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Brachiaria are forage grasses widely cultivated in tropical areas. In vitro pollination was applied to accessions of Brachiaria spp. by placing pollen of non-dehiscent anthers on a solid medium near isolated ovaries. Viability and in vitro germination were tested in order to establish good conditions for pollen development. Comparing sexual to apomictic plants, apomictic pollen has more abortion after meiosis during the microspore stage and a lower viability and, of both types, only some plants have sufficient germination in a high sugar concentration. Using in vitro pollination with the sexual plant, the pollen tube penetrates into the nucellus and micropyle, but the embryo sac degenerates and collapses. In the apomictic B. decumbens, in vitro pollination leads to the transfer of the sperm nuclei into the egg cell and the central cell. The results are discussed according to normal fertilization and barriers in sexual and apomictic plants.

The micropylar exudate of Gasteria verrucosa (Mill.) H. Duval was studied using light and electron microscopic techniques. Ovules may contain micropylar exudate before stigma receptivity. During successive phases of stigma receptivity, the number of ovules with micropylar exudate and the amount of micropylar exudate per ovule increases. At the late phase of stigma receptivity, large amounts of micropylar exudate with a smooth to cauliflowerlike appearance were observed. Micropylar exudate is viscous and contains, among other components, proteins and carbohydrates. At all stages of the stigma investigated, ovules situated at the base of the ovary contain a larger quantity of micropylar exudate than those at the top. The appearance of micropylar exudate is related to the degree of development of the embryo sac and it originates primarily from the filiform apparatus. It is assumed that an uptake of water by the ovule initiates the outflow of micropylar exudate from the filiform apparatus into the micropyle. Both ovular pollen tube ingrowth and seed set mark the optimum pollination stage of the stigma, which for both events lies around the onset of stigma receptivity. When pollen tubes have reached the ovary, young micropylar exudate stimulates their growth rate. The presence of micropylar exudate seems to be a requirement for pollen tube penetration, and an interaction between the pollen tube and the micropylar exudate has been proposed. Possibly, the micropylar exudate serves as a nutritional source and, in an optimum condition, as an attractant for approaching pollen tubes.

Based on the existing data concerning the evolution of the sexual reproduction, it is argued that the processes of sex differentiation and interactions play a key role in evolution. From the beginning environment and organism are unified. In a changing dynamic environment life originates and the interaction between life and environment develops from simple to more complex organisms. Sexual reproduction is introduced after the origin of meiosis and is a key process in evolution. The asexual reproduction process prepares to dispersal. Sexual reproduction process adds the genome renewal and the gamete-gamete interaction. Reproduction and dispersal are connected and the process of reproduction has similarities between asexual and sexual reproduction. Unicellular algae develop the physiological and morphological sex differentiation. Sex differentiation is connected with the way of dispersal. The step to multicellular plants introduces cell isolation after meiosis and by the stay on the mother plant within a cell or organ, plant-cell apoplastic interaction originates and by prolonged stay the plant-plant interaction. This stay influences the type of dispersal. A life cycle with alternation of generations and two moments of dispersal permits plants to go on land. In ferns a shift in the moment of sex differentiation to meiospore happens and the stay of the macrospore leads to the seed plants. In water all types of sexual reproduction, interactions and the alternation of generations are prepared and these are used to conquest land. On land the biotic dispersal is realized. The phylogeny of sexual reproduction reveals that the sex differentiation and interaction are the main causes in the evolution of sexual reproduction. Sexual reproduction shows interactions during gamete fusion, between organism and environment and in multicellular plants between organisms. With respect to other types of interaction as in symbiosis or the nutrient chain, interaction is considered as an important action which is based on a persisting cooperation and points to a push during evolution. The push is expressed as communication: the driving force in the evolution. Based on the interactions between organisms and interactions between organisms and the dynamic environment, communication is considered as a driving force leading to the evolution as explained in the development of plant reproduction. Consequences for reproduction, its regulation and the process of evolution are discussed.

