Combined definition of seed transfer guidelines for ecological restoration in the French Pyrenees

Question: Can genetic tools combined with phytogeography help to define local plants and how geographically close the source population should be to the restoration site? Location: Subalpine and alpine French Pyrenees. Methods: The main phytogeographic boundaries in the French Pyrenees described by different authors were studied and this geographic pattern was compared with the results of genetic analysis for the four Pyrenean plants studied (Trifolium alpinum, Festuca eskia, Festuca gautieri and Rumex scutatus), based on random amplified polymorphic DNA (RAPD) marker analysis, unweighted pair‐group method with arithmetic averages (UPGMA) analysis and Mantel correlograms comparing geographic and genetic distances. Results: The genetic analysis allowed definition of two main evolutionarily significant units (ESUs) for the plants under study. Although the limit between the two zones was slightly variable according to the species considered, an eastern and a western ESU was consistently observed. This delineation was concordant with the main phytogeographic boundaries of the French Pyrenees. Conclusion: RAPD markers and associated Mantel correlograms can be useful to draw ESUs for individual species when the sampling intensity is relatively dense, and similarities were revealed between species sharing the same distribution range. This delineation allowed integration of infraspecific plant variation in the management of natural resources for revegetation in the Pyrenees. Nevertheless, caution is needed for the establishment of seed pools in order to maximize genetic diversity in each of the pools during collection and production.     

Comparative genetic study confirms exceptionally low genetic variation in the ancient and endangered relictual conifer,Wollemia nobilis (Araucariaceae)

The Wollemi pine, Wollemia nobilis (Araucariaceae), was discovered in 1994 as the only extant member of the genus, previously known only from the fossil record. With fewer than 100 trees known from an inaccessible canyon in southeastern Australia, it is one of the most endangered tree species in the world. We conducted a comparative population genetic survey at allozyme, amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) loci in W. nobilis, Araucaria cunninghamii and Agathis robusta - representatives of the two sister genera. No polymorphism was detected at 13 allozyme loci, more than 800 AFLP loci or the 20 SSR loci screened in W. nobilis. In Ag. robusta only one of 12 allozyme loci, five of 800 AFLP loci and none of the 15 SSR loci were variable. For A. cunninghamii, 10 of > 800 AFLP loci and five of 20 SSR loci were variable. Thus low genetic diversity characterizes all three species. While not ruling out the existence of genetic variation, we conclude that genetic diversity is exceptionally low in the Wollemi pine. To our knowledge this is the most extreme case known in plants. We conclude that the combination of small population effects, clonality and below-average genetic variation in the family are probable contributing factors to the low diversity. The exceptionally low genetic diversity of the Wollemi pine, combined with its known susceptibility to exotic fungal pathogens, reinforces current management policies of strict control of access to the pines and secrecy of the pine locations.     

Desiccation tolerance acquisition in developing beech (Fagus sylvatica L.) seeds: the contribution of dehydrin-like protein

The acquisition of desiccation tolerance (DT) in developing beech (Fagus sylvatica L.) seeds and the role of a dehydrin protein in this process were investigated. DT was determined by measurement of electrolyte leakage and germination capacity after drying to 10–12% moisture content (MC). In addition to mass maturity, the presence of heat-stable proteins, dehydrin accumulation and the peak of ABA content were measured in relation to the acquisition of DT. Mass maturity was achieved at 16 weeks after flowering (WAF). The germination capacity increased from 8% at 12 WAF to 80–90% after 16 WAF. Cell membrane integrity, measured as a decrease in electrolyte leakage after desiccation, was acquired at 16 WAF. Additionally, the ratio of heat-stable to soluble proteins was the highest at 16 WAF. One dehydrin-like protein with a molecular mass 44 kDa, named DHN44, was detected in embryonic axes at 16 WAF and in cotyledons at 17 WAF, and its gradual accumulation was observed in mature seeds. With regard to the acquisition of DT, the strongest correlations were detected between electrolyte leakage, DHN44 accumulation, and the percentage of heat-stable proteins. These results suggest that developing beech seeds become tolerant to desiccation at 16 WAF. The effect of desiccation and ABA treatment on DHN44 synthesis was tested before (14 WAF) and after the DT acquisition (18 WAF). Depending on the maturation stage desiccation and ABA treatment can induce or enlarge DHN44 expression.     

