Presidential addresses pose problems. Should one review some area or report a new piece of research; or should one be less predictable? I have chosen the latter, inspired by a BBC radio talk given by Sir Peter Medawar (1964). The talk, ‘Is the scientific paper a fraud?’, introduced a series about how scientific work is really done. Medawar, a biologist and Nobel Laureate, concluded that the scientific paper is a fraud because it misleads the reader, indeed generally lies about the making of scientific discoveries, which are usually presented as well-planned, objective, logical and dispassionate. Scientists, he wrote ‘should not be ashamed to admit, as many of them apparently are ashamed to admit, that hypotheses appear in their minds along uncharted byways of thought; that they are imaginative and inspirational in character; that they are indeed adventures of the mind.’

There followed a series of talks by the likes of Otto Frisch, Edward Bullard, Tom Cottrell and R. V. Jones which amply demonstrated Medawar's conclusions. Finally there was a summary by a historian and philosopher, J. W. N. Watkins (1964), which commented on the conventional style (‘didactic dead-pan’) of scientific papers: ‘if natural scientists … took to writing in a candid, uncensored, autobiographical way, setting out their ideas in their natural order, didactic dead-pan would gradually fall into discredit outside science too. A gratuitous barrier to mutual comprehensibility would have faded away.’ We should heed these words at a time when science has never been so successful in developing understanding of natural phenomena; but a time also when it has abysmally failed to retain public confidence, partly through alienation with its jargon, partly through the arrogance of some of its practitioners, and partly through the suspicion which harnessing of science for exploitative interests naturally brings.

I have a story to tell about how ideas have developed in understanding the role of algae in shallow freshwater ecosystems and I shall tell it in a way that Medawar and Watkins would have approved of. Recently I received a questionnaire asking me which of several things determined what research I do. It had much of the standard terminology of bureaucrat-driven management: Foresight exercise; Competitiveness; Research assessment exercise; Patents; Grant income. It was redolent with the terminology of money, power and influence, none of which have much relevance to the research I do or why I do it. I think that for me, at least, doing research is one way of understanding myself, and my needs, and therefore, possibly, the needs of others. What I do, how I do it, and how I interpret the data are functions of my past experience and of lucky opportunities that have arisen. They have little to do with forward planning and I do not believe that I am unusual in any of this.

As a basis for inferring phylogenetic relationships between Pelvetia and Pelvetiopsis in the family Fucaceae, the complete sequences of the plastid-encoded RuBisCo spacer region were determined for all four species of Pelvetia, for the type species of Pelvetiopsis, P. limitata, and for three other fucacean species (Ascophyllum nodosum, Fucus gardneri and F. vesiculosus). All trees based on the sequences of the RuBisCo spacer region showed that Pelvetia is not monophyletic and consists of two clades, one including P. babingtonii, P. compressa, and P. siliquosa, the other comprising only the type species, P. canaliculata. P. canaliculata is not closely related to any of the other Fucaceae studied, and it may represent a monotypic genus. RuBisCo spacer sequences support the establishment of a new genus for the three Pacific Pelvetia species: P. babingtonii, P. compressa and P. siliquosa. The congruence of the RuBisCo spacer data with reported nuclear rDNA 18S and ITS sequences, and with biogeographical and morphological data, indicates that the RuBisCo spacer region, including its flanking areas, is useful for inferring phylogenetic relationships within the Fucaceae.

Vegetative and reproductive growth of individually marked plants of the brown alga Himanthalia elongata was monitored over 2·5 years at two sites with different wave exposures on the Irish west coast. Macro-recruits were first visible to the unaided eye in February/March. About 65% of all buttons produced receptacles during autumn of the same year, whereas others remained sterile. Growth of receptacles started between late August and late November, when vegetative plants were 9–14 months old, but no further plants became reproductive after December. At both sites, length increase of receptacles was greatest between February and April, but only longitudinal growth occurred and no more new dichotomies were produced. At the more wave-exposed site, growth was fastest in plants growing in red algal turfs and slowest in plants on open rock. Growth rates were maximal when seawater temperatures were 10–12 °C in early spring but decreased from May onwards with the maturation of receptacles aged 7–9 months in June. Release of viable gametes started in June and continued throughout the autumn and winter, until all plants disappeared from the population in February. Plant density was highest in March after the appearance of macro-recruits in the population, and declined during summer when the number of buttons decreased. Percentage plant cover was highest in June immediately before the onset of gamete release and this was followed by the decay and disintegration of receptacles. Since both survival and growth of young buttons was highest in red algal turfs and lowest on exposed rocks, the distribution of H. elongata on semi-exposed shores in Ireland may be limited by the availability of suitable micro-habitats for recruitment, and reduced by the early loss of fertile, adult plants from exposed sites.

