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Sporophyte production in Sphagnum was followed annually in 80 permanent 1-m2 plots at the bog expanse of a pristine mire during 1993–1999 and in 60 plots in peat pits abandoned 50 years ago during 1996–1999 in east central Sweden. The nine most abundant Sphagnum species produced sporophytes, with mean annual production ranging from 0.64 to 20 sporophytes/dm2 of cover among species. An estimated mean of 16 million Sphagnum spores/m2 mire area was produced annually at both mires. At the pristine mire, sporophyte production was positively related to the amount of precipitation the previous summer, suggesting that gametangium formation is especially sensitive to summer droughts. At the wetter peat pits, the amount of precipitation during spring in the year of sporophyte formation appeared more important, probably by positively affecting male gamete dispersal and fertilization. Larger patches had a higher probability of producing sporophytes at least once, showing areas with both sexes present among dioecious species, and thus giving an indication of clone size. Only slight differences in sporophyte production were found between the two mires, apart from effects of hydrological conditions and patch size. This indicates numerous colonizations at the peat pits. Summer droughts affected sporophyte maturation negatively by drying out sporophytes prematurely. Spore release phenology differed among species by up to a month and lasted from the beginning of July until the end of August. The early timing of spore dispersal in the most drought-sensitive, lawn-inhabiting sphagna should reduce the risk of sporophytes drying out prematurely during summer droughts.Key words: bryophyte, long-term study, mire, model, sexual reproduction, strategy.

Sexuality is most often preserved in Sphagnum while asexual reproduction remains responsible for the perennity and multiplication of the species. Sexual reproduction success was assessed for two diecious species and four monecious – polyecious species, using fertilization rates, reproduction rates, and success of the reproduction. The effects of different crossing processes on the preceding parameters were emphasized. Accordingly, gynoecium numbers, archegone numbers per gynoecium, and sporogonia occurrences were assessed in more than 3500 capitula. Variable distribution of gametangia within capitula in different species determines the success of sexual reproduction. An evolutionary interpretation of this variation in the distribution of gametangia is proposed. Key words: Sphagnum, crossing processes, polyecious, sexualization rates, reproduction success. [Journal translation]

Fine structural details of antheridia and oogonia, of cytogamy, plasmogamy, and karyogamy, and finally of the development of the oospore are described. Sexually determined zoospores (most probably zoomeiospores) resemble vegetative primary zoospores (zoomitospores). They form gametangia (antheridia or oogonia) which are similar to vegetative primary cysts. An antheridium germinates with a fertilization tube which penetrates the oogonium. As seen in abnormal cell fusions, the tip of the fertilization tube opens only within an oogonium; presumably, its wall is disintegrated by the latter. Before plasmogamy, both plasmalemmata are closely appressed. The fused protoplasts move into a short zygotial hypha which protudes from the oogonium. The thick-walled oospore is formed herein. It includes nearly all of the cytoplasm of the gametangia. Karyogamy takes place within the developing oospore. It is initiated by an interdigitation of microtubules radiating from the centrioles and by a close association of the latter. The observations are compared with those on other developmental stages of Lagenisma and with those on gametangia and oospores of other Oomycetes.

Nuclear divisions in the hyphae and gametangia of Phytophthora capsici and in hyphae of Phytophthora megasperma var. sojae resembled those of typical mitosis. The chromosomal configurations in prophase are similar to classical angiosperm prophase configurations. However, in metaphase the linear alignment of chromosomes resembled the pattern reported in pollen tubes of Lilium and Tradescantia. The relative size of nuclei and numbers of chromosomes per nucleus remained constant during gametangial development. Somatic and gametangial nuclei were about equal in size and chromosome number. Chromosome numbers in somatic and gametangial nuclei of P. capsici and P. megasperma var. sojae were about six and eight, respectively. There was no evidence of reduction division in gametangia.

The discomycete Pyronema domesticum requires light for the production of its gametangia and apothecia. Effects of a single exposure to light (150 ft-c (1 ft-c = 10.76391 lx)) for periods ranging from [Formula: see text] to 168 h on cultures aged 0–10 days were evaluated. A timetable for major developmental events (e.g., gametangial maturation) was established to determine the reactions of specific morphological events to light. Light was required to initiate gametangial production, but was not required at the time of gametangial differentiation. A minimum single exposure of 6 h was required to initiate gametangia, whereas a single exposure of 12 h was required to allow maximum development of the ascogonia to the fully globose form. Development of the ascogenous hyphae, asci, and ascospores was favored by exposure to a longer period of light and reached maximum development with exposure to at least 36 h of light. Although light favors ascospore formation, they can be delimited in the dark. An extended period of light (over 96 h) inhibits ascospore maturation.Neither gametangia nor apothecia were formed in cultures that were either too young (less than 2 days) or too old (6 days or more) at the time of light exposure. The age of 3 days at the initiation of light exposure was optimum for gametangial production, for development of the ascogenous hyphae and ascospores, and for apothecial expansion. In those cultures that were 4 days old at the time of exposure, many of the apothecia either lacked paraphyses, had very short paraphyses, or had an unusually high proportion of sterile asci.Sclerotia were only formed in the cultures which were exposed to light for comparatively short (18 h or less) periods of time. These sclerotia were intermixed with apothecia in the cultures.