Size and lipid content of nonmyrmecochorous diaspores: effects on the interaction with litter-foraging ants in the Atlantic rain forest of Brazil

Ants are often attracted to diaspores not adapted for dispersal by ants. These diaspores may occasionally benefit from this interaction. We selected six nonmyrmecochorous plant species (Virola oleifera, Eugenia stictosepala, Cabralea canjerana, Citharexylum myrianthum, Alchornea glandulosa and Hyeronima alchorneoides) whose diaspores differ in size and lipid content, and investigated how these features affect the outcome of ant-diaspore interactions on the floor of a lowland Atlantic forest of Southeast Brazil. A total of 23 ant species were seen interacting with diaspores on the forest floor. Ants were generally rapid at discovering and cleaning the diaspore pulp or aril. Recruitment rate and ant attendance were higher for lipid-rich diaspores than for lipid-poor ones. Removal rate and displacement distance were higher for small diaspores. The large ponerine ant Pachycondyla striata, one of the most frequent attendants to lipid-rich arillate diaspores, transported the latter into their nests and discarded clean intact seeds on refuse piles outside the nest. Germination tests with cleaned and uncleaned diaspores revealed that the removal of pulp or aril may increase germination success in Virola oleifera, Cabralea canjerana, Citharexylum myrianthum and Alchornea glandulosa. Gas chromatography analyses revealed a close similarity in the fatty acid composition of the arils of the lipid-rich diaspores and the elaiosome of a typical myrmecochorous seed (Ricinus communis), corroborating the suggestion that some arils and elaiosomes are chemically similar. Although ant-derived benefits to diaspores – secondary dispersal and/or increased germination – varied among the six plant species studied, the results enhanced the role of ant-diaspore interactions in the post-dispersal fates of nonmyrmecochorous seeds in tropical forests. The size and the lipid-content of the diaspores were shown to be major determinants of the outcome of such interactions.     

Temperature conditions control embryo growth and seed germination of Corydalis solida (L.) Clairv., a temperate forest spring geophyte

Spring is often the most suitable period for seedling establishment of temperate woodland species. Different physiological mechanisms resulting in spring emergence have evolved in seeds of such plants. The aim of this study was to determine the requirements for breaking dormancy and for seed germination of the European perennial spring geophyte Corydalis solida (Fumariaceae). Ripe seeds of C. solida contain an underdeveloped embryo, consisting of no more than a clump of cells. As a consequence, the embryo has to differentiate and grow to a critical length before germination can occur. In nature, seeds are dispersed in spring, while growth of the embryo starts in the autumn and continues in winter. Germination starts in late winter, immediately after embryo growth is completed, resulting in seedling emergence in the following spring. Experiments in controlled conditions showed that temperature is the main factor controlling dormancy and germination. Incubation at autumn temperatures (15/6 °C; 20/10 °C) for at least 8 weeks is required to initiate embryo growth, while a transfer to 5 °C is needed for completion of embryo growth and germination. Growth of the embryo of C. solida occurs at different temperatures over an extended period, a feature typical of temperate forest herbs. Our results indicate that the dormancy mechanism in seeds of C. solida is very similar to mechanisms in other Corydalis species studied thus far, suggesting that stasis in the dormancy trait has occurred.     

Changes in late embryogenesis abundant proteins and a small heat shock protein during storage of beech (Fagus sylvatica L.) seeds

Beech seed physiology, including the effect of stress proteins like late embryogenesis abundant (LEA) and small heat shock proteins (sHSP) on viability during storage, is not fully understood. Four lots of beech (Fagus sylvatica L.) seeds have been stored for 1, 4, 6 and 8 years at −10 °C and 8–9% moisture content (MC). Under these conditions, the germination capacity ranges from 81.5% to 100% in the youngest seeds. However, the seeds decrease in vigour with prolonged time of storage. Dehydrins and dehydrin-like proteins were identified both in cotyledons and embryonic axes of the dry stored seeds. In general, decreased contents of LEA proteins as well as reduced content of total soluble protein were detected during prolonged storage. The contents of soluble proteins in embryonic axes and nearly all detected dehydrins and dehydrin-like proteins were correlated with germination capacity. Moreover a sHSP with molecular mass of approximately 22 kDa was identified. The largest content of this protein was observed in the oldest seeds, especially in embryonic axes. The proteins identified may play a protective role during water deficit and storage.     