HistoryAs we enter the 21st year of the journal Sexual PlantReproduction, it seems both fitting and appropriate toconsider the genesis both of this journal and its parentorganization, the International Association for Sexual PlantReproduction Research (IASPRR)—particularly throughits much longer history of plant sexual reproduction con-gresses, informal interactions and this area of scientificpursuit as it is transformed in the modern era.Interestingly, the parent organization for the journal didnot formally exist until 2 years after Sexual Plant Repro-duction was first published in 1988. The IASPRR wasformally founded in Leningrad (now St. Petersburg) in1990 and since that time has represented scientists workingon various aspects of plant sexual reproduction rangingfrom molecular to structural levels. Nowadays, there arefrequent congresses and workshops all over the worldwhere scientists report their work on plant sexual repro-duction, from the local level to regional, national andinternational meetings. The congress series under the aus-pices of the IASPRR, however, is the only one with a longhistory and an exclusive focus on all aspects of sexual plantreproduction providing researchers around the globe with aunique opportunity to discuss most recent progress anddevelopments in the field. Additionally, there have beenperiodic Eastern European Plant Embryology congresses, asymposium series on Frontiers in Sexual Plant Reproduc-tion was initiated in 2000, as well as some other topicalcongresses of a more local nature. Increasingly, emergingmolecular data has made sexual plant reproduction a pop-ular topic at national and international botany and plantbiology conferences.The science of sexual plant reproduction has a longhistory that reaches beyond the 315 years interval sinceCamerarius uncovered the sexuality of plants (Zˇa´rsky´ andTupy´ 1995), passing 150 years of neglect before the dis-covery of gametes, and then a great period of exploration inthe 1800s concluding with the discovery of double fertil-ization in 1898 by Nawashin. It could be argued that ourtrue classical era diminished with the untimely death ofProf. Panchanan Maheshwari, but he was notably present atthe first congress in this series. In the same volume wherevan der Pluijm (1964) presented the first ultrastructuralfindings on degenerate synergid participation in receivingpollen tubes, Prof. Maheshwari asked astute questions onhis findings (see Linskens 1964). This modern era includedelectron microscopic findings and witnessed the rise ofmolecular biology to answer questions in plant repro-duction. Famous names and schools attended theseconferences that preceded the founding of IASPRR andconference proceedings chronicle the collected data andideas leading to concepts that sustain the science of today(Kapil 1967; Hesse 1987; Cresti and Linskens 1999).Over the last 50 years, the number of congresses hasincreased (Mulcahy et al. 1986; Ottaviano et al. 1992;Bednara 1996; Kuta 2005), and congresses, workshops andnewsletters relating to plant sexual reproduction havegradually increased to their current position. In the first half

Callose accumulates in the walls of cells undergoing megasporogenesis during embryo sac formation in angiosperm ovules. Deficiencies in callose deposition have been observed in apomictic plants and causal linkages between altered callose deposition and apomictic initiation proposed. In apomictic Hieracium, embryo sacs initiate by sexual and apomictic processes within an ovule, but sexual development terminates in successful apomicts. Callose deposition and the events that lead to sexual termination were examined in different Hieracium apomicts that form initials pre- and post-meiosis. In apomictic plants, callose was not detected in initial cell walls and deficiencies in callose deposition were not observed in cells undergoing megasporogenesis. Multiple initial formation pre-meiosis resulted in physical distortion of cells undergoing megasporogenesis, persistence of callose and termination of the sexual pathway. In apomictic plants, callose persistence did not correlate with altered spatial or temporal expression of a beta-1,3-glucanase gene (HpGluc) encoding a putative callose-degrading enzyme. Expression analysis indicated HpGluc might function during ovule growth and embryo sac expansion in addition to callose dissolution in sexual and apomictic plants. Initial formation pre-meiosis might therefore limit the access of HpGluc protein to callose substrate while the expansion of aposporous embryo sacs is promoted. Callose deposition and dissolution during megasporogenesis were unaffected when initials formed post-meiosis, indicating other events cause sexual termination. Apomixis in Hieracium is not caused by changes in callose distribution but by events that lead to initial cell formation. The timing of initial formation can in turn influence callose dissolution.

Pollen tubes ofGasteria verrucosa germinate in the stigmatic exudate and penetrate the solid cell walls in the tip of the style. In the direction of the ovary this solid part gradually becomes liquid and the pollen tubes grow in this fluid with an increasing velocity to reach the locule of the ovary. Here papillar cells excrete an exudate. Because of a different composition of this exudate, if compared with the stylar exudate, the pollen tube growth in the ovary is delayed (Willemse & Franssen-Verheijen,1988).