WITH the publication of this volume the whole botanical world, and algologists in particular, owe a special debt of gratitude to Prof. Fritsch. Although ten years have elapsed since the appearance of the first volume, it is no mean achievement under present conditions to have produced this companion work, and both Prof. Fritsch and the Cambridge University Press are to be congratulated on their courage and determination. The Structure and Reproduction of the Algae By Prof. F. E. Fritsch. Vol. 2: Foreword, Phaeophyceae, Rhodophyceae, Myxophyceae. Pp. xiv + 939. (Cambridge: At the University Press, 1945.) 50s. net.

Summary
Deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the Archaean. Geologically best known in seas and lakes, microbial carbonates are also important at the present day in fluviatile, spring, cave and soil environments. The principal organisms involved are bacteria, particularly cyanobacteria, small algae and fungi, that participate in the growth of microbial biofilms and mats. Grain-trapping is locally important, but the key process is precipitation, producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation. Various metabolic processes, such as photosynthetic uptake of CO2 and/or HCO3– by cyanobacteria, and ammonification, denitrification and sulphate reduction by other bacteria, can increase alkalinity and stimulate carbonate precipitation. Extracellular polymeric substances, widely produced by microbes for attachment and protection, are important in providing nucleation sites and facilitating sediment trapping.

Microbial carbonate microfabrics are heterogeneous. They commonly incorporate trapped particles and in situ algae and invertebrates, and crystals form around bacterial cells, but the main component is dense, clotted or peloidal micrite resulting from calcification of bacterial cells, sheaths and biofilm, and from phytoplankton-stimulated whiting nucleation. Interpretation of these texturally convergent and often inscrutable fabrics is a challenge. Conspicuous accumulations are large domes and columns with laminated (stromatolite), clotted (thrombolite) and other macrofabrics, which may be either agglutinated or mainly composed of calcified or spar-encrusted microbes. Stromatolite lamination appears to be primary, but clotted thrombolite fabrics can be primary or secondary. Microbial precipitation also contributes to hot-spring travertine, cold-spring mound, calcrete, cave crust and coated grain deposits, as well as influencing carbonate cementation, recrystallization and replacement. Microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water, and thus relies uniquely on a combination of biotic and abiotic factors. This overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas, and in the past by temporal variation in abundance of marine microbial carbonates. Patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry.

Stromatolites appeared at ∼3450 Ma and were generally diverse and abundant from 2800 to 1000 Ma. Inception of a Proterozoic decline variously identified at 2000, 1000 and 675 Ma, has been attributed to eukaryote competition and/or reduced lithification. Thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the Palaeozoic, and reappeared in the Late Devonian. Microbial carbonates retained importance through much of the Mesozoic, became scarcer in marine environments in the Cenozoic, but locally re-emerged as large agglutinated domes, possibly reflecting increased algal involvement, and thick micritic reef crusts in the late Neogene. Famous modern examples at Shark Bay and Lee Stocking Island are composite coarse agglutinated domes and columns with complex bacterial–algal mats occurring in environments that are both stressed and current-swept: products of mat evolution, ecological refugia, sites of enhanced early lithification or all three?

The Structure and Reproduction of the Algae

Microbial carbonates: the geological record of the calcified bacterial-algal mats and biofilms

Characters of conidiophore and conidium development are used for the separation of some common temperate and a few tropical Hyphomycetes into eight Sections. The need for further studies on the pre...

Conidiophores, conidia, and classification

In our study, chlorophyll a, chlorophyll b and the total amounts of carotenoids in Cladophora glomerata (L.) Kuetzing, Ulva rigita L., Codium tomentosum (Huds.) Stackh and Cladostephus verticillatus Ag. species were determined. Methanol, acetone and diethyl ether were used as solvents. The chlorophyll amount in Cladophora glomerata L. Kuetzing, species and carotenoids in Cladostephus verticillatus Ag. were found the highest. It was observed that sonication had no much contribution to the extraction.

https://journals.tubitak.gov.tr/botany/issues/bot-98-22-1/bot-22-1-3-96040.pdf

Spectrophotometric determination of chlorophyll-A,B and total carotenoid contents of some algae species using different solvents

background

The Evolution of Sex and its Consequences

A fossil Lagerstatte from the 700–750 Ma old Svanbergfjellet Formation of northeastern Spitsbergen offers a substantially enhanced view of late Proterozoic paleobiology. Fossils occur primarily as Organic-walled compressions in shales and permineralizations in chert: secondary modes of preservation include bedding-plane imprints and mineral replacements in apatite and goethite (?). The depositional setting of all fossiliferous horizons is broadly peritidal with highest taxonomic diversity occurring in shallow subtidal settings; the details of included fossil assemblages contribute to improved paleoecological resolution. The often distinct constituents of shale-and chert-hosted fossil assemblages appear to be a product of both paleoenvironment and fundamentally dissimilar taphonomic pathways, such that only forms with inferred wide ecological tolerance appear in both. Consideration of taphonomic processes also provides a variety of useful taxonomic insights, on the one hand permitting some resolution of so-called wastebasket taxa. such as Chuaria, and on the other acknowledging the taxonomic disparity that can occur in simple forms like Siphonophycus and Oscillatoriopsis. True multicellular (including coenocytic) eukaryotes are a conspicuous Component of the Svanbergfjellet assemblage: of eight distinct taxa, one can be identified as a coenobial/colonial chlorococcalean and three as filamentous siphonocladaleans (Chlorophyta). Other forms are problematic, but several show significant cell, or possibly tissue, differentiation. A review of Proterozoic multicellular organisms reveals that a coenocytic grade of organization was common among early metaphytes and supports the view (that a cellularity is a derived condition in many ‘multicellular’ lineages. Nineteen acritarch taxa are preserved in the Svanbergfjellet sediments. Ten of these show a readily identifiable ornamentation and contribute significantly to Neoproterozoic biostratigraphy; a world-wide and exclusively Late Riphean distribution of the acanthomorph Trachyhystrichosphaera aimika identifies it as a particularly valuable index fossil. The Svanbergfjellel fossil assemblage preserves a total of 63 distinct forms, of which 56 are treated taxonomically. As much as possible, principles of ‘natural’ taxonomy are applied, such that taphonomic and ontogenetic variants are declined separate taxonomy status. Major taxonomic revisions are offered for the acritarchs Trachyhystrichosphaera and Chuaria as well as for the prokaryotic-grade filaments: Cephalonyx, Cyanonema, Oscillatoriopsis, Palaeolyngbya, Rugossopsis, Siphonophycus, Tortunema, and Veteronostocale. Newly erected taxa include 7 new genera: Palaeastrum. Proterocladus, Pseudotawuia, Valkyria, Cerebrosphaera, Osculosphera and Pseudodendron; 14 new species in 12 genera: Palaestrum ***dyptocranum, Proterocladus major, Proterocladus minor, Proterocladus ***hermannae. Pseudodendron birenifera, Valkyria borealis, Cerebrosphaera buickii, Osculosphaera hyaline, Pseudodendron anteridium fullerne, Germinosphaera jankauskasii, Trachyhystrichosphaera polaris, Siphonophycus thulenema and thulenema and Digitus adumbrates 7 new combinations: Leiosphaeridia wimanii, Eoentophysalis croxfordii Cephlonyx geminatus. Oscillatoriopsis amadeus. Siphonophycus typicum, Siphonophycus solidum and Tortunema Wernadskii.

Paleobiology of the Neoproterozoic Svanbergfjellet Formation, Spitsbergen

Natural, physical, or material world and its phenomena