Seasonally different modes of seed dispersal in the prostrate annual, <Emphasis Type="Italic">Chamaesyce maculata</Emphasis> (L.) Small (Euphorbiaceae), with multiple overlapping generations

The modes of seed dispersal in the prostrate annual, Chamaesyce maculata, with multiple overlapping generations were investigated. We found that C. maculata has two modes of seed dispersal; autochory in the summer and myrmecochory in the autumn. Seasonally different modes of seed dispersal have not been known in other plant species. The large proportion of seeds produced in the summer was positioned further than the expanse of the parent plants by automatic mechanical seed dispersal. Therefore, autochory would be effective for avoiding competition between parent and offspring plants. No autochory occurred in the seeds produced in the autumn. The seeds of C. maculata without an elaiosome were dispersed by seed-collecting ants in the autumn. Although 18 ant species in total visited the plants of C. maculata at the 50 sites investigated, only two ant species, Tetramorium tsushimae and Pheidole noda frequently carried the seeds of C. maculata. The low frequency of seeds carried out of the nest by P. noda suggests that the workers of P. noda carry the seeds as food into their nest. So, P. noda might be a less effective seed disperser for C. maculata, corresponding to the effectiveness of seed dispersal by harvester ants. However, T. tsushimae ants frequently carried the seeds into and out of their nest, suggesting that T. tsushimae do not regard the seeds of C. maculata as a food resource. Thus, T. tsushimae may be an effective seed disperser for C. maculata.     

Dendroecological investigation of the vitality of Common Beech (Fagus sylvatica L.) in mixed mountain forests of the Northern Alps (South Bavaria)

Time series of radial growth and crown condition were used to assess the vitality of Common Beech (Fagus sylvatica L.) in mixed mountain forests of the Bavarian Alps. The investigation plots are located in three altitudinal belts at the mountains Kranzhorn and Laber. Sites at Kranzhorn are permanent monitoring plots since 1985, where beech show a high and, especially since 1996, at high altitudes increasing degree of crown transparency. No significant and ecological sensible relationship was found neither between crown condition data and weather, nor between crown condition data and water balance parameters. Tree-ring analyses revealed repeated growth depressions during the last decades starting at the end of the 1970s. Their intensity and duration increased with altitude. Climate–growth analyses carried out for the period 1931–2003 point to a temperature dependence of growth. Cool and short vegetation periods and especially late frost events appear as growth-limiting factors. Even in dry and warm years no serious growth-relevant water deficiency occurred. Neither weather fluctuations and extreme events, evaluated by different methods, nor age- or site-related differences provided sufficient explanations for growth disturbances and vitality loss in the last decades. Hence, further investigations are necessary to explain vitality loss, damage and destabilization of Common Beech in mixed mountain forest of Southern Germany. At Kranzhorn, strong relations between radial growth and defoliation were found, indicating the importance of long-term observation and monitoring data for these purposes.     

林木种子园花粉污染与防治措施

林木种子园花粉污染是影响种子园种子遗传品质的重要因子,由于野生同种花粉进入种子园而增加遗传损失。本文综述了国内外林木种子园花粉污染研究的概况、污染水平、影响污染水平的因子和减少污染的措施。研究表明：DNA分子标记在分析种子园交配动态和种子园管理效果方面非常有效（例如,cpDNA、RAPD和SSR）;种子园污染水平比预期的更高;花粉产量好像对污染水平没有影响;空间和生殖隔离也没有产生预期的效果。目前,人工辅助授粉和疏伐是减少花粉污染的两种有效措施。为了改善种子园林木的亲本平衡,人工处理技术的使用,例如：赤霉素A4/7处理技术和无性繁殖技术在种子园很受欢迎。污染程度其他方面的研究工作仍在继续,本文提到的基因流的研究。并对我国种子园花粉污染研究和花粉管理提出建议：当分析种子园花粉污染时,涉及到花粉基因型自然的（花粉扩散）、生理（开花时间）和花粉生活力等因素都应该被考虑。     

Inheritance of seed iron and zinc concentrations in common bean (Phaseolus vulgaris L.)

