄则发育成肉...     

Floral and reproductive biology of Drosophyllum lusitanicum (L.) Link (Droseraceae)

We studied the floral and reproductive biology of Drosophyllym lusitanicum (Droseraceae), a species endemic to the western Iberian Peninsula and northwest Morocco. Flowering lasted from March to August, peaking in April. The species is clearly homogamous, with pollen germination and stigma receptivity occurring even in preanthesis. This was reflected in the high rates of fruit set and seed set in bagged inflorescences. Fructification did not differ significantly between different pollination treatments, although we did find differences between some treatments in the numbers of viable seeds per flower and fruit. However, seed weight did not differ significantly. The importance of self-pollination over cross-pollination was also supported by the low percentages of fructification (24.67%) after emasculation and open pollination. Metameric deviations were seen in flowers, although this abnormality was not translated as any reproductive benefit or disadvantage (fructification, number or weight of seeds) in comparison with normal flowers.     

自花授粉在安徽羽叶报春花色选育中应用的初步研究

安徽羽叶报春是我国特有的一种珍稀濒危花卉。论文对自花授粉在其花色选育中的应用进行了初步研究。结果表明：安徽羽叶报春自花授粉亲和性较高,平均结籽数可达36.03粒/果,能达到正配授粉结籽数的71.11%（正配授粉结籽数为50.69粒/果）,而且自花授粉种子也基本能正常萌发,萌发率为41.13%,达到正配授粉种子萌发率的57.98%。花色分析显示自花授粉子代花色R值比重均值（即红色成分,为0.382）显著高于其亲本群体及正配授粉子代的均值（均为0.375左右）。因此安徽羽叶报春自花授粉虽存在一定的衰退现象,但它有利于花色的选育和纯合品系的获得,在其花色的选育过程中应加以重视和利用。     

Comparison of two cacao (Theobroma cacao L.) clones for the effect of pollination intensity on fruit set and seed content

We compared the influence of pollination intensity (PI) on fruit set and seed number per pod in two cacao (Theobroma cacao L.) clones, IFC5 (Forastero Lower-Amazon Amelonado), which is self-compatible and known to produce a high number of seeds per pod under open pollination, and SCA6 (Forastero Upper-Amazon), which is self-incompatible and known to produce a low number of seeds per pod under open pollination. With both clones, PI had a positive effect on fruit set, with the maximum rate requiring more than 150 pollen grains per pod. One-half of the maximum rate of fruit set was reached with 39 pollen grains per pod for SCA6, and 78 for IFC5. With SCA6, a significant positive effect of PI on seed number per pod was also observed, with maximum seed number requiring more than 200 pollen grains per pod. In contrast, seed numbers with IFC5 were approximately equal over the PI range 100–800 pollen grains per pod. Patterns of seed number per pod were compared after: (1) open insect pollination, (2) low-intensity hand pollination and (3) high-intensity hand pollination. The patterns obtained with IFC5 under open pollination showed a peak of 40–50 seeds per pod, whereas the distribution patterns were more even with SCA6. The pattern of seed number under open pollination was similar to that obtained with high-intensity hand pollination for IFC5, and with low-intensity hand pollination for SCA6. We concluded that the high number of seeds per pod observed with IFC5 under natural insect pollination may be explained by a high number of compatible self-pollen grains on the stigma and by a severe drop of low-pollinated flowers eliminating potential lowfilled fruits. With SCA6, however, the number of compatible pollen grains deposited on the stigma was probably low under open pollination, and the flowers required lower pollen quantities to set fruit, which resulted in a high frequency of low seed numbers per fruit. This difference in the capacity to set low-seeded fruits might be considered as an adaptive trait related to the mode of reproduction.     