Phenolic compounds, packaged within vesicles known as physodes, are a major cytoplasmic constituent of eggs and zygotes of the Australasian fucoid Hormosira banksii. Physode movement in early life stages of Hormosira is described. We have used the cytoskeletal inhibitors cytochalasin B, latrunculin B and nocodazole added during different stages of development to investigate the role of the cytoskeleton in movement of these vesicles to regions of active wall formation in the growing rhizoid tip and the plane of cytokinesis prior to cell division. Actin inhibition prevented polarization, cross-wall formation and physode movement. When microtubules were disrupted polarization was still possible, but cross-wall formation and physode movement were prevented. Both actin microfilaments and microtubules are necessary to move physodes to regions of accumulation and active wall formation.

Two 13·1 m2 ponds at Auchincruive, Scotland, were used to treat the diluted liquid phase of separated piggery slurry, in order to identify the climatic and pond operational parameters which influence biomass production and nutrient removal in these systems at a constant areal loading rate. The ponds were operated from April to November at 0·12, 0·24 and 0·34 m depth as batch-fed reactors. Average 5-day biochemical oxygen demand (BOD5) loading was 6·24 g m−2 d−1 and the ponds were mixed at a mean surface velocity of 0·20 m s−1. Dry matter, chlorophyll, optical density (OD560), NO3, NO2, NH4, urea and total phosphorus were determined daily. Temperature, pH, dissolved oxygen and incident irradiance were monitored continuously. Correlation and multiple regression analyses were used to determine significant interactions between environmental factors, biomass production and nutrient removal. Both chlorophyll a and optical density were accurate predictors of dry matter biomass. All measures of pond biomass were positively correlated with elapsed time, surface daily irradiance, daylength and pH, but negatively correlated with pond depth. Significant correlations between pH and daily irradiance, maximum dissolved oxygen and forms of nitrogen (nitrite or nitrate) suggested that the final pond pH represents an equilibrium between alkalization by photosynthesis and acidification by nitrification. Total nitrogen removal was influenced by biomass, elapsed time, temperature and daily irradiance, but not by either pH or depth. The concentration of ammonium nitrogen (NH4-N) was inversely correlated with temperature, biomass, depth, daily irradiance and daylength. Nitrification was found to occur with nitrate concentration showing a strong negative correlation with daylength, reflecting an increase in nitrifying activity by the pond biomass throughout the season. Nitrate concentrations were positively correlated with elapsed time, but negatively correlated with biomass, temperature and daily irradiance. Phosphorus removal was influenced by elapsed time and biomass concentration. Removal of biological and chemical oxygen demand (COD) at the completion of the batch runs was 96% and 78·6% respectively.

A new species of the widespread genus Mesophyllum Lemoine is described. Mesophyllum macedonis nov. sp. grows in shallow (c. 0·5 m depth) waters, tolerating wide temperature fluctuations (12–26 °C) at a salinity of 32–35‰, protected from direct wave and light exposure. The species forms weakly attached rose-coloured clumps with whitish margins on rocky substrata. Its thallus is composed of superimposed foliose lamellae (to 170 μm thick) with dorsiventral organization, non-coaxial hypothallium, limited perithallial growth (to 60 μm thick), rectangular epithallial cells and solitary terminal trichocytes. Tetrasporangial conceptacles are raised and have convex roofs perforated by up to 108 pores that are bordered by filaments composed of slender and occasionally elongated cells. Tetrasporophytes were first observed in 1984 and their occurrence monitored without finding gametophytes or other populations at the type locality or elsewhere on the coast of the Sithonia Peninsula. A comparative study of literature data and material of selected congeners shows that M. macedonis shares most of its characters with M. ornatum (Foslie et Howe) nov. comb. from the Bahamas and Mariana Islands, and M. incisum (Foslie) Adey from southern Australia and New Zealand. Biogeographic scenarios that may explain the restricted distribution of the new Mediterranean endemic are discussed.