Micronutrients are essential elements needed in small amounts for adequate human nutrition and include the elements iron and zinc. Both of these minerals are essential to human well-being and an adequate supply of iron and zinc help to prevent iron deficiency anemia and zinc deficiency, two prevalent health concerns of the developing world. The objective of this study was to determine the inheritance of seed iron and zinc accumulation in a recombinant inbred line (RIL) population of common beans from a cross of low × high mineral genotypes (DOR364 × G19833) using a quantitative trait locus (QTL) mapping approach. The population was grown over two trial sites and two analytical methods (Inductively Coupled Plasma Spectrometry and Atomic Absorption Spectroscopy) were used to determine iron and zinc concentration in the seed harvested from these trials. The variability in seed mineral concentration among the lines was larger for iron (40.0–84.6 ppm) than for zinc (17.7–42.4 ppm) with significant correlations between trials, between methods and between minerals (up to r = 0.715). A total of 26 QTL were identified for the mineral × trial × method combinations of which half were for iron concentration and half for zinc concentration. Many of the QTL (11) for both iron (5) and zinc (6) clustered on the upper half of linkage group B11, explaining up to 47.9% of phenotypic variance, suggesting an important locus useful for marker assisted selection. Other QTL were identified on linkage groups B3, B6, B7, and B9 for zinc and B4, B6, B7, and B8 for iron. The relevance of these results for breeding common beans is discussed especially in light of crop improvement for micronutrient concentration as part of a biofortification program.     

The role of ants and mammals in dispersal and post-dispersal seed predation of the shrubs Grevillea (Proteaceae)

The role seed predators play in influencing the dynamics of plant populations has been little studied in Australia. The interaction of ant dispersal and seed predation on the soil seedbank in six shrubby species of Grevillea from the Sydney region of southeastern Australia was examined in selective exclusion experiments, seed array trials and placement of single seeds on the ground.Two distinct seed types in Grevillea were examined and different seed dispersal and post-dispersal seed predation patterns were associated with each: (a) seeds lacking an elaiosome were not attractive to ants and annual seed losses of between 82 and 95% were found in vegetation unburnt for greater than 8 years. Native rodents, Rattus fuscipes, and macropods, Wallabia bicolor, were responsible for these seed losses; (b) seeds with an elaiosome were rapidly handled by ants. Two functional types of ants were recognised. Most encounters were by ants that were small (Local) relative to seed size and these ants simply removed the elaiosome in situ or moved seeds only small distances (<20 cm). Some 0–24% of ant/seed encounters were by large (Removalist) ant species that were capable of moving seeds back to nests. In addition, Rattus fuscipes and Wallabia bicolor consumed at least 32–68% of seeds of Grevillea species with an elaiosome.Ants may reduce the overall levels of seed predation where seeds moved by Removalist ant species escape predation and are deposited in safe sites, hence allowing more seeds to reach the persistent soil seedbank. Mammals do not consume all seeds when ants are excluded, allowing for the potential for some seed escape from predation after seeds are discarded by Local ant species.     

Feeding behavior and development response of the perilla seed bugs (Nysius sp.) (Heteroptera: Lygaeidae) on multiple crop seeds combinations

The perilla seed bugs, Nysius plebeius Distant and Nysius hidakai Nakatani, are emerging pests of several field crop species including perilla crop in Korea. Here, we investigated the oviposition, nymphal mortality, development, adult emergence, adult longevity, adult weight and female ratio of N. plebeius and N. hidakai on multiple (MC) and double (DC) combinations of five crop seed species: perilla [Perilla frutescens (L.) Britton.], sesame (Sesamum indicum L.), sorghum [Sorghum bicolor (L.)], proso millet (Panicum miliaceum L.), and foxtail millet (Setaria italic L.) in no-choice test. The life-history variables of N. plebeius and N. hidakai were significantly influenced by the crop seed combinations. The most preferred crop seed combinations for oviposition were MC (perilla + sorghum + sesame + proso millet + foxtail millet), followed by DC (perilla + foxtail millet and perilla + sorghum), whereas the least preferred seed combination was DC (proso millet + foxtail millet). Both Nysius sp. were developed faster in MC (perilla + sorghum + sesame + proso millet + foxtail millet), with minimal nymphal mortality, higher adult emergence, longer adult longevity and heavier adult weight. The positive adult bug’s performance on the MC (perilla + sorghum + sesame + proso millet + foxtail millet) may be due to the nutrient contents and physicochemical components associated with the crop seeds. Further, the findings of this study are discussed in terms of bug's behavioral response to crop seed species combinations and management strategies of Nysius sp. as an alternative to chemical management.     