Floral biology and pollination mechanisms of four Mexico-endemic Fuchsia species with contrasting reproductive systems

Aims The evolution of the outstanding variation of reproductive systems in angiosperms has been considered an important driver of lineage diversification. Closely related hermaphroditic and dioecious species with biotic pollination provide the opportunity to study and compare traits related to pollinator attraction and their consequences on reproductive components. A higher predictability of pollination syndromes is expected in dioecious species, which are dependent on pollinators, than in self-compatible hermaphroditic taxa. Dioecious species may suffer pollen limitation depending on the quality of floral rewards and the kind and abundance of pollinators, whereas no pollen limitation is expected in hermaphroditic species with autonomous self-pollination. Additionally, in the absence of pollen limitation, more or better seeds are expected in dioecious species, according to the sexual specialization hypothesis.Methods In natural populations of the hermaphroditic Fuchsia fulgens and Fuchsia arborescens and dioecious Fuchsia parviflora and Fuchsia obconica, all endemic to Mexico, we first described flower phenology, flower production and longevity and nectar volume and concentration. Then, we evaluated the correspondence between floral visitors and pollination syndromes. In hermaphrodite plants, we determined the level of herkogamy and the potential for autonomous self-pollination. Finally, we evaluated the effect of pollen limitation on fruit set and seed number and assessed seed germination for all species.Important findings In contrast to our prediction, dioecious species did not show a higher correspondence between pollination syndromes and floral visitors than did hermaphrodites; however, male flowers exhibited a higher correspondence than female flowers. No pollen limitation was detected in dioecious species, for which visitation rate did not differ between male and female flowers. The hermaphroditic F. fulgens showed pollen limitation for seed number, despite the presence of autonomous selfing. Fruit set from autonomous pollination was higher in F. arborescens, which showed a lower level of herkogamy compared with F. fulgens. Finally, dioecious species produced fewer but heavier seeds compared with hermaphrodite species. Although Fuchsia is classified as an outcrossing genus, both hermaphroditic species showed autonomous self-pollination. The heavier but lower number of seeds per fruit in dioecious species may be related to the more efficient resource allocation expected from sexual specialization. This could play an important role in the evolution of dioecy; however, a comparative phylogenetic approach is required to confirm this hypothesis.     

薄毛海绵杜鹃结实和萌发特性随环境的变化

选择青藏高原东南林线地区优势植物薄毛海绵杜鹃为对象,研究薄毛海绵杜鹃结实特性和萌发特性随海拔(4183—4673 m)、坡度、坡向等环境梯度的变化规律。对比了不同环境条件下薄毛海绵杜鹃果实的长、宽、重量、单果种子数、种子千粒重等结实特性;并测试了不同环境所产种子的萌发对温度和光照的响应。结果表明:(1)在高海拔低温胁迫环境下,薄毛海绵杜鹃的生殖投入加大,果实大且质量重,种子数量多但质量轻;(2)坡向是影响单果种子数量的主要环境因子,阴坡单果种子数显著大于阳坡,生活在阴坡的薄毛海绵杜鹃的繁衍能力更强;(3)较高和较低土壤湿度都会影响薄毛海绵杜鹃的种子质量,中等土壤湿度(28.3%—32.5%)薄毛海绵杜鹃种子萌发能力最强;(4)薄毛海绵杜鹃的种子是需光性种子,在黑暗条件下几乎不萌发;(5)在光照条件下,温度对种子萌发率和萌发速率有显著影响,高温(25/5℃)有助于提高萌发率并促使萌发进程显著提前。研究揭示了不同海拔薄毛海绵杜鹃结实和萌发特性与环境之间的关系,为薄毛海绵杜鹃的种质资源保护和气候变化背景下藏东南林线动态预测提供了基础资料。     

大花百子莲的结实和结籽格局及种子产量影响因素分析

在2007和2008年对大花百子莲(Agapanthus praecox subsp.orientalis‘Big Blue’)在群体、果序和单果水平上的结实和结籽格局进行了观测,并依据每花序单花数、单花胚珠数和单粒种子质量推算其单株潜在种子产量;此外,采用人工补充授粉方法研究了不同授粉方式对大花百子莲结实和结籽的影响,并对其种子产量的影响因素进行了分析。结果表明:从始花期、盛花期至末花期,随开花时间的延迟,大花百子莲植株的每花序单花数和座果率均逐渐降低,其中始花期开花的植株每花序单花数和座果率均最高。从果序基部、中部至顶端,座果率和结籽率均逐渐减小且差异显著。在果序基部和中部,果实内种子败育率沿果实基部至顶端依次降低,而单粒种子质量则依次增加;且果序基部的果实各部位的种子败育率均低于果序中部的果实,而单粒种子质量则差异不大。大花百子莲的单株潜在种子产量约为43.18 g,而其单株实际种子产量约为2.87 g,远低于其潜在种子产量。自然授粉的大花百子莲每柱头花粉数为27.5粒,而自花授粉、同株异花授粉和异株授粉的每柱头花粉数均超过100粒;与自然授粉、自花授粉和同株异花授粉植株相比,异株授粉植株的座果率和结籽率均显著增加。研究结果显示:大花百子莲的结实和结籽格局呈现非随机分布规律,在引种地存在有性繁殖障碍;养分和授粉状况是制约大花百子莲种子产量的重要因素。     