Relationships between phytoplankton growth and supplies of phosphorus and nitrogen have been variously investigated in three lakes in two contrasted English lake areas using physiological nutrient indices (alkaline phosphatase activity, phosphorus debt, surplus phosphorus, phosphorus uptake kinetics, dark ammonium uptake, ammonium uptake kinetics, stimulation of 14C uptake, and batch bioassay) and by inspection of water chemistry. None of the lakes was significantly affected by wastewater effluent but all lay in agricultural catchments. Physiological indices and water chemistry suggested limitation of phytoplankton biomass mostly by phosphorus, and to some extent by nitrogen in summer in North Ormesby Broad, by nitrogen in summer and to some extent by phosphorus in Lily Broad and by nitrogen in White Mere. Indices did not always accord with one another, though were not severely misleading. They added little to conclusions that could be drawn from water chemistry alone. Reasons for the differential relative importance of nitrogen and phosphorus in the two lake areas are discussed. The paradigm of phosphorus limitation, though unchallenged in upland waters and those on poorly weathered rocks, may be less relevant in lowland lakes.

The unicellular, acido- and thermophilic red alga Galdieria sulphuraria is unique in its ability to grow heterotrophically on at least 27 different sugars and polyols. The enzymatic machinery necessary for metabolizing this variety of compounds is constitutively expressed in the alga. The uptake system, however, has to be induced. From in vivo studies we conclude that the uptake system consists of several transporters with a partly overlapping substrate specificity. These transporters can be grouped into hexose, polyol and pentose transporters. The mode of induction depends on the substrate supplied for heterotrophic growth. When autotrophic cells were supplied with hexoses, hexose and polyol transporters were induced from the onset of heterotrophic conditions. Depletion of substrate in the medium triggered the induction of other transporters. Dulcitol, as well as other polyols and pentoses, led to a co-induction of all transporters as judged from induction and competition experiments. The heterotrophic capabilities of Galdieria are intriguing, because the natural habitat of the alga contains only traces of organic carbon. The substrates for heterotrophic growth apparently originate from decaying cells releasing hydrolysed cell material. Trace amounts of glucose were sufficient for the induction of sugar uptake in Galdieria. The co-induction of transporters obviously enables the cells in endolithic mats to import a wide spectrum of organic carbon in order to survive periods of light limitation.

The degree of synchrony of light/dark-adapted Chlamydomonas reinhardtii cell-wall-less cells was analysed by flow cytometry. The cultures exhibited the classical growth curve reported for synchronously dividing cells. However, analysis of the nuclear DNA content revealed a partial asynchrony of cell division. This allowed us to determine that cell division lasts only 1 h 15 min. The changes in the distribution of nuclei in G1 and S phases did not exhibit the DNA peaks expected for highly synchronous cells. However, these peaks were observed for the G2+M nuclei and reflected the number of cell divisions. Modification of culture conditions including temperature, photoperiod, quantum irradiance and culture density affected the degree of synchrony but did not completely abolish the asynchrony. An overlap between the divisions of cells dividing one, two or three times could account for the partial asynchrony observed. In fact, it is possible that cells perform their divisions synchronously but that the timing and/or the duration of the cell divisions is different for the three kinds of cells. The synchrony seems to be perturbed when the cells move from the G1 to the S phase. The transduction of the release signal, allowing cells to pass through the restriction point of the G1 phase, might be too slow and insufficiently homogeneous between the cells to allow perfect synchronization. Finally, if highly synchronized cells are needed to study Chlamydomonas reinhardtii cell cycle, other synchronization procedures should be considered.