Exploring the potential of food forestry to assist in ecological restoration in North America and beyond

Food forests—edible, perennial, polyculture systems—are of increasing interest in North America and the United Kingdom, as reflected in projects ranging from urban food initiatives to integrated conservation and restoration planning. To examine emerging food forestry (FF) against the backdrop of ecological restoration (ER), we conducted semi‐structured interviews with eight experts each from the fields of FF and ER in conjunction with observations of food forests in Canada, the United States, and the United Kingdom. Using content analysis, our study builds a FF model that encompasses the underlying goals of emerging FF—forest function; diversity of yields; education and culture sharing; healthy habitats for people and other species; and sustainability. We argue that FF has potential as an urban restoration tool in terms of enhancing the multifunctionality of heterogeneous landscapes undergoing significant changes. This will require meaningful consideration of ethical issues (e.g. commodification of nature), landscape contexts, ecological integrity, integration of historical knowledge, and resilience for interdependent, dynamic social and ecological systems. Moreover, systematic, long‐term monitoring of different types of food forests will be crucial in order to mindfully apply FF in ER. This research provides one of the first in‐depth analyses of how emerging FF might contribute to restoration in the time of the Anthropocene, especially outside traditional tropic regions where most FF has been practiced.     

Inheritance of seed yield and quality traits in peas (Pisum sativum L.)

Summary A half diallel analysis involving nine cultivars showed that additive as well as non-additive gene effects were important for the inheritance of seed yield per plant, 100-seed weights, protein content and potassium per cent. For remaining traits non-additive genetic components were important. Overdominance was observed for all traits except for 100-seed weight, which expressed partial dominance. Parents PMR-T10, EC21857, EC109182, T163 and EC109189 were good general combiners for seed yield, seed weight and quality traits. In general there was a good relationship between per se performance and the gca effects of the parents for all traits. Cross combinations such as LMR8 x EC109182,LMR8 x PMR-T10,LMR8 x EC21857,PMRT10 x EC21857 and P23 x EC21857 were found promising. The seed yield was positively correlated with other quality traits. Protein had a positive correlation with methionine and phosphorus. All the values of correlation co-efficients were non-significant except for yield with potassium, 100-seed weight and protein with methionine, indicating that yield and quality attributes can be improved simultaneously by simple selection procedures.     

Consistent associations with beneficial bacteria in the seed endosphere of barley (Hordeum vulgare L.)

The importance of the plant microbiome for host fitness has led to the concept of the “plant holobiont”. Seeds are reservoirs and vectors for beneficial microbes, which are very intimate partners of higher plants with the potential to connect plant generations. In this study, the endophytic seed microbiota of numerous barley samples, representing different cultivars, geographical sites and harvest years, was investigated. Cultivation-dependent and -independent analyses, microscopy, functional plate assays, greenhouse assays and functional prediction were used, with the aim of assessing the composition, stability and function of the barley seed endophytic bacterial microbiota. Associations were consistently detected in the seed endosphere with Paenibacillus, Pantoea and Pseudomonas spp., which were able to colonize the root with a notable rhizocompetence after seed germination. In greenhouse assays, enrichment with these bacteria promoted barley growth, improved mineral nutrition and induced resistance against the fungal pathogen Blumeria graminis. We demonstrated here that barley, an important crop plant, was consistently associated with beneficial bacteria inside the seeds. The results have relevant implications for plant microbiome ecology and for the holobiont concept, as well as opening up new possibilities for research and application of seed endophytes as bioinoculants in sustainable agriculture.     