Associations among cytoplasmic molecular markers,gender, and components of fitness in Silene vulgaris,a gynodioecious plant

It has been suggested that the dynamics of chloroplast DNA (cpDNA) or mitochondrial DNA (mtDNA) genetic markers used in studies of plant populations could be influenced by natural selection acting elsewhere in the genome. This could be particularly true in gynodioecious plants if cpDNA or mtDNA genetic markers are in gametic disequilibrium with genes responsible for sex expression. In order to investigate this possibility, a natural population of the gynodioecious plant Silene vulgaris was used to study associations among mtDNA haplotype, cpDNA haplotype, sex and some components of fitness through seed. Individuals were sampled for mtDNA and cpDNA haplotype as determined using restriction fragment length polymorphism (RFLP) methods, sex (female or hermaphrodite), fruit number, fruit set, seeds/fruit and seed germination. The sex of surviving germinating seeds was also noted. All individuals in the population fell into one of two cytoplasmic categories, designated haplotypes f and g by a unique electrophoretic signature in both the mtDNA and cpDNA. The subset of the population carrying haplotype g included a significantly higher proportion of females when compared with the sex ratio of the subset carrying the f haplotype. Haplotype g had a significantly higher fitness when measured by fruit number, fruit set and seeds/fruit, whereas haplotype f had significantly higher fitness when measured by seed germination. Offspring of individuals carrying haplotype g included a significantly greater proportion of females when compared with offspring of individuals carrying the f haplotype. Other studies of gynodioecious plants have shown that females generally have higher fitness through seed than hermaphrodites, but in this study not all fitness differences between haplotypes could be predicted from differences in haplotype-specific sex ratio alone. Rather, some differences in haplotype-specific fitness were due to differences in fitness between individuals of the same sex, but carrying different haplotypes. The results are discussed with regard to the potential for hitchhiking selection to influence the dynamics of the noncoding regions used to designate the cpDNA and mtDNA haplotypes.     

濒危植物焕镛木的兼性无融合生殖

2001～2002年连续两年在广西环江木论和广西罗城大黄泥的2个焕镛木(Woonyoungia septentrionalis(Dandy)Law)自然种群中,对单性异株的濒危植物焕镛木进行繁育系统测定,对即将开花的雌花花蕾分别进行套袋、套网、人工授粉处理,并用自然授粉雌花作对照,其座果率和结实率统计结果表明:自然授粉、人工授粉、套袋和套网处理的花均能结实,但它们的座果率和结实率存在较大的差异.在两个种群中,人工授粉和自然授粉的总结实率(PERS)均比套袋和套网处理的高,其中人工授粉的最高,套网处理的最低.由此可见,焕镛木既能通过有性生殖方式结实,又能通过无融合生殖方式结实,而且这两种生殖方式获得的种子均能萌发成幼苗,由此断定,焕镛木的繁育系统为兼性无融合生殖.这是首次报道木兰科植物存在无融合生殖现象.     

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.     

濒危植物焕镛木的兼性无融合生殖

2001—2002年连续两年在广西环江木论和广西罗城大黄泥的2个焕镛木(Woonyoungia septentrionalis (Dandy) Law)自然种群中,对单性异株的濒危植物焕镛木进行繁育系统测定,对即将开花的雌花花蕾分别进行套袋、套网、人工授粉处理,并用自然授粉雌花作对照,其座果率和结实率统计结果表明：自然授粉、人工授粉、套袋和套网处理的花均能结实,但它们的座果率和结实率存在较大的差异。在两个种群中,人工授粉和自然授粉的总结实率(PERS)均比套袋和套网处理的高,其中人工授粉的最高,套网处理的最低。由此可见,焕镛木既能通过有性生殖方式结实,又能通过无融合生殖方式结实,而且这两种生殖方式获得的种子均能萌发成幼苗,由此断定,焕镛木的繁育系统为兼性无融合生殖。这是首次报道木兰科植物存在无融合生殖现象。     