That plastids were once free-living cyanobacteria is now taken for granted by many, and for good reasons, for there is a wealth of data – in particular from the comparison of plastid and cyanobacterial genomes – that support this view. There is currently no seriously entertained alternative hypothesis to the view that plastids descend from cyanobacteria. But that was not always the case. Well into the 1970s there was a generally favoured alternative hypothesis, namely that early in evolution plastids arose de novo from within a non-plastid bearing cell (an autogenous origin) rather than through invasion by a cyanobacterium into a non-plastid-bearing cell with subsequent intracellular coexistence and reduction to an organelle (an endosymbiotic origin). Interestingly, the shift from autogenous to endosymbiotic hypotheses during the 1970s was a reversal of state for during the first two decades of this century, the endosymbiont hypothesis for the origins of plastids (and mitochondria, which will not be further discussed here) was very popular among biologists. It fell into disfavour shortly after the First World War, for reasons that are very difficult to summarize briefly, and remained scorned for 50 years (see Sapp, 1994, for an historical account in English, and Höxtermann, 1998, for a succinct historical account in German). So where did the first version of the endosymbiont hypothesis come from? In a nutshell, it came from Konstantin Sergejewiz Merezkovskij (usually written as Constantin Mereschkowsky), a Russian botanist of little standing who worked at a rather small and by no means prominent university in Kasan and who published a very remarkable paper in 1905. We are not aware of any true precedent for his paper, which draws upon three lines of evidence known at the time.

Ultrastructural observations on the vegetative filaments, motile cells and processes leading to zoospore differentiation in Chrysonephos lewisii are presented. Vegetative filaments are embedded in a mucilaginous envelope, preserved by Alcian blue fixation, which favours their aggregation and also the attachment of bacteria, diatoms and various types of debris. The filaments are provided with an external wall consisting of microfibrils positive to the PATAg test and ConA-colloidal gold labelling. Inside the filaments the vegetative cells differentiate into zoospores. This accounts for the ultrastructural similarity between vegetative cells and zoospores, although zoospores are typically provided with a flagellar apparatus. They share an external cell covering or theca, vacuolar or cytoplasmic ‘scale-like structures’, protruding stalked pyrenoids, scattered nucleoids of plastid DNA and absence of a photoreceptor-eyespot complex. The flagellar apparatus of zoospores is characterized by two distinct basal plates, the central pair of flagellar microtubules originating some distance above the transitional plate and basal body angle less than 90°. These results provide strong taxonomic evidence that this genus should be placed in the Sarcinochrysidales sensu stricto, rather than remaining in Chrysomeridales. The key role of the Golgi apparatus in the synthesis of different structural elements – depending upon the functional stages of the cells – and in the processes of exocytosis during zoosporogenesis is also discussed.

The dependence of the cellular (biogenic) and frustule-associated (mineralized) silica content of the diatoms Navicula salinarum and Thalassiosira weissflogii on salinity and aluminium conditions was studied in order to make it possible to manipulate silicification in vitro and maximize it to levels required for physico-chemical frustule characterization by physisorption, X-ray scattering analysis and NMR, which is our ultimate objective. Enrichments with AlCl3 increased growth and the final cell density of the pennate N. salinarum, but not of the centric species T. weissflogii. Aluminium additions did not, however, result in a significant increase in the biogenic or mineralized silica content per cell and could not be detected in the silica matrix of the frustule. In contrast, lowering the salinity from 28 practical salinity units (PSU) to 20 and 15 resulted in a significant increase in the biogenic silica content per cell of both species, which is in line with an increase in density of the chemically derived silica under low salt conditions. The silica content per cell was variable during culture growth; increase in cell densities (during exponential growth) was accompanied by a decrease in contents of biogenic silica per cell. Electron microscopy and energy dispersive X-ray analysis (EDXA) support the chemical analyses and also suggest higher biogenic silica contents at lower salinities. The results indicate that besides silicate concentration and pH, the concentration of salts is an important inorganic factor that affects the silica polymerization inside the silica deposition vesicle of diatoms.