Cache site selection by chipmunks (Tamias spp.) and its influence on the effectiveness of seed dispersal in Jeffrey pine (Pinus jeffreyi)

The effectiveness of Jeffrey pine (Pinus jeffreyi) seed dispersal performed by seed-caching yellow pine chipmunks (Tamias amoenus) and lodgepole chipmunks (Tamias speciosus) was compared to that of wind dispersal in the Sierra Nevada of western Nevada. Wind-dispersed seeds typically fall under or near the parent tree. Chipmunks removed 90 and 97% of 1064 radioactive seeds from each of two simulated wind-dispersed seed shadows in less than 24 h. Wind-dispersed seeds were deployed within 12 m of the two source trees, but chipmunk caches were found from 2–69 m from the trees. Chipmunks carried nearly all seeds away from source trees, greatly reducing the density of seeds under and near source trees. Caches contained from 1–35 seeds and most were buried 7–21 mm deep. Chipmunks cached in open bitterbrush shrubland with mineral soils much more than expected and cached in closed-canopy Jeffrey pine and lodgepole pine forests with thick needle litter much less than expected. Many Jeffrey pine seedlings and saplings grow in the bitterbrush habitat and few grow in the pine forests. Ten and 20% of the original caches survived until April, the time of seed germination, at the two sites. The movement of wind-dispersed seeds is random relative to environmental variables important in seedling survival, and the wind in coniferous forests cannot quickly bury seeds. The quality of seed dispersal rendered by chipmunks was superior to that provided by the wind because the chipmunks quickly harvested seeds on the ground, moved them away from source trees, and buried them in the ground in habitats and microhabitats where they were more likely to establish new seedlings. The increased quality of seed dispersal provided by animals relative to the wind may help explain why over twenty species of pines have evolved seeds and cones that are adapted for dispersal by seed-caching animals.     

Genetic variation of ticks (Ixodes ricinus L.) in the Lithuanian and Norwegian populations

RAPD markers were used to measure the genetic diversity of 119 individuals of Ixodes ricinus collected from Lithuania and Norway. The samples were analysed within and also between the populations. We analysed 74 loci in each of 6 populations. Our results show high levels of diversity within the populations. The percentage of polymorphic loci of the six analysed populations: Birzai, Vilnius, Kretinga, Tjore, Kjosvik and Odderoya were 68.9%, 58.1%, 78.38%, 62.2%, 44.6% and 68.9%, respectively. The percentage of polymorphic loci in the Lithuanian populations was 93.2%, and in the Norwegian populations 81.08%. The genetic distance ranged from 0.019 to 0.079 within Norwegian populations and from 0.005 to 0.0967 within Lithuanian populations and between the countries from 0.022 to 0.146. The genetic variation of I. ricinus among Norwegian populations was lower than among Lithuanian populations. The highest part of genetic variation in I. ricinus ticks depends on variation within Kretinga (Lithuania) and Odderoya (Norway) populations situated in coastal areas where many migratory and sea birds are aggregated.     

Inheritance of seed protein content and other agronomic characters in long bean (Vigna sesquipedalis Fruw.)

Summary Seven varieties of long bean, which included three local and four exotic, were crossed in a complete diallel. This was an attempt to study the inheritance of crude protein content, protein yield, flowering date, pod yield and yield components.Both additive and non-additive gene effects were responsible for the genetic variation in the diallel population. However, dominance variance was more important than additive variance in crude protein content, number of pods per plant and number of seeds per pod. For seed weight and pod length, additive variance was more important.The crude protein content, protein yield and number of pods per plant appeared to be controlled by overdominance effects. Partial dominance seemed to be the case for flowering date, pod length and seed weight; complete to overdominance for pod yield. High protein appeared to be associated with recessive genes whereas there was a general trend of high yielding parents carrying more dominant genes.     

Effect of pollination intensity on fruit and seed set in cacao (Theobroma cacao L.)

We studied the functional relationship between pollination intensity and fruit survival as well as the number of seeds per pod in the tropical tree Theobroma cacao L. on a Forastero Upper-Amazon clone (UPA 409) in Ivory Coast. Cutting the style 24 h after pollination allowed for counting the number of pollen grains deposited on a stigma without affecting fruit set and seed development. Forty-three pollen grains were necessary to reach 50% of maximum fruit set 28 days after pollination. Above 115 pollen grains, the proportion of developing ovaries reached a maximum of 88% 28 days after pollination and 75% at maturity. With fewer than 238 pollen grains per stigma, there was a close relationship between pollination intensity and number of seeds per pod; the pollenseed ratio increased from 1.61 to 3.81 for PI increasing from 30 to 238 pollen grains. For higher pollination intensities, the average number of seeds per pod reached a maximum of 58. The relationship between pollination intensity and seed content was modelled. Results are consistent with the hypothesis that ovules attracted pollen tubes in a similar way regardless of whether or not they had already been reached by another pollen tube.