EFFECTS OF POLLINATION INTENSITY IN CAMPSIS RADICANS

I examined effects of pollination intensity on fruit, seed and seedling characteristics in Campsis radicans, and joint effects of pollen donor and pollination intensity on fruit production. Large pollen loads were more likely to initiate fruit production than small pollen loads, and the former fruits contained more seeds and a greater total seed mass. No further increases in seed number or mass occurred for pollen loads above 4,000 grains. The weight of individual seeds was unaffected by pollen load. Effects of pollen donor were generally larger than effects of pollen load, and fruit production from small loads of pollen from one donor were sometimes equal to fruit production from larger pollen loads from another donor. The ratio of pollen grains deposited to resultant seeds increased with pollen load, and several explanations are proposed. Seeds from heavy pollinations emerged better than seeds from light pollinations, but did not differ in speed of germination or in the performance of seedlings up to 126 days. The emergence differences are probably due to differing intensities of pollen tube competition.     

玉蝉花繁殖生态学研究

通过野外调查、人工授粉和室内种子萌发实验等,对天目山玉蝉花（Iris ensata）种群繁殖生态特征进行了研究。结果显示：玉蝉花自然种群呈聚集型分布,种群更新主要依赖贡献率为0.756的无性繁殖。人工同瓣和异瓣自花授粉座果率分别为10%和20%,结实数分别为0和4±1（n=2）粒/果;同株和异株异花授粉座果率分别为80%和100%,结实数分别为59±7（n=8）和64±9（n=10）粒/果,自交主要来自同株异花授粉,而同株花异熟、雌雄异位和异向等可有效降低自交。自然套袋不结实,不存在无融合生殖。花粉/胚珠比1277±270（n=10）,辅证玉蝉花为兼性异花授粉、异花授粉植物。有效授粉昆虫为蜜蜂（Apismellifica）,访花频率为0.019次.花-1.h-1,单只蜜蜂回访同朵花的比率为3.5%。自然种群立地种子数估算值为368粒/m2,种子宿存,具非深度生理休眠,萌发需光,低温层积60d萌发率达94.9±0.7%。玉蝉花种群繁殖适应对策为k对策,具备自我维持机制,但现正受人为干扰。     

Sequential variation in the components of reproductive success in the distylousJasminum fruticans (Oleaceae)

A 2-year study of three natural populations of the distylousJasminum fruticans showed that mean fruit and seed production were significantly greater in shortstyled plants (thrums) than in long-styled plants (pins). In this study, we investigated the role of four sequential factors which may differentially influence fruit and seed set in the two floral morphs: (1) differences in flowering phenology, (2) a limitation of pollen transfer towards pins, (3) a differential capacity of the two morphs to act through famale and male function and (4) differential fruit abortion in the two morphs. Fruit set was significantly influenced by differences in flowering phenology although there were no differences in flowering time between the two morphs. supplementary pollinations in a natural population significantly increased fruit set and reduced the difference in fruit set between the two morphs in relation to controls, indicating a limitation on pollen transfer which was most severe towards pin stigmas. In reciprocal crosses, seed set was significantly dependent on the paternal and maternal identity of the pin parent. There was no significant variation among thrums for their performance as male or female parent. Furthermore, individual pin plants with relatively high percentage seed set as female parents gave poor seed set as male parents and vice-versa. Whereas fruit removal had no effect on seed number in thrum plants, a greater proportion of viable seeds were produced on pin plants which were left to naturally mature their fruits than on pins which had fruits artificially removed, suggesting the occurrence of selective fruit abortion in pins but not in thrums. The initially greater maternal fitness of thrums due to their greater success as pollen recipients may thus be opposed by increased viable seed set in the pins due to factors acting after the pollination stage. The relative reproductive success of floral morphs in the distylousJ. fruticans is thus differentially influenced by ecological factors occurring at different stages of the reproductive process.