The developmental ontogeny of eugymnohymenial apothecia in Ascodesmis nigricans van Tieghem and A. sphaerospora Obrist, homothallic operculate Discomycetes (Pezizales, Pyronemataceae), was investigated from initiation of the T-shaped gametangial initials through spore discharge. Branching of these T-shaped side branches gave rise to gametangia that paired and coiled helically. Paraphyses proliferated from the base of the rosette of gametangia and enveloped the coils, which appeared to undergo plasmogamy at their apices. Although a loose peridium of paraphyses was formed, a true excipulum was absent. Displacement of the opercula on the positively phototropic asci was towards the more strongly illuminated side.

The long-standing problem of mixed phases in life histories of red algae was investigated by genetic techniques. Diploid tetrasporophytes of Gracilaria sp. growing in culture produced functional male and female gametangia in addition to tetraspores. Sporelings resulting from fertilizations involving these gametangia were polyploid, their chromosome numbers indicating that gametes from the tetrasporophyte were diploid. The tetrasporophytes themselves were heterozygous for two genes affecting plant colour. These markers were observed to become homozygous in twin spots of recombinant tissue at the same time that gametangia were formed. All the observations are consistent with the interpretation that both gametangia and recombinant twin spots arise as a consequence of mitotic recombination. The broader implications of these observations for the Rhodophyceae are discussed.

Zygosporangium and zygospore formation in Phycomyces nitens was followed by correlative light microscopy and scanning and transmission electron microscopy. Compatible multibranched zygophores became interlocked by the interdigitation of their lobes. Progametangia grew up from the substratum in pairs and then differentiated into gametangia and tongs-shaped suspensors. Plasmogamy was deferred until the gametangia were delimited. Development of rings of hyaline appendages on the suspensors was concomitant with plasmogamy. The appendages originated from the tertiary suspensor wall layer and ruptured the outer primary and secondary wall layers prior to development of their terminal thornlike processes.Developing zygosporangia contained a large central vacuole and some organelle zonation; however, these features were not discernible in more mature zygosporangia. A reticulum of electron-opaque fluted warts developed within the secondary zygosporangial wall layer. Cryofractured zygosporangia revealed a smooth hyaline zygospore with truncate ends. Wall layer relations of mature zygosporangia and zygospores were presented. Information obtained was correlated with existing ultrastructural observations on zygosporangiogenesis in the Mucorales.

Light microscopic and scanning and transmission electron microscopic observations were obtained on azygosporogenesis in Mucor azygosporus Benjamin. Terminal gametangia are delimited by centripetally growing septa but plasmodesmata maintain cytoplasmic continuity between the azygophores and gametangia. Warts develop as regularly spaced patches of electron-opaque wall material on, and ultimately within, the inner primary wall. The mature complex azygosporangium wall is composed of (1) remnants of the membranous outer primary wall, (2) the ornamented layer of electron-opaque, stellate, confluent warts, and (3) a fibrillar, electron-opaque, tertiary layer. A homogeneous, hyaline azygospore wall (quaternary layer or endospore) with stellate warts is laid down within the azygosporangium. A comparison of the fine structural aspects of zygosporogenesis and azygosporogenesis in the Mucorales is presented.

The nuclei in hyphae, oospores, and gametangia of Achlya klebsiana and Saprolegnia ferax were examined by light microscopy after stain fixation with acetoorcein. It was found that the vegetative phase is diploid and that meiosis is not zygotic but is gametic in these organisms. The nuclear divisions in hyphae and germinating oospores were similar and were classically mitotic.

A study was made of nuclear behavior in Allomyces during development and germination of thin-walled sporangia, gametangia, and resistant sporangia. The pattern of nuclear migration, division, and multiplication during development in thin-walled sporangia and gametangia was found to be similar. No evidence could be found to indicate that nuclei in developing resistant sporangia multiply by mitosis. The mitotic divisions of nuclei of Euallomyces and Brachyallomyces isolates are described.

Green aboveground shoots of the moss Polytrichum alpinum Hedw., growing on the tundra at Point Barrow, Alaska, were exposed to 14CO2 in the field. Autoradiography and subsequent counting revealed preferential translocation of the labeled compounds into new belowground shoots arising from the extensive underground stem system. Within 24 h all stem systems extracted had been labeled throughout, a maximum distance of 7.5 cm being covered in this time, indicating minimum rates of 3.1 mm h−1.Increases in the number of new shoots aboveground throughout the season revealed the extent and importance of this translocation. Innate markers of seasonal growth enabled ages of the shoots at two sites to be determined and also the ages of shoots at production of gametangia in a third site where fruiting was common. The relative photosynthetic rates of the successive seasons' growth were also determined, and showed that by the 3rd year the photosynthetic capacity had dropped to about 40% of that in the youngest tissue on the same shoot.The patterns of growth and translocation of photosynthate in Polytrichum alpinum are discussed in relation to survival on the tunda.

Monhystrella plectoides Cobb is reported within the white oogonia of two forms of Chara zeylanica Willd. This represents the first report of a nematode relationship with Chara. The nematode is apparently confined to the female gametangia, other parts of the plant organs being free of the organism.